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What are the advantages and disadvantages of using cylindrical Fresnel lenses as PV concentrators?

My goal is to do some research and see which kind of Fresnel lenses are better to concentrate light on a PV cell. So I am comparing normal Fresnel lenses (found on overhead projectors/TVs) to cylindrical ones which are one dimensional and linear. I just can't find much info on the net on cylindrical Fresnel lenses other than they are heavier than the traditional lenses

  • there was a questions here about pv concentrators (that I don't find right now, maybe someone else can help) but hte gist of the answer was the pv concentration does not make a whole lot of sense. – mart Feb 22 '14 at 20:23
  • From a bit of searching it seems that the major disadvantage is that there's not been any research done, so you'll need to start by doing primary research. With planar fresnel lenses there's a lot of experience and they're readily available. – Móż Feb 22 '14 at 23:06
  • For anyone interested, this company uses Fresnel lenses for photovoltaics, though it's likely they aren't cylindrical: soitec.com/en/technologies/concentrix – Highly Irregular Feb 24 '14 at 4:22
  • I am planing on doing extensive research on this and I want to know if something has already been done on this field. I don't want to spend my time researching something that has already been done. From what I am reading here it seems that there hasn't been much done on PVC's using Fresnel lenses. If anybody has some info that could help please share with me. Thanks for your thoughts and time. – sam Feb 24 '14 at 14:35
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There is a big advantage to cylindrical lenses. If you arrange PV cells in vertical stripes (e.g. covering 20% of the surface) and put vertically aligned cylindrical Fresnel lenses, as the sun moves from east to west (or west to east in the southern hemisphere) you just need to move the Fresnel lenses (or probably more easily the PV panel behind it) in the horizontal direction. What's more, this movement is a sinusoidal movement which can be done mechanically with a simple clock-driven gearing and with little power since it only requires movement in the X axis. So you have a PV that can receive highly concentrated sunlight in a small surface covered with high-efficiency cells, without needing complicated sun tracking (the Y axis is irrelevant, as at worse you lose a small fraction of the light at the top or bottom of your panel).

This is all ideal of course, and there are other factors to consider:

  1. Heat accumulation. This shouldn't be a tough one since you still have the same amount of light falling in your total panel, so if you mount the cells on a thermally conductive plate, you should be able to dissipate the energy just as with unconcentrated solar panels. Even more, if you make the space between the PV columns a grooved surface (like a radiator grid or a typical cooler) you can probably cool it much better than in a fully PV covered surface. So unless dissipating between the PV and the backing plate is a big challenge, I would say this probably has better thermal characteristics than non-concentrated PVs.

  2. Losses through the lens. Some lens materials might not be highly transparent to the frequencies that your PV is optimized for, so the lens and the PV need to be matched. Also, the lens has some loses due to reflection and imperfections in the surface.

  3. A Fresnel lens offers only near ideal characteristics from a straight-on angle. So when light shines on it at a low angle (e.g. sideways in a vertically oriented cylindrical lens) much higher loses can be expected.

But all in all, especially on high latitudes, this design should be much more cost efficient than a traditional fully-covered PV panel.

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    Hi user1224, welcome to Sustainability.SE! I think this is a good answer, but I've suggested an edit to the formatting to make it more readable. – Flyto Mar 1 '14 at 8:11
  • It's still east to west in the southern hemisphere. – Sherwood Botsford Mar 6 '15 at 22:13
  • Another disadvantage is taht a PV cell gets less efficient as the temperature goes up. – Sherwood Botsford Mar 6 '15 at 22:14
  • The price of PV is getting so cheap, that concentrators are getting pointless. A concentrator has to intercept at least the same square footage as the unconcentrated PV cell. And PV cells are getting to prices under a dollar a watt. Figure a 20% efficient cell, that's $200/square meter for the PV. Can you make a concentrator for $200/square meter that will work year after year with essentially zero maintenance? – Sherwood Botsford Mar 6 '15 at 22:17
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This is a rather broad question, but in the comments the OP has specified that they are comparing cylindrical Fresnel lenses to "normal" Fresnel lenses. We can get some insight by considering things at a high level, and considering why lenses might be used on PV at all.

Within its normal operating range, the relationship between the amount of light falling on a PV cell and the amount of electricity produced is roughly linear:

Power curve for a PV cell

The amount of electricity produced also scales linearly with the area of the PV panel: more panel = more electricity.

If we put a concentrating lens above a PV panel, what we are effectively doing is collecting the light from a wide area and focussing it on a small bit of PV material. Given the two linear relationships above, all else being equal this should give a similar output to just covering the wider area with unconcentrated PV and doing away with the optics.

Any advantage or disadvantage to concentrating optics must, then, lie in more detailed factors. For instance, it might be worth using optics to allow the use of a smaller quantity of more expensive PV material. On the other hand, concentrating the light on a small area also concentrates the heat, which must then be dealt with... there's an engineering optimisation to be done there.

This allows us to come back to the question of cylindrical (linear) vs spherical lenses. Cylindrical lenses concentrate the incoming light in only one dimension. As such, they can be considered as a compromise between unconcentrated PV and full spherical lens arrays. They may also be cheaper to manufacture and install than large numbers of spherical lenses (but I have no evidence for this, and if microlens arrays are used for the spherical version, it may not be true).

Depending on the exact intent of the question, you may also find the answers to this question on physics.SE to be of interest.

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