feasibility and sizing of limited home battery backup system

[BeerTooth]

Looking for advice on how to assess the feasibility of backup battery during power outage. We have a 14 kW propane standby generator installed by prior homeowner, which is reaching end-of-life. Have a quote for $7,000 for in-kind replacement generator, which includes load-shed devices for heat pump compressors, electric dryer, and induction stove.

Considering alternatives including battery backup option. Obviously we wouldn't operate all appliances the same way during an outage as we do during "grid up" times. Looking at my main panel, the large loads that are "must have" are:
240v / 30a heat pump water heater
240v / 20a well pump
Everything else is 120v outlets: basement sump pump, refrigerator, lights, microwave, cable modem router and TV, etc.

I would load-shed: heat pump compressors, electric dryer, kitchen stove. And plan to generally be very stingy with electricity during an outage. Primary heat is a wood stove, which does not require electricity. We've been in the house for 10 years and we generally lose power 1-3x per winter, probably an average of 4 hours recovery time. The longest outage we've experienced was a little over 24 hours. We didn't have the generator available, so we used some LED lanterns and headlamps to cook dinner on the propane camp stove. I also have a propane pizza oven and charcoal grill/smoker for cooking meals during an outage.

How would I go about sizing a backup battery and estimating the cost? I don't have any type of smart monitor on my electric panel. All I can see is my utility bill with an average of 35-40kWh/day total usage. But I'm sure we can conserve quite a bit compared to that baseline during a grid outage.

I'm fairly tech-savvy but I haven't spent any time on reading up on battery backup systems. Would appreciate a link to a quality summary guide, instead of randomly reading through forum threads.

 

[Brucey]

Consider something like the soon to be released "the one" from Midnite solar. It has three smart breakers of 30A, 50A and 60A which can be used for automated load shedding, gen input etc, might make things simple for you with the stove, dryer and heat pump compressors.

 

[DIYrich]

New Hampshire has battery subsidy program. Unfortunately, only Enphase is currently supported.

Battery Storage Demand Response | Eversource

Home batteries can help you store your clean solar energy or simply provide backup energy in case you need it. Learn more from Eversource.

www.eversource.com

during grid-down, you can turn off the heating elements of the HPHW (eco mode) and reduce the amperage to 2 amps. 30 amps is required for "hybrid" mode. I have mine set to Eco only (don't want it to use the heating elements).

20a for well pump is 5000 watts inverter, minimum.

I would build an EG4 6000xp system, with an EG4 powerpro battery. About $5,000 plus installation. Since it will not export, you don't need PTO from the utility. About $4,000 after the 30% federal credit (if you can benefit).

Better yet, parallel two systems at $10,000, and do your whole house. Don't forget the 30% federal credit that can reduce the cost to $7,000 plus install. For 30-45kWh per day, you will need 3 powerpro batteries.

Eventually, you can add panels to further enhance the system.

If you ever want to export power, then skip the 6000xp, and go for the 18k PV. One 18kpv and 3 powerpro for $16,000 (probably less if you call for a price), $12,000 after federal credit.

Buy a small propane generator (5,000-7,000 watts) and chargeverter for extended outtages.

 

[BeerTooth]

New Hampshire has battery subsidy program. Unfortunately, only Enphase is currently supported.

Battery Storage Demand Response | Eversource

Home batteries can help you store your clean solar energy or simply provide backup energy in case you need it. Learn more from Eversource.

www.eversource.com

during grid-down, you can turn off the heating elements of the HPHW (eco mode) and reduce the amperage to 2 amps. 30 amps is required for "hybrid" mode. I have mine set to Eco only (don't want it to use the heating elements).

20a for well pump is 5000 watts inverter, minimum.

I would build an EG4 6000xp system, with an EG4 powerpro battery. About $5,000 plus installation. Since it will not export, you don't need PTO from the utility. About $4,000 after the 30% federal credit (if you can benefit).

