PG&E \ Off-Grid System Design

[zanydroid]

The manual transfer switch gives you an extra measure of protection against something unexpected happening within the AIO. But for every hour connected to grid you are still at the mercy of the programming doing the righteous (for all hours where it is externally air gapped from grid it cannot cause problems).

 

[TheHappyNomads]

Where is the discussion of UL9540 compliance to pass AHJ inspection? I don’t know of a AHJ in California that would not enforce it

EDIT: did you verify if the exemption for recycled EV modules is still in effect?

I did not. I was unaware of this exemption but will look into it. Thank you.

EDIT: nothing found after a few search queries. Do you have any documentation \ notices about this I could review?

 

[zanydroid]

I did not. I was unaware of this exemption but will look into it. Thank you.

EDIT: nothing found after a few search queries. Do you have any documentation \ notices about this I could review?

The section of code is R328. This is a slightly older version:

https://www.lakecountyca.gov/DocumentCenter/View/5644/Changes-for-Residential-Solar-California-2022-Codes

 

[zanydroid]

Actually I think that code version is still in effect. ESS is covered in a few volumes of building code so you would probably want to double check with the AHJ to see if there are other places to check.

California Residential Code 2022 based on the International Residential Code 2021 (IRC 2021)

UpCodes offers a consolidated resource of construction and building code grouped by jurisdiction

up.codes

Presumably you still need UL1741 inverter in front of it (to satisfy NEC rule on using listed equipment) but that's easy to do.

 

[zanydroid]

The chargeverter may not be listed. You could be slightly naughty and get the recycled EV batteries + off-grid UL1741 + properly configured rapid shutdown system past final inspection.

And then slip in a chargeverter after they leave.

Note you would probably need to pull two separate conduits to an outbuilding (if that is where the EV batteries will live, I bet a lot of people here would be onboard with that vs mounting them on the outside wall of a residence). One for the AC (grid charging and for the EV charging circuits) and one for the solar DC.

 

[TheHappyNomads]

So..... forget the whole permitting process and just never connect it to the grid at all and make my life easier

 

[Hedges]

I am NOT interested in a grid-tie system but simply want to reduce my grid consumption by eliminating EV charger and electric dryer from my main service panel.

Here's my plan:

(8) 415w panels feeding (2) LV6548s feeding a ~30kwh battery bank (we are putting an addition on our house and so I will have room in the future to add more panels if desired)

All of this will feed an AC Load Center from/to which I will run service to my EV Charger and dryer receptacle.

Those are large loads, more difficult to power than most other loads, but could offer significant savings.

How often do you run laundry? A battery bank to be charged all week so you can run dryer once is not going to be cost effective. Used daily it would be.

EV charger makes sense if utility rate to charge at night is high. I think a PV/battery system which provides 100% or less of daily usage can cost $0.10/kWh amortized over 20 years, $0.20/kWh over 10, $0.40/5 (maybe about 5 year break even depending on rates.)

The key would be to have an automatic transfer switch, or grid fed battery charger, so after draining your ~30kWh bank to charge the EV, you finish charging from grid. You can oversize PV and battery to fully charge EV most of the time, but then you are paying for excess capacity which raises cost per kWh. Trade-off between how much wasted capacity vs. how much bought from grid at a higher price.

With a bit more regulatory hassle, how about a zero export GT PV system, and an AC coupled battery configured to avoid export from PV by charging with surplus, avoid import from grid by discharging. This would supply any and all loads in the house, not be dedicated to laundry and EV.

That sort of system is "peak shaving" and runs in parallel with utility. I'm testing out Sunny Boy Storage with LG RESU-10H, which implements this function (together with communicating with Sunny Boy GT PV inverter).

I think any hybrid that uses CT at grid connection would do this. Consider SolArk, EG4, Sunny Boy Smart Energy.
Utility permission to operate in parallel required, but maybe not net metering.

 

[TheHappyNomads]

Those are large loads, more difficult to power than most other loads, but could offer significant savings.

Indeed. It's why I'm trying to target all of my PV to powering them. We have a very small home with minimal power needs outside of those. I recently installed 3 heat pump mini splits that I do not plan on powering with PV at the moment since they're pretty darn efficient.

How often do you run laundry? A battery bank to be charged all week so you can run dryer once is not going to be cost effective. Used daily it would be.

We have 4 children... so pretty much nonstop every day

EV charger makes sense if utility rate to charge at night is high. I think a PV/battery system which provides 100% or less of daily usage can cost $0.10/kWh amortized over 20 years, $0.20/kWh over 10, $0.40/5 (maybe about 5 year break even depending on rates.)

