Upgrading solar on PG&E NEM 1.0

[miimura]

I have been lamenting the small size of my solar system ever since I got my first EV. When I had the house built in 2012, I wanted to go for the New Solar Homes Program and get a 9+kW solar system funded by a huge State rebate. Unfortunately, the solar installer I picked during construction was not up to the paperwork requirements and I had to scale back the solar to something I could afford without the NSHP rebate. Anyway, now we're coming up on 7 years in the house and for the last 4+ years we have had two EVs and paid approximately $1000 to PG&E at true-up in those years.

Since the solar system is old, we are on NEM 1.0 which has no Non-Bypassable Charges. The Tariff states that repairs or upgrades must remain less than 10% or 1kW (whichever is larger) greater than the original interconnected system in order to remain on the NEM 1 tariff. The calculation is based on the "rated generating capacity". I have found out that this is calculated by multiplying the panel's PTC Rating by the Inverter CEC Efficiency rating. I have 18 Motech 240W panels on Enphase M215 microinverters. So, I get 18 x 0.240 x 0.96 = 4.15kW Rated Generating Capacity (rounded up to nearest 10W). I have not had any Enphase failures, so I'm not inclined to change them. So, I'm thinking I should replace some or all of the panels. The problem is that I can only go 5.15kW Rated Generating Capacity. This results in 298W PTC rated panels, if I change them all. I don't think I could use 300W panels because it would technically be over the limit unless I just leave one old panel up there. Also, it would be a 1.376:1 DC-AC ratio, so there would be some clipping. The arrays face SE and SW.

Thoughts?

Pic for reference.

 

[mblakele]

Only you can do the math. But I’d guess leaving an old panel SE might work out well.

I wouldn’t worry about a little clipping. It might be negligible as the new panels age, or when they’re harboring pollen.

 

[SageBrush]

Rather than just add 1 kW of more panels ?

 

[miimura]

Rather than just add 1 kW of more panels ?

I was thinking about DIY-ing it. Replacing panels 1:1 is easier than mounting new ones. I should price it both ways. It would also depend on whether 3 each 330W panels and new micros would integrate into the M215 AC string wiring and the old Enphase Envoy monitoring system or not. I need to look into that. Maybe pro install for 3 panels + micros would be close to the cost of DIY swapping all? I wonder if anyone would buy the used panels from me?

 

[miimura]

Only you can do the math. But I’d guess leaving an old panel SE might work out well.

I wouldn’t worry about a little clipping. It might be negligible as the new panels age, or when they’re harboring pollen.

I'm not actually worried about the clipping. I can also find out which panel location has produced the least kWh lifetime from the Enlighten online site and leave the old panel there.

 

[SageBrush]

DIY mounts and panels is really easy. As for the electric part, you may wish to ask @nwdiver his opinion.
Do you currently have two strings of 9 panels each ? That sounds like 1 amp panels so if you can upgrade your breakers to 15 Amps I think (?) you are good to go. I have no idea about the monitoring system.

 

[miimura]

DIY mounts and panels is really easy. As for the electric part, you may wish to ask @nwdiver his opinion.
Do you currently have two strings of 9 panels each ? That sounds like 1 amp panels so if you can upgrade your breakers to 15 Amps I think (?) you are good to go. I have no idea about the monitoring system.

Two 20A 240V circuits. Adding 3 more to one string should not be a problem. I just want to make sure that newer higher amp micros have the same AC connectors to string them together. Still nervous about doing new roof mounts myself.

 

[Ampster]

The cable for M215 inverters is different than the cable for IG7 inverters but I believe it could be added on to the existing cable with a junction box. You might have to do the math for current. The new monitoring hardware includes a CT so you could get combined statistics on both systems but i don't know if the new hardware will read the old M215s. If not you would have to keep your old Envoy. I agree with SageBrush, that DIY mounts are really easy. 3 or 4 new panels would be a whole lot easier than replacing all the panels.

 

[SageBrush]

Two 20A 240V circuits. Adding 3 more to one string should not be a problem. I just want to make sure that newer higher amp micros have the same AC connectors to string them together. Still nervous about doing new roof mounts myself.

You could always buy close-out 240 - 250 watt panels and close-out micro-inverters like you have now. It will be dirt cheap. I cannot think of any particularly good reason to buy high efficiency panels or upgraded micro-inverters.

 

[Ampster]

In addition, if you used 4 IG7 inverters which max out at 240 Watts you would never add more than 960 Watts to your mid day production. Even though they would clip the 300 Watt panels at mid day your overall production would be better because they would ramp up earlier and ramp down later.

 

[SageBrush]

In addition, if you used 4 IG7 inverters which max out at 240 Watts you would never add more than 960 Watts to your mid day production. Even though they would clip the 300 Watt panels at mid day your overall production would be better because they would ramp up earlier and ramp down later.

