Calculating cost of SCE Net Metering with TOU (Time of Use) rate plan is impossible?!

[iwrate]

I'm in the process of installing a 9kW solar array. Once completed (and I get an electric car), I'll have the option of switching to SCE's TOU plan to take advantage of low 'Super off-peak' rates between midnight-6am.

I've already created a spreadsheet (with macros) that can take SCE's hourly usage data and calculate an expected bill under either their traditional rate plan (4 tiers) or the TOU plan. My problem now is how to incorporate solar generation into the spreadsheet. I don't understand how one's energy usage goes into the 2nd tier (130% of baseline) with a properly sized solar array. I've talked with SCE directly and received no understandable answer. The best way to approach it is with a simple scenario:

Assume usage of 1000 kWh/month 100 on peak, 300 off peak, 600 super off peak
Assume production of 1000 kWh/month 700 on peak, 300 off peak, 0 super off peak

Does anyone know how this bill would be calculated? I've seen posted TOU SCE bills that show credits in Tier 1 and Tier 2 even though usage appears nowhere near baseline. Since generally there is only one meter it is only measuring the net energy use/production of the house. That means that if you use 1 kWh on peak and your system produces 4 kWh, your meter would spin backwards 3 kWh and SCE would never really know the specifics of how much was used and how much was produced. With rate plan D it is simple because 1000 kWh consumed and 1000 kWh produced means $0 bill, but with TOU if you produce during peak and use during super off peak those same consumption/production numbers should produce a usage credit.

Any insights would be greatly appreciated.

[J.P.M.]

I'm in the process of installing a 9kW solar array. Once completed (and I get an electric car), I'll have the option of switching to SCE's TOU plan to take advantage of low 'Super off-peak' rates between midnight-6am.

I've already created a spreadsheet (with macros) that can take SCE's hourly usage data and calculate an expected bill under either their traditional rate plan (4 tiers) or the TOU plan. My problem now is how to incorporate solar generation into the spreadsheet. I don't understand how one's energy usage goes into the 2nd tier (130% of baseline) with a properly sized solar array. I've talked with SCE directly and received no understandable answer. The best way to approach it is with a simple scenario:

Assume usage of 1000 kWh/month 100 on peak, 300 off peak, 600 super off peak
Assume production of 1000 kWh/month 700 on peak, 300 off peak, 0 super off peak

Does anyone know how this bill would be calculated? I've seen posted TOU SCE bills that show credits in Tier 1 and Tier 2 even though usage appears nowhere near baseline. Since generally there is only one meter it is only measuring the net energy use/production of the house. That means that if you use 1 kWh on peak and your system produces 4 kWh, your meter would spin backwards 3 kWh and SCE would never really know the specifics of how much was used and how much was produced. With rate plan D it is simple because 1000 kWh consumed and 1000 kWh produced means $0 bill, but with TOU if you produce during peak and use during super off peak those same consumption/production numbers should produce a usage credit.

Any insights would be greatly appreciated.

A few folks have found:

Study published rate sheets and learn how your utility bill is put together. This is usually much more involved than people at first believe and most give up. A planned systematic approach is helpful. Assume zero knowledge at the start. You'll fight yourself less.

For those who stick around, a few have found:

1.) Utility rate mysteries will yield to spreadsheets.

2.) The process goes quicker if ALL the factors that go rate determination are known before the spreadsheet is started.

3.) The process of understanding POCO rate structures is a bit like getting a root canal by going in thorough your rectum w/out sedation.

4.) Checking for correctness is done most easily by comparing to prior bills, just watch the rate changes which can be frequent and vacillating.

[Bobodude]

Yes, nearly impossible

My 5 kw system is tied to Nevada Energy's grid and I just found out that they offer a TOU tariff for net metering. Our summer peak is from 1 pm to 5 pm and the rest of the time is summer offpeak. That is from June 1 to Sept 30th. The rest of the year is winter off peak. The rate differs from about 6 cents to 40 cents for the top tier. The gotcha is your KWHR (kwh returned to the grid) can only be credited to you bill for the same time period in which it was generated. For the life of me, I cannot predict if this will save me money in the end or not no matter how many spreadsheets I use. But NV Energy has a nice plus, if after a year, the plan has not saved you money over the previous years costs, they will credit the overcharge to your account after the one year commitment has ended and return you to the standard tariff. I end up using the most KWH in the winter due to weather mostly. That is when the rate is the lowest. I believe there are savings to be had, I just can't get my hands around them.

[silversaver]

What you need is TOU-EV with 2 tiers plan. It is nice for solar owner if sizing properly. simple calculation than standard TOU plan.

[J.P.M.]

My 5 kw system is tied to Nevada Energy's grid and I just found out that they offer a TOU tariff for net metering. Our summer peak is from 1 pm to 5 pm and the rest of the time is summer offpeak. That is from June 1 to Sept 30th. The rest of the year is winter off peak. The rate differs from about 6 cents to 40 cents for the top tier. The gotcha is your KWHR (kwh returned to the grid) can only be credited to you bill for the same time period in which it was generated. For the life of me, I cannot predict if this will save me money in the end or not no matter how many spreadsheets I use. But NV Energy has a nice plus, if after a year, the plan has not saved you money over the previous years costs, they will credit the overcharge to your account after the one year commitment has ended and return you to the standard tariff. I end up using the most KWH in the winter due to weather mostly. That is when the rate is the lowest. I believe there are savings to be had, I just can't get my hands around them.

Without some idea of your use patterns by hour, you will be guessing if TOU will save you money. As long as you can really back out after a yr. and made whole if it's not a lower bill, I'd be tempted to take a shot. If I did that however, I' keep real good track of my use pattern. Like I say, welcome to POCO rate hell.

