Shining more light on solar panels

Shining more light on solar panels
Thermal radiation readings on panels help Joshua Pearce and his research team better understand ways to improve low-concentration photovoltaic systems.

Solar panels are the beacon of renewable energy, yet they are not getting as much light as they could be. Joshua Pearce from Michigan Technological University and a team from Queen's University in Canada have found a way to get more sun to shine on the panels and crank up the output by 30 percent or more. The work is published in the Institute of Electrical and Electronics Engineers (IEEE) Journal of Photovoltaics.

"We're looking at this from a systems perspective," Pearce says, who is an associate professor of materials science and engineering and electrical and computing engineering. He explains that the research focused on the system rather than individual panels mostly because the current set up for ground-mounted solar panel arrays is "wasting space."

The iconic flat-faced installed in large-scale utility solar farms are spaced apart to prevent shading. As the sun shines on a photovoltaic system, sending electricity into the grid, a fair amount of that potential energy is lost as the light hits the ground between rows of panels. The solution is simple, says Pearce: Fill the space with a reflector to bounce sunlight back onto the panels.

Reflectors, or planar concentrators, are not widely used, however.

"Panels are usually warranted for 20 to 30 years," Pearce says, explaining the warranty only guarantees under certain circumstances. "If you're putting more sunlight on the panel with a reflector, you will have greater temperature swings and non-uniform illumination, but simple optics makes wrong predictions on the effect."

Because of the uncertainty with potential hot spots, using reflectors currently voids warranties for operators. Pearce and his co-authors, found a way to predict the effects using bi-directional reflectance function, or BDRF.

Although the phrase sounds like a nightmare from algebra class, it is actually a set of math equations that people are used to seeing. BDRF is often used in movies and videogames to create more life-like computer generated imagery (CGI) characters and scenes. This works because BDRF equations describe how light bounces off irregular surfaces and predicts how the light will scatter, creating indirect brightening and shadows.

For their solar panel work, Pearce's team created a BDRF model that could predict how much sunlight would bounce off a reflector and where it would shine on the array. "Real surfaces do not necessarily behave like perfect mirrors, even if they look like it," Pearce says. "So we applied [BDRF] models to these materials, which scatter the light instead."

By showing how the reflectors scatter light, the researchers started to take the risk out of using reflectors with solar panels. But even better, the reflectors greatly increase solar system output.

"The mathematics behind this is complicated," Pearce says, explaining that the team wanted to "validate the predictive model, so the solar industry could start using our equations to design better solar farms."

So the team took their model to the field and ran an experiment on Canada's Open Solar Outdoors Testing Field in Kingston, Ontario. The results shined much more light on the problem than predicted by others.

With standard panels, not tilted at the optimum angle for the latitude, the increase in efficiency reached 45 percent. Even with a panel optimally tilted, the efficiency increased by 18 percent and simulations show it could be pushed to 30 percent with better reflectors.

"We expend a lot of blood, sweat and tears to make solar panels as efficient as possible," Pearce says. "We work so hard to get a fraction of a percent increase on the module level; double digit returns on the systems level was relatively easy.

Such a large increase of efficiency at the system level then could greatly change how solar panels are installed, and with the economic payback, it could even mean major retrofits for existing solar farms.

"Solar farms are already beating antiquated coal technology on cost all over the US," Pearce says. "There are more solar workers than coal workers now as both in the U.S. and Canada, coal plants are being shut down for cheaper and more environmentally-friendly solar. This just offers to sweeten the economic returns for solar farm investors."

"The main goal here was to hand the solar farm developers the data needed on a silver platter, which they can then use to modify their farms and crank up their output and revenue by about a third," Pearce says.


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More information: Photovoltaic system performance enhancement with non-tracking planar concentrators: Experimental results and BDRF based modelling. Photovoltaic Specialists Conference (PVSC), 2013 IEEE 39th DOI: 10.1109/PVSC.2013.6744136
Citation: Shining more light on solar panels (2015, October 22) retrieved 24 July 2019 from https://phys.org/news/2015-10-solar-panels.html
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Oct 22, 2015
"Solar farms are already beating antiquated coal technology on cost all over the US,"

And with a 30% (or even just a 15%) boost for very little additional cost that should put PV below the cost of coal practically everywhere.

Oct 22, 2015
that should put PV below the cost of coal practically everywhere.


Unlikely. The direct cost of plain coal for process heat etc. is so low at around 1 cent per kWh that it's hard to beat, while the LCOE of solar power is still 6-8 cents even in Saudi Arabia, and much much more anywhere that isn't close to the equator. 30% increase in production is just 23% reduction in unit cost.

Furthermore, you may not necessarily even want to employ the improvements because they come about by increasing the peak output of the solar array, which creates additional problems and costs elsewhere in the grid.

It's like breaking up traffic jams along a highway - you get more cars through, but then downtown gets jam packed. By maximizing solar output, you make the slope of the power swing that happens in the morning and afternoon steeper, and cause more excess generation in the middle, which requires more costly peaking powerplants and energy storage to deal with.


Oct 22, 2015
And the big white elephant in the room of course being that the major reason why solar panels cost as much as they do right now is because they're mostly manufactured in China, with cheap Chinese coal power, under government subsidies to boost Chinese exports to steal the market away from everyone else.

Ironically then, a large part of the cost appeal of solar power is smoke and mirrors: "green" politicians in Germany can boast record solar power output while people in Chinese cities are choking in smog.

The important question is, how much would they cost if you were to make solar panels using solar power, or other renewable energies, at all stages of manufacture?

Oct 22, 2015
This is brilliant, and it was achieved with non-tracking reflectors.

I'm considering using reflectors to enable solar panels on my north-facing roof. Mirrors would be mounted on the long flat roof of the porch, which would reflect sunlight onto the panels on the sloped roof of the house. (This would be in addition to the panels on the south-facing rear of the house.) I will definitely show this article to my designer.

Oct 23, 2015


you may not necessarily even want to employ the improvements because they come about by increasing the peak output of the solar array, which creates additional problems and costs elsewhere in the grid.



Sounds to me like the problem is the grid itself. Local generation, local consumption. Maybe the system itself needs an overhaul.

Oct 23, 2015
"By maximizing solar output, you make the slope of the power swing that happens in the morning and afternoon steeper, and cause more excess generation in the middle, which requires more costly peaking powerplants and energy storage to deal with."
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No, you do not, you even it out. The beauty of the diffuse reflector is just that, the spread of the power, not the concentration of it.

Your attempts to discredit alternative energy gets really silly when you try to invent problems. Do you think those who have done it do not know of your concerns, and have compensated for them, if necessary?

Oct 23, 2015
"Sounds to me like the problem is the grid itself. Local generation, local consumption. Maybe the system itself needs an overhaul."
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You are correct. That is why PG&E is spending three billion dollars each year on upgrades.

http://www.utilit.../407605/

What is your utility doing to get into the 21st Century? There are many options open, but the cost maybe high, if not started now.

Oct 23, 2015
You would think the South would be first in Solar, they unfortunately, they are still backward. California leads the United States.

And if you think advanced technologies such as solar wind and other integrated inputs makes the power more costly, go here:

http://www.utilit.../407668/

Check where you are compared to the dots in green.

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