Four 300 watt panels would put OP over the allowed upgrade limit of 1 kW since the inverter CEC is >> 84%

 

[Ampster]

Four 300 watt panels would put OP over the allowed upgrade limit of 1 kW since the inverter CEC is >> 84%

Technically that is correct. Because of their max output they will never output more than 960 Watts. I am on NEM 2.O and I took the literal generating capacity of my inverter when interpreting my NEM agreement. I understand the risk of being wrong is much greater when one is on NEM 1.O

 

[SageBrush]

Technically that is correct. Because of their max output they will never output more than 960 Watts. I am on NEM 2.O and I took the literal generating capacity of my inverter when interpreting my NEM agreement. I understand the risk of being wrong is much greater when one is on NEM 1.O

That is quite reasonable. Too bad the utility is not

 

[miimura]

I looked up my existing panels in the State database again and they are PTC 216.2W. However, the 300W panels I was looking at are similarly downrated, so the result is the same: replacing all 18 240W panels with 300W panels is very slightly over the 1kW increase. Also, the IQ series uses a different Envoy unit, so I assume a mixed IQ and pre-IQ system won't interoperate.

This weekend I will measure my existing panels and clean them to see if that makes much difference. There is one panel that doesn't ramp up like the rest but eventually does kick in to a normal wattage, so I need to look at that one too to see if it's particularly dirty or something.

 

[miimura]

Technically that is correct. Because of their max output they will never output more than 960 Watts. I am on NEM 2.O and I took the literal generating capacity of my inverter when interpreting my NEM agreement. I understand the risk of being wrong is much greater when one is on NEM 1.O

For my purposes, it doesn't matter what they actually generate, I need (PTC * CEC% * NumPanels) to stay below 1kW. Otherwise I would be kicked out of NEM 1.0 and I might as well make it a LOT bigger, like double the current size or more.

 

[Ampster]

Oh, I didnt realize one had to fill out a new NEM application. I have an old system on a commercial building whose BP panels were replaced on a warranty. Several years later I had to replace the inverter. I did not do the math as precisely as you have done here. I will just have to take the consequences if I am ever audited. The NBCs would not be as much of a factor for me as compared to the paperwork.

 

[miimura]

Oh, I didnt realize one had to fill out a new NEM application. I have an old system on a commercial building whose BP panels were replaced on a warranty. Several years later I had to replace the inverter. I did not do the math as precisely as you have done here. I will just have to take the consequences if I am ever audited. The NBCs would not be as much of a factor for me as compared to the paperwork.

The whole purpose of the upgrade is to generate more electricity without getting kicked out of NEM 1. Also, I recently got the letter that they will be calculating the expected solar generation and any exports in excess would not receive NEM credits. So, I figure it's worth the paperwork to not be sneaky about it if I'm going to spend the money on the upgrade.

 

[Ampster]

The whole purpose of the upgrade is to generate more electricity without getting kicked out of NEM 1. Also, I recently got the letter that they will be calculating the expected solar generation and any exports in excess would not receive NEM credits. So, I figure it's worth the paperwork to not be sneaky about it if I'm going to spend the money on the upgrade.

I understand your goal. I also appreciate your adherence to the spirit of the NEM agreement. Do you think the letter is related to your Powerwall install? I have a friend who added a few panels on his garage in the hopes of reducing his true up expense. He is on NEM 2.0 and has recently purchased a Tesla.

 

[miimura]

I understand your goal. I also appreciate your adherence to the spirit of the NEM agreement. Do you think the letter is related to your Powerwall install? I have a friend who added a few panels on his garage in the hopes of reducing his true up expense. He is on NEM 2.0 and has recently purchased a Tesla.

Yes, the letter was specifically sent to "Paired Storage" customers. It is an enforcement mechanism to prevent people from discharging more than their solar into the grid during Peak hours. At some point when they implement a demand response program, they will have to change the interconnect agreements to allow extra discharge in response to high demand events.

I posted the letter here: PG&E Letter - Paired Storage Billing Update

 

[liuping]

The whole purpose of the upgrade is to generate more electricity without getting kicked out of NEM 1. Also, I recently got the letter that they will be calculating the expected solar generation and any exports in excess would not receive NEM credits. So, I figure it's worth the paperwork to not be sneaky about it if I'm going to spend the money on the upgrade.

If you are just a little over 1kW, I would not worry about it. What they see is the solar production, minus the house's usage. That total has to be below the original systems output.

In the summer when you are at risk of hitting the new limits, your house is probably using at least 1KW per hour during max solar production (AC, fans, Powerwall charging, etc), so the grid never sees more than the original system output limit.