jeudi 25 février 2010

Energy storage - It's not all about batteries

Cheap, utility scale energy storage is viewed as the holy grail for the cleantech sector, providing a balancing force to the intermittency of many renewable energies. Some say we are nearly there and that utility scale energy storage will be having its coming out party this year.

While the current focus is on battery technologies, it is expensive to size it up to utility scale. What other energy storage mechanisms are in the pipeline?

Compressed air
Compressed air works by using renewable power to pump air into underground caverns or aquifers, then releasing it to augment a natural gas-fired turbine when power demand peaks. The technology is gaining traction.

Yesterday, Newton, Mass.-based General Compression announced the close of a $17 million Series A round led by US Renewables Group and included Duke Energy. The company has come up with a novel, effective way to use compressed air for energy storage without burning natural gas and plans to begin construction on its first commercial project in the fall of 2011.

The advantages of this type of energy storage are stark. Because the caverns are generally large, hundreds of hours of output can be stored, providing the ability to cover very long periods without sun or wind. The storage method is also economical because the caverns are already there. Estimated costs range from $750/kW of generating capacity up to about $1,200/kW.

Compressed nitrogen
The technology works by using specially designed hydraulic wind turbines to compress nitrogen into the existing gas or oil pipeline infrastructure. When electricity needs to be generated anywhere along the pipeline, the nitrogen gas is released and expands to turn a turbine that generates electricity.

Edmonton-based Lancaster Wind Systems is pioneering development in this area. Lancaster has a working one-megawatt wind turbine producing hydraulic power, and plans to open a pilot project this summer in which 42 minutes of energy will be stored in a short pipeline section. Silicon Valley venture capitalist Vinod Khosla has been talking with Lancaster Wind, but the extent of his involvement is unclear.

Wind bags
Earlier this month, the BBC reported a professor from University of Nottingham is developing wind bags, which would store excess energy from wind turbines as compressed air under the sea. The idea is to hold air in bags the size of 10 double-decker buses, compressed by the sea. The idea has been backed by E.On, which has invested £236,000 ($363,600) toward building two prototypes being tested in tanks. When energy demand is highest, the air would be released through a turbine, converting it to electricity.

Underground heat storage
In January, it was reported that UK-based Energy Technologies Institute (ETI) is embarking on a project this year that will try to store excess energy underground in the form of heat. The ETI plans to investigate how geological formations on the UK's eastern coast could be used to store large quantities of heat generated by power stations lying in close geographical proximity to those formations. At the same time, it intends to look at localized energy storage in "gravel beds" as a way to store heat on a smaller scale. The heat would be stored and pumped to homes and businesses using water, in much the same way as a central heating system operates.

Flywheels are large discs that spin in a vacuum and can be used as backup power for emergency power systems that turn on after a power outage before a generator kicks in.

In December, Massachusetts-based Beacon Power raised $20 million in equity investment and has also received a $43 million conditional loan guarantee commitment from the U.S. Department of Energy (DOE) as well as a $24 million DOE smart grid stimulus grant (see Next round of DOE loan guarantee companies look to follow Solyndra)

Beacon is now planning to construct its first full-scale 20 MW flywheel energy storage plant at its site in New York. A portion of this first plant is expected to begin earning revenue by providing frequency regulation, an essential grid-balancing service, on the New York state electricity grid in the fourth quarter of this year.

Pumped hydro
Pumped hydro-electric storage works by using electricity to pump water to a high level and then letting the water fall through hydroelectric turbines to generate power when needed. Pumped hydro storage is the largest utility energy storage method in the world, with more than 20 GW already in use in the U.S. However, its use has slowed because of limited sites for hydroelectric power dams.

Companies such as New York-based Riverbank Power are trying to get around this problem. Instead of pumping water high up, the company wants to mine underground to create a large cavern 2,000 feet deep, under a body of water such as a river or abandoned quarry. The idea is to then install hyrdroelectric turbines at the bottom of shafts that would pump water to ground level when there's excess power and let water fall underground when power is needed.

Because Riverbank Power has to dig out its own cavern, construction costs are quite high and the plants are designed to run for six continuous hours before the water would need to be pumped back up, making the technology unsuitable to cope with long stretches with no wind or sun.

Only time will tell which technologies will win in the end. Any thoughts? Weigh in below.

Source : The Cleantech Group, 24/02/10

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