df33702021 t1_j38ngx5 wrote
Nevermind the batteries. The claims on powerwalls and backup battery systems are often quite exaggerated. Also they need to be heated. LifePo4 batteries cannot be used in freezing temps. You need to keep that in mind. If you use them in freezing temps, they will be destroyed. Solar power is irregular. For example, the last few days would not have produced any meaningful solar power. One Bluetti EP500 that you reference is 5.1 kwh. I use ~10kwh/day which is super low compared to almost anybody else. (Typical house is more like 30-50 kwh/day.) So if you want to power your house for a long length of time, you'll need a bunch of them. And you will always use more power than you say you will.
Do the whole house propane generator with a 500g tank and automatic transfer switch. You 'll be able to do a whole week without power.
edit: I should mention, the batteries should have BMS that disconnects when temps get low, but that's doesn't always happen.
Real-Pierre-Delecto2 t1_j38seac wrote
> LifePo4 batteries cannot be used in freezing temps.
Yikes so much wrong with this comment in general but this stands out as completely wrong. They do indeed work although you must lower the charge rate and they don't discharge as fast. They even have special low temp versions also powerwalls are installed outside and in unheated garages all over VT so there goes that they also have a liquid cooling/heating system as do many other major brand backup systems. And a 500gal tank for a genny are you nuts a week more like a month and a half at ten gals a day.
df33702021 t1_j38xqzj wrote
It's not wrong. Typical LifePo4 cannot be used in freezing temps. It causes lithium plating. There are some new lifepo4 batteries that have slightly different chemistries to allow for cold weather down to -4f, but you won't find that in typical off the shelf home power products. If you heat the battery then fine. That's not uncommon and exactly my point. At any rate, who wants to test out their $10k battery and see how it behaves in cold weather.
A 20kw propane generator uses ~1.5 to ~3.0 g/hr depending on load. So say 2/hr that's 2g/hr*24hrs= 48g/day. Do the math for an extended outage. A 500 gal propane tank has 300g usable capacity.
Loudergood t1_j39mjte wrote
Noone is installing these batteries outdoors.
df33702021 t1_j39xjhi wrote
Didn’t say they were. I’ve seen them installed in places with marginal heat. Its just something to take into consideration.
Real-Pierre-Delecto2 t1_j3lwdn0 wrote
They can be discharged below freezing try reading up on the tech at play here. In fact many systems will use the heat created by the discharge to warm the entire bank to the point where it is safe to charge it again. Also your genny math is wacked. No one is gonna be running a 20kw (talk about overkill) genny full tilt for those hours. Other than having a 20kw generator here which is of course overkill you are also wrong on your propane capacity. Capacity is 80% full for a tank so in this case 80% of a 500g tank is 400g.
df33702021 t1_j3m4hip wrote
In terms of the tank, you are correct that capacity for a full tank is 80%. However, you need to call the propane company to come fill the tank at ~20%, because you don't know their delivery schedule. This is typical regardless of use case. So you have a real usage capacity of less than 80% and more like 60%. BTW, you want a large tank for multiple reasons, not just run capacity.
20kw generators are fairly standard for whole household. Many people have even larger. You are right, they are not going to run them full tilt for 24 hrs straight. That's why I said 2g/hr which is in on the low side of typical 1.5-3.0 g/hr range. You want your generator load to be in the 30-50% range for efficiency and longevity. I fully expect a full 500g tank to last more than a week typically, but we really don't know the use case here. So you have to use the numbers off the data sheet. Otherwise, you are under sizing. At least with the 500g tank you can go an entire week typically and you don't have to worry about it not.
In terms of batteries, you go ahead and use those batteries in zero temps. As I said there are some which can be used down to -4f, but beyond that they can't be used. Those batteries also aren't being widely used for household power. BTW, standard lifepo4 does not make any significant heat being discharged or charged. That's one of the beauties of that chemistry over lead acid. Sounds like you are quoting marketing for EV use. At least you acknowledge that you need to heat the batteries. There's plenty of horror stories where people put lifepo4 in camps, garages, out buildings, etc and heat failed and the batteries were bricked. You can just google it.
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