How can I create a whole house Battery Backup using a stepwise approach?

[aceinc]

I would like to create a battery backup system for my entire house. I would like to take a step wise approach to this project, to reduce initial capital outlay.

I see the project broken into 4 basic sections;

1. Charging the batteries. (Inverter)
2. Powering the house from the batteries. (Charger)
3. Automatic switching.
4. The batteries.

I have been doing gross monitoring, using the smart power meter on my house. It tells me (if I am reading it correctly) my peak load was 8KW. It doesn't say for how long, however. To me that says I should be able to get away with an 8-10 KW inverter that peaks out at say 16-20 KW for brief periods.

As far as charging is concerned, I am going to charge with AC, because my solar panels are grid connected. I have an 11.7KW DC, 10KW AC array, so matching the charger might capability wise seems reasonable.

Batteries is where I was considering the step wise part. I cannot afford 30-40 KWH of usable batteries at this point, so my goal would be to get the minimum storage that will allow me the wattage I need to run everything for a short time. Say 5-20 minutes at full load. Perhaps 48v at 40-60 AH or 1-2 KWH usable depending on the battery technology used.

My thought on batteries would be to decide on the voltage, and then every time I get some money, I buy a set of batteries to match the voltage, extending amount of time the system will stay up.

So the part I need help with is putting the pieces together, and making sure I size everything right.

One area I get fuzzy in is what pieces I need and how to implement the automatic switch. What I would like is say a 50-60 amp breaker between my battery inverter and the main house. I will need to disconnect my mains when the power drops, then fire up the battery inverter to provide power to the house. To add to to the fun I will want to provide power to Solar Array inverters, so they can continue providing juice to power my home and charge the batteries.

I know that should I be running on batteries and turn everything on in my home it would pop the 60 amp breaker, but I am used to being judicious in power usage when the grid is down. I turn off range & oven breakers for example.

 

[WorthFlorida]

It will take a lot of dollars and batteries are dangerous, high maintenance and eventually need to be replaced. Have you priced out a commercial grade inverter? I mean a real converter, not those that you use on a boat or camp site. While the batteries are being charged your solar power going to the grid will be negated because you'll need more power to charge depleted batteries.

Since you have solar panels, kudos to you, call your solar company and see what it takes to meet the peak load. Of course it will take more panels but the cost may negate the few times to meet the peak demand. I'm sure you may have looked into battery backup system from the solar company but usually the cost doesn't justify. If you really want batteries go with the solar company may have to offer. It'd be all UL approved, installed by licensed electrician and your insurance company would back you up in an accident or incident if damage was done to the system, let alone someone being electrocuted or burned by battery chemicals.

As far as inverters are concerned, many do not put out a clean sine wave, those that do get very expensive. Most are square wave or saw tooth and a lot of electronics will not work. Motors are usually not affected that much but it is still an average power to consider and your refrigerator would not be working at peak efficiency and may not keep up with the cooling. Its own electronics may not work either.

If you want power during outages a whole house generator such as Kohler sells is the way to go. I've lived in Florida for 28 years and the only time we lost power for hours at a time was Christmas Eve and Christmas 1989 because FPL took down the nuclear plant for maintenance then we had a 28 degree weather. That was Palm Beach county. The other two times were five days after two hurricanes events.

 

[Sponsor]

 

[aceinc]

It will take a lot of dollars and batteries are dangerous, high maintenance and eventually need to be replaced. Have you priced out a commercial grade inverter? I mean a real converter, not those that you use on a boat or camp site. While the batteries are being charged your solar power going to the grid will be negated because you'll need more power to charge depleted batteries.

Since you have solar panels, kudos to you, call your solar company and see what it takes to meet the peak load. Of course it will take more panels but the cost may negate the few times to meet the peak demand. I'm sure you may have looked into battery backup system from the solar company but usually the cost doesn't justify. If you really want batteries go with the solar company may have to offer. It'd be all UL approved, installed by licensed electrician and your insurance company would back you up in an accident or incident if damage was done to the system, let alone someone being electrocuted or burned by battery chemicals.

As far as inverters are concerned, many do not put out a clean sine wave, those that do get very expensive. Most are square wave or saw tooth and a lot of electronics will not work. Motors are usually not affected that much but it is still an average power to consider and your refrigerator would not be working at peak efficiency and may not keep up with the cooling. Its own electronics may not work either.

