Remote Cabin Solar????

2680 · June 2012

I have a very small cabin (12x16) that i use twice a month or so for camping. would love to have power there and have been researching solar. problem is the cabin is about 1000ft in deep, thick woods. but outside of the woods in an open field i have a storage shed which gets alot of sun. any thoughts on how to make this work????

my only idea was to have two battery banks and keep the panels on the shed with the batteries and controller. then take them back to the cabin and hook them up to the inverter for my power. when one battery gets low, just swap it out and get it charging. anyone ever done this? any better ideas?

ywhic · June 2012

Re: Remote Cabin Solar????

IF you go that route.. look at the Morningstar 25 Amp Duo Controller.. charges 2 batteries.. and setable..

Maybe get a small rolling cart for the battery..

BB. · June 2012

Re: Remote Cabin Solar????

How much power do you need? (Watt*Hours or Amp*Hours @ XX volts per day, etc.)...

In the end, solar becomes "very expensive" when only used a limited amount of time per year. And, many times, a small genset is a better/more cost effective solution (but not the best idea to bring gasoline exhaust to the camp).

Depending on your daily/weekend power needs, if the system is kept small, it can probably done without being to expensive (most likely carting batteries from shed to site--Unless you want to bury some 120 VAC cable for lighting, cell chargers, etc.).

And, what about security (lots of expensive equipment in the middle of no-where)?

-Bill

2680 · June 2012

Re: Remote Cabin Solar????

not to worried about security, both building are pretty secure. as far as usage, i don't have a specific number, but basically just running a few lights, and maybe a laptop or dvd player for the kids. i was thinking two golf cart batteries for each bank which should run what i need for a day or two. would i be better off just buying an a/c charger and charging the batteries at home, since i have to move them anyway? just brainstorming here, thanks for the replies!

westbranch · June 2012

Re: Remote Cabin Solar????

I would consider an Inverter type genset, 1000W,and if you are after QUIET then use it to charge a GC battery for the 'no noise' period, like trying to get the kids to sleep...

BB. · June 2012

Re: Remote Cabin Solar????

Say you want to charge 2x6volt @ 220 AH * 2 batteries at 5% rate of charge (5-13% recommended, but for a small system used a few days a week, this would be the minimum I would recommend):

2 strings * 2 batteries * 6 volts * 220 AH * 1/0.77 panel+charger derating * 0.05 rate of charge = 343 Watts of solar panels

Using PV Watts, assuming somewhere in the Dayton OH area, fixed array, mounted 40 degrees from horizontal:

Month Solar Radiation (kWh/m 2/day)
1 3.08
2 3.54
3 4.08
4 5.17
5 5.32
6 5.54
7 5.44
8 5.68
9 5.05
10 4.79
11 2.88
12 2.36
Year 4.41

And assuming a minimum of 3.5 hours of "noontime equivalent" sun per day (February) or better, the system with a small AC inverter would be capable of a minimum of:

343 watt array * 3.54 hours of sun * 0.52 system efficiency = 615 Watt*Hours per day (Feb. Average)

If you had a laptop computer you ran for 5 hours per day (30 watts), and 3x 10 watt 120 VAC LED bulbs would run:

5 hours * 30 watts = 150 Watt*Hours per day
3 x 10 watts x 8 hours = 240 WH per day
========================
390 WH per day
615 WH generated - 390 WH used = 115 Watt*Hours for other loads (Feb. daily average)

Your 1/2 battery bank would supply (assuming 50% max discharge for longer battery life):

2 batt * 6 volt * 220 AH * 0.85 inverter eff * 0.50 max recommended discharge = 1,122 WH per discharge cycle

The maximum size inverter surge rating assuming C/2.5 discharge would be:

2 batt * 6 volt * 220 AH * 0.85 inverter eff * 1/2.5 surge rating = 898 Watt max surge rating

"Good Inverters" will typically supply upwards of 2x their name plate rating for surge current, so the (rough) maximum "useful" inverter size would be:

898 surge watts / 2 = 449 Watt inverter rating

Anyway, this is a rough look at what you can do... And how such a system would perform... If you are there for Winter, less sun. If you are there for summer, more sun.

A good place to start is with a Kill-a-Watt meter if you are going for AC power... Otherwise, you can get a DC Current Clamp meter or DC AH/WH meter for DC power measurements (just suggested links for discussion).

And some information about "small" solar PV systems:

BB. wrote: »

Add this link to our Solar Beginner Post:

Emergency Power

Basically a very long thread that starts from the beginning with a few vague requirements through design and assembly for a "portable" solar RE off-grid power box.

And here is another example by Mike90045 called the Solar Monolith:

Update pictures/information here.

Questions?

-Bill

2680 · June 2012

Re: Remote Cabin Solar????

man, you guys are great! let me absorb some of this info and see where i stand. i really appreciate the advice!

2680 · June 2012

Re: Remote Cabin Solar????

ok, so i am planning to put the batteries (2-6v) and inverter in some kind of wheeled case to haul back and forth.... anyone have any suggestions as to what type of case might work? a large tool box maybe?

