How do we store renewable energy so it is available when needed?

Main topic: Science

Other topics: Climate change

Short answer:

There are several sources through which renewable energy can be stored:

• Energy storage with the use of batteries
• Pumped storage hydropower for hydro energy
• Using a large-scale heat pump, pumped thermal electricity storage converts electricity into heat.
• Energy storage with the use of earth's gravity
• Building a compressed air energy storage system

The idea is to store the energy that is generated while the capacity of renewable sources of production is high so that it may be used later on when required. However, as of 20222 the cost of storing energy is still considered to be rather high. And since renewable energy production is only possible when certain conditions are met, such as when the sun shines or the wind blows, storage is an absolutely necessary component.

Although there are now a number of commercially accessible energy storage technologies, new long and short term storage ideas are constantly being developed and refined to lower capital costs and boost energy conversion efficiency. Numerous of the unique concepts discussed here are built upon already-developed technologies that have been upgraded or combined with other forms of energy storage. Other ideas are distinct, such as the storage of electric power and the storage of chemicals by electrolytic processes.

The kind and effectiveness of the storage technology will determine any potential drawbacks of power storage. For instance, batteries contain raw elements like lithium and lead, and if they are not disposed of or recycled appropriately, they might offer environmental dangers. Additionally, some power is lost in this process.

How renewable energy can be stored?

Engineers and scientists are creating methods to store extra energy to use when it is required in order to lessen the effects of intermittent energy production from renewable sources. Energy may be stored in a number of ways, and new and better technology systems are always being developed. The finest and most promising techniques for storing renewable energy are listed below.

Energy storage with the use of batteries

Most people are probably most acquainted with batteries as a form of energy storage. People use batteries in various electrical gadgets, including cell phones and automobiles. Lithium-ion batteries are the most widely used batteries, accounting for over 90% of battery storage on the global power grid. Lithium-ion batteries are used in small devices and are also the most common type of battery.

1 MW 4 MWh Turner Energy Storage Project in Pullman, WA

A battery's negative and positive ends are each linked to an electrode known as the anode and the cathode, respectively. An electrical current is produced by a chemical interaction between the material of the electrodes and the electrolyte, a liquid material of electrically charged ions within the battery. The U.S. Department of Energy shares that, "the anode and cathode of lithium-ion batteries serve as lithium storage (opens in new tab). When the battery is charged, which may be accomplished using renewable energy, to power anything, the electrolyte transports positively charged lithium ions between the anode and cathode.

The downsides of lithium-ion batteries are many. According to the Clean Energy Institute at the University of Washington, batteries lose efficiency with time and become more prone to failure. Additionally, they are costly to manufacture on a big scale, and obtaining the raw materials required to build them has a detrimental effect on the environment. According to a 2020 study by a network of energy leaders advocating sustainable energy, batteries have an efficiency of 85% to 95%, which is lower than that of the majority of other energy-storage technologies.

Pumped hydro energy storage, also known as pumped storage hydropower

Two reservoirs are used in pumped hydro energy storage to store electricity. Using more energy, water is pushed from a lower reservoir to a higher reservoir. Water in the upper reservoir is then freed to flow back down to the lower reservoir via turbines that produce power. According to a 2020 World Energy Council assessment, hydro energy storage has an efficiency of between 75% and 85%, resulting in a loss of around 15% to 25% when it is released back.

The Environmental and Energy Study Institute shares that, the biggest pumped hydroelectric storage project in the world is in Virginia and provides electricity to around 750,000 houses. Along with the generation of hydroelectric energy, pumped hydro energy storage facilities are often constructed in or close to rivers. They may also be utilized with oceanic waters. On the Japanese island of Okinawa, a pumped hydro energy storage device draws saltwater from the lagoon and pumps it up a hill using a pipeline. The mechanism then sends the water back down the pipe to power turbines and produce energy.

Example of Pumped hydro energy storage: Dinorwig Power Station

Pumped thermal electricity storage

In pumped thermal energy storage, the power that is produced from renewable sources is used to heat gravel or similar material that retains heat inside of a tank that is protected from the outside environment using insulation. This heat may then be used to produce power as needed.

Illustration of relevant processes in the ATES-ENA system

Because the process makes use of readily available resources like gravel, it may be established in almost any location. According to a report that was published in the year 2017 in the journal Renewable and Sustainable Energy Reviews, the efficiency range that may be anticipated for pumped thermal power storage is anywhere between 50 and 70 percent. This technology is in the process of being improved. According to a report that was published in the journal Frontiers in Energy Research in the year 2020, the first demonstration pumped thermal power storage plant was located at Newcastle University in England. This facility achieved an efficiency of 65% in the year 2019.

