Energy

Hybrid solar converter harvests both sunlight and heat at 85% efficiency

Hybrid solar converter harvest...
The photovoltaic module of the new hybrid solar converter
The photovoltaic module of the new hybrid solar converter
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The photovoltaic module of the new hybrid solar converter
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The photovoltaic module of the new hybrid solar converter

Engineers have developed a new type of hybrid solar energy converter, which uses energy from the Sun to create both electricity and steam. The device reportedly has high efficiency and runs at low cost, allowing industry to make use of a wider spectrum of solar energy.

The most common way of collecting energy from the Sun is through photovoltaics. These solar cells produce electricity from sunlight, and they’re so simple that they’re built into everything from garden lights to the grid itself.

But it’s not the only way. Solar concentrators collect heat instead of light, focusing the Sun’s rays to heat up a contained fluid. This can then be used to generate electricity – say as steam turning a turbine – or more directly, to heat homes or for other industrial processes.

Normally these two systems are separate, but attempts have been made to pair them up into single hybrid devices, often resulting in lower efficiency or higher cost. But now researchers claim to have created a new hybrid solar energy converter that mixes the best of both worlds.

The device looks like a satellite dish, with a small device suspended over the center of a parabolic collector. The dish part is mirrored, and focuses the sun’s rays onto the box in the middle. The bottom of this section contains multi-junction solar cells, which collect and convert visible and ultraviolet light into electricity.

But the clever part is that these cells redirect the infrared light – the heat energy – to a separate thermal receiver, higher up in the device. This receiver is essentially a cup-shaped cavity surrounded by pressurized water, which captures the heat and turns into steam.

The team says that the total collection efficiency is 85.1 percent, meaning a very high amount of the Sun’s energy is converted into either electricity or heat. The steam can be heated up to 248 °C (478 °F), which is a much higher temperature than many other thermal energy collectors. This means it’s hot enough for many industrial processes, such as drying, curing, sterilizing, and pasteurizing.

The other advantage is cost. The team reports that once scaled up, the hybrid device could run for as little as 3 cents per kilowatt hour.

The team, which is made up of researchers from Tulane University, the University of San Diego, San Diego State University, Boeing-Spectrolab and Otherlab, has been awarded follow-on funding for the next round of development and plans to refine the technology and work towards scaling it up for pilot plant tests.

The research was published in the journal Cell Reports Physical Science.

Source: Tulane University

12 comments
Bucky
I invented something like this, a long time ago.
The parabolic mirror was made of regular PV cells, coated with IR reflecting foil.
That way you don't need to cool the PV cell and it still works when cloudy.

-dphiBbydt
Concentrators work best with direct sunlight. As per Bucky's comment, for cloudy days you need a large area for scattered photon collection. An efficient foil that reflects IR but lets through PV friendly visible photons would be helpful in many situations - but does it exist?
paul314
Wavelength-selective mirrors are way cool. I wonder if you could go another step and divert multiple different parts of the solar spectrum to PV cells optimized for that particular wavelength.
Willyt
Very neat! What about setting up opposing parabolic mirrors, one large and one small with focal points coinciding. The smaller parabola will reflect a concentrated parallel beam which can be deflected with a flat mirror to a desired target, i.e. your hybrid array, boiler, etc.
My search for opposing parabolic mirrors yielded no results. Candidate for someone's thesis?
NL4M
I worked on a project like this well over 20 years ago......the issue here is the tracking - which makes residential difficult and industrial very complex. Good luck though!
jerryd
I like trough style collectors better with heat storage and a low temp heat engine working from that.
Or better would be solar tubes doing the same.
And 1 in 3 as just thermal as a super heater for higher temps
Jason Herring
I had a similar idea to use old satellite dishes as hybrid water heating/concentrated solar about 12 years ago, the thought being to run cooling lines behind the cells sitting on the focal point of the dish thus keeping the cells cooler while heating water for various uses (depending on the exit temp). I still have a dish w/ mirror tiles glued to it that I bought at a craft store. I tried to obtain a few multi-junction solar cells at the time but the sample price was really expensive so I abandoned it. Also, since this requires a tracker, the cost was not going to be as inexpensive as I envisioned. I started looking into passive sun tracking ideas, but...
The thought was low-cost power and water heating/sterilization for off-grid communities with limited utility access, particularly in third-world countries.
Adrian Akau
Any time parabolic mirrors are used, the mirror needs to rotate to follow the sun. The cost of the tracking system increases the expense of the system. Tracking must be E to W during the day and also N to S for change of seasons. Sometimes, you cannot have your cake and eat it too.
Dennis Dickinson
85% efficiency will bring it up to almost 12% usable power the whole problem with the solar schemes it's just like the Enron a grid-tie or batteries you have to overcome the power coming in the whole problem is measured in watts should be measured in amps
John Hogan
I've always figured that our best current use of solar power was simple old solar water heating. One conversion then boom, use it. As a nerd, friends and family have been asking me about solar for years. PV is now cheap enough to be a no-brainer, but my first question is always, "have you done the solar water heater first?"

Despite the costs coming down, we're just messing around. By now PV should have been a cheap coating on most exterior surfaces of a structure. Some added during manufacture, like tiles and corrugated roofing. Others sprayed on in layers after initial construction. Lower efficiency but vastly higher overall output. This era feels like the end of the olden days lol.