Dill · June 2012

Re: Remote Cabin Solar????

how about a 2 wheel dolly with a custom 2x4 rack to hold the batteries? Or maybe a red radio flyer wagon? They make them for gardens now with big off road tires.

niel · June 2012

Re: Remote Cabin Solar????

how about a shopping cart?

westbranch · June 2012

Re: Remote Cabin Solar????

think 2 old Schwinn bicycle tires on a 'balanced' cart with wheel barrow type handles

2680 · July 2012

Re: Remote Cabin Solar????

ok, so the plan now is to build a custom crate out of plywood to house the 2 golf cart batteries, sunforce 10a charge controller, and 880w inverter. i will move it back and forth on a hand cart or wagon or something.... next question: wiring?

everything will be in a very small space. both charge controller and inverter came with 10g wires. i assume this will be sufficient? what about between the 2 - 6v batteries? i have some 0g main aluminum wire, should i use this? it will only be about 10in long.

and finally, i want to have a plug and play setup for the solar panel. so i want some kind of outlet on the crate to plug the solar panels directly into when charging. can anyone give me a link/idea as to what i might be looking for?

thanks!

inetdog · July 2012

Re: Remote Cabin Solar????

2680 wrote: »

ok, so the plan now is to build a custom crate out of plywood to house the 2 golf cart batteries, sunforce 10a charge controller, and 880w inverter. i will move it back and forth on a hand cart or wagon or something.... next question: wiring?

everything will be in a very small space. both charge controller and inverter came with 10g wires. i assume this will be sufficient? what about between the 2 - 6v batteries? i have some 0g main aluminum wire, should i use this? it will only be about 10in long.

and finally, i want to have a plug and play setup for the solar panel. so i want some kind of outlet on the crate to plug the solar panels directly into when charging. can anyone give me a link/idea as to what i might be looking for?

thanks!

You can use MC4 connectors, or you can use binding posts and ring terminals with the binding posts attached to the panel frame, since that is where the voltage will be when they are disconnected. Or you can use a type of connector designed for plugging a DC charger into a golf cart.
What you do not want to use is anything which is normally used for AC, since the chance for confusion is too great.
None of the types of connectors you will normally see can be used to interrupt the current flow while the panels are seeing light. You should have a DC rated switch or breaker to interrupt the circuit or else you will have to cover the panels before unplugging them.

ywhic · July 2012

Re: Remote Cabin Solar????

Some Anderson FORKLIFT quick disconnect mating terminals.. cost is like $12 for a PAIR (which you need)..

They have them for different wire gauges..

http://www.solar-electric.com/anhicupoco.html

icarus · July 2012

Re: Remote Cabin Solar????

Anderson connectors come in many sizes to fit many wire sizes. Reverse polarity protected, they are a great way to make plug and play panel set ups. See our site host for supply.

Tony

2680 · July 2012

Re: Remote Cabin Solar????

cool.... i'll get some of those anderson connectors. what about fuses? i bought some automotive type fuse holders that have a loop of 10g wire on them. was planning on putting them btw panel and controller, controller and battery, and battery and inverter. is this correct? what size fuses should i use?

ywhic · July 2012

Re: Remote Cabin Solar????

2680 wrote: »

cool.... i'll get some of those anderson connectors. what about fuses? i bought some automotive type fuse holders that have a loop of 10g wire on them. was planning on putting them btw panel and controller, controller and battery, and battery and inverter. is this correct? what size fuses should i use?

For the solar panel fusing go 1.5 * larger than the panel ISC rating in AMPS.. usually a 10 or 15 amp fuse will work..

Keep in mind MOST car fuse holders are rated to 32 volts DC.. so systems really above 12v should not use those types.. most 24V systems are 30-35 volts..

between the controller and battery is the RATED amps for the controller..

between the battery and inverter should be in the inverter manual/book..

2680 · July 2012

Re: Remote Cabin Solar????

ywhic wrote: »

Keep in mind MOST car fuse holders are rated to 32 volts DC.. so systems really above 12v should not use those types.. most 24V systems are 30-35 volts..

just to clarify, if i am running a 12v system, i will be ok?

vtmaps · July 2012

Re: Remote Cabin Solar????

2680 wrote: »

what about between the 2 - 6v batteries? i have some 0g main aluminum wire, should i use this? it will only be about 10in long.

No. Aluminum is dangerous and can cause fires if you do not use appropriate technique to transition to copper or bus bars or whatever. The cost of the adapters can't possibly be worth it for 10 inches. Aluminum is used when the runs are very long and the savings over copper are significant.

If the run is only 10 inches you can afford copper. Also, copper is more flexible which you will need to connect to batteries. --vtMaps

BB. · July 2012

Re: Remote Cabin Solar????

They are "OK" voltage wise...

