Whether nuclear power should be considered a form of renewable energy is an ongoing subject of debate. Statutory
definitions of renewable energy usually exclude many present nuclear
energy technologies, with the notable exception of the state of Utah. Dictionary-sourced definitions of renewable energy technologies often omit or explicitly exclude mention of nuclear energy sources, with an exception made for the natural nuclear decay heat generated within the Earth.
Renewable energy is derived from
natural processes that are replenished constantly. In its various forms,
it derives directly from the sun, or from heat generated deep within
the earth. Included in the definition is electricity and heat generated
from sunlight, wind, oceans, hydropower, biomass, geothermal resources, and biofuels and hydrogen derived from renewable resources.
Renewable energy resources exist over wide geographical areas, in
contrast to other energy sources, which are concentrated in a limited
number of countries.
In ISO 13602-1:2002, a renewable resource is defined as "a
natural resource for which the ratio of the creation of the natural
resource to the output of that resource from nature to the technosphere is equal to or greater than one".
Conventional fission, breeder reactors as renewable
Nuclear fission reactors are a natural energy phenomenon, having naturally formed on earth in times past, for example a natural nuclear fission reactor which ran for thousands of years in present-day Oklo Gabon was discovered in the 1970s. It ran for a few hundred thousand years, averaging 100 kW of thermal power during that time.
Conventional, human manufactured, nuclear fission power stations largely use uranium, a common metal found in seawater, and in rocks all over the world, as its primary source of fuel. Uranium-235 "burnt" in conventional reactors, without fuel recycling, is a non-renewable resource, and if used at present rates would eventually be exhausted.
A cutaway model of the 2nd most powerful presently operating fast breeder reactor in the world. The (BN-600), at 600 MW of nameplate capacity is equivalent in power output to a natural gas CCGT. It dispatches 560 MW to the Middle Uralspower grid. Construction of a second breeder reactor, the BN-800 reactor was completed in 2014.
This is also somewhat similar to the situation with a commonly classified renewable source, geothermal energy, a form of energy derived from the natural nuclear decay of the large, but nonetheless finite supply of uranium, thorium and potassium-40 present within the Earth's crust, and due to the nuclear decay process, this renewable energy source will also eventually run out of fuel. As too will the Sun, and be exhausted.
Nuclear fission involving breeder reactors, a reactor which breeds more fissile fuel than they consume and thereby has a breeding ratio for fissile fuel
higher than 1 thus has a stronger case for being considered a renewable
resource than conventional fission reactors. Breeder reactors would
constantly replenish the available supply of nuclear fuel by converting fertile materials, such as uranium-238 and thorium, into fissile isotopes of plutonium or uranium-233,
respectively. Fertile materials are also nonrenewable, but their supply
on Earth is extremely large, with a supply timeline greater than geothermal energy. In a closed nuclear fuel cycle utilizing breeder reactors, nuclear fuel could therefore be considered renewable.
In 1983, physicist Bernard Cohen claimed that fast breeder reactors, fueled exclusively by natural uranium extracted from seawater, could supply energy at least as long as the sun's expected remaining lifespan of five billion years.
This was based on calculations involving the geological cycles of
erosion, subduction, and uplift, leading to humans consuming half of the
total uranium in the Earth's crust at an annual usage rate of 6500
tonne/yr, which was enough to produce approximately 10 times the
world's 1983 electricity consumption,
and would reduce the concentration of uranium in the seas by 25%,
resulting in an increase in the price of uranium of less than 25%.
Proportions of the isotopes, U-238 (blue) and U-235 (red) found in natural uranium, versus grades that are enriched. light water reactors and the natural uranium capable CANDU
reactors, are primarily powered only by the U-235 component, failing to
extract much energy from U-238. While by contrast uranium breeder
reactors mostly use U-238/the primary constituent of natural uranium as
their fuel.
