For a continuous energy supply of photovoltaic operated and off-grid loads, the storage of the solar generated electrical energy is necessary. About 60% of all over the world manufactured solar cells are used for such stand alone systems. In case of photovoltaic systems, mainly electrochemical battery storage systems are used. The paper describes the requirements for batteries in solar systems. The most important storage systems, such as lead-acid, NiMH and Li-ion batteries are described in detail and further developing trends are discussed. As it is well known that the operation conditions strongly influence the battery lifetime, this paper reviews photovoltaic operation conditions and experience in performance and lifetime in photovoltaic systems. (C) 2004 Elsevier Ltd. All rights reserved.