The initial cost of passive design elements depends on the element. Some cost the same (e.g.,
light exterior walls for cooling) or only slightly more than conventional building costs (e.g., light
shelves designed to control sun penetration). Some cost considerably more (e.g., interior thermal
mass materials such as stone and brick). However, these measures can lower operating costs.
Compared to passive solar systems, active solar systems often have a higher initial cost and
longer payback period, which vary widely depending on the size and the specific type of
technology used.6 However, current federal and state tax credits and rising energy costs make
active solar systems an economic alternative to conventional systems.