Off grid inverter choice

nasty

Hello

I am looking to upgrade my system for my remote off grid cabin. I have everything figured out except the inverter. System will consist of 2-130w Kyocera panels, Xantrex 35A Tri Mode controller, 2-Trojan L16 batteries in 12v configuration. Biggest users will be a coffee maker and small microwave possibly at the same time. I have the cabin wired so I would like to hard wire the inverter. Also want one with built in charger that will use AC from a Honda EU3000 generator. I was looking at the Xantrex Posine 2.0. And Magnum brand inverters(USA). I would like to keep it 12v as that is how I have it set up now but I could go to 24v if panels can be used in that configuration. My panels are within 30' of system components and I have a lot of welding cable i can use. Any thoughts or advice will be greatly appreciated.

Thanks
Keith

niel

Re: Off grid inverter choice

it's not enough charge power for l16s. depending on which one you have in mind it would be minimally 320ah and trojans want a 10% charge rate or 32a. figuring the efficiency of pvs at about 77% you need 41.5a from 12v pvs. you're thinking it's only those 2 items to be run, but they are big draw items. coffee pots vary, but will most likely be a minimum of 750w drawn. microwave ovens draw far more than their rated heat power wattage. my 900w microwave draws over 1300w if i remember rightly.
as to the controller i would probably recommend a more sophisticated mppt controller with the proper output capacity to match your pv input.
going to 24v for the inverter can be a good option as most recommendations are 12v for every kw drawn and you would be about 2kw for both items. that would also mean more batteries and another doubling of the pvs to charge them though. that would be your call.

waynefromnscanada

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!

wrdaigle

Re: Off grid inverter choice

If I were you, I would consider living without either of these items. With a propane stove and a bit of imagination, you can easily get by without. Do yourself a favor and get yourself an insulated coffee press. Coffee makers spend most of their time just trying keep your coffee warm. Good luck!

icarus

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

silvertop

Re: Off grid inverter choice

I also agree; way too much power draw to run a coffee maker and microwave at the same time. I run my espresso maker only with peak sun; I don't want to put that much drain on my batteries. If you take care of them, they will last longer. So... espresso then microwave; I run a Panasonic inverter microwave thet can really be backed down in power 40% =540 Watts/ 70% =1165 Watts. But you definitely need more solar. I would try to go at least 24 volt , and more solar will help you avoid stratifying those tall batteries; they need a higher charge to mix up the electrolytes.

nasty

Re: Off grid inverter choice

Excellent information guys thank you.

I guess I was thinking about the prosine 2.0 because my neighbor uses one with A 210w panel and 2 trojan 105's. He says it works great.

Will stepping up to 24v be better? I have two 105's now and if I get two more connected for 24v, with two or three panels will the same controller work? What size inverter/charger can I do? A quiet inverter with remote start would be great as the one we have now is quite loud. Only other things we would need inverter for is lights, laptop and stereo. Maybe TV and satelite in the future. Any suggestions of how I should proceed if I dont have any big loads?

Our cabin is remote with no dealers within 300 miles so your help with getting everything matched up correctly is much appreciated. Thank you!

icarus

Re: Off grid inverter choice

Do your self a favor, do a proper load calc. All design criterion, and ergo hardware choices stem from the load calcs. To properly size a battery bank it is imoortnt to know the realistic loads and their duration. Battery size then determines the size of the PV and to some extent the inverter size.

That said, there are several recurring errors that folks make when strting out. The first is over estimating thier solar potential, while at the same time under estimating thier loads. The next is that loads always grow with time

A general rule of thumb is as followes, take the name plate rating of the PV, divide by two to account for all cumulative system loses, then multiply that number by 4 to account for the average number of hours of good sun one can reasonably expect, per day, on average over the course of the year. ( see rule #1 above!)
So 100 watts of PV might look like this,, 100/2=50*4=200 watt hours, per day.

Tony

nasty

Re: Off grid inverter choice

I am going to rethink things. We have done without coffee maker and nuker for this long so will continue to do without. I will calculate my loads and see what I need. I have done this before but all info is at cabin right now and temp there is currently
-50 at night so will probably be closer to spring.

On another note how do you off grid folks supply water to sink and shower. Right now we use 12v pumps with an on demand water heater and holding tank that works fairly well but never seems to have enough flow even though it is supplied by a pump that is rated at the psi the heater requires. Any links or suggestions?

Thanks

icarus

Re: Off grid inverter choice

Read my thread bout freeze proof water in the water pumping threads.

I can give home more info,, but I am going to be travelling for a week or so and may not have net access.
We hve a shureflow submersible, pressure tank, and a demand hot water heater. It delivers all th water, hot water we could ever need.


Where are you that is currently -50?

nasty

Re: Off grid inverter choice

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.

waynefromnscanada

Re: Off grid inverter choice

Minus 50? Be aware that sealed batteries cost twice that of flooded batteries, and may not last as long - - but they are freeze resistant compared to flooded types.

niel

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.

nasty

Re: Off grid inverter choice

waynefromnscanada wrote: »

Minus 50? Be aware that sealed batteries cost twice that of flooded batteries, and may not last as long - - but they are freeze resistant compared to flooded types.

I should have stated that cabin is only used a few times in the winter and system is off line all winter.

Batteries are at my home in shop on trickle charger for the winter. It was ~-50 at time of post also. It has warmed to a toasty -20 today. And +20 in town. What a difference a mountain range can make.

Thanks for your input.

Volvo Farmer

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.