Photovoltaic Roofs speaks to what are photovoltaic roofs and why photovoltaic roofs.
(PV) materials are metal panels or shingles of asphalt slate, fiber cement or metal laminated with thin film semiconductor materials and capable of converting solar radiation into electrical energy.
When they are installed as part of a building integrated photovoltaic (BIPV) system, the electricity produced by these materials can be used to power a building’s own equipment and systems or where permitted by the public power utility, can be sold back to the utility to offset power consumption charges. Electrical power from BIPV systems is produced without pollution or the depletion of natural resources.
The essential components of a BIPV system are an array of PV modules (the PV roofing material), controller equipment to regulate the current generated by the modules, and an inverter to convert the direct current (DC) output of the modules to alternating current (AC) compatible with the conventional building power.
Standalone or off grid BIPV systems which are systems, not connected to the public utility grid also require a power storage system, usually in the form of rechargeable batteries and often also include a backup power system such as diesel generators.
Estimating the potential power contribution of a BIPV system and evaluating its potential economic payback for a particular project require an analysis of the project’s geographic location, solar exposure, projected power needs, utility costs and additional factors.
A solar panel (also solar module, photovoltaic module or photovoltaic panel) is a packaged, connected assembly of photovoltaic cells. The solar panel can be used as a component of a larger photovoltaic system to generate and supply electricity in commercial and residential applications.
Each panel is rated by its DC output power under standard test conditions, and typically ranges from 100 to 320 watts. The efficiency of a panel determines the area of a panel given the same rated output - an 8% efficient 230 watt panel will have twice the area of a 16% efficient 230 watt panel. Because a single solar panel can produce only a limited amount of power, most installations contain multiple panels.
A photovoltaic system typically includes an array of solar panels, an inverter, and sometimes a battery and or solar tracker and interconnection wiring.
Solar panels use light energy (photons) from the sun to generate electricity through the photovoltaic effect. The majority of modules use wafer-based crystalline silicon cells or thin-film cells based on cadmium telluride or silicon. The structural (load carrying) member of a module can either be the top layer or the back layer. Cells must also be protected from mechanical damage and moisture. Most solar panels are rigid, but semi-flexible ones are available, based on thin-film cells.
Electrical connections are made in series to achieve a desired output voltage and/or in parallel to provide a desired current capability. The conducting wires that take the current off the panels may contain silver, copper or other non-magnetic conductive transition metals. The cells must be connected electrically to one another and to the rest of the system. Externally, popular terrestrial usage photovoltaic panels use MC3 (older) or MC4 connectors to facilitate easy weatherproof connections to the rest of the system.
Bypass diodes may be incorporated or used externally, in case of partial panel shading, to maximize the output of panel sections still illuminated. The p-n junctions of mono-crystalline silicon cells may have adequate reverse voltage characteristics to prevent damaging panel section reverse current. Reverse currents could lead to overheating of shaded cells. Solar cells become less efficient at higher temperatures and installers try to provide good ventilation behind solar panels.
Some recent solar panel designs include concentrators in which light is focused by lenses or mirrors onto an array of smaller cells. This enables the use of cells with a high cost per unit area (such as gallium arsenide) in a cost-effective way.