Revised CPUC plan: California’s New Solar Subsidy Plan Is Really About Batteries

[fromport]

California’s Solar Subsidy Plan Is Really About Batteries

California -- the biggest US solar market -- is poised to overhaul its landmark subsidy for rooftop panels to encourage homeowners to also install batteries to help stabilize its power grid and prevent blackouts.

www.bloomberg.com

California -- the biggest US solar market -- is poised to overhaul its landmark subsidy for rooftop panels to encourage homeowners to also install batteries to help stabilize its power grid and prevent blackouts.

A plan unveiled Thursday would give homeowners bigger incentives to install batteries along with solar systems instead of just panels alone. The plan threatens to slow the pace of rooftop installations, but would strengthen a state grid that’s buckled during repeated summertime stretches of extreme heat.

edit: update direct link to document of CPUC decision:

https://docs.cpuc.ca.gov/PublishedDocs/Efile/G000/M498/K526/498526033.PDF

 

[45North]

So, will all new construction now require batteries in addition to PV panels?

 

[BentleyJ]

CA definitely needs more battery storage that can be used for self consumption to help stabilize the grid. As it is now there is a large mismatch between peak demand and peak solar production. Looking at the CAISO website, NET demand went from about 25,000 MW at 6:30 am down to 6,000 MW at noon and back up to 25,000 MW at 5 PM. There was a recent post on the Forum regarding PG&E not accepting an inverter because it didn't comply with ALL the current provisions of Rule 21. Unfortunately without energy storage systems, having direct communication with grid-tied inverters is almost useless without the ability to supply power to the grid as well as curtail output when necessary.

 

[fromport]

Looking at the CAISO website, NET demand went from about 25,000 MW at 6:30 am down to 6,000 MW at noon and back up to 25,000 MW at 5 PM.

That was me. I came home and started charging my EV since I needed to do another trip this evening. Sorry about that !

 

[fromport]

articles based on the new CPUC proposal:

California proposed decision to cut payments for rooftop solar net metering

The new NEM 3.0 proposed decision has been released. The decision implements a net billing format with a five year glide path that lowers rates based on the "avoided cost" calculator.

pv-magazine-usa.com

The California Public Utilities Commission (CPUC) has released its proposed decision for Net Energy Metering (NEM), implementing a net billing mechanism and slashing payments for excess solar production sent to the grid by 75%. Based on an initial analysis, the new proposed decision would cut the average export rate in California from $0.30 per kW to $0.08 per kW, making the cuts effective in April 2023.

Under the new net metering structure, payments for excess solar production to the grid will be cut to the “avoided cost” to the utility, a minute fraction of the retail rate paid by customers for electricity supplied by the grid. CPUC said the new proposed decision will lead to an average payback of nine years for residential rooftop solar, based on an assumption of a $3.30 cost per Watt. Read the complete proposed decision here.

The net metered payments will be based on hourly Avoided Cost Calculator rates, averaged over days in a month with separate rates for weekends and holidays. An avoided cost “ACC Plus” adder will be applied to boost net metering payment rates as a constant for nine years and varies by utility. Low-income customers are offered a higher adder rate. SDG&E customers are not eligible to receive an adder.

California pushes a new plan to cut rooftop solar incentives

Homes and businesses would receive lower payments for clean power they send to the grid — but not as low as under an earlier proposal.

www.latimes.com

MSN

The revised rules would:
-Remove a proposed $8 monthly fixed charge, a so-called solar tax, on new residential systems.
-Reduce utilities’ payments to homeowners for excess power they sell by as much as 75% compared to current rates. The change would not apply to residents with existing solar systems.
-Encourage the installation of solar panels plus battery storage.
-Set lower rates in an attempt to shift consumers’ use of power to the times of day that improve grid reliability.

