Advice for ESS planning

[extraj]

Hi friends,

I'm looking to install an ESS (solar and battery) at my house in San Diego. I have experience with RV/marine installations and have built my own 12v systems and prismatic cell lifepo4 batteries, but my understanding of anything related to the grid is especially weak.

Let me know if I'm missing important things and I'll come back and update the post.

Usage
We currently use between 8-25kwh per day, but 30kwh is possible. I'd guess that the highest usage would come on sunny days. We have a gas water heater and stove and all heating and cooling is via mini split heat pump. In the future, we could switch to a heat pump water heater, which would obviously increase our usage.

We also recently bought an EV (Chevy Bolt), which I currently charge at work but which we'll want to start charging at home in the future. I don't mind paying grid prices as long as we're paying the overnight rate. Charging at home would add approximately 25kwh/week, and could be spread out however.

PV Capacity
I'm honestly not sure yet, because the house has a historic designation and the city is not being very helpful in telling us where we'll be allowed to put panels. It's possible that the system will have to be on the smaller side, perhaps as small as 3kw, but the time of day electricity pricing is so dramatic that a battery-only system would still make sense and we might move forward initially without PV (but planning for it in the future.)

Location and logistics
The main panel on the house is 100a. I think that I'd like to locate the battery in a detached garage that has a 40a sub-panel off the main. I'm leaning this way because we may want to use the house battery to charge the EV, which would be the biggest individual load. It's also more convenient to put there because the house is small. I also may end up putting more PV on the garage than on the house, which might also prescribe putting everything in the garage.

Desired features
- Supplement battery + PV power with grid. I'd prefer to avoid using daytime grid power unless either the battery drops to a predetermined SOC or the AC loads exceed the inverter's capacity.
- The ability to quickly and easily adjust whether or not the house battery charges overnight. I'd want to be able to look at the weather for the next day, think about whether I'll want to EV charge midday, and then make a quick adjustment to tell the charger whether to charge the battery overnight. Ideally, I'd like to be able to do this over the internet.

Let me know what you think; what hardware to consider; what I'm failing to think about, etc.

Thanks in advance!

 

[Hedges]

ESS I think has to be listed, even listed as a pair with inverter in most cases.

I'll be installing Sunny Boy Smart Energy for a couple people. It will work with BYD high voltage lithium batteries. Those cost about 2x what server rack batteries do. One thing I like about this inverter is it can take 15kW of PV, export 7.7kW to house or grid, charge battery at the same time with up to 10kW. Some of the others like EG4 and SolArk may have similar capability.

The EG4 PowerPro battery is listed and weatherproof. They have a listed ESS consisting of it and an inverter.

I take it you don't have a reservation for net metering with utility yet. So you'll fall under NEM 3.0, which is only tolerable if you have battery. You may want to choose between net metering (backfeed during a couple hours of peak rates to earn credits you can use off-season), or zero-export so you can have a standard rate plan rather than time of use.

For the EV, financially reasonable choices will be either ESS holds the power before charging, or you use export during peak time (about 5:00 to 7:00 PM) to earn credits so it is net or better when you charge overnight.

How many amps is your main panel? That and 120% rule drives PV size.

Some people get weather info that automatically adjusts what is held in battery vs. backfed to grid. I think one guy does that with Schneider, but I'm not familiar with the various offerings and support.

 

[extraj]

ESS I think has to be listed, even listed as a pair with inverter in most cases.

I'll be installing Sunny Boy Smart Energy for a couple people. It will work with BYD high voltage lithium batteries. Those cost about 2x what server rack batteries do. One thing I like about this inverter is it can take 15kW of PV, export 7.7kW to house or grid, charge battery at the same time with up to 10kW. Some of the others like EG4 and SolArk may have similar capability.

The EG4 PowerPro battery is listed and weatherproof. They have a listed ESS consisting of it and an inverter.

I take it you don't have a reservation for net metering with utility yet. So you'll fall under NEM 3.0, which is only tolerable if you have battery. You may want to choose between net metering (backfeed during a couple hours of peak rates to earn credits you can use off-season), or zero-export so you can have a standard rate plan rather than time of use.

For the EV, financially reasonable choices will be either ESS holds the power before charging, or you use export during peak time (about 5:00 to 7:00 PM) to earn credits so it is net or better when you charge overnight.

How many amps is your main panel? That and 120% rule drives PV size.

Some people get weather info that automatically adjusts what is held in battery vs. backfed to grid. I think one guy does that with Schneider, but I'm not familiar with the various offerings and support.

Thanks! The main panel is only 100a, will update the post.

Definitely NEM 3.0, and the buyback rates are awful. I honestly don't really even care about earning those credits and would be fine with zero export.

Does even the battery have to be listed even if I'm not selling anything back to the grid? I.e., I can't build my own from prismatic cells?

 

[Hedges]

Listed battery is about fire safety. The inverter DC coupled to battery is capable of causing its failure. LiFePO4 is much safer, but falls under the new regulations. Other lithium chemistries, including in LG-RESU (H?) have had multiple fires and recalls.

I think AGM may (or may not) still be exempt, and is safe enough for air transport. But cycle life 1/5 as long, and only lithium is price competitive with utility electric rates.

If backfeeding for net metering or into main panel for zero-export, 120% rule says 100A panel busbar x 120% - 100A breaker = 20A max PV breaker. 80% continuous load is 16A, 3600W. I'm upgrading my service in a way that will support 100A fused disconnect (bidirectional PV backfeed + UPS style operation)

If not backfeeding, using inverter as PV powered UPS to feed only downstream loads, 120% rule doesn't apply.
Best setup is grid-interactive, blends inverter output with grid so seamless operation with grid picking up starting surges and loads over what inverter can handle.

In winter you won't produce as much power. Possibly NEM 3.0 backfeed during the couple peak hours is a good deal.

Buying hardware and free DIY labor, I put PV system at $0.03/kWh. Batteries like PowerPro may be $0.05/kWh although you need to consider what an inverter supporting it costs. The BYD battery I plan for my sister's place about $0.10/kWh. Those are cost over lifespan, not cost per kWh of capacity (which is more like dollars per watt hour, not cents per kilowatt hour.) So compared to $0.25 or $0.60/kWh utility rates, there is money to be saved.

SolArk people are happy with performance and service, grumble about price compared to similar Deye available overseas. I'm not sure what listed ESS bundles work with it.

Will liked PowerPro, maybe also 18kpv. EG4 shows the pair around $10k. Newer so less track record but looks promising. Do read up on the vendors.

Everyone seems happy with Dexter and Current Connected, so may be worth buying through them even if not lowest price. But the hardware is under control of the manufacturer, of course. He is just reseller and some support. He does do some of his own compatibility testing.

EG4 PowerPro ESS Kit | 14.3-28.6kWh Capacity | Current Connected

Revolutionize energy management with the EG4 PowerPro ESS Kit: Reliable, safe, and user-friendly. Take control of your energy journey now!

www.currentconnected.com

For my preferred make SMA, I'm not clear on their support for zero export. I got in NEM 2.0 reservations so not needed in my case. Previous models, they were behind on peak shaving and time shifting functionality. I'm running their older models, which are solid off-grid and net metering systems with good surge capability. Will be installing the new and seeing what I get.