Solar Power in Ohio for Off Grid Cabin

Toonces · April 2013

Hi, I'm new to the forum and I'm very impressed with advice that has been given to newbies like myself. If possible I would like to get some feedback on a small solar powered system I would like to set up for my cabin. I will try to provide as much information as possible to make things easier, so please bare with me:

Cabin Description: SE Ohio, 200sq/ft w/loft, used 3-4 days(one trip) at a time every 3-4 weeks.
Current Power Sources: (2) Trojan T-105 6-volt 225AH batteries (charged at home), cheap B&D 400 watt inverter, 3500watt Yamaha Gen(for power tools and sometimes sm. heater & sm. AC unit), Portable propane tanks for sm. unvented propane heater.

--Current Loads--
AC Loads: (5) 13 watt CFL bulbs- max usage- approx 1000 W-Hrs. per trip.
DC Loads: (1) car stereo w/(2) 50watt speakers-max usage-25hrs = 2500 W-hrs /12 volts = 208 W-hrs. per trip.
Total Current Load 1208 W-hrs.

--Future Loads to be Added--
AC Loads: (1) 900 watt coffee pot- max usage 1hr = 900 W-hrs. per trip.
(1) 1080 watt vacuum cleaner - max usage .5 hrs = 540 W-hrs. per trip.
DC Loads: (1) 84watt Shurflo 2088 demand pump- max usage 4hrs = 336/12 volts = 28 W-hrs. per trip.
(2) 50watt speakers to add to stereo-same usage amount = 2500/12 volts = 208 W-hrs. per trip.
Total Future Load 2884 W-hrs. (1208 W-hrs. + 1676 W-hrs.)

--Batteries:--
With the inverter efficiency at 90% and battery DOD at 50% I calculated I would need approx. (6-8 ) 6 volt batteries for my total future load needs. (Does this sound correct?) I am assuming that I should keep a 12 volt system since I am running a car stereo and a 12 volt pump, but I'm not sure if this makes sense.

--Solar Panels:--
I figured the solar insolation at 3.5 hrs in SE Ohio. And I figured a 20% battery charging inefficiency. The distance between the batteries and the panels would be about 100-150 feet one way. And from what I have read online here is that I probably should use a MPPT charge controller. This all leads me to believe I need (5) 7.91 Imp panels for my future load needs. (Does this sound correct?)

I have many more questions to ask the experts, but for now I would like to just confirm that I'm heading in the right direction. Thank you in advance for any help!

Cariboocoot · April 2013

Re: Solar Power in Ohio for Off Grid Cabin

Welcome to the forum.

If you have specific need for a 12 Volt system then stick with it. If you find you have some big power demands coming up you may want to rethink that. And nothing says you can't have one of each!

You want to think of your loads in terms of daily Watt hours, as (hopefully) the solar panels will be recharging the batteries on a daily basis. Since you have a generator available you don't have to worry too much about having power for no-sun days; running a gen for a couple of hours on occasion will be much cheaper than investing in a large system that won't use the capacity most of the time.

What you do not want to do is rig up a battery bank with three or four parallel strings of batteries. This is where you can run in to trouble with current sharing, which will result in premature battery death.

Now let's have a look at just what kind of power you can get out of two 220 Amp hour 6 Volt batteries wired for 12 Volts. 50% DOD would be 110 Amp hours * 12 Volts = 1320 Watt hours. Make allowances for losses, inverter consumption, and conversion to AC and you get about 1 kW hour. For comparison purposes, I have about 2X that capacity to run everything including an electric 'frige (but I rely on load shifting and have some elevation advantage).

What you would want for recharging those batteries from solar:
With PWM type controller; 22 Amps peak current @ 12 Volts needing about three 130 to 140 Watt panels.
With MPPT type controller; 22 Amps peak current @ 12 Volts = 264 Watts, less typical derating = 343 Watts.

If you increase the battery capacity you must increase the charging capacity likewise. When you go over 400 Watts using "GT panels" and MPPT controller becomes much more economical.