If you want power during outages a whole house generator such as Kohler sells is the way to go. I've lived in Florida for 28 years and the only time we lost power for hours at a time was Christmas Eve and Christmas 1989 because FPL took down the nuclear plant for maintenance then we had a 28 degree weather. That was Palm Beach county. The other two times were five days after two hurricanes events.

I am aware of everything you are saying.

However, were I to gain a better understanding of the bits & pieces I do not know, I still may wish to pursue the project.

My neighborhood does not have natural gas, so I would need to buy propane and have it trucked in. Diesel is another alternative, but you need to treat it if it sits too long. Plus generators are noisy & require maintenance, which is something personality wise I find difficult. All that and it supports the dying fossil fuel industry.

BTW, I have lived in Florida 63 years, and both yesterday & today my power was out for 15 - 30 minutes. While this is not a common occurrence, it is a PITA. We also lost power after Katrina, Wilma and Irma for many days over the last 12 years. While it hasn't happened yet, I expect FPL will find a way to end net metering and/or implement time of day power billing. If either or both of those occur a battery system will be very useful.

My goal is to purchase Lithium Titinate (LTO) or worst case Lithium Iron Phospate (LiFePo4) batteries as I can afford them. This way it will reduce the maintenance, and provide long life.

My solar array seems reasonably well sized so far. My last two months electrical usage has been -352 kwh. We are heading into the summer, so we will see how it fares.

 

[Jadnashua]

Tesla sells a complete unit, ready to plug in. YOu can gang more than one together if needed.

https://www.tesla.com/powerwall


BMW is using some of their i3 car battery packs for the same thing, but I don't think they're ready to offer them to residential properties - they've got some commercial installations though. You might be able to pick up a battery pack from a wrecked EV, but they do still have a fair amount of value left in them.

 

[WorthFlorida]

You may already be aware of this company and starting from $9,ooo you get everything you want in one box. It'd be safe and no doubt it will work without hassle. Another part of the install would be during outages a transfer switch would be needed so as not to put power out to the grid. Your solar array converter must already does it.

The first part of this electrical forum is concerning safety when it comes to recommendations. There is a saying, when a plumber messes up you may get a little water on your head or a full house but no one gets hurt. When an electrician or electrical work is messed up, you can get electrocution including burning the house down.

https://humless.com/shop/
https://humless.com/product/home-6-5/

 

[Reach4]

Another part of the install would be during outages a transfer switch would be needed so as not to put power out to the grid. Your solar array converter must already does it.

Shockingly, most solar array controllers for houses provides power into the commercial grid, and will not provide power when the commercial AC goes out. This is not to say that you cannot have a system that will charge your own batteries.

 

[WorthFlorida]

Shockingly, most solar array controllers for houses provides power into the commercial grid, and will not provide power when the commercial AC goes out. This is not to say that you cannot have a system that will charge your own batteries.

Maybe my concern was not stated as I intended but Reach you’re right. I was referring that if aceinc added his own battery backup system that a power transfer switch would be needed to prevent the inverter putting power to the pole.

 

[aceinc]

I am aware I would need a transfer switch. Most automatic transfer switches I have seen have a group of circuits they wish to keep operational during the outage. I would like to transfer the entire load, not just a group of circuits.

People tend to electrocute themself and burn things down when they ignore their ignorance. I am aware of my ignorance, and wish to educate myself before cutting any wires or turning any screws. I have survived lo these many years doing some of my own electric as well as plumbing & construction. No burnt out shells litter my past either.

I need an automatic transfer switch. Since my grid connect PV array is AC (after the inverters), I will need an AC to DC Battery charger/controller. I will need a DC to AC inverter to convert my battery juice to AC.

The last piece of the puzzle (for me) is how everything goes together in such away that each piece operates when it is needed.

I could buy the Humless products, or a Tesla Powerwall 2, or any number of other solutions, but they do not provide the low initial cost that I am looking for.

 

[Dana]

What is the real purpose of this backup?

A propane fired 8kw standby generator costs roughly couple grand (maybe $3.5-4K installed, with a power transfer switch to disconnect from the grid), which a heluva lot cheaper than 8kw of battery output.

