16 August 2012 - A startup company established by a team of MIT students and alumni has developed a patented technology that uses a mirrored parabolic trough to capture sunlight, heating fluid in a pipe along the mirror’s centerline. This system uses the hot fluid and cold air to generate electricity. At the same time, the hot fluid can be used to provide heat and hot water, or, by adding a separate chiller stage, to produce cooling as well.
A prototype of the system has been installed at a small clinic in Lesotho; next year, the MIT team plans to have five fully operational systems installed in isolated clinics and schools there for field-testing. The key element of the system is a device called a scroll expander, used to convert the heat to power.
Matthew Orosz Meng says the idea for the project began years ago, when he spent two years working in a village in Lesotho as a Peace Corps volunteer with no access to electricity or hot water. There are some 30,000 clinics and 60,000 schools around the world that similarly lack access to electricity but have sufficient sunshine to meet their power needs, Orosz says.
Working with fellow student Amy Mueller, their thesis advisor Harold Hemond, a professor of engineering at MIT and others, Orosz set up a nonprofit company called Solar Turbine Group (now known as STG Internatonal) to develop the solar technology that he envisioned as a practical alternative for these off-the-grid facilities.
Today, Orosz explains, there are only two viable options to provide electricity for such places: a solar photovoltaic (PV) array or a diesel generator. Both are somewhat less expensive to install than his company’s solar trough system, but when the costs of replacement parts and fuel are factored in, he estimates the solar trough system will be substantially cheaper over its lifetime.
The pilot system, which Orosz and his colleagues started to assemble at Lesotho’s Matjotjo Village health clinic in 2008, provided the initial proof of principle, though it took years to get all the parts working properly in that remote location. While they were able to demonstrate the successful operation of their heat-powered generator — a system called an organic Rankine cycle (ORC) engine — the system required a skilled operator to adjust the temperatures, pressures and voltages as conditions changed.
Since then, the STG team has developed a computerised control system that allows the system to run virtually hands-free. Once that system is installed, the only routine maintenance required is washing the huge mirrors every six months or so.