The full power generating a capacity of your solar panels is accomplished just when the sun shines opposite to the board, from straight overhead. Something else, as the angle of the sun changes, less power is created. A few frameworks utilize “trackers” which gradually pivot the panels with the goal that they generally face the sun. A few systems utilize mirrors to shine more light onto a similar panel to build the power output. They create less as the panels age over their lifespan (which could be as much as 50 years).

Depending upon what scope your house is at, the length of daylight changes throughout the year. Moreover, climate and clouds significantly reduce solar panels output. Every such factor must be consolidated to frame a yearly normal derating factor appropriate for your home location and introduction. In this manner, your derating would be 4 hours isolated by 24 (hours in multi-day) giving 16.6%.

An overall average system efficiency of 66% is used in the example calculations to account for the following:

88% derate for energy lost due to module heating (12% loss)

95% for inverter efficiency (5% loss)

97% for DC and AC wiring inefficiencies (3% loss) 

95% for module production tolerance and mismatch (5% loss) 

95% for module power loss due to dust and dirt (5% loss)

90% shade factor to account for array shading before 8 a.m. and after 4 p.m. (10% loss)

To arrive at 0.66 (66%), multiply all the efficiency factors together:

0.88 × 0.95 × 0.97 × 0.95 × 0.95 × 0.90 = 0.66

While this 0.66 is a general value used for estimating a battery less PV grid-tied array’s size, a derate factor can be adjusted to match each system and site specifics. For the next example, let’s say the array will consist of micro inverters, which will eliminate losses due to module mismatch, and will use modules that have a positive-only production tolerance. In this case, the module production tolerance and mismatch loss will be zero (or will have an efficiency of 100% for a factor of 1.0), increasing the overall efficiency factor to 69%.

0.88 × 0.95 × 0.97 × 1.00 × 0.95 × 0.90 = 0.69

Conversely, let’s go back to the original string inverter and after performing a shade analysis on the roof, we find that the solar window is really from 8:30 a.m. to 3:30 p.m. and the shading factor is 0.85. This will decrease the efficiency factor to 62%.

0.88 × 0.95 × 0.97 × 0.95 × 0.95 × 0.85 = 0.62