Passive and active residential solar heating: A comparative economic analysis of select designs

This paper compares four passive solar heating concepts to a conventional air collector/rock storage system. Masonry (Trombe) and water walls are considered in the presence and absence of night insulation. The performance of optimally sized systems is evaluated on a state-by-state basis. The effects of low interest loans and National Energy Act (NBA) income tax credits are examined. With natural gas as the alternative fuel, the passive designs evaluated here offer more promise than the active system. This is true with or without inclusion of incentives, although either incentive option enhances economic performance. The passive designs evaluated in this paper are economically competitive against the electric resistance alternative in all but a few states. Moreover, on a life cycle cost basis, these designs are feasible today. Although the optimal solar fractions are generally low, passive designs offer the opportunity to incorporate solar heating into a new home at costs much less than their active counterparts. This is because there are no discernible fixed costs, thereby allowing a simple movement from zero to 100% solar when evaluating economic feasibility. When both active and passive design are shown to be cost competitive against alternative fuels, higher solar fractions will be associated with the active systems. This is principally due to the substantial fixed cost component of active systems, which forces one to achieve a given solar fraction before economic feasibility can be shown.