Thermal energy storage (TES) is achieved with very different technologies. Depending on the specific technology, this allows the excess heat energy to be stored and used for hours, days, or months later, on a scale ranging from individual processes, buildings, multiuser, district, city, or local development. Examples of its use are balancing energy demand between day and night, saving summer heat for winter heating, or winter for summer air conditioning (summer thermal energy storage). Storage media include water tank or ice mud, original soil mass or bedrock accessed by heat exchangers by drill holes, deep aquifers present between waterproof layers; a shallow and lined hole, filled with gravel and water and isolated at the top, as well as eutectic and material phase change solutions.
Other heat energy sources for storage include heat or cold produced with heat pumps from off-peak, lower electrical power, a practice called peak shaving; heat from combined heat and power (CHP) power plants; heat generated by renewable electrical energy that exceeds network demand and waste heat from industrial processes. Thermal storage, both seasonal and short term, is considered an important means of balancing with the inexpensive high portion of variable renewable power production and the integration of electricity and heating sectors in energy systems that are almost or entirely filled with renewable energy.
Video Thermal energy storage
Solar energy storage
Most practical active solar heating systems provide storage from several hours to the energy collected throughout the day. However, there are more and more facilities that use seasonal thermal energy storage (STES), allowing solar energy to be stored in summer for heating use during winter. The Surya Landing Drake Community in Alberta, Canada, has now reached 97% of the solar heating section of the year, a world record possible only by combining STES.
Proper use of latent heat and heat is also possible with high temperature solar thermal input. A variety of eutectic metal mixtures, such as Aluminum and Silicon (AlSi12) offer high melting points suitable for efficient steam generation, while high alumina-based cement materials offer good thermal storage capability.
Maps Thermal energy storage
Molten-salt Technology
The sensible heat of the molten salt is also used to store solar energy at high temperatures. Liquid salts can be used as a method of storing thermal energy to maintain heat energy. Currently, it is a technology used commercially to store the heat collected by concentrated solar power (for example, from sun towers or sun troughs). The heat can then be converted into super-hot steam for conventional steam turbine power and generate electricity in bad weather or at night. It was shown in the Solar Two project from 1995-1999. Estimates in 2006 estimate 99% annual efficiency, referencing to stored energy by storing heat before turning it into electricity, rather than converting direct heat into electricity. A variety of eutectic mixtures of various salts are used (eg, sodium nitrate, potassium nitrate and calcium nitrate). Experience with such a system exists in non-solar applications in the chemical and metals industries as a heat transport fluid.
Salt melts at 131 ° C (268 ° F). This stored liquid at 288 Ã, Â ° C (550Ã, Â ° F) in an isolated "cold" storage tank. The molten salt is pumped through a panel in the solar collector where the focused sun heats it to 566 ° C (1,051 ° F). Then sent to the heat storage tank. With proper tank insulation, heat energy can be stored for a week. When electricity is required, hot molten salt is pumped into a conventional steam generator to produce excessive steam to drive a conventional generator as used in coal or oil or nuclear power plants. The 100-megawatt turbine will require a tank with a height of about 9.1 meters (30 feet) and 24 meters (79 feet) to drive it for four hours with this design.
Single tank with divider plate to hold cold and hot liquid salt, is under development. It is more economical to achieve 100% more heat storage per unit volume over double tank systems because liquid salt storage tanks are expensive because of their complex construction. Change Material Use (PCM) is also used in salt energy storage.
Some parabolic through power plants in Spain and SolarReserve solar tower developers use this thermal energy storage concept. Solana Generating Station in the US can hold a capacity of 6 hours to produce capacity in molten salt. During the summer of 2013, Solar solar/Gemasolar salt-power plants in Spain reached the first by continuing to generate electricity 24 hours per day for 36 days.
Heat storage in tank or rock cave
The steam accumulator consists of an insulated steel pressure tank containing hot water and steam under pressure. As a heat storage device, it is used to mediate heat production by variable or stable sources of variable demand for heat. Steam accumulators can take significance for energy storage in solar thermal energy projects.
Large stores are widely used in Scandinavia to store heat for several days, to separate heat and electricity production and to help meet peak demands. The intersleasonal storage in the caves has been investigated and seems to be economical.
