Mid-July to mid-August was $232. Significant difference. But we only produced about 41% of the power we used.
Our electricity provider APS just instituted rate changes which are like playing 4-dimensional chess to figure out. We are grandfathered into 20 year rate STRUCTURES (not rates) by having solar put in by 8/31/17, but trying to figure out WHICH rate plan to elect is RIDICULOUS. Last night, I posted on our local NextDoor site and a lovely guy who is a software engineer spent nearly 3 hours going over the various calculations (which are based on the limited data we have available, because there are no bills from last year to compare to), and the changed rate structure that they are going to put in.
Just to give you an idea of two of the main plans that are available to me, so long as I change by 8/31 (and which we would be locked into for the next 19.8 years):
Standard plan - tiered billing depending on usage, independent of time of day (there are buttload of other charges too, but this is the rate-based charges).
Winter (Nov - April billing cycle): all kWh are $0.10852
Summer:
First 400 kWh: $0.11161
Next 400 kWh: $0.15920
Next 2200 kWh: $0.18627
Over 3000 kWh: $0.19863
Our usage (over and above our production) for the recent very hot month was about 1850 kWh. So if we had been on this plan last month, the underlying kWh usage we would have been charged (which was about $100 of the $232) for our electrical usage would have been $300, of which nearly $190 would have been the 1050 kWh over the first 800 ($44 + $64 + $190). However, that calculus would shift in the lower usage months.
The plan I'm currently on is a time of use plan - which current has off-peak hours from 7 PM to noon, and weekends and holidays; however, it is changing to 8 PM to 3 PM plus weekends and a couple more holidays (which sneakily means fewer hours of generating on-peak credits during the winter). The good thing about being grandfathered into this plan is that off-peak and on-peak credits generated in Jan - May are individually banked and used 1:1 to off-set the higher usage in June-September (although April-May, and Oct-Nov are generally about break-even, so it's really the Jan-March credits that will mostly offset the summer high usage). Newer solar installations after 8/31 will not get 1:1 payback - they will not get full credit for what they generate back to the system (!!).
Annoyingly, in December, if you have any credits left, you get paid for them to zero them out, but NOT at the full rate that they were generated. I think if we have a lot of credits at the end of the year, we'll use them up on garish National Lampoon Christmas/Hanukkah light displays. This year, our summer charges are higher because we of course have no credits from the earlier, cooler part of the year, but next year, we should have bills below $50 in the summer.
Anyway, that time of use rate schedule (again, this is just usage - there are other fixed costs):
Winter:
On-peak: $0.22900
Off-peak: $0.07005
Summer:
On-peak: $0.28205
Off-peak: $0.07105
Our on-peak usage isn't terrible, compared to what we are using off-peak (it's mostly the A/C), and we're making a significant percentage of the on-peak usage. But at night, when we're STILL using the A/C a lot (it doesn't cool off here that much at night), we are paying for all of it.
The breakdown on that (I'm not sure how to figure out how much electricity we DIRECTLY used from our solar - it doesn't show up here):
Total kWh we drew from APS: 2115 kWh
On-peak: 361 (which is what was over what we made and used directly 12-7 PM)
Off-peak: 1754 (which is what was over what we made and used directly during the time the sun was shining from about 8 AM to noon)
We DID generate more than we were using at some points during the day. Our credits for last month:
On-peak: 118
Off-peak: 143
These credits were used to lower what we were CHARGED for down to 1854 kWh: net usage:
On-peak: 243
Off-peak: 1511
There are other plans available, like a 9 to 9 plan, but I think it would make my head explode to try and figure out which is best, especially since I have no data to compare our expected net usage during spring and winter. The former owners of our house rarely lived here, not that I could get their information anyway.
