Ebike battery as power hub after a disaster.

spinningmagnets

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The power inverters that convert 48V or 52V ebike batteries into 120V AC are common and well understood. However, they are not well known.

For food storage, most people want to have access to a refrigerator or freezer. Of course cans of food are a vital addition to any preparedness plan, as is a propane barbecue, which does not rely on grid electricity. That being said. Imagine your home has been devastated by flooding, and after it recedes, you must decide what to buy with the insurance check. I now believe a chest-style freezer that is rated to be very efficient is a very useful option.

If you have no back-up power, then over the course of the next few days, the frozen food will thaw out and should be cooked and eaten rather than allow it to spoil. Food in a chest freezer will last longer than a cabinet-style kitchen fridge/freezer. Once the frozen food is consumed, you can use any available power to run it as a fridge, with the temps adjusted to 40F.

If running off of a 48V bank of deep-cycle Flooded Lead Acid / FLA, there are charge control units that are readily available which can run off of a small solar panel array.

"2 Solar panels to run old freezer after hurricane"
https://endless-sphere.com/forums/viewtopic.php?f=41&t=89525

My first question is...if we have very small loads (no A/C, no TV, very small fridge, etc) then...I am sure it is possible to run off of a large ebike pack. Of course we can charge laptops, 18650-cell flashlights, and cell-phones off of ebike packs through a DC /DC power supply (I have a 12V output unit, plus 5V USB).

If we are running a small fridge to keep precious food from spoiling just a few days, using an ebike pack...will adding one or several large capacitors to the fridge compressor help on start-up?

If yes, what are the best bang-for-your-buck large capacitors (model numbers), and where would we attach them?
 
Most of the 48V inverters I've seen have a peak rating double their continuous rating, and should have no problem at all starting a compressor. Domestic refrigeration appliances have a start capacitor built in, I would think it would be fairly simple to replace that with a larger one if you're having startup issues, but honestly I don't think it's necessary. I have one of these

http://www.ebay.ca/itm/2000W-Pure-S...2V-24V-48V-to-120V-220V-LCD-USB-/222442279505

but honestly I've never used it for anything more demanding than my computer/monitors/audio workstation gear during an outage. I will try and remember to test it with my freezer (though it's not a very big freezer) before the weather cools off. I'll use the 16S A123 stack to rule out any sag issues on the battery side.
 
I'd skip using the battery for such heavy draw. The company i'm involved with supply foodstuffs for extended hiking. Dehy (as opposed to freeze dry) comes back as good as fresh. Meats will last 12 weeks unfridged.
 
One of my thought behind starting this thread is that often, people who are on the edge of a disaster have not been directly hit, but still suffer from electrical outages and gasoline shortages.

An ebike is better than walking, or having only a pedal-bicycle in a "no gasoline for two weeks" situation.

If all you have are four large FLAs as a home back-up power supply, it's impractical to take four large deep-cycle FLAs on a trailer to power an ebike, but...I would rather buy several large 48V ebike packs to accomplish the same thing (ebike power, plus home back-up power). They can power the ebike, and also act as a mini "Tesla power-wall".

The common solar-PV panels and chargers are set up to provide either 12V, 24V, and 48V. This means that 48V is the sweet spot where back-up power and ebikes overlap. Many of the inverters and charge-controllers will take up to 60V (so 14S 52V is acceptable). However, ALL the mass-produced items that are available and affordable are 48V.
 
It's not really that big of a continuous draw. I just threw my clamp meter on my fridges cord for a second when I heard it start up, it's a fair size side by side, 25cu ft or so, and it's pulling 2.7 amps, so about 300 watts give or take. I have about 2000Wh of 48V battery laying around here, could probably keep it running for a few days if need be.

If you're stationary there's way better (cheaper, better tasting) ways to preserve food than what you'd want if you were on an extended hike.
 
spinningmagnets also don't forget that you could potentially transport the depleted ebike batteries with your ebike and charge them somewhere that power is available, and bring them home to continue providing emergency power at home. You could fairly easily transport 4000Wh of electricity with you this way, if you have the batteries and a way to carry them on your bike (maybe a trailer at that point).

I know here when destructive weather happens power tends to go out in blocks, if you're near the edge of the outage area you might not be too far from somewhere that still has power.
 
spinningmagnets said:
If we are running a small fridge to keep precious food from spoiling just a few days, using an ebike pack...will adding one or several large capacitors to the fridge compressor help on start-up?
AFAIUI, no, because the compressors are AC induction motors.

