Compare annual use and production
Look at annual household consumption alongside estimated annual system output. The percentage offset should be described as an estimate based on the specified period.
Inspect the assumptions
Ask how the proposal treats shade, orientation, equipment, system losses, degradation assumptions and utility export rules. Compare like-for-like system designs.
Understand limits
Weather varies and actual output can differ from modeling. A production estimate does not automatically equal bill savings because utility charges, rates and payment terms also matter.
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