Cooling Solar Cells, Even at High Noon

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There's been a lot of research in the past few years into how to improve the efficiency and lower the cost of solar energy technology. But only now has one rather obvious problem been addressed, and apparently solved: How to keep solar panels cool on a hot, sunny day.

At the same time, the technology makes solar panels more efficient and therefore capable of generating more electricity.

Researchers at Stanford University report in Optica, the journal of The Optical Society, that they simply added a layer of textured silica glass to the surface of traditional solar panels to divert unwanted solar heat, which can hamper the cells' efficiency and longevity.

Solar cells are fairly easy to manufacture and therefore accessible to virtually every budget. But they're not particularly efficient at converting solar energy into usable electricity. Some of this wasted solar energy may be unavoidable, but much of it is due simply to overheating.

Solar cells often heat up to 130 degrees Fahrenheit (55 degrees Celsius), and sometimes even more. Reducing the heat with liquid coolants or even ventilation isn't an option because either method would reduce the panels' exposure to sunlight and make them costlier to manufacture.

The solution, developed by the Stanford team led by electrical engineer Shanhui Fan, doesn't block sunlight, nor does it add unwanted expense to the panels. It simply involves embedding small cone- and pyramid-like structures onto a very thin layer of silica glass to reflect hot infrared radiation away from the panel while maintaining the panel's access to usable solar energy.

"A carefully designed layer of silica would not degrade the performance of the solar cell," Fan explains, "but it would enhance radiation at the predetermined thermal wavelengths to send the solar cell's heat away more effectively."

At best, current solar panels can convert less than 30 percent of the solar energy they collect into electricity. The wasted energy saps the panel's strength even further. In fact, the efficiency of a solar cell declines by about a half of a percentage point for every increase in temperature by 1.8 degrees F, or 1 degree C.

"That decline is very significant," said Stanford postdoctoral scholar Aaswath Raman, a co-author of the Optica paper. "Our method of carefully altering the layers that cover and enclose the solar cell can improve the efficiency of any underlying solar cell. This makes the design particularly relevant and important."

Plus, the waste head shortens the effective life of a solar panel. It's rate of aging doubles for every temperature increase of 18 degrees F (about 8 degrees Celsius).

Zhu's team is now continuing tests of their design in a laboratory, but eventually plan to demonstrate it

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  • Report this Comment On July 27, 2014, at 5:22 PM, phillipzx3 wrote:

    "At best, current solar panels can convert less than 30 percent of the solar energy they collect into electricity."

    In other words, they're (on average) about as efficient as the internal combustion engine, which requires us to first buy fuel to make them run.

    Let's hope they hit 50% in the next few years, which will force the price of the current 20%-30% cells down to (almost) give-away pricing.

  • Report this Comment On July 27, 2014, at 6:14 PM, Petronilus wrote:

    Great news, if it works.

    @phiipzx3, It's irrelevant to compare energy efficiency to combustion engines. Most often their efficiency in the low 20s % but it means effectively 70-80% of the gas you burn in your car really is just gone as heat, vibrations and noise rather than to move you. As we deplete our oil reservoirs rapidly, it really means that some day we can look back in time and be embarrassed about how much we wasted of this limited resource.

    A solar panel might have similar efficiency as your car engine, but the loss is just simply sunshine not doing the work and our sun is going to last billions of years no matter how much we use of that source of energy.

    Efficiency is still highly important as it impacts system cost and how many panels you need for a given need of electricity.

  • Report this Comment On July 27, 2014, at 6:41 PM, stockingshorts wrote:

    Might as well tell everyone how they do it because the Chinese have most probably stolen the idea already........

  • Report this Comment On July 28, 2014, at 9:15 AM, fpl1954 wrote:

    The problem with many innovative ideas like this is cost. Often, the cost of increasing efficiency ends up higher than simply adding more panels. If I remember correctly from my graduate level Solid State Physics courses in 1978, the maximum efficiency of one layer of solar is 14%. A simple version of the physics is imagine sunlight being "captured" by the width of the junction of the positive and negative doped (PN) atoms in the panel. Any one material has a certain "band gap" that will "capture" a certain (narrow) frequency range of sun light. Sunlight has a very wide range of frequencies (why we see rainbows), and again from memory only 14% can be "captured" by one PN junction. You can layer PN junctions so that the widest is at the top and shorter light passes through to the next layer. This has a practical limit of 3 layers, or 42%. Cost goes WAY up when you layer, 42% cells cost 20X as much as 14%. Layering is used by NASA on satellites where maximum power is needed, but anyone with a house has enough roof to use 14% cells and minimize cost. There are other efficiency enhancements, like devices that tilt the cells towards the sun and micro-inverters that eliminate shading issues, and they all cost money. This is why no single solution is optimal for everyone. If this cooling idea adds 5%, but costs 25%, it only makes sense for installations where space is at a premium, like satellites.

  • Report this Comment On July 28, 2014, at 9:26 AM, fpl1954 wrote:

    Hum, let's do some math. Solar panels run about 14% efficiency, maybe a bit less. When they heat up 10 degrees, according to this article efficiency reduces 5%, which I assume means 5% of 14%, they can't drop to 9%. So they drop to roughly 12%.

    Solar cells are roughly $1 a watt installed. Most people decide on a 5kW array, which drops their electric bill to zero. A 5kW array costs about $5,000.

    Assuming 240W panels, I need 21 panels for a 5K array (I'm ignoring quite a few things so probably it's 23, but this is a rough calculation)

    If I want 5kW after it heats up 10 degrees, I simply install one more panel, which costs another $240.

    I can afford to pay $250 for these cooler panels before it's cheaper to just add another panel.

  • Report this Comment On July 29, 2014, at 4:25 PM, DragonFireCK wrote:


    You also missed the part of the article:

    "Plus, the waste head shortens the effective life of a solar panel. It's rate of aging doubles for every temperature increase of 18 degrees F (about 8 degrees Celsius)."

    This means, that in addition, that temperature increase will mean replacing the solar cells more often, however with the better cooling, that won't be the case. As such, If the improved cooling drops the temperature by 10C, you can probably pay more like $5250 extra to see a break even for a 5kW array.

  • Report this Comment On November 17, 2014, at 12:26 AM, RobertCLang wrote:

    I own a 5800 watt solar array with a display that shows me what is being generated at any given time. The array works best between 50 to 72 degrees with a breeze (clouds moving across the sky is great). A cool, crisp sunny day is heavenly. Once the temp starts rising into the 80s the array does not produce as much. It really begins to "lose it" when the temps exceed 90.

    Probably explains why Germany, for example, does so well with solar electricity even though the daylight hours are less in the northern latitudes.

    I have long believed that less heat also may result is longer lasting panels and inverters, too.

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