If you have a DC-motor system (BLDC with electronic control) then that'd be different. They do exist, but I haven't had any refrigeration or A/C system that had one. (other than the blower motor in the main roof A/C we have now). If it was a DC-powered system, then you could put the caps on the input of the main DC bus line inside the system.


Now, if the AC source (inverter) can handle the startup surge, but your battery powering the inverter can't, *then* you could use capacitors on the input to the inverter (output of battery) to provide the surge current without tripping the battery's BMS (or causing voltage sag so great the inverter cuts out from it's own LVC).
 
Now, if the AC source (inverter) can handle the startup surge, but your battery powering the inverter can't, *then* you could use capacitors on the input to the inverter (output of battery) to provide the surge current without tripping the battery's BMS (or causing voltage sag so great the inverter cuts out from it's own LVC)

I didn't know the right question to ask, but I can tell that this is the answer I was looking for! Thanks...
 
Simple diagram of the starting circuit for a single phase AC compressor. Actually almost any single phase AC motor with a substantial startup load will use a variant of one of these systems. Most fridges I've seen use the middle (B) one but it's easy to tell by looking at the wiring. There's probably a diagram very similar to this on the back of your fridge.

domestic-refrigerator-starting-relays.jpg
 
Just keep in mind that "starting capacitor" is not a buffer cap like in DC, it's used for a different purpose, so making it bigger doesn't ease the load on the inverter.
 
I have a Meanwell true sine wave inverter made for 48v. It works great off any of my 52v bike batteries. My inverter is small (300W) so not strong enough to run the refrigerator, but they do make larger models. During a recent power failure, I used it to power my TV and internet modem/router and charge some cell phones. It worked great and I don't think it used even 25% of the charge to run my big TV for a few hours. I have 3 bike batteries in that voltage range, so I could go for quite a while. In the old days, I used to try using car batteries, but that was very inconvenient and the Peukert effect really limited the run time.

I think the 1500W version would run the refrigerator. A true sine wave output will be much better for running an induction motor than a 'modified sine wave'.

Search eBay or Amazon for "48v to 120v true sine wave inverter" and you will see some. They are much more affordable than they used to be. I saw a 1500W version for under $200.
 
I've not yet tested it with motors/freezer/etc, but I still have this inverter
https://endless-sphere.com/forums/viewtopic.php?f=9&t=75149
file.php

and a reasonably-easy-to-reconfigure set of ebike batteries to supply the 12VDC it needs to operate.

Around here the power hasn't failed in years, and the worst it's been was maybe a couple hours (usually a few minutes). I think when I was in the apartment it was out for several hours, maybe overnight, because of a vehicle crash into a transformer or something a mile or two down the road (was quite a fireworks show, with fire, etc, as seen from the apartment). Something similar happened more than a couple of decades ago when I lived in a different house a few miles from here, though that was storm-caused, IIRC.


But at least I have it if I have to. :)

I also have a small deepfreeze, kept full of icepacks filling space between food, plus I have lots of styrofoam I can use to put under and around it should power fail, to keep it colder longer. The refrigerator only holds things defrosting for meals about to be made, and already-cooked things to be eaten for the week, plus again a lot of icepacks and water bottles to fill the airspace to keep it colder for longer, including the two cold-mats for the dog crate when taking them for trips.

I've also got a small solar water heater setup (not presently assembled), if it was long enough outage to need that, too.

I have a few small propane-torch canisters with a little gas in them if I *had* to use fire to cook with.

Only solar I have is three 1-foot-square panels made sometime in the 1970s or '80s, most likely. But I could use them to charge cells slowly if I had to. :)
 
i had trouble starting the freezer on 2 FLA's that start my cars easy. why? i ran 30' of 14awg from the cars, to the inverter, and the v drop set off the ups alarm. no start.
SO i had to jump start it using 2 9ah SLA's right at the ups. i used a foot of 12awg wire and it got warm fast! so it must have one heck of a surge to get warm while connected to 2 car FLA's. :shock:
running it takes 100-135w.
At 1st i wanted to use my ebike pack, but having 2 cars doing nothing made more sense for me for a 24v inverter. "Get to work, you lazy cars" :lol:
 
You're supposed to put the inverter next to the cars and run a long wire for the 120v. 10X less current at 120v.
 
