PG&E NEM 2 with EVA rate plan with powerwall question charging from grid

[Smilen65]

My question comes from not knowing the ins and outs of NEM and the confusing PGE statement if you have paired storage. Long story short I have the option to charge my powerwall from the grid during off peak hours, should I?

I usually have a yearly true-up around $500

I have a 5kW solar system and a powerwall2 which in the past did not have the option to charge from the grid. Had a inverter fail and after a month I called Tesla and they gave me the option to charge from the grid. Now here is where the questions start. If I charge over night at off-peak rates and send back during the day is it financially advantageous? My intuition says yes but I don't fully understand the NEM 2 structure. I fear I am not getting credited the full cost of a kWH consisting mainly of generation and distribution costs. Now on my normal PG&E bill I can see my generation provider (EBCE) credits me at peak rates. I just don't know about the distribution part. Any insights would be much appreciated.

 

[Redhill_qik]

I was going to so that this doesn't make any sense, but after looking at the EVA TOU hours, this makes sense for Mon-Fri, but not on Sat-Sun.

EV-A TOU Hours

• Peak: 2:00 p.m. to 9:00 p.m. Monday through Friday. 3:00 p.m. to 7:00 p.m. Saturday, Sunday and Holidays.
• Partial-Peak: 7:00 a.m. to 2:00 p.m. and 9:00 p.m. to 11:00 p.m. Monday through Friday, except holidays.
• Off-Peak: All other hours

So, on Mon-Fri your solar could be exported at a higher rate (both Summer and Winter) than it costs for you to import Off-Peak even including the NBCs for the imported kWh to charge the PWs. On Saturday and Sunday since there isn't a Partial-Peak and Peak starts and hour late, so there is a cost disadvantage paying for those NBCs instead of recharging from solar.

 

[h2ofun]

I was going to so that this doesn't make any sense, but after looking at the EVA TOU hours, this makes sense for Mon-Fri, but not on Sat-Sun.

EV-A TOU Hours

• Peak: 2:00 p.m. to 9:00 p.m. Monday through Friday. 3:00 p.m. to 7:00 p.m. Saturday, Sunday and Holidays.
• Partial-Peak: 7:00 a.m. to 2:00 p.m. and 9:00 p.m. to 11:00 p.m. Monday through Friday, except holidays.
• Off-Peak: All other hours

So, on Mon-Fri your solar could be exported at a higher rate (both Summer and Winter) than it costs for you to import Off-Peak even including the NBCs for the imported kWh to charge the PWs. On Saturday and Sunday since there isn't a Partial-Peak and Peak starts and hour late, so there is a cost disadvantage paying for those NBCs instead of recharging from solar.

I just the PW's to now 70%, and do nothing else. I love not having to worry about what things cost, I have SO much extra I produce

 

[swedge]

My question comes from not knowing the ins and outs of NEM and the confusing PGE statement if you have paired storage. Long story short I have the option to charge my powerwall from the grid during off peak hours, should I?

I usually have a yearly true-up around $500

I have a 5kW solar system and a powerwall2 which in the past did not have the option to charge from the grid. Had a inverter fail and after a month I called Tesla and they gave me the option to charge from the grid. Now here is where the questions start. If I charge over night at off-peak rates and send back during the day is it financially advantageous? My intuition says yes but I don't fully understand the NEM 2 structure. I fear I am not getting credited the full cost of a kWH consisting mainly of generation and distribution costs. Now on my normal PG&E bill I can see my generation provider (EBCE) credits me at peak rates. I just don't know about the distribution part. Any insights would be much appreciated.

Smilen,

I am a fan of charging PowerWall from the grid so that we can avoid peak pricing even on cloudy days. Last year before Tesla gave us the option in the app, I went so far as to grid charge by making unauthorized adjustments via our PW installer menu . But along with grid charging, Tesla gave us the surprising "Export Everything" option which turned out to be an even bigger benefit for us. Being able to top up on a cloudy day at off peak price so as to avoid drawing during peak is nice, but getting peak credit for exporting excess solar is cake under the icing.

