Like many others in the solar world, I have my concerns about large-scale concentrated solar power (CSP). These center around the paradoxical use (and potential abuse) of thousands of acres of pristine public land in the name of renewable energy, serious water shortages in the deserted regions most apt for the power plants, and limited or nonexistent transmission infrastructure, among other issues. All this while thousands of parking lots, commercial and industrial rooftops, brownfields, and homes exist on already developed land in close proximity to existing transmission lines.
Photo Credit: International Rivers
Such concerns have spawned a powerful opposition to the deployment of CSP projects in the desert Southwest. In response, the federal government is taking steps to ameliorate the problem for environmentalists and Big Solar companies. These steps so far include environmental impact studies to determine and declare solar energy zones where permitting and implementation of CSP plants would be fast-tracked, as well as support advancing technologies such as the Stirling engine.
Sandia and Stirling
Stirling engines create electricity based on the difference between hot and cold. The engine alternately compresses or expands hot and cold air or gas, which drives a piston that in turn drives an electric generator. The solar-powered version utilizes several mirrors that reflect and concentrate sunlight onto the Stirling engine, creating the heat necessary to drive the process.
Stirling Energy Systems (SES) and National Solar Thermal Test Facility (NSTTF) have worked together for the past five years to refine the engines. And the newest versions, dubbed SunCatchers, are 5,000 pounds lighter than the original and use 60 percent fewer parts. Four SunCatchers are now on demonstration at the NSTTF.
Tessera Solar, a solar developer, operator and sister company to SES, has big plans for the 3-kW engines, including a 1.5-MW plant in Arizona or California and two much larger plants in southern California, potentially reaching a combined 1,000 MW of power.
For me, the true potential of the Stirling engine and the SunCatcher is twofold: its comparable “lack of thirst” and relatively small demand for land.
- Water shortages are a major setback for solar thermal power plants. A parabolic solar thermal plant can require close to 1,000 gallons of water per megawatt-hour of power produced. The water is used for cooling and condensing the steam produced in the solar thermal process. According to those involved in manufacturing SunCatchers, their stirling engine collectors use less water than any other thermal electric system in existence.
- Land is another key issue. The desert Southwest is full of unpopulated and very sunny public land that is ideal for large solar power plants. So what’s the problem? That the conventional mode of building these plants sacrifices the desert landscape upon which they’re built - a landscape many see as barren, but environmentalists and local citizens view as precious and vibrant. SunCatchers are also considerably smaller than other collectors and modular in nature, therefore requiring less land to produce the same amount of power as typical solar thermal plants.
The argument about which is better – concentrated solar power or distributed generation (rooftop solar) – will continue. I still believe that distributed generation is ideal for many reasons, not least of which is the potential energy independence for homeowners and families. Still, I am not uniformly opposed to CSP plants, and innovations such as these new Stirling engines only help to assuage my concerns. I also find no reason why these efficient engines, which set the current record for conversion efficiency (31.25%), couldn’t be utilized in or near urban populations as well. If they’re truly modular, we should be able to back them into Wal-Mart’s driveway, right?