Sea breeze moving across the water (towards the viewer) in Hobart, Tasmania, AustraliaLake - Sea breeze and atmospheric depth
A sea breeze or onshore breeze is any wind that blows from a large body of water toward or onto a landmass. By contrast, a land breeze or offshore breeze is any wind that blows from a landmass toward or onto a large body of water. The term offshore wind may refer to any wind over open water. Sea breezes and land breezes are both important factors in coastal regions' prevailing winds.
Sea breeze and land breeze develop due to differences in air pressure created by the differing heat capacities of water and dry land. As such, Sea breezes and land breezes are more localised than prevailing winds. Since land heats up much faster than water under solar radiation, a sea breeze is a common occurrence along coasts after sunrise.
On the other hand, dry land also cools faster than water without solar
radiation, so the wind instead flows from the land towards the sea when
the sea breeze dissipates after sunset.
The land breeze at nighttime is usually shallower than the sea
breeze in daytime. Unlike the daytime sea breeze, which is driven by
convection, the nighttime land breeze is driven by convergence.
Cause
Sea breeze
The sea has a greater heat capacity than land, so the surface of the sea warms up more slowly than the surface of the land. As the temperature of the surface of the land rises, the land heats the air above it by convection. The hypsometric equation
states that the hydrostatic pressure depends on the temperature. Thus,
the hydrostatic pressure over the land decreases less at higher
altitude. As the air above the coast has a relatively higher pressure,
it starts moving towards the sea at high altitude. This creates an
inverse airflow near the ground.
The strength of the sea breeze is directly proportional to the
temperature difference between the land and the sea. If a strong
offshore wind is present (that is, a wind greater than 8 knots
(15 km/h)) and opposing the direction of a possible sea breeze, the sea
breeze is not likely to develop.
Land breeze
At
night, the land cools off faster than the ocean due to differences in
their heat capacity, which forces the dying of the daytime sea breeze as
the temperature of the land approaches that of the ocean. If the land
becomes cooler than the adjacent sea surface temperature,
the air pressure over the water will be lower than that of the land,
setting up a land breeze blowing from the land to the sea, as long as
the environmental surface wind pattern is not strong enough to oppose
it.
Effects
Sea breeze
Schematic cross section through a sea-breeze front. If the air inland is moist, cumulus often marks the front.
A sea-breeze front is a weather front created by a sea breeze, also known as a convergence zone. The cold air from the sea meets the warmer air from the land and creates a boundary like a shallow cold front. When powerful this front creates cumulus clouds, and if the air is humid and unstable, the front can sometimes trigger thunderstorms.
If the flow aloft is aligned with the direction of the sea breeze,
places experiencing the sea breeze frontal passage will have benign, or
fair, weather for the remainder of the day. At the front warm air
continues to flow upward and cold air continually moves in to replace it
and so the front moves progressively inland. Its speed depends on
whether it is assisted or hampered by the prevailing wind, and the
strength of the thermal contrast between land and sea. At night, the
sea breeze usually changes to a land breeze, due to a reversal of the
same mechanisms.
Sea breeze convergence in Cuba is very similar to that in Florida. The northern sea breeze meets the southern sea breeze, creating a sharp convergence line in the cumulus field.
Thunderstorms caused by powerful sea breeze fronts frequently occur in Florida, a peninsula bounded on the east and west by the Atlantic Ocean and Gulf of Mexico,
respectively. During the wet season, which typically lasts from June
through September/October, any direction that the winds are blowing
would always be off the water, thus making Florida the place most often
struck by lightning in the United States, and one of the most on Earth. These storms can also produce significant hail due to the tremendous updraft it causes in the atmosphere especially during times when the upper atmosphere is cooler such as during the spring or fall.
On calm summer afternoons with little prevailing wind, sea
breezes from both coasts may collide in the middle, creating especially
severe storms down the center of the state. These thunderstorms can
drift towards either the west or east coast depending on the relative
strengths of the sea breezes, and sometimes survive to move out over the
water at night, creating spectacular cloud-to-cloud lightning shows for
hours after sunset. Due to its large size Lake Okeechobee may also contribute to this activity by creating its own lake breeze which collides with the east and west coast sea breezes.
In Cuba similar sea breeze collisions with the northern and southern coasts sometimes lead to storms.
Land breeze
Land
breeze, which consists of cool air coming from the land, pushes the
warmer air upwards over the sea. If there is sufficient moisture and
instability available, the land breeze can cause showers, or even
thunderstorms, over the water. Overnight thunderstorm development
offshore due to the land breeze can be a good predictor for the activity
on land the following day, as long as there are no expected changes to
the weather pattern over the following 12–24 hours. This is mainly
because the strength of the land breeze is weaker than the sea breeze. The land breeze will die once the land warms up again the next morning.
Utilisation
Wind farms are often situated near a coast to take advantage of the normal daily fluctuations of wind speed resulting from sea or land breezes. While many onshore wind farms and offshore wind farms do not rely on these winds, a nearshore wind farm
is a type of offshore wind farm located on shallow coastal waters to
take advantage of both sea and land breezes. For practical reasons,
other offshore wind farms are situated further out to sea and rely on
prevailing winds rather than sea breezes.
A wind farm or wind park, also called a wind power station or wind power plant, is a group of wind turbines in the same location used to produce electricity.
Wind farms vary in size from a small number of turbines to several
hundred wind turbines covering an extensive area. Wind farms can be
either onshore or offshore.
Because they require no fuel, wind farms have less impact on the
environment than many other forms of power generation and are often
referred to as a good source of green energy.
Wind farms have, however, been criticised for their visual impact and
impact on the landscape. Typically they need to be spread over more land
than other power stations and need to be built in wild and rural areas,
which can lead to "industrialization of the countryside", habitat loss,
and a drop in tourism. Some critics claim that wind farms have adverse
health effects, but most researchers consider these claims to be
pseudoscience (see wind turbine syndrome).
Wind farms can interfere with radar, although in most cases, according
to the US Department of Energy, "siting and other mitigations have
resolved conflicts and allowed wind projects to co-exist effectively
with radar".
Siting considerations
Location
is critical to the overall success of a wind farm. Additional
conditions contributing to a successful wind farm location include: wind
conditions, access to electric transmission, physical access, and local
electricity prices.
Wind conditions
Map of available wind power over the United States. Colour codes indicate wind power density class
The faster the average wind speed, the more electricity the wind
turbine will generate, so faster winds are generally economically better
for wind farm developments.
The balancing factor is that strong gusts and high turbulence require
stronger more expensive turbines, otherwise there is a risk of damage.
The average power in the wind is not proportional to the average wind
speed. For this reason, the ideal wind conditions would be strong but
consistent winds with low turbulence coming from a single direction.
Mountain passes are ideal locations for wind farms under these
conditions. Mountain passes channel wind, blocked by mountains, through a
tunnel like pass towards areas of lower pressure and flatter land. Passes used for wind farms like the San Gorgonio Pass and Altamont Pass
are known for their abundant wind resource capacity and capability for
large-scale wind farms. These types of passes were the first places in
the 1980s to have heavily invested large-scale wind farms after approval
for wind energy development by the U.S. Bureau of Land Management. From
these wind farms, developers learned a lot about turbulence and
crowding effects of large-scale wind projects, which were previously
unresearched, in the U.S. due to the lack of operational wind farms
large enough to conduct these types of studies.
Usually sites are screened on the basis of a wind atlas, and validated with on-site wind measurements via long term or permanent meteorological-tower data using anemometers and wind vanes. Meteorological
wind data alone is usually not sufficient for accurate siting of a
large wind power project. Collection of site specific data for wind
speed and direction is crucial to determining site potential in order to finance the project.
Local winds are often monitored for a year or more, detailed wind maps
are constructed, along with rigorous grid capability studies conducted,
before any wind generators are installed.
The wind blows faster at higher altitudes because of the reduced
influence of drag. The increase in velocity with altitude is most
dramatic near the surface and is affected by topography, surface
roughness, and upwind obstacles such as trees or buildings. At altitudes
of thousands of feet/hundreds of metres above sea level, the power in
the wind decreases proportional to the decrease in air density.
