Delirium tremens (DTs), (Latin, "shaking frenzy"), is a rapid onset of confusion usually caused by withdrawal from alcohol. When it occurs, it is often three days into the withdrawal symptoms and lasts for two to three days. Physical effects may include shaking, shivering, irregular heart rate, and sweating. People may also hallucinate. Occasionally, a very high body temperature or seizures (colloquially known as "rum fits") may result in death. Alcohol is one of the most dangerous drugs to withdraw from.
Delirium tremens typically only occurs in people with a high intake of alcohol for more than a month. A similar syndrome may occur with benzodiazepine and barbiturate withdrawal. Withdrawal from stimulants such as cocaine does not have major medical complications. In a person with delirium tremens it is important to rule out other associated problems such as electrolyte abnormalities, pancreatitis, and alcoholic hepatitis.
Prevention is by treating withdrawal symptoms using similarly
acting compounds to taper off the use of the precipitating substance in a
controlled fashion. If delirium tremens occurs, aggressive treatment improves outcomes. Treatment in a quiet intensive care unit with sufficient light is often recommended. Benzodiazepines are the medication of choice with diazepam, lorazepam, chlordiazepoxide, and oxazepam all commonly used. They should be given until a person is lightly sleeping. Non-benzodiazepines are often used as adjuncts to manage the sleep disturbance associated with condition. The antipsychotichaloperidol may also be used,
as a major tranquilizer, in order to combat the overactivity and
possible excitotoxicity caused by the withdrawal from a GABA-ergic
sedative. The vitamin thiamine is recommended to be given intramuscularly,
because long term high alcohol intake and the often attendant
nutritional deficit damages the small intestine, and so leads to a
thiamine deficiency which sometimes cannot be rectified by supplement
pills alone.
Mortality without treatment is between 15% and 40%. Currently death occurs in about 1% to 4% of cases.
About half of people with alcoholism will develop withdrawal symptoms upon reducing their use. Of these, 3% to 5% develop DTs or have seizures.
The name delirium tremens was first used in 1813; however, the symptoms were well described since the 1700s. The word "delirium" is Latin for "going off the furrow," a plowing metaphor. It is also called the shaking frenzy and Saunders-Sutton syndrome. There are numerous nicknames for the condition, including "the DTs" and "seeing pink elephants" (see below).
Signs and symptoms
The
main symptoms of delirium tremens are nightmares, agitation, global
confusion, disorientation, visual and auditory hallucinations, tactile hallucinations, fever, high blood pressure, heavy sweating, and other signs of autonomic hyperactivity (fast heart rate
and high blood pressure). These symptoms may appear suddenly but
typically develop two to three days after the stopping of heavy
drinking, being worst on the fourth or fifth day.
These symptoms are characteristically worse at night.
For example in Finnish, this nightlike condition is called "liskojen
yö", "the night of the lizards", for its sweatiness, general unease, and
hallucinations tending towards the unseemly and frightening.
In general, DT is considered the most severe manifestation of
alcohol, or other GABA-receptor active drug, withdrawal, and occurs 2–10
days following the last drink.
It often overcomes the patient by surprise, because a brief period of
uneventful sobriety of 1–2 days tends to precede it, it can fully
manifest itself within a single hour, and unlike usual withdrawal
symptoms experienced by an alcoholic, the condition will not easily go
away using the typical intake amount or schedule of the drug.
Other common symptoms include intense perceptual disturbance such as visions or feelings of insects, snakes,
or rats. These may be hallucinations or illusions related to the
environment, e.g., patterns on the wallpaper or in the peripheral vision
that the patient falsely perceives as a resemblance to the morphology
of an insect, and are also associated with tactile hallucinations such
as sensations of something crawling on the subject—a phenomenon known as
formication.
Delirium tremens usually includes extremely intense feelings of
"impending doom". Severe anxiety and feelings of imminent death are
common DT symptoms.
DT can sometimes be associated with severe, uncontrollable tremors of the extremities and secondary symptoms such as anxiety, panic attacks, and paranoia.
Confusion is often noticeable to onlookers as those with DT will have
trouble forming simple sentences or making basic logical calculations.
DT should be distinguished from alcoholic hallucinosis,
the latter of which occurs in approximately 20% of hospitalized
alcoholics and does not carry a risk of significant mortality. In
contrast, DT occurs in 5–10% of alcoholics and carries up to 15%
mortality with treatment and up to 35% mortality without treatment.
Causes
Delirium tremens is mainly caused by a long period of drinking being stopped abruptly. Withdrawal leads to a biochemical regulation cascade.
Delirium tremens is most common in people who are in alcohol withdrawal, especially in those who drink 10–11 standard drinks (equivalent of 7 to 8 US pints (3 to 4 L) of beer, 4 to 5 US pints (1.9 to 2.4 L) of wine or 1 US pint (0.5 L) of distilled beverage)
daily. Delirium tremens commonly affects those with a history of
habitual alcohol use or alcoholism that has existed for more than 10
years.
Pathophysiology
Delirium
tremens is a component of alcohol withdrawal hypothesized to be the
result of compensatory changes in response to chronic heavy alcohol use.
Alcohol positively allosterically modulates the binding of GABA, enhancing its effect and resulting in inhibition of neurons projecting into the nucleus accumbens, as well as inhibiting NMDA receptors. This combined with desensitization of alpha-2 adrenergic receptors, results in a homeostatic upregulation of these systems in chronic alcohol use.
When alcohol use ceases, the unregulated mechanisms result in hyperexcitability of neurons as natural GABAergic systems are down-regulated and excitatory glutamatergic systems are upregulated. This combined with increased noradrenergic activity results in the symptoms of delirium tremens.
