Heat is often plentiful during the daytime for people in developing countries – but at night, when they’re cooking and the sun is down, they don’t typically have access to that heat and must use a material like dung or wood for fuel. A new chemical composite developed by three Massachusetts Institute of Technology (MIT) scientists could offer an alternative by storing the sun’s heat during the day in what MIT described as a thermal battery, and releasing that heat on demand later for cooking or heating.
Scientists commonly approach thermal storage with a phase change material (PCM): when heat melts the PCM, it changes from solid to liquid stores energy, according to MIT. When it’s cooled and changes back into a solid, it releases the stored energy as heat. But all current PCMs need a lot of insulation, and MIT said they go through “that phase change temperature uncontrollably, losing their stored heat relatively rapidly.”
Researchers overcame challenges to thermal storage with a system drawing on molecular switches that alter shape in response to light. They integrated these molecules into traditional PCM materials to release heat on demand. MIT professor Jeffrey Grossman said in a statement, “By integrating a light-activated molecule into the traditional picture of latent heat, we add a new kind of control knob for properties such as melting, solidification, and supercooling.”
Their chemical heat battery could harness solar heat and potentially even waste heat from vehicles or industrial processes. With the system, heat could stay stable for at least 10 hours – and a device of around the same size storing heat directly would release it in just a few minutes. The MIT material can store around 200 joules per gram. Postdoctoral researcher Grace Han said there’s already been some interest in their thermal battery for use in cooking in rural India.
The journal Nature Communications published the research online earlier this month.