Think about your system "now" and "later", because if there's any chance of future expansion it's better to plan for it now then re-do everything later.

niel · April 2013

Re: Solar Power in Ohio for Off Grid Cabin

you may be able to shave a bit off of the watt hours by going with a propane burner. in summer you can take it outside so as to not add to the interior heat and of course it will add heat in the winter inside. propane is an expense too though and lugging it can be a pain in the butt. it isn't a case where you can only have one or the other as you can have both and use as you see fit for the circumstances.

now the speakers do not draw power from the batteries, but the audio amp does draw up to around double of what the audio power in watts is so that may still be about right for the power consumption overall.

what do you consider se ohio, near steubenville, or farther down the ohio like marietta?

westbranch · April 2013

Re: Solar Power in Ohio for Off Grid Cabin

If you power the vacuum with the genny it will make a substantial difference in power consumption ... do you have a Kill a Watt meter yet?

vtmaps · April 2013

Re: Solar Power in Ohio for Off Grid Cabin

Toonces wrote: »

DC Loads: (1) car stereo w/(2) 50watt speakers-max usage-25hrs = 2500 W-hrs /12 volts = 208 W-hrs. per trip.

DC Loads: (1) 84watt Shurflo 2088 demand pump- max usage 4hrs = 336/12 volts = 28 W-hrs. per trip.

Welcome to the forum.
I can't make sense of your DC load calculations.

I don't know how many watts your stereo will really draw, but dividing 2500 wattHours by 12 will give you AmpHours, not wattHours.

As far as the pump is concerned, if you run an 84 watt pump for 4 hours you will consume 336 wattHours. period. Dividing that by 12 will give you 28 AmpHours.

--vtMaps

Toonces · April 2013

Re: Solar Power in Ohio for Off Grid Cabin

Cariboocoot wrote: »

Welcome to the forum.

If you have specific need for a 12 Volt system then stick with it. If you find you have some big power demands coming up you may want to rethink that. And nothing says you can't have one of each!

You want to think of your loads in terms of daily Watt hours, as (hopefully) the solar panels will be recharging the batteries on a daily basis. Since you have a generator available you don't have to worry too much about having power for no-sun days; running a gen for a couple of hours on occasion will be much cheaper than investing in a large system that won't use the capacity most of the time.

What you do not want to do is rig up a battery bank with three or four parallel strings of batteries. This is where you can run in to trouble with current sharing, which will result in premature battery death.

Now let's have a look at just what kind of power you can get out of two 220 Amp hour 6 Volt batteries wired for 12 Volts. 50% DOD would be 110 Amp hours * 12 Volts = 1320 Watt hours. Make allowances for losses, inverter consumption, and conversion to AC and you get about 1 kW hour. For comparison purposes, I have about 2X that capacity to run everything including an electric 'frige (but I rely on load shifting and have some elevation advantage).

What you would want for recharging those batteries from solar:

With PWM type controller; 22 Amps peak current @ 12 Volts needing about three 130 to 140 Watt panels.
With MPPT type controller; 22 Amps peak current @ 12 Volts = 264 Watts, less typical derating = 343 Watts.

If you increase the battery capacity you must increase the charging capacity likewise. When you go over 400 Watts using "GT panels" and MPPT controller becomes much more economical.

Think about your system "now" and "later", because if there's any chance of future expansion it's better to plan for it now then re-do everything later.

thanks for the great advice! I see now what you mean about the MPPT controller being more efficient. With the solar panels being so far away from the batteries, I guess I'm having trouble deciding which system would be best for my usage. This may be a ignorant question, but can I run a 24 volt system from panels to controller to minimize the wiring size, and then have the controller step the voltage down to a 12volt system?

Cariboocoot · April 2013

Re: Solar Power in Ohio for Off Grid Cabin

Toonces wrote: »

thanks for the great advice! I see now what you mean about the MPPT controller being more efficient. With the solar panels being so far away from the batteries, I guess I'm having trouble deciding which system would be best for my usage. This may be a ignorant question, but can I run a 24 volt system from panels to controller to minimize the wiring size, and then have the controller step the voltage down to a 12volt system?