Advancements at Oak Ridge National Laboratory and the University of Alabama, as published in a 2012 issue of the American Chemical Society, towards the extraction of uranium from seawater have focused on increasing the biodegradability
of the materials used reducing the projected cost of the metal if it
was extracted from the sea on an industrial scale. The researchers'
improvements include using electrospun Shrimp shell Chitin mats that are more effective at absorbing uranium when compared to the prior record setting Japanese method of using plastic amidoxime nets. As of 2013 only a few kilograms (picture available) of uranium have been extracted from the ocean in pilot programs
and it is also believed that the uranium extracted on an industrial
scale from the seawater would constantly be replenished from uranium leached from the ocean floor, maintaining the seawater concentration at a stable level. In 2014, with the advances made in the efficiency of seawater uranium extraction, a paper in the journal of Marine Science & Engineering suggests that with, light water reactors as its target, the process would be economically competitive if implemented on a large scale. In 2016 the global effort in the field of research was the subject of a special issue in the journal of Industrial & Engineering Chemistry Research.
Presently, as of 2022, only 2 breeder reactors are producing industrial quantities of electricity, the BN-600 and BN-800. The retired French Phénix reactor also demonstrated a greater than one breeding ratio and operated for ~30 years, producing power when Our Common Future was published in 1987.
To fulfill the conditions required for a nuclear renewable energy
concept, one has to explore a combination of processes going from the
front end of the nuclear fuel cycle to the fuel production and the
energy conversion using specific fluid fuels and reactors, as reported
by Degueldre et al. (2019).
Extraction of uranium from a diluted fluid ore such as seawater has
been studied in various countries worldwide. This extraction should be
carried out parsimoniously, as suggested by Degueldre (2017).
An extraction rate of kilotons of U per year over centuries would not
modify significantly the equilibrium concentration of uranium in the
oceans (3.3 ppb). This equilibrium results from the input of 10 kilotons
of U per year by river waters and its scavenging on the sea floor from
the 1.37 exatons of water in the oceans.
For a renewable uranium extraction, the use of a specific biomass
material is suggested to adsorb uranium and subsequently other
transition metals. The uranium loading on the biomass would be around
100 mg per kg. After contact time, the loaded material would be dried
and burned (CO2 neutral) with heat conversion into electricity.e.g.
The uranium ‘burning’ in a molten salt fast reactor helps to optimize
the energy conversion by burning all actinide isotopes with an excellent
yield for producing a maximum amount of thermal energy from fission and
converting it into electricity. This optimisation can be reached by
reducing the moderation and the fission product concentration in the
liquid fuel/coolant. These effects can be achieved by using a maximum
amount of actinides and a minimum amount of alkaline/earth alkaline
elements yielding a harder neutron spectrum. Under these optimal
conditions the consumption of natural uranium would be 7 tons per year
and per gigawatt (GW) of produced electricity.e.g.
The coupling of uranium extraction from the sea and its optimal
utilisation in a molten salt fast reactor should allow nuclear energy to
gain the label renewable. In addition, the amount of seawater used by a
nuclear power plant to cool the last coolant fluid and the turbine
would be ~2.1 giga tons per year for a fast molten salt reactor,
corresponding to 7 tons of natural uranium extractable per year. This
practice justifies the label renewable.
Fusion fuel supply
If it is developed, fusion power would provide more energy for a given weight of fuel than any fuel-consuming energy source currently in use, and the fuel itself (primarily deuterium) exists abundantly in the Earth's ocean: about 1 in 6500 hydrogen (H) atoms in seawater (H2O) is deuterium in the form of (semi-heavy water).
Although this may seem a low proportion (about 0.015%), because nuclear
fusion reactions are so much more energetic than chemical combustion
and seawater is easier to access and more plentiful than fossil fuels,
fusion could potentially supply the world's energy needs for millions of
years.
If
nuclear power were classified as renewable energy (or as low-carbon
energy), additional government support would be available in more
jurisdictions, and utilities could include nuclear power in their effort
to comply with Renewable portfolio standard (RES).
In 2009, the State of Utah passed the "Renewable Energy Development Act" which in part defined nuclear power as a form of renewable energy.