I believe Wayne from N.S. Canada had a big issue with automotive/after-market fuse holders.:

waynefromnscanada wrote: »

I've been down the road of both automotive and car audio fuses and their holders, and in both cases I was lucky to not have a fire!
Apparently, these fuses work OK with light to intermittent loads as would be expected in their intended use. To my shock, when subjected to hour after hour of heavy loads, yet still well below their blowing point, the buildup of, and sustained high temperature causes some changes in the metal to metal connections between the blades of the plug in fuses and their holders. These gradual changes increase slightly the resistance in those connections, which increases even more the temperature. Eventually the fuse blade and it's holder connection arcs, welds the connections, continues to heat, melting and scorching the holder and finally burning off one of the fuse legs. Not a pretty sight. I'm very thankful both cases were enclosed within a metal box, so a spreading fire was hopefully unlikely. I now have bolt on fuses with the fuses securely bolted to their holders. Just a heads up to what can happen.

-Bill

2680 · July 2012

Re: Remote Cabin Solar????

one other thing on fuses, my inverter is a cobra cpi 880, but i do not see anything about fusing it in the manual. it is continuous 800w, surge 1600w. can i determine the fuse amp rating from this?

BB. · July 2012

Re: Remote Cabin Solar????

A good estimate for fusing/wiring sizes:

800 watts * 1/10.5 volts cutoff * 1/0.85 inverter eff * 1.25 NEC derating for fuse/wire = 112 Amps circuit design minimum

So, round up to the next standard fuse/breaker/wiring standard size--say 125 amps or so...

The actual max continuous current would be:

800 watts * 1/10.5 volts cutoff * 1/0.85 inverter eff = 90 Amps DC current

-Bill

mike95490 · July 2012

Re: Remote Cabin Solar????

2680 wrote: »

.... i have some 0g main aluminum wire, should i use this? it will only be about 10in long. .....

Bad idea. a foot of proper copper wire, will cost less then a tube of the no-ox goo you have to use on aluminum connections. And there are few good crimp terminals rated for aluminum, so they cost a LOT.

2680 · July 2012

Re: Remote Cabin Solar????

ok, i found the perfect storage container for my setup at home depot. will post pics later.

i would like to run my wiring idea by you guys to make sure i am headed in the right direction.

pv - instapark 50w 2.8a
http://www.amazon.com/Instapark%C2%AE-Black-Mono-crystalline-Solar-Panel/dp/B004OZDI7O/ref=sr_1_1?s=automotive&ie=UTF8&qid=1340387184&sr=1-1&keywords=solar+panel+50w

charge controller - sunforce 10a
http://www.amazon.com/Sunforce-60031-Digital-Charge-Controller/dp/B001DZONCW/ref=sr_1_2?ie=UTF8&qid=1340387104&sr=8-2&keywords=sunforce+controller

inverter - cobra 880w

i plan to use #2 wire to connect the battery to a bus bar. neg straight and pos fused with an 80a dc fuse (for any system short as well as for the inverter).

then from the bus bar i will run:
1.) #10 to 12v car socket (with 5a fuse)
2.) #10 to my charge controller
3.) #8 to my inverter (wire it came with)

from the charge controller to my pv i will run #10 (with 5a fuse), length will be under 10ft and will have an mc5 connector do take off when needed to transport.

sound correct???? any suggestions????

2680 · July 2012

Re: Remote Cabin Solar????

here are the pics. plan to make a plywood compartment in the middle to mount everything. case also has a nice lip around the edge so i plan to drill numerous holes under it to allow for venting. the lid can also be closed with cables coming out, so i can keep it safe from kids when in use, but also be water tight if it gets left outside charging and happens to rain!

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2680 · July 2012

Re: Remote Cabin Solar????

got it all wired up. so i can just plug it into the solar array to charge, then unplug and it's a self contained unit. also buying an a/c charger if i need to do a fast charge with a generator.

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niel · July 2012

Re: Remote Cabin Solar????

looks good. but keep in mind the heat being generated by the inverter. some inverters should not be mounted in that fashion unless they specifically state they can be or they will blow the excess heat out via a fan. this also means it's not a good idea to operate it with the lid shut as then the heat has nowhere to go.

2680 · July 2012

Re: Remote Cabin Solar????

good call. i read through the manual and it says the inverter can be mounted horizontally or vertically, but must maintain 1" of clearance for ventilation. i was planning to prop the lid open if i was running any substantial loads, but just thought about maybe mounting a small 12v computer fan in the box to help aid in venting if the lid needs to be closed. maybe put it on a switch so it can be turned on when needed.

what about during charging? i drilled 27 1/4" holes around the perimeter of the case under the lip. do you think this will be enough for any gasses that might build up during charging? does charging create alot of heat as well?

niel · July 2012

Re: Remote Cabin Solar????

yes, charging can also build up some heat, but the batteries will take more to damage them than a piece of electronic equipment will.

the air holes may be enough, but i'd do a test run with the lid closed and have a means of measuring the temperature inside to determine if those holes will suffice. this can vary with the amount of loading on the inverter, for how long, the ambient air temp, and if sitting in the sun. it isn't so much the air temp inside that's important, but the heatsink temp on the inverter. a cheap and easy way might be if it feels hot to you by touch then it may need extra ventilation. it probably would not hurt to have a small computer fan on it that you could switch on/off and be sure it is fused.

Remote Cabin Solar????

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