This module on solar system economics is one of six in a series intended for use as supplements to currently available materials on solar energy and energy conservation. Together with the recommended texts and references (sources are identified), these modules provide an effective introduction to energy conservation and solar energy technologies. The module is divided into these sections: (1) set of objectives; (2) programed instructional material, consisting of short readings describing ideas and techniques one step at a time, and a question or problem on each reading; (3) review questions and answers at intervals; and (4) posttest. Objectives for this module are for the student to be able to discuss major ideas involved in life cycle costing of combination solar and conventional heating systems and compare life cycle costs of conventional and combination solar/conventional heating systems. (YLB)