# Would putting a magnifying glass on a solar panel be beneficial? [duplicate]

During my childhood, it was common to use magnifying glasses to burn paper and dead leaves.

But would it be a good idea to place a lens above a solar panel, making sure that all the magnified light hits every solar cell on the solar panel? I know that some people have used this method to harvest more energy, but I was wondering if this is reliable and durable.

Wouldn't the magnified light burn the solar panel or would it be converted to electrical energy right away?

## marked as duplicate by John Rennie thermodynamics StackExchange.ready(function() { if (StackExchange.options.isMobile) return; $('.dupe-hammer-message-hover:not(.hover-bound)').each(function() { var$hover = $(this).addClass('hover-bound'),$msg = $hover.siblings('.dupe-hammer-message');$hover.hover( function() { $hover.showInfoMessage('', { messageElement:$msg.clone().show(), transient: false, position: { my: 'bottom left', at: 'top center', offsetTop: -7 }, dismissable: false, relativeToBody: true }); }, function() { StackExchange.helpers.removeMessages(); } ); }); }); Jun 25 '17 at 16:29

This is possible to some extent.

However, solar panels are still quite inefficient. Even with top panels, about 80% of the power heats the panel instead of coming out in electrical form.

Semiconductors stop being semiconductors above some temperature. That's about 150 °C for silicon. You can't let the panel get that hot, since it won't produce any electric power anymore.

Even below the max semiconductor temperature, solar panels become less efficient. The current is roughly proportional to the light flux, but the voltage goes down with temperature. Since output power is current times voltage, a hot solar panel is less efficient than a cool one, all else being equal.

Consider that full-on sunlight has a power of about 1.2 kW per square meter at optimum conditions at the surface of the earth. Even using a more realistic value of 1 kW/m2, that's still 800 W/m2 to get rid of to keep the panel operational. That's about 520 mW per square inch, which may be helpful if you're used to heat sinking transistors and the like.

So some amount of extra flux works, but you can't take it too far. The efficiency will go down, but the total power output is still more than a bare panel. However, if you overdo it, the panel gets too hot and you get no power at all, plus possible permanent damage to the panel.

In terms of absolute power collection, it's always better to add more panel area than to spend that area concentrating light onto a smaller panel. In some cases, economics favors some concentration of light (mirrors are cheaper than solar panels).

• If temperature is a concern, then we can design a cooling system. For example, let water to wash over the panel surface. Even better, we may design a recuperating system to make use of the heated water. This is especially feasible in northern remote town. – user115350 Jun 25 '17 at 16:03
• I actually like that idea. But instead of putting water on the surface, we could use a thermoelectric generator in between the solar panel and cold water to make energy harvest more efficient. – Nathan Ramanathan Jun 25 '17 at 16:56
• @Nathan: A thermoelectric generator will have a temperature drop across it, so putting one between the solar panel and the water will reduce the cooling effect on the solar panel. Since the temperature difference won't be very high, the thermoelectric generator will be very inefficient. I doubt that the added power from the thermoelectric generator offsets the loss from the solar panel due to higher temperature, not to mention the drawback of added complexity and expense. – Olin Lathrop Jun 25 '17 at 20:24