Article published Photovoltaic modules
The solar panel in lighter mode
Together with the companies Apollon Solar and Vincent Industries, the LITEN is developing a new type of photovoltaic module, without resin or welding. The advantage is a reduction in cost without loss of performance.
Although solar energy benefits from an associated proactive policy, the costs of photovoltaic devices remains high. Hence, for an individual house, installation of solar cells takes more than six years to become profitable. The principle objective for research carried out on solar modules is reduction of manufacturing costs. Traditional modules consist of a stack of diverse components. “Photovoltaic cells are enrobed with ethylene vinyl acetate (EVA) resin, whose role is to increase the robustness of the solar panel and to avoid humidity penetration, while satisfactorily preserving the electrical and optical properties”, explains Eric Pilat, a researcher at the LITEN. However, EVA is an expensive material which leads to the use of welds. These have their own problems when it comes to linking the cells together. There is also an issue with recycling materials. Finally, EVA is sensitive to UV light and so filters must be attached to absorb that part of the solar spectrum. This alters the overall performance of the cell.
This is where the interest in Apollon Solar's patent arose, the development of which is been continued at the LITEN. The idea is to replace the EVA resin with a simple joint and to use a relative internal depression to ensure electrical contacts. The joint, which is made from polyisobutylene (PIB), was inspired by joints used in double glazing. “The principle is somewhat similar to a gherkin bottle: the joint is applied and closed, a pressure drop is created and it is sealed!”
In January the CEA took delivery of a prototype manufactured by Vincent Industries. The aim is to develop a robust process which is directly transferable to industry. Researchers have optimised the robustness of PIB by reducing the damage which occurs to cells during the pressurisation, while guaranteeing optimal leak tightness. To make the cells pressure resistant, it is imperative that the copper blades are perfectly positioned to avoid any shearing effects. “To achieve this, we added an elastomer cushion which minimises any shearing force experienced by the cell.” The formulation of the joint itself has been optimised, in collaboration with a resin manufacturer, so that it does not exhibit any bubbles which could harm the bond to the substrate. In parallel, a test bench has been developed to study and possibly improve the sealing of the joint, using a mock-up.
The CEA teams are also looking at ways to optimise performance of the device. In particular they wish to compensate the energy lost through reflection of the solar spectrum which is linked to the absence of encapsulating material: an antireflective layer for improving the optical properties of the module is under development. In the meantime, a 2,000 Watt solar device has been manufactured and will be tested by exposure to sunshine on the Ines* site at Chambery. The first results were favourable, with 12.5 % efficiency.
* National Solar Energy Institute
