Off Grid Set Up

[WGA]

First post to the forum. Probably a pretty basic set up but I would appreciate some opinions before I spend the money. I have an off grid cabin in a river bottom located about an hour from Houston, Texas. I would like a setup that will power about a 10 watt radio for 12 hours a day, 7 days a week. There are also times when I stay at the cabin that I may run a TV and a few LED lights at night for maybe about 5 hours each night. I am basing this set up off the usage of 5 hours per night for three consecutive nights at most. By reading the sticky I have figured these numbers:

- 200 watts x 5 hrs/day = 1000 watt hours
- 1.5 fudge factor = 1500 watt hours
- I kind of guessed that 5.5 sun hours is good
- 1500 watt hours / 5.5 = 273 watt panel array

The next calculation of battery amp hour and controller size kind of confuses me
- 5 x 1000 = 5000
Based on 12 volt system 5000/12 = 416 amp hour battery, or I could use a 24 volt system =208 amp hour battery
Now the controller confuses me too. Panel wattage is 273 so if I use the 12 volt system the controller would need to be a 30 amp MPPT I'm thinking, or if i use 24 volt system the controller would need to be 15 amp MPPT if one that size is available. So, does this sound like I am on the right track? If it ends up being more expensive that what I want spend I may just base the system off the usage of a 10 watt radio for 12 hours a day. I have a Honda EU2000is that I can always use for the TV and lights anyway.

[Suprasoup]

You might be overestimating the # of sun hours for your area. You want to size the array based on the shortest month, Houston gets 3.33 sun hours in December.
Revised #'s

1500/3.33=450 watt panel array

450 watts / 12 Volts = 40 amp MPPT Controller
450 watts / 24 Volts = 20 amp MPPT Controller

Others will hopefully chime in but I'd go with the 24v system. The charge controller will be cheaper as well as the batteries. Oy the thought of hauling around 2 L-16 6v batteries is giving me a hernia.

[morgandc]

Can you meet your radio/tv requirements with 12 volt devices? This would allow you to avoid an inverter and reduce the cost of the system.

[PNPmacnab]

Almost every system by a beginner is shy on solar panels and these provide the best payoff. The minimum I would use is two 280W grid tie type panels. I have two in a test setup and many times of the day it can produce less than 50W at power point. At my camp I only have a single battery, but a number of panels, That gives me free hot water, refrigeration and even a dishwasher on a system that only costs $1K. You just do things when the sun shines..

[WGA]

Thanks for the responses. Sounds like it would be best to go with a 24 volt system with more panel wattage. I don't currently have any 12 volt devices. Would it be simpler and easier to just buy 12 volt lights and a 12 volt TV and stay with 12 volt system? I also want to think about the future and design a system that can be added onto. Just knowing how I do things that is typically what I do...keep adding and making improvements no matter what the project is.

[ButchDeal]

Would it be simpler and easier to just buy 12 volt lights and a 12 volt TV and stay with 12 volt system?
I also want to think about the future and design a system that can be added onto.

those two things are not compatible with each other.
12V lighting and appliances is not really simple and definitely not cheap.

[Sunking]

- 200 watts x 5 hrs/day = 1000 watt hours
- 1.5 fudge factor = 1500 watt hours
- I kind of guessed that 5.5 sun hours is good
- 1500 watt hours / 5.5 = 273 watt panel array.

Unless you live near the equator, you get no where near 5.5 sun hours year round. 5.5 Sun hours would be great on a summer day in TX or somewhere in the USA with lots of Sun. Then fall and winter come around and now you get 1 or 2 Sun hours. That is when you learn an expensive lesson when you go dark and destroy your batteries.

[Sunking]

Can you meet your radio/tv requirements with 12 volt devices? This would allow you to avoid an inverter and reduce the cost of the system.

Not possible when you go over 1000 watts and very expensive even at 1000 watts. All that huge copper wiring and the copper mine and profits they will make from you. Even then the power losses will exceed an Inverter. $2000 in copper vs $1000 Inverter does not add up.

At 1500 watts of panels operating into a 12 volt battery requires two very expensive 60 amp charge controllers, and a ton of copper wire. At 48 volts requires 1 inexpensive 30 amp controller and very small wire. The 12 volt system would be twice as expensive with higher losses.

There is a reason utilities use high voltage.

[Mike90250]

River bottom, to me, indicates shade. And as has been said 5hrs is optimistic.

The problem with 12V appliances, is that the 12V battery system can vary from 11v to 16v, many appliances choke/burn after 14V

[morgandc]

You stated 3 consecutive days at most for TV, is that per week, per month? If you have a couple weeks to recharge between visits you don't have to size the system to recover completely in 24 hours. Or, get a small 2k generator for recharging the batteries on the days you visit and watch TV.

[WGA]

Usually its just 3 days per month or so. I remember that I looked into this a few years ago and determined the cost was just not worth what is received in return. I think I'm thinking that again. Maybe just continue using the EU2000is for TV and lights, it more than does the job. I may just downgrade the system to run the little 10 watt radio about 12 hours a day. Really don't even need that, I was just wanting a radio to be on when I'm not there. I figure it might...and that is a big might...make someone think twice about breaking in if they stumble across the place.

[morgandc]

Year around or mostly just in the nice weather and/or summer?

And what is the objective, just avoiding running the generator continuously or to run with no generator at all?

[PNPmacnab]

How do you find 5 hours of TV to watch a day? Estimates and calculations are a good place to start. Camp life is just a little different and you have been living it. When you don't have it, you just don't use it. For years I just plugged my car into the house for power. Now it is a single 12V battery and I find it very livable. You just need a low voltage disconnect on the non essential items to train you and enough panels to meet daily expected needs. I just can't wrap my head around these high needs for a camp.

[WGA]

5 hours of TV is very doable for me. I'm a night person and when the sun goes down at 6PM there is nothing to do in the middle of the woods at night. Go shoot a hog, run a trotline, ehh...I don't have that ambition any longer. Sit around a campfire...ehh, very boring by yourself. Usually end up doing some sort of indoor project and I like to have the TV on in the background for noise mainly. If I'm lucky I may fall asleep around midnight.

[WGA]

PNPmacnab got me thinking and it really is not 200 watts running at a time. Its usually a couple of 13 watt LED lights and a 45 watt TV. So the watt hours could be pulled down to 355 (plus inverter watts) rather than the 1000 that I originally calculated. I think my original mind set was to over compensate but with the cost of this equipment it may be better to figure out what I need to just get by.