August 1, 2007 9:15 AM PDT

FAQ: A concentrated power boost for solar energy

Concentrating solar power, which has been around for decades, is one of the most promising techniques being tried today to make solar electricity more cost effective.

The concept is simply to focus light in order to boost electricity output. But there's a wide disparity in the types of solar concentrators being built, from utility-scale solar thermal projects to specialized photovoltaic solar panels that could one day go on a homeowner's roof.

In this FAQ, we will specifically discuss concentrating photovoltaics, a design being pursued by a number of solar companies seeking to lower the cost per kilowatt the sun can deliver.

What are the primary forms of solar concentrators?
Solar concentrators use lenses, mirrors, parabolic dishes or other optics to concentrate energy from the sun. Very often, they have a mechanism so that these devices track the path of the sun during the day. In solar thermal applications, troughs or large mirrors amplify sunlight to create heat, which heats a liquid or gas that turns turbines to make electricity. Solar thermal is used for large-scale power plants operated by utilities, usually in the desert. After a 16-year hiatus, companies are opening up new plants or contemplating new ones in the southwestern U.S., India, southern Europe and North Africa.

This same technique is also being pursued in conjunction with photovoltaic solar cells, which convert light to electricity. Among concentrating photovoltaic companies, there is a wide range of approaches. There are systems designed for utilities' central power stations, mounted concentrators that can go on the roof of an office building, and those that are the same size as traditional solar panels.

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Why is there interest in concentrating photovoltaics?
Three words: the solar constant. The sun radiates about a kilowatt of energy per square meter on the surface of Earth, according to B.J. Stanberry, CEO of HelioVolt. There are 2.6 million square meters in a square mile. Thus, every square mile gets about 2.6 gigawatts. It's a number that just can't be increased.

Concentrators essentially try to artificially increase the constant by virtually expanding the size of solar cell with mirrors or lenses. The quality of the concentrator is rated by how much solar real estate it can cram onto a solar cell without creating things like shadows or interfering with other solar cells.

One number you hear a lot is how many suns a concentrator replicates. GreenVolts, which is commercializing technology licensed from Lawrence Livermore National Laboratory, has a concentrator it says can deliver the equivalent of the energy of 625 suns to a solar cell.

Why not just improve solar cells?
That's also being done. Without concentration, the efficiency of commonly used solar cells made from silicon tops out at around 22 percent. Physics says that crystalline silicon PV cells will top out at around 29 percent.

High-efficiency cells, historically used for satellites or spacecraft and made from different layers of materials, can exceed 40 percent efficiency or more, but this pushes up the price. Focusing more light onto cells makes them more productive.

The relatively high cost of photovoltaic material--the most common being silicon, which is in short supply--represents a significant cost to an overall solar power device. Using concentration, manufacturers are looking to lower the overall cost per kilowatt-hour of a solar power purchase. People often believe that since most solar cells are made of silicon, panel manufacturers inherit Moore's Law, which stipulates that the performance of microprocessors double every 24 months. But the same dynamics don't play out, solar industry executives say. Instead, the solar industry is focused exclusively on cost and making solar power competitive with traditional fossil fuel-based power generation. That's why many companies, including a number of start-ups, are trying to concentrate solar power, along with thin-film solar cells made from other materials, and lowering their manufacturing costs.

CONTINUED: But does it cost less?…
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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 )
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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 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 )
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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:
Posted by sonnyle30 (2 comments )
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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 )
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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.
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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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