Often in heavily saturated energy markets, the first step in site
selection for large-scale wind projects, before wind resource data
collection, is finding areas with adequate available transfer capability
(ATC). ATC is the measure of the remaining capacity in a transmission
system available for further integration of two interconnected areas
without significant upgrades to existing transmission lines and
substations. Significant equipment upgrades have substantial costs,
potentially undermining the viability of a project within a location,
regardless of wind resource availability.
Once a list of capable areas is constructed, the list is refined based
on long term wind measurements, among other environmental or technical
limiting factors such as proximity to load and land procurement.
Many independent system operators
(ISOs) in the United States such as the California ISO and Midcontinent
ISO use interconnection request queues to allow developers to propose a
new generation for a specific given area and grid interconnection.
These request queues have both deposit costs at the time of request and
ongoing costs for the studies the ISO will make for up to years after
the request was submitted to ascertain the viability of the
interconnection due to factors such as ATC.
Larger corporations who can afford to bid the most queues will most
likely have market power as to which sites with the most resource and
opportunity get to be developed upon. After the deadline to request a
place in the queue has passed, many firms will withdraw their requests
after gauging the competition in order to make back some of the deposit
for each request that is determined too risky in comparison to other
larger firms' requests.
Design
Turbine spacing
A
major factor in wind-farm design is the spacing between the turbines,
both laterally and axially (with respect to the prevailing winds). The
closer the turbines are together, the more the upwind turbines block
wind from their rear neighbors (wake effect). However, spacing turbines
far apart increases the costs of roads and cables, and raises the amount
of land needed to install a specific capacity of turbines. As a result
of these factors, turbine spacing varies by site. Generally speaking,
manufacturers require a minimum of 3.5 times the turbine's rotor
diameter of clear space between each adjacent turbine's respective
spatial envelope.
Closer spacing is possible depending on the turbine model, the conditions at the site, and how the site will be operated.
Airflows slow down as they approach an obstacle, known as the 'blockage
effect', reducing available wind power by 2% for the turbines in front
of other turbines.
An aerial view of Whitelee Wind Farm, the largest onshore wind farm in the UK and second-largest in EuropeRoscoe Wind Farm An onshore wind farm in West Texas
The capacity of the world's first wind farm was 0.6 MW, produced by
20 wind turbines rated at 30 kilowatts each, installed on the shoulder
of Crotched Mountain in southern New Hampshire in December 1980.
Onshore
turbine installations in hilly or mountainous regions tend to be on
ridges generally three kilometres or more inland from the nearest
shoreline. This is done to exploit the topographic acceleration
as the wind accelerates over a ridge. The additional wind speeds gained
in this way can increase energy produced because more wind goes through
the turbines. The exact position of each turbine matters, because a
difference of 30 metre could potentially double output. This careful
placement is referred to as 'micro-siting'.
Europe is the leader in offshore wind energy, with the first offshore wind farm (Vindeby)
being installed in Denmark in 1991. As of 2010, there are 39 offshore
wind farms in waters off Belgium, Denmark, Finland, Germany, Ireland,
the Netherlands, Norway, Sweden and the United Kingdom, with a combined
operating capacity of 2,396 MW. More than 100 GW (or 100,000 MW) of
offshore projects are proposed or under development in Europe. The European Wind Energy Association has set a target of 40 GW installed by 2020 and 150 GW by 2030.
As of 2017, The Walney Wind Farm in the United Kingdom is the largest offshore wind farm in the world at 659 MW, followed by the London Array (630 MW) also in the UK.
Offshore wind turbines are less obtrusive than turbines on land,
as their apparent size and noise is mitigated by distance. Because water
has less surface roughness than land (especially deeper water), the
average wind speed is usually considerably higher over open water. Capacity factors (utilisation rates) are considerably higher than for onshore locations.
The province of Ontario in Canada is pursuing several proposed locations in the Great Lakes, including the suspended Trillium Power Wind 1 approximately 20 km from shore and over 400 MW in size. Other Canadian projects include one on the Pacific west coast.
In 2010, there were no offshore wind farms in the United States, but
projects were under development in wind-rich areas of the East Coast,
Great Lakes, and Pacific coast; and in late 2016 the Block Island Wind Farm was commissioned.
Offshore
windfarms, including floating windfarms, provide a small but growing
fraction of total windfarm power generation. Such power generation
capacity must grow substantially to help meet the IEA's Net Zero by 2050 pathway to combat climate change.
Installation
and service / maintenance of off-shore wind farms are a specific
challenge for technology and economic operation of a wind farm. As of
2015, there are 20 jackup vessels for lifting components, but few can lift sizes above 5MW.
Service vessels have to be operated nearly 24/7 (availability higher
than 80% of time) to get sufficient amortisation from the wind turbines.
Therefore, special fast service vehicles for installation (like Wind
Turbine Shuttle) as well as for maintenance (including heave
compensation and heave compensated working platforms to allow the
service staff to enter the wind turbine also at difficult weather
conditions) are required. So-called inertial and optical based Ship
Stabilization and Motion Control systems (iSSMC) are used for that.
Experimental wind farms consisting of a single wind turbine for testing purposes have been built. One such installation is Østerild Wind Turbine Test Field.
Airborne wind farms have been envisaged. Such wind farms are a
group of airborne wind energy systems located close to each other
connected to the grid at the same point.
Wind farms consisting of diverse wind turbines have been proposed
in order to efficiently use wider ranges of wind speeds. Such wind
farms are proposed to be projected under two criteria: maximization of
the energy produced by the farm and minimization of its costs.
The Australian Greens have been significant supporters of Australian wind farms, however the party's previous leader Bob Brown and former leader Richard Di Natale
have now both expressed concerns about environmental aspects of wind
turbines, particularly the potential danger they impose for birds.
In July 2022 Brazil reached 22 GW of installed wind power in about 750 wind farms. In 2021 Brazil was the 7th country in the world in terms of installed wind power (21 GW), and the 4th largest producer of wind energy in the world (72 TWh), behind only China, USA and Germany. The largest wind farm in the country is the Complexo eólico Lagoa dos Ventos in the State of Piauí, onshore with a current capacity of 1,000 MW being expanded to 1,500 MW.
In just five years, China leapfrogged the rest of the world in wind
energy production, going from 2,599 MW of capacity in 2006 to 62,733 MW
at the end of 2011. However, the rapid growth outpaced China's infrastructure and new construction slowed significantly in 2012.
At the end of 2009, wind power in China accounted for 25.1 gigawatts (GW) of electricity generating capacity, and China has identified wind power as a key growth component of the country's economy. With its large land mass and long coastline, China has exceptional wind resources. Researchers from Harvard and Tsinghua University have found that China could meet all of their electricity demands from wind power by 2030.
By
the end of 2008, at least 15 Chinese companies were commercially
producing wind turbines and several dozen more were producing
components. Turbine sizes of 1.5 MW to 3 MW became common. Leading wind power companies in China were Goldwind, Dongfang Electric, and Sinovel along with most major foreign wind turbine manufacturers.
China also increased production of small-scale wind turbines to about
80,000 turbines (80 MW) in 2008. Through all these developments, the
Chinese wind industry appeared unaffected by the financial crisis of 2007–2008, according to industry observers.
According to the Global Wind Energy Council, the development of wind energy in China, in terms of scale and rhythm, is absolutely unparalleled in the world. The National People's Congress
permanent committee passed a law that requires the Chinese energy
companies to purchase all the electricity produced by the renewable
energy sector.
In 2011 the European Union
had a total installed wind capacity of 93,957 MW. Germany had the
third-largest capacity in the world (after China and the United States),
with an installed capacity of 29,060 MW at the end of 2011. Spain had
21,674 MW, and Italy and France each had between 6,000 and 7,000 MW. By January 2014, the UK installed capacity was 10,495 MW.
But energy production can be different from capacity – in 2010, Spain
had the highest European wind power production with 43 TWh compared to
Germany's 35 TWh.
Europe's largest windfarm is the 'London Array', an off-shore wind farm in the Thames Estuary in the United Kingdom, with a current capacity of 630 MW (the world's largest off-shore wind farm). Other large wind farms in Europe include Fântânele-Cogealac Wind Farm near Constanța, Romania with 600 MW capacity, and Whitelee Wind Farm near Glasgow, Scotland which has a total capacity of 539 MW.
