Demonstration of a Thermosyphon Thermal Valve for Controlled Extraction of Stored Solar Thermal Energy

For concentrated solar power (CSP) to be an effective replacement for power generation by fossil fuels, the thermal energy must be stored and then released for when demand exceeds production, such as during off-sun hours. Until now, there has been limited methods to reliably and efficiently release and control the extraction of thermal energy from a material containing stored sensible or latent heat. Due to their isothermal property, phase change materials (PCMs) storing latent heat are an ideal choice for storage, though it has proven challenging to reliably extract and utilize that heat. To solve this problem, the geometry of a thermosyphon was rearranged to create a thermal valve that is able to turn the flow of thermal energy from a PCM "on" and "off". A stainless steel thermal valve using sodium as the working fluid was designed, fabricated, assessed, and found to effectively and selectively extract heat from a 577°C molten aluminum PCM. It is expected that thermal valves will significantly contribute to more widespread implementation of CSP as a stored energy source from distributed generation to utility-scale power production.