Why not put smaller solar panels beneath much larger lenses?

This idea seems kind of obvious, so I’m sure there’s a reason solar panels aren’t build like this, but the idea is…

Instead of building a solar panel of some given size (let’s say one square meter), why not build a much smaller solar panel, but place it beneath a 1 square meter lens, that concentrates one square meter’s worth of solar energy on to the smaller solar panel?

Would you still generate a comparable amount of energy this way?

And if so, wouldn’t these types of solar installations be far cheaper to build?

These exist - they’re called Concentrating Photovoltaics. Often a fresnel lens is used, or a parabolic reflector.

They have the disadvantage that the panel must be aimed at the light source, otherwise the focal point doesn’t fall on the photovoltaic element - so they’re not suitable for just slapping onto the roof of your house.

Thanks for sharing, Mangetout! I learned something today.

The wikipedia article has a lot more info:

In addition to the aiming problem, the disadvantage include:
[ul]cost of that huge lens, including its support[/ul]
[ul]solar panel must withstand much higher temperature[/ul]

You could have a cylindrical lens or mirror, that focuses in just one dimension, paired with a long strip of photovoltaic panel. That way, you could keep it aimed at the Sun all day, without moving it. You would still need to move it with the seasons, but that’s a much easier proposition than continual movement.

The cost structure just doesn’t support this.

Photovoltaic cells are actually not that expensive compared to the installation and maintenance of a large piece of moving machinery. It’s probably much simpler and more efficient to just cover more space with cells.

Another problem is that mass-produced solar panels are (probably) optimized to be most efficient for the power density of sunlight. If you concentrate sunlight, you probably require a different panel design.

in pure cost of manufacturing I would imagine a 1 meter square solar panel is now cheaper than a 1 meter square lens. Lenses aren’t cheap! Maybe in the 80s it was the other way round but I doubt it’s true now. Never mind the moving parts required to keep it focused.

As others have noted, it need not be a lens. You can use a parabolic reflector or (arguably even better) a Compound Parabolic Concentrator (which need not be aimed precisely).


One problem with lenses and mirror devices is that you inevitably introduce reflection loss (for lenses, unless you apply an antireflection coating) and scattering losses (and, no matter how good your mirror or lens intitially is, after being out in the open it will have weathered and collected dust and dirt). You avoid that by putting out your solar cells with a mere protective plastic or glass covering, ideally one that won’t scratch easily, and can be easily cleaned, or “washes” itself in the rain or snow. Simpler is generally better.

Read about a electric car (prototype) on cNET (IIRC) with a PV panel on the roof to recharge the batteries, it would be parked under a large lens, the car would move to keep the lens focuses on the PV panel.

What is this, a car for ANTS?

Are you talking about mounting the cylinder sort-of-vertically or sort-of-horizontally?

I’m assuming the former, but there will be losses even if you do aim it seasonally - the amount by which the elevation of the sun changes in a day is greater than the amount by which the arc height of the sun changes throughout the seasons, at least in the temperate zone I think.

Because people would stick their penis in front of it and show it to the world

This was a Ford concept car. I think this is a rare case where a solar concentrator might make sense. The size of the solar panel on the car is limited by the size of the car’s roof. If you want to get more solar power for charging when the car is parked at home, you could connect it to additional solar panels, or park it under a lens. A plastic Fresnel lens may be cheaper, and the car already has the ability to move, so tracking the sun just requires appropriate software.

On the other hand, a rooftop solar panel would still be generating power all day, even when the car isn’t there, so maybe that would make more sense…

Another problem is that lenses and mirrors only work on absolutely clear days. Even a light haze completely destroys their ability to focus.

Non-concentrated photovoltaics can gather light from any angle, so although their power output goes down with clouds, it does not drop to nearly zero as it does with concentrating systems.

It wouldn’t be aimed at a constant elevation: You’d need some funky curved shape to do that.

Thanks everyone. I didn’t think about the need to keep the lens focused based on the sun’s position.

Yes, I think this is an important consideration. Basically, on a hazy / cloudy day, a solar panel with a lens is no better than the same solar panel without the lens.

I was surprised by how expensive 2-axis actuation is. Adjacently it’s a killer for the tower based CSP. I wish I had those numbers handy.

this is where my mind went as well. on top of extra complexity and associated maintenance, these effects are almost certain to eat up any potential gain unless you scale the hell out of it all.

However now that the question has been answered we can get into more radical discussion, like some sort of device or vapor generator that generates a permanent ‘edge of cloud’ effect - an increase in power without the need for precision focus. Or does the edge of cloud effect still require a very specific directionality? Scientific information is lacking online.

Do you have a cite for this? I don’t claim otherwise, but it surprises me that clouds actually scatter light so fully that lenses cease to work at all.

And I realize that the focusing power of a lens probably doesn’t drop to actual 0, but if it gets to < 20% or so, I’d consider it close enough.