Delirium tremens due to alcohol withdrawal can be treated with benzodiazepines. High doses may be necessary to prevent death. Amounts given are based on the symptoms. Typically the person is kept sedated with benzodiazepines, such as diazepam, lorazepam, chlordiazepoxide, or oxazepam.
In some cases antipsychotics, such as haloperidol may also be used. Older drugs such as paraldehyde and clomethiazole were formerly the traditional treatment but have now largely been superseded by the benzodiazepines.
Acamprosate
is occasionally used in addition to other treatments, and is then
carried on into long-term use to reduce the risk of relapse. If status epilepticus occurs it is treated in the usual way.
It can also be helpful to provide a well lit room as people often have hallucinations.
Alcoholic beverages can also be prescribed as a treatment for delirium tremens, but this practice is not universally supported.
High doses of thiamine often by the intravenous route is also recommended.
Society and culture
Drawing by Donald Ogden Stewart published in 1921 showing Little Elmer's father with DTs and seeing pink elephants.
Nicknames for delirium tremens include "the DTs", "the shakes", "the
oopizootics", "barrel-fever", "the blue horrors", the rat's,
"bottleache", "bats", "the drunken horrors", "seeing pink elephants", "gallon distemper", "quart mania", "heebie jeebies", "pink spiders", and "riding the ghost train", as well as "ork orks", "the zoots", "the 750 itch", and "pint paralysis". Another nickname is "the Brooklyn Boys", found in Eugene O'Neill's one-act play Hughie set in Times Square in the 1920s. Delirium tremens was also given an alternate medical definition since at least the 1840s, being known as mania a potu, which translates to 'mania from drink'.
English author George Eliot provides a case involving delirium tremens in her novel Middlemarch
(1871–72). Alcoholic scoundrel John Raffles, both an abusive stepfather
of Joshua Riggs and blackmailing nemesis of financier Nicholas
Bulstrode, dies, whose "death was due to delirium tremens" while at
Peter Featherstone's Stone Court property. Housekeeper Mrs. Abel
provides Raffles' final night of care per Bulstrode's instruction whose
directions given to Abel stand adverse to Dr. Tertius Lydgate's orders.
"'Remember, if he calls for liquors of any sort, not to give it to him.'"
(Lydgate to Bulstrode). "...he gave directions to Bulstrode as to the
doses, and the point at which they should cease. He insisted on the risk
of not ceasing, and repeated his order that no alcohol should be
given.'
(Bulstrode reflecting): "The thought was, that he had not told Mrs. Abel
when the dose of opium
must cease. ... He walked up-stairs, candle in hand, not knowing
whether he should straitaway enter his room and go to bed, or turn to
the patient's room and rectify his omission. ... He turned to his room.
Before he had quite undressed, Mrs. Abel rapped at his door ...'If you
please sir, should I have no brandy
nor nothing to give the poor creetur? ...When I nursed my poor master,
Mr. Robisson, I had to give him port-wine and brandy constant, and a big
glass at a time,' added Mrs. Abel with a touch of remonstrance in her
tone. ...a key was thrust through the inch of doorway, and Mr. Bulstrode
said huskily, 'That is the key of the wine-cooler. You will find plenty
of brandy there.'"
— George Eliot, Middlemarch, Pages 700–710, Chapters 69-70
French writer Émile Zola's novel The Drinking Den (L'Assommoir) includes a character – Coupeau, the main character Gervaise's husband – who has delirium tremens by the end of the book.
American writer Mark Twain describes an episode of delirium tremens in his book The Adventures of Huckleberry Finn
(1884). In chapter 6, Huck states about his father, "After supper pap
took the jug, and said he had enough whisky there for two drunks and one
delirium tremens. That was always his word." Subsequently, Pap Finn
runs around with hallucinations of snakes and chases Huck around their
cabin with a knife in an attempt to kill him, thinking Huck is the
"Angel of Death".
One of the characters in Joseph Conrad's novel Lord Jim experiences "DTs of the worst kind" with symptoms that include seeing millions of pink frogs.
English author M. R. James mentions delirium tremens in his 1904 ghost story "'Oh, Whistle, and I'll Come to You, My Lad'".
Professor Parkins while staying at the Globe Inn when in coastal
Burnstow to "improve his game" of golf, despite being "a convinced
disbeliever in what is called the 'supernatural'",
when face to face with an entity in his "double-bed room" during the
story's climax, is heard "uttering cry upon cry at the utmost pitch of
his voice" though later "was somehow cleared of the ready suspicion of
delirium tremens".
In the 1945 film The Lost Weekend, Ray Milland won the Academy Award for Best Actor
for his depiction of a character who experiences delirium tremens after
being hospitalized, hallucinating that he saw a bat fly in and eat a
mouse poking through a wall.
Writer Jack Kerouac details his experiences with delirium tremens in his book Big Sur.
The M*A*S*H
TV series episode "Bottoms Up" (season 9, episode 15, aired on March 2,
1981) featured a side story about a nurse (Capt. Helen Whitfield) who
was found to be drinking heavily off-duty. By the culmination of the
episode, after a confrontation by Maj. Margaret Houlihan, the character
swears off alcohol and presumably quits immediately. At mealtime,
roughly 48 hours later, Whitfield becomes hysterical upon being served
food in the Mess tent,
claiming that things are crawling onto her from it. Margaret and Col.
Sherman Potter subdue her. Potter, having recognized the symptoms of
delirium tremens orders 5 ml of paraldehyde from a witnessing nurse.