But whether or not you "should" depends on many factors. If one did choose to take the IRS solar tax credit (ITC) on the battery, the old rules said it must be exclusively charged from solar. On the other hand, 1)Tesla's Storm Watch violated this, 2) we never heard of any enforcement 3)how would IRS know anyway, 4) and the new rules explicitly include (as they should) storage cost in the ITC. (So many other hands!) Export Everything has it's own wrinkles around grid interconnection rules and Tesla's opaque decisions to enable or not to enable. Then there are the particulars of your time-of-use rates and Non Bypassable Charges. So probably each of us has a different situation and and different degrees of attraction to adventure and cost savings.

In our case, because our PowerWall was funded by an SGIP rebate, we did not need the ITC so grid charging is completely permissible. Exporting from the PW is also allowed by PG&E on our small size system. We are on the EV2-A rate with peak from 4 to 9, partial peak 3-4 and 9-12, and off peak 12-3. So untill 3 we draw from the grid and solar for the house and charging the PW to 100%, and then discharge to run the house and export any extra to get down to reserve at midnight. We only import from the grid at off peak times, and export as much as we can at peak.

We are in the middle of our first year with both of these features as well as additional solar, so I only have estimates so far. But I calculated that using both Grid Charging and Export Everything would reduce my true-up by a few hundred dollars, helping cover the cost of charging our EV. We'll know for certain in July when our true-up comes around.

A back of the envelope estimate goes like this: Our house typically uses ~50% of PW's charge during partial and peak time to avoid using pricy power, and we set the reserve to 20%, which is enough to get us from midnight to sunup in a blackout. This leaves 30%, or ~4 kWh to export daily during peak time. Assuming that comes from the grid (or if from solar it didn't get exported) at $.23/kWh and exported at $0.42, or netting $0.29 each, $.76 per day or $185 for the winter rated 2/3 of the year. During summer the peak credit is around $0.52 so the daily net is $0.29 X 4 = $1.16 for the 1/3 of 365 or $121, for a yearly true-up reduction of something around $300.

A second PW would let us store more of our excess solar each day rather than export some of it during off-peak times. More solar would allow even more arbitrage, but adding too much solar would take the true-up below zero, which results in a credit balance which is zeroed out by PG&E. So it is a balancing act and everyones milage will be different.

I hope this helps.

SW

 

[h2ofun]

Smilen,

I am a fan of charging PowerWall from the grid so that we can avoid peak pricing even on cloudy days. Last year before Tesla gave us the option in the app, I went so far as to grid charge by making unauthorized adjustments via our PW installer menu . But along with grid charging, Tesla gave us the surprising "Export Everything" option which turned out to be an even bigger benefit for us. Being able to top up on a cloudy day at off peak price so as to avoid drawing during peak is nice, but getting peak credit for exporting excess solar is cake under the icing.

But whether or not you "should" depends on many factors. If one did choose to take the IRS solar tax credit (ITC) on the battery, the old rules said it must be exclusively charged from solar. On the other hand, 1)Tesla's Storm Watch violated this, 2) we never heard of any enforcement 3)how would IRS know anyway, 4) and the new rules explicitly include (as they should) storage cost in the ITC. (So many other hands!) Export Everything has it's own wrinkles around grid interconnection rules and Tesla's opaque decisions to enable or not to enable. Then there are the particulars of your time-of-use rates and Non Bypassable Charges. So probably each of us has a different situation and and different degrees of attraction to adventure and cost savings.

In our case, because our PowerWall was funded by an SGIP rebate, we did not need the ITC so grid charging is completely permissible. Exporting from the PW is also allowed by PG&E on our small size system. We are on the EV2-A rate with peak from 4 to 9, partial peak 3-4 and 9-12, and off peak 12-3. So untill 3 we draw from the grid and solar for the house and charging the PW to 100%, and then discharge to run the house and export any extra to get down to reserve at midnight. We only import from the grid at off peak times, and export as much as we can at peak.