Last I heard S. FL was still a first-world country with pretty reasonable grid reliability, occasional hurricane outages notwithstanding. (I wish the same could be said for Puerto Rico's grid. )

One of the guys on my ski team lives in the woods in a semi rural area in central MA where powerline failures on the local distribution grid during major snow storms are fairly common due to falling tree branches, etc. His propane fired standby generator is about that size, and automatically operates the power transfer switch to the sub panel with the critical circuits. During a major December ice storm about a decade ago brought major portions of the distribution grid down for a week or so his was the only house in the neighborhood with operational central heating and a Christmas light display.

Powering anything more than your most-critical circuits with batteries would be cost prohibitive. And with most grid-tie inverters you won't be able to charge the batteries with the PV, since the inverter needs the grid to operate correctly. With a fair amount of engineering and heaps of cash you can rework it to become a self-islanding nano-grid, but that's even more cost prohibitive.

 

[aceinc]

What is the real purpose of this backup?

Partly to take care of hurricane scenarios. Partly to avoid investing in fossil fuels. Partly to help during minor (10 minute to 1 hour) outages. Lastly because it interests me.

Yes I could get a generator. Yes the initial cost would be less, although I would go for a 20-22KW generator. I suffered through the last post hurricane with a 5.5kw (8kw peak) generator. I energized my entire home with it, and turned on & off circuit breakers as needed. I was even able to run some A/C as needed.

Regarding costs, as I have indicated, I want to put together the electronics for the entire system, and then add KWHs of batteries as I can afford to (or I find good deals).

BTW lest you think I endangered FPL, I disconnected the meter (belt) as well as turned of the 200 AMP breaker (suspenders) to my home before attaching the generator.

 

[Dana]

The total material cost and environmental impact of a battery back big enough to do anything useful is still pretty substantial, and won't get you through the hurricane scenario, even if it'll glide through the hour long outages.

The total fossil-fuel input to the mining and manufacturing of a Tesla Powerwall is (for the time being) probably going to be more than the propane you'd use during the next 100 power outages in the sub-1-hour time frame. If you lived in P.R. there would be a clear net fossil-fuel reduction benefit to going this route, but for most of S.FL it's probably going to be at best a zero net benefit on lifecycle environmental impact unless you're using re-purposed scrap electric vehicle batteries that no longer have sufficient peak output capacity for powering a car, but still plenty of capacity for residential backup battery purposes or grid-batteries.

Nissan already has a steady stream of retired Leaf batteries that it is re-using commercially in streetlight backup and grid battery pack purposes. As the expanding fleet of ageing EVs reaches battery retirement mileage I would expect repurposed EV battery packs to show up as cheap home-storage and home backup battery packs.

In a commercial setting there is often a pretty good to VERY good financial rationale to have a sufficient battery backup system to get you through 10-100 minute outages at full power. But for residential (unless there is a powered life support backup need) it's just an expensive hobby, not for the faint of wallet.

 

[aceinc]

In a commercial setting there is often a pretty good to VERY good financial rationale to have a sufficient battery backup system to get you through 10-100 minute outages at full power. But for residential (unless there is a powered life support backup need) it's just an expensive hobby, not for the faint of wallet.

Being an IT consultant for 40+ years and still in the field, I am very aware of the reasons for data centers in particular to use full load UPS systems, backed up by diesel generators.

The point of all this is to fill in my knowledge gaps as it applies to implementing a whole house battery backup system. In the classic UPS under your desk, or rackmount UPS, some grid electricity goes into a charge controller which charges the batteries while sending the bulk of the power to the load. If the grid power fails, it quickly (< 30ms) switches to providing battery power to the load through an inverter. I believe larger true UPS systems have the full load running on batteries all the time, while charging the batteries at the rate of depletion.

A true UPS used in a whole house environment would be costly if for no other reason than the losses involved. I suspect the size and cost of the various electronic components would be problematic as well. So where can I find a design, suggested parts and schematics for what I am trying to accomplish? Or perhaps a group of folks that are receptive and willing to collaborate on this type of project?

 

[aceinc]

I am beginning to put the pieces of the puzzle together. I have found a device that I believe will do most of what I need.

https://www.aimscorp.net/12000-Watt-Inverter-Charger-48-volt-to-120-240vac.html

The part I am trying to work out is how to disconnect the mains and then feed my entire house with the power from the battery. I need some sort of automatic transfer switch, which this has a built in transfer switch, but I am not totally sure how it could be integrated.