How to select best UPS and Solar to be off-grid 24 hour for 2kw

The claim of 'you'll spend more fuel transporting panels' is a total fantasay

"generator that will sip fuel."

For this discussion to be usefull, you have to provide some numbers. From generator efficiency I was able to find, you need to consume roughly 1 liter of fuel to create 2 KWh of electricity. Playing around with batteries won't change that.

If you look at my calculation above, a single solar panel produces the equivalent of half a ton of diezel. There is no possibility anywhere outside the arctic that a solar installation won't pay for itself.

A single solar panel will produce the equivalent of half-a ton of diesel/year for his location. There is no way in hell a generator is a better option for a permanent installation.

There is a reason all remote meteostations, etc. have long switched to renewable.

Not really. I can run 1500-2000W during the day if I care, but there's no way I can run a 2kW load, 24/7, without massive generator use. My battery bank is way, way too small for that. I typically idle around 75W overnight in the winter, can run a bit higher in the summer, but 2kW would drain my battery bank stone, stone dead about 5h after sunset.

(Solar Shed guy here, I currently have 5kW of panel hung on my office, 10kWh of lead acid, 2kW of inverter, etc)

Unclear as to what you mean "off-grid for 24 hours" - do you need to be off-grid 24/7, or simply run a 2kW device for 24h after the power grid goes down?

Both are quite expensive, the second somewhat less so than the first (though still very expensive). You can probably do the second for under US$10k, probably not the first.

And depending on the use case, the suggestion of "Use a generator..." is very, very much the cheapest option for short term use.

Taking both options here, and going with hardware I would trust to do the job:

If you want to run a 2kW load for 24h after the grid goes down, are OK with charging from the grid, and simply need a really long term, high capacity UPS for infrequent use, your best bet will be something like an Aims Power inverter/charger or similar. I would go with minimum a 24V system for this, and for 2kW, you really should be up at 48V. Yes, I know there are 5kW 12V inverters, and, no, you really don't want to be dorking around with hundreds of amps if you can avoid it.

A 4kW Aims Power inverter/charger will comfortably run a 2kW load, and will charge the battery bank afterwards. At 48V, you'll need a minimum of 1000Ah at a 20 hour rate, and will probably want 1250-1500Ah. If you can at all avoid parallel strings with lead acid, do so. A bunch of battery strings in parallel just guarantees early death, because they won't charge equally over time.

You could use a Trojan SPRE 02 1255 or SIND 06 1225 to build a single string that would run the load, as long as they're warm. This will almost certainly be cheaper than lithium unless you've got a good source of scrap cells and want to build your own. However, this is really hard on the cells (running them down to 80+% depth of discharge), and they won't last more than a few years if they're getting cycled like that daily. If it's infrequent use, have a ball, it'll be fine.

Now, if you want to do it with solar, it becomes a harder question. How long does it really need to run, and do you care about a generator? "Sun is not a problem here" is a common claim, rarely backed by data. You never get clouds or storms? With well aimed panels, in winter, you may only have 6h of usable sun (unless you're using trackers) to generate your 48kWh daily use (plus some overhead for charging), so you're looking at about 10-12kWh, /minimum/ - and realistically, if you want to ride through cloudy days, you'll need far more. Or, you have to have an automatic generator start. Another option would be to have far more battery capacity so you can ride through a few more days, but then you run into the problem of having to have enough solar to recharge it. Practically, for fixed panels, to ride through winter, you're looking at 20-30kW of panel hung.

Something like a string of SIND 02 2450 would get you around 115kWh nameplate of battery, which might be overkill, but you won't drain it too deeply with normal overnight use, and you have capacity for two days of "no solar input" with the pack capacity. The pack will be 3.25 tons, give or take, but still cheaper than a similar capacity in lithium.

I would estimate a system cost in the US$50k-US$75k range in materials if you do it yourself, easily $100k if you're having someone else do it.

The right answer here is to either connect to the power grid, or figure out a way to reduce your loads when there's no sun. Running a 2kW on solar, 24/7, is doable, but it's a very, very expensive project.

