A new version of the ENERGY-10 computer program simulates the performance of photovoltaic systems, in addition to a wide range of opportunities to improve energy efficiency in buildings. This paper describes two test cases in which the beta release of ENERGY-10 version 1.4 was used to evaluate energy efficiency and building-integrated photovoltaics (BIPV) for two Federal building projects: a 16,000-ft2 (1,487 m2) office and laboratory building at the Smithsonian Astrophysical Laboratory in Hilo, Hawaii, and housing for visiting scientists [three 1400-ft2 (130 m2) and three 1564-ft2 (145 m2) houses] at the Smithsonian Environmental Research Center in Edgewater, Maryland. The paper describes the capabilities of the software, the method in which ENERGY-10 was used to assist in the design, and a synopsis of the results. The results indicate that ENERGY-10 is an effective tool for evaluating BIPV options very early in the building design process. By simulating both the building electrical load and simultaneous PV performance for each hour of the year, the ENERGY-10 program facilitates a highly accurate, integrated analysis.