A wind farm in a mountainous area in Galicia, Spain
An important limiting factor of wind power is variable power
generated by wind farms. In most locations the wind blows only part of
the time, which means that there has to be back-up capacity of dispatchable generation capacity to cover periods that the wind is not blowing. To address this issue it has been proposed to create a "supergrid" to connect national grids together across western Europe, ranging from Denmark across the southern North Sea to England and the Celtic Sea to Ireland, and further south to France and Spain especially in Higueruela which was for some time the biggest wind farm in the world. The idea is that by the time a low pressure area has moved away from Denmark to the Baltic Sea
the next low appears off the coast of Ireland. Therefore, while it is
true that the wind is not blowing everywhere all of the time, it will
always be blowing somewhere.
In July 2022, it became operative Seagreen, the world's deepest fixed-bottom wind farm. Located 26 miles off the Angus coastline, in Scotland, it has 114 turbines that generate 1.1 gigawatts (GW) of electricity.
India has the fifth largest installed wind power capacity in the world. As of 31 March 2014, the installed capacity of wind power was 21136.3 MW mainly spread across Tamil Nadu state (7253 MW).Wind power accounts nearly 8.5% of India's total installed power
generation capacity, and it generates 1.6% of the country's power.
In Japan's electricity sector, wind power
generates a small proportion of the country's electricity. It has been
estimated that Japan has the potential for 144 gigawatts (GW) for
onshore wind and 608 GW of offshore wind capacity.
As of 2020, the country had a total installed capacity of 4.2 GW.
As of 2018, government targets for wind power deployment were
relatively low when compared to other countries, at 1.7% of electricity
production by 2030.
In December 2020, the Japanese government announced plans to install up to 45 GW of offshore wind power by 2040.
The 117 MW Tafila Wind Farm in Jordan was inaugurated in December 2015, and is the first large scale wind farm project in the region.
Morocco
Morocco
has undertaken a vast wind energy program, to support the development
of renewable energy and energy efficiency in the country. The Moroccan
Integrated Wind Energy Project, spanning over a period of 10 years with a
total investment estimated at $3.25 billion, will enable the country to
bring the installed capacity, from wind energy, from 280 MW in 2010 to
2000 MW in 2020.
Pakistan has wind corridors in Jhimpir, Gharo and Keti Bundar in
Sindh province and is currently developing wind power plants in Jhimpir
and Mirpur Sakro (District Thatta). The government of Pakistan decided
to develop wind power energy sources due to problems supplying energy to
the southern coastal regions of Sindh and Balochistan.
The Zorlu Energy Putin Power Plant is the first wind power plant in
Pakistan. The wind farm is being developed in Jhimpir, by Zorlu Energy
Pakistan the local subsidiary of a Turkish company. The total cost of
project is $136 million.[3] Completed in 2012, it has a total capacity
of around 56MW.
Fauji Fertilizer Company Energy Limited, has built a 49.5 MW wind Energy
Farm at Jhimpir. Contract of supply of mechanical design was awarded to
Nordex and Descon Engineering Limited. Nordex a German wind turbine
manufacturer. In the end of 2011 49.6 MW will be completed. Pakistani
Govt. also has issued LOI of 100 MW Wind power plant to FFCEL. Pakistani
Govt. has plans to achieve electric power up to 2500 MW by the end of
2015 from wind energy to bring down energy shortage.
Currently four wind farms are operational (Fauji Fertilizer 49.5
MW (subsidiary of Fauji Foundation), Three Gorges 49.5 MW, Zorlu Energy
Pakistan 56 MW, Sapphire Wind Power Co Ltd 52.6 MW) and six are under
construction phase ( Master Wind Energy Ltd 52.6 MW, Sachal Energy
Development Ltd 49.5 MW, Yunus Energy Ltd 49.5 MW, Gul Energy 49.5 MW,
Metro Energy 49.5 MW, Tapal Energy ) and expected to achieve COD in
2017.
In Gharo wind corridor, two wind farms (Foundation Energy 1 &
II each 49.5 MW) are operational while two wind farms Tenaga Generasi
Ltd 49.5 MW and HydroChina Dawood Power Pvt Ltd 49.5 are under
construction and expected to achieve COD in 2017.
According to a USAID report, Pakistan has the potential of
producing 150,000 megawatts of wind energy, of which only the Sindh
corridor can produce 40,000 megawatts.
Philippines
The Philippines has the first windfarm in Southeast Asia. Located
Northern part of the countries' biggest island Luzon, alongside the
seashore of Bangui, Ilocos Norte.
The wind farm uses 20 units of 70-metre (230 ft) high Vestas V82
1.65 MW wind turbines, arranged on a single row stretching along a
nine-kilometer shoreline off Bangui Bay, facing the West Philippine Sea.
Phase I of the NorthWind power project in Bangui Bay consists of
15 wind turbines, each capable of producing electricity up to a maximum
capacity of 1.65 MW, for a total of 24.75 MW. The 15 on-shore turbines
are spaced 326 metres (1,070 ft) apart, each 70 metres (230 ft) high,
with 41 metres (135 ft) long blades, with a rotor diameter of 82 metres
(269 ft) and a wind swept area of 5,281 square metres (56,840 sq ft).
Phase II was completed in August 2008, and added 5 more wind turbines
with the same capacity, and brought the total capacity to 33 MW. All 20
turbines describes a graceful arc reflecting the shoreline of Bangui
Bay, facing the West Philippine Sea.
Adjacent municipalities of Burgos and Pagudpud followed with 50 and 27 wind turbines with a capacity of 3 MW each for a Total of 150 MW and 81 MW respectively.
Sri
Lanka has received funding from the Asian Development Bank amounting to
$300 million to invest in renewable energies. From this funding as well
as $80 million from the Sri Lankan Government and $60 million from
France's Agence Française de Développement, Sri Lanka is building two
100MW wind farms from 2017 due to be completed by late 2020 in Northern
Sri Lanka.
As of September 2015 a number of sizable wind farms have been constructed in South Africa mostly in the Western Cape region. These include the 100 MW Sere Wind Farm and the 138 MW Gouda Wind Facility.
Most future wind farms in South Africa are earmarked for locations along the Eastern Cape coastline.
Eskom has constructed one small scale prototype windfarm at Klipheuwel
in the Western Cape and another demonstrator site is near Darling with phase 1 completed. The first commercial wind farm, Coega Wind Farm in Port Elisabeth, was developed by the Belgian company Electrawinds.
U.S. wind power installed capacity in September 2019 exceeded 100,125 MW and supplies 6.94% of the nation's electricity. The majority of wind farms in the United States are located in the Central Plains, with slow expansion into other regions of the country.
New installations place the U.S. on a trajectory to generate 20% of the nation's electricity by 2030 from wind energy.
Growth in 2008 channeled some $17 billion into the economy, positioning
wind power as one of the leading sources of new power generation in the
country, along with natural gas.
Wind projects completed in 2008 accounted for about 42% of the entire
new power-producing capacity added in the U.S. during the year.
Texas, with 27,036 MW of capacity, has the most installed wind power capacity of any U.S. state, followed by Iowa with 8,965 MW and Oklahoma with 8,072 MW. Iowa is the leading state in terms of wind energy accounting for nearly 40% of total energy production in 2019. The Alta Wind Energy Center (1,020 MW) in California is the nation's largest wind farm in terms of capacity. Altamont Pass Wind Farm is the largest wind farm in the U.S. in terms of the number of individual turbines.
At the end of 2019, about 114,000 people were employed in the U.S. wind industry, and GE Energy was the largest domestic wind turbine manufacturer.
In 2018, US wind power provided enough electricity to power
approximately 25 million homes, avoiding the emissions of 200 million
tons of carbon.
Impact on environment and landscape
Greenhouse gas emissions per energy source. Wind energy is one of the sources with the least greenhouse gas emissions.Livestock grazing near a wind turbine.
Onshore (on-land) wind farms can have a significant visual impact and impact on the landscape.Due to a very low surface power density and spacing requirements, wind farms typically need to be spread over more land than other power stations. Their network of turbines, access roads, transmission lines, and substations can result in "energy sprawl"; although land between the turbines and roads can still be used for agriculture.
