Is my system large enough?

[silversaver]

10% or 1kW to your existing system, but not that simple. It really depends on how your system originally design and type of inverter/array setup. my system is running off a string inverter with 2 X13 panels. Adding one panel to each array still within specs for the inverter so I end up doing that.

[TSHRED]

1.) This isn't my first round trip with this question which was when I was doing the preliminary design of my system in 2012 and considering the question of (possible) future system expansion. The rules have not changed since then to now for either NEM 1.0 (what I'm on) or 2.0 (what you're on) and I believe are still good for NEM 3.0.

Your installer is wrong. Refer your installer to sheet 15 of SDG & E Schedule NEM, C.P.U.C sheet # 26209-E dated 02/22/2017, Under Special conditions, para. # 7.b., the limit is 10% of the system's capacity or 1kW, "whichever is greater". The wording in the paragraph is a bit obtuse, but the bottom line is that's what it says.
I've also had several phone conversations w/SDG & E over the years to clarify the wording.

BTW, If you call them, be careful what you say as there is also wording in that same para #7.b that limits an eligible expansion to those systems that are "...sized to meet but not exceed the customer's annual onsite load...".

So technically, if SDG & E got porky, they might well try to make a case for throwing a lot of oversized systems out of NEM. Al they'd need do is see who consistently overproduced and consistently got money back at trueup. Just sayin'.

2.) STC = Standard Test Conditions. The conditions at which panels are rated for their output. The rating can be used to compare efficiency between and among panels. The test conditions are also those used when testing panel output at the end of the manufacturing process.
The conditions were mostly chosen to be simple and easily maintained under (indoor) conditions. Although a lot of uninformed folks assume so, STC output is NOT a measure of a panel's expected maximum sustained output under installed and operating conditions.
That's a mistake a lot of new and potential users make when they think they got screwed when looking at their brand new 5 STC kW array's monitor under bright sun at noon in mid spring and see only something like 4.2 kW or so coming out of the inverter.

3.) POCO == POwer COmpany. In your case, that's SDG & E.

Screenshot_20230427_103132_Samsung Notes.jpg

[J.P.M.]

I was just informed by my installer that it's whichever is "lower".
For my 4kW system that means just one 400W panel to remain in NEM 2.0.

Newbie questions:

What is STC?
What is POCO?

1.) This isn't my first round trip with this question which was when I was doing the preliminary design of my system in 2012 and considering the question of (possible) future system expansion. The rules have not changed since then to now for either NEM 1.0 (what I'm on) or 2.0 (what you're on) and I believe are still good for NEM 3.0.

Your installer is wrong. Refer your installer to sheet 15 of SDG & E Schedule NEM, C.P.U.C sheet # 26209-E dated 02/22/2017, Under Special conditions, para. # 7.b., the limit is 10% of the system's capacity or 1kW, "whichever is greater". The wording in the paragraph is a bit obtuse, but the bottom line is that's what it says.
I've also had several phone conversations w/SDG & E over the years to clarify the wording.

BTW, If you call them, be careful what you say as there is also wording in that same para #7.b that limits an eligible expansion to those systems that are "...sized to meet but not exceed the customer's annual onsite load...".

So technically, if SDG & E got porky, they might well try to make a case for throwing a lot of oversized systems out of NEM. Al they'd need do is see who consistently overproduced and consistently got money back at trueup. Just sayin'.

2.) STC = Standard Test Conditions. The conditions at which panels are rated for their output. The rating can be used to compare efficiency between and among panels. The test conditions are also those used when testing panel output at the end of the manufacturing process.
The conditions were mostly chosen to be simple and easily maintained under (indoor) conditions. Although a lot of uninformed folks assume so, STC output is NOT a measure of a panel's expected maximum sustained output under installed and operating conditions.
That's a mistake a lot of new and potential users make when they think they got screwed when looking at their brand new 5 STC kW array's monitor under bright sun at noon in mid spring and see only something like 4.2 kW or so coming out of the inverter.

3.) POCO == POwer COmpany. In your case, that's SDG & E.

[TSHRED]

... has always been 10% of the system's STC wattage or 1 STC kW, whichever is larger.
See your NEM 2.0 agreement for confirmation of that and a few other details that don't usually affect small system owners.

...

I was just informed by my installer that it's whichever is "lower".
For my 4kW system that means just one 400W panel to remain in NEM 2.0.

Newbie question:

What is STC?

[TSHRED]

And that's where education, reasonable lifestyle adjustments (like, if on T.O.U., time shifting within reason) and conservation come in.

If we're writing about SDG & E's rates, if a user has something like the common and usual usage patterns of the type the SDG & ET.O.U. rate times are built around then it may make sense to try to get on to (or back on to) tiered rates (plain old schedule "DR").