Energy storage with the use of earth's gravity

The process involves the use of electricity to hoist weights that are attached to a winch. Once the weights have been lifted, they are released to crank a generator for electricity, recovering most of the energy that was first required to lift them. According to a story by The Guardian in 2019, the machinery needed to lower around 13,200 tonnes (12,000 metric tonnes) down a hole that is more than 2,620 feet (800 meters) deep might be constructed in abandoned mine shafts. According to the information provided on the Gravitricity website, the technology is expected to have an efficiency level of 80% to 90%. According to prior information provided by Live Science, another gravity-based technology utilizes surplus electricity to pull trains up an incline before allowing them to tumble back down to release the accumulated energy. According to the website for ARES, a firm known as Advanced Rail Energy Storage (ARES) is in the process of creating one of these systems in the state of Nevada.

Energy storage with the use of earth's gravity at Lough Nahanagan

Compressed air energy storage system

According to a previous study by Live Science, compressed air energy storage systems involve pumping air into an underground chamber in order to build pressure. This increased pressure may then be released on demand in order to power gas turbines. When the plant fires natural gas in high-pressure air, this results in the production of more energy; however, this also results in the generation of carbon dioxide. According to the research put forward by the 2020 World Energy Council, the potential efficiency of this system ranges anywhere from 70% to 89%. There are at least two compressed air energy storage plants that are currently in operation. According to a report that was published in the year 2021 in the journal Renewable and Sustainable Energy Reviews, the first plant was created in the year 1978 in Huntorf, Germany, and the second facility in Alabama has been operating continuously since the year 1991.

Compressed Air Loco

Hydrogen as a form of chemical energy storage

According to the United States Department of Energy, a technique known as electrolysis may turn electricity into hydrogen by separating the hydrogen and oxygen components of water. This process also helps break up water into its component parts. After that, the hydrogen may be stored and used later as a fuel for the generation of energy. In order to cut down on the emissions of greenhouse gases caused by transportation, hydrogen may also be utilized to power hydrogen-powered automobiles.

According to the research from the 2020 World Energy Council, the efficiency of storing energy via the use of hydrogen ranges from 35% to 55%. Because they need precious metals such as platinum, hydrogen fuel cells come with a hefty price tag. According to the Environmental and Energy Study Institute, they are used to power and back up important infrastructure such as telecom relays and credit card processing. In other words, they provide electricity to these facilities.

Hydrogen as a form of chemical energy storage

Heat (Sunlight) energy storage via mirrors

Mirrors are used in concentrated solar power facilities to focus the sun's rays, which then heat hundreds of thousands of tonnes of salt to the point where it melts. This molten salt is then utilized to drive an electric generator, much in the same way that typical power plants use coal or nuclear power to heat the steam in order to drive an electric generator.

These heated materials may also be stored so that energy can be produced even at night or when the sun is not shining. Using this method makes it possible for concentrated solar electricity to be used continuously.

This concept has the potential to be used in power-generating methods that do not rely on the sun. For instance, energy generated from wind power may be used to heat salt so that it can be used at a later time when the wind isn't blowing as strongly.

The cost of concentrating solar electricity is now considered to be rather high. It has to grow more efficient in order for it to be able to compete with other kinds of energy production and storage. One strategy for accomplishing this goal is to raise the temperature to which the salt is cooked, which will make the generation of power more effective. The salts that are now being used do not maintain their stability at high temperatures.

Energy storage through heat batteries

Batteries that store heat may be used to store either excess heat or power, and they are often used in renewable energy systems. When a substance transforms from its solid to a liquid state, there is an opportunity for the material to store heat. The term "phase-change material" refers to these kinds of substances (PCM). The PCM that is included inside the heat battery may be charged using any unused heat or power. The phase change material reverts back into a solid state whenever heat is required. This process causes the material to give off heat, which is then put to use to heat water.

Heat batteries are often more compact and less heavy than their full counterparts, thermal storage. This indicates that even if you are unable to find room for a conventional hot water cylinder, it is possible that you will still be able to install one in a position that is appropriate for you. Batteries that store heat don't experience the same level of degradation as electrical batteries, hence they should have a much longer shelf life.

Kinetic rotational energy storage through Flywheels

Flywheels, which are a sort of rotor, may be accelerated with the help of electricity, and this process ensures that the energy is kept in the form of kinetic rotational energy. When it is necessary to produce energy, the force created by the flywheel's rotation is used to turn a generator. Some flywheels make use of magnetic bearings and can achieve rotating rates of up to 60,000 RPM, and operate in a vacuum to limit the amount of drag they experience.