CPUC NEM 3.0 discussion

[swedge]

Beyond that it would also be nice to know if someday permitted if one were allowed a home generator to feed the grid during the highest peak summer days at spot market prices.

Backup generators do not have grid-tie capability, so they can not export to the grid. In contrast, solar inverters match the grid frequency, phase and voltage, and also trip offline for any deviation from normal parameters. PowerWalls can do this too.

SW

 

[fresnoboy]

I ran some quick numbers based on a Generac 10kW stationary natural gas generator and my PG&E gas bill

$2.77/therm (Tier 2 gas price on 11/28/2022 bill)
There are 99976 Btu/US Therm
datasheet running efficiency at 1/2 load (5kW) is 101 ft^3/hr of Nat Gas. Datasheet says ft^2/hr x 1000 for BTU/hr

So, $2.77 * 101000 / 99976 / 5 = $0.56/kWh

This is almost exactly the same as the PG&E EV2 Summer Peak rate. Seems like it's not worth it to put that wear and tear on a reciprocating piston generator.

Also, you would have to figure out how to grid tie the generator's output. In a normal case, it's only used for backup and the waveform directly follows the engine rpm, so you can't connect it to the grid. The easiest thing I can think of is to use a hybrid inverter that has generator battery charging, then export energy from the grid tied inverter. This is not practical for a Powerwall owner.

The cheaper home "backup" NG generators really aren't designed for this kind of use anyway. You'd end up having to service them fairly often, and maybe it would not be there for an outage when they were really needed.

The industrial units are a whole different animal though. We got a 30KW Kohler unit on ebay that was new at less than 1/3 of the new price, and it's prime power rated, which means it can be used for continuous power generation. These units are more efficient. too Ours is a diesel unit - we live in PG&E land, Who really thinks their NG plant will still work after an earthquake, and our insurance company required a seismic gas shutoff valve as well. That unit at 1/4 load is a gallon an hour of diesel, so $5 /gal / 7.5 kWh $0.66/kWh. At 50% load though, its 1.5*5/15 kwh = $0.50 kWh, which is pretty competitive.

NG units are a little cheaper, but again, who thinks PG&E will survive a quake. The Kohler 30REZG at 50% load consumes 179 cf/h, or 2.77*255000/99976/15=$0.47 kWh.

And gensets don't really like to run well at low load levels either - you get soot buildup etc... The ideal situation would be to see them integrated in a battery management system where if the solar was inadequate to charge the batteries (or unavailable), then you kick the generator on, and charge the batteries at the most efficient load rate of the generator, and then kick the genset off and run off battery power. This avoids long runs at very low load rates, and improves efficiency as well.

It's pretty amazing though that a user with a generator can come close to PG&E peak rates in generation efficiency. Of course, EIA data says that CA users pay 80% higher prices than the rest of the US, so I guess I shouldn't be surprised.

 

[sunwarriors]

The cheaper home "backup" NG generators really aren't designed for this kind of use anyway. You'd end up having to service them fairly often, and maybe it would not be there for an outage when they were really needed.

The industrial units are a whole different animal though. We got a 30KW Kohler unit on ebay that was new at less than 1/3 of the new price, and it's prime power rated, which means it can be used for continuous power generation. These units are more efficient. too Ours is a diesel unit - we live in PG&E land, Who really thinks their NG plant will still work after an earthquake, and our insurance company required a seismic gas shutoff valve as well. That unit at 1/4 load is a gallon an hour of diesel, so $5 /gal / 7.5 kWh $0.66/kWh. At 50% load though, its 1.5*5/15 kwh = $0.50 kWh, which is pretty competitive.

NG units are a little cheaper, but again, who thinks PG&E will survive a quake. The Kohler 30REZG at 50% load consumes 179 cf/h, or 2.77*255000/99976/15=$0.47 kWh.

And gensets don't really like to run well at low load levels either - you get soot buildup etc... The ideal situation would be to see them integrated in a battery management system where if the solar was inadequate to charge the batteries (or unavailable), then you kick the generator on, and charge the batteries at the most efficient load rate of the generator, and then kick the genset off and run off battery power. This avoids long runs at very low load rates, and improves efficiency as well.

It's pretty amazing though that a user with a generator can come close to PG&E peak rates in generation efficiency. Of course, EIA data says that CA users pay 80% higher prices than the rest of the US, so I guess I shouldn't be surprised.

This is how the Enphase system with generator works. Geny kicks on to charge the batteries, then shuts off and you use batteries again after it's topped off. I've been reading about generator makers starting to come out with solar focused generators, but haven't researched it much yet on really what's the difference.