Better yet, parallel two systems at $10,000, and do your whole house. Don't forget the 30% federal credit that can reduce the cost to $7,000 plus install. For 30-45kWh per day, you will need 3 powerpro batteries.

Eventually, you can add panels to further enhance the system.

If you ever want to export power, then skip the 6000xp, and go for the 18k PV. One 18kpv and 3 powerpro for $16,000 (probably less if you call for a price), $12,000 after federal credit.

Buy a small propane generator (5,000-7,000 watts) and chargeverter for extended outtages.

thanks for the pointer to the state subsidy program

curious why you feel the EG4 system is still a better value than the Enphase even after rebate? Overall cheaper per kWh, or additional features the Enphase is lacking?

 

[DIYrich]

curious why you feel the EG4 system is still a better value than the Enphase even after rebate? Overall cheaper per kWh, or additional features the Enphase is lacking?

Enphase IQ10T is about $6,000 for 10kWh. Net of $230/kwh incentive, that is $4,000. But, max incentive is $3,000. $15,000 for 30kWh net of $3,000 incentive.
EG4 Indoor Powerpro is about $3,500 for about 14kWh. $7,000 for 28kWh. And, you are not required to participate in Demand Response.

Note: Demand Response WITHOUT solar has a round-trip cost issue. About 85% efficient round-trip. 30kWh of battery, 80% dischcarge, that is 3.6kWh "cost" per event, with 40 events per year. At 20 cents per kWh, that is $29 per year, or $290 over 10 years offsetting your rebate.

Both will need some type of controller. Enphase is about $2,000 for the IQ System Controller, and about $1,500 for an EG4 6000xp.

If you ever add solar, EG4 microinverters (includes Rapid Shutdown) are about $150 per panel. The EG4 6000xp can take the panels directly (each panel may need a $50 rapid shutdown device). Enphase adds $100 per panel.

 

[BeerTooth]

wow I'm surprised that kind of price disparity hasn't been arbitraged out of the market yet

is it just a "brand name recognition" thing with Enphase? Or are they using better components?

agree that dealing with utility rebate and Demand Response is undesirable esp. if no cost savings

any tips on rough estimating demand? If my "normal" usage is 40 kWh/day, my "grid down" usage would certainly be far less than that. Critical appliances only. No heat pump, no electric dryer, no kitchen stove. Sump pump, lights, fridge only. Could I assume I'd cut usage by ~1/2? so 20 kWh battery gives me 24 hours backup?

 

[DIYrich]

wow I'm surprised that kind of price disparity hasn't been arbitraged out of the market yet

is it just a "brand name recognition" thing with Enphase? Or are they using better components?

Captive market. People get a quote for solar. Most installers use Enphase. Consumer not knowing any better, accept the quote. Later, they ask about battery ...

I had to go through a "qualified installer" to participate in the ESS program that subsidize battery cost. 70% of the installers used Enphase. 25% used Solaredge. ONE installer used Sol-Ark.

agree that dealing with utility rebate and Demand Response is undesirable esp. if no cost savings

any tips on rough estimating demand? If my "normal" usage is 40 kWh/day, my "grid down" usage would certainly be far less than that. Critical appliances only. No heat pump, no electric dryer, no kitchen stove. Sump pump, lights, fridge only. Could I assume I'd cut usage by ~1/2? so 20 kWh battery gives me 24 hours backup?

Adding battery is easy. One powerwall at 14 kWh is marginal if you are really good at cutting back. Two powerwalls at 28 kWh will probably work. If it doesn't, then add a 3rd powerwall.

Benefit of 3 powerwalls: If the grid-down is short-term (sever storm came through), then you don't have to cut back. If it looks extended (3 feet of snow, hurricane, etc.), then you can cut back and have more time.

In either case, having a Plan B (portable generator with a chargeverter) can recharge battery in an 8 hour run. Toyota hybrid (or PHEV) can also recharge your battery (with a plug-out adapter).