Yes. An MPPT type controller can take high array Voltage and reduce it to proper charging Voltage with an increase in current. The higher the array Vmp is in relation to system Voltage, however, the lower the efficiency of the controller. It is not an extreme loss and is sometimes necessary due to long wire runs.

Toonces · April 2013

Re: Solar Power in Ohio for Off Grid Cabin

now the speakers do not draw power from the batteries, but the audio amp does draw up to around double of what the audio power in watts is so that may still be about right for the power consumption overall.

Honestly I really wasn't sure how to calculate the 12 volt stereo demands. Are you saying my guess was close?

what do you consider se ohio, near steubenville, or farther down the ohio like marietta?

Ha ha, good guess! I'm about 35 minutes west of steubenville, in Pineyfork.

Toonces · April 2013

Re: Solar Power in Ohio for Off Grid Cabin

I can't make sense of your DC load calculations.

I don't know how many watts your stereo will really draw, but dividing 2500 wattHours by 12 will give you AmpHours, not wattHours.

As far as the pump is concerned, if you run an 84 watt pump for 4 hours you will consume 336 wattHours. period. Dividing that by 12 will give you 28 AmpHours.

Oops, you are correct! For some reason I only showed the DC load AmpHours. I should be showing 226 AmpHours (AC loads) and 444.67 AmpHours (DC loads) for a total of 670.67 Amphours per trip. Hope this makes more sense.

Toonces · April 2013

Re: Solar Power in Ohio for Off Grid Cabin

If you power the vacuum with the genny it will make a substantial difference in power consumption ... do you have a Kill a Watt meter yet?

I could run the vacuum and the coffee pot off the genny (or propane grill for the coffee pot), but I thought I would try to include it in the solar panel system just so I wouldn't have to run the genny every trip. I have the genny hidden from potential thieves, so its kinda a pain to bust it out for little usage. The Kill a Watt meter is on my short list.

Cariboocoot · April 2013

Re: Solar Power in Ohio for Off Grid Cabin

Toonces wrote: »

I could run the vacuum and the coffee pot off the genny (or propane grill for the coffee pot), but I thought I would try to include it in the solar panel system just so I wouldn't have to run the genny every trip. I have the genny hidden from potential thieves, so its kinda a pain to bust it out for little usage. The Kill a Watt meter is on my short list.

The problem is you end up building a larger, more expensive system just to accommodate those two items.

For example, most everything you have would run off the Morningstar 300 Watt pure sine inverter: http://www.solar-electric.com/moin.html Less than $300. Now throw in big things like a microwave or coffee pot and you need over 1,000 Watts power just when you run them, so all of a sudden you need a bigger inverter or two inverters and larger battery cables and more battery capacity just for that.

Otherwise if you take your 670 Amp hours @ 12 Volts per trip (very odd way of looking at it) and divide by 3 days there you get just about 220 Amp hours per day, mean two parallel strings of golf cart batteries would probably handle it (remembering that some of the daytime load will be supplied "directly from the panels").

So with that battery bank, a 60 Amp MPPT controller (to give yourself some expansion room), and about 700 Watts of panel you're on to a viable system.

Timinator · April 2013

Re: Solar Power in Ohio for Off Grid Cabin

I would ditch the coffee maker and get a French Press or pour heated water through a filter into a thermos. The vacuum could be a battery operated and recharged and brought down with you when you come. Those little Swifter's work very well for day to day for hard floors. I have an off-grid cabin in Adam's County, OH that's worked very well for us.

niel · April 2013

Re: Solar Power in Ohio for Off Grid Cabin

Toonces wrote: »

Honestly I really wasn't sure how to calculate the 12 volt stereo demands. Are you saying my guess was close?

Ha ha, good guess! I'm about 35 minutes west of steubenville, in Pineyfork.

yes you were close. now you probably won't be listening full blast all of the time so it could go to a smaller power requirement as your audio volume needs lessen. it doesn't hurt figuring for the worst though.

by google earth drawing a line between there and here where i am i get about 51 miles.

