Excerpt from: building green elizabeth kibler one of the biggest impacts a building has on earth is the energy it uses. currently, most of the world’s energy comes from burning fossil fuels. these fuels are dirty and when they are burned they pollute the air and water. one way to burn fewer fossil fuels is to reduce the amount of electricity a building has to use. passive solar heating, which uses heat from the sun, reduces the amount of fossil fuel used to heat buildings. passive solar heating requires a south-facing wall made of glass. when sunlight shines through the wall, it is collected and used to warm the building. another way green buildings reduce their electricity use is to install other energy sources. for example, some green buildings use panels that turn energy from the sun into useable electricity. what system uses heat from the sun? a) gray water system b) low-flow toilets c) passive solar heating d) green roofs and walls