Science has been claiming for years ditch fossil fuels and embrace renewable energy to tackle the climate crisis that threatens the survival of the planet. With electricity prices at their highest in history, all eyes are now more than ever on energy like solar and wind.
But there is a technological problem: there is no system capable of storing and producing this energy economically on demand. A group of Spanish researchers seems to have found the solution by discovering a photovoltaic battery system with enormous storage potential for long periods of time at low cost and to provide heat and electricity on demand.
The finding is the work of researchers from the Solar Energy Institute of the Polytechnic University of Madrid (IES-UPM). Described in an article titled ‘Latent Heat Thermophotovoltaic Batteries’ and published in the scientific journal ‘Joule’, the system uses surplus generation from intermittent renewable energy, such as solar or wind, to melt down cheap metalssuch as silicon or ferrosilicon alloys, at temperatures above 1,000ºC.
Silicon alloys can store large amounts of energy during their fusion process. This type of energy is calledlatent heat”.
For example, a liter of silicon stores more than a kWh of energy in the form of latent heat, which is precisely the amount of energy contained in a liter of hydrogen pressurized at 500 bar. Nevertheless, unlike hydrogen, silicon can be stored at atmospheric pressurewhich makes the system potentially cheaper and safer.
Miniature photovoltaic installations
The system, which has already been patented by UPM researchers, combines thermionic and photovoltaic effects to achieve direct conversion of heat into electricity.
Unlike conventional thermal machines, this system does not require physical contact with the thermal sourcesince it is based on the direct emission of electrons (thermionic effect) and photons (thermophotovoltaic effect).
A key to the system refers to the way that stored heat is converted into electricity. When silicon melts at more than 1,000ºC it shines like the sun. Therefore, it is possible to convert radiated heat back into electricity using photovoltaic cells..
The so-called thermophotovoltaic generators are like miniature photovoltaic installations what can produce up to 100 times more power than a conventional solar power plant. In other words: if a square meter of solar panel produces 200 W, a square meter of thermophotovoltaic panel produces 20 kW. And not only the power is greater; efficiency, too.
Because the efficiency of thermophotovoltaic cells ranges between 30 and 40% depending on the temperature of the heat source, while commercial photovoltaic solar panels have efficiencies between 15% and 20%. Half.
The use of thermophotovoltaic generators, instead of conventional heat engines (such as Stirling, Brayton or Rankine cycles), avoids the use of moving parts, fluids or complex heat exchangers. Thus, the whole system can be made economical, compact and quiet. They are all advantages.
Hundred times cheaper than lithium batteries
According to the study, latent heat thermophotovoltaic batteries could store large amounts of surplus renewable electricity. “Much of this electricity will be produced when there is no demand, so it will be sold very cheap in the electricity market”, says Alejandro Datas, a researcher at IES-UPM who leads the project.
“It is essential to store this electricity in a very cheap system, since it would not make sense to store something so cheap in a very expensive box. So, storing surplus electricity as heat makes a lot of sense, as it is one of the cheapest ways to store energy”, continues the researcher.
In particular, silicon and ferrosilicon alloys can store energy at a cost of less than 4 euros per kWh, which is 100 times cheaper than current stationary lithium-ion batteries.
It is true that the total cost will be higher after incorporating the container and the thermal insulation, but also, as detailed in the study, that it would be possible to reach “costs of around 10 euros per kWh if the system is large enoughtypically more than 10 MWh, since the cost of thermal insulation would be a small fraction of the total cost of the system”.
The fact that only a fraction of the heat stored with these latent heat batteries is converted back into electricity is not necessarily a problem. “If the system is cheap enough, it would be enough to recover only 30 or 40% of the energy in the form of electricity for them to be preferable to other more expensive technologiessuch as lithium-ion batteries”, the researchers point out.
The first prototype, ready
The 60 or 70% of the heat that is not converted into electricity could also be delivered directly to buildings, factories or cities, which would reduce the consumption of natural gas.
Heat accounts for more than 50% of global energy demand and 40% of global CO2 emissions. In this way, the storage of wind or photovoltaic energy in thermophotovoltaic latent heat batteries would not only allow substantial cost savings, but would also satisfy part of this great demand for heat through renewable sources.
Therefore, “developing this type of system can be key to reducing our dependence on fossil fuelsnot only in the electricity sector, but also in the thermal sector”, concludes Datas.
The first prototype On a laboratory scale, the system that has been manufactured within the framework of a European project (AMADEUS) is now available at the IES-UPM, and the first experimental results have been published in the study.
This is the culmination of more than 10 years of research at IES-UPM. Nevertheless, the technology still needs a lot of investment before it can reach the market, points out the Madrid university. For example, the current laboratory prototype has less than 1 kWh of storage capacity, but energy storage capacities of more than 10 MWh are needed for this technology to be profitable.
The next challenge is to scale the technology and test its feasibility on a large scale.. To do this, IES-UPM researchers are already putting together the team that will make it possible.
Reference report: https://www.sciencedirect.com/science/article/abs/pii/S2542435122000423?via%3Dihub