Batteries aren’t perfect, they have their shortcomings. For instance, they are made of scarce minerals often obtained through unsustainable mining practices. When dumped, they release harmful chemicals into the environment and have limited lifespans.
When it comes to energy storage, although we currently rely heavily on batteries, we need a much greener and cleaner solution. One such promising avenue is thermal energy (electrical) storage (TES) systems, which store electricity as thermal energy by converting it into heat, which can later be converted back into electricity when needed.
TES require low-cost materials, have much longer lifespans compared to batteries, and are easier to scale up for grid-sized systems. They can stabilize renewable energy grids by storing extra solar or wind power when it’s available and supplying it during peak demand.
Researchers at Rice University have developed a highly efficient thermal emitter that can contribute to the development of practical and scalable TES systems. A thermal emitter is the key component in TES that absorbs heat, gets hot and converts heat into electromagnetic radiation, which is then captured by a photovoltaic cell to generate electricity.
The significance of a good thermal emitter
TES designs often use a thermophotovoltaic (TPV) system for heat-to-electricity conversion.
“This systems involve two main components ⎯ photovoltaic (PV) cells that convert light into electricity and thermal emitters that turn heat into light. Both of these components have to work well for the system to be efficient,” the Rice University team notes.
Until now scientists have largely focused on improving PV cell technology. However, the main hurdle in realizing practical TPV systems is the energy losses during conversion. This is where thermal emitters, the technology that receives comparatively less attention, come into play.
An efficient thermal emitter is crucial to minimize the loss of energy as it gets converted from heat to electricity. Unfortunately, traditional TPV designs have, so far, failed to incorporate such a device.
“Using conventional design approaches limits thermal emitters’ design space, and what you end up with is one of two scenarios: practical, low-performance devices or high-performance emitters that are hard to integrate into real-world applications,” Gururaj Naik, one of the study authors and an associate professor at Rice University, said.
With this innovation, “we essentially showed how to achieve the best possible performance for the emitter given realistic, practical design constraints,” Ciril Samuel Prasad, study co-author and graduate student at Rice University, added.
An innovation with talking resonators
The Rice University researchers arranged numerous silicon nanocylinders on a metal sheet made of tungsten to make the thermal detector. When this system receives heat, photons are released. Meanwhile, the nanocylinders behave as resonators designed to absorb specific wavelengths or energies of these photons.
They interact or “talk” with one another in a way that lets them selectively pick and emit only the photons with the right energy. These photons are then sent to the photovoltaic (PV) cells, where they can be converted into electricity.
“This selective emission, achieved through insights from quantum physics, maximizes energy conversion and allows for higher efficiencies than previously possible,” the study authors note.
Using the quantum effects, the resonators are able to control photons released at the quantum level, ensuring that only the most useful photons for the photovoltaic (PV) cell are emitted, improving the overall efficiency of the system.
Their quantum-inspired thermal emitter showed an impressive efficiency of 60 percent, and the researchers claim that they can further improve this using new material.
“If our approach could lead to an increase in efficiency from 2% to 5% in such systems, that would represent a significant boost for missions that rely on efficient power generation in extreme environments,” Naik explained.
Hopefully, the new thermal emitter will make thermal energy storage highly scalable and help boost the adoption of renewable energy on a large scale.
