Solar Power Breakthrough Claimed By Stanford Researchers
Posted: 03/10/11 09:39 AM

From EarthTechling’s Pete Danko:

It’s the Holy Grail at clean energy research labs all over the world and something which could address long term energy issues domestically and beyond: more efficient photovoltaic solar. We’ve told you about scientists studying full-spectrum cells, using textured substrates, trying self-regenerating nanomaterials – we’ve even reported on an anti-reflective film inspired by a coating found in moth eyes. Now a Stanford team is claiming a breakthrough in making cheaper, more efficient panels by adding a single layer of organic molecules to solar cells.

The researchers studied this technique on a fairly new type of solar cell that uses tiny particles of semiconductors called quantum dots. Quantum dot solar cells are cheaper to produce than traditional silicon cells, but they haven’t caught on due to their relative inefficiency.

For Stacey Bent, a chemical engineering professor at Stanford, this represented something of a challenge. She knew that solar cells made of a single material have a maximum efficiency of about 31 percent, a limitation of the fixed energy level they can absorb, and that quantum dot solar cells didn’t share this limitation. “Quantum dots can be tuned to absorb a certain wavelength of light just by changing their size,” the Stanford report on her research says. “And they can be used to build more complex solar cells that have more than one size of quantum dot, allowing them to absorb multiple wavelengths of light.”

So Bent and her team coated a titanium dioxide semiconductor in their quantum dot solar cell with a very thin single layer of organic molecules. They found that just that single layer, less than a nanometer thick, was enough to triple the efficiency of the solar cells.

Even with this breakthrough, there’s still work to do: Bent said the cadmium sulfide quantum dots she’s been using aren’t ideal for solar cells, so her group plans to try other molecules for the organic layer, while also tinkering with the solar cell increase light absorption.

Her theory is, said Stanford, that once the sun’s energy creates an electron and a hole, the thin organic layer helps keep them apart, preventing them from recombining and being wasted. The group has yet to optimize the solar cells, and they have currently achieved an efficiency of, at most, 0.4 percent. But the group can tune several aspects of the cell, and once they do it is said, the threefold increase caused by the organic layer would be even more significant.

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Xcel cuts solar incentive

Solar-energy execs are in an uproar as the utility asks for further reductions.
By Steve Raabe, The Denver Post
UPDATED: 02/17/2011 10:40:10 AM MST

Xcel Energy said Wednesday that it is cutting the financial incentives it offers to customers for solar-energy installations.

In addition, the utility is asking state regulators to approve further cutbacks in the subsidy program.

Xcel said the reductions are justified because the cost of solar panels has been declining and customers no longer need higher incentives to offset installation costs.

But solar-industry officials said the cutbacks will have a severe effect on investments and jobs in the sector.

“This is absolutely devastating to the solar industry,” said Neal Lurie, executive director of the Colorado Solar Energy Industries Association. “No industry can survive this kind of shock.”

Lurie said the subsidy cutback endangers the sector’s growth, which has seen Colorado solar-energy jobs increase from 500 to 5,300 since the incentive program started in 2006.

State law provides for incentives and rebates on the installation of solar-energy equipment to meet renewable-energy mandates. The law allows Xcel to establish the level of incentives; the amount of rebates is set separately by the Colorado Public Utilities Commission.

The combined incentive and rebate drops from $2.35 per watt to $2.01, effective immediately, based on Xcel’s change for residential- scale systems that range from 0.5 to 10 kilowatts. Larger systems will incur similar reductions.

Xcel also is asking the PUC to lower rebate amounts so that combined subsidies would drop further to $1.25 per watt — a 47 percent reduction from previous levels.

Solar-industry officials estimated that typical residential systems now costing $5,000 to $12,000 could rise to $8,000 to $16,000 after the reduced incentives and rebates.

Customers whose incentive applications already have been approved will still qualify for the higher subsidies.

Xcel cited a Deutsche Bank study saying the cost of solar panels dropped 50 percent from 2008 to 2009.

“We look forward to the industry’s continued progress so that it can ultimately become self-supporting,” Xcel Colorado president David Eves said in a statement. “Just as wind energy is now more competitive, solar energy is moving in that direction too.”

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