Conflicts arise especially in scenic and culturally-important landscapes. Siting restrictions (such as setbacks) may be implemented to limit the impact. The land between the turbines and access roads can still be used for farming and grazing. They can lead to "industrialization of the countryside". Some wind farms are opposed for potentially spoiling protected scenic areas, archaeological landscapes and heritage sites. A report by the Mountaineering Council of Scotland concluded that wind farms harmed tourism in areas known for natural landscapes and panoramic views.
Habitat loss and fragmentation are the greatest potential impacts on wildlife of onshore wind farms, but they are small and can be mitigated if proper monitoring and mitigation strategies are implemented. The worldwide ecological impact is minimal. Thousands of birds and bats, including rare species, have been killed by wind turbine blades,
as around other manmade structures, though wind turbines are
responsible for far fewer bird deaths than fossil-fuel infrastructure. This can be mitigated with proper wildlife monitoring.
Many wind turbine blades are made of fiberglass and some only had a lifetime of 10 to 20 years. Previously, there was no market for recycling these old blades, and they were commonly disposed of in landfills.
Because blades are hollow, they take up a large volume compared to
their mass. Since 2019, some landfill operators have begun requiring
blades to be crushed before being landfilled. Blades manufactured in the 2020s are more likely to be designed to be completely recyclable.
Wind turbines also generate noise. At a distance of 300 metres (980 ft)
this may be around 45 dB, which is slightly louder than a refrigerator.
At 1.5 km (1 mi) distance they become inaudible. There are anecdotal reports of negative health effects on people who live very close to wind turbines. Peer-reviewed research has generally not supported these claims. Pile-driving to construct non-floating wind farms is noisy underwater, but in operation offshore wind is much quieter than ships.
There have been multiple scientific, peer-reviewed studies into wind
farm noise, which have concluded that infrasound from wind farms is not a
hazard to human health and there is no verifiable evidence for 'Wind Turbine Syndrome' causing Vibroacoustic disease, although some suggest further research might still be useful.
In a 2009 report about "Rural Wind Farms", a Standing Committee
of the Parliament of New South Wales, Australia, recommended a minimum
setback of two kilometres between wind turbines and neighboring houses
(which can be waived by the affected neighbor) as a precautionary
approach.
A 2014 paper suggests that the 'Wind Turbine Syndrome' is mainly caused by the nocebo effect and other psychological mechanisms. Australian science magazine Cosmos
states that although the symptoms are real for those who suffer from
the condition, doctors need to first eliminate known causes (such as
pre-existing cancers or thyroid disease) before reaching definitive
conclusions with the caveat that new technologies often bring new,
previously unknown health risks.
Utility-scale wind farms must have access to transmission lines to
transport energy. The wind farm developer may be obliged to install
extra equipment or control systems in the wind farm to meet the
technical standards set by the operator of a transmission line.
The intermittent
nature of wind power can pose complications for maintaining a stable
power grid when wind farms provide a large percentage of electricity in
any one region.
However wind farms are more resistant to military attack than
thermal power plants as many missiles are needed to destroy them not
just one.
Ground radar interference
Wind farm interference (in yellow circle) on radar map
Wind farms can interfere with ground radar systems used for military, weather and air traffic control.
The large, rapidly moving blades of the turbines can return signals to
the radar that can be mistaken as an aircraft or weather pattern.
Actual aircraft and weather patterns around wind farms can be accurately
detected, as there is no fundamental physical constraint preventing
that. But aging radar infrastructure is significantly challenged with
the task. The US military is using wind turbines on some bases, including Barstow near the radar test facility.
Effects
The
level of interference is a function of the signal processors used within
the radar, the speed of the aircraft and the relative orientation of
wind turbines/aircraft with respect to the radar. An aircraft flying
above the wind farm's turning blades could become impossible to detect
because the blade tips can be moving at nearly aircraft velocity.
Studies are currently being performed to determine the level of this
interference and will be used in future site planning. Issues include masking (shadowing), clutter (noise), and signal alteration. Radar issues have stalled as much as 10,000 MW of projects in USA.
Some very long range radars are not affected by wind farms.
Mitigation
Permanent problem solving include a non-initiation window to hide the turbines while still tracking aircraft over the wind farm, and a similar method mitigates the false returns.
England's Newcastle Airport is using a short-term mitigation; to "blank" the turbines on the radar map with a software patch. Wind turbine blades using stealth technology are being developed to mitigate radar reflection problems for aviation. As well as stealth windfarms, the future development of infill radar systems could filter out the turbine interference.
A mobile radar system, the Lockheed MartinTPS-77, can distinguish between aircraft and wind turbines, and more than 170 TPS-77 radars are in use around the world.
Federal Aviation Administration advises aircraft without position-reporting technologies such as transponders to avoid flight within 1 nautical mile (1.9 km; 1.2 mi) at all altitudes from wind turbine farms.
Radio reception interference
There
are also reports of negative effects on radio and television reception
in wind farm communities. Potential solutions include predictive
interference modelling as a component of site selection.
Impact on agriculture
A
2010 study found that in the immediate vicinity of wind farms, the
climate is cooler during the day and slightly warmer during the night
than the surrounding areas due to the turbulence generated by the
blades.
In another study an analysis carried out on corn and soybean
crops in the central areas of the United States noted that the
microclimate generated by wind turbines improves crops as it prevents
the late spring and early autumn frosts, and also reduces the action of
pathogenic fungi that grow on the leaves. Even at the height of summer
heat, the lowering of 2.5–3 degrees above the crops due to turbulence
caused by the blades can make a difference for the cultivation of corn.
Simplified electrical grid with energy storageSimplified grid energy flow with and without idealized energy storage for the course of one day
Grid energy storage (also called large-scale energy storage) is a collection of methods used for energy storage on a large scale within an electrical power grid. Electrical energy is stored during times when electricity is plentiful and inexpensive (especially from intermittent power sources such as renewable electricity from wind power, tidal power and solar power) or when demand is low, and later returned to the grid when demand is high, and electricity prices tend to be higher.
Developments in battery
storage have enabled commercially viable projects to store energy
during peak production and release during peak demand, and for use when
production unexpectedly falls giving time for slower responding
resources to be brought online. Green hydrogen, which is generated from electrolysis of water
via electricity generated by renewables or relatively lower carbon
emission sources, is a more economical means of long-term renewable
energy storage in terms of capital expenditures than pumped-storage hydroelectricity or batteries.
Two alternatives to grid storage are the use of peaking power plants to fill in supply gaps and demand response to shift load to other times.
Benefits
Any electrical power grid
must match electricity production to consumption, both of which vary
drastically over time. Any combination of energy storage and demand
response has these advantages:
fuel-based power plants (i.e. coal, oil, gas, nuclear) can be more efficiently and easily operated at constant production levels
electricity generated by intermittent sources can be stored and used
later, whereas it would otherwise have to be transmitted for sale
elsewhere, or shut down
peak generating or transmission capacity can be reduced by the total potential of all storage plus deferrable loads (see demand side management), saving the expense of this capacity
more stable pricing – the cost of the storage or demand management
is included in pricing so there is less variation in power rates charged
to customers, or alternatively (if rates are kept stable by law) less
loss to the utility from expensive on-peak wholesale power rates when
peak demand must be met by imported wholesale power
emergency preparedness – vital needs can be met reliably even with
no transmission or generation going on while non-essential needs are
deferred
Energy derived from solar, tidal and wind sources inherently varies
on time scales ranging from minutes to weeks or longer – the amount of
electricity produced varies with time of day, moon phase, season, and
random factors such as the weather. Thus, renewables in the absence of
storage present special challenges to electric utilities. While hooking
up many separate wind sources can reduce the overall variability, solar
is reliably not available at night, and tidal power shifts with the
moon, so slack tides occur four times a day.
How much this affects any given utility varies significantly. In a summer peak utility, more solar can generally be absorbed and matched to demand. In winter peak
utilities, to a lesser degree, wind correlates to heating demand and
can be used to meet that demand. Depending on these factors, beyond
about 20–40% of total generation, grid-connected intermittent sources such as solar power and wind power tend to require investment in grid interconnections, grid energy storage or demand-side management.
