Simulations are tools of major importance in the design of solar energy systems. Only with simulations can a variety of system designs be studied and evaluated in a comparative way. Simulations are used both for systems research and as a design tool for large, one-of-a-kind systems using programs such as TRNSYS. Simulations are also the basis for development of quick design methods for standard system configurations for solar heating; these quick methods are also programmed for easy use in combination with economic analyses (e.g. f-chart).