I was thinking a bit lately about how to really be grid independent and am wondering if for long cloud spells (like these 2-3 days), one should ideally get a massive generator which doesn't have to be on for a long period of time to minimize noise/having to run it vs. smaller units. These last few days have been very cloudy so can see solar alone being a big problem. It doesn't matter how much batteries you have when all you generated all day was 5kWh.

I suppose if we can charge from the grid, you can top off your batteries overnight from grid charging, but I'm still avoiding that due to those old ITC rules to only charge from solar (I don't use storm watch/storm guard/etc). Won't matter in an outage of course.

 

[YRide]

That is what Export Everything" is good for, If they let you do that.... I don't see a regulatory justification for denying that capability, though NEM retail credits are still limited only to exports less than solar production over the month.

Perhaps exporting from 7 PW's, i.e. 35kW, could present problems, but I don't see how: each 200 amp home connection and transformer is good for 48 kW.

SW

For the NEM2 math…is it that in any given month you are capped at an estimated maximum of kW sent to the grid based on what PGE expects your solar production to be (for that month). However, the amount of $ credit you can receive is dependent on when you export, per TOU plan (ie EV2A if you have EV’s and opted into that rate plan)?

But those credits, while the energy export is capped monthly, can be saved up and trued up at the end of your annual cycle?

And then how does your own home consumption come into the equation? If for example PGE estimates I can produce 2,000kWh in June, and i actually use 1,500 for my home…am I only able to export 500kWh for credit (and their given TOU retail rate)?

Or if I was able to charge the ESS/PW from the grid, would i actually be allowed to export 2,000kWh (hopefully all at peak TOU retail rates), and capture the arbitrage on 1,500kWh + the full credit for 500kWh?

 

[astrorob]

For the NEM2 math…is it that in any given month you are capped at an estimated maximum of kW sent to the grid based on what PGE expects your solar production to be (for that month). However, the amount of $ credit you can receive is dependent on when you export, per TOU plan (ie EV2A if you have EV’s and opted into that rate plan)?

yes, that's how it works.

But those credits, while the energy export is capped monthly, can be saved up and trued up at the end of your annual cycle?

yes, though some CCAs do monthly trueup/billing on the generation portion of the bill. at least the east bay CCA is going to allow you to switch to yearly true ups at some point in 2023.

And then how does your own home consumption come into the equation? If for example PGE estimates I can produce 2,000kWh in June, and i actually use 1,500 for my home…am I only able to export 500kWh for credit (and their given TOU retail rate)?

they don't really know what was generated or consumed, they just know the net flow to/from the grid. if you have a powerwall or a solar inverter then you personally would know what your consumption is because you know what the gross generation was from solar. i think powerwalls also have a current clamp that measures the house consumption. but that data doesn't go to the IOU. some subset of it does when you participate in a VPP event for sure, but i don't know if that gives the IOU to see all of your data all of the time.

Or if I was able to charge the ESS/PW from the grid, would i actually be allowed to export 2,000kWh (hopefully all at peak TOU retail rates), and capture the arbitrage on 1,500kWh + the full credit for 500kWh?

i'm certainly hoping for this, but personally have to wait until the ITC credit period is over. somewhere along the line i got the idea that the IOUs didn't want you arbitraging power with storage, but obviously that's what storage-only customers will have to do, so maybe i had gotten the wrong idea.

 

[swedge]

For the NEM2 math…is it that in any given month you are capped at an estimated maximum of kW sent to the grid based on what PGE expects your solar production to be (for that month). However, the amount of $ credit you can receive is dependent on when you export, per TOU plan (ie EV2A if you have EV’s and opted into that rate plan)?

But those credits, while the energy export is capped monthly, can be saved up and trued up at the end of your annual cycle?

And then how does your own home consumption come into the equation? If for example PGE estimates I can produce 2,000kWh in June, and i actually use 1,500 for my home…am I only able to export 500kWh for credit (and their given TOU retail rate)?

Or if I was able to charge the ESS/PW from the grid, would i actually be allowed to export 2,000kWh (hopefully all at peak TOU retail rates), and capture the arbitrage on 1,500kWh + the full credit for 500kWh?

Sounds like you understand it pretty well.

They use software called PV Watts I think on each month’s billing cycle to estimate your maximum possible solar production. Export up to that amount is given full retail credit each month. NBC’s of around 3 cents per exported kWH are tallied as well each month.

