Photovoltaic Panels Installation Design Guide
Photovoltaic (PV), also known as solar panels, are modules that use silicone and wires to convert sunlight into an electrical current. Each module generates and circulates an electric current and modules are interconnected into metal-framed panels that are installed in an array, usually on top of a roof to collect as much sunlight as possible. A few key design considerations must be considered for solar energy success.
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Electrical Current
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An electrical current is the electrical charge that flows through wires. All modules and panels connected together must carry the same current or they will cease to operate after the failure point. It is the same process that occurs when one Christmas light bulb goes out along the line and the rest that occur after that light bulb fail to light. All PV modules and panels must be connected in a series that carries the same current. Because light affects the amount of current flowing, all PV materials must be placed on the roof so they get the same amount of light. Bypass diodes can be used to create alternate current paths in case of shading at different times of year, but it is best to research and address seasonal changes in foliage and sun angles before installing panels. Bypass diodes do not prevent failure, they just delay it.
PV Panels and Heat
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PV panel electrical output has an inverse relationship to heat; the greater the temperature is, the lower the output. Sunlight naturally heats the silicon surface. To increase efficiency of output, it is necessary to allow air to circulate around panels, cooling them for greater output. Mount panels at least 3 inches off the roof to create a clean air flow path under the array. The panels will operate under cooler temperatures.
Azimuth
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Azimuth is the horizontal angle measured in degrees clockwise from a northern or southern point. In the northern hemisphere, correct azimuth for sunlight to reach panels for the longest time is true south. Plus or minus 20 degrees from true south will not affect annual energy production too much and west of true south takes advantage of afternoon sun and peak load demands.
In addition to aligning to true south, tilting the angle of PV panels on your roof will provide the most energy output over the full year. The best tilt angle is aligned with your latitude. Wind load requirements in your region supersede tilt angle output considerations.
Mounting Hardware
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Use the mounting hardware that comes with your PV panels because it has specific design features for proper PV functioning. Roof mounting is complex because of electrical current flow, bypass diodes, tilt angle and wind load requirements. Roof seal penetration and resulting leaks are inevitable. If possible, hire certified installers, trained under the National Electrical Code Article 690 Solar Photovoltaic Systems.
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