Spiny Norman said:
Up to 50% of the energy absorbed by a solar cell is lost as heat. Scientists are now developing a third generation of “hot carrier” solar cells that take advantage of this heat, potentially breaking the Shockley-Queisser limit of silicon-based PV.
Better-performing solar cells are a key pathway to the acceleration of the active clean energy revolution. Most solar panels today are silicon-based and have a single junction. The upper theoretical limit of energy absorption efficiency for silicon solar cells, called the Shockley-Queisser limit, is about 33.7%.
Currently, Fraunhofer holds the record for commercial silicon single-junction solar cells at about 26%, so there is much room for improvement to hit the limit. But researchers at Arizona State University and the University of Oklahoma may have discovered a way to burst through the theoretical limit by taking advantage of excess heat.
As much as 50% of the energy absorbed by a solar cell is lost as heat. This excess energy comes as a result of the charged particles in the photovoltaic process taking in more energy than is needed to excite an electron and send it on its way as electricity. The teams are developing pathways to build what are called hot carrier solar cells (HCSC) to combat these thermal energy losses and improve efficiency.
https://www.pv-magazine.com/2022/04/07/could-hot-carrier-solar-cells-break-the-theoretical-efficiency-limit/
I like that 26%. I can remember back to a time when 5% was the limit for single junction. Then 10%.
Looking up Shockley-Queisser limit. https://en.wikipedia.org/wiki/Shockley%E2%80%93Queisser_limit
“The Shockley–Queisser limit only applies to conventional solar cells with a single p-n junction; solar cells with multiple layers can (and do) outperform this limit, and so can solar thermal and certain other solar energy systems.”
I’ll have to check whether what is being newly proposed is a solar-thermal system.
“Any energy lost in a cell is turned into heat, so any inefficiency in the cell increases the cell temperature when it is placed in sunlight. As the temperature of the cell increases, the outgoing radiation and heat loss through conduction and convection also increase, until an equilibrium is reached. In practice, this equilibrium is normally reached at temperatures as high as 360 Kelvin, and consequently, cells normally operate at lower efficiencies than their room-temperature rating.”
“Recombination losses. Recombination of electrons and holes, decreases the amount of current that could be generated otherwise.” and increases with increasing temperature.
“Spectrum losses. Only photons with more than that amount of energy will produce an electron-hole pair, and any photon energy above and beyond the bandgap energy is lost”. For silicon this limits efficiency to 44%, and for an ideal material to 48%. “
“Impedance matching, If the resistance of the load is too high, the current will be very low, while if the load resistance is too low, the voltage drop across it will be very low. There is an optimal load resistance” with an efficiency near 86.5%.”
So, back to the original article.
> hot carrier solar cells (HCSC) combat these thermal energy losses and improve efficiency. HCSC was first conceived decades ago by R.T. Ross and A.J. Nozik. The two researchers theorized that particles carrying excess heat, or hot carriers, could be isolated and stored in a lattice structure that captures the energy.
So it’s a solar-thermal system, but more subtle than the obvious solar-thermal option of combining solar electricity with a water heater. How is the heat carried away? They don’t say, they only say that the heat energy is stored. It can’t be stored forever, not when the heat energy generated is three times the electrical energy generated.
But keep going.