Anyone who’s ever walked on a hot beach will know how quickly sand heats up in the Sun.
Italian company Magaldi is exploiting that fact to harvest solar rays in a novel way. Its Solar Thermo Electric Magaldi (STEM) system, in Milazzo, Sicily, uses an array of 786 seven-square-metre heliostats to reflect sunlight on to a large mirror. This in turn concentrates the light on to a tank filled with 270 tonnes of silica sand. “Essentially, STEM is like a boiler, but it runs on sand and Sun,” explains Magaldi research engineer Gennaro Somma.
On the ground, sunlight only warms the sand’s uppermost layers. Inside the STEM tank, however, compressed air blown through a cluster of nozzles keeps the sand constantly moving. This makes it better at uniformly reaching high temperatures and enhances its ability to transfer heat. Once the sand has reached temperatures of up to 650˚C, it relays the heat to water flowing through pipes, transforming it into hot steam, measuring around 500˚C, that shoots through turbines to produce energy. Each STEM module has an output of two megawatts; a typical plant would be made up of ten modules, for 21.5 megawatts of output. The Milazzo module, which debuted in June 2016, is the first of its kind – Magaldi plans to build 29 more units by October 2017.
Somma, 35, believes STEM could even give photovoltaic stations a run for their money. “A cloud covering the Sun is enough to bring a photovoltaic system to a halt,” says. “But sand can store heat for longer and keep generating energy undisturbed. Its production is extremely stable.”
Land occupation is obviously a downside: the Milazzo unit occupies 22,500 square metres, the equivalent of three football pitches. That’s why Somma says desert-like areas such as Chile and Australia could benefit from the technology. “We’re looking at using STEM to desalinate water on the side,” he says. “Places where there’s a lot of Sun are also very dry. This could be a way to solve one thing with the other.”