Residential photovoltaics

Abstract

Photovoltaic (PV) modules are large-area solid-state semiconductor devices that convert solar energy directly into electrical energy. Individual PV modules produce direct-current (dc) electricity, and are available in sizes from 10 W to 300 W. The actual power output depends upon the intensity (W/m ) of sunlight, the operating temperature of the 2 module, and other factors. PV modules are designed and sized to produce the desired electrical output. Addition of electrical power conditioning components (electrical switches, diode protection circuits, dc-to-ac inverters, etc.) are required to interface the PV output with the electrical load. The resulting assembly of components is known as the photovoltaic system. A residential PV system was selected for this Technology Characterization because it is a well-defined application of the technology, it can have a significant impact on energy use within the United States, and it is an application that effectively utilizes the attributes of PV systems for maximum economical benefit. Customer-sited, grid-tied PV systems are expected to be an early large-scale market for PV energy systems, because these systems take maximum economical advantage of PV technology's positive attributes. Customer siting means that the PV systems is located at, or very near, the point of use, and includes applications like residential roof-top PV systems, commercial-building roof PV systems, and building-integrated PV systems. This report examines residential PV systems, but many of the comments pertain to other types of customer-sited PV systems as well.The residential rooftop PV system (Figure 1) considered in this report has no energy storage. Some (or most) of the energy may be used on site, and a power purchase agreement allows the remaining electricity produced to be fed into the existing utility grid. These PV systems are generally between 1 and 5 kW, and the nominal system considered in this report is 3 kW. (In reality, for this characterization, the system size is held constant at 20 m and the dc rating 2 increases over time to 4 kW). The PV modules are mounted on the roof or, in the future, may be specifically designed as roofing elements (e.g., PV shingles, etc.). The modules characterized here use crystalline-silicon solar cells. In the future, by about 2020, advanced PV technologies -crystalline-silicon ribbon or sheet, and various thin-film (amorphous RESIDENTIAL PHOTOVOLTAICS4-6 silicon, cadmium telluride, or copper indium diselenide) materials may be used. While no energy storage is included in the system presented here, energy storage may become economical in the future. The PV modules described here are wired to a single dc-to-ac inverter or, in the future, may include their own individual dc-to-ac inverter. The ac power is tied to the grid through protective switches which disconnect the PV system should the utility power be disrupted. The system costs described here do not include the roof or the building, which are assumed to already exist.Two sets of systems are described ...