Solar energy has been widely promoted as a method of reducing the nation's fossil fuel consumption. Usually, the calculation of energy savings includes only direct energy, i.e. direct use of such items as gasoline, natural gas, heating oil, and electricity. However the purchase of a non-energy product requires energy use somewhere in the economy. For example, a pane of glass is not an energy product, yet requires energy to produce it as well as energy to produce the equipment that produces the glass, and so on. The energy required to support non-enrrgy purchases is called indirect energy. Americans use more energy indirectly than directly so energy analyses should include indirect energy. Several studies have investigated the total (direct plus indirect) energy used by solar energy systems.

Unfortunately, comparison between different solar energy systems is difficult because the parameters are so different in each study. Therefore this study will calculate the total energy costs of seven different conceptual houses that are exactly the same except for the system used to heat them. Included are two fossil fuel systems, two active solar energy systems, and three passive solar energy systems. The results show how much energy different solar systems will save and how much energy is required to build different solar systems.