Jef Poortmans, imec fellow and scientific director photovoltaics at imec
At the end of 2016, the World Economic Forum published a report stating that renewable energy had reached a tipping point: solar and wind energy had become as cost-efficient – or even cheaper – than new fossil fuel capacity in more than 30 countries. It is also considerably cheaper than nuclear power: solar power can now be produced at a cost of 2 to 2.5 eurocents per kWh, versus nuclear power’s cost of 6 to 7 eurocents per kWh.
A shifting energy market
In 2017, the global energy market picked up on this. Before, investing in solar energy was mostly an environmentally-motivated decision, but in the meantime it has become an economic opportunity as well. China jumped on the bandwagon, establishing itself as a world leader in renewable energy production: the global photovoltaics energy market is estimated at 100 gigawatt-peak, half of which is installed in China. Europe, on the other hand, has been slower to respond to this trend. The EU played an important role in laying the foundations for renewable energy and still delivers top-notch R&D, but there is little consensus between member states on regulations or policy. To stay in the game, the EU has to come up with a long-term energy plan, clearly outlining the position renewables take in this.The fact that renewable energy is an interesting option – not only from an environmental, but also from a practical and economic point of view – also became clear in a 2017 study conducted by EnergyVille, an initiative uniting KU Leuven, VITO, imec and UHasselt for research on sustainable energy and intelligent energy systems. The study suggested that the most cost-efficient way forward for Belgium would be to step up renewable energy production so it would account for 50% of the country’s energy production by 2020-2030; this in combination with natural gas to make up for the volatile nature of solar and wind energy.
Optimizing sustainable energy production and storage
Though renewable energy has become much more efficient, there is still room for improvement. One path that imec is exploring is the development of bifacial solar cells. With a transparent backside and comparable front and back contact schemes, they can capture light on both sides, thus profiting from indirect sunlight that is reflected by the ground or surrounding buildings. In 2017, we managed to upgrade our bifacial solar cells to reach an average conversion efficiency of 22.4 percent with the best cell topping 22.8 percent, a record for this type of cell.
Another method to enhance efficiency is experimenting with new materials, like perovskite microcrystals. Because perovskite solar cells are flexible and semi-transparent, they could be integrated in building materials, e.g. curved surfaces or even windows. In 2017, imec researchers managed to optimize our 4x4cm2 perovskite module, achieving a record conversion efficiency (12.4%). Another, perhaps even more promising, approach is stacking the perovskite cells on top of silicon solar cells. Because the perovskite modules can be engineered to absorb a spectral range complementary to that of silicon cells, this can boost efficiency. We already demonstrated this kind of tandem module – together with Solliance – in 2016, but in 2017 we optimized them to outperform standalone high-efficiency silicon solar cells.
In 2017, we have also been working on the next big renewable energy challenge: how can we compensate for the volatility of renewable energy? Or in other words: what do we do when there is not enough wind to keep our wind turbines spinning or not enough sunlight to activate our solar cells?