Double sided, or bifacial solar panels cannot only capture light on the front side but also on the rear side of the panel and transfer this into electricity. With bifacial solar panels (PV) we can increase electricity 10% to 20%. This can lower the costs of electricity tremendously. For example, PV installations or projects can produce the same amount of electricity on a smaller roof surface, or fewer PV modules and system components are needed on the same ground surface, so more light and rainfall remains available for ecology.

TNO develops knowledge and technology for bifacial solar panels and a complete energy yield prediction model.

Predict energy yield

To accurately predict the energy that will be generated by a PV system consisting of bifacial modules, TNO has developed a very advanced - and to our knowledge the most complete - PV system simulation model, called BIGEYE. With BIGEYE, PV systems of any configuration, at any location on earth can be simulated. Using weather and environmental data, the electricity produced can be calculated on an hourly, daily, monthly or yearly basis.

For PV installers, project developers and systems owners it will be of great value to know the electricity generation profile accurately in order to provide optimal connections to the local, national or global electricity grid. Furthermore, BIGEYE can be used to design PV systems in such a way that the generated power better matches the daily need, for instance by increasing generation in mornings or afternoons.

A bifacial PV panel generally consists of 60 or 72 bifacial solar cells. These cells have an almost identical metal grid on the front and rear side, which leaves more than 95% of both areas open to catch the light. Bifacial panels are installed in regular PV power plants, but also in upcoming market segments such as infrastructure integrated PV, for example noise barriers and so-called floated PV on open water or dual-use hydro- or aquaculture farms.

Cross section of TNOs polysilicon based passivating contact solar cell

TNO develops knowledge and technology for bifacial PV on cell, module and system level. We are working on several new cell concepts that aim to increase the efficiency while also reducing the manufacturing costs. One of our novel bifacial solar cell concepts is the industrial TOPCon solar cell. This cell has special interface layers on the rear side, i.e. very thin oxide and polysilicon, which reduce the losses. This cell concept is co-developed with, amongst others, Tempress Systems in a TKI Urban Energy subsidy project as well as in some commercial projects. The technology is accepted by the solar cell industry and cell efficiencies of over 23% are achieved in industrial manufacturing lines.

With bifacial modules light from all directions can be captured

One of the latest bifacial cell concepts employs very thin metal oxide layers as interfaces layers. These layers can be applied on both sides and have the same electrical quality as those in the TOPCon solar cell. In addition, they are very transparent, thus increasing the amount of sun rays that can be harvested. This also increases the bifaciality, but at the same time, the production process becomes, in principle, less complex thus cheaper. The concepts is still under development, in close collaboriton with Solmates, Levitech and the universities of Eindhoven and Delft. We expect that the efficiency of the cells can increase significantly, potentially beyond 25%.

TNO designs and develops bifacial modules to comply with specific requests: for instance reduced silver consumption to optimize cost and performance under lower light conditions, the use of various light trapping materials to improve light coupling in and on the modules, and solutions for cell and bypass diode positioning to account for increased shading due to robust frames, e.g., in solar noise barriers. TNO has also developed a novel bifacial solar panel design with a white layer around the cells. These bifacial solar panels show a 5% increase in energy yield compared to bifacial panels with only transparent glass and polymer layers around the solar cells. 

More info about bifacial solar panels?

Contact Bas van Aken

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