In an electrical grid
without energy storage, generation that relies on energy stored within
fuels (coal, biomass, natural gas, nuclear) must be scaled up and down
to match the rise and fall of electrical production from intermittent
sources (see load following power plant).
While hydroelectric and natural gas plants can be quickly scaled up or
down to follow the wind, coal and nuclear plants take considerable time
to respond to load. Utilities with less natural gas or hydroelectric
generation are thus more reliant on demand management, grid
interconnections or costly pumped storage.
The French consulting firm Yole Développement estimates the
"stationary storage" market could be a $13.5 billion opportunity by
2023, compared with less than $1 billion in 2015.
Demand side management and grid storage
A sense of units and scale for electrical energy production and consumption
The demand side can also store electricity from the grid, for example charging a battery electric vehicle stores energy for a vehicle and storage heaters, district heating storage or ice storage provide thermal storage for buildings. At present this storage serves only to shift consumption to the off-peak time of day, no electricity is returned to the grid.
The need for grid storage to provide peak power is reduced by demand side time of use pricing, one of the benefits of smart meters.
At the household level, consumers may choose less expensive off-peak
times to wash and dry clothes, use dishwashers, take showers and cook.
As well, commercial and industrial users will take advantage of cost
savings by deferring some processes to off-peak times.
Regional impacts from the unpredictable operation of wind power has created a new need for interactive demand response,
where the utility communicates with the demand. Historically this was
only done in cooperation with large industrial consumers, but now may be
expanded to entire grids.
For instance, a few large-scale projects in Europe link variations in
wind power to change industrial food freezer loads, causing small
variations in temperature. If communicated on a grid-wide scale, small
changes to heating/cooling temperatures would instantly change
consumption across the grid.
A report released in December 2013 by the United States Department of Energy
further describes the potential benefits of energy storage and demand
side technologies to the electric grid: "Modernizing the electric system
will help the nation meet the challenge of handling projected energy
needs—including addressing climate change
by integrating more energy from renewable sources and enhancing
efficiency from non-renewable energy processes. Advances to the electric
grid must maintain a robust and resilient electricity delivery system,
and energy storage can play a significant role in meeting these
challenges by improving the operating capabilities of the grid, lowering
cost and ensuring high reliability, as well as deferring and reducing
infrastructure investments. Finally, energy storage can be instrumental
for emergency preparedness because of its ability to provide backup
power as well as grid stabilization services". The report was written by a core group of developers representing Office of Electricity Delivery and Energy Reliability, ARPA-E, Office of Science, Office of Energy Efficiency and Renewable Energy, Sandia National Laboratories, and Pacific Northwest National Laboratory; all of whom are engaged in the development of grid energy storage.
Energy storage for grid applications
Energy storage assets are a valuable asset for the electrical grid. They can provide benefits and services such as load management, power quality and uninterruptible power supply to increase the efficiency and supply security. This becomes more and more important in regard to the energy transition and the need for a more efficient and sustainable energy system.
Numerous energy storage technologies (pumped-storage hydroelectricity, electric battery, flow battery, flywheel energy storage, supercapacitor
etc.) are suitable for grid-scale applications, however their
characteristics differ. For example, a pumped-hydro station is well
suited for bulk load management applications due to their large
capacities and power capabilities. However, suitable locations are
limited and their usefulness fades when dealing with localized power quality issues. On the other hand, flywheels and capacitors are most effective in maintaining power quality
but lack storage capacities to be used in larger applications. These
constraints are a natural limitation to the storage's applicability.
Several studies have developed interest and investigated the
suitability or selection of the optimal energy storage for certain
applications. Literature surveys comprise the available information of
the state-of-the-art and compare the storage's uses based on current
existing projects. Other studies take a step further in evaluating energy storage with each other and rank their fitness based on multiple-criteria decision analysis. Another paper proposed an evaluation scheme through the investigation and modelling of storage as equivalent circuits.An indexing approach has also been suggested in a few studies, but is still in the novel stages.
In order to gain increased economic potential of grid connected energy
storage systems, it is of interest to consider a portfolio with several
services for one or more applications for an energy storage system. By
doing so, several revenue streams can be achieved by a single storage
and thereby also increasing the degree of utilization. To mention two examples, a combination of frequency response and reserve services is examined in, meanwhile load peak shaving together with power smoothing is considered in.
One grid energy storage method is to use off-peak or renewably generated electricity to compress air, which is usually stored in an old mine or some other kind of geological feature. When electricity demand is high, the compressed air is heated with a small amount of natural gas and then goes through turboexpanders to generate electricity.
Compressed air storage is typically around 60–90% efficient.
Another electricity storage method is to compress and cool air, turning it into liquid air,
which can be stored, and expanded when needed, turning a turbine,
generating electricity, with a storage efficiency of up to 70%.
A commercial liquid-air energy storage plant is under construction in the North of England,
with commercial operation planned for 2022.
The energy storage capacity of 250MWh of the plant will be nearly twice
the capacity of the world's largest existing lithium-ion battery, the Hornsdale Power Reserve in South Australia.
Gaseous carbon dioxide can be compressed to store energy at grid
scale. The gas is well suited to this role because, unlike air, it
liquifies at ambient temperatures. Liquid CO2 can be stored indefinitely in high-pressure cylinders, for use when needed.
The main proponent of the technology is start-up company Energy
Dome, which in 2022 built a 2.5MW/4MWh demonstrator plant in Sardinia.
The company claim a round trip efficiency of 75% and a projected cost of
EUR220/kWh of storage capacity, which is half that of Li-ion batteries.
A 900 watt direct current light plant using 16 separate lead acid battery cells (32 volts) from 1917.Learning curve of lithium-ion batteries: the price of batteries declined by 97% in three decades.
Battery storage was used in the early days of direct current electric power. Where AC grid power was not readily available, isolated lighting plants run by wind turbines
or internal combustion engines provided lighting and power to small
motors. The battery system could be used to run the load without
starting the engine or when the wind was calm. A bank of lead–acid
batteries in glass jars both supplied power to illuminate lamps, as well
as to start an engine to recharge the batteries. Battery storage
technology is typically around 80% to more than 90% efficient for newer
lithium-ion devices.
Battery systems connected to large solid-state converters have
been used to stabilize power distribution networks. Some grid batteries
are co-located with renewable energy plants, either to smooth the power
supplied by the intermittent wind or solar output, or to shift the power
output into other hours of the day when the renewable plant cannot
produce power directly (see Installation examples).
These hybrid systems (generation and storage) can either alleviate the
pressure on the grid when connecting renewable sources or be used to
reach self-sufficiency and work "off-the-grid" (see Stand-alone power system).
Contrary to electric vehicle applications, batteries for
stationary storage do not suffer from mass or volume constraints.
However, due to the large amounts of energy and power implied, the cost
per power or energy unit is crucial. The relevant metrics to assess the
interest of a technology for grid-scale storage is the $/Wh (or $/W)
rather than the Wh/kg (or W/kg). The electrochemical grid storage was
made possible thanks to the development of the electric vehicle, that
induced a fast decrease in the production costs of batteries below
$300/kWh. By optimizing the production chain, major industrials aimed to
reach $150/kWh by the end of 2020, but actually achieved $140/kWh. The
rate of decline in battery prices has consistently outpaced most
estimates, reaching $132/kWh in 2021. These batteries rely on a lithium-ion
technology, which is suited for mobile applications (high cost, high
density). Technologies optimized for the grid should focus on low cost
per kWh. Lithium iron phosphate batteries are increasingly being used
in both vehicles and grid storage because of their low cost, scale and
acceptable energy density for many applications.
Grid-oriented battery technologies
Sodium-ion batteries
are a cheap and sustainable alternative to lithium-ion, because sodium
is far more abundant and cheaper than lithium, but it has a lower power
density. However, they are still on the early stages of their
development.
Automotive-oriented technologies rely on solid electrodes, which
feature a high energy density but require an expensive manufacturing
process. Liquid electrodes represent a cheaper and less dense
alternative as they do not need any processing.
Molten-salt/liquid-metal batteries
These
batteries are composed of two molten metal alloys separated by an
electrolyte. They are simple to manufacture but require a temperature of
several hundred degree Celsius to keep the alloys in a liquid state.
