Solar power is taking off around the world. Europe is planning to deploy various types of solar power to the Sahara to provide for the European Union's energy needs. Meanwhile, here in the U.S., California is expanding its solar efforts as well.
However, amid the progressing adoption of solar technology, one perpetual criticism that persists is that solar power is inefficient and expensive. To some extents this is true. The current generation of photovoltaic solar panels -- the type of solar power perhaps most associated with the field -- is only around 20 percent efficient and thus costs remain relatively high, like many forms of alternative energy.
A new breakthrough from U.S. Department of Energy's National Renewable Energy Laboratory (NREL) is looking to solve those problems. It pushes solar cells to uncharted technology with a record 40.8 percent efficiency. The new work shatters all previous records for photovoltaic device efficiencies.
The researchers first used a special type of cell, an inverted metamorphic triple-junction solar cell. The custom cell was designed, fabricated, and independently measured at NREL. The next step was to expose the solar cell to concentrated light of 326 suns, yielding the record-breaking efficiency. A sun is a common measure in the solar power industry which represents the amount of light that hits the Earth on average.
The new cell targets a variety of markets. One potential market is the satellite solar panel business. Satellites natural absorb more intense sunlight, thanks to no atmospheric interference. Another possible application is deployment in commercial concentrated PV cells. Concentrated PV is a burgeoning field, with several companies currently contracted worldwide to build the first utility grade plants.
The new record was welcome news, but little surprise at NREL -- they held the previous record as well. In order to beat their old design, one key was to replace the germanium wafer at the bottom junction with a composite of gallium indium phosphide and gallium indium arsenide. The mixture splits the spectrum into three parts, each of which gets absorbed by one of the junctions. Both the middle and bottom junction become metamorphic in the new design. This means their crystal lattices are misaligned, trapping light in the junction and absorbing more of it. This yields an optimal efficiency.
One key advantage is the new solar cell can be conveniently processed by growth on a gallium arsenide wafer. It is also both thin and light. The NREL believes this cell will be cheaper than current commercial models, while delivering far more power.
Some of the credit for the work goes to NREL's Mark Wanlass, who invented the cell's predecessor. The new cell was redesigned by a team led by John Geisz.
The NREL is operated by the DOE by Midwest Research Institute and Battelle.