Batteries possess direct current power (DC), which the solar panel also generates. For feeding power to appliances, DC energy cannot be used on its own, as electric appliances run on alternating current for which one needs an inverter, for converting direct current into alternating current to make it usable. http://www.vaticanroom.it/index.php?option=com_k2&view=itemlist&task=user&id=1076531