Image: Alberto Masnovo – Shutterstock.

The new “solar” cells reflect 99% of the energy that they cannot convert into electricity and could help reduce the price of storing renewable energy as heat, as well as collecting waste heat from heat. exhaust pipes and chimneys.

Informally known as the “sun in a box,” it stores the extra generation of wind and solar power in a heat bank.

There is general interest in this grid-scale energy storage approach because it is estimated to be ten times cheaper than using batteries.

Andrej Lenert, Assistant Professor of Chemical Engineering.

The most expensive parts of these systems are the photovoltaic panels which convert stored heat into electricity.

Comparados con los paneles solares convencionales que convierten la luz, en lugar del calor, en electricidad, los fotovoltaicos térmicos son capaces de aceptar fotones de menor energía – packets de luz o calor – porque la fuente de calor está a una temperatura más baja que la from the sun. To maximize efficiency, engineers sought to send very low energy photons back to the heat bank. This way the energy is reabsorbed and has another chance of being packed into a higher energy photon which produces electricity.

It’s a recycling jobSays Steve Forrest, professor of engineering at Peter A. Franken Distinguished College and professor of engineering Paul G. Goebel. “The energy emitted by the heat bank has a more than 100 chance of being absorbed by the solar cell before being lost.

Conventional gold-backed thermophotovoltaics reflect 95% of the light that it cannot absorb, not bad, but if 5% of the light is lost with each bounce, that light has an average of 20 chances of being re-emitted in a photon with enough energy to convert into electricity.

The increased number of opportunities means higher voltages and less energy wasted during power outage.

To improve reflectivity, the team added a layer of air between the semiconductor – the material that converts photons into electricity – and the gold backing. Gold is a better reflector if light hits it after traveling through air, rather than coming directly from the semiconductor.

It was not clear at first whether this “airlift” structure, with such a long span and no mechanical support in between, could be built with great precision and survive multiple difficult manufacturing processes.

But he did… and very quickly.

Now they are looking for a way to increase the efficiency even more, by adding additional “nines” to the percentage of reflected photons. For example, increasing the reflectivity to 99.9% would give heat a 1000 chance of turning into electricity.

The study is titled “Almost perfect use of photons in a thermo-photovoltaic air transport cellUM has filed for patent protection and is looking for business partners to bring the technology to market.

More information: news.umich.edu