Swwils wrote: ↑Tue Dec 13, 2022 4:45 pm
Also, energy ratings are not calculated perfectly and are often "optimised". One test for the classification of a washing machine is 100 cycles on eco mode - a mode that many will not use because it doesn't wash a full load; similar for cookers where it heats to a 55C standard.
I found a really good example of this, years ago. When building this house I first installed a hot water tank, that had a stated heat loss rate (and the appropriate efficiency rating label). Great, I thought, that means I can work out the heat loss per day easily.
Not true at all! It turned out that the measurement method used was some ancient British Standard that assumed a coal boiler fired up once (might have been twice) a day to heat the tank, so the family could take a bath. This test was done by cycling the tank. and the heat loss was the mean value between when the tank was hot and when it was cold, over a 24 hour period.
Anyway, if the tank was kept mostly hot, say by using an immersion run by excess PV generation as I was doing, the true heat loss rate was around three times higher than the label suggested. This is the reason I ripped it out and fitted the Sunamp thermal battery, as at least that has an honest number in the spec for the leat loss rate per 24 hours.
As always, the devil is in the detail, and it's very easy to get suckered into thinking things means something other than they really do.
25 off 250W Perlight solar panels, installed 2014, with a 6kW PowerOne inverter, about 6,000kWh/year generated
6 off Pylontech US3000C batteries, with a Sofar ME3000SP inverter