Among the parameters which decrease the efficiency of the photovoltaic solar cells, we can note the solar IR radiations. This kind of radiation increases the temperature and then disturbs often the good operation of solar cells. How is-it possible to eliminate them ?
Photons above the band gap wavelength (photon energy below the band gap energy) are transmitted through the semiconductor material without absorption. Although these photons can eventually be absorbed by other materials behind the semiconductor (back sheet, mounting, etc.) The heating caused by the IR is minimal. Most of the heating comes from thermalization losses of photons below the band gap wavelength (photon energy above the band gap energy). These photons are absorbed but part of their energy is released as heat. This is because the e-h pair generated is more energetic than the band gap separation and the pairs have to relax (via release of heat) to the band edges. Filtering light above the band gap wavelength offers minimal improvement because of the absorption properties of the semiconductor. Conversely, is not possible to filter light below the band gap (where most of the heat comes from) without reducing performance (efficiency). This is why cooling the cell/device offers the best performance improvement (reducing temperature and increasing open circuit and MPP voltages). I measured this (effects of filtering) in the attached SPIE proceedings paper. This process is explained here: http://pvcdrom.org/pvcdrom/pn-junction/absorption-of-light . The most complex solution is to use tandem (multi-junction) cells or spectrum splitting. These devices and configurations have multiple cells in order to reduce the thermalization losses (that generate the heat) below the band gap energy.
http://pvcdrom.org/pvcdrom/pn-junction/absorption-of-light
Article Spectral Characterization of the Temperature Performance of ...
Dear Kebabb
One option is to filter the infrared energy from your PV panel.
This can be done by a nano material screen over a panel for direct thermal energy transport, solar heat energy that can be utilised for other purposes.
https://www.researchgate.net/publication/257136835_Trends_and_Opportunities_in_Direct-Absorption_Solar_Thermal_Collectors
You will find the article above and illustrations in it useful.
Regards Gerro
Article Trends and Opportunities in Direct-Absorption Solar Thermal Collectors
I am very grateful for your precious documents which are disponible freely online in the researchgate forum.
Great thank for you.
Cordially.
Kebbab Zoubir
Dear Mr. Zoubir,
though I like Mr. Prinsloo's approach, it will require more advanced - and more expensive - equipment to make use of the thermal energy harvested.
In case a less advance and thus cheaper solution is desired, coating the panels with a filter layer, tuned to reflect IR only might help.
There should be good experience in this, as glass panes for modern buildings have the same feature to reduce the amount of heat getting into the building to save energy on airconditioning systems.
New developments combine PV-panels and warm-water generation. This approach is similar to what Mr. Prinsloo described but more simple to build as it does not rely on using nanoparticles.
Filtering the infrared energy could be a solution, but yes as commented by Martin, one should evaluate the cost of such approach and see whether it is worth adding such filters to gain the amount of energy we usually lose with the heat resulting from infrared radiation. The use of PCMs (Phase Change Materials) at the module level ( at the back of the module) can be a solution to remove heat. Also here, the cost of added PCM should be carefully studied to evaluate the efficiency of such approach.
There was an International Solar Energy Society (ISES) webinar on PV-SWH combinations.
I think Ali is on the right track. Lifecycle Costs of the panel (especially first costs, O&M, and energy production) need to be carefully considered. IR radiation can actually improve energy production of a panel, if you are able to cost-effectively capture the heat via an integrated heat exchanger and transfer it to another material, such as air, or water/glycol, depending on the thermal need. Removing the heat off the panel makes the semiconductive panel more efficient in producing electrical power.
Last August we purt a heat exchanger on th eback of a standard 60 cell PV module to create a hybrid PV-T module. I t took about $50 worth of parts to do this and we expect to get about 500 watts of heat energy in the form of hot water at around 50º C. Next summer, I should have some good data on this simple device but you can go to ourwww.mainesolar.org website and download the Fall2014 Maine Sun for more information.
