Compressed Air Energy Storage
July 24, 2013
One problem with the various sources of renewable energy is the need to store energy when it's in surplus to use it at other times. The prime example is solar energy, which you can harvest only when the Sun shines, although you would like to use it at night. Wind power is also notoriously intermittent, although it's become a very popular renewable energy source.
On July 4, which is the anniversary of the US independence from Great Britain, the United Kingdom was asserting its own energy independence with the inauguration of the London Array wind farm located offshore in the Thames Estuary. This wind farm, which has a planned gigawatt capacity, is presently producing 630 MW. This makes it the world's largest offshore wind farm.
In this blog I've reviewed many means of energy storage, but few of these are applicable to grid energy storage. Surprisingly, some exotic batteries, such as the sodium-sulfur battery, are up to the task, and they have been deployed in systems at least up to 70 megawatt-hours. I've written about another grid energy storage possibility, the flywheel, in a previous article (Flywheel Energy Storage, July 21, 2011).
One of the more interesting energy storage ideas is a virtual energy storage scheme that uses cold storage warehouses. I mentioned this system in an older article (Peak Power, March 2, 2007). Sietze van der Sluis of the Netherlands Organization for Applied Scientific Research calculated that the equivalent heat capacity of all large cold storage warehouses in Europe is nearly 10,000 megawatt-hours per degree Celsius.
Letting the temperature of these warehouses drop by a degree during the night, and then letting them rise by a degree during the day, would allow storage of 50,000 megawatt-hours of energy. All this is done without melting the food. Since the warehouses are already there, there's no new capital investment, although the longer continuous running time for the refrigeration units at night might lead to more required maintenance.
Another way to store energy, as I described in an earlier article (Potential Energy Storage, February 15, 2012), is to use the Earth's gravitational field as a source of gravitational potential energy. When power is available, you can pump water up a height, and later use the downwards flow to run a turbine-generator when power is needed.
Gravitational potential energy U in joules is given simply as
U = mgh
where m is the mass in kilograms, g is the gravitational acceleration (9.8 m/sec/sec), and h is the difference in height between the initial and final states in meters. A megawatt-hour is 3.6 x 109 joules, so a height differential of a hundred meters would require 3.67 million kilograms of water, or 970,427 gallons, to store a megawatt of energy.
The main problem with this type of energy storage is the need to have juxtaposed reservoirs at a higher and lower height. One other option is to pump a compressible fluid, such as air, to pressurize it. Compressed air technology is quite advanced, since a substantial fraction of electricity is presently used to create compressed air for various industrial applications. Compressed air has been proposed as a vehicle power source.
Along with the cost of the pressure vessel and pumping apparatus, compressed air has the additional problem that it has a low energy density as an energy storage medium. A reasonable pressurization for air is about 4,500 psi (30 MPa), and this results in an energy density of 50 Watt-hour per liter. This is comparable to a lead-acid battery, about a fifth as dense as a lithium ion battery, and only a half percent of the energy density of gasoline when converted to energy at a hundred percent efficiency.
Although volume energy density is a problem in a vehicle, it isn't a limiting number when you have a lot of liters to spare. When the salt deposited in geological structures called salt domes are dissolved away, huge caverns are formed that are often used for storing oil and natural gas. A salt dome at Huntorf, Germany, was used to create a 290 MW compressed air storage system in 1978 (see figure).
The US Pacific Northwest has an abundance of renewable energy sources, including hydroelectric and wind. The availability of cheap electrical power has lured many Internet giants to site data centers there. At times there's actually too much power, and the federally-run Bonneville Power Administration has at times told wind farms there to generate less power than they're capable of generating.
The region can produce 8,600 megawatts of wind power, but the peak production occurs in the same seasonal time period as mountain snow melt and an upsurge in hydroelectric capacity. A long-term energy storage solution is definitely needed, so scientists from the Bonneville Power Administration and the Department of Energy's Pacific Northwest National Laboratory have just completed a study that recommends compressed air energy storage in the porous rock structures in the region.
Unlike the salt dome cavern approach, the compressed air would be stored in porous subterranean volcanic rock. If this seems to be an unlikely scenario, you just need to remember the 1980 eruption of Mount St. Helens in Washington state. The study identified two sites with a storage capacity equivalent to powering 85,000 homes for a month. The average US home uses about 920 kilowatt-hours of electricity each month, or 11 megawatt-hours annually.
Similar formations have held natural gas under pressure for millions of years, and porous rock formations are common throughout the world. California's San Joaquin Valley also has geology suitable for compressed air energy storage, including depleted natural gas fields. Some regions of Washington state could be used for a combined geothermal and compressed air facility, with the geothermal energy heating the expanding air and providing energy to cool the compression equipment.
There's no question that the economics are there. As reported in National Geographic, the Bonneville Power Administration was selling electrical power in late May, when there's an overabundance of renewable energy, for a dollar per megawatt-hour My residential electrical cost is more than a hundred dollars per megawatt-hour.
Climate change, with possible changes in the amount of rainfall and snowpack, may influence hydroelectric production, making storage of renewable energy that much more important.
|The 290 MW Huntorf, Germany, compressed air energy storage facility stores air in a salt cavern solution-mined specifically for that application.|
Multi-stage compressors are used for air injection, and reheat cycle combustion turbines are used for power production.
(Fig. 59 of ref. 4.)
- London Array Web Site.
- Erik Spek, "Battery of Possibilities," Letter to New Scientist (3 February 2007), issue no. 2589, p. 21.
- Declan Butler, "Fridges could save power for a rainy day," Nature Online, February 7, 2007, doi:10.1038/news070205-9.