fechter said:
You're supposed to put the inverter next to the cars and run a long wire for the 120v. 10X less current at 120v.
i know. BUT
cars in a 100F garage, 30' away my 84F workshop.
there was also 70' of 14 from the panels to the workshop. aren't you supposed to put the PV AND LA's all near each other, then run 120v the long run? of course, but sometimes. like the hot garage all boarded up, it just is not going to happen in an emergency. NO WAY i'd do this experiment in 100F.
One of the things i learned was, where to put the PV next time. i plan to drill a hole in the rear wall and shorten the 70' to 20'. Now with the MPPT working so well, i might stick it and the ups in the hot garage, as i now have the confidence that it won't catch fire :lol: and i won't have to baby sit as much.
i wish it were this easy. every 1/2 hour i noticed the amps drop, and the PV needed an adjustment. I found it entertaining to watch the amps vs. sun-clouds, so the cooler workshop was nice.
i'll probably try it different next time. It all depends on the mosquitoes! WITH LOTS of bugs, i go into workshop.
NO bugs and i could open 1 gar door and cool the place off.
 
I've been thinking of building an emergency battery backup, but we live in a very stable area for power, so something multi-functional would make much more sense than something I might never use. The idea of using an eBike battery I already own is brilliant. My concerns are:
1) how much power does an ebike battery have as compared to a golf cart or marine battery (which is a more typical choice for emergency power). I've looked before at pairing two CG2 batteries (https://www.samsclub.com/p/duracell-golf-car-battery-group-size-gc2/prod3590228) to get a 12v system. Trying to compare to my Shark 52v 13.5Ah battery, the CG2 lists:
20 amp hour rate:215
5 amp hour rate:157
6 amp hour rate:156
Battery Electrolyte Composition:Acid
Battery End Type:Top Post
Battery Purpose:Deep Cycle
BCI Group Size:GC2
Contents:ONE EACH
Freight Class:65
Minutes at 25 amps:395
Minutes at 75 amps:105
Terminal Type:DIN
Volts:6
But how does an amp hour rate convert to Ah? (and why is the 20 Ah rate higher than the 5 Ah rate?)

2) How do you hook an inverter up to a 52v battery? I'm considering buying a 2nd cradle (https://www.aliexpress.com/item/4001174798825.html?spm=a2g0o.cart.0.0.8bcd3c00q4vTpy&mp=1) with the leads coming off so I can move the battery around in the house where it's needed without needing to mount it to the cradle on the bike and disconnect that from the mid-drive to connect it to the inverter. Does this seem reasonable? I'm considering these two inverters: (https://www.aliexpress.com/item/2054310314.html?spm=a2g0o.cart.0.0.8bcd3c00E4PTNv&mp=1) and (https://www.aliexpress.com/item/1005001914585958.html?spm=a2g0o.productlist.0.0.798a584enkPtde&algo_pvid=65418e61-045e-436f-ac14-14731426de7f&algo_expid=65418e61-045e-436f-ac14-14731426de7f-1&btsid=0bb0623216130094543238828e2392&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_); does anyone have any recommendations for a specific model they've used? Thanks!
 
curranb79 said:
20 amp hour rate:215
5 amp hour rate:157
6 amp hour rate:156
<snip>
But how does an amp hour rate convert to Ah? (and why is the 20 Ah rate higher than the 5 Ah rate?)

The way it should be worded is 20-hour rate, 5-hour rate, 6-hour rate, etc. What it means is, if you drew out the entire capacity of the battery in 20 hours, you would get a certain number of Ah. If you drew it out over 5 hours, you would get a lot less Ah, because of the Peukert effect that is much worse in lead-acid batteries than lithium (almost unnoticeable).

So it means in their case that you would get 215Ah if you took 20 hours to draw it out, which means drawing only around 10A (20hours x 10A is 200Ah). You'd get 157Ah if you took 5 hours to do it, which means drawing around 30A (5hours x 30A is 150Ah). Divide the Ah you'd get by the rate you draw it out to get the amps you'd have to pull to get that rate.

Since the current draw isn't actually constant in most applications, it is difficult to really predict what you'd get for capacity.... Additionally, with lead-acid, it's not a good idea to draw more than 50% of that capacity out, as doing this degrades the battery--doing it a lot does it quickly. And the longer they stay below full charge, the more physical damage occurs to them (sulfating).

Also, because they are made with acid (sulfuric), they have a physical lifespan even if you keep them all charged up all the time...and if you don't keep them charged up all the time they sulfate and die. :(

Those are not problems you really have to worry about with lithium batteries. (they have their own limitations, of course, and have their own "shelf life" depending on the specific cells used).

