Boston solar retrofits: studies of solar access and economics

Abstract

Studies of solar access and solar retrofit economics are described for residential applications in the City of Boston. The study of solar access was based upon a random sample of 94 buildings; the sample was stratified to ensure a broad geographic representation from the city's various sections. Using available data on the heights and orientations of the sampled structures and surrounding buildings, each building's hourly access to sunlight was computed separately for the roof and south facing walls. These data were then aggregated by broad structural classifications in order to provide general measures of solar access. The second study was a comparative analysis of the economics of several solar heating and hot water systems. An active hot water system, installed using pre-assembled, commercially purchased equipment, was selected as a reference technology. A variety of measures of economic performance were computed for this system, with and without existing tax credits and under various financing arrangements. Next, a number of alternative approaches for solar space and water heating were identified from interviews with individuals and groups involved in solar retrofit projects in the Boston area. The objective was to identify approaches that many of those interviewed believe to be low-cost means of applying solar energy in residential settings. The approaches selected include thermal window covers, wall collectors, bread box water heaters, and sun spaces. Preliminary estimates of the performance of several representative designs were developed and the economics of these designs evaluated.