Bringing thermochemical water splitting to the next level
HEST-HY (High efficiency solar thermal hydrogen) is a project to develop new methods and reactors for operating thermochemical looping cycles for solar production of hydrogen. HEST-HY is part of a larger ongoing effort by the US Department of Energy called STCH (Solar thermochemical hydrogen) and is run by Sandia National Laboratories.
Previous projects have demonstrated that cycling metals oxides like CeO2 and Fe2O3 through reduction (oxygen release) under sunlight and oxidation to split water and produce hydrogen is a promising method for hydrogen production.
HEST-HY envisions a new type of receiver/reactor for these cycles with several key innovations. First, the active material is formed into particles for easy transport, heat recovery, and continuous operation. Second, the particles are directly irradiated in a thin layer on a conveying plate, part of a patented DLR system. Third, the reduction is done at low pressure and in several stages of decreasing pressure for optimum efficiency. The innovations here should allow for a reactor system with more flexibility and efficiency than any reactor demonstrated in the 20+ years of solar thermochemical water splitting research.
The entire system, including reduction of the particles and splitting of water will be demonstrated by Sandia National Laboratories in 2016. The prototype is designed to take a solar input of about 5 kW and produce at least 3 litres of hydrogen in 8 hours of continuous operation. DLR is constructing the system for the high temperature input of solar radiation and heating of particles, while Sandia is constructing the remainder of the system. Prior to full system assembly, DLR is designing and testing the chambers where radiation enters a cavity and heats the particles while oxygen is removed.
In order to develop the prototype system, DLR has investigated new-to-solar-research technologies for particle movement and control like variable orifice flow control and slip-stick particle conveying. Lab testing validated several of these subsystems and the full particle heating receiver is currently awaiting thermal testing, which will occur in mid-late 2016 in the DLR high-flux solar simulator and solar furnace. The goal will be to heat inert particles to 1450C for several hours. With successful demonstration of particle heating, the receiver will be transported to Albuquerque, USA to be integrated with the rest of the reactor system and used to reduce reactive particles and produce hydrogen.
DLR is also contributing to the conceptual design of a scaled-up version of the particle redox cycle reactor, including solar field design and technoeconomic analysis, led by Arizona State University.