Many countries are already using (1)_________ energy. Solar (2)_________ are placed on the roofs of a house and the Sun’s energy is used to (3)_________ water. The energy can be stored for a number of days, so on (4)_________ days you can use solar energy, too. Sweden has an advanced solar energy program. There, all buildings will be heated by solar energy and cars (5)_________ solar power instead of gas by the year 2015.