Using battery banks helps quite a bit, as you can use a larger, more efficient generator to charge the banks quickly and can size it perfectly to do so, then shut it off. So you might only be running the generator for 4-5 hrs a day or less. This helps with wear and tear, lets you be more efficient, etc. How efficient you can get depends a lot on the specific battery chemistry (columb efficiency), bank voltage, max charge rate (C rate, which is very high for lithium, less high for lead/acid), etc. so hard to calculate here.

I personally use a small inverter generator to power ~ 2kw (1.8 specifically) loads for long periods of time off grid. I don't bother with a battery pack in this case, though eventually I will. I also use propane (since I can store/refill a 1000 gallon tank with no worries about it going bad - it will be fine for a decade or more, it's easy to transfer to portable bbq size containers, etc), and propane is $2.4/gal where I'm at in bulk.

It supports that 1.8~kw/h load continuously, and burns ~ a 5 gallon propane tanks worth in 10 hours at that load. Lower loads, it will go as long as 18. This is at altitude (4500 ft), no supercharging or anything, so you'd get ~ 30% more efficiency at sea level. That is roughly half a gallon of propane for 1.8kw/h, or about $1.50/kwh - pretty much the most expensive and inefficient way to generate power using a generator I imagine. Diesel generators are far more efficient for the power they produce, but generally also output much more power and idle burns more fuel, but fuel is less stable - important for me in this case, not if you're running it a lot. If I was using diesel, I'd be charging a battery bank. In general, larger generators are more efficient (often MUCH more efficient) per unit power produced, as long as you can sustain load within their sweet spot. An over provisioned generator will waste a lot of fuel idling, and an overloaded generator will burn fuel inefficiently. This 'small' commercial generator [https://www.ckpower.com/what-you-need-to-know-about-fuel-eff...] (CK300VM-T4 Final) outputs 225kW, and puts out 14.25 kwH per gallon of fuel (rated capacity). If diesel was $3 a gallon like it is here, thats $.21 per kWh - damn cheap!

So, assuming our friend here is running 24/7 at 2kw continuous using my terribly inefficient setup, he'd be going through 72 dollars a day in fuel. Quite a bit! But let's compare to solar!

A 48kwh system is non-trivial in size and expense. A system rated to produce ~ 40kWh/day in winter (wholesale, DIY installation, no racking or batteries) is ~ 36k, and has 54 large panels. [https://unboundsolar.com/1891324/unbound-solar/solar-kits/17...]

Battery option price varies. Lead acid is cheap, but needs to be over provisioned to avoid stupid short cell life (> 50% discharge will severely shorten cell life), and even overprovisioned if you're actually drawing down the cells much every day, you'll be lucky to get 3-5 years out of them. To have a day buffer (essential, even if you get perfect sunny weather 99% of the time) and not kill your cells quickly, you're looking at ~ $30k worth of batteries on top of that, at nnearly wholesale prices [https://unboundsolar.com/1891324/unbound-solar/solar-kits/17...]

Lithium allows faster charging, deeper discharging, and longer cell life, but is expensive. A ~ 45-50kwh usable battery bank is going to run you an additional $60k at current market prices [https://unboundsolar.com/shop/solar-batteries-backup/battery...], and might not give you an actual full day buffer, depending on how much charge you got in the prior day.

So let's assume we can do free racking somehow (racking and installation costs are often almost as much as a normal system), etc. We're looking at about 66k for a bare bones 'works when everything is perfect' system without much redundancy or backup.

If you split that out over two years, you are paying $91/day, or $19/day more than if you were using that woefully inefficient generator, with a woefully expensive/inefficient fuel, at altitude with all it's associated losses. If you amortize it further over 5 years AND ignore maintenance, racking costs, battery wear, it starts to look like it would win. The reality is, you can't ignore those though.

Unlike the generator, you're also stuck in place (those panels are huge and need to be very solidly anchored), and also unlike the generator the capex is all spent up front. You can't change plans a week in and do something else, you're out that money. Did I mention that the generator I'm talking about cost $850?

Solar has it's place - mainly when you can predict the usage far in advance and can amortize the cost over many, many years (a decade or more).

I get the impression you've never actually had to provision or budget a system like this? I've had to several times.