By Irina Slav
The world’s geothermal power generation capacity this year hit 14.9 GW. The figure is minuscule compared with fossil fuel or even renewable generation capacity but a figure that’s growing. And now, a team of scientists may have found a way to add a battery storage system tailored specifically for geothermal power.
Led by Dr. Sachiko Matsushita, the team from the Tokyo Institute of Technology has developed a battery that can convert heat directly into power at temperatures of 100 degrees Celsius or even less. The scientists have called their invention sensitized thermal cells (STCs) and say they can be buried in the ground and generate and store electricity directly from the Earth’s crust.
Here’s how they explain the process in simple terms: the STC is “a battery that consists of three layers sandwiched between electrodes: an electron transport layer (ETM), a semiconductor layer (germanium), and a solid electrolyte layer (copper ions). In short, electrons go from a low-energy state to a high-energy state in the semiconductor by becoming thermally excited and then get transferred naturally to the ETM.”
“Afterwards, they leave through the electrode, go through an external circuit, pass through the counter electrode, and then reach the electrolyte. Oxidation and reduction reactions involving copper ions take place at both interfaces of the electrolyte, resulting in low-energy electrons being transferred to the semiconductor layer so that the process can begin anew, thus completing an electric circuit.”
Initially, the team expected that electricity generation would stop at some point, when equilibrium is reached. But what they found with some surprise was that the reaction could restart with a simple flip of an on/off switch in the external circuit. Effectively, this means that you could bury two such batteries in a geothermal spot and use them to switch each other on and off to generate electricity, according to Matsushita.
Discoveries like this could indeed turn geothermal power into a more significant part of the world’s energy mix. While there aren’t as many of them as there are potential breakthroughs in other battery technologies, some successful work has been done in this field as well.
Earlier this year, for example, an Australian company announced it had designed the world’s first working thermal battery. CCT Energy Storage called its product a Thermal Energy Device and says it can accept electricity from any source and store it in the form of latent heat.
That battery works by heating up and melting a unique material and sports 12 times the energy density of a lead acid battery. When necessary, the power stored is extracted through a thermic generator. Separately, another Australian team of researchers is working on a thermal battery to be used specifically for energy storage at solar power sites.
“The battery uses a high-temperature metal hydride or metal carbonate as the heat storage medium and a low temperature gas storage vessel for storing the hydrogen or carbon dioxide,” the project leader, Professor Craig Buckley from Curtin University says. “At night, and in times of cloud cover, hydrogen or carbon dioxide is released from the gas storage vessel and absorbed by the higher temperature metal to form a metal hydride/metal carbonate, which produces heat used to generate electricity.”’
This year, Wood Mackenzie expects the global battery storage capacity to expand to almost 8 GWh, with the United States leading the way, accounting for 21 percent of the total growth. South Koreas will be next, with 16 percent, and China will account for 15 percent of storage capacity growth.
Energy storage is unquestionably a high growth potential market. True, costs are for now often prohibitive of mass adoption and a lot of batteries have yet to leave the lab and prove scalability. Yet the fact work is being done to find cleaner, more efficient, and hopefully cheaper alternatives to current power generation and storage technology means we’re on the right track.