2) How do you hook an inverter up to a 52v battery? I'm considering buying a 2nd cradle <snip> with the leads coming off so I can move the battery around in the house where it's needed without needing to mount it to the cradle on the bike and disconnect that from the mid-drive to connect it to the inverter. Does this seem reasonable?
If the battery has a connector that you can get separately from the cradle, taht may be less expensive. Some use Julet or Higo connectors, some use something else. Otherwise, a cradle is convenient as you can mount it to the same box/etc that holds the inverter and outlets and whatnot, to make a simple unit you can just carry around to run different things.

I'm considering these two inverters: <snip> does anyone have any recommendations for a specific model they've used?
Which inverter you need depends on a few things. First, what kind of loads you'll have. If they are motors, especially induction motors like refrigerators, etc., typically have, you have to get one that can handle that kind of load, *and* can also handle the *peak* power that load will demand on startup, as well as whatever continous power it needs, *while also* supplying the peak and continous loads of anything else connected to the inverter.

Given the likely cheapness of design and probable overstatement of capability of many products, I recommend getting something that says it can do at least half again what you need, preferably twice as much. (or more). Better overkill than bricked smoke generator. ;)

You also have to consider how much power your battery is capable of outputting, as that has to be *more* than what the inverter outputs under the above load conditions, since nothing is (even close to) 100% efficient. To keep from pushing the battery hard (which will wear it out faster) make sure the battery itself can handle at least half again, preferably twice as much, as the worst-case inverter demand.


You'll need to make sure the inverter will operate over the whole charged range of your battery, too. Meaning, if your 52v pack runs from around 58v full down to around 46-48v empty, the inverter has to be able to operate normally over that same range, if you want to use the battery's full capacity for the longest runtime.
 
You want to calculate the energy available in the batteries and compare that.

A 52v shark pack at 13.5Ahr is around 700 Watt-hours.

A 12v, 150Ahr lead acid is around 1800 Watt-hours, so more that double, but it's much larger and heavier.

As Amberwolf points out, with lead-acid, the energy you can use drops significantly at higher discharge rates whereas the lithium battery will be only slightly less at higher rates.

Here's a topic showing some inverters: https://endless-sphere.com/forums/viewtopic.php?f=41&t=100355

This is my 3kwhr pack with an inverter I use for backup power:
Img_1446A.jpg
 
amberwolf said:
You'll need to make sure the inverter will operate over the whole charged range of your battery, too. Meaning, if your 52v pack runs from around 58v full down to around 46-48v empty, the inverter has to be able to operate normally over that same range, if you want to use the battery's full capacity for the longest runtime.

fechter said:
You want to calculate the energy available in the batteries and compare that.

A 52v shark pack at 13.5Ahr is around 700 Watt-hours.

A 12v, 150Ahr lead acid is around 1800 Watt-hours, so more that double, but it's much larger and heavier.

amberwolf and fechter, this is incredibly helpful, thank you!

Given your clear knowledge, I'll state my project parameters and if you have time to give feedback, thank you so much.

I am in the process of installing PV on my house, and will be expanding to battery backup that would allow me to be totally off-grid when state battery incentives are in place next year. So I don't want to spend a bunch of money on an emergency backup system when a pretty significant system is on the way. That said, I was contemplating the GC2 system that was going to run me around $500 (≈ $200 for batteries, ≈ $200 for inverter, ≈ $100 for charger).

The idea was, in case of a hurricane-like disaster where power is out for multiple days, to be able to run the car with an inverter on it for a couple hours each morning to charge the battery bank and plug in the fridges for a cool down (BTW, I live in a multi-family so I'm wanting to provide some level of power for my family and my three small apartment units), and potentially run a small AC unit to cool down a room. My bigger concern is if such a disaster were to occur in winter, when I would need a small amount of power to keep my natural-gas boiler running for the main house, and to run the heat pumps which are the only heat source for the apartment building. Obviously everything would not run "as normal" but I'm wondering if I'd be able to run the heat pumps alternately (these are the heat pumps I have: https://www.fujitsugeneral.com/us/products/split/wall/asu15rls3hy.html).

I already have the 52v 13.5Ah Shark pack, and a 12v to 800watt (1600 peak) Cobra inverter to run off the car. We aren't looking for the ability to run four fridges, 2 heat pumps and a natural gas combi-boiler continuously, but to provide power to each unit briefly to keep things above freezing in winter (during which time fridge stuff could be put out in the cold if the outage goes on for a long time), or to cool off fridges and provide some power to run some small fans and lighting, etc. in summer.