Hot storage in hot, concrete, gravel etc.
Water has one of the highest thermal capacities Hot capacity - 4,2 J/(cmÃ,³Ã, K) whereas concrete has about one third of it. On the other hand, the concrete can be heated to a much higher temperature - 1200 ° C by mis. electric heating and therefore has a much higher volumetric capacity. So in the example below, an isolated cube of about 2.8 m will appear to provide enough storage for a single house to meet 50% of the heating demand. This can, in principle, be used to store excess wind or PV heat due to the ability of an electric heater to reach high temperatures. At the environmental level, the development of Wiggenhausen-SÃÆ'¼d solar in Friedrichshafen has received international attention. It features 12,000 mÃ,³ (420,000 cu ft) reinforced concrete thermal stores linked to 4,300 mÃ, ² (46,000 sq ft) of solar collectors, which will supply 570 homes with about 50% of heating and hot water. Siemens built thermal storage of 36 MWh near Hamburg with a basalt of 600  ° C and a 1.5 MW power output. A similar system is scheduled for SorÃÆ'¸, Denmark, with 41-58% of the 18 MWh heat being re-stored for city district heating, and 30-41% returning as electricity.
Miscibility gap alloy (MGA) technology
The alloy of miscibility gap depends on the phase change of the metallic material (see latent heat) to store heat energy.
Instead of pumping the molten metal between the tanks as in the molten system, the metal is encapsulated in other metals which can not be mixed with (non-mixed). Depending on the two selected materials (phase change materials and encapsulation materials) the storage density can be between 0.2 and 2 MJ/L.
The working fluid, usually water or steam, is used to transfer heat in and out of the MGA. The thermal conductivity of MGAs is often higher (up to 400 W/m K) than competing technologies which means faster "charge" and "discharge" of thermal storage is possible. This technology has not been implemented on a large scale.
Electric heat-storage heaters
Heating storage is common in European homes with measurements of usage time (traditionally using cheaper electricity at night). They consist of high-density ceramic bricks or feolite blocks that are heated to high temperatures with electricity, and may or may not have good insulation and control to release heat for several hours.
Ice-based technology
Some applications are being developed where ice is produced during off-peak periods and used for cooling at a later time. For example, air conditioning can be provided more economically by using cheap electricity at night to freeze water to ice, then using the ice cooling capacity in the afternoon to reduce the electricity needed to handle the AC demands. Thermal energy storage using ice utilizes a large hot water fusion. Historically, ice was transported from mountain to city to be used as a cooler. A metric ton of water (= one cubic meter) can store 334 million joules (MJ) or 317,000 BTU (93kWh). A relatively small storage facility can hold enough ice to cool a large building for a day or a week.
In addition to using ice in direct cooling applications, it is also used in heat pump based heating systems. In this application the phase change energy provides a very significant layer of thermal capacity that is close to the most basic temperature range that can be operated by a water source heat pump. This allows the system to break out of the heaviest heating load conditions and extend the period in which the source energy element can contribute heat back into the system.
Cryogenic energy storage
It uses the liquefaction of air or nitrogen as energy storage.
A pilot cryogenic energy system that uses liquid air as an energy store, and low heat waste to encourage air re-expansion, has been operating at power plants in Slough, UK since 2010.
Hot silicon technology
Solid or liquid silicon offers a much higher storage temperature than salt with greater capacity and efficiency. This is being investigated as a storage technology that may be more energy efficient. Silicon is capable of storing more than 1MWh of energy per cubic meter at 1400 ° C.
Hot-powered electricity storage
In heat-pumped electrical storage (PHES), a heat-recoverable pump system is used to store energy as the temperature difference between two hot stores.
Isentropic
One system being developed by the now-bankrupt Isentropic UK company operates as follows. It consists of two insulated containers filled with crushed stone or gravel; heat ships that store thermal energy at high temperatures and high pressure, and cold vessels that store heat energy at low temperatures and low pressure. The vessels are connected above and below by pipes and the entire system is filled with an inert gas argon.
