August 1, 2007 9:15 AM PDT

FAQ: A concentrated power boost for solar energy

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OK, concentrating light onto solar cells means more power output. But does that mean it's more cost-effective?
Not necessarily. Concentrating photovoltaic systems often require lenses or mirrors to focus the light onto solar cells. To maximize the amount of light they receive, high-concentration systems can be mounted and need a motor so that the cells track the movement of the sun over the course of the day. So although manufacturers may be saving money on solar cells, the additional equipment can raise the price.

But solar concentrators stand to benefit from the incremental improvements in solar cell efficiency. Brad Hines, the chief technology officer of solar concentrator company Soliant Energy, says that concentrators are becoming more cost-effective as cell efficiency climbs. A company can build a concentrator that's cost-competitive with traditional solar panels when cells are 16 or 17 percent efficient, he figures. Once manufacturers start using cells with efficiency above 18 percent, there's a significant cost advantage. "When I make a concentrator, it costs me the same to build the frame and the tracking system and optics regardless of the solar cell I put in," Hines said. The same basic math holds true with high-efficiency cells, even though they are more expensive, he says.

Photos: More solar power bang for the buck

So what do these solar concentrators that use photovoltaic cells look like?
Designs vary greatly (see a few of them in this photo gallery). One could segment the industry into high-, mid- and low-concentration categories.

An example of a high-concentration company is SolFocus, a venture spun off from Xerox's Palo Alto Research Center. The company is using a series of curved lenses that focus light on high-efficiency triple-junction (i.e. multi-material) cells. The company's "honeycomb" structure places 16 of these dishes on a flat panel, which is mounted on a pole. This design magnifies light by 500 times normal sunlight, according to the company. There are a number of companies pursuing this basic design of concentrating solar arrays, essentially large assemblies with several panels. When scaled up into many very large arrays mounted on the ground, they can be used for multi-megawatt power plants. Or, one or a few arrays can be used on the rooftop of a commercial building to supplement their power consumption.

Energy Innovations is another company targeting the flat commercial rooftop business, but with a different design. It, too, uses high concentration--on the order of 800 times--and high-efficiency cells with its Sunflower product. It has a tracking system that can follow the sun's altitude and azimuth (its angle on the horizon) and a specially designed mounting system meant to keep a low profile on the roof.

Makers of low-concentration panels are satisfied with much lower magnification--as low as two or three times concentration. Companies pursuing this general track are Soliant Energy, Solaria and Silicon Valley Solar, which recently acquired NuEdison. Although they have different optical techniques for directing sunlight, the end product is meant to have the same shape and size as traditional solar panels. That should make it easier for installers and distributors familiar with solar panels able to work with these products without any special training or mounting equipment.

What are the tradeoffs of this approach?
Magnifying light many times, of course, creates a lot of heat, which lowers the efficiency of solar cells. As a result, high-concentration manufacturers often use specialized cooling systems. In addition, large-scale systems with several mounted arrays can be big civil engineering projects. As noted, all the additional equipment and engineering involved in building an entire system that tracks the sun during the day can raise the overall cost of the system, even if manufacturers are being thrifty with solar cells.

Very large concentrating photovoltaic arrays, which could be used for a medium-size power plant, are designed mainly for very sunny environments like the desert of the southwestern United States, according to solar industry executives.

Because they align with the sun very closely, a concentrating photovoltaic power plant will not perform as well on cloudy days, whereas a power field with hundreds of traditional flat-plate solar panels could still generate a significant amount of electricity, said Nancy Hartsoch, vice president of marketing at CPV start-up SolFocus.

"Put us in the Mojave Desert and we'll significantly outperform flat-plate photovoltaics. Put us in a power field in Germany and we won't," she said.

Because concentrating photovoltaic is a relatively new technology, Hartsoch expects that utilities will use a combination of flat-plate solar panels with concentrating photovoltaic arrays in the near term.

Are these concentrating photovoltaic systems commercially available?
Many of these systems are being tested now with utilities and commercial customers. A number of vendors have promised commercial availability of their systems late this year or next year. It doesn't appear that panels aimed at residential rooftops will be coming in the near future.

How will things look a few years from now?
With so much investment and engineering being poured into concentrating solar power, it is likely to endure once products are commercially available. What is less clear is which designs will win out. Solar industry executives expect that different approaches will find their market niches, such as smaller power plants for utilities looking to boost the amount of renewable energy they produce to meet government mandates. For on-site power generation, rather than centralized power plants, the success of commercial customers will help sort out the winners and losers, as they represent the mass market.

Apart from design, one of the major factors of success is manufacturing processes, argues Suvi Sharma, CEO of Solaria. With so much competition among solar companies--as well as other forms of electricity generation--the cost-effectiveness of the end product will hinge heavily on a provider's scale and operational efficiency, he said.

