Read the passage, then answer the questions below (2.5pts)

Are you looking for a cheap, clean, effective source of power that doesn't cause pollution or waste natural resources? Look no further than solar energy from the Sun.

At present, most of our electricity comes from the use of coal and gas, oil or nuclear power. This power could be provided by the Sun. One percent of the solar energy that reaches the Earth is enough to provide power for the total population.

Many countries are already using solar energy. Solar panels are placed on the roofs of a house and the Sun's energy is used to heat water. The energy can be stored for a number of days, so on cloudy 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 will use solar power instead of gas by the year 2015.

Questions: Where are the solar panels placed?