New type of solar cell can generate electricity on both sides of the module

Skiers know this well: One Sunday they didn’t apply sunscreen properly – and by the evening they’d be burning up. This happens because the snow reflects the sun, so the skin is exposed to a much higher dose of ultraviolet (UV) rays than if you were sitting on a balcony in the winter.

The photovoltaic industry wants to exploit this effect to increase the efficiency of solar power plants. Conventional solar panels have a drawback: They can only generate electricity on the side the sun hits, meaning the front of the panel cannot take advantage of reflected sunlight.

Therefore, research institutes and businesses are looking at a type of solar cell that can convert the solar energy in the background into electricity. Depending on the installation location and type, it can increase productivity by up to 25% compared to conventional solar panels.

Major players in the industry such as SolarWorld, Trina Solar, Yingli or LG have launched the first modules of this type on the market. The most obvious difference compared to conventional solar panels is that behind these panels there is a thin glass sheet, which is responsible for weathering, but still allows reflected rays to pass through. Conventional modules are covered with a thin, non-transparent film.

The second difference: the metal contact points for electricity – usually made of Aluminum – behind the solar panel, do not cover the entire area as usual."Instead, the contacts [in the new module] are made of aluminum or silver, as thin as a hair, no more than 100 micrometers thick. Therefore, the reflected light rays easily reach the solar panel without any obstruction.", explains Dr. Thorsten Dullweber, of the Hameln Institute for Solar Energy Research (ISFH).

How much the increase in efficiency depends largely on the reflectivity of the back of the solar panels and how much space is available behind them. If installed on a dark saddle roof, the new panels are ineffective. But if installed on a light-backed rack or on white gravel on a flat roof, the efficiency increases by 10% to 15% compared to conventional panels, according to Dr. Dullweber.

For solar parks in deserts or other landscapes with a high sand content, the efficiency is as high as that of light-colored soil or white gravel. Mounting solar panels on a rack facing the sun can increase the efficiency by up to 25%."This is mainly because the amount of sunlight hitting the front of the modules increases. The back of the modules also attracts more light.", said Dr. Dullweber.

Meanwhile, the cost of these new solar panels is not too high, only 4% to 7% higher than the standard system, compared to increasing productivity from 10% to 15%, which is already very good, according to scientists at ISFH.

Another reason why this new type of solar panel is attractive is that the modules here allow for the generation of electricity twice a day. A small field experiment conducted by Berlin-based Start Up Next2Sun in Saarland, Germany, used a vertical east-west installation, with the front of the solar panels producing electricity in the morning and the back in the afternoon.

However, compared to wind parks or other solar power plants, these new solar power plants take up more space - the rows of modules must be spaced far apart so as not to block each other. However, this can also be an advantage, according to Heiko Hildebrand, CEO of Next2Sun: Because the rows of modules are spaced far apart and are upright, the space for these modules is not lost. Instead, they can take on ecological functions or serve agricultural production. For example, these solar power parks can be used as grazing grounds for cattle or to grow crops for animal feed.

"For Germany, this option is really suitable", says researcher Forscher Kopecek of the ISC Energy Research Center in Konstanz. Next2Sun is now preparing to continue building solar parks of this type. By this summer the Saarland region will have another 2-megawatt solar power plant.