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salem mo
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# Posted: 1 Jun 2011 12:37pm
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I have a 540 sq foot cabin that I build in Salem MO, zip code 65560. And I am looking to start a small solar system. I have a wood burning stove for heat and I plan on buying a Camp Chef HWDS Triton Hot Water Heater or similar system for a shower. I am bringing down a small apartment range that I will power off of a BBQ propane tank until I can purchase a 100 gal tank. I plan on buying a yahmaha 6300 inverter for running a 15000 btu air conditioner and maybe a small mini fridge in the summer (it ofter gets to 100+) I have a friend who gave me several Deka intimidator agm batteries with 100 aph each. They are old and used and hold between 13.7 and 14.6 volts when I charge them. I currently go down about once a month for 1-2 days. But some times I can not make it for 4 months at a time. The batter box would sit inside the cabin.
My short term plan is to run 4 intimidators in parallel, then put between 4-6 outlets on the batter box and get a small inverter (to power the pilot on the range). I want to is to run 7 led lights(3-4 hours a night), one 50 watt RV light( up to to 4 hr night), a surflow classic pump 3.5(?), pilot light on the range(?), and charging various items like a cell phone or a radio. Then I would take the batteries home after our 2-4 day trip and charge the batteries at home.
My long term plan is to buy is between 4-6 T105 batteries and one large solar panel, leave the batteries down at the cabin for spring, summer, and fall and bring them home in the winter. I would also like to get a small 12 volt TV and DVD player to keep my daughter entrained until she is old enough to help out around the cabin.
My questions are?
1) Will my short term plan do what I want it to do?
2) What size panel will I need to recharge the t105 batteries fast enough so that I do not ruin them?
3) are the 6 volt t105 batteries the best for what I had in mind?
4) What is the best battery arrangement for my situation 6 volt in a series and parallel or 12 volt straight parallels or 24 volt?
5) What are some examples of a good charge controller for a system that I am looking for?
6) What is the smallest inverter that I could use for the pilot light on the range?
7) Will the batteries be ok if I left them at the cabin for four months UN monitored?
8) Should I create a small metal shed 10-15 feet from my cabin to store the battiest in?
9) What gauge wire should I use?
10) Is it ok to run 12 volt electricity through a regular two prong outlet or do I have to use the 12 volt outlets?
11) Will my pump and shower work on both systems.
12) What other equipment will I need to develop a long term system?
13) Did I miss anything?
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Kithera
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# Posted: 2 Jun 2011 04:59pm
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Okay, a few answers. Bare in mind that this is going to be a big project that you'll want to learn from and develope. What you have described is a big system, and needs to be carefully planned.
2.) work with weekly averages with that usage pattern. you can bring it down on a weekend trip and charge for an average week.
3.) Trojan L16s are better batteries, but of course you pay more.
4.) Battery arrangement has more to do with the ratings of your charge controller and inverter than anything else. Those two components need to match, and 12V is by far the most common.
5.) Outback makes some good equipment, but you pay for it. Xantex sales chinese crap.
6.) This is the scary part. Electric start home ranges and ovens often have resistance electric heaters, eating as much as a few hundred watt always on as "Pilot Lights". Using one of these makes your cabin completely unsuitable for solar. The best alternative is pienzo electric elements, which make rapid shocking sounds when started. These use practically nothing, and even then only when starting a burner or the oven. You can for the most part complete ignore these.
7.) Kinda. A good charge controller will float charge your batteries, meaning you should only need to check them for water level every 6 months or so. Completely left alone, they will self drain, and can freeze.
8.) Batteries work best when insulated, but should be vented, as they produce explosive hydogen gas when operating. A buried box with some scrap solid foam should do nicely. A vented box on your interior though is just as good.
9.) Depends on length, acceptable loss, and current. This varies greatly.
10.) absolutely not. DC power is much harder on switching and contacts than AC, and a descent load will melt a standard wall outlet. Either use those cigar shaped connectors, or anderson powerpole connectors. Make sure all switches are rated for DC.
11.) There is no reason why it couldn't. This is much more a question of capacity than capibility. How much power do they create and how much do they produce?
13.) An AC is going to kill your system. That AC will most likely such 2 to 3 thousand watts, while running a 50% duty cycle. That is 24 to 36 kilowatt hours per day. Lets assume you have 8kw/M2/day of solar radiation (that is 8 kilowatts per square meter per day, very good summer average for that area of the country.). Now, solar panels are rated at 1kw/m2/day, so 36000/8 = 4500 watts of solar panels. That is a massive system, and will cost you at least $12,000. That is just for your AC.