During the charging cycle, the system uses off-peak electricity to work as a heat pump. Argon at ambient temperature and pressure from the top of the cold store are compressed adiabatically to 12 bar pressure, heating to about 500 ° C (900 ° F). The compressed gas is transferred to the top of the hot vessel where it seeps down through the gravel, transferring its heat to the rock and cooling to ambient temperature. The cooled but still pressurized gas, which appears at the bottom of the vessel is then expanded (back adiabatically) back to 1 bar, which lowers the temperature to -150 ° C. The cold gas is then passed through a cold vessel where it cools the stone when it is warmed back to its original state.
Energy is restored as electricity by reversing the cycle. The hot gas from the hot vessel is expanded to drive the generator and then supplied to the cold store. The cooled gas is taken from the bottom of the compressed cold store which heats the gas to ambient temperature. The gas is then transferred to the bottom of the hot vessel to be reheated.
The compression and expansion process is provided by a specially designed reciprocating machine using a sliding valve. The excess heat generated by the inefficiency in the process is discharged into the environment through a heat exchanger during the life cycle.
Developers claim that 72-80% of the round trip efficiency can be achieved. This is proportional to & gt; 80% can be achieved with hydro pumped energy storage.
Another proposed system uses a turbomachinery and is capable of operating at much higher power levels. The use of Phase Change Material (PCM) as a heat storage material will improve further performance.
Endothermic/exothermic chemical reaction
Salt hydrate technology
One example of an experimental storage system based on the energy of chemical reactions is the technology of salt hydrate. This system uses the reaction energy created when the salt is hydrated or dehydrated. It works by storing heat in a container containing 50% sodium hydroxide (NaOH) solution. Heat (eg from using a solar collector) is stored by evaporating water in an endothermic reaction. When water is added again, heat is released in an exothermic reaction at 50 ° C (120 ° F). The system currently operates at a 60% efficiency. This system is very advantageous for the storage of seasonal thermal energy, since dry salt can be stored at room temperature for long periods of time, without loss of energy. Containers with dehydrated salts can even be transported to different locations. This system has a higher energy density than heat stored in water and system capacity can be designed to store energy from several months to years.
In 2013, the Dutch technology developer TNO presented the MERITS project results to store heat in a salt container. The heat, which can come from a solar collector on the roof, repels the water contained in the salt. When water is added again, heat is released, almost without loss of energy. A container with a few cubic meters of salt can save a considerable amount of this thermochemical energy to heat the house throughout the winter. In temperate climates such as in the Netherlands, low-energy households on average require about 6.7 GJ/winter. To store this energy in water (at a temperature difference of 70 ° C), 23 m 3 isolated water storage would be necessary, exceeding the storage capability of most households. Using salt hydrate technology with a storage density of about 1 GJ/m 3 , 4-8 m 3 is sufficient.
In 2016, researchers in several countries are experimenting to determine the best salt type, or salt mixture. Low pressure in the container seems to be advantageous for energy transport. Particularly promising is organic salts, called ionic liquids. Compared with their lithium halide-based sorbents are less problematic in terms of limited global resources, and compared to most of their halides and sodium hydroxide (NaOH) are less corrosive and are not negatively affected by CO 2 contamination.
Molecular bond
Storing energy in molecular bonds is being investigated. Energy density equivalent to lithium-ion battery has been reached.
See also
References
External links
- ASHRAE white paper on load transfer economy
- MSN Articles on Storage Ice Storage at Archive.ini (archived 2013-01-19)
- ICE Thermal Energy Storage Tests - IDE-Tech
- http://thermalbatterysystems.com/featured-systems/laramie-wyoming-thermal-battery-system-example/#.U8Whdo1dXx8
- "Prepared for the Collaborative Thermal Energy Storage System of the California Energy Commission" Report entitled "Energy Sources and Environmental Impacts of Thermal Energy Storage." Tabor Caramanis & amp; Assoc energy.ca.gov
Further reading
- Hyman, Lucas B. Sustainable Thermal Storage System: Planning, Design, and Operation . New York: McGraw-Hill, 2011. Print.
- Henrik Lund, Renewable Energy Systems: Intelligent Energy Systems Approach for Choice and 100% Renewable Solutions , Academic Press 2014, ISBN 978-0-124-10423-5.
Source of the article : Wikipedia
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