Tuesday, October 27, 2009

Solar Thermal Power Getting Ready For Prime Time With Caveats

Solar thermal power systems appear to be ready for prime time. That's the claim of a company preparing to build a multiple array solar thermal power system in California's Mojave desert. It involves using a matrix of 82 mirrors focusing light on a single point to heat up hydrogen gas to 1,450F, which would in turn power a Stirling engine to generate electricity. Each of these free-standing arrays would produce 25kw of power. Linking 40 of these units together would send power to the grid and produce 1mw of power.

This design is far more efficient than the parabolic collectors now in use in California and Arizona. It also means that power generators can work on individual units without shutting down power production for the entire facility as must be done with the parabolic collectors.

All that sounds great, until you hear the caveats.
The enormous scale of the Abengoa and Stirling Energy plants provides an answer to skeptics who doubt whether a few rooftop panels here and there can ever play a meaningful role in the world’s energy portfolio. But size also creates its own set of problems. For one thing, the power has to be transmitted to where it’s needed, and the empty deserts best suited for sprawling CST plants tend to be in the middle of nowhere. The site of Stirling Energy’s future plant for the San Diego market currently has enough transmission capacity for 300 Mw, or 12,000 dishes. The remaining 24,000 dishes will be built only if San Diego Gas & Electric is able to complete a proposed 150-mile transmission line between the plant and the city.

Water use is another issue. CST plants with steam turbines can require hundreds of millions of gallons of water to cool their con­densers—a challenge in regions where water is already at a premium. In this respect, Stirling Energy’s hydrogen­-based system has a significant advantage, since it only uses water to rinse the mirrors every few weeks. Osborn estimates that the San Diego plant, when producing power for 500,000 households, would use the same amount of water as 33 average homes.

Utility-scale solar power also requires enormous capital, which keeps it out of reach of people in the developing world, where such solutions are desperately needed. That’s a challenge RawSolar, an MIT spinoff, is trying to meet with a dish that is just 12 ft. wide, and simple and cheap enough to make for stand-alone operation. The nonprofit Solar Turbine Group, another MIT spinoff, built an even more bare-bones mini-CST system in Lesotho last summer, using spare car parts for the heat engine.
In other words, until the transmission lines are built from these remote locations, the full application of solar thermal power will not be achieved. That's the same problem that killed a Pickens' wind power project in Texas, and opposition to transmission line siting rules promulgated by the federal government is fairly widespread, including here in New Jersey where Governor Corzine announced his opposition to the rule claiming it would allow cheaper non-renewable or non-green power sources to provide power decimating New Jersey's green power initiatives.

Yet, it is the lack of those transmission lines that are going to keep large scale alternative energy facilities from being built in the first place.

At the same time, water usage is a major concern at power plants because of the scarcity of water in the desert Southwest and competing needs for water are only expected to grow as the population increases there.

Meanwhile, photovoltaics are showing signs of improvement and may end up being a small scale power producer at the local level. Instead of utilities building photovoltaic facilities, individual homeowners or businesses may install arrays and reduce the need for power from the grid, reducing the load on utility infrastructure.

It would also mean that President Obama's energy infrastructure program is needed more than ever since a smart grid would be needed to handle the diverse input of energy from multiple and variable sources to maintain reliability.

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