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Project: STREET: high-efficiency solar cells for electric utility vehicles

The joint project STREET investigates the benefit-cost ratio of vehicle integrated photovoltaics (VIPV) on electric utility cars to unveil environmental and economic advantages. VIPV provide electrical power without any CO2 emission making it possible to supply electric cars with 100 % emission free power. Especially for delivery cars, which make up an increasing proportion of city traffic, solar power can provide a significant amount of energy due to the large available area on the car top and in this way reduce the CO2 pollution of the cities. The project employs high-efficiency crystalline Silicon solar cells since they offer a good compromise between manufacturing costs and energy generation. These cells enable the minimization of the electricity generation costs (€/kWh) of VIPV in comparison to other technologies (e.g. III/V photovoltaics).

The project follows three iterative steps in which solar modules are mounted on the top and sides of an e-transporter from the company Streetscooter. The first iterative step uses Silicon heterojunction (SHJ) solar cells as generation#1 cells which are manufactured by the project partner Meyer Burger (Germany) and reach conversion efficiencies of 22.5 %. The components of the prototype VIPV are further developed on the basis of test results obtained in test drives and single module tests. In the second iterative step the solar cells are substituted by SHJ solar cells offering higher efficiencies of 23 %. The increase in efficiency of the generation#2 cells is achieved by further development of highly transparent window layers on the basis of nano-crystalline Silicon-oxide and Indium Tungsten-oxide layers. The final step integrates polycrystalline Silicon on oxide interdigitated back-contact (POLO-IBC) solar cells into the modules, which reach effiencies over 25 % in the laboratory. Bypass-diodes are further added to the generation#3 cells to achieve an additional energy yield under partial shadowing of the modules, which occurs during driving. The test results collected in every step are further used to generate an energy profit model.

The consortium of STREET consists of eight partners from leading companies and institutes in the photovoltaics and (electric) automotive industry. Together, the partners provide the complete value-added chain of VIPV: manufacturing and development of solar cells (ISFH, MBE, Jülich, HZB, MBG), solar cell strings (MBG, ISFH), solar modules (a2-solar), integration into on board power system (Continental) and into the vehicle (Streetscooter).