solar cells can be used to power tools or to recharge a storage battery. the first actual request of photovoltaics was to power orbiting satellites and other spacecrafts, but today the most photovoltaic modules are used for grid connected power creation. in this case a tool called an inverter is required to convert the direct current to alternating current. cells require protection from the environment and are usually packaged tightly behind a glass sheet. when more power is required than a single cell can give off, cells are electrically connected together to form photovoltaic modules, or solar panels. a single module is enough to power an emergency telephone, but for a house or a power station the modules must be arranged in multiples as arrays.