During the filming of the 1975 film Monty Python and the Holy Grail, Graham Chapman
developed delirium tremens due to the lack of alcohol on the set. It
was particularly bad during the filming of the bridge of death scene
where Chapman was visibly shaking, sweating and could not cross the
bridge. His fellow Pythons were astonished as Chapman was an
accomplished mountaineer.
Irish singer-songwriter Christy Moore has a song on his 1985 album, Ordinary Man,
called "Delirium Tremens" which is a satirical song, directed towards
the leaders in Irish politics and culture. Some of the people mentioned
in the song include former Fianna Fáil leader Charles Haughey, at the time a Labour TD, later the party leader Ruairi Quinn, former Labour Party leader Dick Spring and Roger Casement, who was captured bringing German guns to Ireland for the 1916 Easter Rising.
The Belgian beer "Delirium Tremens," introduced in 1988, is a
direct reference and also uses a pink elephant as its logo to highlight
one of the symptoms of delirium tremens.
In the 1995 film Leaving Las Vegas, Nicolas Cage
plays a suicidal alcoholic who rids himself of all his possessions and
travels to Las Vegas to drink himself to death. During his travels, he
experiences delirium tremens on a couch after waking up from a binge and
crawls in pain to the refrigerator for more vodka. Cage's performance as Ben Sanderson in the film won the Academy Award for Best Actor in 1996.
Russian composer Modest Mussorgsky (1839-1881) died of delirium tremens.
The Llyn Stwlan dam of the FfestiniogPumped Storage Scheme
in Wales. The lower power station has four water turbines which can
generate a total of 360 MW of electricity for several hours, an example
of artificial energy storage and conversion.
Energy storage is the capture of energy produced at one time for use at a later time to reduce imbalances between energy demand and energy production. A device that stores energy is generally called an accumulator or battery. Energy comes in multiple forms including radiation, chemical, gravitational potential, electrical potential, electricity, elevated temperature, latent heat and kinetic.
Energy storage involves converting energy from forms that are difficult
to store to more conveniently or economically storable forms.
Some technologies provide short-term energy storage, while others
can endure for much longer. Bulk energy storage is currently dominated
by hydroelectric dams, both conventional as well as pumped. Grid energy storage is a collection of methods used for energy storage on a large scale within an electrical power grid.
Common examples of energy storage are the rechargeable battery, which stores chemical energy readily convertible to electricity to operate a mobile phone; the hydroelectric dam, which stores energy in a reservoir as gravitational potential energy; and ice storage tanks, which store ice frozen by cheaper energy at night to meet peak daytime demand for cooling. Green hydrogen, from the 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. Fossil fuels
such as coal and gasoline store ancient energy derived from sunlight by
organisms that later died, became buried and over time were then
converted into these fuels. Food (which is made by the same process as fossil fuels) is a form of energy stored in chemical form.
History
In the
20th century grid, electrical power was largely generated by burning
fossil fuel. When less power was required, less fuel was burned. Hydropower,
a mechanical energy storage method, is the most widely adopted
mechanical energy storage, and has been in use for centuries. Large
hydropower dams have been energy storage sites for more than one hundred years. Concerns with air pollution, energy imports, and global warming have spawned the growth of renewable energy such as solar and wind power. Wind power is uncontrolled and may be generating at a time when no additional power is needed. Solar power varies with cloud cover and at best is only available during daylight hours, while demand often peaks after sunset (seeduck curve). Interest in storing power from these intermittent sources grows as the renewable energy industry begins to generate a larger fraction of overall energy consumption.[6]
Off grid electrical
use was a niche market in the 20th century, but in the 21st century, it
has expanded. Portable devices are in use all over the world. Solar
panels are now common in the rural settings worldwide. Access to
electricity is now a question of economics and financial viability, and
not solely on technical aspects. Electric vehicles
are gradually replacing combustion-engine vehicles. However, powering
long-distance transportation without burning fuel remains in
development.
Methods
Comparison of various energy storage technologies
Outline
The following list includes a variety of types of energy storage:
Energy can be stored in water pumped to a higher elevation using pumped storage methods or by moving solid matter to higher locations (gravity batteries).
Other commercial mechanical methods include compressing air and flywheels that convert electric energy into internal energy or kinetic energy and then back again when electrical demand peaks.
Hydroelectric dams with reservoirs can be operated to provide electricity at times of peak demand.
Water is stored in the reservoir during periods of low demand and released when demand is high.
The net effect is similar to pumped storage, but without the pumping loss.
While a hydroelectric dam does not directly store energy from
other generating units, it behaves equivalently by lowering output in
periods of excess electricity from other sources.
In this mode, dams are one of the most efficient forms of energy
storage, because only the timing of its generation changes.
Hydroelectric turbines have a start-up time on the order of a few
minutes.
At times of low electrical demand, excess generation capacity is
used to pump water from a lower source into a higher reservoir. When
demand grows, water is released back into a lower reservoir (or waterway
or body of water) through a turbine, generating electricity. Reversible turbine-generator assemblies act as both a pump and turbine (usually a Francis turbine
design). Nearly all facilities use the height difference between two
water bodies. Pure pumped-storage plants shift the water between
reservoirs, while the "pump-back" approach is a combination of pumped
storage and conventional hydroelectric plants that use natural stream-flow.
Compressed air energy storage (CAES) uses surplus energy to compress air for subsequent electricity generation.
Small-scale systems have long been used in such applications as
propulsion of mine locomotives. The compressed air is stored in an underground reservoir, such as a salt dome.
Compressed-air energy storage (CAES) plants can bridge the gap
between production volatility and load. CAES storage addresses the
energy needs of consumers by effectively providing readily available
energy to meet demand. Renewable energy sources like wind and solar
energy vary. So at times when they provide little power, they need to be
supplemented with other forms of energy to meet energy demand.
