SDG&E Time-of-Use Metering

A few months after getting my EV1 I had San Diego Gas & Electric install a special Time-of-Use meter under their Domestic Time-of-Use for Households with Electric Vehicles rate. Compared to their standard Domestic Service, I get cheap (61% of the regular rate) electricity during the morning and evening, and ultra-cheap (34% of the regular rate) electricity after midnight. The catch is that on summer afternoons I have to pay 2.59x the regular rate.

I don't have air conditioning and use little electricity in the afternoon. And I have a timer on my EV charger that I can program to kick on at midnight. So this seems like a good deal, and it probably is. But the summer afternoon rate is so high that I find it worthwhile to monitor usage and to look for ways to reduce my already minimal consumption. Possibilities include packing my refrigerator with "blue ice" packs and turning up the thermostat, and using a battery/inverter combination to provide afternoon power to the computer I have on all the time.

Reading the TOU meter

SDG&E didn't give me any info on how to read the TOU meter, a GE model TM-900, so I had to figure that out for myself. It's an ordinary mechanical mechanism (rotating aluminum disc and gears) plus optical sensors, electronic circuits and an LCD display for registering usage during programmed time periods. There's a bidirectional optical connector on the front of the enclosure for programming and automatic reading.

The numeric LCD cycles through a series of digits. The entries are as follows:
Channel number Interpretation
00# ###### Meter serial number (matches number on faceplate)
01 ###### Date in MMDDYY format (Y2K problems here?)
02 ## ## Time of day in 24-hr HHMM format
03 ##### Cumulative on-peak kW-hr
05- ##### Cumulative off-peak kW-hr; the '-' indicates this is the currently active rate period
07 ##### Cumulative super-off-peak kW-hr
10 ##### Total cumulative kW-hr (may not match sum of above due to truncation effects)
20 ##### Cumulative kW-hr at end of previous season
23 ##### Cumulative peak kW-hr at end of previous season
25 ##### Cumulative off-peak kW-hr at end of previous season
27 ##### Cumulative super-off-peak kW-hr at end of previous season
88 661 Battery backup time, minutes. Increments during power failures.
89 40 Meter program number
888 888888 all segments display test