CPUC releases new NEM 3.0 proposal almost one year after the first

Almost a year after its first proposed NEM 3.0 decision that sent the state's solar industry into an uproar, the CPUC has released a new version.

www.solarpowerworldonline.com

----------------

The more I read about it, the more I think it is sneaky, very sneaky

 

[Goboatingnow]

It’s not sneaky it’s the way way most grids are moving. In many countries nett metering is flat capped. Ie you get nothing beyond a certain point.

At least this proposal keeps paying you albeit at a low rate

This is typical of what we are seeing in the developed world to protect “ grid economics” from micro generation

In essence compensating micro generators at significant proportion of retail price is nonsense for a grid. In essence it’s being forced to buy high priced micro generation units when large scale spot market generations will be offering much lower cost to the grid.

Ultimately the grid operator must buy units at the most favourable costs at the point in time it needs it.

In reality microgenerstion should participate in that “ spot” wholesale pricing but then users will see feed in tarriffs way way lower then the artificial pricing of net metering.

It’s one thing to pay for electricity you don’t use. It’s another to be paid not to use it.
.

 

[400bird]

Can anyone explain the avoided costs? I assume that would be charged to a NEM 3 customer, but in what way? I read through portions of the 241 page CPUC decision and I still don't understand.

Is the avoided costs the kWh rate the customer would be credited?

 

[zanydroid]

Can anyone explain the avoided costs? I assume that would be charged to a NEM 3 customer, but in what way? I read through portions of the 241 page CPUC decision and I still don't understand.

Is the avoided costs the kWh rate the customer would be credited?

That is my understanding from NEM3 discussion from last year — it’s the new decreased credit level for backfeed, that I guess isn’t an incentive subsidy but rather closer to economically sustainable for the utility and grid to provide.

It’s definitely different from wholesale cost. I think it bakes in a factor of being high enough to still be an incentive and reducing transmission and distribution costs on the grid

 

[Goboatingnow]

Ultimately “ avoided cost “ is the difference between the cost of supplying you the units.

Ie if it cost the grid say $0.10 to potentially generate the units & supply them to you , you made yourself. That’s the avoided cost cause you made them instead. Hence you get paid that

In essence it takes the best case generation cost plus utility overhead. It’s supposed to be a computation of what the utility would have paid to supply you with those units.

Hence in theory paying you the equivalent cost of you generate is P&L neutral for the grid.

It’s an attempt to generate a metric for feed in tarriff. It’s largely finger in the air.

It’s essentially an alternative to NEM , which essentially is much more expensive to the grid as it’s paying for electricity generation ( you ) it actually may not need or can source at lower costs.

For example you may be paid in one month for net metering and rebuy that units in a future month that could be a bad proposition for the grid.

Ultimately microgeneration needs to participate in the bid/offer mechanism that’s used typically by big generators to price grid supply

 

[fafrd]

Can anyone explain the avoided costs? I assume that would be charged to a NEM 3 customer, but in what way? I read through portions of the 241 page CPUC decision and I still don't understand.

Is the avoided costs the kWh rate the customer would be credited?

‘Avoided cost’ translates to the utilities cost per kWh to build a new power plant and produce it with the fuel needed to produce power.

Solar is supposed to have provided the utilities with ‘virtual power plants’ resulting in their ability to sell and distribute electrical power without having had to invest in new facilities.

That ‘virtual investment’ which was avoided is the driver of the ‘avoided cost’ calculation (amortized over whatever period and with adders for fuel, maintenance, etc…).

While wholesale and spot-market electricity rates reflect the instantaneous value of a kWh of power, the avoided cost calculation is supposed to reflect the cost of electricity averaged over the lifetime of a new generation plant in a way that it averages to about the same as wholesale rates but without the peaks and valleys…

It’s supposed to reflect the averaged cost it would take the utility to invest in a new plant that produces an equal amount of power.

 

[fafrd]

articles based on the new CPUC proposal:

California proposed decision to cut payments for rooftop solar net metering

The new NEM 3.0 proposed decision has been released. The decision implements a net billing format with a five year glide path that lowers rates based on the "avoided cost" calculator.

pv-magazine-usa.com

The California Public Utilities Commission (CPUC) has released its proposed decision for Net Energy Metering (NEM), implementing a net billing mechanism and slashing payments for excess solar production sent to the grid by 75%. Based on an initial analysis, the new proposed decision would cut the average export rate in California from $0.30 per kW to $0.08 per kW, making the cuts effective in April 2023.

