Energy

Solar thermal record sees 97% conversion of sunlight into steam

Scientists at ANU have set a new record for solar thermal efficiency
Scientists at ANU have set a new record for solar thermal efficiency
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Scientists at ANU have set a new record for solar thermal efficiency
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Scientists at ANU have set a new record for solar thermal efficiency
The Big Dish at ANU in Canberra, Australia, reflects sunlight from the concave surface onto the small receiver at the top, where water is heated into steam to generate electricity
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The Big Dish at ANU in Canberra, Australia, reflects sunlight from the concave surface onto the small receiver at the top, where water is heated into steam to generate electricity
Felix Venn, one of the project's researchers, on the surface of the dish
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Felix Venn, one of the project's researchers, on the surface of the dish
Concentrating solar power systems are generally more efficient and less expensive than photovoltaic solar panels
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Concentrating solar power systems are generally more efficient and less expensive than photovoltaic solar panels

Australian scientists are no strangers to world records for solar power. Back in 2014, the CSIRO created supercritical steam at the highest temperature and pressure, and in May this year, engineers at UNSW achieved 34.5 percent efficiency in directly converting sunlight to electricity. Now, scientists at the Australian National University (ANU) have managed a new record of 97 percent efficiency for converting sunlight into steam.

Unlike photovoltaic solar panels, which absorb sunlight and directly convert it into electricity, concentrating solar power (CSP) systems reflect sunlight from a wide area and focus it in on a small receiver. As that receiver heats up, water inside turns into steam, which drives a turbine to generate electricity. Rather than storing that power in potentially costly batteries, the thermal energy is stored in molten salts, so that water can be added to create steam (and subsequently electricity) long after the sun's gone down.

The so-called Big Dish at ANU is made up of a concave surface of reflectors, directing sunlight to a receiver suspended at the focal point. A new receiver for the dish, designed and built by the team, was responsible for halving previous losses and achieving the 97 percent conversion.

"When our computer model told us the efficiency that our design was going to achieve, we thought it was alarmingly high," says Dr John Pye, from the ANU Research School of Engineering. "But when we built it and tested it, sure enough, the performance was amazing."

The team describes its receiver design as resembling a top hat, with a wide brim running around the bottom of a narrower cavity that extends upwards. The dish reflects sunlight onto water pipes that wrap around the bottom of the receiver's brim and up into the cavity, heating the water to 500º C (932º F) and turning it into steam. To minimize heat loss, the steam hits that peak temperature at the deepest part of the cavity, so that any heat that is lost can feed back into the pipes around the brim.

Concentrating solar power systems are generally more efficient and less expensive than photovoltaic solar panels
Concentrating solar power systems are generally more efficient and less expensive than photovoltaic solar panels

With the reflectors focusing the equivalent of about 2,100 suns onto the receiver, the components can actually be damaged if it isn't aligned just right, so the team initially had to use the softer light of the full moon to calibrate the system.

"Ultimately the work in this project is all about reducing the cost of concentrating solar thermal energy," says Pye. "Our aim is to get costs down to 12 cents per kilowatt-hour of electricity, so that this technology will be competitive. This new design could result in a 10 per cent reduction in the cost of solar thermal electricity. I'm optimistic that our technology can play a role in the grid, by helping to provide power at night without fossil fuel power stations running."

The research was presented at the SolarPACES conference last year.

The team discusses the project in the video below.

Source: Australian National University

ANU scientists set solar thermal record

5 comments
S Michael
I'm not a scientist. So here is a question for those that are. If I made a similar dish with about six foot in circumference area focusing on a salt oven, which would heat water, turning it into steam, would it produce enough power for my home? The other question I have is this. If I placed solar panels around the perimeter of the dish. Would the panels produce enough power to keep a 12 volt battery charged which would drive the sun-tracker of the dish.
BenG
S Michael, It depends on how much energy your house uses as well as the efficiency of the system you are proposing. If we call your 6 ft diameter reflector a 1 meter radius reflector for easy numbers, and we make a number of other assumptions that benefit the potential electricity production (arid location with minimal pollution in the tropics with elevation with thin atmosphere and at a local maximum considering directions east and west through south east to south west with ocean views from east to southeast and west to southwest, tracking system works perfectly, birds never poop on your reflector and you keep it all perfectly clean, minimal losses in the steam plant and generators and highly efficient storage, abundant supply of cooling water from a cold stream from the mountain to the north, an intimate knowledge of steam plant chemistry, etc....) then we can arrive at a rough estimate that you can be confident the usable electricity production will not exceed. About 3 m^2 tracking the sun perfectly, @ 10 kWhr/m^2 per day (generous) is 30 kWhr/day add in losses for steam generator, pumping losses, heat transfer losses, waste heat rejected to cooling water, turbine generator losses, electrical losses, inverter losses and battery charging and discharging losses....leaving you with at most 6 kWhr/day. 250 watts for continuous, does not leave much for air conditioning, computers,toast ovens, b8g refrigerators, etc . Your second question is much quicker to answer....Yes, that is easily achievable....but why? You are already investing in a solar thermal plan to generate electricity...just use some of that, enlarge slightly if needed, though the energy drawn by tracking won't amount to much. . In reality, running a steam plant for power generation isn't something conducive to residential operation.
jonyah
At .12/kwh this is still nearly 71% more than I pay now (.07/kwh). And this doubles previous efficiency. This is why solar has a very very very long way to being cost effective. Sure .12 will be competitive in certain parts of the country, but I'm guessing the efficiency there (up north) won't be as good.
Joseph Dunfe
The only really viable alternative energy source is home hot water heat. The back-up electric hot water is cheap as well. All the other alternative energy sources have failed to become viable, despite decades of promises. That is unless the user agrees to pay extra for their energy, or the government takes money from other people to pay for their higher energy costs. And don't forget the cost of the extra back-up (and sometimes inefficient) system for when the solar or wind fails.
blacksmithaus
7c / kwh ? Where are you buying your power from? Even off peak it's 14c.
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