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Hot top hat!

By David, 18 September 2016

A big shiny dish.

ANU’s solar dish has a new top hat.
Image: Stuart Hay, ANU

Perched high atop a giant shiny dish, sits a strange top hat. This hat is filled with high pressure steam, and it’s the secret to efficient solar power that can work even after the Sun sets. Welcome to the world of concentrated thermal energy.

For several years, scientists from the Australian National University (ANU) have been harvesting heat energy from the Sun. Their big dish collects sunlight over a huge area and focuses it on a very small target. All that sunlight makes the target very hot – and that’s exactly what they want.

The recent challenge has been to make that heat useful. To do this, the team designed and built a solar receiver, shaped like an upside-down vase, or a very curvy top hat. The hat is made from a long coil of pipe and inside the pipe is some very hot steam.

“Hot steam is what we use to make power in coal power stations around Australia,” says Dr John Pye, an ANU solar researcher. “We’re trying to do the same thing, only with no fossil fuels required.”

The solar dish produces steam at 500 degrees Celsius. “You can’t get a lot hotter than that,” says John. “The turbines you’d be putting this steam into, they’d just melt.”

A cool circle with a very hot centre.

Thermal images of the inside of the hat.
Image: Ehsan Abbasi, ANU

John is particularly proud of the new solar hat. That’s because it’s very good at catching heat and not wasting it. “We achieved 97 per cent conversion of light into steam,” says John. This is a good result – commercial systems can lose 10 per cent of the Sun’s energy, and this new collector only loses three per cent.

Solar thermal systems are bigger and more complicated than solar panels, but they have a secret superpower – they can work at night. “Solar thermal energy can be stored as heat,” says John. Instead of generating electricity directly, the heat is stored in a big tank of molten salts. That heat can produce steam after sunset, when solar panels no longer work.

The team is now working to make new hat designs for other solar collectors. They’re also in talks with mining companies that want to use their dish and collector technology. It’s early days yet, but there’s a bright future for solar thermal power.

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