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November 13, 2008 – Vol.13 No.34

SOLAR THERMAL AND FOSSIL ENERGY WORKING TOGETHER.

Like it or not, coal-fired power plants are going to be around for a while. We hate to admit it, but we’re as addicted to coal as we are to oil. For now the best we can do is use electricity from coal plants as efficiently as possible and continue to add more renewables to the mix of electricity sources on the grid to lessen the need for more coal plants. The wait for so-called “clean coal” may be a long one and possibly a waste of time. Carbon sequestration? This won’t happen on a large scale until coal companies are told to do so by government.

Electricity generated from natural gas will be with us for a while too. As much as T. Boone Pickens would like to close natural gas fired power plants and replace them with wind turbines planted in the country’s North-South midsection, this would take some time too. (He’s already cut back plans for his own mega wind farm, blaming the financial crisis.) In terms of emissions, natural gas power generation isn’t nearly as bad as electricity from coal, but natural gas is relatively expensive and consumes copious amounts of fuel, particularly when aero-derivative gas turbine generators are involved. Of course we import some natural gas by ship and by pipe: not a great thing for energy independence. Pickens thinks we’d be better off using domestic natural gas to fuel cars and trucks than for powering the grid.

Coal, natural gas (with the exception of those fuel hungry gas turbines), and now resurgent solar thermal power generation all have one thing in common: They make steam used to generate power.

However, they could work together in consort, combining their steam for the common cause of making electricity. There’s already a history of this partnership. Since the 1980’s the Solar Energy Generating Stations (SEGS) spread out in the deserts of California have been combining solar boiled steam with natural gas made steam in off-peak hours to supply electricity ‘round-the-clock to the grid.

Now, in new projects being led by the Electric Power Research Institute (EPRI), the organization is asking why can’t hybrids of solar thermal/coal or solar thermal/ natural gas can be more common? That is, why can’t steam generated by a solar thermal field be added to a conventional fossil fuel-powered steam cycle, either to offset some of the coal or natural gas required to generate electric power or to boost overall plant power output?

Dynegy Inc. and NV Energy will each host case studies with project participants including Salt River Project, Southern Company and Progress Energy. The projects will be conducted in parallel, with one focused on natural gas plant technologies and the other on coal plant technologies. As part of the natural gas project, case studies will be conducted at Dynegy’s Griffith Energy Facility in Kingman, Ariz., and at NV Energy’s Chuck Lenzie Generating Station near Las Vegas.

The result of these projects will be conceptual design studies and two detailed case studies. Design options to retrofit existing plants will be analyzed and new plant design options will be identified. EPRI will rely on its expertise in solar technologies, steam cycles, and plant operation, as well as past solar and fossil plant studies. EPRI holds two patents in solar steam cycle optimization, by the way.

Aside from adding more emission-free power to the grid (even if it’s only a portion of the power generated from the coal or gas plant) the utilization of steam turbines already in place at a fossil fuel plant would cut the cost of solar thermal power. Further, it would reduce the emissions from peaking power. Peak period on the grid is within a few hours of the sunniest part of the day, so more solar generated electricity would be put to work.

Probably the only limiting factors to the scheme are the proximity of existing fossil fired plant to areas with enough sunlight for solar thermal generating plants to be feasible; or the availability of the acreage near a fossil plant where a solar plant could be build. Since steam can’t travel long distances, the two have to be neighbors – a short pipeline apart. Often, all too often, fossil power plants are built in or near urban areas where real estate might be unavailable or too expensive.

 

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