Photovoltaic technology, which converts solar energy into a usable source, has not been widely applied to railway carriages. It can lead to considerable reductions in greenhouse gas emissions: for each kWh of energy produced by traditional plants, a reduction of 750g carbon dioxide emitted into the atmosphere is achieved with the photovoltaic modules. Applying photovoltaic modules to rolling-stock also has the potential to reduce dangerous waste by extending the life of accumulators. The current practice is to use a buffer system fed by a continuous current. Suspension of the energy supply sets off the accumulators which continually recharge when run down. In a photovoltaic system, however, accumulators are kept continually charged by solar energy and, as a result, are subject to less damage.