Compressed-air energy storage plants can take in the surplus energy
output of renewable energy sources during times of energy
over-production. This stored energy can be used at a later time when
demand for electricity increases or energy resource availability
decreases.
Compression of air creates heat; the air is warmer after compression. Expansion
requires heat. If no extra heat is added, the air will be much colder
after expansion. If the heat generated during compression can be stored
and used during expansion, efficiency improves considerably. A CAES system can deal with the heat in three ways. Air storage can be adiabatic, diabatic, or isothermal. Another approach uses compressed air to power vehicles.
Flywheel energy storage (FES) works by accelerating a rotor (a flywheel) to a very high speed, holding energy as rotational energy. When energy is added the rotational speed of the flywheel increases, and when energy is extracted, the speed declines, due to conservation of energy.
Most FES systems use electricity to accelerate and decelerate the
flywheel, but devices that directly use mechanical energy are under
consideration.
FES systems have rotors made of high strength carbon-fiber composites, suspended by magnetic bearings and spinning at speeds from 20,000 to over 50,000 revolutions per minute (rpm) in a vacuum enclosure. Such flywheels can reach maximum speed ("charge") in a matter of minutes. The flywheel system is connected to a combination electric motor/generator.
FES systems have relatively long lifetimes (lasting decades with little or no maintenance; full-cycle lifetimes quoted for flywheels range from in excess of 105, up to 107, cycles of use), high specific energy (100–130 W·h/kg, or 360–500 kJ/kg) and power density.
Changing the altitude of solid masses can store or release energy via
an elevating system driven by an electric motor/generator. Studies
suggest energy can begin to be released with as little as 1 second
warning, making the method a useful supplemental feed into an
electricity grid to balance load surges.
Efficiencies can be as high as 85% recovery of stored energy.
This can be achieved by siting the masses inside old vertical
mine shafts or in specially constructed towers where the heavy weights
are winched
up to store energy and allowed a controlled descent to release it. At
2020 a prototype vertical store is being built in Edinburgh, Scotland
Thermal energy storage (TES) is the temporary storage or removal of heat.
Sensible heat thermal
Sensible heat storage take advantage of sensible heat in a material to store energy.
Seasonal thermal energy storage
(STES) allows heat or cold to be used months after it was collected
from waste energy or natural sources. The material can be stored in
contained aquifers, clusters of boreholes in geological substrates such
as sand or crystalline bedrock, in lined pits filled with gravel and
water, or water-filled mines. Seasonal thermal energy storage (STES) projects often have paybacks in four to six years. An example is Drake Landing Solar Community
in Canada, for which 97% of the year-round heat is provided by
solar-thermal collectors on garage roofs, enabled by a borehole thermal
energy store (BTES). In Braedstrup, Denmark, the community's solar district heating system also uses STES, at a temperature of 65 °C (149 °F). A heat pump,
which runs only while surplus wind power is available. It is used to
raise the temperature to 80 °C (176 °F) for distribution. When wind
energy is not available, a gas-fired boiler is used. Twenty percent of
Braedstrup's heat is solar.
Latent heat thermal (LHTES)
Latent
heat thermal energy storage systems work by transferring heat to or
from a material to change its phase. A phase-change is the melting,
solidifying, vaporizing or liquifying. Such a material is called a phase change material (PCM). Materials used in LHTESs often have a high latent heat so that at their specific temperature, the phase change absorbs a large amount of energy, much more than sensible heat.
A steam accumulator is a type of LHTES where the phase change is between liquid and gas and uses the latent heat of vaporization of water. Ice storage air conditioning
systems use off-peak electricity to store cold by freezing water into
ice. The stored cold in ice releases during melting process and can be
used for cooling at peak hours.
Air can be liquefied by cooling using electricity and stored as a
cryogen with existing technologies. The liquid air can then be expanded
through a turbine and the energy recovered as electricity. The system
was demonstrated at a pilot plant in the UK in 2012.
In 2019, Highview announced plans to build a 50 MW in the North of
England and northern Vermont, with the proposed facility able to store
five to eight hours of energy, for a 250-400 MWh storage capacity.
Electrical energy can be stored thermally by resistive heating or
heat pumps, and the stored heat can be converted back to electricity via
Rankine cycle or Brayton cycle. This technology has been studied to retrofit coal-fired power plants into fossil-fuel free generation systems.
Coal-fired boilers are replaced by high-temperature heat storage
charged by excess electricity from renewable energy sources. In 2020, German Aerospace Center started to construct the world's first large-scale Carnot battery system, which has 1,000 MWh storage capacity.
A rechargeable battery comprises one or more electrochemical cells. It is known as a 'secondary cell' because its electrochemicalreactions are electrically reversible. Rechargeable batteries come in many shapes and sizes, ranging from button cells to megawatt grid systems.
Rechargeable batteries have lower total cost of use and
environmental impact than non-rechargeable (disposable) batteries. Some
rechargeable battery types are available in the same form factors as
disposables. Rechargeable batteries have higher initial cost but can be
recharged very cheaply and used many times.
Common rechargeable battery chemistries include:
Lead–acid battery:
Lead acid batteries hold the largest market share of electric storage
products. A single cell produces about 2V when charged. In the charged
state the metallic lead negative electrode and the lead sulfate positive electrode are immersed in a dilute sulfuric acid (H2SO4) electrolyte.
In the discharge process electrons are pushed out of the cell as lead
sulfate is formed at the negative electrode while the electrolyte is
reduced to water.
