Using battery storage to boost peak load capacity

[Jeff in CA]

I have a new 12kw solar system on microinverters, and 200A grid service. I’m converting my gas apploances to electric and adding loads via remodeling projects. In approaching my local utility, upgrading to 400A service will likely run $15k, which seems outrageous. I’m wondering if I can reallocate that capital to a battery system that both serves as backup during an outage and complements grid power to handle higher peak loads.

Requirements:
1. Couples to Solar via AC
2. Acts as a backup when the grid goes down
3. Uses solar and/or batteries to provide additional power when my load exceeds 200A
4. When generating excess solar, charges batteries with only the excess power, preventing drawing from the grid
5. Prefers using solar, then battery power during peak times to avoid drawing from the grid

I’m looking at a Sol Ark 15k. Its max output is 200A, but if it’s possible to parallelize with grid power (via AC coupling) into a 400A panel, could that work in theory somehow? Would need to get the unit a signal on grid draw and solar generation but perhaps complementing with a charge controller could do that. Would Victron units be more flexible for my goals? Are all 5 goals achievable at the same time?

Thanks,

Jeff

 

[Texican]

have you calculated the loads expected to run at the same time ?
seems really hard to need more than 200 amps at one time

 

[Jeff in CA]

3 ACs plus 1-2 mini splits, 3 electric kitchens, EV charger, electric hot water, 2 laundry rooms

2 kitchens @ 40 amps = 80 amps
3 ACs @ 40 amps = 120 amps

Either one laundry load or kicking in the water heater would exceed 200 amps.

 

[DIYrich]

For the AC's, is that Startup or Running Amps? 40 amps seems a little high for running amps.

 

[Jeff in CA]

Min circuit breaker size is 26 amps. Regardless, we didn’t factor in that in addition to these units we’re adding 1-2 mini splits, there’s a third heat pump unit, and each kitchen has both a 40 amp induction surface plus a 40 amp oven. I may not exceed 200 amps often, but there’s definitely enough load to do it occasionally.

If you need a plausible scenario to illustrate, here’s another one:
2 active cooktops and one oven = 120 amps
2 acs = 52 amps
Water heater = 40 amps
1 dryer = 30 amps

 

[Jeff in CA]

Here’s an idea that might work:

Inverter 1: normal set up
Load is main panel, capped at 200A
Generator is PV
Grid is grid
Battery array

Inverter 2: DC coupled via batteries
Load is a different panel with load separated
No generator or grid input

If I set inverter 1 to charge batteries when either there’s excess PV power, or battery charge is low, then:
1. I can drive more than 200A
2. I have battery backup that can be use for the whole house (up to inverter capacity)
3. I don’t charge batteries with grid energy unless batts are below a set threshold
4. Since excess solar gets shunted to the DC circuit, it’ll get used first for load, second for charging the batteries, only when either is needed.

I was skeptical about coupling two inverters via batteries but it’s in Sol Ark’s parallel wiring diagram.

Since I’d be using 2 inverters I might be able to down spec (price, really) and go with Victrons.

Thoughts? Could this work? Will it wear the batteries excessively, even if the load on inverter 2 is right sized?

 

[shopman]

I have a new 12kw solar system on microinverters, and 200A grid service. I’m converting my gas apploances to electric and adding loads via remodeling projects. In approaching my local utility, upgrading to 400A service will likely run $15k, which seems outrageous. I’m wondering if I can reallocate that capital to a battery system that both serves as backup during an outage and complements grid power to handle higher peak loads.

Requirements:
1. Couples to Solar via AC
2. Acts as a backup when the grid goes down
3. Uses solar and/or batteries to provide additional power when my load exceeds 200A
4. When generating excess solar, charges batteries with only the excess power, preventing drawing from the grid
5. Prefers using solar, then battery power during peak times to avoid drawing from the grid

I’m looking at a Sol Ark 15k. Its max output is 200A, but if it’s possible to parallelize with grid power (via AC coupling) into a 400A panel, could that work in theory somehow? Would need to get the unit a signal on grid draw and solar generation but perhaps complementing with a charge controller could do that. Would Victron units be more flexible for my goals? Are all 5 goals achievable at the same time?

Thanks,

Jeff

The Solark has a transfer switch that is capable of passing 200 amps, but its inverter output is nowhere near that. For what you are proposing, you'll need 4 Solark 15k's and a hell of a lot of battery capacity to add 200 amps to parallel with your 200 amps of grid capacity in your 400 amp panel. The Solark will do what you want but at a very premium price. Maybe try performing an energy audit to be sure you're not overestimating your requirements.

