CONCENTRATING PHOTOVOLTAICS

Solar Companies Merge Technologies in Bid for Utility-Scale Production
Katie Howell, July 7, 2009 (NY Times)

SUMMARY
Concentrating photovoltaic (CPV) technology is a hybrid of 2 familiar solar energy concepts. The most widely recognized and developed concentrating solar energy technologies use mirrors to concentrate the sun’s heat, on a solar power plant (SPP) scale. The familiar rooftop solar systems use solar photovoltaic (PV) panels to transform the sun’s light into electricity.

The hybrid concentrating PV concept uses a small, highly efficient mirror-lens system to concentrate the sun’s light on a small, highly efficient PV panel and transform the sun’s light into electricity with a very high degree of efficiency.

CPV is a new variation that could improve the cost-effectiveness of solar power plants but has yet to prove itself. A few companies, including SolFocus, are working to perfect and demonstrate it.

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The SolFocus CPV system directs sunlight onto an optical rod with a 2-mirrored system. The rod acts as a lens to concentrate and focus the light "of 500 suns" on a tiny, 1-square centimeter PV cell. A panel consists of several of these units. A row of panels is mounted on a tracking rack that rotates with the sun across the sky, maximizing the light hitting the panels.

Emcore Corp. uses powerful lenses that focus a 500-sun concentration of light onto a highly efficient multi-junction (thin film) solar cell. The “multi-junction” architecture makes the cell capable of capturing more of the light concentrated on it.

Semprius Solar is using a similar concept but concentrates "1,000 suns" and is working to make the its micro-transfer thin film manufacturing technology that simulates a printing process less expensive so the price of the CPV panels will be more affordable and, therefore, cost effective.

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Cost remains CPV’s obstacle. It is still more expensive than rooftop silicon solar panels or thin film solar panels, though SolFocus says it is on track to match the other panel materials by 2010 and be cheaper by 2011. A recent report from Spain estimated CPV will reach grid parity, the cost for electricity production that matches the cost of traditional generation sources, between 2011 and 2015. That is the same time frame in which the other solar panel materials manufacturers anticipate reaching grid parity.

To bring its costs down, CPV will have to get a bigger part of the market. And, of course, to get a bigger part of the market it will have to bring its costs down. Estimates put present CPV investment at ~$1 billion worldwide, which represents a few small-scale projects, mostly in Europe.

SolFocus has done a half-megawatt installation in Spain and is doing a 10-meagawatt installation in Greece but only has ~10 kilowatts installed domestically. Emcore has installed a megawatt of CPV in Spain but less than 500 kilowatts in the U.S.

SolFocus panels. (click to enlarge)

Advocacy group CPV Consortium wants federal buy-in. Federal labs and grants have pushed CPV R&D. Now the CPV industry wants the government to provide loan guarantees or installation money for demonstration projects on federal lands.

As many as a dozen companies, from start-ups to a 50-year veteran solar panel manufacturer Sharp Corp, are experimenting with a variety of mirrors, lenses, dishes, troughs and carousels to maximize reliability, increase the delivery of sunlight to ever-smaller, ever more efficient PV cells or cut production costs.

Semprius panels. (click to enlarge)

COMMENTARY
Because CPV panels use less silicon, they are – like solar thin film – less expensive. Also like thin film, CPV is better suited for use in larger, solar power plant (SPP) arrays than for small, rooftop systems where silicon panels remain the standard because of their durability and lack of need for maintenance.

The competition will be between CPV, which uses the sun’s light, and SPP technologies that use large flat mirrors to concentrate the sun’s heat on a solar power tower or parabolic trough mirrors to concentrate the sun’s heat on flowing liquid.

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Because solar power plants are built in intensely hot desert areas, CPV’s most immediate advantage over SPP mirror technologies is that it uses significantly less water. The SolFocus technology uses 4 gallons of water per megawatt-hour of electricity produced, mostly to keep the panels clean of dust. The widely-used solar power plan technologies reportedly use 850 gallons of water per megawatt-hour.

CPV systems are also largely made of aluminum and glass and are, therefore, 97% recyclable. The energy payback for all materials in a CPV system may be as little as 6 months.

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Finally, the modular configuration of CPV allows installations to be set up to accommodate the space rather than dominating the space the way the larger plants do. SolFocus says its panels can even be set up to allow the growing of crops or grazing of animals in between.

Because CPV is modular, it lends itself to SPP installations of any size whereas the economics of the big-mirror SPP technologies make them more cost-effective at larger sizes. Perhaps, for the time being, CPV might work better as 1-to-10 megawatt supplementary installations, such as those currently being tried at natural gas plants, while the 50-megawatt and up solar power tower and parabolic trough mirror systems would be the cost-effective choice for stand-alone power plants.

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QUOTES
- Nancy Hartsoch, vice president of marketing, SolFocus and director, CPV Consortium trade group: "In a lot of ways, it's merging the advantages of photovoltaic technology with the efficiency and ability to capture more sunlight that you get with concentrated…You're basically focusing 650 suns onto that cell, so you're able to use a very, very small amount of photovoltaic material to capture a tremendous amount of sunlight and then convert it at very high efficiency."
- Brad Collins, director, American Solar Energy Society (ASES): "I think there's a huge space [for CPV technology]…Solar deployment on a utility scale will explode in the next five years…It doesn't compete with traditional PV. The applications are different…One's going to be a power plant, and one is a distributed resource. It's not comparing apples to apples."
- Hartsoch, SolFocus and CPV Consortium: "There are the big concentrating solar power plants -- the solar thermal stuff that's been around a long time -- and they use mirrors as we do in a different way…I guess you could say [CPV’s water use is] a drop in the bucket [compared to that]…"

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- Sarah Kurtz, CPV researcher, National Renewable Energy Laboratory (NREL) of the U.S. Department of Energy (DOE): "When compared with solar thermal approaches, CPV provides a qualitatively different approach, typically with lower water usage, greater flexibility in size of installation and the ability to respond more quickly when the sun returns on a cloudy day…"
- Hartsoch, SolFocus and CPV Consortium: "The battle for a new technology like this, the challenge it faces, is the reason it's good…What it brings is high efficiency, low carbon footprint, all those things. What comes with it is the risk of new technology…You're now talking about small grants ... to develop new technologies and some showcasing, but if you want to take this big-scale, there's one more hurdle…What can you do to help us assure that it's safe to deploy?"
- Anita Balachandra, senior vice president, TechVision21: "So many of these technologies have originated in the United States, but where they've really flourished and been taken to scale has been outside of the United States…They've drawn them, and long term, we lose competitive advantage."

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- Brian Gibson, director of business development, Emcore: "We are pursuing larger projects at this point in time, but as with any newer technology, there's going to be reluctance of the financial institution to take risk…It's difficult to get anything sizable financed. We are looking at some 10- and 20-megawatt projects, but from a practical standpoint, you've got to do some 1- to 3-megawatt projects before anyone will finance you."
- Kurtz, NREL: "In the last 10 years, the solar industry has mushroomed, and the CPV industry is now growing rapidly…With the overall PV market growing in the gigawatt range, CPV has an opportunity to enter the market with production of tens or hundreds of megawatts per year... This is significant because CPV is unlikely to achieve low costs when manufacturing at less than tens of megawatts per year."