Friday, July 21, 2017

Solar Panels need to be positioned just right to maximize power harvesting.

The current and power output of RENOGY 100W are approximately proportional to the sun’s intensity. At a given intensity, a solar panel's output current and operating voltage are determined by the characteristics of the load. If that load is a battery, the battery's internal resistance will dictate the module's operating voltage.

A solar panel, which is rated at 17 volts will put out less than its rated power when used in a battery system. That’s because the working voltage will be between 12 and 15 volts. Because wattage (or power) is the product of volts multiplied by the amps, the module output will be reduced. For example, a 50-watt solar panel working at 13.0 volts will products 39.0 watts (13.0 volts x 3.0 amps = 39.0 watts). This is important to remember when sizing a PV system.

An I-V curve (see image on right) is simply all of a RENOGY 100W possible operating points (voltage/current combinations) at a given cell temperature and light intensity. Increases in cell temperature increase a solar panel’s current slightly, but significantly decrease voltage output.

PV solar panels are very sensitive to shading. Unlike solar thermal panels used in hot water heating that can tolerate some shading, many brands of PV solar panels cannot even tolerate shading from the branch of a leafless tree.

Shading obstructions can be from “soft” or “hard” sources. If a tree branch, roof vent, chimney or other item is shading from a distance, the shadow is diffuse or dispersed. These soft sources significantly reduce the amount of light reaching a solar panel’s cells. Hard sources are defined as those that stop light from reaching solar cells, such as a blanket, tree branch, bird dropping sitting directly on top of the glass. If even one full cell is hard shaded, the voltage of that module will drop to half of its un-shaded value in order to protect itself. If enough cells are hard shaded, the module will not convert any energy and will, in fact, become a tiny drain of energy on the entire system.

Tilt Angle

To capture the maximum amount of RENOGY 100W over the course of a year, a solar array should be tilted at an angle approximately equal to a site's latitude, and facing 15 degrees of due south. To optimize winter performance, the solar array can be tilted 15 degrees more than the latitude angle, and to optimize summer performance, 15 degrees less than the latitude angle. At any given instant, an array will output maximum available power when pointed directly at the sun.

To compare the energy output of your array to its optimum value, you will need to know the site's latitude, and actual tilt angle of your array--which may be the slope of your roof if your array is flush-mounted. If your solar array tilt is within 15% of the latitude angle, you can expect a reduction of 5% or less in your system's annual energy production. If your solar array tilt is greater than 15 degrees off the latitude angle, the reduction in your system's annual energy production may fall by as much as 15% from its peak available value. During the winter months at higher latitude, the reduction will be greater.