I'm thinking I could get by with just a hi-capacity inverter (like 2000k watt continuous) that could run off either the car's 12v for the large-draw items for a few hours each day (and to charge the battery pack) or the Shark pack's 52v for small loads when the "car-generator" is off: Are there such inverters? And could such a goal stay under the $500 range?
 
The inverters are out there and they are cheap enough.

You problem will be with a car running at idle, you won't get enough out of the alternator to keep up with a large load. Maybe a refrigerator, but not likely an AC unit. For short bursts, you can run the full rating of the inverter, but the battery won't last very long. Unless the loads are very small, plan on needing to run the car engine continuously.

My refrigerator will use up my 3kWh pack in about 24 hours with no other loads.

You will also need a bunch of extension cords to plug everything in.
 
curranb79 said:
So I don't want to spend a bunch of money on an emergency backup system when a pretty significant system is on the way. That said, I was contemplating the GC2 system that was going to run me around $500 (≈ $200 for batteries, ≈ $200 for inverter, ≈ $100 for charger).

Some thoughts:
Do you want to spend $300 on batteries/charger you won't use on anything else? ;)

If you need more battery to do the backup tasks you want, you could instead invest that into a spare ebike pack similar to what you have, or better (same voltage (14s) but bigger capacity, better cells, or whatever you happen to need).

For how much battery capacity (Wh, kWh) you need, you would need to know how many Wh that all the things you're going to run will need to use during the times you'll be using them. For instance, let's just say some item needed 1000w, and needed to run for an hour out of the day (either all at once, or a few minutes here and there). That's 1000Wh, or 1kWh, each day. Let's say you have another item that needs 500Wh over the day. And another that needs 200Wh over the day. And another that needs 700Wh over the day. That's a total of 1000 + 500 + 200 + 700, or 2400Wh, 2.4kWh, per day.

Inverters are not 100% efficient, and probably run better at some loadings than others, so let's just use 75% efficient as a rough number, to be on the safe side (even though you'd probably get better than that). So it means it takes 1.33 as much power input to get however much power on the output. (1/0.75). So to get 2.4kWh out of the inverter, you'd have to put in 2.4 x 1.33 = 3.192kWh.

For those SLA batteries you started with, if they were about 1800Wh usable per pair (I didn't do the calculations, am trusting Fechter's math; he's probably better at it than I am anyway), you'd need at least four (two pairs) of them to get enough Wh to run that example system. Which means $400 for batteries, plus the charger...for something you'll only use for the power outages, if they ever happen. ;)

If you have a 52v 13.5Ah pack, then 52 x 13 (round down with your supply, round up with your demand...it's safer ;) ) is 676Wh, or 0.676kWh. So to meet the likely demand of almsot 3200Wh, you'd need at least 5 of those. Prices (depending on the crappiness or goodness of the cells inside, and their BMS, and the pack build quality, none of which you can see on the outside or tell until you actually have it and use it :( ) range from $250 to $700+ per pack. So it's a lot more expensive, but these batteries are something you can use for your ebikes...and if you don't, you could sell them to other ebikers, whcih is a lot more likely a possiblity than selling the SLA setup. ;)




The idea was, in case of a hurricane-like disaster where power is out for multiple days, to be able to run the car with an inverter on it for a couple hours each morning to charge the battery bank and plug in the fridges for a cool down (BTW, I live in a multi-family so I'm wanting to provide some level of power for my family and my three small apartment units), and potentially run a small AC unit to cool down a room.

First, as Fechter notes, the alternator wont' run at sufficient revs with the car idling to keep the battery charged under that kind of load, most likely--you'd probably have to sit there and keep the revs up during the usage period. :( Some cars don't have sufficient engine cooling to do this for long periods without actually moving to keep cooling air flowing, so that's a potential concern. Also, do you have enough gasoline around to be able to run the car at revved-up states for long periods?

If you have to run the car anyway, an efficient generator (honda, etc) capable of handling the loads you'll throw at it would be a better investment, and simpler.


Second...is the inverter rated for inductive motor loads? If it isn't, it's probably going to explode the first time the AC or fridge compressors kick on. If you have more than one hooked up at a time, it'd probably do it when more than one kicks on, if it didn't do it before. (ask me how I know :oops:)

Then...is the inverter rated for sufficient peak power to handle the motor startup load (whcih is a LOT more than when it's running, and may not be stated anywhere)? If not....again, could poof the inverter.