 

[DIYrich]

If you need a plausible scenario to illustrate, here’s another one:
2 active cooktops and one oven = 120 amps
2 acs = 52 amps
Water heater = 40 amps
1 dryer = 30 amps

Load controller. Turns off low priority devices (water heater), and let's only one of the ac's run at a time, when energy demand is high.

That can keep you under 200 amps.

If you add a sol-ark, the sol-ark can supply additional power to a sub panel so more things can run when at the limit.

 

[timselectric]

Agree with shopman.
Sounds like a second mortgage, to get what you want.

 

[Jeff in CA]

Okay no sol ark, thanks for the feedback.

Any thoughts on the dual victron dc coupled idea?

I do really like the load controller idea. I’ll google around but if anyone has a recommended product that’d be appreciated.

Thanks all for the feedback!

 

[Jeff in CA]

Here’s another idea I had, curious if this could work:



And a diagram for DC coupling:

 

[DIYrich]

I have a new 12kw solar system on microinverters, and 200A grid service. I’m converting my gas apploances to electric and adding loads via remodeling projects. In approaching my local utility, upgrading to 400A service will likely run $15k, which seems outrageous. I’m wondering if I can reallocate that capital to a battery system that both serves as backup during an outage and complements grid power to handle higher peak loads.

If you use 2 Sol-Ark 15k's in parallel, it would work.

Per the specs, each Sol-Ark can support 200 amps "continuous AC Power with Grid".
You would set Grid Peak Shaving to 48,000 watts (200 amps).
You would set the "Load Limit Power" to 72,000 watts (200 amps from the grid, and 50 amps from each sol-ark, for a total of 300 amps @ 240v).

When power is over 200 amps (Grid Peak Shaving level), the Sol-Ark supports the load up to 50 amps from each Sol-Ark.
If you AC Couple to the Gen Line, then that PV can also add to amps available (over the 200 amps from the Grid).

Maybe you can ask how much you can upgrade the grid service without incurring a huge expense. Upgrading to 250amp or 300amp would be helpful.

 

[zanydroid]

$15k for underground service upgrade is minimum in Northern California. The only time you get out of it is if service drop does not have to move (common to trigger mandatory move for older homes due to safety rule changes), AND the conduit is above the minimum PG&E size, AND the conduit is in good enough shape.

In fact I’ve gone through the same theorycrafting as OP, wrt putting that $15k towards batteries.

But they clearly have a bigger house than I do. Answer for me was to do load management for EVSE and water heater, and upgrade to 125A service (PG&E allows it for free (less MSP changeout) sometimes with existing conduit and service lateral)

 

[zanydroid]

If you are looking around with a $15k budget, consider span.io or Eaton smart breakers. Span.io is turnkey but last I checked (long ago in early 2022 because I chickened out of spending real money) primarily targets load shedding to avoid service upgrade (presumably with modest added appliances) and to conserve battery when grid is down.

It may not be capable of enabling letting you go nuts with adding huge appliances by leveraging your ESS, not really one of the applications I’m aware of. On paper it will work but details like what ESS it can interop with in this mode are critical.

TBH if the remodeling is as extensive as it sounds (basically two houses on one 200A service), the service upgrade would be the way I would do it.

 

[hwy17]

Just let go of the electric on demand water heaters, man. They're not a good development for the grid and they're much worse than that for any off grid system. Set aside the space for HPWH's.

 

[zanydroid]

Just let go of the electric on demand water heaters, man. They're not a good development for the grid and they're much worse than that for any off grid system. Set aside the space for HPWH's.

That is a good start but it’s not clear in the original post that it was an on demand water heater, just one with an odd current draw (40A, most are 24A on 30A circuit). ie it doesn’t help with what seems like two homes worth of appliances (HVAC and cooking), with the shared infrastructure primarily being EVSE which anyway is easy-ish to load manage.

 

[GuyG]

My advice would be not to do anything until after conducting a thorough and realistic evaluation of historical consumption and peak demands. Many power companies will let you download this data. Look for usage in 15-minute intervals, or one-hour intervals at the most. If they don’t provide data at this level of granularity, install an Emporia Vue or similar energy monitor and get at least a month or two of data. I’d focus on actual KW demand rather than theoretically potential max amps.

My guess is that you’ll find 48,000 watts (200 amp service) to be more than enough, even with all the potential theoretical loads you’ve listed. If not, at least it will guide you on whether you really need another 200 amps, or some lesser amount that a single SolArk 15 could provide.

After getting a true picture of actual needs, come back here and people can weigh in on the best way to get there.