Our recent ARPA-E award is on heat storage materials. The second law of thermodynamics allows us to collect heat for free, or almost.
Heat can be used to generate electricity using either steam engines or thermoelectric devices. Storing it is important and very useful for power plants where a constant supply of electricity can be sustained even during the peak hours. Furthermore, solar energy is an infinite and free source or light (for photovoltaics) and heat (thermophotovoltaics and thermoelectrics) which can be used and stored for our energy needs.
A large amount of heat can be stored in the form of latent heat. Our goal is therefore to design novel materials with a large latent heat, able to store up to 1 MJ/kg or more. Furthermore to be able to quickly extract this stored heat, the material needs to have a large thermal conductivity as well. Other considerations are safety, stability, abundance and low fabrication cost. For these reasons, we are considering metallic alloys instead of traditionally used salts, as the phase change material.