So, don’t charge from the grid, you’ll never reach the export limit - your export will be you solar production less the house consumption.

PG&E does not know your house consumption, so that is not part of their calculation.

If one grid charges and Exports Everything, it is possible to export more than the limit, in which case some export wont receive credit. You’d pay retail but not get credit for some of the returned kWh. It is easy to control this by increasing the backup reserve setting.

One of the odd things about adding a battery is that they split the details of your electric bill out to a multi page “black and white” bill. Someone posted a nice example and explanation, if you want to prep yourself to avoid spreadsheet shock.

 

[h2ofun]

Sounds like you understand it pretty well.

They use software called PV Watts I think on each month’s billing cycle to estimate your maximum possible solar production. Export up to that amount is given full retail credit each month. NBC’s of around 3 cents per exported kWH are tallied as well each month.

So, don’t charge from the grid, you’ll never reach the export limit - your export will be you solar production less the house consumption.

PG&E does not know your house consumption, so that is not part of their calculation.

If one grid charges and Exports Everything, it is possible to export more than the limit, in which case some export wont receive credit. You’d pay retail but not get credit for some of the returned kWh. It is easy to control this by increasing the backup reserve setting.

One of the odd things about adding a battery is that they split the details of your electric bill out to a multi page “black and white” bill. Someone posted a nice example and explanation, if you want to prep yourself to avoid spreadsheet shock.

My last month was rather interesting. with all this rain, and cold, using lots of energy but not producing worth beans. Yesterday my worse ever, list than 2 kWh, and today could be worse.

Last month my PGE estimate for max export was 2395 Kwh. But I only exported to the grid 17 kWh since was using all my solar to try and charge batteries and heat the house.

What a change, in August I sent 2592 kWh to the grid.

 

[YRide]

Sounds like you understand it pretty well.

They use software called PV Watts I think on each month’s billing cycle to estimate your maximum possible solar production. Export up to that amount is given full retail credit each month. NBC’s of around 3 cents per exported kWH are tallied as well each month.

So, don’t charge from the grid, you’ll never reach the export limit - your export will be you solar production less the house consumption.

PG&E does not know your house consumption, so that is not part of their calculation.

If one grid charges and Exports Everything, it is possible to export more than the limit, in which case some export wont receive credit. You’d pay retail but not get credit for some of the returned kWh. It is easy to control this by increasing the backup reserve setting.

One of the odd things about adding a battery is that they split the details of your electric bill out to a multi page “black and white” bill. Someone posted a nice example and explanation, if you want to prep yourself to avoid spreadsheet shock.

Ok, cool. Thx for checking my understanding.

I’ve actually been using PVWatta to try and precisely model my generation. Had to create 7 models, one for each PV array (each MPPT), since I have a complex roof setup, and then combined the composite together to create an hour-by-hour model for PV generation throughout the year ahead. Then based on that generation model, created an hour-by-hour household consumption model based on historical usage (and also added planned consumption, since well have 2 EV’s but they’ll now be charging in a different pattern…more quickly with Level 2 and also in middle of night).

What I still haven’t done yet is apply the rate plan (ie EV2A or E-ELEC) to see how this plays out when it comes to $, not just kW’s. Initially it seemed counterintuitive, but I think since I have PV + ESS and hopefully at a minimum can do EE with a peak offload ability, that actually the EV2A is the better rate because it has higher peak and lower off peak, meaning I can get more $ retail credit for dumping off the ESS in peak period, and then can charge the EV’s at a lower rate in middle of night.

So I guess I’m already quite deep in spreadsheet hell.

 

[YRide]

My last month was rather interesting. with all this rain, and cold, using lots of energy but not producing worth beans. Yesterday my worse ever, list than 2 kWh, and today could be worse.

Last month my PGE estimate for max export was 2395 Kwh. But I only exported to the grid 17 kWh since was using all my solar to try and charge batteries and heat the house.

What a change, in August I sent 2592 kWh to the grid.

So does this mean that last month, in theory you could have grid charged at off peak, and then exported at peak from ESS, 2377 kWh (2395-17)? Or is that 2377kWh not considered “export” since its net zero with the amount of power you will consume from the grid?

Technically not net zero (more like -237kWh, because 10% loss round trip).

 

[YRide]

So, don’t charge from the grid, you’ll never reach the export limit - your export will be you solar production less the house consumption.

PG&E does not know your house consumption, so that is not part of their calculation.

If one grid charges and Exports Everything, it is possible to export more than the limit, in which case some export wont receive credit. You’d pay retail but not get credit for some of the returned kWh. It is easy to control this by increasing the backup reserve setting.