Toonces · April 2013

Re: Solar Power in Ohio for Off Grid Cabin

Thanks guys, the advice is definitely helping me put some of the puzzle pieces together.
I guess I will just start with my current load needs(lights and stereo approx 291AH), but allow room for expansion(definitely a 12 volt pump and two more speakers approx another 236AH). I will leave out the coffee pot and vacuum. But who knows what I would want to add in the distant future(mini fridge?), so maybe I should just say that I would like to start with a system around 291AH, but allow for expansion up to approx 1000AH (a nice round number).

Where I start getting confused is, what wattage panels I should be using, and what size line(panels to controller)? I understand that a 12 volt system needs 18 volts to charge it, but would I be better off using GT panels (higher wattage) since I will be using a MPPT controller? And with the panels being 100-150 ft away I really want to make sure I put the correct size cable in the ground to allow myself a good amount of flexibility with potential future loads.

Cariboocoot · April 2013

Re: Solar Power in Ohio for Off Grid Cabin

When using an MPPT controller the Watts can figure 'directly' for charging power as the controller can convert extra Voltage into charge current. This also makes it possible to use the "GT panels" which are almost always cheaper per Watt than "off grid panels". Enough so that the cost difference in panels can make up for the cost difference in controller.

1000 Amp hours is not a size you want to build around. This is because when sizing the array you try for roughly 10% of the battery capacity as peak charge current. Since there is no single charge controller that can handle 100 Amps, that much battery (at any Voltage) would require two charge controllers.

Another thing is that batteries don't come in any size you like. if you want your base capacity to be 291 Amp hours, you're not going to find it. Instead you either shed loads and round down or round up to the nearest available size. For example you might buy East Penn PS2200's @ 232 Amp hours or you might double up on some inexpensive GC2's @ 220 Amp hours (440 total). Or you could go to L16 size batteries and have 320 Amp hours, et cetera.

Once you get the battery bank size fixed calculating enough array and proper controller to charge it becomes fairly easy. Most of the time the "10% rule of thumb" will work. If you have less available sun you would want to "size up". If you have more you might get away with sizing down. Again the array will not be available in exactly the size the formula results in: 10% of 232 is 23.2 Amps * 12 Volts = 278 Watts derated, 361.5 Watts array. Since you don't get panels in such a size rounding up to the nearest available will give you a little edge here as well.

With that much distance between array and charge controller you will need to make a few calculations for power loss then, to balance Voltage drop against an affordable wire size over that distance. It may be necessary to use a MidNite Classic 200 or 250 and run a very high Voltage array.

My dog is bugging me, but how are we doing so far?

Toonces · April 2013

Re: Solar Power in Ohio for Off Grid Cabin

Thanks Cariboocoot!
T-105 batterys (6 volt 225AH @20hrs) are easy to purchase nearby, so I was keeping those in mind for my setup. But after talking to you guys, I'm seeing that I shouldn't be using those.
Example:
If my current loads are roughly 300AH, and my near future loads are roughly another 300AH for a total of 600AH.
I would be looking at setting up (6) T-105's in series/parallel for a total of 12V @ 675AH, but this would require 3 parallel strings, so probably not a good idea.

By your info: I could use (4) L16 6V@320AH in series/parallel for a total of 12V @ 640AH, with 2 parallel strings which makes for acceptable charging.
But using the 10% rule you stated, the CC would not be able to handle either one of these battery setups, since the largest CC is 60 amps. I'm confused, please send help:)

Cariboocoot · April 2013

Re: Solar Power in Ohio for Off Grid Cabin

So you're looking at a total of 600 Amp hours @ 12 Volts (7.2 kW hours) per day?

This is the primary reason for going up in system Voltage: http://forum.solar-electric.com/showthread.php?15989-Battery-System-Voltages-and-equivalent-power

Not to say you can't have 1200 Amp hours @ 12 Volts but ... You would have, say, four parallel strings of L16's @ 320 Amp hours each and two charge controllers. See? It gets messy and expensive. All the same batteries in two parallel strings on a 24 Volt system reduces wiring, reduces current, reduces power loss, and reduces cost (one controller as they can handle rated current on 12, 24, or 48 Volts).

