Highly energetic, “hot” electrons have the potential to help solar panels more efficiently harvest light energy.

But scientists haven’t been able to measure the energies of those electrons, limiting their use. Researchers at Purdue University and the University of Michigan built a way to analyze those energies.

“There have been many theoretical models of hot electrons but no direct experiments or measurements of what they look like,” said Vladimir “Vlad” Shalaev (shal-AYV), Purdue University’s Bob and Anne Burnett Distinguished Professor of Electrical and Computer Engineering, who led the Purdue team in this collaborative work.

Solar power systems with double-sided (bifacial) solar panels—which collect sunlight from two sides instead of one—and single-axis tracking technology that tilts the panels so they can follow the sun are the most cost effective to date, researchers report June 3rd in the journal Joule. They determined that this combination of technologies produces almost 35% more energy, on average, than immobile single-panel photovoltaic systems, while reducing the cost of electricity by an average of 16%.

“The results are stable, even when accounting for changes in the weather conditions and in the costs from the solar panels and the other components of the photovoltaic system, over a fairly wide range,” says first author Carlos Rodríguez-Gallegos, a research fellow at the Solar Energy Research Institute of Singapore, sponsored by the National University of Singapore. “This means that investing in bifacial and tracking systems should be a safe bet for the foreseeable future.”

Research efforts tend to focus on further boosting energy output from solar power systems by improving solar cell efficiency, but the energy yield per panel can also be increased in other ways. Double-sided solar panels, for example, produce more energy per unit area than their standard counterparts and can function in similar locations, including rooftops. This style of solar panel, as well as tracking technology that allows each panel to capture more light by tilting in line with the sun throughout the day, could significantly improve the energy yield of solar cells even without further advancements in the capabilities of the cells themselves. However, the combined contributions of these recent technologies have not been fully explored.

Although perovskites are a promising alternative to the silicon used to make most of today’s solar cells, new manufacturing processes are needed to make them practical for commercial production. To help fill this gap, researchers have developed a new precision spray-coating method that enables more complex perovskite solar cell designs and could be scaled up for mass production.

Perovskites are promising for next-generation solar cells because they absorb light and convert it to energy with better efficiency and potentially lower production costs than silicon. Perovskites can even be sprayed onto glass to create energy-producing windows.

“Our work demonstrates a process to deposit perovskite layer by layer with controllable thicknesses and rates of deposition for each layer,” said research team leader Pongsakorn Kanjanaboos from the School of Materials Science and Innovation, Faculty of Science, Mahidol University in Thailand. “This new method enables stacked designs for solar cells with better performance and stability.”

The thermoelectric generator harnesses the flow of heat between two surfaces — one exposed to the cold sky at night. It could be the nocturnal cousin of solar power, lighting the lives of the 1.7 billion people worldwide living with an unreliable electricity connection.