We are in the middle of our first year with both of these features as well as additional solar, so I only have estimates so far. But I calculated that using both Grid Charging and Export Everything would reduce my true-up by a few hundred dollars, helping cover the cost of charging our EV. We'll know for certain in July when our true-up comes around.

A back of the envelope estimate goes like this: Our house typically uses ~50% of PW's charge during partial and peak time to avoid using pricy power, and we set the reserve to 20%, which is enough to get us from midnight to sunup in a blackout. This leaves 30%, or ~4 kWh to export daily during peak time. Assuming that comes from the grid (or if from solar it didn't get exported) at $.23/kWh and exported at $0.42, or netting $0.29 each, $.76 per day or $185 for the winter rated 2/3 of the year. During summer the peak credit is around $0.52 so the daily net is $0.29 X 4 = $1.16 for the 1/3 of 365 or $121, for a yearly true-up reduction of something around $300.

A second PW would let us store more of our excess solar each day rather than export some of it during off-peak times. More solar would allow even more arbitrage, but adding too much solar would take the true-up below zero, which results in a credit balance which is zeroed out by PG&E. So it is a balancing act and everyones milage will be different.

I hope this helps.

SW

Great stuff>
Your comments on too much solar is right on. But the positive is I never had to think about what things cost, I just set and leave alone. I can set my temps in the house all year long to crazy stuff and never have to think about cost. I can have friends come over and charge their EV and never think about it. I did get a 700 credit against my 5000 PGE extra. For me, all of the above makes the money I spend for extra solar worth every penny.

 

[swedge]

I don't fully understand the NEM 2 structure

NEM, both 1 and 2, in effect let your excess summer solar production be "stored" on the grid and used during the winter when you have less production. It is done by billing or crediting each month for your net consumption, that is the difference between your solar production and your house consumption. During the summer it is typically a net credit and winter a net debit. At the end of the year you pay the remaining balance if, or if the balance is a credit, the utility just pockets it. The entire point of NEM is that we need only enough solar to handle only our average consumption, by banking during daytime and summer, and withdrawing during winter and night time. Very clever in that it saves money for both the solar customer and the utility. ("NEM3" in not really net metering at all, but that is off your topic.)

In both NEM1 and 2, you are credited at retail for your exports, but NEM2 charges a small fee, around $0.03 per kWh against those credits.

Time of Use rates create financial incentives to draw from the grid during off peak and export to the grid during peak periods. Generally, peak periods are during evening when solar production is low, so battery storage can help one avoid drawing from the grid during higher peak pricing. Grid charging lets one do that even on cloudy days. But it is not a big deal here in California because there are so few cloudy days. I figure it save me less that $100 last year.

PW is pretty smart about both grid charging and Export Everything, but to make decisions it needs to know the prices for import and export for each time period, which they call buy and sell prices. To account for NEM2, I just set the sell price at 3 cents less than the buy price. PW only grid charges when it needs to in order to be fully charged each day before the higher rates begin. It seems to know the weather forecast, and sometimes starts charging early in the morning if it thinks it will be cloudy, though I'm not sure about this. In any case, it will top off as the higher price time approaches. Sometimes, if I anticipate a serious storm which might cause an early morning outage, I will set my reserve to 100% which starts it charging right away.

I am on PG&E, so your EBCE rates and rules may be different.

 

[Ampster]

More solar would allow even more arbitrage, but adding too much solar would take the true-up below zero, which results in a credit balance which is zeroed out by PG&E. So it is a balancing act and everyones milage will be different.

I am actually a Net consumer of one mWh at True Up and had a small dollar credit. Zeroing out that credit meant that the one mWh of consumption was free.

 

[h2ofun]

I am actually a Net consumer of one mWh at True Up and had a small dollar credit. Zeroing out that credit meant that the one mWh of consumption was free.

I had a huge credit. PGE gave me about 10% of it, and its now a credit on my actual PGE total, so I do not have any bill now, but I have asked for some of the money since I could never use it up.

I am a net generator of a huge amount.