Hollowgate Farm

The parlour runs twice a day and the vacuum pump runs through the middle of it. That load profile is the reason this array is eleven kilowatts and not the eighteen the roof could physically carry.

What the survey found

Two usable planes: the barn roof at twenty-two degrees facing just west of south, and the farmhouse rear at thirty-five degrees. The barn takes twenty of the twenty-six panels because it is unshaded from ten until four, which is the window the parlour actually draws in.

A third plane on the east elevation was measured and rejected. It would have added two kilowatts of nameplate and almost nothing to the self-consumption figure, because it produces at seven in the morning when the tank is already full.

What it cost and what it saves

Thirteen thousand nine hundred pounds installed, including scaffolding on both elevations and a DNO application for the export limit. The bill has gone from four thousand one hundred and eighty a year to one thousand two hundred and forty.

At forty-two percent self-consumption, most of what the array makes is used on site. That is the figure that carries the payback, not the eleven point four kilowatts on the front of the quote.