Yes, our electricity bill was only 68 cents, but…

Yes, our electricity bill was only 68 cents thanks to our solar electric panels, but… what I am personally more interested in is the KWh. So here we go! (We have a grid-tied PV system. 30 panels. 6.9 KW total.)

It’s actually a little tricky to figure out how many KWh we actually used because the way our particular utility-meter works (maybe it’s different for some other people) is that it can’t show/know how much electricity we used straight off the PVs. It only knows what we took from the power plant, and what we sent out to the plant/grid.
(It shows 2 numbers rather than just 1 as a house without solar-electricity panels does.)

Anyway, here’s the math:

Available to use = Actually used

Available to use:
a) The 875 KWh we generated (from an avg of July and August from our monthly PV stats as reported by our Enphase microinverters — they DO know what they are doing, unlike the meter!)
b) The 231 KWh we used from the power plant (from our bill)
TOTAL: 1106 KWh

Actually used:
a) 714 (used by someone else out there on the grid… as reported by our bill)
b) X (or… “smiley face” in honor of Francis “Sandy” Hill who liked to use little drawings of clouds, squirrels, etc. instead of X, Y, Z, greek letters, etc when doing math in his lectures.)

Available to use = Actually used
1106 = 714 + (smiley face)
(smiley face) = 392 KWh

OK, so we used 392 Kwh. Not bad! Especially considering our silly heat pumps have (as far as I can tell) had on the coil “pre-heater” which pulls approximately 50W 24/7. So we can subtract roughly 36 KWh (50 * 24 * 30 / 1000) from this in future bills I hope. So that’s ~350 KWh per month. And that is not only electricity use for lights, computers, etc. But also:
2. cooking (our stove is electric)
3. AC
4. hot water for showers, etc (our hot water heater is electric… soon to also be a heat pump too)

Vs (to get a point of reference as to what is typical… again, not usually including cooking or hot water I imagine… since most people will use natural gas and such… which, unless you are using a heat pump with electricity is a good idea):
“The average residential electric bill in Wellesley is for approximately 950-kilowatt hours”

Anyway…. Go negawatts! That’s what is really cool. More so than our $0.68 electricity bill.


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