‘Thermal batteries’ could efficiently store wind and solar power in a renewable grid
Excerpt: How do you bottle renewable energy for when the Sun doesn’t shine and the wind won’t blow? ...Massive battery banks are one answer. ...Another strategy is to use surplus energy to heat a large mass of material to ultrahigh temperatures, then tap the energy as needed. This week, researchers report a major improvement in a key part of that scheme: a device for turning the stored heat back into electricity. A team at the Massachusetts Institute of Technology (MIT) and the National Renewable Energy Laboratory achieved a nearly 30% jump in the efficiency of a thermophotovoltaic (TPV), a semiconductor structure that converts photons emitted from a heat source to electricity, just as a solar cell transforms sunlight into power. ...The idea is to feed surplus wind or solar electricity to a heating element, which boosts the temperature of a liquid metal bath or a graphite block to several thousand degrees. ...TPVs ...Funnel the stored heat to a metal film or filament, setting it aglow like the tungsten wire in an incandescent light bulb, then use TPVs to absorb the emitted light and turn it to electricity. ...With researchers at the National Renewable Energy Laboratory, [Asegun] Henry’s team laid down more than two dozen thin layers of different semiconductors to create two separate cells stacked one on top of another. The top cell absorbs mostly visible and ultraviolet photons, whereas the lower cell absorbs mostly infrared. A thin gold sheet under the bottom cell reflects low-energy photons the TPVs couldn’t harvest. The tungsten reabsorbs that energy, preventing it from being lost. The result, the group reports today in Nature, is a TPV tandem that converts 41.1% of the energy emitted from a 2400°C tungsten filament to electricity.…