Most people are familiar with solar power by now – you’ve seen solar panels on rooftops, solar charges on car dashboards, even solar flashlights and backpacks.

But did you know there are two very different types of solar power?

The first – the one with the panels – operates on photovoltaics, using chemical energy to convert sunlight directly to electricity.  Over the past 50 years costs have come down, but for a home-size installation, the up-front costs are still high, and typically take 5 years or more to hit the break even point.

Photovoltaics also have other issues:
- Some of the fancy high-tech materials used in the manufacturing process are toxic; others are rare elements that are hard to come by
- It takes a very big installation to generate enough electricity for a house, and a huge one to provide enough juice for a whole town.
- Because of the size, large projects have a substantial environmental impact even when located out in the desert (which also means you have to build transmission lines through the desert to get the power to the cities where it’s needed; this has been a big fight in California).

And of course, you can’t generate power when the sun isn’t shining.

This brings us to the other flavor: Concentrated Solar.

Ever burn paper by focusing the sun’s rays with a magnifying glass? Then you’ve seen the power of concentrated solar.

Direct solar has been used for years to heat everything from swimming pools to home hot water for showers. At its most simple you run water through a black hose across a black background,  and let the sun heat it up.

Concentrated Solar installations do the same thing on a larger scale. The biggest one in the U.S.,  eSolar’s Sierra Sun Tower in Lancaster, California, went online in August of 2009 and provides 5 megawatts of power - enough for 4,000 homes.

Bill Gross, eSolar’s CEO, says their goal is “ …making solar energy for less than the price of coal, without subsidies. This is not only attainable, but will truly change the world.”

eSolar’s array of 24,000 mirrors focuses the sun’s rays on the central tower, concentrating the energy and producing super-heated steam with an average temperature of 800°F at a pressure of 900 psi (don’t try this at home!). Power Engineering magazine was so impressed they named the facility their Project of the Year, and the company was named Technology Pioneer by the World Economic Forum.

- Materials are basic (mirrors, steel mounts and motors), without needing toxics or rare elements
- The installations can be much smaller (Sierra Sun Tower takes up just 20 acres), so they can go anywhere – in an industrial park, for instance.
- The environmental impact is negligible, and they can be sited near transmission lines.

“eSolar demonstrates that pristine wildlands do not have to be sacrificed in order to keep the lights on with clean energy,” says David Myers, Executive Director of the Wildlands Conservancy. “eSolar’s efforts to reduce its impact on the surrounding environment demonstrates a level of foresight we hope to see from other solar developers in the future.”

California’s Pacific Gas & Electric power company has announced a 92 megawatt plant using eSolar’s technology that will go online in 2012, and India is looking to put 1 gigawatt of these plants in place over the next decade.