Toonces · April 2013

Re: Solar Power in Ohio for Off Grid Cabin

Ok, I guess I just realized that my assumption that my system was too small to need two charge controllers was completely wrong. And after thinking about it, thats probably why I have been confused about the CC'c lug size being so small(#2 wire max) not to mention being confused about CC's in generally;) .

For some reason I didn't think such a small amount of batteries would need more than one charge controller. This whole time I was thinking that I had to run a very large size wire to handle my loads and potential future loads, but its sounding like I will be running multiple sets of wire for more than one charge controller.

Which means I will definitely be installing conduit/conduits in the ground for adding wire sets as my system grows. Am I more on track with this thinking?

Toonces · April 2013

Re: Solar Power in Ohio for Off Grid Cabin

Wow, thanks for the speedy reply! You sent that faster than I incorrectly corrected myself, lol!
I will let this new info sink in and get back to you. Thanks again!

Cariboocoot · April 2013

Re: Solar Power in Ohio for Off Grid Cabin

I make up for being speedy by periodically falling asleep all day long.

Size of a battery bank isn't the number of batteries so much as their capacity. And when it comes to matching up peak charge current to Amp hours there's a few variations on the theme as well.

Most charge controllers only have output lugs capable of 6 AWG or 4 AWG because that's really all that's needed to handle 60 or 80 Amps. If you need more charge current than that you'd have a second controller with its own wires.

It really is important to plan all this stuff out before you start spending the money!

Now I think I'll take a nap.

Toonces · April 2013

Re: Solar Power in Ohio for Off Grid Cabin

Cariboocoot wrote: »

So you're looking at a total of 600 Amp hours @ 12 Volts (7.2 kW hours) per day?

This is the primary reason for going up in system Voltage: http://forum.solar-electric.com/showthread.php?15989-Battery-System-Voltages-and-equivalent-power

Not to say you can't have 1200 Amp hours @ 12 Volts but ... You would have, say, four parallel strings of L16's @ 320 Amp hours each and two charge controllers. See? It gets messy and expensive. All the same batteries in two parallel strings on a 24 Volt system reduces wiring, reduces current, reduces power loss, and reduces cost (one controller as they can handle rated current on 12, 24, or 48 Volts).

After the lastest info, I am re-thinking my system again. A 24V system would probably make more sense from what I understand. A 48V system might be too much for my wallet (I don't want to buy eight batterys at a time).

I was trying to stay with a 12V system for the 12V stereo and future 12V pump, but I suppose I could find an AC version of those items (minus some efficiency I'm sure).

Cariboocoot · April 2013

Re: Solar Power in Ohio for Off Grid Cabin

Toonces wrote: »

After the lastest info, I am re-thinking my system again. A 24V system would probably make more sense from what I understand. A 48V system might be too much for my wallet (I don't want to buy eight batterys at a time).

I was trying to stay with a 12V system for the 12V stereo and future 12V pump, but I suppose I could find an AC version of those items (minus some efficiency I'm sure).

Depending on the power draw you could use a DC to DC converter like this: http://www.solar-electric.com/12to24or24to.html

There are others available that can handle more current; just siting a convenient example.

Toonces · April 2013

Re: Solar Power in Ohio for Off Grid Cabin

I am starting to understand why a 24V system would be better for my needs.
If I figured 600AH for a 12V system, then I would have 300AH for a 24V system, which would equate to the following:
( 8 ) T-105's 6V@225AH
( 2 ) 315W panels (39.8V @ 7.92A)

And assuming that the above is true, and if the panels were 100-150ft away I would use a 2ga wire (panels to bats).

Am I on the right track?

Cariboocoot · April 2013

Re: Solar Power in Ohio for Off Grid Cabin

Eight 225 Amp hour 6 Volt batteries on a 24 Volt system would be 450 Amp hours @ 24 Volts (two parallel strings of four in series).

Panel do not connect directly to batteries; they connect to the charge controller. Two 315 Watt panels total 630 Watts; enough to warrant an MPPT controller. They could provide about 20 Amps: enough charging for 200 Amp hours but not enough for 450 (less than 5% peak current).