Photovoltaics (PV) were initially solely used as a source of electricity for small and medium-sized applications, from the calculator powered by a single solar cell to remote homes powered by an off-grid
rooftop PV system. Commercial concentrated solar power plants were
first developed in the 1980s. Since then, as the cost of solar panels
has fallen, grid-connected solar PV systems' capacity and production has doubled about every three years. Three-quarters of new generation capacity is solar, with both millions of rooftop installations and gigawatt-scale photovoltaic power stations continuing to be built.
Geography affects solar energy potential because different locations
receive different amounts of solar radiation. In particular, with some
variations, areas that are closer to the equator generally receive higher amounts of solar radiation. However, solar panels
that can follow the position of the Sun can significantly increase the
solar energy potential in areas that are farther from the equator. Daytime cloud cover can reduce the light available for solar cells. Land availability also has a large effect on the available solar energy.
Concentrated solar power
(CSP) systems use mirrors or lenses to concentrate sunlight to extreme
heat to make steam, which is converted into electricity by a turbine.
A solar cell, or photovoltaic cell, is a device that converts light into electric current using the photovoltaic effect. The first solar cell was constructed by Charles Fritts in the 1880s. The German industrialist Ernst Werner von Siemens was among those who recognized the importance of this discovery. In 1931, the German engineer Bruno Lange developed a photo cell using silver selenide in place of copper oxide, although the prototype selenium cells converted less than 1% of incident light into electricity. Following the work of Russell Ohl in the 1940s, researchers Gerald Pearson, Calvin Fuller and Daryl Chapin created the silicon solar cell in 1954. These early solar cells cost US$286/watt and reached efficiencies of 4.5–6%. In 1957, Mohamed M. Atalla developed the process of silicon surface passivation by thermal oxidation at Bell Labs. The surface passivation process has since been critical to solar cell efficiency.
As of 2022 over 90% of the market is crystalline silicon. The array of a photovoltaic system, or PV system, produces direct current (DC) power which fluctuates with the sunlight's intensity. For practical use this usually requires conversion to alternating current (AC), through the use of inverters.
Multiple solar cells are connected inside panels. Panels are wired
together to form arrays, then tied to an inverter, which produces power
at the desired voltage, and for AC, the desired frequency/phase.
Many residential PV systems are connected to the grid when available, especially in developed countries with large markets. In these grid-connected PV systems,
use of energy storage is optional. In certain applications such as
satellites, lighthouses, or in developing countries, batteries or
additional power generators are often added as back-ups. Such stand-alone power systems permit operations at night and at other times of limited sunlight.
In "vertical agrivoltaics" system, solar cells are oriented vertically on farmland, to allow the land to both grow crops and generate renewable energy. Other configurations include floating solar farms, placing solar canopies over parking lots, and installing solar panels on roofs.
Solar-cell efficiencies of laboratory-scale devices using these materials have increased from 3.8% in 2009 to 25.7% in 2021 in single-junction architectures, and, in silicon-based tandem cells, to 29.8%,exceeding the maximum efficiency achieved in single-junction silicon
solar cells. Perovskite solar cells have therefore been the
fastest-advancing solar technology as of 2016.
With the potential of achieving even higher efficiencies and very low
production costs, perovskite solar cells have become commercially
attractive. Core problems and research subjects include their short- and
long-term stability.
Concentrated solar power
(CSP), also called "concentrated solar thermal", uses lenses or mirrors
and tracking systems to concentrate sunlight, then uses the resulting
heat to generate electricity from conventional steam-driven turbines.
A wide range of concentrating technologies exists: among the best known are the parabolic trough, the compact linear Fresnel reflector, the dish Stirling and the solar power tower. Various techniques are used to track the sun and focus light. In all of these systems a working fluid is heated by the concentrated sunlight and is then used for power generation or energy storage. Thermal storage efficiently allows overnight electricity generation, thus complementing PV. CSP generates a very small share of solar power and in 2022 the IEA said that CSP should be better paid for its storage.
As of 2021 the levelized cost of electricity from CSP is over twice that of PV.