Under the new net metering structure, payments for excess solar production to the grid will be cut to the “avoided cost” to the utility, a minute fraction of the retail rate paid by customers for electricity supplied by the grid. CPUC said the new proposed decision will lead to an average payback of nine years for residential rooftop solar, based on an assumption of a $3.30 cost per Watt. Read the complete proposed decision here.

The net metered payments will be based on hourly Avoided Cost Calculator rates, averaged over days in a month with separate rates for weekends and holidays. An avoided cost “ACC Plus” adder will be applied to boost net metering payment rates as a constant for nine years and varies by utility. Low-income customers are offered a higher adder rate. SDG&E customers are not eligible to receive an adder.

California pushes a new plan to cut rooftop solar incentives

Homes and businesses would receive lower payments for clean power they send to the grid — but not as low as under an earlier proposal.

www.latimes.com

MSN

The revised rules would:
-Remove a proposed $8 monthly fixed charge, a so-called solar tax, on new residential systems.
-Reduce utilities’ payments to homeowners for excess power they sell by as much as 75% compared to current rates. The change would not apply to residents with existing solar systems.
-Encourage the installation of solar panels plus battery storage.
-Set lower rates in an attempt to shift consumers’ use of power to the times of day that improve grid reliability.

CPUC releases new NEM 3.0 proposal almost one year after the first

Almost a year after its first proposed NEM 3.0 decision that sent the state's solar industry into an uproar, the CPUC has released a new version.

www.solarpowerworldonline.com

----------------

The more I read about it, the more I think it is sneaky, very sneaky

The more I read about it, the more I am happy with the revised proposal (much, much happier than I was with the previous one).

First and foremost, no solar tax.

Second of all, no changes to the terms for grandfathered NEM 1.0 and NEM 2.0 customers.

And lastly, whether it comes into effect abruptly or over a glide-path, this new proposal translates to meaning new solar customers will need to capture and consume most/all of their solar generation rather than exporting to grid.

We know that’s the reality and technologies make that much more feasible today than even five years ago.

So if you already invested in solar, you’ll get the full benefit of the 20-year agreement you invested in.

If you are contemplating solar, you’ll understand the economics in advance to determine whether it makes economic sense for you or not.

Obviously if the economics got new installs is impacted enough, the residential rooftop solar industry will be severely impacted.

But equally obviously, as solar panel cost / Wh and now battery cost / Wh continues to decline while fuel costs and utility electricity costs / Wh continue to increase, it is inevitable that there will be a point in the future where residential rooftop solar + storage will make economic sense eventually.

Hopefully the ‘glide-path’ will be planned to tide the residential rooftop solar installer industry through any possible chasm.

This newly-released preliminary decision is better news than I dared hope for.

 

[zanydroid]

I am super happy about removal of the grid access charge based on DC nameplate. That seemed like a pretty awkward and unsound way of achieving policy goals. Vs say requiring revenue grade production metering on AC and then calculating a tax formula to compensate for providing grid backup, etc.

I think it’s perfectly reasonable to have a transition plan away from 1:1 net metering. It’s not economically nor engineering sustainable.

What were the other major changes from previous version?

 

[fafrd]

Here is a bit more context on what caused the change: https://pv-magazine-usa.com/2022/11...n-to-cut-payments-rooftop-solar-net-metering/

‘CPUC determined that the NEM 2.0 structure “negatively impacts non-participating ratepayers; disproportionately harms low-income ratepayers; and is not cost-effective.” These assumptions, which were determined by CPUC in a “Lookback Study” have been challenged by the rooftop solar industry. CALSSA said a number of the study’s assumptions are flawed, and the source code necessary to investigate or replicate the study’s main conclusions is not provided. It said the CPUC also failed to make the Lookback Study analysts available for discovery or cross-examination.

