Researchers have come up with all sorts of innovative new chemistries to boost the efficiency of solar cells, but it looks plain old fish oil could do the trick. The nature-based solution applies to solar systems that produce heat as well as electricity. In that combo, a research team in Korea has assessed a solar conversion efficiency of 84.4% with the fish oil enhancement.
Solar Cells & Heat
More sunlight is good for solar cell efficiency, but not when excess heat is involved. Solar cells function more efficiently in cooler temperatures.
A workaround has emerged in the form of decoupled photovoltaic thermal systems. These systems deploy a liquid to filter out inefficient light from the spectrum, helping to keep the solar cells cooler. Heat from the liquid is drawn away by a heat exchanger. It can be applied to other uses, such as heating a room in the winter.
That sounds simple enough, but the devil is in the details. Water is not particularly good at filtering out ultraviolet rays.
“De-coupled photovoltaic-thermal systems utilize liquid filters to absorb non-effective wavelengths, such as ultraviolet, visible light, and near-infrared. However, water, a popular filter, cannot effectively absorb ultraviolet rays, which limits system performance,” explains a research team based at the Korea Maritime & Ocean University.
The KOUM team focused on fish oil as a more effective alternative to other workarounds. As noted by the leader of the team, Assistant Professor Jae Won Lee, some water-based filters use a solution of nanoparticles to absorb inefficient parts of the spectrum. However, the nanoparticles tend to settle over time, reducing efficiency.
“In contrast, the proposed [fish oil] emulsion remains stable at high temperatures of up to 70 °C. Furthermore, the oil droplets within the emulsion are effective at absorbing UV light with wavelengths below 500 nm,” KOUM observes.
A Fish Oil Fix For Solar Systems
The KMOU team published their fish oil findings the journal Energy Conversion and Management last July under the title, “Development of solar radiation spectrum-controlled emulsion filter for a photovoltaic-thermal (PVT) system.”
“The emulsion filter effectively absorbs ultraviolet, visible light, and near-infrared wavelengths, which do not contribute to electricity generation in PV modules, and converts them into thermal energy,” they reported. “The emulsion filter showed a thermal stability up to 70 °C and lowered the temperature of the PV module from 46.7 °C to 33.1 °C.”
The combined efficiency of 84.4% reported by the team represents an improvement over other water-based decoupled systems, which the team assessed at 79.3%
By way of comparison, the team also assessed standalone solar cells at 18.0%, and standalone solar thermal systems at 70.9%.
Beyond Solar Cells
Compared to solar thermal technology, solar cells typically grab more of the media spotlight. That’s understandable from a horserace perspective that focuses on increases in solar conversion efficiency alongside falling costs.
As the field of solar cell R&D matures, however, attention is focusing less on the incremental improvements and more on use cases. That provides more room for solar thermal systems to show off.
That brings up the topic of concentrating solar power systems. Instead of using solar cells to harvest energy from light, these systems use troughs or fields of mirrors to divert light from many points onto one central station, to heat up a liquid. The liquid can then be deployed to generate electricity or provide heat for other processes.
If that sounds expensive and complicated, it is. Concentrating solar power systems have caught on in other parts of the world, but the so far they have languished in the US.
Nevertheless, recent developments indicate that concentrating solar power could find a place in the US energy landscape. Researchers are exploring liquid carbon dioxide (aka supercritical CO2) as a cost reducer, and the emerging green hydrogen field could improve the economic basis for investing in concentrating systems (see more CleanTechnica coverage here).
The US Department of Energy, for one, is still pursuing concentrating solar. Last February, the agency broke ground on a new plant in New Mexico as part of a $100 million, multi-national project to demonstrate the use of concentrating solar systems for energy storage, in addition to producing electricity, solar fuels, and heat for industrial processes, all with an eye on promoting economic viability.
Solar fuels refers to the new field of electrofuels, which deploys solar energy (or other renewables) to synthesize liquid replacements for fossil hydrocarbon fuels. The e-fuels angle also popped up earlier this week, when the Energy Department announced a new round of $30 million in funding for projects that deploy concentrating solar thermal systems in the service of solar fuels and energy storage.
Whatever Happened To Perovskite Solar Cells?
Circling back around to that fish oil solution, the KMOU team builds an economic case for decoupled systems.
“The researchers found that, under a standard solar irradiance of 1000 W/m², the de-coupled PVT system with emulsion filter produced electrical and thermal energies amounting to 72.2 Wh and 1176.7 Wh per day, respectively,” KMOU reported. “This proved to be economically beneficial, with a lower cost payback time than both PVT systems and de-coupled PVT systems with water filter.”
The KMOU team also suggests that decoupled systems can be used flexibly under seasonal conditions.
“The proposed system can even be operated under specific requirements and environmental conditions. For example, during summer, the fluid in the liquid filter could be bypassed to maximize electricity production, while in winter, the liquid filter could capture thermal energy for heating applications,” KMOU explains.
A new generation of efficient but less expensive solar cells could also help build the economic case for decoupled systems.
Perovskite solar cells have been one area of focus, due to their low cost and efficient optical properties. Synthetic perovskite materials are relatively easy to concoct, based on the structure of the naturally occurring mineral perovskite (see more CleanTechnica coverage here).
The challenge is to concoct a formula that builds stability and longevity into the solar cell, as standalone perovskites tend to fall apart in ambient conditions.
Various solutions have been emerging, including a new aluminum oxide coating newly reported by the University of Surrey.
“With the maturing of perovskite solar modules, the levelised cost of electricity will significantly decrease further, and that is why this is such an exciting area to work,” notes corresponding author Professor Ravi Silva, of the school’s Advanced Technology Institute.
With low cost solar cells in hand and new advances in solar thermal technology, the energy transition continues to gather steam even as the enemies of climate science gather their forces.
