(Page 2 of 2)
In a conventional TPV system, most of the photons generated in the heated material are reflected back into the material when they reach its surface; it's the same phenomenon that traps light in fiber-optic cables. When the solar cell and the heated material are brought close together, so that the gap between the two is shorter than the wavelength of the light being emitted, the surface no longer reflects light back. The photons travel from one material to the other as if there were no gap between them. The close spacing also allows electrons on one side of the gap to transfer energy to electrons on the other side. (A vacuum between the heated material and the solar cell maintains a temperature difference between the two that is required to achieve high efficiencies.) Since the heated material emits more photons, the solar cell can generate 10 times as much electricity for a given area, compared with a solar cell in a conventional TPV.
That makes it possible to use one-tenth as much solar-cell material, which cuts costs significantly. Alternatively, it makes it possible to generate more power at lower temperatures, which Peter Peumans, a professor of electrical engineering at Stanford University, says is one of the key advantages of the approach. Conventional thermal photovoltaics can require temperatures of 1,500 °C, he says. The first prototypes from MTPV work well at less than 1,000 °C, and DiMatteo says that, in theory, the technology could economically generate electricity at temperatures as low as 100 °C. This large temperature range could make the technology attractive for generating electricity from heat from a variety of sources, including automobile exhaust, that would otherwise be wasted.
But Peumans says that the technology has a trade-off: because the heated material and solar cell are placed so close together, it's not possible to put a filter between them to help tune the wavelengths of light that reach the solar cell. This could limit the ultimate efficiencies that the system can reach.
DiMatteo first published work on the MTPV concept in the late 1990s, but it has taken until now to engineer prototypes large enough to be practical. One main challenge has been finding ways to create a gap that's just one-tenth of a micrometer across and yet can be maintained over the relatively large areas needed for a practical device. DiMatteo says that the company will improve the performance of the devices by making the gap steadily smaller, which computer models suggest will improve efficiency.
Nanomaterials could be used for lower-emission cars and solar panels.
New thermophotovoltaic materials could replace alternators in cars and save fuel.
Guest (michel.jansens@ulb.ac.be)
Getting heat transformed into electricity in a glass factory seems strange to me:
If such heat is lost, why not use it to pre-heat the incoming materials.
The technology to do this is already able to reclaim more than 80% heat even at low temperatures.
Also using a car exhaust imply use of heat exchangers which blocks the flow of gases, which in turn raises fuel usage.
Michel
Can't place a filter in there?
What do you mean there's no room in there for a filter? A thin film coating is on the order of angstroms. Are these guys for real?
If these devices can be tuned to provide direct electrical generation from a heat source as stated, can they be adapted to function as the direct convesion device in a Hot Dry Rock application so there's no need to convert liquid to steam per se? Essentially they would function like a Heat Pump, but instead of transferring heat (or cooling) to an home or something, they convert the heat straight into useable energy. If they operate as low as 100F, then there may be no need to tap really deep hot dry bedrock, but only tap into the ground a couple hundred meters to becoem useful.
If the spacing is less than a wavelength could you just have two gaps less than the wavelength?
have the filter spaced between the two?
What is the physics that allow the coupling efficency below a wavelength?
can the filter even though transparent to the photon reproduce the effect if each space is less than a wavelength
how does its efficiency change over the length of a wavelength?
ie 1/4 1/2 3/4 7/8 of a wavelength?
why not have the filter on the PV/TPV?
Other wavelengths would be reflected back to the heat source one to multiple times until reabsorbed allowing energy to be recycled and re-transmitted at a wavelength that will pass the filter and be converted by TPV.
Also their are materials that transmit in narrow bands that can be chosen for TPV.
This is a very cool stuff and is coupling my curiosity to my creativity!
So, does this mean the technology can replace steam turbine and change the way power plant work?
A super-critical steam turbine can achieve only 47%ish efficiency, so if it can reach 50%+, it will at least mean 10% or 20% improvement which is a lot. Not to mention they can build close-looped nuclear power reactor.
Are any venture capital fund investing in it? I want to put my money in. XD
Manufacturing in the United States is in trouble. That's bad news not just for the country's economy but for the future of innovation.
On Twitter
Become a Fan on Facebook
Subscribe to the Feed
Guest (michel.jansens@ulb.ac.be)
Max theoretical efficiency
"...the maximum theoretical efficiency of a conventional solar cell is 30 percent, or 41 percent if the sunlight is first concentrated using a mirror or lens...."
Well luckily, Fraunhofer ISE people don't know about this limit: they reached 41.1% efficiency recently. Look here
I read somewhere else a "practical/theoretical" limit of 60% for CPV and 40% for PV. Somewhere else that 100% was the limit... anybody knows more about this?
Michel
Reply
Kevin Bullis
178 Comments
Re: Max theoretical efficiency
Was that a single-junction cell? The stated theoretical limits are for single junction, not double or triple-junction cells (which are more expensive).
Reply
Guest (michel.jansens@ulb.ac.be)
Re: Max theoretical efficiency
Indeed, it is a multi-junction cell.
I didn't get that "conventional solar cell" meant single-junction.
Reply