Occasionally a Sales Rep will chat in about why the 1st year System Production changed. The reason they will want to know this is because it affects the Offset. System Production is a complex calculation that involves several factors.

Globally a formula E = A x r x H x PR is followed to estimate the electricity generated in output of a photovoltaic system.
​
E is Energy (kWh), A is total Area of the panel (m²), r is solar panel yield (%), H is annual average solar radiation on tilted panels and PR = Performance ratio, constant for losses (range between 0.5 and 0.9, default value = 0.75). r is the yield of the solar panel given by the ratio : electrical power (in kWp) of one solar panel divided by the area of one panel.

The question brought up in chat was about panels because the Sales Rep switched from 360w panels to Tesla 435w panels, reduced the panel count by 3 to keep system size small and cost down and wanted to know why the production went down which obviously changed the Offset. According to the formula, A is total area of the panel. Even though the wattage on the panel was higher, reducing the area of the collective system affects production.

There are also other variables that will affect production of a system such as shading and placement on the roof. If panels are moved to other areas of a rooftop that will also affect production as well due to positioning and azimuth calculations.

Understanding the variables that make up the System Production can help customers and Sales Reps figure out how to build the highest producing system while keeping the cost of the total system down.