Protect Our Communities (PCF) said the Lookback Study underestimates the benefits of behind-the-meter generation because the calculator does not adequately quantify avoided transmission costs or the resiliency benefits of net energy metering solar, or account for the air quality and climate benefits.’

So the cliff-notes version is that the ‘Lookback Study’ which motivated much of the nonsensical ‘equity’-motivated provisions including the solar tax was successfully challenged by CALSSA and the CPUC understood that study and the provisions it drove were unlikely to withstand scrutiny.

While, in contrast, the study that resulted in the Avoided Cost Calculation’ was much more solid / defendable and the CPUC knew that changes to NEM driven primarily by that study were on much more solid ground.

This is a really clean and rational evolution for the NEM program. I’m happy to see that rational minds prevailed and just hope this moves through the final stages without significant modification.

If the remaining debate and any tweaking remain centered on the ‘glide path’ and how to juice the economics for solar + storage until it becomes self-sustaining to minimize impact on the residential rooftop installer industry, everything will be about as good as it can get…

 

[400bird]

Ok, so NEM 3.0 redefines the "Net" in Net Energy Metering. Now, the customer (I'm PGE) gets credit for $0.018/kWh for each kWh sold to the grid and buys back at retail rates overnight?
Doesn't sound very "net"...

What about SDG&E? They get credited at $0/kWh?

I understand NEM2.0 isn't fair to the power co and supposedly other customer. I see it needed to change. I'd just like to understand the new program.

 

[fafrd]

I am super happy about removal of the grid access charge based on DC nameplate. That seemed like a pretty awkward and unsound way of achieving policy goals. Vs say requiring revenue grade production metering on AC and then calculating a tax formula to compensate for providing grid backup, etc.

I think it’s perfectly reasonable to have a transition plan away from 1:1 net metering. It’s not economically nor engineering sustainable.

What were the other major changes from previous version?

The previous version lopped 5-years off of the 20-year grandfathering period for NEM 1.0 and NEM 2.0.

I’d probably suggest we make a distinction when analyzing proposals between impact on legacy customers and impact on new customers.

The proof proposal had a much more negative impact on legacy customers (what I’ve called a ‘bait and switch’) while these new proposal largely leaves legacy customers unmaffected.

For new customers, this new proposal seems to be structured more as an abrupt change to the economics / value of export requiring new solar installs to include storage or they won’t make economic sense.

The old proposal seemed to be driven by the concept of motivating the 1.4 million existing NEM1.0 and NEM2.0 customers to add storage (by both carrots and sticks) at least as much as it was driven by requiring new solar installs to include storage.

This new proposal leaves legacy customers alone for the remaining lifetime of their contract periods and just focuses on assuring new solar installs will include storage (or they won’t make economic sense).

Much, much cleaner.

 

[fafrd]

Ok, so NEM 3.0 redefines the "Net" in Net Energy Metering. Now, the customer (I'm PGE) gets credit for $0.018/kWh for each kWh sold to the grid and buys back at retail rates overnight?
Doesn't sound very "net"...

They are also talking about changing to Net Monthly Billing (not sure whether NEM changes to NMB or NMM or not…).

So while I have not yet read the proposal in detail to be certain this is correct or not, the idea could be this:

On a monthly basis, if meter has run forward, you will be charged for net kWh consumed (beyond any Minimum Delivery Charges).

If meter has run backwards, you will be credited per kWh of generation based on the Avoided Cost calculation (which is pretty much what is done today on an annual basis).

So it is likely still ‘net’ but on a monthly rather than annual basis (and presumably only for new customers).

What about SDG&E? They get credited at $0/kWh?

That is the adder/juice to institute a ‘glide path’. That only impacts new customers. Terms for existing customers are pretty much not going to change.

I understand NEM2.0 isn't fair to the power co and supposedly other customer. I see it needed to change. I'd just like to understand the new program.

The new program means you will no longer be able to generate credits over summer months to offset consumption over winter months.

