SDG&E Standard vs TOU-2 Plans for Charging Tesla?

Joined
Mar 29, 2018
Messages
12
Location
Del Mar, CA
Tesla Owner
Model 3
Country
Country
#1
I live in San Diego. We have had PV Solar on our roof for about two years, generating 140-150% of our use every year, without EVs - we originally sized the system with the idea of getting EVs later. Now, we have just taken delivery of two Tesla Model 3s :).
I have calculated that, based on our driving, and the past two years of Solar data, we will go from generating excess power to using approximately 160-180 kWh/month. On our current Standard DR plan with SDG&E, we should never exceed our baseline allowance lowest Tier 1 rate, which allows around 270 kWh/mo. As far as I can tell (and its confusing!), the per-kWh rate for TOU-2 time of use super off peak is usually a penny or two lower than the DR Tier 1 rate. So far, though, it is convenient for us to plug in our Teslas whenever we need to - we have a single 14-50 UMC in the garage. I would be inclined to stay on the tiered plan, but I want to be sure I am not missing something. Others must have worked this out in the past...?
I have read that, although it would appear that daytime solar generation on the TOU plan would appear to offset nighttime use by more than double - that is not the case, because of the way the excess generation is credited.
Any thoughts or advice appreciated!
 

PNWmisty

Legendary Member
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Aug 19, 2017
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Anacortes, WA
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#2
I live in San Diego. We have had PV Solar on our roof for about two years, generating 140-150% of our use every year, without EVs - we originally sized the system with the idea of getting EVs later. Now, we have just taken delivery of two Tesla Model 3s :).
I have calculated that, based on our driving, and the past two years of Solar data, we will go from generating excess power to using approximately 160-180 kWh/month. On our current Standard DR plan with SDG&E, we should never exceed our baseline allowance lowest Tier 1 rate, which allows around 270 kWh/mo. As far as I can tell (and its confusing!), the per-kWh rate for TOU-2 time of use super off peak is usually a penny or two lower than the DR Tier 1 rate. So far, though, it is convenient for us to plug in our Teslas whenever we need to - we have a single 14-50 UMC in the garage. I would be inclined to stay on the tiered plan, but I want to be sure I am not missing something. Others must have worked this out in the past...?
I have read that, although it would appear that daytime solar generation on the TOU plan would appear to offset nighttime use by more than double - that is not the case, because of the way the excess generation is credited.
Any thoughts or advice appreciated!
Without knowing your typical schedule/usage it's just a guess but you might want to consider adding another charge outlet or even a HPWC so you can charge as much as possible if one or both EV's happen to be home during periods when you generate the most electricity and it's the cheapest to buy.
 
Joined
Mar 29, 2018
Messages
12
Location
Del Mar, CA
Tesla Owner
Model 3
Country
Country
#3
Unfortunately, our older home has only a 125 amp service from our utility, and we do not have power to add additional charging capability.
I am seeing that SDG&E's time of use billing sets the on-peak usage period from 4pm - 9pm. Given that the Solar system puts out minimal power after 6pm (depending on time of year), we would be running our house, irrespective of EV charging, during peak periods. I think we would lose.
Our annual true up for our electric billing is at the end of this month; we will be fine for this past year, as we just got the cars. It is really a year from now that I will be paying a bill. I cannot use the utilities "compare our billing plans" against my actual usage yet, but I will be able to over the next few months.
 
Joined
Mar 29, 2018
Messages
12
Location
Del Mar, CA
Tesla Owner
Model 3
Country
Country
#4
Extremely helpful, thank you!

So - given my assumption that, at net usage of 170 kWh/mo I will not go above Tier 1 under the standard DR Tier billing I have now - we are talking winter (7 months) TOU .23/kWh any time, DR .23/kWh any time; summer (5 months) TOU .23/kWh off peak, DR .27 any time. So .04 x 170kWh x 5 mo = $34 more under DR compared to TOU with ALL charging done at off-peak in summer months. I suspect the higher cost of running my house in the evening under TOU would more than offset the $34 savings. Staying where I am for now, I think.

EV-TOU-2: http://sdge.com/tm2/pdf/ELEC_ELEC-SCHEDS_EV-TOU-2.pdf

DR http://sdge.com/tm2/pdf/ELEC_ELEC-SCHEDS_DR.pdf