Photovoltaic panels (PF), combined with lead-acid battery (AE), are increasingly used, to produce electricity. To work in maximum power points, between (PF) and (AE) is interposed a static converter (DC-DC), which is a harmonic pollution source. Within the paper there are calculated the power losses, due to current harmonics, of a photovoltaic system working at its maximum power. Photovoltaic system works at its maximum power, if in the electronic system there is permanently voltage control among solar battery terminals.