From an Israeli startup: double-sided solar cells

The vast majority of solar cells today generate electricity by directly facing the sun. But what if you could engineer the backside of the solar cell to make use of reflected light as well? That’s the idea underlying the technology of bSolar, an Israeli startup who recently launched its so-called bifacial solar cells.

Bsolar showed off its solar cells at a German trade show last month and announced a 730KW project in Japan that will use its new cells. The venture-backed company, founded in 2007, is bringing its solar tech to the market for the first time, and its cells could produce over 20 percent more electricity compared to conventional, single-sided cells, according to Yossi Kofman, co-founder and CEO of bSolar.

Bifacial solar cell research has been around for about four decades, but bifacial cells are still more of a novelty product today. Bringing the tech to market successfully requires overcoming technical challenges, including finding ways to produce bifacial cells cheaply. The technology may be attracting more attention these days as conventional silicon solar cells become low-price commodities and manufacturers scramble to boost their products’ performances to gain a competitive edge. “Everyone is looking for high-power and differentiated products, and that’s what we are providing,” Kofman said.

BSolar took silicon wafers and engineered into them the ability to capture reflected light on both sides. That means the cells’ backside can absorb light and contain electrodes to ferry the electricity produced out of the cells. The use of boron is a key to making bifacial cells, and a lot of research has been done by both companies and universities to investigate this chemical.

Nothing boron about it

What makes boron a good candidate is not just that it makes the rear side of a solar cell more receptive to light. It also promises to be a good alternative to aluminum, which historically has been used to minimize the loss of electrons during the energy production process. But aluminum, when interacting with silicon, can create enough stress to bow or break silicon wafers, particularly with the use of thinner silicon wafers. As solar companies look at using thinner silicon wafers to reduce costs, they also are considering using boron to replace aluminum to reduce breakage. Using boron also improves the efficiency of the front side of the cells to convert sunlight into energy, Kofman said.

But boron doesn’t make an easy substitute, or else bifacial cells would have become widely available by now. Getting the boron layer right during solar cell production is difficult, Kofman noted.

A solar panel with bifacial cells requires different designs than traditional solar panels. For example, a conventional silicon solar panel is covered in layers of polymer materials to protect solar cells and a piece of glass as the top cover to let the light in. The same or similar setup will have to need to be created to cover the backside of the panel, said Bhushan Sopori, a researcher at the National Renewable Energy Laboratory.

“The technologies are there. The big question is the additional costs of doing it – how much reflected light can be harvested and do the benefits justify the cost?” Sopori pointed out.

Companies that have been working on bifacial cells include Sanyo (now part of Panasonic) in Japan and Shinsung in Korea. Sanyo’s cells are silicon wrapped with amorphous-silicon layers, and the design is very different than what bSolar and others are creating.

BSolar is making bifacial solar cells with monocrystalline silicon wafers, which are harder and more expensive to make, but they also can convert a higher rate of sunlight into electricity than the more popular multicrystalline silicon. Solar panels with bSolar’s bifacial cells could produce 20-25 percent more energy than single-sided solar panels when they are installed on a flat rooftop, the ideal setting for getting the most reflected light, Kofman said.

The startup has a 30MW factory in Germany that it acquired from Systaic during a bankruptcy proceeding, said Kofman, who declined to disclose the company’s production cost. BSolar has only raised $10 million in venture capital since its inception, including $3 million from Genesis Partners and some investors from Japan, Kofman said. That $10 million is awfully low to bring a technology into commercial production, even though bSolar is using mostly standard factory equipment. Kofman wouldn’t say whether the company used any part of the $10 million to buy the German factory.

Solar panel makers who have agreed to give bSolar’s cells a shot include Aleo Solar, Asola Solarpower and Solar-Fabrik.

Photos courtesy of bSolar