This technology includes ZEBRA, sodium-sulfur batteries and liquid metal. Sodium sulphur batteries are being used for grid storage in Japan and in the United States. The electrolyte is composed of solid beta alumina. The liquid metal battery, developed by the group of Pr. Donald Sadoway,
uses molten alloys of magnesium and antimony separated by an
electrically insulating molten salt. It is being brought to market by
MIT spinoff company Ambri, which is currently contracted to install a first 250MWh system for TerraScale data centre company near Reno, Nevada.
Flow batteries
In rechargeable flow batteries,
that store energy in liquids, such solutions of transition metal ions
in water at room temperature. Flow batteries have the advantages of low
capital cost for charge-discharge duration over 2-4 h, and of long
durability (many years). Flow batteries are inferior to lithium-ion batteries in terms of energy efficiency. Flow batteries are currently deployed for storing energy from intermittent renewable sources, such as wind and solar.
Vanadium redox batteries is most technologically and commercially advanced type of flow battery. Currently there are dozens of Vanadium Redox Flow batteries installed at different sites including; Huxley Hill wind farm (Australia), Tomari Wind Hills at Hokkaidō (Japan), as well as in non-wind farm applications. A 12 MW·h flow battery was to be installed at the Sorne Hill wind farm (Ireland). These storage systems are designed to smooth out transient wind fluctuations.
Examples
In Puerto Rico a system
with a capacity of 20 megawatts for 15 minutes (5 megawatt hour)
stabilizes the frequency of electric power produced on the island. A 27
megawatt 15-minute (6.75 megawatt hour) nickel-cadmium battery bank was
installed at Fairbanks Alaska in 2003 to stabilize voltage at the end of
a long transmission line.
In 2016, a zinc-ion battery was proposed for use in grid storage applications.
In 2017, the California Public Utilities Commission installed 396 refrigerator-sized stacks of Tesla batteries at the Mira Loma substation in Ontario, California.
The stacks are deployed in two modules of 10 MW each (20 MW in total),
each capable of running for 4 hours, thus adding up to 80 MWh of
storage. The array is capable of powering 15,000 homes for over four
hours.
The largest grid storage batteries in the United States include
the 31.5 MW battery at Grand Ridge Power plant in Illinois and the
31.5 MW battery at Beech Ridge, West Virginia. Two batteries under construction in 2015 include the 400 MWh (100 MW for 4 hours) Southern California Edison project and the 52 MWh project on Kauai, Hawaii to entirely time shift a 13MW solar farm's output to the evening. Two batteries are in Fairbanks, Alaska (40 MW for 7 minutes using Ni-Cd cells), and in Notrees, Texas (36 MW for 40 minutes using lead–acid batteries). A 13 MWh battery made of used batteries from Daimler's Smart electric drive cars is being constructed in Lünen, Germany, with an expected second life of 10 years.
In 2015, a 221 MW battery storage was installed in the US, with total capacity expected to reach 1.7 GW in 2020.
The UK had a 50 MW lithium-ion grid-battery installed in Hertfordshire in 2018.
In February 2021, construction began on a 50 MW battery storage
development in Burwell, Cambridgeshire and a 40 MW site in Barnsley,
South Yorkshire.
In November 2017 Tesla installed a 100 MW, 129 MWh battery system in South Australia. The Australian Energy Market Operator
stated that this "is both rapid and precise, compared to the service
typically provided by a conventional synchronous generation unit".
Companies are researching the possible use of electric vehicles to
meet peak demand. A parked and plugged-in electric vehicle could sell
the electricity from the battery during peak loads and charge either
during night (at home) or during off-peak.
Plug-in hybrid or electric cars could be used for their energy storage capabilities. Vehicle-to-grid technology can be employed, turning each vehicle with its 20 to 50 kWh battery pack
into a distributed load-balancing device or emergency power source.
This represents two to five days per vehicle of average household
requirements of 10 kWh per day, assuming annual consumption of
3,650 kWh. This quantity of energy is equivalent to between 60 and 480
kilometres (40 and 300 mi) of range in such vehicles consuming 0.1 to
0.3 kilowatt-hours per kilometre (0.16 to 0.5 kWh/mi). These figures can
be achieved even in home-made electric vehicle conversions.
Some electric utilities plan to use old plug-in vehicle batteries
(sometimes resulting in a giant battery) to store electricity
However, a large disadvantage of using vehicle to grid energy storage
would be if each storage cycle stressed the battery with one complete
charge-discharge cycle. However, one major study showed that used intelligently, vehicle-to-grid storage actually improved the batteries longevity.
Conventional (cobalt-based) lithium-ion batteries break down with the
number of cycles – newer li-ion batteries do not break down
significantly with each cycle, and so have much longer lives. One
approach is to reuse unreliable vehicle batteries in dedicated grid
storage as they are expected to be good in this role for ten years.
If such storage is done on a large scale it becomes much easier to
guarantee replacement of a vehicle battery degraded in mobile use, as
the old battery has value and immediate use.
Mechanical inertia is the basis of this storage method. When the electric power flows into the device, an electric motor
accelerates a heavy rotating disc. The motor acts as a generator when
the flow of power is reversed, slowing down the disc and producing
electricity. Electricity is stored as the kinetic energy of the disc. Friction must be kept to a minimum to prolong the storage time. This is often achieved by placing the flywheel in a vacuum and using magnetic bearings,
tending to make the method expensive. Greater flywheel speeds allow
greater storage capacity but require strong materials such as steel or composite materials to resist the centrifugal forces.
The ranges of power and energy storage technology that make this method
economic, however, tends to make flywheels unsuitable for general power
system application; they are probably best suited to load-leveling
applications on railway power systems and for improving power quality in renewable energy systems such as the 20MW system in Ireland.
Applications that use flywheel storage are those that require very high bursts of power for very short durations such as tokamak and laser experiments where a motor generator is spun up to operating speed and is partially slowed down during discharge.
This potential solution has been implemented by EDA in the Azores on the islands of Graciosa and Flores. This system uses an 18 megawatt-second flywheel to improve power quality
and thus allow increased renewable energy usage. As the description
suggests, these systems are again designed to smooth out transient
fluctuations in supply, and could never be used to cope with an outage
exceeding a couple of days.
Powercorp in Australia have been developing applications using
wind turbines, flywheels and low load diesel (LLD) technology to
maximize the wind input to small grids. A system installed in Coral Bay,
Western Australia, uses wind turbines coupled with a flywheel based
control system and LLDs. The flywheel technology enables the wind
turbines to supply up to 95 percent of Coral Bay's energy supply at
times, with a total annual wind penetration of 45 percent.
Hydrogen is being developed as an electrical energy storage medium.
Hydrogen is produced, then compressed or liquefied, cryogenically
stored at −252.882 °C, and then converted back to electrical energy or
heat. Hydrogen can be used as a fuel for portable (vehicles) or
stationary energy generation. Compared to pumped water storage and
batteries, hydrogen has the advantage that it is a high energy density
fuel. Green hydrogen, from electrolysis of water, is a more economical means of long-term renewable energy storage in terms of capital expenditures than pumped-storage hydroelectricity or batteries.
The AC-to-AC efficiency of hydrogen storage has been shown to be on the order of 20 to 45%, which imposes economic constraints.
The price ratio between purchase and sale of electricity must be at
least proportional to the efficiency in order for the system to be
economic. Hydrogen fuel cells can respond quickly enough to correct
rapid fluctuations in electricity demand or supply and regulate
frequency. Whether hydrogen can use natural gas infrastructure depends
on the network construction materials, standards in joints, and storage
pressure.
The equipment necessary for hydrogen energy storage includes an electrolysis plant, hydrogen compressors or liquifiers, and storage tanks.
Biohydrogen is a process being investigated for producing hydrogen using biomass.
Some nuclear power plants may be able to benefit from a symbiosis
with hydrogen production. High temperature (950 to 1,000 °C) gas cooled
nuclear generation IV reactors have the potential to electrolyze hydrogen from water by thermochemical means using nuclear heat as in the sulfur-iodine cycle. The first commercial reactors are expected in 2030.
