Squeezing More Solar Energy From Solar Panels, With Ground Albedo

By Tina Casey for Clean Technica

If the NIMBY syndrome ever runs amok and the US runs out of places to put new solar farms, we can always go back and get more electricity from the old ones. That’s one takeaway from an ongoing study by the National Renewable Energy Laboratory. They are taking a good, hard look at what happens when you invest in bifacial solar panels instead of regular run-of-the-mill ones. The study kicked off last summer and so far the results are encouraging. In fact, they could help motivate additional solar arrays for parking lots and other built surfaces, too.

First things first: what’s all this about ground albedo? It’s not something you add to your curry, and there is no such thing as whole albedo or, for that matter, mashed albedo.

If you can see the moon, you’re seeing ground albedo, aka light reflected from a surface.

The NREL study is a three-year venture into the impact of ground albedo on the energy output of bifacial PV panels, which refers to solar panels that can collect light from the backside as well as the front.

If you’ve ever seen a solar farm, that bifacial thing might not make too much sense. After all, the backside is the side facing away from the sun.

However, when you consider light reflected from the surface, everything falls into place. In fact, so far the results of the study are exceeding expectations in the first year.

Collecting solar energy from the backside does not mean creating a whole new solar cell. It simply means using glass or clear plastic on the backside.

NREL estimates that a bifacial solar panel costs about 10% more than its one-sided equivalent. So then the question is how to convince solar developers and investors that the extra cost will pay off.

The idea is to establish the benefit of bifacial solar panels in terms of balance-of-system costs. In other words, higher energy output from each solar panel corresponds to lower hardware costs per megawatt. You can potentially get the same output using fewer solar panels, and that cuts down on other hardware including inverters, racking, tracker systems, interconnects, and so on.

This is where it sure helps to have the data in hand. The NREL study is aimed at establishing best practices that make the additional up-front investment worthwhile.

Aside from collecting hard data on the ground-mounted array at the lab, the study includes computer simulations that apply the data to all sorts of other situations. Solar panels for parking lots and carports are a particular area of interest, considering the light that could be reflected from paved surfaces and parked cars.

Here’s the explainer from the lab:

“NREL researchers anticipate new data will remove barriers to advancing the cutting-edge technology by providing information and best practices that increase installation efficiency, reduce costs, and improve durability.”

So far, so good. The lab has already enlisted support from the solar industry for the effort. US solar companies including Prism Solar, Sunpreme, and Lumos Solar are partners along with three “major international manufacturers.” The end result will be benchmarks for conventional and bifacial solar panels from the same brands.

As may be expected, so far NREL has found that light reflected from snow has the most impact on energy production from bifacial solar panels, compared to a ground cover of grass.

That’s an interesting twist considering that the snowy state of Alaska has been leaning on solar farms to provide remote, off-road villages with affordable, reliable clean power.

Solar panels are known to function more efficiently in colder weather, and light reflected from snow is also known to improve solar conversion efficiency on the front side. The bifacial aspect could help accelerate solar adoption in Alaska and other cold-weather parts of the US.

The economic justification for investing in bifacial solar panels in non-snowy areas of the US is a matter of figuring out how to maximize ground albedo with different surfaces.

Some of that research is already underway piecemeal in the private sector, but NREL’s three-year study is the first comprehensive analysis with data open to the public, so group hug taxpayers!

Last year the focus was on snow cover and grass, with the best results going to snow. Grass did better as it turned brown during the growing season.

The lab will be looking at additional vegetation for ground cover this year. In the final year of the study, they will turn to crushed rock. A white fabric cover of some type is another option under consideration.

Hmmm…our money is on vegetation. The field of agrivoltaics is already beginning to attract attention from farmers interested in combining PV arrays with grazing crops and pollinator habitats. Why let all that nice ground go to waste on a crushed rock or whatever?

Meanwhile, it’s worth noting that the study also includes an energy storage component, but not just any old energy storage. The system under study sports cutting edge vanadium flow batteries, from the company Avalon.

The energy storage element is a critical one. Increasing the output from solar panels during peak periods is all well and good, but if nobody is around to use the electricity then you’ve got a curtailment issue unless you can park the electricity for later use.

Interesting! CleanTechnica is reaching out to the lab to find out why they are dipping into the relatively new field of flow batteries instead of relying on a conventional lithium-ion battery array, so stay tuned for more on that.

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