"Not every Silicon Valley company getting funding will be standing five years from now, but there will be some great successes," said Sharma. "Once things get more cost sensitive and commoditized, there will be a weeding-out process...it's very important to bridge the gap from a technology development phase to mass production."

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8 comments

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Efficiency doesn't increase!!!
Concentrating the sun's radiant power into smaller cells do not increase the overall solar to electric energy conversion efficiency.

Often, in the city where the piece of land is prime real estate, you are limited with the amount of space for sunlight capture. If you are intercepting the sunlight that would have otherwise fallen into other areas, you are in fact stealing solar energy from them and diverting it for your own solar cells.

What the net effect of PV solar concentration is to increase the energy output per unit amount of silicon used, and in no way in Physics you can call this as improvement of solar conversion efficiency. The perceived increased is only for marketing purpose, and to declare that there is an overall increase of efficiency is very misleading.

The real inquiry or the bottom line then would be to know if by concentrating the solar beams, will it result to lesser cost of production per unit energy output per unit area of land.
Posted by Joe Real (1217 comments )
Reply Link Flag
conversion efficiency is an important issue with some type of solar conversion. i.e., solar thermal. If you can concentrate the suns energy more efficiently then you can produce more heat per area of sun gathering.

This has big implication for the effectively using the sun... not as sun to electricity directly, but sun to create steam to turn generators. Now you can not only create new powerplant based on solar, but you can lessen the need for fossil fuels in traditional steam turbine plants by using solar thermal as a co-generation source.
Posted by Bubbasolar (1 comment )
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Solar concentrators make sense...
... for large solar electricity production farms. Where land is cheap, the sun shines all day, and there are no construction constraints (e.g., pitched roofs), this approach makes a lot of sense. It's clear that these technologies offer greater output per square foot, and at lower cost.

This leads to the next question of whether it makes more sense to do solar in a distributed (roof by roof) or centralized model. Much of the legislation seems to be encouraging distributed energy production - large subsidies are available to residents who put solar on their roofs. Technologies like concentrators just don't really apply here. The cost goes way up, and the extra weight and equipment may be impossible to mount on most roofs.

The biggest barrier to widespread residential solar is information. Most people find this topic so complex that they just don't bother, despite having high interest in being 'green'. Sites like www.solar4sf.org help in cutting through the complexity to make the information accessible to non-solar geeks.
Posted by rdbarahona (2 comments )
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Not Information... Price Rules
There is tons of information on the internet and in libraries if one actually wants to learn about solar.

The true barrier to solar is cheap panels and accessories. Also I'm gonna take a gamble and say that until hydrogen fuel cells replace batteries, there is no hope of people adopting solar power widely.

Installation costs are too high also. What we need is a cheap (under $3000 in current 2007 US Dollars) kit from WalMart that includes everything you need to get power from the Sun and could be easily self-installed....
Posted by SiXiam (69 comments )
Reply Link Flag
Actually, you can build your own solar panels to power your appliances and reduce your energy bill by 80% for less than $200. You can buy most of the materials and supplies at local hardware stores.

Go to this site and download the ebook guide and video. It has easy step by step instructions to show you how you can build your own solar panels for your home.

Here's the website: http://7peter7.earth4.hop.clickbank.net
Posted by sonnyle30 (2 comments )
Link Flag
Actually, you can build your own solar panels to power your appliances and reduce your energy bill by 80% for less than $200. You can buy most of the materials and supplies at local hardware stores.

Go to this site and download the ebook guide and video. It has easy step by step instructions to show you how you can build your own solar panels for your home.

Here's the website: http://*******.com/solarpw
Posted by sonnyle30 (2 comments )
Link Flag
I agree with most of the comments. The equipments for the solar power is expensive, and there are many issues about how to efficiently collect the solar power. However, I think that the solar power is still valuable to the human's life. Everyone would agree with me that the solar power is renewable and pollution-free. We must find a way to use it efficiently. The project, "Apple's solar strategies", is a great example of how to use the solar power efficiently. We should always try to discover and create new solutions. I believed that, in the future, humans will fully manipulate the solar power.
<a class="jive-link-external" href="http://pctechedu.blogspot.com/" target="_newWindow">http://pctechedu.blogspot.com/</a>
Posted by pan cheng (1 comment )
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Rooftop is inherently more expensive (more labor and pricy parts per watt). Also, in keeping with the laws of passive solar energy, it may be more efficient to use shade trees for cooling (and CO2 absorbtion). Also, most people don't live in a desert, the perfect place for very large arrays of mirrors and molten salt heat resevoirs (for 24/7 power generation).

Personally, I think it would be cheaper to let (inforce) the utilies to pay the extra for largescale than to do it all myself on my roof top.
Posted by fireofenergy (18 comments )
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