- BP McGrail, CL Davidson, DH Bacon, MA Chamness, SP Reidel, FA Spane, JE Cabe, FS Knudsen, MD Bearden, JA Horner, HT Schaef and PD Thorne, "Techno-economic Performance Evaluation of Compressed Air Energy Storage in the Pacific Northwest," Report No. PNNL-22235 of the Pacific Northwest National Laboratory, February, 2013.
- James Glanz, "Data Barns in a Farm Town, Gobbling Power and Flexing Muscle," The New York Times, September 23, 2012.
- Josie Garthwaite, "Too Much Wind Energy? Save it Underground in Volcanic Rock Reservoirs," National Geographic, July 1, 2013.
- Matthew Lynley, "SolarReserve Snags $737M Loan Guarantee for Solar Power Tower," The New York Times, May 20, 2011,
Permanent Link to this article
Linked Keywords: Renewable energy; energy storage; solar energy; Sun; wind power; United States Declaration of Independence; Great Britain; United Kingdom; energy independence; London Array; wind farm; Thames Estuary; gigawatt; megawatt; MW; Aeolus; Greek mythology; Wikimedia Commons; grid energy storage; battery; batteries; sodium-sulfur battery; flywheel energy storage; cold storage warehouse; Netherlands Organisation for Applied Scientific Research; heat capacity; Europe; Celsius; temperature; food; capital investment; refrigeration; maintenance; gravity of Earth; Earth's gravitational field; gravitational potential energy; pump; water; turbine-generator; joule; mass; kilogram; gravitational acceleration; meter; reservoir; compressed air; electricity; industry; industrial; compressed-air vehicle; vehicle power source; pressure vessel; pump; pumping apparatus; energy density; energy storage medium; pressure; pressurization; pounds per square inch; psi; pascal; MPa; liter; lead-acid battery; lithium ion battery; gasoline; energy conversion efficiency; vehicle; salt; geology; geological structure; salt dome; cave; cavern; petroleum; oil; natural gas; Germany; Pacific Northwest; hydroelectric; Internet; data center; federal government of the United States; Bonneville Power Administration; season; seasonal; mountain snow melt; scientist; United States Department of Energy; Pacific Northwest National Laboratory; porosity; porous; volcanic rock; 1980 eruption of Mount St. Helens; Washington state; home; month; California; San Joaquin Valley; geothermal energy; geothermal; free expansion; expanding air; gas compressor; compression equipment; economics; National Geographic; May; dollar; residential; climate change; rainfall; snowpack.
Latest Books by Dev Gualtieri
Thanks to Cory Doctorow of BoingBoing for his favorable review of Secret Codes!
Blog Article Directory on a Single Page
- J. Robert Oppenheimer and Black Holes - April 24, 2017
- Modeling Leaf Mass - April 20, 2017
- Easter, Chicks and Eggs - April 13, 2017
- You, Robot - April 10, 2017
- Collisions - April 6, 2017
- Eugene Garfield (1925-2017) - April 3, 2017
- Old Fossils - March 30, 2017
- Levitation - March 27, 2017
- Soybean Graphene - March 23, 2017
- Income Inequality and Geometrical Frustration - March 20, 2017
- Wireless Power - March 16, 2017
- Trilobite Sex - March 13, 2017
- Freezing, Outside-In - March 9, 2017
- Ammonia Synthesis - March 6, 2017
- High Altitude Radiation - March 2, 2017
- C.N. Yang - February 27, 2017
- VOC Detection with Nanocrystals - February 23, 2017
- Molecular Fountains - February 20, 2017
- Jet Lag - February 16, 2017
- Highly Flexible Conductors - February 13, 2017
- Graphene Friction - February 9, 2017
- Dynamic Range - February 6, 2017
- Robert Boyle's To-Do List for Science - February 2, 2017
- Nanowire Ink - January 30, 2017
- Random Triangles - January 26, 2017
- Torricelli's law - January 23, 2017
- Magnetic Memory - January 19, 2017
- Graphene Putty - January 16, 2017
- Seahorse Genome - January 12, 2017
- Infinite c - January 9, 2017
- 150 Years of Transatlantic Telegraphy - January 5, 2017
- Cold Work on the Nanoscale - January 2, 2017
- Holidays 2016 - December 22, 2016
- Ballistics - December 19, 2016
- Salted Frogs - December 15, 2016
- Negative Thermal Expansion - December 12, 2016
- Verbal Cues and Stereotypes - December 8, 2016
- Capacitance Sensing - December 5, 2016
- Gallium Nitride Tribology - December 1, 2016
- Lunar Origin - November 27, 2016
- Pumpkin Propagation - November 24, 2016
- Math Anxiety - November 21, 2016
- Borophene - November 17, 2016
- Forced Innovation - November 14, 2016
- Combating Glare - November 10, 2016
- Solar Tilt and Planet Nine - November 7, 2016
- The Proton Size Problem - November 3, 2016
- Coffee Acoustics and Espresso Foam - October 31, 2016
- SnIP - An Inorganic Double Helix - October 27, 2016
- Seymour Papert (1928-2016) - October 24, 2016
- Mapping the Milky Way - October 20, 2016
- Electromagnetic Shielding - October 17, 2016
- The Lunacy of the Cows - October 13, 2016
- Random Coprimes and Pi - October 10, 2016
- James Cronin (1931-2016) - October 6, 2016
- The Ubiquitous Helix - October 3, 2016
- The Five-Second Rule - September 29, 2016
- Resistor Networks - September 26, 2016
- Brown Dwarfs - September 22, 2016
- Intrusion Rheology - September 19, 2016
- Falsifiability - September 15, 2016
- Fifth Force - September 12, 2016
- Renal Crystal Growth - September 8, 2016
- The Normality of Pi - September 5, 2016
- Metering Electrical Power - September 1, 2016
Deep Archive 2006-2008