Then...is the inverter rated for sufficient continous power to handle the running loads....at the same time as when a peak load occurs from something else running on it?

Then...is the inverter a true pure sinewave inverter, or a "modified sinewave", or just a basic "can't be bothered to tell you" ;) inverter? Some devices don't work well on anything ohter than pure sinewave input, and some will actually be damaged by non-sine inputs. :(


If you really have a critical load that *can't* go without power...give it it's own inverter. If there are several critical loads...give each it's own inverter. The battery power source you probably wont' have just fail. But the inverters can just die if overloaded, and if you don't have a spare, then *all* your stuff is down, for the duration of the power failure.


y bigger concern is if such a disaster were to occur in winter, when I would need a small amount of power to keep my natural-gas boiler running for the main house,
If this is a 24VAC system run from a 115VAC to 24VAC transformer (some are, some arent') then you might be able to run it on 24VDC, but you would have to check to find out how it is made. If it is, then a likely very small battery would run it for quite a while, like two little 12V SLA like many UPSs use. (or a 24v lithium battery, etc) Or a 24v DC-DC that runs off an ebike battery, or the car's 12v.



and to run the heat pumps which are the only heat source for the apartment building. Obviously everything would not run "as normal" but I'm wondering if I'd be able to run the heat pumps alternately (these are the heat pumps I have: https://www.fujitsugeneral.com/us/products/split/wall/asu15rls3hy.html).
It doesn't say how much continous or peak power it needs, so I don't know if they would work or not. I'd recommend asking the manufacturer:
--Will these run on an inverter?
--Do they need a special type of inverter, or will any inverter do? (the whole sine/non-sine/etc thing)
--What is their peak startup power demand? (worst case)
--What is their continous running power demand? (worst case)


There are always solutions to stuff like this...but first you have to know for sure what it is you need, or you might end up with stuff that doesn't do the job you want, and have to spend more money (and have wasted the other money, or worse be stuck in a power outage without the backup you thought you had).


If I were doing this, and the likelihood of a power outage was minimal but potentially long enough to be very costly in lost refrigerated items and/or health/etc problems from lack of building thermal control, and a long-term solution was already on it's way:

--I'd total up the worst-case continuous load I *had* to have on the inverter all the time, to know what it's continous output has to be. Then I'd total up the worst-case peak load it might have to provide, ever, to know what it's peak output has to be. Then I'd get an inverter that was pure-sinewave output (just in case I ended up with things that didn't tolerate less-than-perfect power input), that had a peak and continous rating at least half again what I'd determined as "minimum necessary".

Then I'd invest the battery money into more / bigger / better ebike batteries, that could easily handle the inverter's worst-case peak and continous loads, with enough capacity to run as long as necessary for any continuous loads.

Then ensure the charger for those would work on the car's inverter, so that I could charge those with the car just idling, if they were going to be needed for longer than their best-guess runtime (how many Wh (kWh) you would need them to output over a typical outage, given that inverters aren't 100% efficient, perhaps 75% guesstimate). And ensure the charger could charge them fast enough (and that the batteries can safely *be* charged fast enough) to keep up with the demands that will be made of them during the outage.



If I were doing this *as* a long term solution, I'd probably go to places like BatteryHookup, etc., and get some of the ex-EV battery modules they have (designed for high-power usage) and build a powerwall with them, and just get inverters that would handle the entire house power usage....but you'll already be doing this, most likely, with the solar system setup (though with a prebuilt powerwall rather than DIY).

(keeping in mind that if one battery alone can't handle a peak or continous load, two or three wired in parallel probably could, depending on the ratings).
 
I agree with Amberwolf that a generator would work out best for your situation. Here is a cheap 3.5kW one for $300.

https://www.cabelas.com/shop/en/champion-power-equipment-3550w-weekender-portable-generator?ds_e=GOOGLE&ds_c=Shop%7CGeneric%7CAllProducts%7CHigh%7CSSCCatchAll&gclid=CjwKCAiA65iBBhB-EiwAW253W1KaXSDLYWn6WB2jQSujMhJbyVqQ2whlXYC6lCN_DlCpc8GdK9B0AxoCsKkQAvD_BwE&gclsrc=aw.ds

Even better is to buy a plug in hybrid car that you can charge with your future solar system. I own a Volt and use a 3000W inverter on its 12V battery for emergency power. It will run my house for many days with just the gas in its tank,
 
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