Still not quite understanding this comment. Are you saying that it’s impossible to exceed your export limit? Or are you saying don’t exceed your export limit?

If you grid charge then export later (effectively TOU arbitrage) is that considered a net zero export? Or does all “export” only count outbound flow, not net flow?

 

[miimura]

Still not quite understanding this comment. Are you saying that it’s impossible to exceed your export limit? Or are you saying don’t exceed your export limit?

If you grid charge then export later (effectively TOU arbitrage) is that considered a net zero export? Or does all “export” only count outbound flow, not net flow?

I believe the number he's talking about is the level where PG&E will start disallowing NEM credits in their billing system. It is PG&E's estimation of the most your solar could possibly produce, so you're not going to get NEM credits beyond that level. In theory, you could grid charge your batteries during Off-Peak and then export it during Peak to earn higher credits, at least up to that number of kWh on your billing cycle. This number is the sum of the negative (toward grid) flows of kWh during any metered intervals during the billing period. Technically, it may be possible for the meter to count and accumulate positive and negative flows within a metering interval that is net zero, but I've never seen anyone prove that this is happening.

 

[wwu123]

I believe the number he's talking about is the level where PG&E will start disallowing NEM credits in their billing system. It is PG&E's estimation of the most your solar could possibly produce, so you're not going to get NEM credits beyond that level. In theory, you could grid charge your batteries during Off-Peak and then export it during Peak to earn higher credits, at least up to that number of kWh on your billing cycle. This number is the sum of the negative (toward grid) flows of kWh during any metered intervals during the billing period. Technically, it may be possible for the meter to count and accumulate positive and negative flows within a metering interval that is net zero, but I've never seen anyone prove that this is happening.

I think what folks are asking is if the export limit is strictly based on what the meter 'exports', or whether it is based on the meter's 'net' exports (exports less imports). Because any grid-charging arbitrage nets out as zero, since the import (grid-charge) offsets the export (peak discharge), by the latter definition, and wouldn't move you any closer to the limit....

 

[YRide]

I believe the number he's talking about is the level where PG&E will start disallowing NEM credits in their billing system. It is PG&E's estimation of the most your solar could possibly produce, so you're not going to get NEM credits beyond that level. In theory, you could grid charge your batteries during Off-Peak and then export it during Peak to earn higher credits, at least up to that number of kWh on your billing cycle. This number is the sum of the negative (toward grid) flows of kWh during any metered intervals during the billing period. Technically, it may be possible for the meter to count and accumulate positive and negative flows within a metering interval that is net zero, but I've never seen anyone prove that this is happening.

Ok…so the point where you switch from getting “retail” credit to getting “wholesale”, right?

And this is threshold is calculated by PGE using PVWatts, or a close proximity as was previously noted by @swedge?

Does PGE tell you exactly this threshold? And if so, do they tell you in advance? During? Or after? Ie I assume weather (especially cloud cover) significantly impacts your max generation.

 

[YRide]

I think what folks are asking is if the export limit is strictly based on what the meter 'exports', or whether it is based on the meter's 'net' exports (exports less imports). Because any grid-charging arbitrage nets out as zero, since the import (grid-charge) offsets the export (peak discharge), by the latter definition, and wouldn't move you any closer to the limit....

Yep, that’s the core part of my question. And as I notes earlier, if we’re getting really precise…if you did TOU arbitrage, from a net power (not cost) perspective, you’re always gonna lose something (~10%?) on the round trip from grid to ESS back to grid.

 

[h2ofun]

So does this mean that last month, in theory you could have grid charged at off peak, and then exported at peak from ESS, 2377 kWh (2395-17)? Or is that 2377kWh not considered “export” since its net zero with the amount of power you will consume from the grid?

Technically not net zero (more like -237kWh, because 10% loss round trip).

Does not matter how much I consume from grid, etc. Each month, based on the number of approved panels, I get a maximum amount I can send back to the grid, no matter what the source. Under NEM2, I get retail at time sent back. If I send back more than this monthly amount, which I have had happen before, I do not get any credit for the above this number amount.

Clearly this NVwatts number assume no rain, smoke, etc. that makes it lower.

 

[h2ofun]

Still not quite understanding this comment. Are you saying that it’s impossible to exceed your export limit? Or are you saying don’t exceed your export limit?

If you grid charge then export later (effectively TOU arbitrage) is that considered a net zero export? Or does all “export” only count outbound flow, not net flow?