Lead-acid battery technology has been developed extensively.
Upkeep requires minimal labor and its cost is low. The battery's
available energy capacity is subject to a quick discharge resulting in a
low life span and low energy density.
Nickel–cadmium battery (NiCd): Uses nickel oxide hydroxide and metallic cadmium as electrodes.
Cadmium is a toxic element, and was banned for most uses by the
European Union in 2004. Nickel–cadmium batteries have been almost
completely replaced by nickel–metal hydride (NiMH) batteries.
Nickel–metal hydride battery (NiMH): First commercial types were available in 1989. These are now a common consumer and industrial type. The battery has a hydrogen-absorbing alloy for the negative electrode instead of cadmium.
Aluminium-sulfur battery with rock salt crystals as electrolyte: aluminium and sulfur are Earth-abundant materials and are much more cheaper than traditional Lithium.
A flow battery works by passing a solution over a membrane where ions are exchanged to charge or discharge the cell. Cell voltage is chemically determined by the Nernst equation
and ranges, in practical applications, from 1.0 V to 2.2 V. Storage
capacity depends on the volume of solution. A flow battery is
technically akin both to a fuel cell and an electrochemical accumulator cell. Commercial applications are for long half-cycle storage such as backup grid power.
Supercapacitor
One of a fleet of electric capabuses powered by supercapacitors, at a quick-charge station-bus stop, in service during Expo 2010 Shanghai China. Charging rails can be seen suspended over the bus.
Supercapacitors bridge the gap between conventional capacitors and rechargeable batteries. They store the most energy per unit volume or mass (energy density) among capacitors. They support up to 10,000 farads/1.2 Volt, up to 10,000 times that of electrolytic capacitors, but deliver or accept less than half as much power per unit time (power density).
While supercapacitors have specific energy and energy densities
that are approximately 10% of batteries, their power density is
generally 10 to 100 times greater. This results in much shorter
charge/discharge cycles. Also, they tolerate many more charge-discharge
cycles than batteries.
Supercapacitors have many applications, including:
Power for cars, buses, trains, cranes and elevators, including
energy recovery from braking, short-term energy storage and burst-mode
power delivery
Chemical
Power to gas
The new technology helps reduce greenhouse gases and operating costs at two existing peaker plants in Norwalk and Rancho Cucamonga.
The 10-megawatt battery storage system, combined with the gas turbine,
allows the peaker plant to more quickly respond to changing energy
needs, thus increasing the reliability of the electrical grid.
In the first method, hydrogen is injected into the natural gas
grid or is used for transportation. The second method is to combine the
hydrogen with carbon dioxide to produce methane using a methanation reaction such as the Sabatier reaction,
or biological methanation, resulting in an extra energy conversion loss
of 8%. The methane may then be fed into the natural gas grid. The third
method uses the output gas of a wood gas generator or a biogas plant, after the biogas upgrader is mixed with the hydrogen from the electrolyzer, to upgrade the quality of the biogas.
At penetrations below 20% of the grid demand, renewables do not
severely change the economics; but beyond about 20% of the total demand,
external storage becomes important. If these sources are used to make
ionic hydrogen, they can be freely expanded. A 5-year community-based
pilot program using wind turbines and hydrogen generators began in 2007 in the remote community of Ramea, Newfoundland and Labrador. A similar project began in 2004 on Utsira, a small Norwegian island.
Energy losses involved in the hydrogen storage cycle come from the electrolysis of water, liquification or compression of the hydrogen and conversion to electricity.
About 50 kW·h (180 MJ) of solar energy is required to produce a
kilogram of hydrogen, so the cost of the electricity is crucial. At
$0.03/kWh, a common off-peak high-voltage line rate in the United States, hydrogen costs $1.50 per kilogram for the electricity, equivalent to $1.50/gallon for gasoline. Other costs include the electrolyzer plant, hydrogen compressors or liquefaction, storage and transportation.
Hydrogen can also be produced from aluminum and water by stripping aluminum's naturally-occurring aluminum oxide
barrier and introducing it to water. This method is beneficial because
recycled aluminum cans can be used to generate hydrogen, however systems
to harness this option have not been commercially developed and are
much more complex than electrolysis systems. Common methods to strip the oxide layer include caustic catalysts such as sodium hydroxide and alloys with gallium, mercury and other metals.
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 for many years without any difficulties.
The European Hyunder project indicated in 2013 that storage of wind and
solar energy using underground hydrogen would require 85 caverns.
Powerpaste is a magnesium and hydrogen -based fluid gel that releases hydrogen when reacting with water. It was invented, patented and is being developed by the Fraunhofer Institute for Manufacturing Technology and Advanced Materials (IFAM) of the Fraunhofer-Gesellschaft. Powerpaste is made by combining magnesium powder with hydrogen to form magnesium hydride in a process conducted at 350 °C and five to six times atmospheric pressure. An ester and a metal salt
are then added to make the finished product. Fraunhofer states that
they are building a production plant slated to start production in 2021,
which will produce 4 tons of Powerpaste annually. Fraunhofer has patented their invention in the United States and EU. Fraunhofer claims that Powerpaste is able to store hydrogen energy at 10 times the energy density of a lithium battery of a similar dimension and is safe and convenient for automotive situations.
Methane is the simplest hydrocarbon with the molecular formula CH4. Methane is more easily stored and transported than hydrogen. Storage and combustion infrastructure (pipelines, gasometers, power plants) are mature.
