As Europe strives to position itself as a world leader in renewable energy, one challenge it must solve is the often inefficient process of converting renewable resources into energy. For example, due to a mismatch between the solar spectrum and the spectral response of solar cells, the process of converting solar radiation into electricity is highly inefficient. In fact, conventional solar cells have an upward limit of 30 % efficiency for converting radiation into electricity – meaning that 70 % of the potential energy is lost.
It is inefficiencies like this that the EU-funded NLO for PV project set out to address. According to project leader Carmel Rotschild, the researchers initially aimed to use conventional methods in nonlinear optics to convert the inefficient parts of the solar spectrum to wavelengths that are more suitable for photovoltaics. But this proved to be a very difficult task that produced little improvements in efficiency. So it was back to the drawing board.
“A year after the beginning of the project, we reached a breakthrough in both fundamental science and engineering,” says Rotschild. The team discovered that, because they can extract heat without generating additional photons, photoluminescence works as an ideal heat pump. “From our experiments, we realised that one can harvest the heat losses of photovoltaics, thereby doubling their maximum possible efficiency to 70 %,” adds Rotschild.
New methods, same objective
Based on these new understandings, the project had to shift its methods in order to achieve its original objective. However, even this change in methods was not without challenges. “Although we had the experimental evidence, it was very hard to convince high-level scientific journals to publish such unexpected claims,” explains Rotschild. However, in part due to the level of credibility, networking and knowledge exchange that comes with this project being funded under the EU’s Career Integration Grant (CIG) scheme, the breakthrough in optical energy conversion was ultimately validated by the scientific community.
The project produced the first proof of principle of an energy conversion device – which was accepted for publication in Nature magazine. In addition, a provisional application to patent a process for combining photonic and thermal excitation to create electricity has been submitted.
A disruptive approach
The project continues its efforts to build a full-scale conversion device, with the support of a new European Research Council grant. Research is primarily focused on gaining a fundamental understanding of the thermodynamics of photoluminescence and its transition to thermal emissions and, based on this understanding, demonstrate a full-scale efficient device.
“I fully believe that within four years we will demonstrate a new photovoltaics technology capable of offering record efficiency,” concludes Rotschild. “From here, we will commercialise this technology, thus disrupting the way solar energy is converted to electricity and ensuring Europe’s place at the forefront of the renewable energy market.”
Project acronym: NLO for PV
Participants: Israel (Coordinator)
Project N°: 303921
Total costs: € 100 000
EU contribution: € 100 000
Duration: April 2012 – March 2016