Li/I/sub 2/ electrochemical engines both store and generate electric power. These dual capabilities complement solar photovoltaic generation in critical areas: Photovoltaics need backup storage at least for nights and, if possible, for two or three days' needs. Such storage must be relatively cheap and compact--aqueous batteries would have trouble filling these requirements. Likewise, photovoltaics need backup generation based on combustion of fossil fuels for periods of bad weather--solar residences or communities will probably have to supply their own backup generation because central generating stations cannot be expected to keep large amounts of equipment on standby for solar users. Li/I/sub 2/ engine designs are described which could be developed to fill these needs of solar users, i.e., storing electricity generated by photovoltaics and generating additional electricity from fossil fuels as needed. Calculations based on laboratory performance indicate that the devices could be simple to manufacture, economically competitive, and efficient both in storage and generation. These engines also could directly use solar energy from focused and tracking solar collectors, or they could indirectly use solar energy through the combustion of biomass materials