[Bobodude]

Northern Nevada TOU with Net Metering

What you need is TOU-EV with 2 tiers plan. It is nice for solar owner if sizing properly. simple calculation than standard TOU plan.

After talking to a very polite snd informitive net metering lady, I got the full scoop. Nevada is divided into north and south areas. The south has a different time and fee schedual than the north. The north has actually 4 tiers for summer and two tiers for winter. They must have changed it recently because all the info on Google showed just 3 tiers. But anyway, the bad news is the summer peak is $.41 a kwh between 1pm and 6pm. Now that seems a little steep. It was $.39 from 1pm to 5pm before it was changed sometime this year. Then they have thrown in these Summer NEAR Peak zones from 10am to 1pm and 6pm to 9pm at $.20 a kwh. All other times is $.06 a kwh. Geez. The good news is the weekends are void of any tiers except one, and that is Summer Weekends at $.06 kwh all 24 hours.

The winter tiers are on peak from 5pm to 9pm at $.08 and off peak at $.06. This applies 7 days a week. Now my "solar girl" isn't too crazy about the summer peak "no fly zone" that has been adorned upon her domestic duties. Now this poster is getting a little flack on the idea you have to change our lifestyle a bit. Like being careful not to doing laundry or bake cookies between those hours. She awknowledged that any sane woman wouldn't be doing those chores at that time anyway. But how about the AC? She put her foot down on that one. "I'm not going to sweat to death to save a few bucks when it's hot". That message was loud and clear. Sure I am generating from 1 pm to at least 5pm but on a sliding scale as there is a 7200 ft mountain to my west that cuts off the sun at that time. So I think I may end up paying a bit during the summer but getting the savings back during the winter when I have my biggest electric bills. The crapy part of this scheme is that our legislature, in all it's wisdom, has passed a new law that directs NV Energy to now collect all those nasty little taxes on "delievered kwh" instead of "net kwh". That adds about $5 to $10 more to the bill. All those "green program" taxes is a whole nother thread.

[jimqpublic]

I sure appreciate J.P.M.'s comforting words of wisdom... But never having seen a year's worth of SCE TOU bills I can't be sure that how I interpret the tariff structure is correct.

Once a solar system is installed of course you can just try out the various rate plans to see which fits best.

My problem is in system sizing. One installer is suggesting that my net SCE TOU annual bill would be almost zero with a solar array of 4.3 kW for 9,000 kWh annual use. I figure that array would put out around 7,000 kWh. He says that when the meter spins backward during peak times I will receive the peak rate, and if it spins backward enough to put me in "negative tier 2" I would be credited with the tier 2 rate. I find that hard to believe and am inclined to go with a larger system to more completely zero out my use.

Can anyone with SCE Time of Use billing comment on how surplus gets credited in summer and debited in winter and at night?

[sensij]

I sure appreciate J.P.M.'s comforting words of wisdom... But never having seen a year's worth of SCE TOU bills I can't be sure that how I interpret the tariff structure is correct.

Once a solar system is installed of course you can just try out the various rate plans to see which fits best.

My problem is in system sizing. One installer is suggesting that my net SCE TOU annual bill would be almost zero with a solar array of 4.3 kW for 9,000 kWh annual use. I figure that array would put out around 7,000 kWh. He says that when the meter spins backward during peak times I will receive the peak rate, and if it spins backward enough to put me in "negative tier 2" I would be credited with the tier 2 rate. I find that hard to believe and am inclined to go with a larger system to more completely zero out my use.

Can anyone with SCE Time of Use billing comment on how surplus gets credited in summer and debited in winter and at night?

I think your installer could be right. With SCE's TOU system, you get retail credit for the energy you generate. A net generation of 1000 kWh (amount generated - amount used) during peak hours in summer would be worth $280, using the rates Silversaver posted. That $280 can be used to offset 2333 kWh of summer off-peak tier 1 usage, or 2545 kWh of winter off-peak tier 1 usage. The key to benefiting from that multiplier is to make sure you are generating more than you are using during the peak hours. If that condition is true, then yes, you can size your system smaller because some kWh are worth more than others.


Edit: See this thread for some specific examples when generation slides into Tier 2 levels.

[OftheSeven]

I'm in the process of installing a 9kW solar array. Once completed (and I get an electric car), I'll have the option of switching to SCE's TOU plan to take advantage of low 'Super off-peak' rates between midnight-6am.

I've already created a spreadsheet (with macros) that can take SCE's hourly usage data and calculate an expected bill under either their traditional rate plan (4 tiers) or the TOU plan. My problem now is how to incorporate solar generation into the spreadsheet. I don't understand how one's energy usage goes into the 2nd tier (130% of baseline) with a properly sized solar array. I've talked with SCE directly and received no understandable answer. The best way to approach it is with a simple scenario:

Assume usage of 1000 kWh/month 100 on peak, 300 off peak, 600 super off peak
Assume production of 1000 kWh/month 700 on peak, 300 off peak, 0 super off peak

Does anyone know how this bill would be calculated? I've seen posted TOU SCE bills that show credits in Tier 1 and Tier 2 even though usage appears nowhere near baseline. Since generally there is only one meter it is only measuring the net energy use/production of the house. That means that if you use 1 kWh on peak and your system produces 4 kWh, your meter would spin backwards 3 kWh and SCE would never really know the specifics of how much was used and how much was produced. With rate plan D it is simple because 1000 kWh consumed and 1000 kWh produced means $0 bill, but with TOU if you produce during peak and use during super off peak those same consumption/production numbers should produce a usage credit.

Any insights would be greatly appreciated.

Did you ever switch to TOU rate after you installed solar?