If you size your system to perfectly offset consumption over summer months, you’ll be paying for some electricity in Spring & Fall and alot of Electricity in Winter.

If you size your system to
perfectly offset consumption in Spring & Fall, you be a net generator over the summer but will only be credited for that over generation at ~25% the full retail rate NEM1.0 and NEM2.0 get. And then in winter, you’ll be a net consumer, but your generation credits ought to cover at least half the cost of your winter consumption (so this will likely be the most economically viable system to install).

And if you size your system to perfectly offset winter consumption, you won’t ever be paying anything other than Minimum Delivery Charges for electricity, but your more expensive system is not going to generate enough export credit over spring, summer, and fall to pay off your added cost on much under 10years.

For someone installing a system sized to cover all but Minimum Delivery Charge’s-worth of kWh in December, pretty much no impact at all.

For those installing a system sized to offset annual consumption (meaning slightly under the size needed to perfectly offset Spring & Fall consumption), their summer generation credit will no longer offset all winter consumption beyond Minimum Delivery Charge so they will be paying for some consumption over winter (unless they install a larger system).

And while I explained the simple example of checking the meter monthly, it is possible that they will be tracking generation seperately from consumption and only crediting Avoided Cost on all export, not merely Net Export.

Without that, there is less incentive for new installs to have a battery since daytime generation is credited at the same rate needed to offset overnight consumption (from grid).

If you do that. I agree with you, there is no longer any ‘Net’ in NEM3.0.

On the other hand, the shift to TOU billing already creates a motivation to have battery storage (and one which impacts legacy customers as well as new customers) so if they feel TOU is enough, they may stick to NEM on a monthly true-up basis (which is much cheaper and easier for them to implement).

 

[zanydroid]

perfectly offset consumption in Spring & Fall, you be a net generator over the summer but will only be credited for that over generation at ~25% the full retail rate NEM1.0 and NEM2.0 get. And then in winter, you’ll be a net consumer, but your generation credits ought to cover at least half the cost of your winter consumption (so this will likely be the most economically viable system to install).

Under the new rules, do you think this (sized for spring/fall) is the most economical to install for parts of California that are winter heating dominated (EG San Francisco, Peninsula, ...)? I'm working on updating my new install, which was grossly undersized by my installer (they messed up the modeling and I didn't catch it before install) and only covers my annual need outside of heating (IE, their model over-estimated by 2x). I have a contract signed to swap from gas to heat pump (coming in a few months) and my electricity bills are going to be brutal unless I do something about the solar system

 

[fafrd]

They are also talking about changing to Net Monthly Billing (not sure whether NEM changes to NMB or NMM or not…).

So while I have not yet read the proposal in detail to be certain this is correct or not, the idea could be this:

On a monthly basis, if meter has run forward, you will be charged for net kWh consumed (beyond any Minimum Delivery Charges).

If meter has run backwards, you will be credited per kWh of generation based on the Avoided Cost calculation (which is pretty much what is done today on an annual basis).

So it is likely still ‘net’ but on a monthly rather than annual basis (and presumably only for new customers).

That is the adder/juice to institute a ‘glide path’. That only impacts new customers. Terms for existing customers are pretty much not going to change.

The new program means you will no longer be able to generate credits over summer months to offset consumption over winter months.

If you size your system to perfectly offset consumption over summer months, you’ll be paying for some electricity in Spring & Fall and alot of Electricity in Winter.

If you size your system to
perfectly offset consumption in Spring & Fall, you be a net generator over the summer but will only be credited for that over generation at ~25% the full retail rate NEM1.0 and NEM2.0 get. And then in winter, you’ll be a net consumer, but your generation credits ought to cover at least half the cost of your winter consumption (so this will likely be the most economically viable system to install).

And if you size your system to perfectly offset winter consumption, you won’t ever be paying anything other than Minimum Delivery Charges for electricity, but your more expensive system is not going to generate enough export credit over spring, summer, and fall to pay off your added cost on much under 10years.