However, their very high temperatures may prove useful to help
decarbonize industries (perhaps via hydrogen) which need to be hotter
than electricity can provide.
A hybrid system combines solar with energy storage and/or one or more other forms of generation. Hydro, wind and batteries
are commonly combined with solar. The combined generation may enable
the system to vary power output with demand, or at least smooth the
solar power fluctuation.
There is much hydro worldwide, and adding solar panels on or around
existing hydro reservoirs is particularly useful, because hydro is
usually more flexible than wind and cheaper at scale than batteries, and existing power lines can sometimes be used.
The share of electricity production from solar, 2022 Yearly solar generation by continentBenefitting
from favorable policies and declining costs of modules, photovoltaic
solar installation has grown consistently, with China expected to
account for 50% of new global solar photovoltaic projects by 2024.The growth of solar PV on a semi-log scale since 1996Electricity production by source
Early days
The early development of solar technologies starting in the 1860s was
driven by an expectation that coal would soon become scarce, such as
experiments by Augustin Mouchot. Charles Fritts installed the world's first rooftop photovoltaic solar array, using 1%-efficient selenium cells, on a New York City roof in 1884.
However, development of solar technologies stagnated in the early
20th century in the face of the increasing availability, economy, and
utility of coal and petroleum.
Bell Telephone Laboratories’ 1950s research used silicon wafers with a
thin coating of boron. The “Bell Solar Battery” was described as 6%
efficient, with a square yard of the panels generating 50 watts. The first satellite with solar panels was launched in 1957.
By the 1970s, solar panels were still too expensive for much other than satellites.
In 1974 it was estimated that only six private homes in all of North
America were entirely heated or cooled by functional solar power
systems. However, the 1973 oil embargo and 1979 energy crisis caused a reorganization of energy policies around the world and brought renewed attention to developing solar technologies.
Deployment strategies focused on incentive programs such as the
Federal Photovoltaic Utilization Program in the US and the Sunshine
Program in Japan. Other efforts included the formation of research
facilities in the United States (SERI, now NREL), Japan (NEDO), and Germany (Fraunhofer ISE). Between 1970 and 1983 installations of photovoltaic systems grew rapidly. In the United States, President Jimmy Carter set a target of producing 20% of U.S. energy from solar by the year 2000, but his successor, Ronald Reagan, removed the funding for research into renewables. Falling oil prices in the early 1980s moderated the growth of photovoltaics from 1984 to 1996.
Mid-1990s to 2010
In the mid-1990s development of both, residential and commercial rooftop solar as well as utility-scale photovoltaic power stations began to accelerate again due to supply issues with oil and natural gas, global warming concerns, and the improving economic position of PV relative to other energy technologies. In the early 2000s, the adoption of feed-in tariffs—a
policy mechanism, that gives renewables priority on the grid and
defines a fixed price for the generated electricity—led to a high level
of investment security and to a soaring number of PV deployments in
Europe.
2010s
For several years, worldwide growth of solar PV was driven by European deployment, but it then shifted to Asia, especially China and Japan,
and to a growing number of countries and regions all over the world.
The largest manufacturers of solar equipment were based in China. Although concentrated solar power capacity grew more than tenfold, it remained a tiny proportion of the total,
because the cost of utility-scale solar PV fell by 85% between 2010 and
2020, while CSP costs only fell 68% in the same timeframe.
2020s
Despite the rising cost of materials, such as polysilicon, during the 2021–2022 global energy crisis, utility scale solar
was still the least expensive energy source in many countries due to
the rising costs of other energy sources, such as natural gas. In 2022, global solar generation capacity exceeded 1 TW for the first time. However, fossil-fuel subsidies have slowed the growth of solar generation capacity.
Current status
About half of installed capacity is utility scale.
Map of solar resources from World bank
Forecasts
Actual
annual deployments of solar PV vs predictions by the IEA for the period
2002–2016. Predictions have largely and consistently underestimated
actual growth.
Most new renewable capacity between 2022 and 2027 is forecast to be
solar, surpassing coal as the largest source of installed power
capacity. Utility scale is forecast to become the largest source of electricity in all regions except sub-Saharan Africa by 2050.
