Alternative Energy: Storage Problems Addressed
One of the problems with alternative energy sources such as wind and solar is that the power generation may come at the wrong time, and there haven’t been easy ways to store the power. With coal or oil-fired power generation, you can power up the turbine to generate electricity during peak times, and reduce the fuel input for non-peak times. But wind power “dumps” electricity into the grid when the wind is blowing, and not necessarily when the demand is there. And the same happens with solar power … it generates when the sun is shining, but not when lights are needed at night.
When alternative energy sources are less than 20% of the total, you can depend on grid management techniques to vary the sources they can, with coal and oil fired plants adapting to the demands. But as we move toward more and more alternative energy, that becomes more of a chore. You cannot store enough energy in battery banks to make that a viable alternative.
Catch the Wind
Now comes two innovative solutions to the energy storage problem. For wind power, two companies are utilizing windmill-run compressors to pump air into “vaults” underground, with the ability to tap that compressed air to turn a turbine’s blades when the grid needs more power. Business Week reports:
The group is building a system that will steer surplus electricity generated by a nearby wind farm to a big air compressor (diagram). Connected to a deep well, the compressor pumps air into layers of sandstone. Some 3,000 feet down and sealed from above by dense shale, the porous sandstone acts like a giant balloon. Later, when demand for power rises, this flow is reversed. As the chamber empties, a whoosh of air flows back up the pipe into a natural-gas-fired turbine, boosting its efficiency by upwards of 60%.
This trick does more than capture wind that might otherwise be wasted. It also lets the utility sell the stored energy when demand is peaking and prices are highest, says Kent Holst, the park’s development director.
Backed by funding from the Energy Dept., more than 100 municipal utilities in Iowa, Minnesota, and the Dakotas are ponying up a total of $200 million to build the 268-megawatt system. Begun in 2003, the project is on track to go online in 2011.
Although Iowa’s compressed air energy storage (CAES) project will be the first of its type to bank green energy, it may soon have company. In West Texas, TXU CORP. (TXU ) is working with Shell WindÂÂEnergy to build a massive installation of windmills with 3,000 megawatts of
capacity.
Follow the Sun
Individual home use of photo-voltaic solar cells, that convert sunlight into electricity directly, can be workable, but on a large scale it isn’t cost effective or practical. Thermal solar power, where the sun’s rays are focused to heat a liquid that in turn heats water to steam to power a turbine has been proven successful, but expensive. An array of parabolic or trough shaped mirrors focus the sun’s rays in these installations, and the expense of the installation puts thermal solar plants at over twice the cost per KWh as a coal fired plant. But now Ausra, an Australian firm, has found a way to use nearly flat mirrors, reducing installation costs dramatically. And they have developed a way to heat water to steam directly:
In late September, Ausra, Pacific Gas & Electric (PCG ), and Florida Power & Light (FPL ) announced commitments for 1,000 megawatts of solar power–as much as a nuclear plant. The details are still in negotiation. But the current plan is to start with a 10-MW demonstration plant in Florida, then expand to 300 MW. With PG&E, Ausra expects to kick off with a 175-MW plant. These facilities could be ready to flip the switch as early as 2010. The main lure: Ausra believes it has solved the biggest problem solar power has faced previously–its high cost. “What I find
attractive about Ausra is that it’s taking approaches used in the past and driving the price down, making it cheap,” says PG&E CEO Peter A. Darbee. “It’s lower risk and environmentally friendly. I’m very enthusiastic about the technology.
The Business Week article includes a diagram with a storage tank … storing the steam until it can be used later, when peak periods demand it. This storage feature is among the innovations that can bring the anticipated cost of the pilot project down to the “magic” .10 per KWh that makes thermal solar power competitive with coal or oil fired plants.
There is enough land in sunny areas available to provide 100% of our power needs through thermal solar supplies … if you can store the energy. Ausra’s solution is simple, but could be revolutionary.
Conservation will never be able to get us to the 80% reduction said to be needed to reverse “global climate change”, but generating all our electric power from renewable resources would certainly help.
Update: Green Wombat has more on the Florida project. A great article on these and other methods of energy storage is at
Green Thoughts , and Grippsland examines the use of underground storage of wind energy in more detail. Good Clean Tech includes a simplified graphic that shows how ground storage works.
