Are Thin-Film Solar Efficiency Standards Unfair?

Thin-film solar companies are tired of being asked about their conversion efficiency, which is basically the amount of sunlight a panel can convert into electricity. Part of that is because the thin-film manufacturers say the efficiency standard is flawed. And increasingly some thin-film companies are pushing for a new standard.

At a Credit Suisse party last month, John Argo, vice president of operations for Bloo Solar, said he would like to see the formation of an independent body to come up with an objective standard more reflective of the sunlight a panel would get on an average day.

“No standards measure for that,” he said. “It should be possible to come up with an equation to do this.” He argues that what really matters is the total kilowatt-hours a panel produces, not the cost per watt. (This is in contrast to the viewpoints of people like Suntech Power CEO Zhengrong Shi, who has said that cost per watt is the only metric that matters.)

What’s the problem with the current efficiency measurement? Commercially available thin films aren’t as efficient as conventional silicon-based solar cells, at least the way efficiency is measured today. The standard of measurement is based on peak power, or the maximum amount of electricity that a panel can produce in ideal conditions.

For comparison, take a look at these numbers. First Solar, the world’s No. 1 thin-film solar manufacturer, said it had reached an average cell efficiency of 10.6 percent at the end of last year. Meanwhile, SunPower Corp., which makes the most efficient commercially available silicon-based cell, sells panels with 22-percent efficiency.

Thin film manufacturers claim their panels produce more electricity in actual conditions, even though the efficiency number makes it look like they produce less.

That’s partly because as traditional panels heat up (as they tend to do when they absorb sunlight all day), they become less efficient at converting sunlight into electricity, while thin films lose less efficiency at higher temperatures.

Another reason is that thin films can make electricity in diffuse light, while regular silicon-based panels need more direct light, which advocates say means that means thin films can produce more electricity throughout the day.

Thin-film technologies such as Bloo’s might deliver the same or higher cost per watt as a monocrystalline panel, but a lower cost per kilowatt-hour, Argo said, adding that his company is already getting contracts that agree to pay more per watt, as long as the technology meets its performance goals.

Keshav Prasad, vice president of business development for Signet Solar Inc., thinks the total system output is most important, and says the current efficiency numbers don’t matter when it comes to customer purchases: “I do not believe anybody buys panels based on efficiency numbers,” he said last month. “I don’t know if it’s an important criteria. It’s [certainly] not the only criteria.”

Marcelino Susas, vice president of strategic marketing for Energy Conversion Devices Inc. agrees on the total output being the key metric: “On the measurement of kilowatt-hours per kilowatt installed, we perform better than triple-junction,” he said. “Installations around the world are seeing this. We want to say, ‘Think of thin film a little differently.'”

But as you’d expect, not everyone agrees with this idea, particularly manufacturers of traditional silicon-based solar panels. Take SolarWorld AG, for example.

“What they are trying to push here is where they believe they have an advantage – the only tiny advantage they have – to try to get customers’ trust,” said Boris Klebensberger, chief operating officer of SolarWorld and president of SolarWorld Industries America, speaking of thin-film manufacturers (read more about his views on thin film and other topics here).

It’s unlikely crystalline-silicon manufacturers will go along with a new measurement that could put them at less of an advantage – and crystalline-silicon manufacturers still own the bulk of the market.

Thin-film manufacturers’ best bet might be to come up with a new standardized calculation they can use — in addition to, not instead of — the current efficiency number to help customers more easily suss out what technology would make the most sense for them, depending on where they live.

After all, as Prasad said, efficiency is one gauge – but it’s not everything customers need to know to make their decision.

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