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ernieriddle

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Posts: 8
Reply with quote  #1 
I have a small cabin I have been powering by generator when I am there (on the weekend). It is very over kill in the winter since I only power a TV. and a couple of lights. In the summer I need it for a small window unit so it makes sense. My goal is to have a solar system that can run dehumidifier and small dorm fridge all year with the occasional tv. (Sinewave)and light. I will still use the generator for the air unit. I may expand a little but 11x14 not much expantion room
This is very remote and want to keep all forms of government oversight out that's why I am looking diy. Problem is I am clueless on this and don't want to burn the place down. I do understand some on the 120 end and have dabbled on the 240 as well, just a new thing for me to grasp DC.
Solar Suppliers DIY?
I am in SC.
any thoughts or wisdom would be appreciated. Just keep in mind I am a toddler at this, Small baby spoons of info.
Thank You for any help you can give

Gordy

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Posts: 137
Reply with quote  #2 
ernieriddle,

Here is a link for you to study, I think you will find it helpful with getting your head around some of this.

http://www.backwoodssolar.com/learning-center


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Gordy,
Minnesota
stmbtwle

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Reply with quote  #3 
Hi Ernieriddle, welcome to the forum!

What you're looking to build is very similar to what I have on my houseboat (aka floating cabin).  While it seems complicated it's simple enough taken one step at a time.

Fridges draw a lot of power over time.   Before you start you'll want to get a "kill a watt" portable power meter and plug everything into it for several hours.  This will give you an idea how much energy per hour/day you're actually using and will help you to size your system.  Then you can go from there...

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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
ernieriddle

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Posts: 8
Reply with quote  #4 
I have looked at some of Backwoods products. Has anyone heard or used Renogy products?
I didn't do well in math so want to have a system rather then components.
ernieriddle

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Reply with quote  #5 
Yes hoping to run small fridge and dehumidifier
stmbtwle

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Reply with quote  #6 
A small fridge can use about 1 kwh/day, if you still have the yellow tag that came with it you can get a better estimate. The Kill-a-watt will give you the best info and can measure the dehumidifier and all your other equipment as well. Well worth the small investment.


So let's GUESS you need 1500w (max) and use 1500 wh/day. A 1500w inverter will do the job. Sine-wave is best but a cheaper MSW will work, even with a TV.

Now for that 1500wh/day. To start with, how many days AT A TIME do you expect WITHOUT SUN in the winter? This is your worst case and what you have to plan for, otherwise you may end up with a fridge full of spoiled food.
I will GUESS three days, so that would be 4500wh total. A "regular sized" deep cycle or golf cart battery will hold about 600wh at 50% discharge. 4500/600 comes to about 8 batteries for 3 days. If you get bigger batteries, you'll need fewer, as long as the math comes out.

Now for the solar. You need 1500wh (1.5kwh)/day, or 45kwh/month. According to http://pvwatts.nrel.gov/pvwatts.php, a 1kw array in Charleston will get you about 94 kwh in December, or about 3 kwh/day. A .5kw (500w) solar array should be good for 47kwh.

The charge controller will depend on your array and battery configuration. If you go with 24v, a 30 amp controller should do it. If you choose 12v, you'll need 45 amps.

The reason for so many batteries is to carry the fridge through periods of bad weather. If you're willing to shut it down, you can get away with fewer batteries.




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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
Rick H Parker

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Reply with quote  #7 
"hoping to run small fridge and dehumidifier"

The first step is to quantify your energy needs.

For example: There is a high variation in what a "small" refrigerator is, quantify it better. For starters how many cubic feet?


Willie: "Just keep in mind I am a toddler at this, Small baby spoons of info."

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Rick H Parker
Kansas, USA
Electronics Engineering Technologist
ernieriddle

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Posts: 8
Reply with quote  #8 
2.6 cubic feet ref is plenty and the smallest electric dehumidifier that is electric. We are only talking 165 sq ft of space.
I haven't purchased anything yet.
I am not scared of having too much battery just to small inverter.
Rick H Parker

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Reply with quote  #9 
I am not scared of having too much battery just to small inverter.

Legitimate concern, anything with a motor has a high startup current and the manufacturers do not tell you what it is. Your best course of action would be to pick and acquire the dehumidifier and refrigerator, take measurements of peak startup power. Then size the inverter to cover the maximum peak power you might encounter. After that we can figure out the rest.

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Rick H Parker
Kansas, USA
Electronics Engineering Technologist
stmbtwle

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Reply with quote  #10 
I have a 7 cu ft fridge and it runs nicely on a 1750w MSW inverter, with plenty of power to spare for everything else, TV, laptop, lights, fans etc. I even run light power tools with it, and I don't have to turn the fridge off.  A 2000 watt should be more than enough.

But as Rick says, the ONLY way to know for sure is to get the equipment and then measure the actual startup and running watts, and the average watt-hours per day (this will vary according to temperature and setting). This is why the Kill-a-Watt (or other power meter), otherwise you're just guessing.  Once you have this info, you can size the rest of the system.  Also bear in mind that most inverters have a built-in "surge" capability for a few seconds, long enough to get the fridge started.

My belief is that a 3 cu ft fridge probably has the same compressor and the same startup load as, say a mid-size fridge (of the same brand), though the consumption over time should be less.

Just out of curiosity how big is your generator, or have you purchased it yet?  The same requirements you apply to the inverter also apply to the generator.





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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
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