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BP Solar Sticks with Silicon

An industry giant says a tweak to silicon manufacturing could beat more exotic materials approaches over the next decade.

It’s boom time for solar power, as a rising tide of startups tout various approaches–from organic thin films to concentrating light with holograms–for harvesting energy from the sun. But amid the flurry of nascent technologies, BP Solar, a 30-year-old subsidiary of oil giant BP, is betting that old-fashioned silicon still holds the most potential for cost-effective solar power in the next decade.

In its latest move, the company has developed a solar module–a collection of solar cells–using a new silicon-manufacturing approach that the company says drives down the cost of generating solar power. The new technology boosts power production 8 percent without a price increase, the company says. BP Solar will begin production of these modules by mid 2007.

Technology Review caught up with Lee Edwards, president and CEO of BP Solar, to ask about the new technology and other efforts at the company.

Technology Review: You say your new silicon prototype–which you call Mono2–increases efficiency of your solar cells without increasing the cost. What is Mono2?

Lee Edwards: Over the next 10 years, BP Solar believes that a silicon-based cell technology will continue to drive cost efficiency. This announcement of the Mono2 approach to creating the silicon wafer was driven by an acknowledgement of the two different types of silicon available: monocrystalline and multicrystalline. Monocrystalline silicon makes for high efficiency, but it’s relatively expensive, and the solar-power industry competes with the microprocessor industry for this type of silicon. Multicrystalline is cheaper, but it is lower quality. Mono2, broadly speaking, gives the same electrical-efficiency benefits as monocrystalline wafers but uses a multicrystalline casting approach that is less expensive.

TR: How does it work?

LE: In the traditional multicrystalline manufacturing, you basically put a bunch of rocks in a ceramic crucible, heat it to 1,500 degrees C, let it sit there for a day, and cool it slowly. You get a block of silicon, but the crystal structure is random. Some people say it’s more visually appealing because of the way light reflects off it, but each one of those grain boundaries creates a barrier to electron flow. The beauty of our technique is that we’ve found, in our protected intellectual property, a way to essentially get a single crystal using another approach. The details are proprietary, but it’s a combination of metallurgy and the process that allows us to do it.

TR: What’s the efficiency or cost-per-watt benefit?

LE: When we say “efficiency,” there are two components to it. There are some who love to advertise their cell-conversion efficiency, so you’ll see 19 or 20 percent efficiency quoted. That is the amount of sunlight that hits the surface that is converted to electricity. When we talk about efficiency within BP Solar, it is the dollar-per-watt cost to convert sunlight into electricity. The Mono2 module can produce 8 percent more power for the same price as a module made from multicrystalline silicon modules on the market today. This decreases the price per watt.

TR: What other ways are you trying to squeeze extra watts from silicon?

LE: We’ve got two approaches within BP Solar to do that. One involves grooving the wafer itself with precision lasers that increase the surface area, allowing more sunlight to be converted to electricity. And the other is printing material on the front and the back to create electrical contacts that pull out the electricity without blocking too much sunlight in the process.

TR: But there’s still the cost issue of installing solar modules. What approaches are you taking to reduce costs there?

LE: There are some innovations in the value chain that we’re on the front edge of, including how you access your customer. In the U.S. we are selling products in more than 250 Home Depots, in California, New Jersey, and New York. Having in-store solar-sales capability basically simplifies the value chain so you don’t have BP Solar selling to a group that sells to another group that goes out and markets the product. There’s only the installer in between, and we endorse their capabilities.

Another aspect that we’re looking at is how you actually construct a frame [for a solar module]. Rather than using extruded aluminum framing, we’re looking at a cast polyurethane mold. It’s stronger, it’s lighter, it’s easier to install, and it looks cool. And if you were really into the architecture, you could have different colors, different types of arrays. [Aesthetics] is a big barrier for going mainstream within solar because people don’t want to feel like they’ve got a bunch of screen doors screwed into their roofs. And then the ultimate is if you make the solar as part of the roof, so you bring together building materials with the photovoltaic industry and say, Let’s build a new roofing material that’s pre-wired for new construction.

TR: Do you think that in the next couple of years we’ll see more economically successful solar efforts?

LE: What’s different now is that we’ve had a few years of high oil prices, we’ve had increased public pressure for policies that will allow for energy independence, and the environmental reality of making a difference in the carbon footprint of the planet is more accepted. So I think all those say there will be a big jump in continued demand. What we see is the demand forecast is significantly higher this year–and it just keeps getting bigger as more countries and more states enact policies to enable continued growth.

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