Energy Input Sunlight kWm maximum

System Boundary

20 m2 3 kW maximum

Roof-mounted moc

Roof-mounted moc

Figure 1. Residential photovoltaic energy system schematic.

Photovoltaic (PV) modules are large-area solid-state semiconductor devices that convert solar energy directly int o 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/m2) of sunlight, the operating temperature of the 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 th e photovoltaic system.

A residential PV system was selected for this Technology Characterization because it is a well-defined application o f the technology, it can have a significant impact on energy use within the United States, and it is an application tha t 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 int o the existing utili ty grid. These PV systems are generally between 1 and 5 kW, and the nominal system considered i n this report is 3 kW. (In reality, for this characterization, the system size is held constant at 20 m 2 and the dc rating 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 th e future, by about 2020, advanced PV technologies - crystalline-silicon ribbon or sheet, and various thin-film (amorphous silicon, cadmium telluride, or copper indium diselenide) materials may be used. While no energy storage is include d in the system presented here, energy storage may become economical in the future. The PV modules described her e are wired to a single dc-to-ac inverter or, in the future, may include their own individual dc-to-ac inverter. The a c power is tied to the grid through protective switches which disconnect the PV system should the utility power b e 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 here - that for a single homeowner, who finances and owns the system - and th e neighborhood bulk system by a utility or other generating company which installs PV systems on the roofs of man y clustered customers. For the latter, the utility finances and owns the systems and achieves certain economies of scal e in capital cost, installation, and operations and maintenance (O&M).

Getting Started With Solar

Getting Started With Solar

Do we really want the one thing that gives us its resources unconditionally to suffer even more than it is suffering now? Nature, is a part of our being from the earliest human days. We respect Nature and it gives us its bounty, but in the recent past greedy money hungry corporations have made us all so destructive, so wasteful.

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