A community based pilot program using wind turbines and hydrogen generators was started in 2007 in the remote community of Ramea, Newfoundland and Labrador. A similar project has been going on since 2004 in Utsira, a small Norwegian island municipality.
Underground hydrogen storage
Underground hydrogen storage is the practice of hydrogen storage in caverns, salt domes and depleted oil and gas fields. Large quantities of gaseous hydrogen have been stored in caverns by Imperial Chemical Industries (ICI) for many years without any difficulties. The European project Hyunder
indicated in 2013 that for the storage of wind and solar energy an
additional 85 caverns are required as it cannot be covered by PHES and CAES systems.
Power to gas
Power to gas is a technology which converts electrical power to a gas fuel. There are 2 methods, the first is to use the electricity for water splitting and inject the resulting hydrogen into the natural gas grid. The second less efficient method is used to convert carbon dioxide and water to methane, (see natural gas) using electrolysis and the Sabatier reaction.
The excess power or off peak power generated by wind generators or
solar arrays is then used for load balancing in the energy grid. Using
the existing natural gas system for hydrogen, fuel cell maker Hydrogenics and natural gas distributor Enbridge have teamed up to develop such a power to gas system in Canada.
Pipeline storage of hydrogen where a natural gas network is used for the storage of hydrogen. Before switching to natural gas, the German gas networks were operated using towngas,
which for the most part consisted of hydrogen. The storage capacity of
the German natural gas network is more than 200,000 GW·h which is enough
for several months of energy requirement. By comparison, the capacity
of all German pumped-storage power plants amounts to only about 40 GW·h.
The transport of energy through a gas network is done with much less
loss (<0.1%) than in a power network (8%). The use of the existing natural gas pipelines for hydrogen was studied by NaturalHy
The power-to-ammonia concept
The power-to-ammonia concept offers a carbon-free energy storage route with a diversified application palette. At times when there is surplus low-carbon power,
it can be used to create ammonia fuel. Ammonia may be produced by
splitting water into hydrogen and oxygen with electricity, then high
temperature and pressure are used to combine nitrogen from the air with
the hydrogen, creating ammonia. As a liquid it is similar to propane,
unlike hydrogen alone, which is difficult to store as a gas under
pressure or to cryogenically liquefy and store at −253 °C.
Just like natural gas, the stored ammonia can be used as a
thermal fuel for transportation and electricity generation or used in a
fuel cell.
A standard 60,000 m³ tank of liquid ammonia contains about 211 GWh of
energy, equivalent to the annual production of roughly 30 wind turbines.
Ammonia can be burned cleanly: water and nitrogen are released, but no
CO2 and little or no nitrogen oxides. Ammonia has multiple uses besides being an energy carrier, it is the basis for the production of many chemicals, the most common use is for fertilizer.
Given this flexibility of usage, and given that the infrastructure for
the safe transport, distribution and usage of ammonia is already in
place, it makes ammonia a good candidate to be a large-scale,
non-carbon, energy carrier of the future.
In 2008, world pumped-storage generating capacity was 104 GW,
while other sources claim 127 GW, which comprises the vast majority of
all types of grid electric storage – all other types combined are some
hundreds of MW.
In many places, pumped-storage hydroelectricity is used to even
out the daily generating load, by pumping water to a high storage
reservoir during off-peak hours and weekends, using the excess base-load
capacity from coal or nuclear sources. During peak hours, this water
can be used for hydroelectric
generation, often as a high value rapid-response reserve to cover
transient peaks in demand. Pumped storage recovers about 70% to 85% of
the energy consumed, and is currently the most cost effective form of
mass power storage.
The chief problem with pumped storage is that it usually requires two
nearby reservoirs at considerably different heights, and often requires
considerable capital expenditure.
Pumped water systems have high dispatchability, meaning they can come on-line very quickly, typically within 15 seconds, which makes these systems very efficient at soaking up variability in electrical demand from consumers. There is over 90 GW of pumped storage in operation around the world, which is about 3% of instantaneous global generation capacity. Pumped water storage systems, such as the Dinorwig storage system in Britain, hold five or six hours of generating capacity, and are used to smooth out demand variations.
Another example is the 1836 MW Tianhuangping Pumped-Storage Hydro Plant in China, which has a reservoir capacity of eight million cubic meters (2.1 billion U.S. gallons or the volume of water over Niagara Falls in 25 minutes) with a vertical distance of 600 m (1970 feet). The reservoir can provide about 13 GW·h of stored gravitational potential energy (convertible to electricity at about 80% efficiency), or about 2% of China's daily electricity consumption.
A new concept in pumped-storage is utilizing wind energy or solar power to pump water. Wind turbines or solar cells that direct drive water pumps for an energy storing wind or solar dam
can make this a more efficient process but are limited. Such systems
can only increase kinetic water volume during windy and daylight
periods. A study published in 2013 showed rooftop solar, coupled to
existing pumped-storage, could replace the reactors lost at Fukushima
with an equivalent capacity factor.
Hydroelectric dams with large reservoirs can also be operated to
provide peak generation at times of peak demand. Water is stored in the
reservoir during periods of low demand and released through the plant
when demand is higher. The net effect is the same as pumped storage,
but without the pumping loss. Depending on the reservoir capacity the
plant can provide daily, weekly, or seasonal load following.
Many existing hydroelectric dams are fairly old (for example, the Hoover Dam
was built in the 1930s), and their original design predated the newer
intermittent power sources such as wind and solar by decades. A
hydroelectric dam originally built to provide baseload power
will have its generators sized according to the average flow of water
into the reservoir. Uprating such a dam with additional generators
increases its peak power output capacity, thereby increasing its
capacity to operate as a virtual grid energy storage unit. The United States Bureau of Reclamation reports an investment cost of $69 per kilowatt capacity to uprate an existing dam,
compared to more than $400 per kilowatt for oil-fired peaking
generators. While an uprated hydroelectric dam does not directly store
excess energy from other generating units, it behaves equivalently by
accumulating its own fuel – incoming river water – during periods of
high output from other generating units. Functioning as a virtual grid
storage unit in this way, the uprated dam is one of the most efficient
forms of energy storage, because it has no pumping losses to fill its
reservoir, only increased losses to evaporation and leakage.
A dam which impounds a large reservoir can store and release a
correspondingly large amount of energy, by controlling river outflow and
raising or lowering its reservoir level a few meters. Limitations do
apply to dam operation, their releases are commonly subject to
government regulated water rights
to limit downstream effect on rivers. For example, there are grid
situations where baseload thermal plants, nuclear or wind turbines are
already producing excess power at night, dams are still required to
release enough water to maintain adequate river levels, whether
electricity is generated or not. Conversely there's a limit to peak
capacity, which if excessive could cause a river to flood for a few
hours each day.
Superconducting magnetic energy storage (SMES) systems store energy in the magnetic field created by the flow of direct current in a superconducting coil which has been cryogenically
cooled to a temperature below its superconducting critical temperature.
A typical SMES system includes three parts: superconducting coil, power
conditioning system and cryogenically cooled refrigerator. Once the
superconducting coil is charged, the current will not decay and the
magnetic energy can be stored indefinitely. The stored energy can be
released back to the network by discharging the coil. The power
conditioning system uses an inverter/rectifier to transform alternating current
(AC) power to direct current or convert DC back to AC power. The
inverter/rectifier accounts for about 2–3% energy loss in each
direction. SMES loses the least amount of electricity
in the energy storage process compared to other methods of storing
energy. SMES systems are highly efficient; the round-trip efficiency is
greater than 95%. The high cost of superconductors is the primary
limitation for commercial use of this energy storage method.
Due to the energy requirements of refrigeration,
and the limits in the total energy able to be stored, SMES is currently
used for short duration energy storage. Therefore, SMES is most
commonly devoted to improving power quality. If SMES were to be used for utilities it would be a diurnal storage device, charged from base load power at night and meeting peak loads during the day.
There are significant technical challenges yet to be solved for superconducting magnetic energy storage to become practical.
In Denmark the direct storage of electricity is perceived as too
expensive for very large scale usage, albeit significant usage is made
of existing Norwegian Hydro. Instead, the use of existing hot water
storage tanks connected to district heating schemes, heated by either
electrode boilers or heat pumps, is seen as a preferable approach. The
stored heat is then transmitted to dwellings using district heating pipes.