For someone installing a system sized to cover all but Minimum Delivery Charge’s-worth of kWh in December, pretty much no impact at all.

For those installing a system sized to offset annual consumption (meaning slightly under the size needed to perfectly offset Spring & Fall consumption), their summer generation credit will no longer offset all winter consumption beyond Minimum Delivery Charge so they will be paying for some consumption over winter (unless they install a larger system).

And while I explained the simple example of checking the meter monthly, it is possible that they will be tracking generation seperately from consumption and only crediting Avoided Cost on all export, not merely Net Export.

Without that, there is less incentive for new installs to have a battery since daytime generation is credited at the same rate needed to offset overnight consumption (from grid).

If you do that. I agree with you, there is no longer any ‘Net’ in NEM3.0.

On the other hand, the shift to TOU billing already creates a motivation to have battery storage (and one which impacts legacy customers as well as new customers) so if they feel TOU is enough, they may stick to NEM on a monthly true-up basis (which is much cheaper and easier for them to implement).

I read through the entire preliminary decision (quickly).

There is a name change - it is called Net Billing Tariff (NBT?).

The ‘Net’ means you will be billed (or credited) for the cost of your monthly consumption net of the (Avoided Cost) value of your monthly export.

And the other big change is that there in no longer any Net Energy Interval, meaning that import or export will be detected ‘instantaneously’ and will be tracked seperately (two ‘channels’ as they call it).

NEM1.0 and NEM2.0 looks as though they will be unaffected for their full 20-year grandfathering period but NBT / NEM3.0 customers will only get 9 years of grandfathering (and non-transferable as well).

Anybody installing solar under the terms of NBT / NEM3.0 is going to also want storage or it’s just not going to make any sense…

 

[fafrd]

Under the new rules, do you think this (sized for spring/fall) is the most economical to install for parts of California that are winter heating dominated (EG San Francisco, Peninsula, ...)?

Well first, it you get this install done by next Spring, you should fall under NEM2.0 and shouldn’t have to worry about these ‘new rules’ until 2043…

And secondly, you should be able to put in any system sized to offset consumption you can attest you are planning over the following 12 months.

The big question for a NEM2.0 install would be whether you are going to include a battery or not…

I'm working on updating my new install, which was grossly undersized by my installer (they messed up the modeling and I didn't catch it before install) and only covers my annual need outside of heating (IE, their model over-estimated by 2x). I have a contract signed to swap from gas to heat pump (coming in a few months) and my electricity bills are going to be brutal unless I do something about the solar system

I’m not understanding whether you’ve already got a system installed or not nor whether it’s 50% the size you need or 200%.

In general, my advice would be to install the largest solar system you can justify (or afford or fit).

Under NEM 2.0 you can get away without a battery (which can always be added later if/when necessary) and the savings from no battery will pay for an awful lot of additional solar panels.

The utility limits the amount of solar power you can add without losing your grandfathering, while the new rules explicitly stated that NEM1.0 and NEM2.0 customers must be allowed to add storage without losing their grandfathering.

So I’d suggest you estimate the highest consumption you can justify (didn’t I hear yo say your planning to get a new EV next year?) and install the largest solar array your utility will let you get away with based on your attestation.

In answer to your original question, though, my earlier statements were based on an assumption of roughly equal seasonal electrical consumption. If you consume about the same number of kWh per monthly, sizing to produce about that amount in September and March and having a battery large enough to store excess energy during daylight hours in September and March to offset overnight consumption is going to be a natural sweetspot in terms of minimum years to break-even.

If you’re consuming twice the monthly kWh over winter, it probably doesn’t change that and you’re just going to be paying for your heating.

You’d need a 100-150% increase in the size of your solar system to go from ~100% coverage in March/September to ~100% coverage in December based on flat per-month consumption.

If your consumption in December is 200% that of March & September, you’d need to increase the array by 200-300% over an array sized for March / September offset.

