Economic Feasibility of Retrofit Solar Hot Water Systems

Abstract

This paper presents the results of an economic feasibility study of 177 public buildings (schools, hospitals, local government buildings, and public care facilities) in the Commonwealth of Virginia to determine if active flat-plate solar collector systems could economically augment or replace existing hot water heating installations. Utilizing the F-CHART method and life-cycle costing techniques, two collector areas were determined for each facility: the optimum collector area (where the present worth of the lifetime net savings was maximized) and the maximum collector area (where the amount of solar energy that could be utilized without losing money was maximized). Solar systems that would pay for themselves within 25 years could be installed in 77 of the 177 buildings (43.5%), with a mean discounted payback period of 17.7 yr. These units would provide 78.8% of the facilities' hot water loads. The study also reveals that for a given fuel cost, the collector areas of these systems are directly proportional to the total hot water loads. In addition, the shortest discounted payback period of an optimally designed solar system may be obtained directly from the fuel cost. These relationships could lead to simplified sizing techniques for active solar hot water system retrofits.