Tell me why this will not work

Clyde

Hello,

Thanks to everyone that helped with my barn lighting project! It was a success and thats all yalls fault:D

My next idea is to build a small cabin and have it off the grid. Easy to do just very very expensive. In order to combat that expense and to stretch that expense and future maintenance over a period of time I came up with a hair brained scheme as follows.

Would it be possible to have several smaller fully independent systems that would work like a large system? What I mean by that is have each circuit on a different set of panels/charge controller/battery/inverter. Why in the world would someone do that you ask? One month I could get the lights done, the next month or so get the HVAC powered, month or two after that have fridge/freezer, etc. Well here are my numbers:

lighting - 305 watt/hr total - all led - average 585 watt/hrs daily avg use
585 watts / .8 (e of inv) /.5 (d of d)*4 (days) /24 = +/- 250 ah@24v dc to work out to 450 watts of panels, 15 amp charge cont, 3-400 watt inv
allways on appliances - 1000 watt/hrs daily avg use
1000/.8/.5*4/24 = +/- 425 ah@24v dc to work out to 800 watts of panels, 20 amp charge cont, 1000 watt inv
HVAC - 4500 watt/hrs daily avg summer use
4500/.8/.5*2/48= +/- 450 ah@48v dc to work out to 800 watts of panels, 20 amp charge cont, 1000 watt inv

this would total to:

Three groups of panels, 450w, 800w, 800w
three battery banks 24v 250ah, 24v 425ah, 48v450ah
three inverters 400w 1000wx2
three charge controllers 20amp x 2 and 15amp

VS

2000w of solar panel, 1600ah battery bank, 3000w inverter and 50amp charge controller.

Just surf shopping that would be about 10-12k lump sum payment before tax credits. vs 13-14k spread out over many months or possible years.

of course you would buy all the batteries in each individual bank at the same time but your total bank would be divided into three sub banks that would theoretically not burn out at the same time. Multiple inverters, three times as much wiring, multiple charge controllers while giving more to go wrong also gives duplicity so that if one did fail there would still be two other systems running.

I understand the problems associated with not being able to add on to your pv array, but this seems to be one way of "growing" a system.

Maybe I am living in a fantasy land, would explain all the beautiful women, but it seems to me it could work and help someone (me) out that has less than the ideal budget.

*NOTE* While this is a purely theoretical exercise it is something that one day I would like to have, a completely off grid, paid for, retirement home. (On the lake of course:p) Certian assumptions on my part have been made to include generator backup is a given, there will probably need to be additional circuits and what I dont know will not matter or hurt me!

Thanks in advance for your replies

Clyde

vtmaps

Re: Tell me why this will not work

Many folks have done what you are talking about. Most of them wish they could have done it "right" the first time through. Ultimately it costs much less to build a single larger system than to build multiple smaller systems. And a single larger system is MUCH easier to maintain.

--vtMaps

waynefromnscanada

Re: Tell me why this will not work

vtmaps wrote: »

Many folks have done what you are talking about. Most of them wish they could have done it "right" the first time through. Ultimately it costs much less to build a single larger system than to build multiple smaller systems. And a single larger system is MUCH easier to maintain.

--vtMaps

I have to agree. Been there, and that's how I got where I am now. It works, but I've ended up with a system that cost far more than it should have, plus I've painted myself into a 12 volt corner with no reasonable financial way out, when I most definitely should, in hindsight, gone 24 volts from the beginning.
On the other hand, if I hadn't done it this way, I'd still be on grid.

stephendv

Re: Tell me why this will not work

Also agree, one big system is much better and cheaper. But that's not to say that you can't build it in phases, e.g.:

Phase 1: lighting, only runs at night, so you buy a fuel efficient inverter-generator and just run it at night.
Phase 2: Fridge/freezer, Inverter + batteries + generator - you might end up spending a fortune on fuel here, so best to get to phase 3 quickly
Phase 3: Solar charge controller + minimal solar panels. You can still use the gen to bulk charge the batteries, then have just enough solar to complete the absorb phase
Phase 4: More solar so you don't need to run the generator except on really bad days
Phase 5: Even more solar so that you can power opportunity loads like water heating in good weather, and just scrape by in bad weather- even less gen runtime
Phase 6: Still more solar so that your partner starts complaining that you're obsessed and starts holding interventions to "cure" you.

upa123

Re: Tell me why this will not work

stephendv wrote: »

Phase 6: Still more solar so that your partner starts complaining that you're obsessed and starts holding interventions to "cure" you.

ROFL I have a pre-emptive plan in anticipation of phase 6. I just bought an new ATV it should throw my wife off for a bit

Clyde

Re: Tell me why this will not work

stephendv wrote: »

Also agree, one big system is much better and cheaper. But that's not to say that you can't build it in phases, e.g.:

Phase 1: lighting, only runs at night, so you buy a fuel efficient inverter-generator and just run it at night.
Phase 2: Fridge/freezer, Inverter + batteries + generator - you might end up spending a fortune on fuel here, so best to get to phase 3 quickly
Phase 3: Solar charge controller + minimal solar panels. You can still use the gen to bulk charge the batteries, then have just enough solar to complete the absorb phase
Phase 4: More solar so you don't need to run the generator except on really bad days
Phase 5: Even more solar so that you can power opportunity loads like water heating in good weather, and just scrape by in bad weather- even less gen runtime
Phase 6: Still more solar so that your partner starts complaining that you're obsessed and starts holding interventions to "cure" you.

i really like this idea! I would love to just jump in but I have already got one mortgage!

Thanks guys!

Clyde

couchsachraga

Re: Tell me why this will not work

I'd look at minimizing your loads first - and considering using 12v where it makes sense.

I have a bit of a hybrid system at my off-grid barn / cabin - 12v fans (get heat up or push heat down depending on season), 12v LED lights (6w is super bright, 3w is fine for many things, these are "edison" (screw in) bulbs, so work in many fixtures), 12v water pumping (biggest draw) and 12v pumps for heating (El Sid pumps... again very low power usage for what you get). I also have a small inverter and 110 AC for things like propane fired hot water heater, charging things, and some of the controls for the HVAC systems. I have a small 12v freezer fridge, I plan on getting a chest fridge for this summer... more expensive up front, but far less power... which means less panels now, and more importantly less batteries needed down the road (less ongoing costs).

I minimized my loads first, then sized the system correctly. I'm thrilled with how it worked all this winter....and summer will be much better.

oh, and even in the Northeast US (where I am) solar hot water rocks...using mine for space heating in the winter, and reducing propane usage in the summer (pre-heating (or completely heating) domestic hot water).

Good luck, have fun, and do it right the first time... in stages or not....