According to a 2021 study, global electricity generation potential of rooftop solar
panels is estimated at 27 PWh per year at costs ranging from $40 (Asia)
to $240 per MWh (US, Europe). Its practical realization will however
depend on the availability and cost of scalable electricity storage
solutions.
A photovoltaic power station, also known as a solar park, solar farm, or solar power plant, is a large-scale grid-connected photovoltaic power system (PV system) designed for the supply of merchant power. They are different from most building-mounted and other decentralized solar power because they supply power at the utility level, rather than to a local user or users. Utility-scale solar is sometimes used to describe this type of project.
This approach differs from concentrated solar power,
the other major large-scale solar generation technology, which uses
heat to drive a variety of conventional generator systems. Both
approaches have their own advantages and disadvantages, but to date, for
a variety of reasons, photovoltaic technology has seen much wider use. As of 2019, about 97% of utility-scale solar power capacity was PV.
In some countries, the nameplate capacity of photovoltaic power stations is rated in megawatt-peak (MWp), which refers to the solar array's theoretical maximum DC
power output. In other countries, the manufacturer states the surface
and the efficiency. However, Canada, Japan, Spain, and the United States
often specify using the converted lower nominal power output in MWAC,
a measure more directly comparable to other forms of power generation.
Most solar parks are developed at a scale of at least 1 MWp. As of 2018, the world's largest operating photovoltaic power stations surpassed 1 gigawatt. At the end of 2019, about 9,000 solar farms were larger than 4 MWAC (utility scale), with a combined capacity of over 220 GWAC.
Most of the existing large-scale photovoltaic power stations are owned and operated by independent power producers, but the involvement of community and utility-owned projects is increasing.[75] Previously, almost all were supported at least in part by regulatory incentives such as feed-in tariffs or tax credits, but as levelized costs fell significantly in the 2010s and grid parity has been reached in most markets, external incentives are usually not needed.
Commercial concentrating solar power (CSP) plants, also called "solar
thermal power stations", were first developed in the 1980s. The 377 MW Ivanpah Solar Power Facility,
located in California's Mojave Desert, is the world's largest solar
thermal power plant project. Other large CSP plants include the Solnova Solar Power Station (150 MW), the Andasol solar power station (150 MW), and Extresol Solar Power Station
(150 MW), all in Spain. The principal advantage of CSP is the ability
to efficiently add thermal storage, allowing the dispatching of
electricity over up to a 24-hour period. Since peak electricity demand
typically occurs at about 5 pm, many CSP power plants use 3 to 5 hours
of thermal storage.
The typical cost factors for solar power include the costs of the
modules, the frame to hold them, wiring, inverters, labour cost, any
land that might be required, the grid connection, maintenance and the
solar insolation that location will receive.
Photovoltaic systems use no fuel, and modules typically last 25 to 40 years. Thus upfront capital and financing costs make up 80% to 90% of the cost of solar power, which is a problem for countries where contracts may not be honoured, such as some African countries. Some countries are considering price caps, whereas others prefer contracts for difference.
In many countries, solar power is the lowest cost source of electricity.
In Saudi Arabia, a power purchase agreement (PPA) was signed in April
2021 for a new solar power plant in Al-Faisaliah. The project has
recorded the world's lowest cost for solar PV electricity production of
USD 1.04 cents/ kWh.
Installation prices
Expenses of high-power band solar modules has greatly decreased over
time. Beginning in 1982, the cost per kW was approximately 27,000
American dollars, and in 2006 the cost dropped to approximately 4,000
American dollars per kW. The PV system in 1992 cost approximately 16,000
American dollars per kW and it dropped to approximately 6,000 American
dollars per kW in 2008. In 2021 in the US, residential solar cost from 2 to 4 dollars/watt (but solar shingles cost much more) and utility solar costs were around $1/watt.
The productivity of solar power in a region depends on solar irradiance, which varies through the day and year and is influenced by latitude and climate. PV system output power also depends on ambient temperature, wind speed, solar spectrum, the local soiling conditions, and other factors.
