Off grid small system for my cabin

spareparts · April 2016

Hi all, I am wanting to create a small solar system for a rustic cabin I own in Indiana. Got 72 acres adjacent to the Hoosier National Forest and LOOOVE it! The cabin is rustic, no power or water and about 3/4 of a mile of the road, so I am looking at hooking up a basic solar setup to run a couple strings of lights and maybe a mini-fridge. So far what I've done is bought a deep cycle battery from Walmart, hooked up an inverter and run the lights off it. I've also bought a Renogy 200 watt solar kit, but haven't installed it yet. We're out there about 3-4 days at a time and usually by the third day the battery runs out (I take it home to charge it). So I want to get solar panels to keep it charged while onsite. Here is what I have so far:

A Renogy 200 watt starter kit:
http://www.amazon.com/Renogy-Monocrystalline-Solar-Starter-Wanderer/dp/B00BCRG22A?ie=UTF8&psc=1&redirect=true&ref_=od_aui_detailpages00

The Walmart battery:
http://www.walmart.com/ip/EverStart-Group-Size-29DC-Marine-Battery/20531543

I have a few questions. Will this battery be ok for my intended purpose? Use the Renogy panels to charge / maintain the charge and use the inverter to power 2 100 watt light strings and a 100 watt minifridge? Do I need another battery? And, when I leave, does the charge controller "shut off" when the battery is fully charged? I don't know how that works.

Thanks in advance!

vtmaps · April 2016

Welcome to the forum,

spareparts said:

Will this battery be ok for my intended purpose?

No. It is not a true deep cycle battery. Look for golf cart batteries.

spareparts said:

use the inverter to power 2 100 watt light strings and a 100 watt minifridge

100 watt light strings?! Are you kidding? Get some LED lights. I would have to turn on every light in three rooms of my house to draw 100 watts. As far as the 100 watt minifridge, it's probably an energy hog. You need to know how many hours per day it is drawing 100 watts. Get a kill-a-watt meter and measure its consumption.

spareparts said:

So far what I've done is bought a deep cycle battery from Walmart, hooked up an inverter and run the lights off it.

What inverter? How efficient is it? How much current does it draw when you have no load?

System design begins with a number... the number of watthours of energy you use in a day. You can't design a system without that number.

--vtMaps

spareparts · April 2016

I'm pretty sure it's this inverter (it's at the cabin, I'm not):

http://www.tractorsupply.com/tsc/product/traveller-1-000w-digital-power-inverter?cm_vc=-10005

And the strings of lights I'm currently using I got from Menards a couple years ago. Not sure of the actual wattage, they are 6 LED pucks with a tactile knob for on/off. I may overestimate saying they're 100 watts each. I may also be overestimating the refrigerator as well.

Golf cart batteries, hmm, hadn't thought of that. Thank you!

vtmaps · April 2016

spareparts said:

I'm pretty sure it's this inverter (it's at the cabin, I'm not):

http://www.tractorsupply.com/tsc/product/traveller-1-000w-digital-power-inverter?cm_vc=-10005

That is NOT a pure sine wave inverter. Resistive loads will run OK, not sure about your fridge. It is hard to predict which (non-resisitive) items it will destroy, which items it will shorten the life of, and which items will work OK.

--vtMaps

zoneblue · April 2016

As is so often the case ones shopping gets ahead of ones design. We all do it so dont feel bad.

First we need to figure out your load requirements. Then we need to understand your irradiance data. Then, we specify a battery, then some ways to charge it. Thats the order we do things here, and if you want we can certainly hold your hand while you go through this. OK?

spareparts · April 2016

As best I can tell, my load requirements would be the aforementioned 2 strings of lights, running 4 hours a day (evening/early night), drawing probably 40 watts each since their LED's. The fridge is an older one, an energy hog, I estimate 100 watts when running. It would be "on" all day, not sure how often it runs. Regarding irradiation, the cabin is under trees, without a doubt, It has a steep tin roof that faces East / West. I was thinking I'd put one panel on the East face and one on the West. Here's a pic of the cabin (I've since removed the leaf debris):

vtmaps · April 2016

spareparts said:

Regarding irradiation, the cabin is under trees, without a doubt, It has a steep tin roof that faces East / West. I was thinking I'd put one panel on the East face and one on the West.

Save your money for a generator... the panels will be nearly worthless in the shade. --vtMaps

spareparts · April 2016

Well, the cabin gets plenty of sunshine in the winter, maybe some potential to use solar then?

JoshK · April 2016

Even a thin shadow from a tree trunk will shut down the solar panel. You need to cut some trees if you really want solar. And don't tilt them any direction but south.

zoneblue · April 2016

Load budget, taken literally would then be:

Lighting, 80W, x 4h =320Wh/d
Refrigeration, 100W x 24h x 0.5 = 1200Wh/d
Inverter tare, 15W x 24h = 360Wh/d
Contingency, 10%
------------------------------------------------
Total, 2068Wh/d

However, the caveats are these.
1. Are you certain thats the extent of it? Loads have a habit of growing. Have you no cell chargers, laptops, music, etc. Kitchen things, power tools... Water pump? A fridge (and the inverter it requires) is a system defining load, so you may as well include anything else that will make you comfortable but which generally doesnt add much to the overall load budget. But the time to do that is now, as these systems dont grow well.

2. Your wattage estimates are pretty rough. Solar isnt cheap, so you want the best data you can get. I assume the leds will be less, the fridge sounds within cooeee. The best thing to do there is to actually measure them, for which a kilawatt will work well.

3. Because solar is expensive, you might want to consider the idea that replacing any old appliances that are known to be inefficient. For example an retail energy efficinet fridge might run 800h/d , and but some fridges from scandanavia and those designed for the marine/rv market run as low as 500Wh/d. Maybe such a tradeoff will pay for itself by saving money on the power system. Do the math and see.

As a rough guide a well designed 2kW/d system will set you back about 6 or 7K,

Off grid small system for my cabin

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