Utility limit is 10 kW AC for net metering, delete one inverter?

[n.one.one]

TLDR - A very unique case that will only be of interest to those that like taking a deep dive (the type of person who might enjoy doing only the most difficult crossword puzzles).

This is definitely an edge case but I'd appreciate any input as I'm searching for a creative solution.

Georgia Power (GaPwr) limits system size to 10kW AC in order to qualify for either of their two net metering programs (Monthly Netting and Instantaneous Netting). Neither program is very good, but that's all GaPwr offers.

My system has 15.2 kW AC from the inverters in two PW+. I have 20 kW solar panels, 4 Powerwalls, and Tesla installed it in March 2023.

I just got my first full/regular bill and used only 116 kWh but I sent 1,187 kWh back to the grid. I got zero credit for what I sent to the grid. If I knew I wasn't getting credit I could have easily avoided using the 116 kWh so my bill would have been only a minimum bill in the $20 to $25 range.

On the positive side GaPwr offers a very good EV rate with overnight power at about 1.6 cents/kWh. During the worst solar months I'll be able to time shift my grid use and my bill will still be very low. These low bills limit what I'm willing to spend for a solution.

I'm exploring the (crazy?) possibility of taking one inverter out of my system so that I qualify for some bill relief from GaPwr. I'd leave it in place but just wire it out of the system, if that's a possibility. That would create some clipping, but with the excess I'm generating in the summer that shouldn't be a problem. In the winter there would be less clipping.

I'm looking for any thoughts on whether this can be done from a system/wiring standpoint, whether Tesla would do the work, and what the cost might be. I'm thinking that if GaPwr ever comes up with a better and less restrictive net metering program I could restore the retired inverter.

 

[LoudMusic]

I would think you'd want the full inverter power for making power for yourself. Is there not a way to limit the outbound power in software?

 

[n.one.one]

I would think you'd want the full inverter power for making power for yourself. Is there not a way to limit the outbound power in software?

You are on the same track I am, unfortunately I don't know the answer. I think GaPwr goes only by "Nameplate kW (AC)" capacity to determine eligibility so a software solution may not actually be a solution.

 

[arnolddeleon]

Tesla systems with Powerwalls in theory can be configured to limit exports using the PCS features. Whether your utility will accept it is another question. I believe there are utilities that have accepted this. I'm sure @Vines would have the answer.

 

[SummitX]

My system is almost exactly the same as yours, and I had this issue with CORE in Colorado and they let me qualify for 1:1 net metering by having Tesla program my Powerwalls to limit grid export to 10kW. Definitely worth asking your utility.

 

[dafish]

Here in ameren territory they go by the configured output of the inverter connected to the grid. it would sure be tempting to run a second inverter connected only to a power wall. i assume, perhaps incorrectly, that a powerwall never backfeeds the grid…

 

[n.one.one]

My system is almost exactly the same as yours, and I had this issue with CORE in Colorado and they let me qualify for 1:1 net metering by having Tesla program my Powerwalls to limit grid export to 10kW. Definitely worth asking your utility.

Great suggestion and as a result of your post I contacted my utility (Georgia Power). They absolutely don't allow a software limitation, they go by hardware nameplate AC capacity only.

I went a step further and contacted a commissioner on the Georgia Public Service Commission who was well aware of the issue and said many others have raised the same question, primarily with regard to the amount of the kW limitation. He said they won't revisit the tariff until 2025 (every 3 years). I'm still looking for a creative solution but hope is fading.

 

[arnolddeleon]

It's interesting that your utility is looking only at our PV inverter capacity. You have the theoretical ability to export at 30 kW between your Powerwalls and PV inverters. So, they clearly "trust" the software in the Powerwall control system. But logic doesn't always apply when it comes to utility policies.

What mode are you running the Powerwalls? Self-powered? What reserved?

At the risk of stating the obvious, $0.0 is cheaper than $0.016. Since you are not currently getting net metering, you should try to self-consume all your solar production since you either have paid for it already or committed to paying it.

