A team from Berkeley has broken a new record in thermal photovoltaic efficiency and marks the way towards an ultralight engine capable of powering drones for days.
Over the past 15 years, the efficiency of converting heat to electricity has stalled at 23%. Today a brilliant intuition has allowed a group of researchers to take another step, bringing it to 29%. The goal, finally concrete, is now to reach 50% efficiency with a new design and an even wiser use of these new criteria.
Berkeley's research has direct and important consequences on all technologies that require heavy batteries to function.
Thermal photovoltaics is an ultralight alternative source that will allow a wide range of unmanned aircraft to fly continuously for days before discharging. It can also be used to power space probes for centuries, and in the near future to be able to power an entire house with a generator the size of an envelope.
UC Berkeley's researchers' work was collected in a paper published this week in the journal Proceedings of the National Academy of Sciences.
"Thermal photovoltaics are compact and very efficient for a wide range of applications. From those that require a minimum of 100 watts (a small drone) to those that require 100 megawatts (electricity for 36.000 homes)," it says Eli Yablonovitch, Professor of electrical engineering and computational sciences, as well as co-author of the study.
How the principle works
According to Yablonovitch these results stem from the work he did with his students and published 8 years ago, in 2011. In that extremely talented work the idea was that the key to improving the solar it should not only have been to absorb more photons, but also to emit them. By adding a high reflectance mirror to the back of a photovoltaic cell the team broke the efficiency record, and by perfecting the technique it continues to get results.
"What the mirror can do is create a dense infrared luminescent photonic gas inside the solar cell. A phenomenon that increases the voltage," says Yablonovitch.
The team found that the presence of this mirror can solve one of the biggest challenges in the field of thermophotovoltaic research: how to use photons that have too little energy to produce electricity.
A mirror simply makes them "come back" into play and bounce back onto the battlefield, engaging them in the power generation process.
"A feat never before achieved in history with a simple gold mirror. Now we will add a layer of electrical under that of the mirror, and we will immediately bring the efficiency to 36%," says Luis M. Pazos Outόn, another of the authors.
This is an already extraordinary result, and reaching 50% efficiency is now really within our reach.
Here is the study: Zunaid Omair et al. Ultraefficient thermophotovoltaic power conversion by band-edge spectral filtering, Proceedings of the National Academy of Sciences (2019). DOI: 10.1073 / pnas.1903001116