More efficient solar power plants using concentrated sunlight are a step closer to reality thanks to an EU-funded project which fosters an innovative and competitive solar energy industry in Europe.
© Marta Victoria, 2016
Solar photovoltaic power panels are now commonplace on rooftops and in field installations across Europe. But for heftier applications eyes are turning to a technology called concentrating photovoltaics (CPV) where mirrors or lenses are used to capture sunlight and focus it on small but much more efficient solar cells.
The last decade has seen a growing interest in CPV, says Simon Philipps of the Fraunhofer Institute for Solar Energy Systems (ISE) in Freiburg who is coordinating the EU-funded CPVMatch project. “The technology is quite far advanced but there is still room for improvement with respect to efficiency and cost. Some designs are already on the market but now we need large-scale production to bring costs down.”
Early optimism for CPV was dampened by an unexpectedly rapid fall in the cost of conventional panels. Many small and medium-sized CPV companies were unable to compete with an oversupply of cheap, imported panels.
Efficient and competitive
This second wave of CPV is different. Researchers now know that CPV systems must compete on cost as well as efficiency.
Solar cells contain semiconductor junctions that absorb light and turn it into electric current. A conventional silicon cell has a single junction that absorbs just one band of wavelengths. Cells used in CPV contain a stack of two or more junctions each absorbing a different part of the solar spectrum. Together they can capture more of the incident sunlight than a conventional cell.
These multi-junction cells use several different materials and are too expensive to be deployed in flat panels except in space applications but are ideal for CPV systems where concentration factors of 800 are now feasible.
The CPVMatch partners are developing novel and cost-effective methods of making cells with four junctions and also improving the design of the module that contains the cell and the concentrating optics.
Philipps is confident they will achieve a cell efficiency of 48% and a module efficiency of 40%, about twice that of conventional silicon technology. He sees cell efficiency soon reaching 50% which is ample for practical applications. “The cells are rather complex and the focus of research will then go even more towards designs that can be produced cheaply.”
A new industry
Commercialisation will be rapid as the cells developed in CPVMatch are being made in a machine that is commonplace in the semiconductor industry. “We can just copy the ‘recipe’ to industry and they can start production immediately,” Philipps says.
CPV technology will be used in power plants rather than small domestic installations. The collectors require direct sunlight so ideal European locations would be in the Mediterranean countries and are steered to track the Sun across the sky.
Worldwide, total installed CPV power is only about 400 megawatts but some individual plants now exceed 50 megawatts and the potential for expansion is huge. The main players are Europe, Japan and the US and Philipps sees an opportunity for Europe to develop a fully indigenous CPV sector.
“The whole value chain of production can be built in Europe,” he says. “For CPV we are building up a new industry we already have the largest producer of multi-junction solar cells and the rather complex CPV technology is not easily transferable to other countries. That’s why we see a big opportunity for European industry in CPV.”