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In 2020, Change Inc. wrote about a successful test of double-sided solar panels. Solliance, a research collective that includes TNO and the technical universities of Delft and Eindhoven, investigated a way to cover panels on two sides with solar cells. With this, light reflected from buildings and plants, for example, can be converted into usable energy. At the time, it remained to be seen when the technology would become commercially available. How is it now, three years later?

Different kinds

Bas van Aken, a scientist at TNO and a specialist in solar energy, wants to clear something up before he can talk about recent developments in double-sided solar panels. In fact, there are different types of solar panels, each of which is subjected to testing with double-sidedness.

"There is a difference between crystalline-silicon and thin-film solar panels," he explains. "Thin film is often cheaper, requires fewer materials and is lightweight. But crystalline silicon is the most widely used and has 90 percent of the market."

That has to do with the fact that crystalline-silicon solar panels are more applicable on rooftops and at solar farms. Solliance's experiments that Change Inc. wrote about in 2020 were done with thin-film panels. But crystalline-silicon solar panels, and so-called glass-glass solar panels, are also well capable of being double-sided.

Double-sided already commonplace

And about that, Van Aken comes with interesting news: in solar farm applications, almost all crystalline-silicon and glass-glass panels are now double-sided. "Around 2020, the first Dutch bifacial solar park was opened. After that, such parks started to appear more and more in the landscape. And now when applications from project developers come in - you're talking about applications from 10 to more than 100 megawatts - almost all of them are double-sided."

Agri-PV

That's because the technology lends itself well to large-scale application. Today, there is a lot of experimentation with growing fruit under solar panels, also known as "Agri-PV. This makes double use of the space scarce in the Netherlands. Van Aken explains that all those Agri-PV projects are being done with double-sided glass-glass panels. "These are panels consisting of two sheets of glass with rows of double-sided solar cells in between. The glass ensures that enough light remains for the plants. And at the same time, the panels are high above the ground so that the light coming through on the plants can reflect back to the bottom of the solar cells."

What exactly does a double-sided solar panel entail?

Double-sided solar panels have photovoltaic cells that capture light from both sides and convert it to solar power. This allows the screens to take advantage of the albedo effect: a unit of measure to express reflected, or diffused, light. Much of the sunlight is reflected by buildings, plants, roads and forests. Double-sided solar cells can be used to extract additional energy from this diffuse light.

Solliance tested double-sided panels with thin-film solar cells for the first time in 2020. In this case, the panels are so thin that you can see through them. "Because the light also passes through the panel itself and then reflects on the other side, we can achieve nearly equal yields," Ron Andriessen, a Solliance employee at the time, told 2020.

Read the full article from 2020 here.

So in three years, the concept of two-sidedness in solar energy has grown like cabbage. "But it's going to become even more important," Van Aken believes. He sees opportunities for other applications of the technology in the near future. In time, for example, he expects to see more vertical solar panels. "These are panels that stand in the field like garden fences - Vrijstad Energie in Culemborg is a good example. There the panels are combined with animals that can walk around them. With a panel that stands straight up, two-sidedness is a logical choice."

Along with the sun

And then there are solar tracking systems; long tables of solar cells that face east in the morning and turn west with the sun during the day. "Solar tracking systems have to be high above the ground so they can make the whole turn. That also allows sun to fall between the panels on the ground, and with two-sided panels you could convert that reflected light back into energy."

Responding to grid congestion

So Van Aken is positive about the developments, and thinks that two-sidedness can be of increasing added value. By this he means more efficient use of sun and space, but also a contribution to solving grid congestion. "With the use of vertical solar panels, for example, the peak of solar energy can be shifted from lunchtime to mid-morning and afternoon. So that's a broader generation profile, allowing us to provide solar power for a greater portion of the day."

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