Molten salt is used to store heat collected by a solar power tower so that it can be used to generate electricity in bad weather or at night.
Building heating and cooling systems can be controlled to store
thermal energy in either the building's mass or dedicated thermal
storage tanks. This thermal storage can provide load-shifting or even
more complex ancillary services
by increasing power consumption (charging the storage) during off-peak
times and lowering power consumption (discharging the storage) during
higher-priced peak times. For example, off-peak electricity can be used to make ice
from water, and the ice can be stored. The stored ice can be used to
cool the air in a large building which would have normally used electric
AC, thereby shifting the electric load to off-peak hours. On other
systems stored ice is used to cool the intake air of a gas turbinegenerator, thus increasing the on-peak generation capacity and the on-peak efficiency.
A pumped-heat electricity storage
system uses a highly reversible heat engine/heat pump to pump heat
between two storage vessels, heating one and cooling the other. The
UK-based engineering company Isentropic that is developing the system
claims a potential electricity-in to electricity-out round-trip
efficiency of 72–80%.
A Carnot battery
is a type of energy storage systems that stores electricity in heat
storage and converts the stored heat back to electricity via
thermodynamics cycles. This concept has been investigated and developed
by many research projects recently.
One of the advantage of this type of system is that the cost at
large-scale and long-duration of thermal storage could be much lower
than other storage technologies.
Physical battery; Gravitational potential energy storage with solid masses
Alternatives include storing energy by moving large solid masses
upward against gravity. This can be achieved inside old mine shafts or in specially constructed towers where heavy weights are winched up to store energy and allowed a controlled descent to release it.In rail energy storage,
rail cars carrying large weights are moved up or down a section of
inclined rail track, storing or releasing energy as a result;
In disused oil-well potential energy storage, weights are raised or lowered in a deep, decommissioned oil well.
Using battery storage is said to have a levelized cost of $120 to $170 per MWh. This compares with open cycle gas turbines which, as of 2020, have a cost of around $151–198 per MWh.
Generally speaking, energy storage is economical when the marginal cost
of electricity varies more than the costs of storing and retrieving the
energy plus the price of energy lost in the process. For instance,
assume a pumped-storage reservoir can pump to its upper reservoir a volume of water capable of producing 1,200 MW·h
after all losses are factored in (evaporation and seeping in the
reservoir, efficiency losses, etc.). If the marginal cost of electricity
during off-peak times is $15 per MW·h, and the reservoir operates at
75% efficiency (i.e., 1,500 MW·h are consumed and 1,200 MW·h of energy
are retrieved), then the total cost of filling the reservoir is $22,500.
If all of the stored energy is sold the following day during peak hours
for an average $40 per MW·h, then the reservoir will see revenues of
$48,000 for the day, for a gross profit of $25,500.
However, the marginal cost of electricity varies because of the
varying operational and fuel costs of different classes of generators. At one extreme, base load power plants such as coal-fired power plants and nuclear power
plants are low marginal cost generators, as they have high capital and
maintenance costs but low fuel costs. At the other extreme, peaking power plants such as gas turbinenatural gas
plants burn expensive fuel but are cheaper to build, operate and
maintain. To minimize the total operational cost of generating power,
base load generators are dispatched most of the time, while peak power
generators are dispatched only when necessary, generally when energy
demand peaks. This is called "economic dispatch".
Demand for electricity
from the world's various grids varies over the course of the day and
from season to season. For the most part, variation in electric demand
is met by varying the amount of electrical energy supplied from primary
sources. Increasingly, however, operators are storing lower-cost energy
produced at night, then releasing it to the grid during the peak periods
of the day when it is more valuable.
In areas where hydroelectric dams exist, release can be delayed until
demand is greater; this form of storage is common and can make use of
existing reservoirs. This is not storing "surplus" energy produced
elsewhere, but the net effect is the same – although without the
efficiency losses. Renewable supplies with variable production, like wind and solar power, tend to increase the net variation in electric load, increasing the opportunity for grid energy storage.
It may be more economical to find an alternative market for unused electricity, rather than try and store it. High Voltage Direct Current allows for transmission of electricity, losing only 3% per 1000 km.
The United States Department of Energy's International Energy
Storage Database provides a free list of grid energy storage projects,
many of which show funding sources and amounts.
Load leveling
The demand for electricity from consumers and industry is constantly changing, broadly within the following categories:
Seasonal (during dark winters more electric lighting and heating
is required, while in other climates hot weather boosts the requirement
for air conditioning)
Weekly (most industry closes at the weekend, lowering demand)
Daily (such as the morning peak as offices open and air conditioners get switched on)
Hourly (one method for estimating television viewing figures in the
United Kingdom is to measure the power spikes during advertisement
breaks or after programmes when viewers go to switch a kettle on)
Transient (fluctuations due to individual's actions, differences in
power transmission efficiency and other small factors that need to be
accounted for)
There are currently three main methods for dealing with changing demand:
Electrical devices generally having a working voltage
range that they require, commonly 110–120 V or 220–240 V. Minor
variations in load are automatically smoothed by slight variations in
the voltage available across the system.
Power plants can be run below their normal output, with the facility
to increase the amount they generate almost instantaneously. This is
termed 'spinning reserve'.
Additional generation can be brought online. Typically, these would
be hydroelectric or gas turbines, which can be started in a matter of
minutes.
The problem with standby gas turbines is higher costs; expensive
generating equipment is unused much of the time. Spinning reserve also
comes at a cost; plants running below maximum output are usually less
efficient. Grid energy storage is used to shift generation from times of
peak load to off-peak hours. Power plants are able to run at their peak
efficiency during nights and weekends.
Supply-demand leveling strategies may be intended to reduce the
cost of supplying peak power or to compensate for the intermittent
generation of wind and solar power.
Portability
This
is the area of greatest success for current energy storage
technologies. Single-use and rechargeable batteries are ubiquitous, and
provide power for devices with demands as varied as digital watches and
cars. Advances in battery technology have generally been slow,
however, with much of the advance in battery life that consumers see
being attributable to efficient power management rather than increased
storage capacity. Portable consumer electronics have benefited greatly from size and power reductions associated with Moore's law.
Unfortunately, Moore's law does not apply to hauling people and
freight; the underlying energy requirements for transportation remain
much higher than for information and entertainment applications. Battery
capacity has become an issue as pressure grows for alternatives to internal combustion engines in cars, trucks, buses, trains, ships, and aeroplanes. These uses require far more energy density (the amount of energy stored in a given volume or weight) than current battery technology can deliver. Liquid hydrocarbon fuel (such as gasoline/petrol and diesel), as well as alcohols (methanol, ethanol, and butanol) and lipids (straight vegetable oil, biodiesel) have much higher energy densities.
There are synthetic pathways for using electricity to reduce carbon dioxide and water to liquid hydrocarbon or alcohol fuels.
These pathways begin with electrolysis of water to generate hydrogen,
and then reducing carbon dioxide with excess hydrogen in variations of
the reverse water gas shift reaction. Non-fossil sources of carbon dioxide include fermentation plants and sewage treatment
plants. Converting electrical energy to carbon-based liquid fuel has
potential to provide portable energy storage usable by the large
existing stock of motor vehicles and other engine-driven equipment,
without the difficulties of dealing with hydrogen or another exotic energy carrier. These synthetic pathways may attract attention in connection with attempts to improve energy security
in nations that rely on imported petroleum, but have or can develop
large sources of renewable or nuclear electricity, as well as to deal
with possible future declines in the amount of petroleum available to import.
Because the transport sector uses the energy from petroleum very
inefficiently, replacing petroleum with electricity for mobile energy
will not require very large investments over many years.
Reliability
Virtually
all devices that operate on electricity are adversely affected by the
sudden removal of their power supply. Solutions such as UPS (uninterruptible power supplies)
or backup generators are available, but these are expensive. Efficient
methods of power storage would allow for devices to have a built-in
backup for power cuts, and also reduce the impact of a failure in a
generating station. Examples of this are currently available using fuel cells and flywheels.
.jpg)
.jpg)