The KD315 have a Vmp of 39.8, so they can be used either in parallel or series on a 24 Volt system. If you put them in series you get 80-ish Volts @ 8 Amps. Over 150 feet 10 AWG would handle this.

If you double the PV size to handle the 450 Amp hours of battery the current or Voltage could double for the array. But a Vmp of 160 is too high for most controllers, so you could use them in series & parallel configuration for 80 Volts @ 16 Amps. This would require 8 AWG or 6 AWG to go 150 feet (remember V-drop is maximum at maximum power, and some V-drop is allowable).

Getting it?

Toonces · April 2013

Re: Solar Power in Ohio for Off Grid Cabin

Two 315 Watt panels total 630 Watts; enough to warrant an MPPT controller. They could provide about 20 Amps: enough charging for 200 Amp hours but not enough for 450 (less than 5% peak current).

I think I better throw out the spreadsheet I have been using because it seems to be sending me in the wrong direction.
On my spreadsheet its figuring 272.67 Ah per week divided by 7 days a week= 38.95 Ah per day.

I have a 20% compensation for charging/discharging inefficiency which brings me to 46.74 Ah per day.

And with solar insolation at 3.5 hrs, its showing I need 13.36A from my solar array.

Which lead me to believe that (2) 7.91 Imp panels would be sufficient.

But I am seeing that this doesn't meet your 10% ratio of panel amperage to battery amphours.

I guess I'm still confused where I'm going wrong. If I was on a game show, I think I would need to "phone a friend" right now;)

niel · April 2013

Re: Solar Power in Ohio for Off Grid Cabin

you will find efficiency to be much worse than 20% as it may be closer to 50% overall. 58ah or so may be a better figure for your daily requirements. 58ah/3.5hrs=16.57a so you are a bit shy. more conservation on the loads or the time of use can bring this in line.

btw, if you go with a 150ft run the #10 will have too high of a v drop loss %. if the run is under 120ft then ok on the #10 otherwise go to #8. that is for being around a 3% v drop loss and going lower is a good idea. if you add more in pv, as is indicated you may want to do, then putting this extra pv in series will raise your voltage even higher with a voc total at 49.2v x 3 = 147.6v and if colder this could exceed most controllers abilities. the classic 200 would be good for such a voltage and if you ever decide to go another 4th pv then consider a classic 250. you will lose a bit on efficiency for the higher in/out conversion ratio even though gaining in efficiency over the wire with higher voltages so that can be a wash. there isn't a good substitute for thicker copper wires in most cases. now i should say you could have 2 series strings of 2 in parallel for the 4 pv solution, but for 3 of those pvs it will be all in series and quite higher in voltage than most ccs can handle.

Toonces · April 2013

Re: Solar Power in Ohio for Off Grid Cabin

Thanks Niel and Cariboocoot! I think I'm starting to understand where I have been going wrong.
I have one more question for for you on this thread, if you don't mind.

I spec'd the largest 24V nominal panel I could find on that last example. Is there any reason I should entertain the idea of using smaller panels in series/parallel? Would more smaller panels work more efficiently on a cloudy day or just overall? Sorry I think thats more than one question

Cariboocoot · April 2013

Re: Solar Power in Ohio for Off Grid Cabin

Nope. Different sizes of the same kind of panel will not offer any advantage under varying light intensity on an MPPT input. They all add up to the same Watts. The only reason you might choose physically smaller units is to be able to fit them to the available mounting space (hence the desire for monocrystalines on RV apps). This is not the same thing as one being hit with a shadow.

Someone is bound to point out that amorphous panels perform better under diffused light (lower efficiency loss), but their performance is so bad per square area anyway that there's not much reason to consider them at all.

niel · April 2013

Re: Solar Power in Ohio for Off Grid Cabin

the larger pvs in wattage are larger in size and weight. it may make a difference in mounting costs, but you would need to do some detailed homework to find differences. don't forget that if paralleling pvs or strings of pvs that this increases the need for combining and fusing/circuit breakers not to mention possibly more costs in wire.

Toonces · April 2013

Re: Solar Power in Ohio for Off Grid Cabin

Thanks niel and cariboocoot!

Solar Power in Ohio for Off Grid Cabin

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