Onshore wind power tends to be the cheapest source of electricity in Northern Eurasia, Canada, some parts of the United States, and Patagonia
in Argentina whereas in other parts of the world mostly solar power (or
less often a combination of wind, solar and other low carbon energy) is
thought to be best.
Modelling by Exeter University suggests that by 2030, solar will be
least expensive in all countries except for some in north-eastern
Europe.
The locations with highest annual solar irradiance lie in the
arid tropics and subtropics. Deserts lying in low latitudes usually have
few clouds and can receive sunshine for more than ten hours a day.These hot deserts form the Global Sun Belt circling the world. This belt consists of extensive swathes of land in Northern Africa, Southern Africa, Southwest Asia, Middle East, and Australia, as well as the much smaller deserts of North and South America.
Thus solar is (or is predicted to become) the cheapest source of
energy in all of Central America, Africa, the Middle East, India,
South-east Asia, Australia, and several other regions.
Different measurements of solar irradiance (direct normal irradiance, global horizontal irradiance) are mapped below:
North America
South America
Europe
Africa and Middle East
South and South-East Asia
Australia
World
Self-consumption
In cases of self-consumption of solar energy, the payback time is
calculated based on how much electricity is not purchased from the grid.
However, in many cases, the patterns of generation and consumption do
not coincide, and some or all of the energy is fed back into the grid.
The electricity is sold, and at other times when energy is taken from
the grid, electricity is bought. The relative costs and prices obtained
affect the economics. In many markets, the price paid for sold PV
electricity is significantly lower than the price of bought electricity,
which incentivizes self-consumption. Moreover, separate self-consumption incentives have been used in e.g., Germany and Italy.
Grid interaction regulation has also included limitations of grid
feed-in in some regions in Germany with high amounts of installed PV
capacity. By increasing self-consumption, the grid feed-in can be limited without curtailment, which wastes electricity.
A good match between generation and consumption is key for high
self-consumption. The match can be improved with batteries or
controllable electricity consumption.
However, batteries are expensive, and profitability may require the
provision of other services from them besides self-consumption increase, for example avoiding power outages. Hot water storage tanks with electric heating with heat pumps or resistance heaters can provide low-cost storage for self-consumption of solar power.
Shiftable loads, such as dishwashers, tumble dryers and washing
machines, can provide controllable consumption with only a limited
effect on the users, but their effect on self-consumption of solar power
may be limited.
The original political purpose of incentive policies for PV was to
facilitate an initial small-scale deployment to begin to grow the
industry, even where the cost of PV was significantly above grid parity,
to allow the industry to achieve the economies of scale necessary to
reach grid parity. Since reaching grid parity, some policies are
implemented to promote national energy independence, high tech job creation and reduction of CO2 emissions.
In net metering
the price of the electricity produced is the same as the price supplied
to the consumer, and the consumer is billed on the difference between
production and consumption. Net metering can usually be done with no
changes to standard electricity meters,
which accurately measure power in both directions and automatically
report the difference, and because it allows homeowners and businesses
to generate electricity at a different time from consumption,
effectively using the grid as a giant storage battery. With net
metering, deficits are billed each month while surpluses are rolled over
to the following month. Best practices call for perpetual roll over of
kWh credits.
Excess credits upon termination of service are either lost or paid for
at a rate ranging from wholesale to retail rate or above, as can be
excess annual credits.
A community solar
project is a solar power installation that accepts capital from and
provides output credit and tax benefits to multiple customers, including
individuals, businesses, nonprofits, and other investors. Participants
typically invest in or subscribe to a certain kW capacity or kWh
generation of remote electrical production.
Energy
from sunlight or other renewable energy is converted to potential
energy for storage in devices such as electric batteries or
higher-elevation water reservoirs. The stored potential energy is later
converted to electricity that is added to the power grid, even when the
original energy source is not available.
