MIT-based nonprofit STG International is looking to make isolated African clinics and schools much more self-sufficient with a new hybrid power and heat solar system. The unique system combines off-the-shelf technologies to provide electricity, hot water and space heating, with potential cooling as well. The heart of the system is a brilliant type of refrigeration cycle – instead of using hot refrigerant gases to remove heat, it uses heat to run a common compressor in reverse to make electricity. The unique solution does double and triple duty for a small African clinic, saving significant amounts of money on fuel.
The system is designed to be built using readily available materials and technologies available in Africa, and its inventors MIT graduate PHDs Matthew Orosz and Amy Mueller are opening a non-profit company to install at least five units to test the viability of the design. Parobolic troughs (common in solar thermal plants) heat a tube filled with refrigerants, and the hot gasses are sent to an “organic Rankine cycle (ORC) engine“, which is basically a typical scroll compressor run in reverse to spin a generator. We surmise the hot gasses spin the ORC Engine and then are cooled by air and water to turn the refrigerant back into a liquid state to start the process over again.
The Solar ORC replaces solar electric panels and diesel engines for electricity and adds the very useful benefit of plentiful hot water and even space heating. The extra heat could also run an absorption chiller for air conditioning. While it is cheaper and less complex to install discrete technologies to provide electricity or hot water, the team hopes that cost of their system will be much lower in the long term. The first installation is at a health clinic in the Berea District of Lesotho, where temperatures can get near freezing, making space heating a valuable asset. The system will provide 18-24kW-hr of energy and 200-300 gallons of hot water daily.
The technology is proven to be effective, but its complexity leave a huge question mark about its long-term reliability. Products like Magic Boxes (which combine all of a home’s HVAC and hot water) have proven to be expensive and sometimes unreliable – if one component breaks the entire system stops working. And architects and engineers in Africa have learned that designing low maintenance buildings and systems in isolated regions is the best long-term approach. If the Solar ORC is to be viable it will need to be proven to be robust as well as advanced.