Characterization of indoor photovoltaic devices and light

Indoor photovoltaic (ipv) is a growing market area due to increasing numbers of wireless sensor node networks in green and intelligent buildings. The sensor nodes should be powered without batteries or wiring in order to reduce cost. One of the most promising sources of energy is light. Results of radiometric measurements depend on the test environment. However, the expected irradiance is essential for the dimensioning of the required module area and a reliable operation. Ipv designers therefore need a tool to determine irradiance values for their applications. This paper presents a simulation method for indoor irradiance combining different models of user presence, and the ray tracing programs Radiance and DAYSIM. The authors analyze a best case and a worst case scenario. Typical values of irradiance for these scenarios, the influence of the latitude and of the orientation, of the contribution of electric light in dependence of user presence, and the required complexity of a simulation model are discussed. Based on these studies, the authors provide expectable power densities for ipv devices.