Or, have a serious look at the various T.O.U. schedules and rates with an eye toward minimizing use during peak summer hours which are, perhaps somewhat surprisingly perhaps, a total of 765 hours or only 8.73 % of the 8,760 hours in a year.

If I lived in Encinitas, with what's probably (or could be) close to zero A/C loading, with a 4 STC kW (note TSHRED: not a 4 kWh system) I'd go back to tiered rates (schedule "DR"), quit fooling around with this T.O.U. business and work to stay in tier one usage as much as possible, particularly in the summer, which, depending on orientation and shading might be quite possible after the 6,000 or so kWh/yr. a 4 kW system might produce. in that neighborhood.

Jeff, I'm pretty sure you're knowledgeable of all this, but for those reading this mental spoor who are less knowledgeable, and as for being careful and knowledgeable about oversizing, in applications where system cost effectiveness is an important consideration, consider this:
One important parameter in a cost analysis is the value of a kWh of electricity that the system offsets from the POCO.
The more expensive that kWh is, and regardless of how sophisticated or simple the analysis is, for the same system with the same system cost, the more cost effective the system will be (or, the sooner will breakeven be reached, or the higher will the ROI be).
So, for as an oversimplified example, let's say a theoretical system is sized to offset exactly 100% of an annual load - won't happen, but stick with me.
Without going into life cycle costing or engineering economics or a LCOE type of analysis, let's also say that the electricity produced by that system costs the same as the POCO purchased electricity.
Now, under many/most NEM agreements - and the OP's is one of them - any excess generation is paid to the customer at a much lower rate than non-excess generation.
So, if a NEM customer deliberately oversize's a system, that portion of the system that represents the oversizing generates electricity that's worth (for this year so far) $0.0948/kWh compared to somewhere between $0.35 and $0.80/kWh as the value for the no excess generation portion of the system production (per current schedule DR-SES). That means the entire system's cost effectiveness will be dragged down and/or the system cost effectiveness will be reduced - depending on the degree of oversizing - to a point where the LCOE of the PV produced electricity may well be greater than the LCOE purchased from the POCO. Happens in my HOA quite a bit. Folks think they're giving the finger to and getting even with SDG & E and all their doing is boning themselves and don't have a clue.

Look, some oversizing makes sense and a slight oversizing is probably a good idea, but for the love of the Almighty, go about it with some knowledge of what you're doing and the consequences. At least walk in with your eyes open.

Cost effectiveness and figuring what makes economic sense is more than net initial system cost divided by annual savings.
Most folks I've run into over the years and tried to help are utterly clueless about even the rudiments of PV, much less the relationship between system size, electrical load, system economics and cost effectiveness, and more often than not work against their initial and usual goal of saving money on the cost of providing electricity for their homes.

I appreciate your knowledge.
I'm a newbie.

But I do have a system under NEM 2.0 and I'm happy for that.

[bcroe]

There are coils embedded in the ceiling of the rooms.
NO central HVAC unit.
Fortunately we are very temperate here near the coast and these last few months have been very unusually chilly.

My mini split heat pumps are ductless, zone units. Several required to
cover the house. In somewhat cold weather they reduce heating energy
to only about 1/3 that of resistance heat. Bruce Roe

[J.P.M.]

I would add that this tradeoff depends hugely on what plan you are on; DR vs TOU, and whether you can keep yourself in the lowest tier with the system you have,

And that's where education, reasonable lifestyle adjustments (like, if on T.O.U., time shifting within reason) and conservation come in.

If we're writing about SDG & E's rates, if a user has something like the common and usual usage patterns of the type the SDG & ET.O.U. rate times are built around then it may make sense to try to get on to (or back on to) tiered rates (plain old schedule "DR").

Or, have a serious look at the various T.O.U. schedules and rates with an eye toward minimizing use during peak summer hours which are, perhaps somewhat surprisingly perhaps, a total of 765 hours or only 8.73 % of the 8,760 hours in a year.

If I lived in Encinitas, with what's probably (or could be) close to zero A/C loading, with a 4 STC kW (note TSHRED: not a 4 kWh system) I'd go back to tiered rates (schedule "DR"), quit fooling around with this T.O.U. business and work to stay in tier one usage as much as possible, particularly in the summer, which, depending on orientation and shading might be quite possible after the 6,000 or so kWh/yr. a 4 kW system might produce. in that neighborhood.

