Leveraging SDGE TOU rates with an EV?

[Ampster]

FWIW, the TOU tariffs I have chosen over the past 8 years have never had a tiered overlay. I have always had two EVs during that time and tiered rates are something I avoided because of the diminishing returns as kWhr usage goes up.

[J.P.M.]

Thanks for your insight. The fixed roof orientation is hard to get around. For me it's 191 deg, az and 23 deg. tilt. As you said, under NEM 2.0 it's much harder to find a rate schedule that makes it possible to pull off. I am in a position where I'm currently paying the minimum ($0.338 per day) and I have room to increase my usage with a PHEV to get more bang for my buck. The EV-TOU-5 rate plan would be great, as there's a big differential btwn on-peak and super-off-peak, but the $16.00/month fee cancels out any savings I could anticipate under any realistic EV charging scenario I can dream up.

You're welcome. I believe I found similar to what you found with respect to the EVTOU rates.

I appreciate the roof/fixed orientation bind/limitations.

FWIW, a 191 deg. az., 23 deg. tilt yields ~ $465/yr. per STC kW in bill offset under DR-SES in/around N. County San Diego. So, for example, if you only used power at super off peak rates of ~ $0.24558/kWh blended summer/winter, you could use ~ ($465/yr.-STC kW)/($0.24558/kWh) = 1,894 kWh/yr per STC kW and avoid most of your bill. At the other rate extreme of summer on-peak pricing of $0.53571/kWh you could use ~ $465/$0.53571/kWh = 862 kWh/yr. per STC kW and avoid most of a bill.

Your usage and times will result in a blended average price per kWh. But, if you assume the PVWatts model as a reasonable dart throw of irradiance and generation patterns and quantities, then the amount of "revenue" a system produces (and that can only be used to offset regular billing charges) will be as fixed and representative of what's likely to happen as the PVWatts model's generation. Generation used internally and not exported to the grid will have the same revenue value as if it was exported to the grid.

The method also provides a means to help game the system as Ampster is writing about. You start out with what is an approximately fixed $$ amount per year or billing period that is the $$ value of the electricity an array generates. Then you get to look at how to spend those $$'s at various times and in various amounts, or see the effects of time shifting of loads has on a residual bill.

The method works for DR-SES but will work for most any T.O.U. tariff, including those that have a tiered rate system laid over them. In such cases, a billing schedule needs to be inserted into the spreadsheet to account for when to stop applying the tier one billing credit per kWh. That also means all the variables that affect the basic monthly allowance need to be accounted for, as will which actual billing schedule is being used by the account. PITA details but not hard to understand, and need be done only once per account/residence.

[RichardCullip]

I have two excel files to do NEW calculation that may be of use.......

Thanks. I'll take a look at those.

[scrambler]

Thanks for the quick overview. This will give me enough to work on for now. I'll just have to brush up on my Excel modeling skills and review various SDG&E rates options.

I have two excel files to do NEM calculation that may be of use

https://1drv.ms/x/s!At3vMAQjaOZLkRp6...jb4jK?e=EyjbIH

https://1drv.ms/x/s!At3vMAQjaOZLkSOv...i8r1o?e=2lI4b2


Mod note - use these files at your own risk. They are not sponsored or endorsed by this forum.

[RichardCullip]

For SDG & E on the NEM T.O.U. rate for PV users which is DR-SES, it amounts to shifting as much use to super off peak rate times as possible and then off peak for as much of the rest as possible, and avoiding as much peak time usage as possible.

Under the old T.O.U. rates it was realistically possible to have a PV system that generated less than was used and still wind up with a bill that was <0.

While that's still possible under the new raates and times, a min. bill while using more than generating is a lot harder to pull off, mostly because the hours of peak charges have shifted to times away from hours when high solar generation is likely.

Long and short of it is to minimize all usage and then stay away from use during peak pricing as much as possible. Then, and if possible, have an array orientation that produces the highest annual bill offset per installed STC kWh. That 2d part is mostly not possible for fixed roof orientations.

For you, your optimum array orientation in Poway is about 200 - 215 deg. az and about a 30 deg. tilt. At current DR-SES rates an array at your house and at that ~~ orientation will produce about $470/yr. in "revenue" per installed STC kW of capacity. You can then "spend" that revenue on your electric bill. So, a 5 kW system will produce ~ $470/yr. * 5 kW =`$2,350/yr.

More info if you want it.

Thanks for your insight. The fixed roof orientation is hard to get around. For me it's 191 deg, az and 23 deg. tilt. As you said, under NEM 2.0 it's much harder to find a rate schedule that makes it possible to pull off. I am in a position where I'm currently paying the minimum ($0.338 per day) and I have room to increase my usage with a PHEV to get more bang for my buck. The EV-TOU-5 rate plan would be great, as there's a big differential btwn on-peak and super-off-peak, but the $16.00/month fee cancels out any savings I could anticipate under any realistic EV charging scenario I can dream up.

[J.P.M.]

For SDG & E on the NEM T.O.U. rate for PV users which is DR-SES, it amounts to shifting as much use to super off peak rate times as possible and then off peak for as much of the rest as possible, and avoiding as much peak time usage as possible.

Under the old T.O.U. rates it was realistically possible to have a PV system that generated less than was used and still wind up with a bill that was <0.

While that's still possible under the new raates and times, a min. bill while using more than generating is a lot harder to pull off, mostly because the hours of peak charges have shifted to times away from hours when high solar generation is likely.

Long and short of it is to minimize all usage and then stay away from use during peak pricing as much as possible. Then, and if possible, have an array orientation that produces the highest annual bill offset per installed STC kWh. That 2d part is mostly not possible for fixed roof orientations.

For you, your optimum array orientation in Poway is about 200 - 215 deg. az and about a 30 deg. tilt. At current DR-SES rates an array at your house and at that ~~ orientation will produce about $470/yr. in "revenue" per installed STC kW of capacity. You can then "spend" that revenue on your electric bill. So, a 5 kW system will produce ~ $470/yr. * 5 kW =`$2,350/yr.

More info if you want it.

[RichardCullip]

I'm on the road so initially this will be brief. Essentially it is buy low and sell high. With summer differentials between Peak and Off Peak of at least$0.30 per KWhr for every hour you store on the grid at $0.50/kWh you can almost drawn down 4kWhrs at $0.15. I would be happy to discuss in more detail later.

Thanks for the quick overview. This will give me enough to work on for now. I'll just have to brush up on my Excel modeling skills and review various SDG&E rates options.

[Ampster]

I'm on the road so initially this will be brief. Essentially it is buy low and sell high. With summer differentials between Peak and Off Peak of at least$0.30 per KWhr for every hour you store on the grid at $0.50/kWh you can almost drawn down 4kWhrs at $0.15. I would be happy to discuss in more detail later.

[RichardCullip]

I've seen Ampster refer to the ability to leverage TOU rates with an EV to reduce electric bills to near minimum while consuming more electricity than solar produces on an annual basis. I'd send a PM for the details on how to accomplish this, but, alas, this forum software preclude that. So the next best thing, is to ask about this is a new (at least new to me) topic. I would love to get a general outline of how to leverage TOU rates to minimize the final POCO bill come True-up time.