You can exceed your export limit, you just get zero credit for it. One month I lost credit of 1000kwh's

 

[h2ofun]

Ok…so the point where you switch from getting “retail” credit to getting “wholesale”, right?

And this is threshold is calculated by PGE using PVWatts, or a close proximity as was previously noted by @swedge?

Does PGE tell you exactly this threshold? And if so, do they tell you in advance? During? Or after? Ie I assume weather (especially cloud cover) significantly impacts your max generation.

Your max generation, per month, is fixed by pvwatts. Has nothing to do with weather, smoke, etc. Clearly, because my house is all electric, etc., I will never get close to exporting close to this max, even though I have a huge solar setup. But during the summer months, I get real close to the number, and if a cool summer month, still might exceed the max generation again. But at like 5000kwh, ...

 

[YRide]

Does not matter how much I consume from grid, etc. Each month, based on the number of approved panels, I get a maximum amount I can send back to the grid, no matter what the source. Under NEM2, I get retail at time sent back. If I send back more than this monthly amount, which I have had happen before, I do not get any credit for the above this number amount.

Clearly this NVwatts number assume no rain, smoke, etc. that makes it lower.

I think your first two sentences are a bit contradictory, at least in the context I was trying to ask about (PV + ESS, TOU arbitrage).

Do you have PV only? Or PV+ESS?

I understand ow that the “export” threshold (moving from retail to wholesale) is a number derived, monthly, by PGE using PVWatts.

What I don’t understand still is your second sentence. Is PGE counting outflow-only as export? For example if you charge your ESS off the grid with 100kWh at off peak and then export 90kWh back at on-peak accounting for round trip losses)…does that mean you “exported” 90kWh that month? Or did you export -10kWh?

 

[h2ofun]

I think your first two sentences are a bit contradictory, at least in the context I was trying to ask about (PV + ESS, TOU arbitrage).

Do you have PV only? Or PV+ESS?

I understand ow that the “export” threshold (moving from retail to wholesale) is a number derived, monthly, by PGE using PVWatts.

What I don’t understand still is your second sentence. Is PGE counting outflow-only as export? For example if you charge your ESS off the grid with 100kWh at off peak and then export 90kWh back at on-peak accounting for round trip losses)…does that mean you “exported” 90kWh that month? Or did you export -10kWh?

As my tag line states, I have a generator, solar, and batteries.
Under NEM2, there is no wholesale info. At true up, the cost I get back is in the wholesale
yes, export onto the grid is outflow excess.
Does not matter where the 90kwh comes from, solar, batteries, generator, etc. If the meter sees 90hwh coming from you past meter back to meter to grid, you get 90kwh credit.
Now for the month, there is on the black and white bill, the total month usage from grid, and month how much you sent back. They net this out per month. At 12 months they net it all out and either you pay, or get pennies back on the dollar, like I do.
so if you pulled 100kwh from the grid, and sent back 90kwh, your net would be -10kwh. But its not the amount, it is the cost of energy
at the time you send and pull that is what is the bottom net dollar amount on the bill, positive or negative. I have large negatives on my net monthly bill. This time of the year I use these credits from the summer when pump huge amounts to PG.

 

[fresnoboy]

This is how the Enphase system with generator works. Geny kicks on to charge the batteries, then shuts off and you use batteries again after it's topped off. I've been reading about generator makers starting to come out with solar focused generators, but haven't researched it much yet on really what's the difference.

I was thinking a bit lately about how to really be grid independent and am wondering if for long cloud spells (like these 2-3 days), one should ideally get a massive generator which doesn't have to be on for a long period of time to minimize noise/having to run it vs. smaller units. These last few days have been very cloudy so can see solar alone being a big problem. It doesn't matter how much batteries you have when all you generated all day was 5kWh.

I suppose if we can charge from the grid, you can top off your batteries overnight from grid charging, but I'm still avoiding that due to those old ITC rules to only charge from solar (I don't use storm watch/storm guard/etc). Won't matter in an outage of course.

Indeed. This is why Powerwalls are not really an alternative to a generator. They might be able to help (if they acted like the enphase system you outlined), but they are not a substitute, as this weather is showing everyone. I'm not sure why people ever thought they would be.

Massive is all relative to demand. You can find a ton of industrial units (both NG and Diesel) that at 20KW and higher, but higher has challenges sometimes due to permitting etc... 20-40KW is a sweet spot. but you still would need the space and WAF approval for one of those units, as well as making sure noise isn't an issue for neighbors etc...