That means 200-300% more export credit in sumner, but those credits are only valued at ~25% of retail. So you get enough extra credit during summer to cover 50-75% of your increased wintertime consumption, but the system probably cost you enough more to not make it worthwhile.

Plus, if one were to try to justify sizing a system for 200-300% of estimated annual consumption, I’m guessing the utility would not be onboard…

 

[zanydroid]

Well first, it you get this install done by next Spring, you should fall under NEM2.0 and shouldn’t have to worry about these ‘new rules’ until 2043…

And secondly, you should be able to put in any system sized to offset consumption you can attest you are planning over the following 12 months.

Yes, I already am working on getting it done before April for exactly this reason. The main reason for asking this is so I can understand what to tell people for NEM3 and so I can test my understanding.

Do you know what happens if you submitted interconnect agreement at 14MWh annual estimate in June, and then submit again for 14MWh again in February later but with double the panels? I guess worst case someone asks you to give more details...

The big question for a NEM2.0 install would be whether you are going to include a battery or not…

I’m not understanding whether you’ve already got a system installed or not nor whether it’s 50% the size you need or 200%.

I'm not interested in getting a battery, the markup is too high and the grid works perfectly fine. Isn't it a pure negative with NEM2 even if I switched to a superpeak plan and exported all production during superpeak at $0.60?

The system is installed. The installer estimated 14MWh annual generation, based on my attestation for gas to electric conversion and buying an EV. I noticed some discrepancies / really bad system design in other areas, and went back and compared the estimate with another proposal that I got, along with PVWatts data. The other proposal used 50% total solar access based on Aurora shade simulation; to achieve 14MWh it had double the panels. The installer I used appears to have used PVWatts with 100% solar access (I noticed this with while thinking about expanding the system "for fun" before NEM3.0. Now I think I need to expand it to properly justify gas -> electric conversion. Or cancel those projects and take the contract penalty).

I'm pretty sure the 50% solar access is correct.

It's the 50% solar access that really triggered me about the per-DC-W solar tax of previous NEM3.0. Basically no glide path, or whatever, would ever make solar make sense.

In answer to your original question, though, my earlier statements were based on an assumption of roughly equal seasonal electrical consumption. If you consume about the same number of kWh per monthly, sizing to produce about that amount in September and March and having a battery large enough to store excess energy during daylight hours in September and March to offset overnight consumption is going to be a natural sweetspot in terms of minimum years to break-even.

If you’re consuming twice the monthly kWh over winter, it probably doesn’t change that and you’re just going to be paying for your heating.

You’d need a 100-150% increase in the size of your solar system to go from ~100% coverage in March/September to ~100% coverage in December based on flat per-month consumption.

If your consumption in December is 200% that of March & September, you’d need to increase the array by 200-300% over an array sized for March / September offset.

What do you mean by "just paying for your heating"? Do you mean importing it from the grid?

The kWh only goes up during the winter where I am. Only 1-2 weeks worth of serious cooling days in the summer. Fall/winter/Spring has longer days plus heating for half of fall, all of winter, and half of spring. I do have all the monthly data available, but as you said it's irrelevant as long as I get the expansion done in time, and I should focus on that.

Yeah PVWatts said I needed to 2-3x. I haven't tried to extrapolate from the Aurora I have to see how the seasonal solar access affects it. The solar access is better in the summer anyway so my gut feeling is it's not worth the investigation time.

As part of the "fun" project, I was considering to put vertical panels in on south facing wall, which would be pretty bad for summer but decent for winter and has decent solar access due to a gap in the tree cover. The idea here was to have the DC size locked in for NEM2.0 before the solar tax, etc. kicked in (from the old NEM3)

That means 200-300% more export credit in sumner, but those credits are only valued at ~25% of retail. So you get enough extra credit during summer to cover 50-75% of your increased wintertime consumption, but the system probably cost you enough more to not make it worthwhile.

Thanks. I'll go over these numbers in depth, but this matched my intuition.

It feels like the right answer for handling this type of seasonal consumption is to import electricity from the south during winter rather than try to produce it on-site.