Synthetic natural gas (syngas or SNG) can be created in a multi-step process, starting with hydrogen and oxygen. Hydrogen is then reacted with carbon dioxide in a Sabatier process,
producing methane and water. Methane can be stored and later used to
produce electricity. The resulting water is recycled, reducing the need
for water. In the electrolysis stage, oxygen is stored for methane
combustion in a pure oxygen environment at an adjacent power plant,
eliminating nitrogen oxides.
Methane combustion produces carbon dioxide (CO2) and
water. The carbon dioxide can be recycled to boost the Sabatier process
and water can be recycled for further electrolysis. Methane production,
storage and combustion recycles the reaction products.
The CO2 has economic value as a component of an energy storage vector, not a cost as in carbon capture and storage.
Power to liquid
Power to liquid is similar to power to gas except that the hydrogen is converted into liquids such as methanol or ammonia. These are easier to handle than gases, and requires fewer safety precautions than hydrogen. They can be used for transportation, including aircraft, but also for industrial purposes or in the power sector.
Various biofuels such as biodiesel, vegetable oil, alcohol fuels, or biomass can replace fossil fuels. Various chemical processes can convert the carbon and hydrogen in coal, natural gas, plant and animal biomass and organic wastes into short hydrocarbons suitable as replacements for existing hydrocarbon fuels. Examples are Fischer–Tropsch diesel, methanol, dimethyl ether and syngas. This diesel source was used extensively in World War II
in Germany, which faced limited access to crude oil supplies. South
Africa produces most of the country's diesel from coal for similar
reasons. A long term oil price above US$35/bbl may make such large scale synthetic liquid fuels economical.
Aluminum
Aluminum has been proposed as an energy store by a number of researchers. Its electrochemical equivalent (8.04 Ah/cm3) is nearly four times greater than that of lithium (2.06 Ah/cm3). Energy can be extracted from aluminum by reacting it with water to generate hydrogen. However, it must first be stripped of its natural oxide layer, a process which requires pulverization, chemical reactions with caustic substances, or alloys. The byproduct of the reaction to create hydrogen is aluminum oxide, which can be recycled into aluminum with the Hall–Héroult process, making the reaction theoretically renewable.
If the Hall-Heroult Process is run using solar or wind power, aluminum
could be used to store the energy produced at higher efficiency than
direct solar electrolysis.
Boron, silicon, and zinc
Boron, silicon, and zinc have been proposed as energy storage solutions.
Other chemical
The organic compound norbornadiene converts to quadricyclane
upon exposure to light, storing solar energy as the energy of chemical
bonds. A working system has been developed in Sweden as a molecular
solar thermal system.
This
mylar-film, oil-filled capacitor has very low inductance and low
resistance, to provide the high-power (70 megawatts) and the very high
speed (1.2 microsecond) discharges needed to operate a dye laser.
A capacitor (originally known as a 'condenser') is a passivetwo-terminalelectrical component used to store energyelectrostatically. Practical capacitors vary widely, but all contain at least two electrical conductors (plates) separated by a dielectric (i.e., insulator). A capacitor can store electric energy when disconnected from its charging circuit, so it can be used like a temporary battery, or like other types of rechargeable energy storage system.[74]
Capacitors are commonly used in electronic devices to maintain power
supply while batteries change. (This prevents loss of information in
volatile memory.) Conventional capacitors provide less than 360 joules per kilogram, while a conventional alkaline battery has a density of 590 kJ/kg.
Capacitors store energy in an electrostatic field between their plates. Given a potential difference across the conductors (e.g., when a capacitor is attached across a battery), an electric field
develops across the dielectric, causing positive charge (+Q) to collect
on one plate and negative charge (-Q) to collect on the other plate. If
a battery is attached to a capacitor for a sufficient amount of time,
no current can flow through the capacitor. However, if an accelerating
or alternating voltage is applied across the leads of the capacitor, a displacement current can flow. Besides capacitor plates, charge can also be stored in a dielectric layer.
Capacitance is greater given a narrower separation between
conductors and when the conductors have a larger surface area. In
practice, the dielectric between the plates emits a small amount of leakage current and has an electric field strength limit, known as the breakdown voltage.
However, the effect of recovery of a dielectric after a high-voltage
breakdown holds promise for a new generation of self-healing capacitors. The conductors and leads introduce undesired inductance and resistance.
Research is assessing the quantum effects of nanoscale capacitors for digital quantum batteries.
Superconducting magnetic energy storage (SMES) systems store energy in a magnetic field created by the flow of direct current in a superconducting coil that has been cooled to a temperature below its superconducting critical temperature. A typical SMES system includes a superconducting coil,
power conditioning system and refrigerator. Once the superconducting
coil is charged, the current does not decay and the magnetic energy can
be stored indefinitely.
The stored energy can be released to the network by discharging
the coil. The associated 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 offer round-trip efficiency greater than 95%.
Due to the energy requirements of refrigeration and the cost of superconducting wire, SMES is used for short duration storage such as improving power quality. It also has applications in grid balancing.
Applications
Mills
The classic application before the industrial revolution was the control of waterways to drive water mills for processing grain or powering machinery. Complex systems of reservoirs and dams were constructed to store and release water (and the potential energy it contained) when required.
Home energy storage is expected to become increasingly common given
the growing importance of distributed generation of renewable energies
(especially photovoltaics) and the important share of energy consumption
in buildings. To exceed a self-sufficiency of 40% in a household equipped with photovoltaics, energy storage is needed.
Multiple manufacturers produce rechargeable battery systems for storing
energy, generally to hold surplus energy from home solar or wind
generation. Today, for home energy storage, Li-ion batteries are
preferable to lead-acid ones given their similar cost but much better
performance.
Tesla Motors produces two models of the Tesla Powerwall. One is a 10 kWh weekly cycle version for backup applications and the other is a 7 kWh version for daily cycle applications.
