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trhood
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# Posted: 26 Oct 2010 10:45am
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In a couple of years my family and I are looking to move on some land we have and go to mostly self sustained off grid living. I have designed a cabin that will suit our needs and plan to do a combination of Solar and diesel generator power set up. Is there a way to feed both the solar and diesel power into the same storage source then invert to AC power? I've read some online but I'm not finding this question answered. We will have some lighting needs of course but the major power draw will be from household appliances like fridge, freezer, washer, and dryer. Any insight will be appreciated.
TR
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MtnDon
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# Posted: 26 Oct 2010 11:51am - Edited by: MtnDon
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Yes, you can feed power from PV modules, wind generators, micro hydro ,fossil fuel powered generators and so on into the same storage batteries. Each source needs its own separate charge controller.
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MtnDon
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# Posted: 26 Oct 2010 11:55am - Edited by: MtnDon
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You can run all the normal household appliances and be off grid. That does require a large battery bank to avoid having to run a fuel powered generator frequently. It can be done, there are 100% solar powered homes. Most of those though will use propane for things like cooking and clothes drying. The first thing would be to accurately calculate your power requirements. This can be done by taking an existing situation and adding/subtracting power uses. A Kill-A-Watt meter is a handy tool for recording actual appliance use instead of nameplate ratings. There are also many online calculators available. I wrote my own which is HERE.
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trhood
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# Posted: 26 Oct 2010 03:32pm
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Thanks, I'm planning on a combination of solar, diesel generator, propane, wood heat and cookstove. Planing on a rainwater harvesting system and purifing stream and river water. Any tips on the water?
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MtnDon
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# Posted: 26 Oct 2010 04:26pm
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UV works great for purifying ground water after the initial sediment filtering.
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trhood
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# Posted: 27 Oct 2010 05:03pm
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my last electric bill was for 1195 kilowatt hours, but everything is electric in this house. In the planned set up we would have propane for fridge, washer, dryer, and wood for the cookstove. What size generator would you recommend?
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Rob_O
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# Posted: 27 Oct 2010 05:33pm
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a 3KW listeriod would suit you quite well. You can even grow and press your own fuel
http://cgi.ebay.com/Listeroid-Lister-CS-Diesel-Slow-Speed-ST-Generator-3kw-/270655463 739?pt=BI_Generators&hash=item3f0452a13b
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MtnDon
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# Posted: 27 Oct 2010 06:18pm - Edited by: MtnDon
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Well, my way of looking at electric off grid power is to try to avoid using a generator at all. That said, I know I am fortunate in being located in the sunny SW, PV modules are king where we are. I only run the generator once a month just to keep in running or every four months or so to equalize them.
Note that when saying battery here, I mean flooded cell lead acid batteries, not AGM, not gel, not sealed in any way. Those may have different rules.
How big a generator is needed depends on how big the battery bank is. As a rough rule of thumb the maximum current applied to the batteries should be what is known as the C/10 rate. Some say C/8, where C is the capacity of the battery bank in amp-hours at the 20 hour rating. EG: a battery bank with a capacity of 840 amp-hours could be charged at 84 amps (C/10) or maybe 105 amps if you subscribe to the C/8 idea. Higher charge rates can be used with chargers that are equipped with battery temperature sensors
So picking a generator that could power a charger delivering that would be adequate. Say 84 amps at 24 volts = 2016. Add 10% to that for good measure = 2217 watts. To that add an altitude correction of approx 3% per one thousand feet above sea level. If at 5000 feet the a normal combustion engine has it's power output reduced by about 15%. Add 15% to that 2217 = 2550 watts. That's not exactly the correct math but it is close enough for estimating requirements. So for this example a generator with a minimum constant capacity of 2550 watts would be needed. I'd probably round that up to 3000 watts myself and then go shopping and round up a little agin depending on what I found available.
How big a battery bank depends on one's use. Note that a friend who has been in the business of designing systems and selling his maintenance services to off grid home owners, and who has lived off grid for over ten years himself tells me that the number one cause of failures to perform in an off grid system is not designing in enough battery storage capacity and overdrawing energy from one's batteries.
Many readers will already know that even deep cycle batteries should not be cycled deeply as a regular matter. There is a direct corelation between battery life and depth of discharge. The shallower the discharge, the longer a batteries life.
Any particular reason diesel? If the gen is a backup only, seldom used a gasoline generator that can also run on propane, if you have adequate propane supplies, might be worth a look.
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