Off grid inverter choice

Re: Off grid inverter choice

Time to rethink a couple of things. First thing that hits me is the relatively huge load you plan for the battery pack you have, running either a coffee maker, OR the smallest microwave oven alone is a really big load for your batteries, but both together? From my experience, you'll very quickly draw down your battery voltage to the point where inverter alarms, or shut downs will be happening. Especially so if the batteries are cold, as in Winter. Even if the batteries could maintain 12 volts under such a load, the draw on them could be over 160 amps, and that would go even higher as the voltage continued to rapidly fall.
You'll need a much bigger system if you want to successfully run heavy loads, and these are heavy loads for an off grid cabin system. You'd be better off having a generator to fire up whenever you want coffee or the microwave, and let solar handle the rest. That said, you still need need more PV to properly charge your batteries, and a good controller to match.
Second thing that hits me is that living off grid requires a whole different way of thinking than the wasteful ways that most of us were brought up to accept as normal while living on grid with limitless power available at our fingertips. Going off grid suddenly changes all that, and it can be difficult to adjust. Suddenly we have to live with what we have available, and use only what Nature provides, when Nature feels like providing it. We have to live with Nature, like our ancestors did, not in spite of Nature as we were brought up to accept as normal. But the awesome thing is, once we grab hold of that way of living, it opens up a whole new way of life, a life very in tune with Nature, the changing weather and seasons. We become one with nature. And be warned - - it's addictive! :D
On a sobering thought, I gave a drive home to a neighbour/friend last night. His wife had gone out for the evening and when we got there the place was lit like the proverbial whorehouse on a Saturday night! Every room in their huge house was lit with not one, but at least two lamps each, two big yard lights were on, and the 50 inch TV blabbing away without even a cat to witness any of it! The shocking thing is - - this is totally normal for them! A real life nightmare for anyone used to living off grid!

Re: Off grid inverter choice

1500 watts of coffee pot or micro, for 15 minutes will draw ~ 350 wh, about half of what we use in total in an entire day!

As comparison,, we live off grid, with 450 ah of T-105 batteries, charged with 400 watts of PV, and our daily use is between 6-800 wh/day.

All calculations come from the loads. Determine your loads, then design around them. Also consider reducing any and all loads you can. For example, a Coleman Mr Coffee on a propane camp stove will make great coffee using no power,, then you can pour it into an insulated caraffe and it will keep coffee hot nearly all day.

We also use no micro, and indeed we have a propane fueled toaster! Also realize that running a large inverter for small loads is very inefficient. For example using a 1500 watt inverter to power a few lights, would be better served with a much smaller inverter. MY inverter of choice is the Morning star Suresine 300. When it gets right down to it, most cabins have very little need for more power, if they are not running a coffee pot, micro, or fridge.

You could also consider building a dual inverter system,, one small one for normal loads,,the larger one for peak loads.

Hope this helps,

Tony

Re: Off grid inverter choice

also, be aware that battery capacity suffers during colder temps. keep in mind we are talking about the temp of the batteries themselves even though the ambient air temps do influence this. you could wind up needing up to 5x the capacity than you designed for just to overcome a temp of -50 degrees on the batteries. this would also up the charging requirements. it gets complicated because when using or charging a battery it will heat it up and change the derating. also, during the warmer months the derating most likely won't be this bad and you will need more power to feed a larger capacity battery bank and hence a larger pv array. the variabilities of all of this can make your head hurt, but do a basic load calculation and determine how long you will use the loads for to start with so we aren't taking stabs in the dark on this. btw, the t105 capacity is about 220ah, but that's at 25 degrees c or 77 degrees f. think of how your car batteries act up there and you will quickly grasp what i'm talking about for the temps.

Re: Off grid inverter choice

nasty wrote: »

I am in Valdez Alaska. Cabin is in Wrangell St. Elias Park in the interior. Is the submersible pump for a well? I only have clean lake water pumped to a holding tank for shower and haul drinking water. We use a 12v Flojet quadra pump 3.3 gpm auto on/off. Propane on demand water heater. System works good but would love to have a system that is like a house system just gotta figure it out.

We use a Shurflo 2088 for the whole house, but we hooked it to a 20 gallon pressure tank. The Shurflo will only do 2.8GPM, but it's rated at 45 PSI instead of 35 like your Flojet. The Shurflo has a screw that you can turn to increase the pressure. I wonder if your Flojet has the same feature? The nice thing about a pressure tank is that the pump doesn't come on every time we flush a toilet or wash hands. We let the pumps internal pressure switch turn it on and off and it works fine with our on demand water heater, so long as we only use one fixture at a time.