October 17, 2013
Green energy’s storage conundrum
Critics of solar and wind as alternative clean energy sources are fond of saying that the wind doesn’t always blow and the sun doesn’t always shine.
There’s truth there, but rather than taking it as the abrupt dismissal the critics often intend it to be, the industry has applied itself to solving the problems. That means there has been a concentrated research effort to find energy-storage technologies that work well and are economically feasible.
Among the firms building solar plants that sidestep the problem — at least in part — is Abengoa Solar, a Spanish-based international technology and engineering firm. It has built the Solana plant in the American desert southwest of Phoenix, Ariz., and it is in the process of testing it before it is plugged into the grid.
The Institute of Electrical and Electronic Engineers publishes a journal, IEEE Spectrum that deals with energy matters. The editors there have been watching the Solana trials, and recently reported that the plant, using parabolic trough mirrors to heat synthetic oil, and molten salts to store that heat, has successfully generated full power for six hours after the sun had set.
The first of the operational tests involved running the plant’s generator at full power, while also sending heat to the reservoirs of molten salt. After sunset, the second test involved running the generator using only stored thermal energy. It worked.
In a report on the tests, IEEE Spectrum said that “proving that this storage technology can work is a huge step for the solar industry.” It noted that “intermittency is still among the most common complaints about industrial-scale renewable energy.”
The Solana plant is huge. Spread across 7.8 square kilometres of desert. Its 3,200 parabolic trough mirrors follow the sun as it moves across the sky, concentrating the rays onto a tube filled with synthetic oil, which heats water to produce steam to drive turbines to generate electricity.
It has a total generating capacity of 280 megawatts, enough to serve about 70,000 homes. Abengoa has a contract to provide all of the Solana output to Arizona’s biggest electricity utility, Arizona Public Service. With the addition of power from Solana, the utility will have 750 megawatts of solar power on its system by the end of the year, enough to serve roughly 185,000 customers.
The utility expects power from Solana to add $1.28 a month to a typical bill. That drops to $1.09 a month after five years, and to 94 cents after 10 years
Solana is thought to be the biggest solar plant of its type in the world. But that doesn’t make it the biggest of any type. That laurel goes to the Ivanpah plant in California’s Mojave desert, which, coincidentally, is also ramping up before plugging into the grid.
When all three of its units are running by the end of the year, Ivanpah’s output of 392 megawatts will power about 140,000 homes, making it the largest concentrating solar power plant in the world.
The Ivanpah plant concentrates its power by using thousands of mirrors focused on towers where the energy heats molten salts to run turbines. Where Ivanpah differs from Solana, though, is that Ivanpah doesn’t have any way to store the solar energy for use when the sun isn’t shining. Neither do most other solar thermal plants built so far.
Abengoa is building two other large solar plants, both in California. One, generating 200 megawatts, is a solar photovoltaic plant due to come on-line later this year. The other, in the Mojave desert, is another parabolic trough plant that will produce 250 megawatts.
And Abengoa continues testing storage technology near Seville, Spain, under a contract with the American department of energy. Taken together, all this, says IEEE Spectrum, means Abengoa “seems to be a bit ahead of . . . other major solar developers.”
Korky Koroluk is an Ottawa-based freelance writer. Send comments to firstname.lastname@example.org
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