In 2016, a limited version of the Tesla Powerpack 2 cost $398(US)/kWh
to store electricity worth 12.5 cents/kWh (US average grid price) making
a positive return on investment doubtful unless electricity prices are higher than 30 cents/kWh.
RoseWater Energy produces two models of the "Energy & Storage System", the HUB 120 and SB20.
Both versions provide 28.8 kWh of output, enabling it to run larger
houses or light commercial premises, and protecting custom
installations. The system provides five key elements into one system,
including providing a clean 60 Hz Sine wave, zero transfer time,
industrial-grade surge protection, renewable energy grid sell-back
(optional), and battery backup.
Enphase Energy
announced an integrated system that allows home users to store, monitor
and manage electricity. The system stores 1.2 kWh of energy and
275W/500W power output.
Storing wind or solar energy using thermal energy storage
though less flexible, is considerably cheaper than batteries. A simple
52-gallon electric water heater can store roughly 12 kWh of energy for
supplementing hot water or space heating.
For purely financial purposes in areas where net metering is available, home generated electricity may be sold to the grid through a grid-tie inverter without the use of batteries for storage.
Construction of the Salt Tanks which provide efficient thermal energy storage so that electricity can be generated after the sun goes down, and output can be scheduled to meet demand. The 280 MW Solana Generating Station
is designed to provide six hours of storage. This allows the plant to
generate about 38% of its rated capacity over the course of a year.The 150 MW Andasol solar power station in Spain is a parabolic troughsolar thermal power plant that stores energy in tanks of molten salt so that it can continue generating electricity when the sun is not shining.
The largest source and the greatest store of renewable energy is
provided by hydroelectric dams. A large reservoir behind a dam can store
enough water to average the annual flow of a river between dry and wet
seasons. A very large reservoir can store enough water to average the
flow of a river between dry and wet years. While a hydroelectric dam
does not directly store energy from intermittent sources, it does
balance the grid by lowering its output and retaining its water when
power is generated by solar or wind. If wind or solar generation exceeds
the region's hydroelectric capacity, then some additional source of
energy is needed.
Many renewable energy sources (notably solar and wind) produce variable power.
Storage systems can level out the imbalances between supply and demand
that this causes. Electricity must be used as it is generated or
converted immediately into storable forms.
The main method of electrical grid storage is pumped-storage hydroelectricity. Areas of the world such as Norway, Wales, Japan and the US have used elevated geographic features for reservoirs,
using electrically powered pumps to fill them. When needed, the water
passes through generators and converts the gravitational potential of
the falling water into electricity.
Pumped storage in Norway, which gets almost all its electricity from
hydro, has currently a capacity of 1.4 GW but since the total installed
capacity is nearly 32 GW and 75% of that is regulable, it can be
expanded significantly.
Surplus power can also be converted into methane (sabatier process) with stockage in the natural gas network.
In 2011, the Bonneville Power Administration in the northwestern United States
created an experimental program to absorb excess wind and hydro power
generated at night or during stormy periods that are accompanied by high
winds. Under central control, home appliances absorb surplus energy by
heating ceramic bricks in special space heaters to hundreds of degrees and by boosting the temperature of modified hot water heater tanks.
After charging, the appliances provide home heating and hot water as
needed. The experimental system was created as a result of a severe 2010
storm that overproduced renewable energy to the extent that all
conventional power sources were shut down, or in the case of a nuclear
power plant, reduced to its lowest possible operating level, leaving a
large area running almost completely on renewable energy.
Another advanced method used at the former Solar Two project in the United States and the Solar Tres Power Tower in Spain uses molten salt
to store thermal energy captured from the sun and then convert it and
dispatch it as electrical power. The system pumps molten salt through a
tower or other special conduits to be heated by the sun. Insulated tanks
store the solution. Electricity is produced by turning water to steam
that is fed to turbines.
Since the early 21st century batteries have been applied to utility scale load-leveling and frequency regulation capabilities.
In vehicle-to-grid
storage, electric vehicles that are plugged into the energy grid can
deliver stored electrical energy from their batteries into the grid when
needed.
Thermal energy storage (TES) can be used for air conditioning.
It is most widely used for cooling single large buildings and/or groups
of smaller buildings. Commercial air conditioning systems are the
biggest contributors to peak electrical loads. In 2009, thermal storage
was used in over 3,300 buildings in over 35 countries. It works by
chilling material at night and using the chilled material for cooling
during the hotter daytime periods.
The most popular technique is ice storage,
which requires less space than water and is cheaper than fuel cells or
flywheels. In this application, a standard chiller runs at night to
produce an ice pile. Water circulates through the pile during the day to
chill water that would normally be the chiller's daytime output.
A partial storage system minimizes capital investment by running
the chillers nearly 24 hours a day. At night, they produce ice for
storage and during the day they chill water. Water circulating through
the melting ice augments the production of chilled water. Such a system
makes ice for 16 to 18 hours a day and melts ice for six hours a day.
Capital expenditures are reduced because the chillers can be just 40% -
50% of the size needed for a conventional, no-storage design. Storage
sufficient to store half a day's available heat is usually adequate.
A full storage system shuts off the chillers during peak load
hours. Capital costs are higher, as such a system requires larger
chillers and a larger ice storage system.
This ice is produced when electrical utility rates are lower. Off-peak cooling systems can lower energy costs. The U.S. Green Building Council has developed the Leadership in Energy and Environmental Design
(LEED) program to encourage the design of reduced-environmental impact
buildings. Off-peak cooling may help toward LEED Certification.
