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Solar PV’s 44% Efficiency Record, Thanks To NREL & Solar Junction

Here’s a great solar PV story from the good folks over at NREL (note that we’ve already covered Solar Junction’s 44% solar cell efficiency record, but this post below goes above & beyond that first one):

An operator inspects a photolithography tool used to manufacture high-efficiency Solar Junction concentrator solar cells. NREL’s pioneering multijunction work led to the Solar Junction SJ3 solar cell with tunable bandgaps, lattice-matched architecture, and ultra-concentrated tunnel junctions. Credit: Daniel Derkacs/Solar Junction

It takes outside-the-box thinking to outsmart the solar spectrum and set a world record for solar cell efficiency. The solar spectrum has boundaries and immutable rules. No matter how much solar cell manufacturers want to bend those rules, they can’t.

So how can we make a solar cell that has a higher efficiency than the rules allow?

That’s the question scientists in the III-V Multijunction Photovoltaics Group at the U.S. Department of Energy’s (DOE) National Renewable Energy Laboratory (NREL) faced 15 years ago as they searched for materials they could grow easily that also have the ideal combinations of band gaps for converting photons from the sun into electricity with unprecedented efficiency.

A band gap is an energy that characterizes how a semiconductor material absorbs photons, and how efficiently a solar cell made from that material can extract the useful energy from those photons.

“The ideal band gaps for a solar cell are determined by the solar spectrum,” said Daniel Friedman, manager of the NREL III-V Multijunction Photovoltaics Group. “There’s no way around that.”

But this year, Friedman’s team succeeded so spectacularly in bending the rules of the solar spectrum that NREL and its industry partner, Solar Junction, won a coveted R&D 100 award from R&D Magazine for a world-record multijunction solar cell. The three-layered cell, SJ3, converted 43.5% of the energy in sunlight into electrical energy — a rate that has stimulated demand for the cell to be used in concentrator photovoltaic (CPV) arrays for utility-scale energy production.

Last month, that record of 43.5% efficiency at 415 suns was eclipsed with a 44% efficiency at 947 suns. Both records were verified by NREL. This is NREL’s third R&D 100 award for advances in ultra-high-efficiency multijunction cells. CPV technology gains efficiency by using low-cost lenses to multiply the sun’s intensity, which scientists refer to as numbers of suns.

Friedman says earlier success with multijunction cells — layered semiconductors each optimized to capture different wavelengths of light at their junctions — gave NREL a head start.

The SJ3 cells fit into the market for utility-scale CPV projects. They’re designed for application under sunlight concentrated to 1,000 times its normal intensity by low-cost lenses that gather the light and direct it at each cell. In regions of clear atmosphere and intense sunlight, such as the U.S. desert Southwest, CPV has outstanding potential for lowest-cost solar electricity. There is enough available sunlight in these areas More


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