It is. Where I am at during summer rates my overnight charging comes in at ~$0.60kwh or something like that even on an E-Elec plan with PG&E

The key would be to have an automatic transfer switch, or grid fed battery charger, so after draining your ~30kWh bank to charge the EV, you finish charging from grid. You can oversize PV and battery to fully charge EV most of the time, but then you are paying for excess capacity which raises cost per kWh. Trade-off between how much wasted capacity vs. how much bought from grid at a higher price.

Yeah, this was originally an idea for our situation. One thing to note that our EV is really a PHEV so battery bank capacity is 16kwh which means that if battery bank is full there should be some meat left on the bone for dryer.

With a bit more regulatory hassle, how about a zero export GT PV system, and an AC coupled battery configured to avoid export from PV by charging with surplus, avoid import from grid by discharging. This would supply any and all loads in the house, not be dedicated to laundry and EV.

That sort of system is "peak shaving" and runs in parallel with utility. I'm testing out Sunny Boy Storage with LG RESU-10H, which implements this function (together with communicating with Sunny Boy GT PV inverter).

I think any hybrid that uses CT at grid connection would do this. Consider SolArk, EG4, Sunny Boy Smart Energy.

Utility permission to operate in parallel required, but maybe not net metering.

Ah ok, so other than legality this is the reason for permitting as the utility will need to be notified during the process.

Thanks for your input!

 

[TheHappyNomads]

Looks like the transfer switch maxes out at 30a. I have a 40a EV charger so not sure this will work unless I find a higher amp rated switch. I have seen some 50a options but, if I understand how these work, then the total circuitry in the switch box = 50a. If this is correct, then I wouldn't be able to run the EV charger (40a) and dryer (30a) at the same time, right?

 

[onokai]

Looks like the transfer switch maxes out at 30a. I have a 40a EV charger so not sure this will work unless I find a higher amp rated switch. I have seen some 50a options but, if I understand how these work, then the total circuitry in the switch box = 50a. If this is correct, then I wouldn't be able to run the EV charger (40a) and dryer (30a) at the same time, right?

Yes thats right .its no big deal just takes some thought

 

[TheHappyNomads]

I knew Briggs and Stratton made lawn mowers but not transfer switches lol. Seems like a pretty good deal for an automatic one... B&S 50a

 

[Hedges]

Yeah, this was originally an idea for our situation. One thing to note that our EV is really a PHEV so battery bank capacity is 16kwh which means that if battery bank is full there should be some meat left on the bone for dryer.

Looks like the transfer switch maxes out at 30a. I have a 40a EV charger so not sure this will work unless I find a higher amp rated switch. I have seen some 50a options but, if I understand how these work, then the total circuitry in the switch box = 50a. If this is correct, then I wouldn't be able to run the EV charger (40a) and dryer (30a) at the same time, right?

16kWh / 10 hours = 1.6kW charge rate
1.6kW / 120V = 13A

Use a level-1 charger, and no problem for transfer switch.

Older dryers can be wired for 120V operation. Newer might be only 240V but can be operated on low setting.
Ideally put dryer at 120V on other phase.

Oversize PV array so it supply what you need year-round.
As a dump load when battery full, divert excess power to water heating. Install an tank type electric water heater as pre-heater if present one is gas.

Put an interlocked "generator" breaker in main panel, and when grid is down the same system can provide backup to the house.

Never operating in parallel with grid, utility isn't involved (but maybe should be told you have a "generator" on premises.)

Looks like the transfer switch maxes out at 30a. I have a 40a EV charger so not sure this will work unless I find a higher amp rated switch. I have seen some 50a options but, if I understand how these work, then the total circuitry in the switch box = 50a. If this is correct, then I wouldn't be able to run the EV charger (40a) and dryer (30a) at the same time, right?

If you do operate both at full power, you could wire a relay, coil powered by 240V circuit for heating element inside dryer, to disconnect charger. Don't know if it objects to cycling that frequently.

Running both low power would be better. Plenty of time for charger. Dryer will be slower, but not 4x longer on 120V; thermostat remains on longer.

 

[TheHappyNomads]

I think the for time being I am going to eliminate any grid interaction at all -- including a transfer switch. I really just need to offset the cost of PHEV.

Eventually I'll install a switch to run the dryer from both. Thanks everyone!

 

[Stiffmeister]

I was told while having Tesla batteries installed, that your house in CA must be connected to PG&E. I didn't read everything on here, but I would do a system that does NOT connect to PG&E and not tell anyone about it. BTW eight panels isn't much in my opinion. I'm off grid in Mexico now (PG&E burned everything in Paradise, CA Nov 8th 2018) and 50 panels isn't enough for the summer heat in Cabo.

 

[TheHappyNomads]

My house is still connected to PG&E running all my other loads. I know 8 panels isn't a ton but I have a small house and that's all I can fit right now. We're adding on soon and I should be able to add another 4-5 panels down the road. I'm in the Bay Area so we don't deal with sustained high temps like you have in Cabo