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6 min read
We quote self-consumption before we quote panels
Two houses with identical roofs and identical arrays can have paybacks nine years apart. The variable is not the roof. It is when the kettle goes on.
Written by Nell Fairhurst
We ask for a fortnight of half-hourly meter data before we specify a single panel. Most installers ask for a roof plan and a postcode.
Two identical roofs
Take two houses with the same roof, the same pitch, the same orientation and the same array. One is occupied through the day, one is empty from eight until six. On the same tariffs, their paybacks can sit nine years apart.
The variable is not the roof. It is when the load is.
What we do with the data
We overlay a modelled generation curve for your roof against your actual consumption curve, and we size the array to the overlap rather than to the rafters. It usually means fewer panels than you were expecting and a shorter payback than you were quoted.
Next step
Run the numbers this argues about
The calculator carries every effect described here. Change one input at a time and see which of them your payback is actually sensitive to.