Thermal storage for heating is less common than for cooling. An
example of thermal storage is storing solar heat to be used for heating
at night.
Latent heat can also be stored in technical phase change materials (PCMs). These can be encapsulated in wall and ceiling panels, to moderate room temperatures.
Public transport systems like trams and trolleybuses require
electricity, but due to their variability in movement, a steady supply
of electricity via renewable energy is challenging. Photovoltaic
systems installed on the roofs of buildings can be used to power public
transportation systems during periods in which there is increased
demand for electricity and access to other forms of energy are not
readily available.
Upcoming transitions in the transportation system also include e.g.
ferries and airplanes, where electric power supply is investigated as an
interesting alternative.
Storage capacity is the amount of energy extracted from an energy storage device or system; usually measured in joules or kilowatt-hours and their multiples, it may be given in number of hours of electricity production at power plant nameplate capacity;
when storage is of primary type (i.e., thermal or pumped-water), output
is sourced only with the power plant embedded storage system.
Economics
The
economics of energy storage strictly depends on the reserve service
requested, and several uncertainty factors affect the profitability of
energy storage. Therefore, not every storage method is technically and
economically suitable for the storage of several MWh, and the optimal
size of the energy storage is market and location dependent.
Moreover, ESS are affected by several risks, e.g.:
Techno-economic risks, which are related to the specific technology;
Market risks, which are the factors that affect the electricity supply system;
Regulation and policy risks.
Therefore, traditional techniques based on deterministic Discounted Cash Flow
(DCF) for the investment appraisal are not fully adequate to evaluate
these risks and uncertainties and the investor's flexibility to deal
with them. Hence, the literature recommends to assess the value of risks
and uncertainties through the Real Option Analysis (ROA), which is a
valuable method in uncertain contexts.
The economic valuation of large-scale applications (including
pumped hydro storage and compressed air) considers benefits including: curtailment avoidance, grid congestion avoidance, price arbitrage and carbon-free energy delivery. In one technical assessment by the Carnegie Mellon Electricity Industry Centre, economic goals could be met using batteries if their capital cost was $30 to $50 per kilowatt-hour.
A metric of energy efficiency of storage is energy storage on
energy invested (ESOI), which is the amount of energy that can be stored
by a technology, divided by the amount of energy required to build that
technology. The higher the ESOI, the better the storage technology is
energetically. For lithium-ion batteries this is around 10, and for lead
acid batteries it is about 2. Other forms of storage such as pumped
hydroelectric storage generally have higher ESOI, such as 210.
Pumped-storage hydroelectricity is by far the largest storage technology used globally.
However, the usage of conventional pumped-hydro storage is limited
because it requires terrain with elevation differences and also has a
very high land use for relatively small power. In locations without suitable natural geography, underground pumped-hydro storage could also be used. High costs and limited life still make batteries a "weak substitute" for dispatchable power sources, and are unable to cover for variable renewable power
gaps lasting for days, weeks or months. In grid models with high VRE
share, the excessive cost of storage tends to dominate the costs of the
whole grid — for example, in California
alone 80% share of VRE would require 9.6 TWh of storage but 100% would
require 36.3 TWh. As of 2018 the state only had 150 GWh of storage,
primarily in pumped storage and a small fraction in batteries. According
to another study, supplying 80% of US demand from VRE would require a
smart grid covering the whole country or battery storage capable to
supply the whole system for 12 hours, both at cost estimated at $2.5
trillion.
Similarly, several studies have found that relying only on VRE and
energy storage would cost about 30-50% more than a comparable system
that combines VRE with nuclear plants or plants with carbon capture and storage instead of energy storage.
Research
Germany
In
2013, the German government allocated €200M (approximately US$270M) for
research, and another €50M to subsidize battery storage in residential
rooftop solar panels, according to a representative of the German Energy
Storage Association.
Siemens AG commissioned a production-research plant to open in 2015 at the Zentrum für Sonnenenergie und Wasserstoff (ZSW, the German Center for Solar Energy and Hydrogen Research in the State of Baden-Württemberg),
a university/industry collaboration in Stuttgart, Ulm and Widderstall,
staffed by approximately 350 scientists, researchers, engineers, and
technicians. The plant develops new near-production manufacturing
materials and processes (NPMM&P) using a computerized Supervisory Control and Data Acquisition (SCADA) system. It aims to enable the expansion of rechargeable battery production with increased quality and lower cost.
United States
In
2014, research and test centers opened to evaluate energy storage
technologies. Among them was the Advanced Systems Test Laboratory at the
University of Wisconsin at Madison in Wisconsin State, which partnered with battery manufacturer Johnson Controls. The laboratory was created as part of the university's newly opened Wisconsin Energy Institute. Their goals include the evaluation of state-of-the-art and next generation electric vehicle batteries, including their use as grid supplements.
On September 27, 2017, Senators Al Franken of Minnesota and Martin Heinrich
of New Mexico introduced Advancing Grid Storage Act (AGSA), which would
devote more than $1 billion in research, technical assistance and
grants to encourage energy storage in the United States.
In grid models with high VRE share, the excessive cost of storage tends to dominate the costs of the whole grid — for example, in California
alone 80% share of VRE would require 9.6 TWh of storage but 100% would
require 36.3 TWh. According to another study, supplying 80% of US demand
from VRE would require a smart grid covering the whole country or
battery storage capable to supply the whole system for 12 hours, both at
cost estimated at $2.5 trillion.
United Kingdom
In
the United Kingdom, some 14 industry and government agencies allied
with seven British universities in May 2014 to create the SUPERGEN
Energy Storage Hub in order to assist in the coordination of energy
storage technology research and development.
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