Jim Fraser of the Energy Blog wrote an excellent follow-up to our discussion on solar PV concentrators, with a lot of depth of several of the various technologies, which I felt merited its own posting on CleantechBlog. With minor edits, his note is below:

Excuse a few technicalities to keep the terminology clear. Solar energy devices can be divided into three types; 1) photovoltaic (PV) solar panels, composed of a number of PV cells, these are the type that are seen on the roofs of homes and covert solar energy directly into electricity 2) thermal systems that use concentrators to magnify the solar radiation so that it is more powerful. This concentrated thermal energy is then used to heat a fluid to a high enough temperature so that it can drive some sort of a generator to make electricity. These systems are of two types solar dish systems and solar trough systems and 3) concentrating solar photovoltaic systems that focus solar energy on an expensive, but very efficient PV cell, which can tolerate the more intensive solar energy.

These systems can either use a lens or mirrors to do the concentrating. An overview of concentrating solar power can be found in my blog.

Only some of these products use plastic Fresnel lenses, other use some form of a mirror which have less distortion and are more efficient. Most of these systems use advanced multi-junction solar cells developed by NASA with an efficiency approaching 40%, compared to the 12-22% efficiency achieved by cells used in typical solar panels. Their high cost is justified by reducing the number of cells by a factor of 25 or more in most systems. The concentration factor is limited to 250 to prevent degradation of the cells.

Energy Innovations was started by Bill Gross the entrepreneur behind NetZero, FreePC, CitySearch, eToys, Eve.com, FirstLook and several other dotcom companies. Their product, the 25X Sunflower uses utilizes 25 – 1′ x 1′ mirrors that concentrate the sunlight by a factor of 25 and focus the light on a photovoltaic receiver which produces 200 watts of electricity. The system, as do most concentrating systems, uses an active tracking system to follow the sun in order to capture as much of the suns energy as possible. They claim their system would cost about $4.50 per watt installed, which is 25-50% less than traditional PV systems. My post on Energy Innovations is on my blog.

I was not at all familiar with Prism Solar, but a brief look at their technology indicates that they are using two stage (read 2X concentration) mirror like optics combined with holographic techniques to both concentrate and divide the light into the most desirable spectrums. The ability to select the desirable part of the light spectrum enables them to collect more sunlight at dawn and dusk. They call this passive tracking. They claim their system reduces the number of cells required by 50 to 85% and cuts the cost about in half compared to traditional solar panels. Using only 2X concentration allows then to use normal relatively low cost solar cells.

I couldn’t find any technical information on Whitfield Solar. They have artists renderings of their products on their website which don’t tell much. Three other companies in this arena, that you didn’t mention are Amonix, Sunball and SolFocus.

Amonix, which was established in 1989, uses plastic Fresnel lenses to concentrate the sun by a factor of 250 onto 26.5% efficient solar cells to produce 5 kW panels that are mounted to a tracking system. Amonix is focusing on utility scale applications. They announced in 2005 that they have plans to install a 3 megawatt system in the southwestern U.S. They also have a joint venture with Spain’s Guascor to build a 10 megawatt system in 2006. Installed costs of $3.00 per watt at production rates of 10 megawatts per year are anticipated.

Australian Green and Gold Energy has developed the SunBall rooftop solar concentrator which comes in two models, a 42 W model and a 1.3 kW model. They use a plastic Fresnel lens to achieve their concentration onto a high efficiency solar cell. They just started delivering the small unit and will start shipping the larger unit as soon as they iron out some supply problems. They anticipate that their units will be competitive with grid power in the sunniest parts of the country and slightly higher in the northern regions. Export to the US is anticipated later in the year. Initially their intended market is homes and small businesses. See my post at The Energy Blog for more information.

SolFocus who is collaborating with Xerox’s Palo Alto Research Center is the most recent and one of the most innovative of these companies. They use precisely shaped curved optical mirrors molded or stamped from glass to focus sunlight on the solar cell. They point out that their optics are more efficient than a Fresnel lens. They end up with modules that are only slightly thicker than a conventional PV panel. Their design has been highly influenced by the ability to mass produce their product. Initially the installed cost is expected to be $5.00 per watt but in mass production they are targeting an installed cost of $1.00 per watt which is competitive with grid power. See my post at for more information.

Concentrating solar photovoltaic systems are still but one of several technologies in the run for the lowest cost solar technology. Currently the solar dish and solar trough technologies are believed to be the lowest cost of the solar technologies. A 354 megawatt complex built in California during the 80’s is still operating efficiently and delivering power to the grid with high reliability. Significant improvements in the optics, mechanical fabrication and the tracking system have been made since the original plants were built.

There are about eight plants of over 100 megawatts in capacity under construction in California, Israel, Nevada, Portugal and Spain. Six different companies are supplying the plants. The cost of electricity from these plants will be less that that from natural gas plants but more than from conventional power plants or wind power. Efficiency of scale and cost reductions discovered during this construction boom are hoped to keep them competitive in the future.

Thin film solar is finally coming into its own and production volumes are being ramped up to hundreds of megawatts of capacity. They are taking advantage of the severe shortage of silicon that is preventing significant growth of producers of the more expensive, but more proven conventional silicon solar cells. Cost projections by Daystar and ECD Ovonics, who are the leaders in this technology, indicate that costs of $1.00 per watt may be possible when they reach gigawatt production capacity. Daystar expects to reach that milestone by 2008 and Ovonics will lag by a few years.

The technology seems to be very sound as compared to some questions that were raised a few years ago. A recent happening was that Shell sold off its silicon cell production facilities in order to concentrate on its thin film product. (See Previous Cleantech Blog post by Peter Beadle) Sharp, the leading silicon cell producer, with capacity already near a gigawatt, expects that their costs will be cut in half by 2010. Evergreen who makes thinner silicon cells, by a different process than the rest of the industry, is making some inroads due to the lower silicon content of its cells. The eventual winner of the race to produce the lowest cost solar power is not going to be determined for quite awhile, but some strong indications should be available by 2010.