If I were in your shoes, I would run in self-consumption mode. I would lower my reserve to as low as needed so I'm drawing zero at night and potentially charge the EV partially if not entirely during the day. Basically, focus on exporting zero to the grid since you are not getting paid for your exports. This has the advantage of costing you nothing but your time to mess around with the configuration. It will probably be helpful to the control system to set the grid prices in the Powerwall settings. Come to think of it, you can probably run in "time-based control" as long as rates are set correctly (i.e., sell price $0.00). You just need to have your reserve low enough.

 

[n.one.one]

It's interesting that your utility is looking only at our PV inverter capacity. You have the theoretical ability to export at 30 kW between your Powerwalls and PV inverters. So, they clearly "trust" the software in the Powerwall control system. But logic doesn't always apply when it comes to utility policies.

What mode are you running the Powerwalls? Self-powered? What reserved?

At the risk of stating the obvious, $0.0 is cheaper than $0.016. Since you are not currently getting net metering, you should try to self-consume all your solar production since you either have paid for it already or committed to paying it.

If I were in your shoes, I would run in self-consumption mode. I would lower my reserve to as low as needed so I'm drawing zero at night and potentially charge the EV partially if not entirely during the day. Basically, focus on exporting zero to the grid since you are not getting paid for your exports. This has the advantage of costing you nothing but your time to mess around with the configuration. It will probably be helpful to the control system to set the grid prices in the Powerwall settings. Come to think of it, you can probably run in "time-based control" as long as rates are set correctly (i.e., sell price $0.00). You just need to have your reserve low enough.

I'm thankful for your post and very proud to say I am already doing exactly what you suggest. I'm running self powered, 5% reserve, and charging my MX on sunny days when PWs are full. If there are numerous consecutive bad solar days I'll manipulate settings to run on the grid at night (all night or partial depending on need). I do have the sell rate at zero and if I switch to time-based control I may play with the low rate hours schedule to further limit grid use. At this time of year I shouldn't use any grid power but winter may require some overnight use. At this point the Tesla app doesn't allow charging the PWs from the grid but I understand that can be done so I'm exploring charging them overnight as needed.

Thanks again for a very thoughtful response.

 

[arnolddeleon]

Doing some quick arithmetic after looking at Georgia power rates, it looks like you "gave away" about $125 to your utility in the example that you provided. I suspect going forward it won't be that bad given your awareness and actions you are already taking. So, I'm guessing worst case, you are looking at $500 to $600/year.

My other suggestion is taking a page from @h2ofun playbook and enjoy life. This means not thinking about time of use (once you programmed it into the batteries) so you can run your air conditioner at the temperature that makes you most comfortable and not trying to micromanage it. I had to "untrain" myself from that (and I still occasionally revert to old habits). You can do more electrification if you haven't done so already. For example: Heat pump water heater, induction cooking and electric/heat pump clothes dryers.

 

[n.one.one]

Doing some quick arithmetic after looking at Georgia power rates, it looks like you "gave away" about $125 to your utility in the example that you provided. I suspect going forward it won't be that bad given your awareness and actions you are already taking. So, I'm guessing worst case, you are looking at $500 to $600/year.

My other suggestion is taking a page from @h2ofun playbook and enjoy life. This means not thinking about time of use (once you programmed it into the batteries) so you can run your air conditioner at the temperature that makes you most comfortable and not trying to micromanage it. I had to "untrain" myself from that (and I still occasionally revert to old habits). You can do more electrification if you haven't done so already. For example: Heat pump water heater, induction cooking and electric/heat pump clothes dryers.

I was literally laughing out loud as I read your post because once again we're on the exact same page. This is new to me and as of now I'm having fun playing the game trying to optimize everything.

The reality is I'll probably only have a minimum electric bill in the $20 to $25 range so none of this amounts to much and it's not worth spending anything for a fix given the small amount I could save. In anticipation of getting solar I got two very efficient HVAC heat pumps when the HVAC needed replacing two years ago. My backup fuel for heat is natural gas and with cheap overnight electric rates I should be able to keep the house warm with almost no natural gas use which will lead to a minimum bill for that (I've tested the system with a crossover from heat pump to natural gas at 15 degrees F and it worked fine).

To summarize, I'll have minimal electric and natural gas bills, and 95%+ of my driving should be from solar.