Salt Tanks provide thermal energy storage so that output can be provided after sunset, and output can be scheduled to meet demand requirements. The 280 MW Solana Generating Station
is designed to provide six hours of energy storage. This allows the
plant to generate about 38% of its rated capacity over the course of a
year.
The overwhelming majority of electricity produced worldwide is used
immediately because traditional generators can adapt to demand and
storage is usually more expensive. Both solar power and wind power are sources of variable renewable power, meaning that all available output must be used locally, carried on transmission
lines to be used elsewhere, or stored (e.g., in a battery). Since solar
energy is not available at night, storing it so as to have continuous
electricity availability is potentially an important issue, particularly
in off-grid applications and for future 100% renewable energy scenarios.
Solar is intermittent due to the day/night cycles and variable weather conditions. However solar power can be forecast
somewhat by time of day, location, and seasons. The challenge of
integrating solar power in any given electric utility varies
significantly. In places with hot summers and mild winters, solar tends
to be well matched to daytime cooling demands.
Energy storage
Concentrated solar power plants may use thermal storage
to store solar energy, such as in high-temperature molten salts. These
salts are an effective storage medium because they are low-cost, have a
high specific heat capacity, and can deliver heat at temperatures
compatible with conventional power systems. This method of energy
storage is used, for example, by the Solar Two power station, allowing it to store 1.44 TJ in its 68 m3 storage tank, enough to provide full output for close to 39 hours, with an efficiency of about 99%.
In stand alone PV systems, batteries are traditionally used to store excess electricity. With grid-connected photovoltaic power systems, excess electricity can be sent to the electrical grid. Net metering and feed-in tariff
programs give these systems a credit for the electricity they produce.
This credit offsets electricity provided from the grid when the system
cannot meet demand, effectively trading with the grid instead of storing
excess electricity.
When wind and solar are a small fraction of the grid power, other
generation techniques can adjust their output appropriately, but as
these forms of variable power grow, additional balance on the grid is
needed. As prices are rapidly declining, PV systems increasingly use
rechargeable batteries to store a surplus to be used later at night. Batteries used for grid-storage can stabilize the electrical grid by leveling out peak loads
for a few hours. In the future, less expensive batteries could play an
important role on the electrical grid, as they can charge during periods
when generation exceeds demand and feed their stored energy into the
grid when demand is higher than generation.
Common battery technologies used in today's home PV systems include nickel-cadmium, lead-acid, nickel metal hydride, and lithium-ion.Lithium-ion
batteries have the potential to replace lead-acid batteries in the near
future, as they are being intensively developed and lower prices are
expected due to economies of scale provided by large production facilities such as the Tesla Gigafactory 1. In addition, the Li-ion batteries of plug-in electric cars may serve as future storage devices in a vehicle-to-grid
system. Since most vehicles are parked an average of 95% of the time,
their batteries could be used to let electricity flow from the car to
the power lines and back.
Retired electric vehicle (EV) batteries can be repurposed. Other rechargeable batteries used for distributed PV systems include, sodium–sulfur and vanadium redox batteries, two prominent types of a molten salt and a flow battery, respectively.
Seasonal
cycle of capacity factors for wind and photovoltaics in Europe shown
under idealized assumptions. The figure illustrates the balancing
effects of wind and solar energy at the seasonal scale (Kaspar et al.,
2019).
Other technologies
Solar power plants, while they can be curtailed, usually simply
output as much power as possible. Therefore in an electricity system
without sufficient grid energy storage, generation from other sources (coal, biomass, natural gas, nuclear, hydroelectricity) generally go up and down in reaction to the rise and fall of solar electricity and variations in demand (see load following power plant).
Conventional hydroelectric dams work very well in conjunction
with solar power; water can be held back or released from a reservoir as
required. Where suitable geography is not available, pumped-storage hydroelectricity
can use solar power to pump water to a high reservoir on sunny days,
then the energy is recovered at night and in bad weather by releasing
water via a hydroelectric plant to a low reservoir where the cycle can
begin again.
