A year in the life of three solar arrays - Actual energy production versus estimated
There is an art and science behind designing solar arrays and modelling their energy production. Annual energy yield varies over the lifetime of an array due to many factors including weather patterns, smoky skies due to wildfires, as well as local factors including pollen production, snow accumulation etc.
Sweet Spot Solar uses the most advanced modelling and design software available.
Below are three examples of arrays with energy production from June 20 2017 to June 20 2018 to show you some of this variability.
Here's a roof mounted array in Kamloops composed of 16 280 Watt modules using M250 micro-inverters. We originally estimated annual production for this 4.48 kW DC array to be 5012 kWh/year. You'll see from the data below that it performed slightly better than expected (+2%) in spite of a very smoky Summer in the region during 2017. In early March 2017, snow accumulation on the roof prevented energy from being generated for approximately 10 days.
In nearby Rayleigh an array of the exact same size and using the same technology was modelled to generate 4900 kWh/year. It has a slightly shallower roof which reduces its annual production moderately but also increases snow accumulation. For this time period it generated 98.6% of what would be expected under ideal conditions. Again, there was significant smoke in the atmosphere during the Summer of 2017 when solar production is optimal. For this array, snow accumulated on the modules for a few weeks in early November, for a large part of January, and for a short period of time in March. Snow accumulation is not a significant issue as you'll infer from the data given that it occurs at times when performance of the array is lower to begin with.
Our last example is from a solar array on Gabriola Island composed of 28 LG310 Watt modules coupled with M250 micro-inverters. We modelled annual production at 9765 kWh/year, and the array overproduced by 1.4% during this period of time. There was no snow accumulation and only episodic impairment from smoke due to wildfires.
In short, a properly designed solar array using high-quality equipment can perform close to the expected level, or better in some cases, taking into account local and annual variation.