Sometime people ask why does a solar panel in an array operate at different voltage and current level, the answer probably is simply how the solar panel are made. Current technology involved in the panel manufacturing produces solar module with a set of characteristic known as panel specification sheet. It may look intimidating initially, but there are only four to six pieces of data you need to take note of (rest is for the electrician to use during installation), one of the factor that play an important role is power tolerance. Power tolerance is a measure of actual range a module can deviate from its specified STC max power. STC is the standard test condition under which the panel is lab tested.
One of the purposes of power tolerance is to estimate how much electrical power a solar panel can produce. For example, a power tolerance of -10% / +10% on a 330-watt peak (Wp) panel tells you the panel could produce 297 W to 363 W under real-world conditions. Leading tier 1 panel manufacturers uses state of the art technology to reduce these deviations. As the technology behind solar panel manufacturing continues to advance, it is becoming more common for panels to have zero percent negative power tolerance, meaning it will always produce power equal to its maximum rated power at STC.
It is a factor worth considering while purchasing solar panels. Any variation in the power output directly impacts revenue generation. A smaller power tolerance range promises more accuracy.
Power tolerance is specific to each solar panel series (product line), as mentioned in the respective product data sheet. Solar panels are segregated after manufacturing. To understand why, consider an example where for the same rated power of 300 W, two panels having -5% / 5% power tolerance operate at different level of electrical output range: i.e., at 285 W and 315 W. One may operate at a current of 11.4 amps and a voltage of 25 volts (25 x 11.4 = 285 W), and the other may take 12 A and 26.25 V (26.25 x 12=315 W).
When solar panel is connected in series voltage drops across each panel adds up but by producing power at different current levels it generates system losses which is known as solar panel mismatch and also accelerates solar panel degradation. Hence it is important for solar panels in an array to operate at near equal current levels to incur lesser losses and prevent degradation of solar panels.
A solar panel’s production varies according to sun irradiance and environmental conditions. To achieve maximum power output every system has an optimal voltage-current combination know as maximum power point (MPP). A combination of voltage and current can be varied by changing the resistance of the system. So if there are three data sets (V,I): (35V,8A), (36V,9A) & (38V,7A), then the second condition yields maximum power production (324W = 36 X 9). This point can be identified as the maximum power point. An MPP tracker is a device that combines a series of solar panels with mismatched current and finds the effective MPP at the string level.
To ensure your panels perform as expected, Rigava solutions recommends only considering tier 1 make Solar Panels with positive tolerance while developing solar power plants and use module level DC to DC optimiser to reduce the energy loss. For help decoding your specification sheet, or to learn more about solar for your home or business, give Rigava solutions a call on 91 9137074775, or Click here!!
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