While hydroelectric and natural gas plants can quickly respond to
changes in load; coal, biomass and nuclear plants usually take
considerable time to respond to load and can only be scheduled to follow
the predictable variation. Depending on local circumstances, beyond
about 20–40% of total generation, grid-connected intermittent sources like solar tend to require investment in some combination of grid interconnections, energy storage or demand side management.
In countries with high solar generation, such as Australia, electricity
prices may become negative in the middle of the day when solar
generation is high, thus incentivizing new battery storage.
The combination of wind and solar PV has the advantage that the
two sources complement each other because the peak operating times for
each system occur at different times of the day and year. The power generation of such solar hybrid power systems is therefore more constant and fluctuates less than each of the two component subsystems.
Solar power is seasonal, particularly in northern/southern climates,
away from the equator, suggesting a need for long term seasonal storage
in a medium such as hydrogen or pumped hydroelectric.
Greenhouse gas emissions per energy source. Solar power is one of the sources with the least greenhouse gas emissions.Part of the Senftenberg Solarpark, a solar photovoltaic power plant located on former open-pit mining areas close to the city of Senftenberg, in Eastern Germany. The 78 MW Phase 1 of the plant was completed within three months.
Solar power is cleaner than electricity from fossil fuels, so can be better for the environment.
Solar power does not lead to harmful emissions during operation, but
the production of the panels creates some pollution. The carbon
footprint of manufacturing is less than 1kg CO2/Wp, and this is expected to fall as manufacturers use more clean electricity and recycled materials. Solar power carries an upfront cost to the environment via production with a carbon payback time of several years as of 2022, but offers clean energy for the remainder of their 30-year lifetime.
Lifecycle surface power density of solar power varies but averages about 7 W/m2, compared to about 240 for nuclear power and 480 for gas.
However, when the land required for gas extraction and processing is
accounted for, gas power is estimated to have not much higher power
density than solar. PV requires much larger amounts of land surface to produce the same nominal amount of energy as sources
with higher surface power density and capacity factor. According to a
2021 study, obtaining 25% to 80% of electricity from solar farms in
their own territory by 2050 would require the panels to cover land
ranging from 0.5% to 2.8% of the European Union, 0.3% to 1.4% in India, and 1.2% to 5.2% in Japan and South Korea.
Occupation of such large areas for PV farms could drive residential
opposition as well as lead to deforestation, removal of vegetation and
conversion of farm land. However some countries, such as South Korea and Japan, use land for agriculture under PV, or floating solar, together with other low-carbon power sources. Worldwide land use has minimal ecological impact. Land use can be reduced to the level of gas power by installing on buildings and other built up areas.
Harmful materials are used in the production of solar panels, but generally in small amounts. As of 2022, the environmental impact of perovskite is difficult to estimate, but there is some concern that lead may be a problem.
A 2021 International Energy Agency study projects the demand for copper
will double by 2040. The study cautions that supply needs to increase
rapidly to match demand from large-scale deployment of solar and
required grid upgrades. More tellurium and indium may also be needed.
Recycling may help.
As solar panels are sometimes replaced with more efficient panels, the
second-hand panels are sometimes reused in developing countries, for
example in Africa. Several countries have specific regulations for the recycling of solar panels. Although maintenance cost is already low compared to other energy sources, some academics have called for solar power systems to be designed to be more repairable.
A very small proportion of solar power is concentrated solar power.
Concentrated solar power may use much more water than gas-fired power.
This can be a problem, as this type of solar power needs strong sunlight
so is often built in deserts.
Politics
Acceptance
of wind and solar facilities in one's community is stronger among U.S.
Democrats (blue), while acceptance of nuclear power plants is stronger
among U.S. Republicans (red).
Solar generation cannot be cut off by geopolitics once installed, unlike oil and gas, which contributes to energy security.
As of 2022 over 40% of global polysilicon manufacturing capacity is in Xinjiang in China, which raises concerns about human rights violations (Xinjiang internment camps).
According to the International Solar Energy Society
China's dominance of manufacturing is not a problem, both because they
estimate solar manufacturing cannot grow to more than 400b USD per year,
and because if Chinese supply was cut off other countries would have
years to create their own industry.
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