Jeff, I'm pretty sure you're knowledgeable of all this, but for those reading this mental spoor who are less knowledgeable, and as for being careful and knowledgeable about oversizing, in applications where system cost effectiveness is an important consideration, consider this:
One important parameter in a cost analysis is the value of a kWh of electricity that the system offsets from the POCO.
The more expensive that kWh is, and regardless of how sophisticated or simple the analysis is, for the same system with the same system cost, the more cost effective the system will be (or, the sooner will breakeven be reached, or the higher will the ROI be).
So, for as an oversimplified example, let's say a theoretical system is sized to offset exactly 100% of an annual load - won't happen, but stick with me.
Without going into life cycle costing or engineering economics or a LCOE type of analysis, let's also say that the electricity produced by that system costs the same as the POCO purchased electricity.
Now, under many/most NEM agreements - and the OP's is one of them - any excess generation is paid to the customer at a much lower rate than non-excess generation.
So, if a NEM customer deliberately oversize's a system, that portion of the system that represents the oversizing generates electricity that's worth (for this year so far) $0.0948/kWh compared to somewhere between $0.35 and $0.80/kWh as the value for the no excess generation portion of the system production (per current schedule DR-SES). That means the entire system's cost effectiveness will be dragged down and/or the system cost effectiveness will be reduced - depending on the degree of oversizing - to a point where the LCOE of the PV produced electricity may well be greater than the LCOE purchased from the POCO. Happens in my HOA quite a bit. Folks think they're giving the finger to and getting even with SDG & E and all their doing is boning themselves and don't have a clue.

Look, some oversizing makes sense and a slight oversizing is probably a good idea, but for the love of the Almighty, go about it with some knowledge of what you're doing and the consequences. At least walk in with your eyes open.

Cost effectiveness and figuring what makes economic sense is more than net initial system cost divided by annual savings.
Most folks I've run into over the years and tried to help are utterly clueless about even the rudiments of PV, much less the relationship between system size, electrical load, system economics and cost effectiveness, and more often than not work against their initial and usual goal of saving money on the cost of providing electricity for their homes.

[TSHRED]

Possibly a modern heat pump could make your energy do more
than straight electric resistance heating. Bruce Roe

There are coils embedded in the ceiling of the rooms.
NO central HVAC unit.
Fortunately we are very temperate here near the coast and these last few months have been very unusually chilly.

[bcroe]

Possibly a modern heat pump could make your energy do more
than straight electric resistance heating. Bruce Roe

[jflorey2]

- Besides, and contrary to what the green mafia and PV peddlers and their shills would imply or tell you, within reason, paying a slightly larger annual bill is usually more cost effective than paying the excess cost of an oversized system.

I would add that this tradeoff depends hugely on what plan you are on; DR vs TOU, and whether you can keep yourself in the lowest tier with the system you have,

[J.P.M.]

I have been told now that NEM 3.0 has kicked in I'm limited to an additional 1kWh of panels to avoid triggering NEM 3.0. Is this true?

If you are a current NEM 2.0 customer, the limit on increasing an existing system's size without exposing yourself to penalties (either getting the whole system kicked out of whatever NEM you're on when the size increase is done and moving it to the current NEM 3.0 or putting the system increase on a separate meter with that additional capacity billed under NEM 3.0) has always been 10% of the system's STC wattage or 1 STC kW, whichever is larger.
See your NEM 2.0 agreement for confirmation of that and a few other details that don't usually affect small system owners.

NEM 3.0 will not change those limits or their consequences.
They've always been in effect that way since way back in NEM 1.0.

As for the size increase and whether it's a good idea:
- Your usage will fluctuate as your situation and the weather changes.
- Reading up on and incorporating lifestyle adjustments and conservation measures will go a long way to lowering usage toward system output.
- Besides, and contrary to what the green mafia and PV peddlers and their shills would imply or tell you, within reason, paying a slightly larger annual bill is usually more cost effective than paying the excess cost of an oversized system.

[SolTex]

You are gonna need really good months in May and June to make up the shortfall for the year. Have you tried running your system through the PVWatts calculator? You enter the details on your physical location and system, and the calculator will predict annual production. The production numbers are presented for each individual month, so you can see what you might expect to make between now and your true-up date. Give it a try!

https://pvwatts.nrel.gov

[TSHRED]

Our 4kWh system went online last Aug 11th. It was configured for 110% of the previous years useage.

We have a moderate climate but this last winter and early spring were unseasonably cold and we used the electric heat more than usual.

Our true-up date is July 13th. due to the billing schedule according to SDGE.

I have been told now that NEM 3.0 has kicked in I'm limited to an additional 1kWh of panels to avoid triggering NEM 3.0. Is this true? I'm currently under NEM 2.0.

Looking at this lifetime chart since activation I'm thinking I won't zero out by the true up date and will owe.

What do you think?

Screenshot_20230426_071020_Enlighten.jpg