One simple option to improve power output is to spray water on module surface to reduce heat of solar cell. A programmed common garden watering system is suficient as a first approach.
Yes indeed, what has been suggested by Duarte is the oldest and simplest way as of today to reduce PV's heat ... when possible.
Photons above the band gap wavelength (photon energy below the band gap energy) are transmitted through the semiconductor material without absorption. Although these photons can eventually be absorbed by other materials behind the semiconductor (back sheet, mounting, etc.) The heating caused by the IR is minimal. Most of the heating comes from thermalization losses of photons below the band gap wavelength (photon energy above the band gap energy). These photons are absorbed but part of their energy is released as heat. This is because the e-h pair generated is more energetic than the band gap separation and the pairs have to relax (via release of heat) to the band edges. Filtering light above the band gap wavelength offers minimal improvement because of the absorption properties of the semiconductor. Conversely, is not possible to filter light below the band gap (where most of the heat comes from) without reducing performance (efficiency). This is why cooling the cell/device offers the best performance improvement (reducing temperature and increasing open circuit and MPP voltages). I measured this (effects of filtering) in the attached SPIE proceedings paper. This process is explained here: http://pvcdrom.org/pvcdrom/pn-junction/absorption-of-light . The most complex solution is to use tandem (multi-junction) cells or spectrum splitting. These devices and configurations have multiple cells in order to reduce the thermalization losses (that generate the heat) below the band gap energy.
http://pvcdrom.org/pvcdrom/pn-junction/absorption-of-light
Article Spectral Characterization of the Temperature Performance of ...
All IR are not harmful for PV. In fact, it depends on the material of the PV cell. Say for example Silicon material the best photon is in the IR range. Cooling of PV is the old concept popularly know as Hybrid PVT
The aluminum at the rear of the solar cell tends to absorb the IR light which has an energy below that of the band gap. In solar cells which do not have full aluminum coverage at the rear of the solar cell, the infrared may pass through the solar cell and exit from the module. You can consider an optimization of your cell's rear side which will also save you some raw material. You can even consider the bifacial technology.
I would recommend you read some publications about the bifacial and SmartWire technologies. They are not directly responding your need, but the rear-side designs are suitable for your case.
http://www.meyerburger.com/fileadmin/user_upload/meyerburger.com/Factsheets/Verschalten/FS_SWCT_EN_10-2014_LowRes.pdf
If one considers the most popular silicon cell PV modules, then it is known that IR only contributes to heating up the cells, thus reducing efficiency. They don't really harm the cells but only reduce the efficiency due to heating up. The glass of the PV module may be made with a coating that filter off IR but the costs will be high when compared to the gain. Therefore, the best is to have free ventilation under the modules to cool them as much as possible.
How about harvesting the subband gap photons (NIR) and upconverting them to the (presumably) UV light that your solar cell needs?
In my mind, if solar radiation is predominantly UV light I suppose solar cells will be more efficient.
Upconversion is a good way of boosting the efficiency of solar cells. However, the efficiencies of the so called rare-earth upconversion nanoparticles are very low...
The multijunction cells composed of three materials with low energy gap like germanium, medium energy gap like GaAs and a third high energy gap material GaInP is one solution to convert the a large part of the infrared radiation to electricty. Ge is the material to do that as its bandgap is= .67 eV.
I agree with the colleagues saying that the infrared radiation passes through the solar cell materials without absorption if it is not intercepted by back metal metallization. So if the back metal is made in from of grid like it can pass the infrared radiation to the environment. This would be the simplest solution.
As hinted before ,back cooling may be also to drain heat from the solar cells and decrease their operating temperature and increasing their conversion efficiency
The question is how far such part of the incident solar radiation raises the temperature of the cell, i think it makes out relatively small fraction of the incident solar radiation. It may not so very effective in increasing the solar cell temperature compared to shorter wave length radiation.
Best wishs
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