Increasing solar energy conversion efficiency

[Ingrid Eldevj]

You can burn a hole in paper using a magnifying glass and light. What would happen if you applied this large-scale on a solar panel?

 

[mfb]

That approach is called concentrator photovoltaics. You save some photovoltaics area, but the system gets more complex, and you are limited to direct sunlight - scattered light from elsewhere doesn't hit the solar cell any more. The higher temperatures of the solar cell are an issue as well.

 

[Ingrid Eldevj]

thank you..
could this concept be used to produce steam to power turbines when used on water?

 

[mfb]

Concentrated solar power, already linked in the article I linked.

 

[Ingrid Eldevj]

thankyou for those resources, I'm currently investigating increasing efficiency of renewable power, but I am new to the subject.

 

[sophiecentaur]

thankyou for those resources, I'm currently investigating increasing efficiency of renewable power, but I am new to the subject.

If you can afford to use a tracking mechanism, any concentrating system can give you a useful return but tracking is complicated,, expensive and definitely not 'passive'. Probably not worth while considering for large PV farms. Sometimes it's best just to go for a bigger area - depending. . . . . .

 

[russ_watters]

thankyou for those resources, I'm currently investigating increasing efficiency of renewable power, but I am new to the subject.

Concentration doesn't increase efficiency in PV, it reduces efficiency...and for solar thermal it isn't really a function of concentration amount. Are you sure that is really what you are after? Maybe you are really just looking for increased output? Or cost effectiveness?

When the energy source is free, the normal physics concept of efficiency isn't what is most important.

 

[sophiecentaur]

Concentration doesn't increase efficiency

Actually, a lenticular lens can put more of the incident light onto the active parts of each PV element. It's producing concentration on the 'pixel' level. (But only over a limited angle range, of course.)
There is another point in 'concentration' and that is (as in your original burning glass example) the possibility of obtaining much higher temperatures. But, as russ_waters says, that's not strictly an increase in efficiency.

 

[mfb]

Actually, a lenticular lens can put more of the incident light onto the active parts of each PV element. It's producing concentration on the 'pixel' level.

That is just a redistribution. It means you can make a smaller active area, and you can afford more efficient solar cells (as they don't have to cover the whole area). This alone (the use of small, more expensive but more efficient solar cells) leads to an effective increase in the efficiency.

Higher temperatures are better for solarthermal power plants (you absolutely need concentration for them), but worse for photovoltaics.

 

[russ_watters]

Yes, the reduced efficiency with increased temperature is what I was referring to for PV. For solar thermal, concentration is an inherrent part of the system. My suspicion though is that desingers aren't thinking "more concentration = higher efficiency", they are designing from the other direction: picking the thermodynamic cycle first, then designing the concentration system around it.

Again, for solar sometimes you want to maximize efficiency of conversion of light to electricity, but I think it is more often the case that you want to maximize cost effectiveness: $/watt or $/watt-hour.

 

[sophiecentaur]

It means you can make a smaller active area,

I don't suggest reducing the active area; that has its own cost in efficiency reduction due to higher running temperature. The pictures I have seen of PV cells show a border of substrate without PV. That border represents wasted incident light and suitable optics can eliminate it. That, in a reasonable definition of efficiency, implies an improvement. Incidentally, that 'redistribution' wouldn't affect the running temperature so there wouldn't be a diminution of efficiency.
Google PV cells Images.

 

[mfb]

I don't suggest reducing the active area

That is literally the only point of concentrator photovoltaics.

 

[sophiecentaur]

That is literally the only point of concentrator photovoltaics.

Not if you are dealing with the ones that are available at present. If there is 'wasted' area then you can get more Power from the array. I was not suggesting that they should be deliberately manufactured with a large border of non-PV material. It has already been pointed out that reduced area can increase the operating temperature which reduces efficiency. What would be the point of doing that deliberately?

 

[mfb]

You save active area. That is the point.

Instead of 1 m² of cheap photovoltaic cells, you make a cheap 1 m² mirror/lens system focusing the light onto a single, expensive, high-quality 1 cm² cell. The high-quality cell has a higher efficiency than the cheaper cells, but covering a whole square meter with that better cell type would be too expensive (it is done for satellites in space). Overall, you get a higher efficiency for direct sunlight, but worse (nearly zero) efficiency for scattered light. In some applications the conventional solar cells are better, in some applications concentrator cells are better.

 

[sophiecentaur]

you make a cheap 1 m2 mirror/lens system focusing the light onto a single, expensive, high-quality 1 cm2 cell

That assumes a technology that allows very high operating temperatures for your PV element. Do you know of any such thing that's available at the moment?

 

[mfb]

Those cells are installed and producing electricity. See the article linked in post 2.

 

[OmCheeto]

Concentration doesn't increase efficiency in PV, it reduces efficiency...

"testbook" maybe, but we don't live on a textbook world.
Depending on your latitude, my calculations from last year indicated that "textbook" efficiency increased from between 19%(summer) and 58%(winter) with the inclusion of concentration.

And cloud cover... Don't even get me started on that...

...
When the energy source is free, the normal physics concept of efficiency isn't what is most important.

Agreed.

 

[sophiecentaur]

Those cells are installed and producing electricity. See the article linked in post 2.

From what I could gather from that link, the market penetration is around 0.1% and they say that "the near term outlook for CPV industry growth has faded with closure of all of the largest CPV manufacturing facilities".
That doesn't seem to suggest that it's a particularly good system . . . .yet. There must be some problems still to solve and I can't see them being on any of my neighbours' roofs in the foreseeable future.
My suggestion was to use some 'weak glasses' in front of a conventional PV element to eliminate the wasted periphery at high noon. The concentrator could, of course, be tracked with a fairly cheap mechanism. Whether or not it is worth while would depend entirely on the details of the cost. The optics could be extremely crude and could be varied by pumping a fluid into the screen - no major moving parts needed. (The eye does a similar thing)

 

[mfb]

That doesn't seem to suggest that it's a particularly good system . . . .yet. There must be some problems still to solve and I can't see them being on any of my neighbours' roofs in the foreseeable future.

The necessary steering is certainly one of them. You cannot do rooftop solar with CPV, installation costs will always be higher, and the modules are more complex.

 

[sophiecentaur]

The necessary steering is certainly one of them. You cannot do rooftop solar with CPV, installation costs will always be higher, and the modules are more complex.

Steering is a snag. You need to leave space between panels or, when they're steered, they can shadow each other. So they have to be spaced out more than you'd want. Steering a small array can be done on a single panel but you can't tilt a field.