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Snubber

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Posts: 8
Reply with quote  #1 
I'm new here and just beginning to study solar feasibility for a future cabin in the west texas desert. I know NOTHING about solar other than what I've gathered from YouTube. I'm studying what size system I will need , future expansion etc. Question : Does it make sense , from a conservation / usage / efficiency standpoint , to have a ac / dc hybrid system for my cabin? In other words , 12 volt dc for LED lights , fans , water pump etc. , and a converter for 110 volt ac power for a small fridge and television? All help appreciated.

stmbtwle

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Reply with quote  #2 
Sure. I think you'll find many boats and RVs are set up that way (including my houseboat). Basically you build a 12v battery based system for your DC accessories, and power those directly from the batteries. You also connect a DC-AC inverter to power AC appliances such as your fridge, TV, etc. You can do all this with the same set of batteries, charged by the same set of solar panels. It works just fine. My boat has 6 golf batteries arranged to provide 12 volts. Off the batteries I have a 12v wiring system to run all the marine accessories, an automotive stereo, lights, and other stuff. The batteries are charged by solar panels. Also connected to this same battery bank is a 12v to 120v inverter, which powers a second, 120v wiring system. This powers my fridge, TV, more lights, fans, etc. The whole system has been working fine for over ten years. The trick is having enough batteries to run the total load, and enough PV panels to keep the batteries charged.

That said, I went with a 12v/120v system because it was a boat and I had an engine and accessories to deal with.  However over the years I find myself using more and more 120v accessories and less and less 12v stuff.  For a cabin you might save money going with a higher voltage (24 or 48 volts), skipping all the DC accessory wiring and using only 120v lights, etc.  You would configure your batteries for 24 or 48 volts, and use 24v panels (much less expensive than 12v) and configure them to match the batteries.  You'll save money on the charge controller. You'll save money on wiring. Get a 24 or 48v inverter (about the same price as 12v) and skip all the 12v wiring entirely (more $ saved).  You can get 120v lights and accessories at Big Box for less than the equivalent quality 12v stuff at the RV or marine store.
 
Something to consider, at least. 


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

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Reply with quote  #3 
Great! Thanks.
Snubber

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Posts: 8
Reply with quote  #4 
Would the 120v be as efficient ( less power consumption / battery drain ) as the 12? I'm only considering running lights , a fan and a water pump 12v.  Would save enough to make it worthwhile?
stmbtwle

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Reply with quote  #5 
It would be hard to determine.  In a small system running ONLY a few lights, a 12v fan and a 12v RV water pump you would be ahead with 12v ONLY), but as soon as you add a fridge and TV per your original post, you've complicated the system considerably. 

If there is no engine involved my choice would probably be 24v/120v.  Solar panels are a big cost. 24v panels are considerably cheaper than the same power in 12v. Charge controllers can handle twice the power.  Inverters, pumps, and many other DC accessories are available at about the same price in 12 or 24v.  Wiring would be smaller (and cheaper) in 24v as opposed to 12v.  A 120v household fridge is less than half the price of a 12v RV/marine fridge, enough to pay for the inverter to run it with $ to spare.  Now that you have the inverter, you might as well use it, it's running anyway, and 120v LEDs are cheaper than the equivalent 12v.  You can use off-the-shelf fixtures, etc.  

If electrical "efficiency" is your only goal I'd go with 48v (less electrical losses) and hang the cost.  But 48v appliances aren't as common or cheap as 12v or 24v if they're available at all.

However COST is ALWAYS a consideration.  Compare the prices from West Marine or Camping World with the prices from Home Depot and Walmart, and go from there.  Look here http://www.solar-electric.com/
or here http://www.solarblvd.com/index.php for panels and accessories. 



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

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Reply with quote  #6 
Ya know , the more I read , the more I'm inclined to just use a 120v system. My "energy shed" ( as I like to call it ) is approx. 20 feet from my cabin as well. It's where my panels and bank are located so there's the issue of wire size also.    Thanks for your response.
stmbtwle

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Reply with quote  #7 
I think that would work well. Running wiring for two separate systems adds to complication, cost, work, and aggravation.
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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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