Even if you're hauling batteries, each one will hold about 1KW, so you would need to haul 24 to 36 of them per day, just to run your AC. That is still from full charge to completely drained, a cycle that will quickly destroy them.
The real solution is that off grid = no AC. Look at alternative. A well insulated cabin, no direct sunlight (awnings) and some amount of thermal mass such as bricks, sand, or water will help your place stay cool until the late evening, when you can open your windows and let the breeze take any accumulated heat out.
On the plus side, the led lights, cell phone chargers, even a small laptop or lcd based all on one dvd player won't put much stress on your system at all compared to that.
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TomChum
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# Posted: 2 Jun 2011 10:31pm - Edited by: TomChum
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Quoting: salem mo 10) Is it ok to run 12 volt electricity through a regular two prong outlet or do I have to use the 12 volt outlets?
Quoting: Kithera 10.) absolutely not. DC power is much harder on switching and contacts than AC, and a descent load will melt a standard wall outlet. Either use those cigar shaped connectors, or anderson powerpole connectors. Make sure all switches are rated for DC.
....and.... if you put standard AC plugs on your 12vDC devices, at SOME point, someone is going to plug your 12v device into the 120vAC outlet on your generator or inverter.
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Just
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# Posted: 3 Jun 2011 09:00am
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do i understand you correctly that,, the stove is propane,, and you intend to run the air and the fridge with a generator. if so, you seem to be getting close to me,, but i'am no pro .
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Kithera
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# Posted: 3 Jun 2011 09:06am
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To keep more to the point of your original post, an off grid solar system is pretty simple. You have:
Panels (parallel for 12V) -> Charge controller -> Battery -> DC Distribution -> Inverter -> AC Distribution.
Every thing else is about capacity.
First, find the us geological survey's site on solar radiation. It will give you daily average solar radiation in a value of watts per square meter per day. Comercial solar panels are rated at 1 kw per meter square, so if that page says you have 8kwatts per m2 per day, and you have a 200 watt panel, then you will generate (on an average day) 8 * 200 watts, or 1.6 KWatts.
For the charge controller, you want to get one rated at the maximum output of all your panel combined. Say, you have 4 200 watt, 12 V panels. Amps = Watts / Volts, so you have (4 * 200 ) / 12 = 66.7 amps, so you'll want a charge controller rated for 800 watts or 66 amps.
For the batteries, you want to think about how far appart those average or better days are. Do you go for several days of cloudy and overcast? A weekly average for a full time home is pretty normal, but you can say 2 days for a weekend only cabin.
For wire, again, it's based upon the length of the run and the amount of power going through it. Long runs of high amperage cable forces some pretty big wires. This site has a calculator: http://www.freesunpower.com/wire_calc.php. Here is a second one for AC: http://www.csgnetwork.com/wiresizecalc.html, note than when you convert 12V DC to 120V AC, your amps are divided by 10 as well. running 60 amps of DC 25 feet requires guage 1, 6 amps of AC the same distance requites guage 14, much less. If you have any significant amount of distance between your panels and your cabin, a shed near them is a good idea.
Finally, for the inverter, consider the largest AC appliances that you'll run at any one time. If the absolute worse case, you have a 3KW AC, 500W Water Pump, a 50W laptop and a 1W cell phone charger running at one time, then you need an inverted rated at 3551 watts or higher.
I hope this makes more sense.
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Rob_O
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# Posted: 4 Jun 2011 08:40pm
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Quoting: salem mo 1) Will my short term plan do what I want it to do?
I use one of those Deka batteries for power at my place, and my gut instinct says you will run down that set of four batteries in less than 2 days with the loads you listed. That RV light alone will run one of those batteries down 20% (recommended maximum) in 5 hours.
At 20% discharge each of those batteries will have 240 watt/hours of power available. Start totaling up all your loads and you will see exactly how many days of power you have available.
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MtnDon
Member
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# Posted: 8 Jun 2011 01:13am
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The first thing to do is to accurately estimate the number of hours of use for each electrical device. Then do the math to get the watts used. As was mentioned it may be best to do this for a weeks use and average it out to a day. If you don't do the math you are guessing or using somebody else's guesstimates.
Once you know the actual estimated use add a safety factor; use will grow. Been there, done that.
Then you can size the battery bank. Then the required PV capacity can be calculated.
This calculator may help estimate capacities.
CALC
Points:
A PV system with a quality charge controller can be left to run itself for months on end. We do it. The key is to be certain the cells are properly filled if the batteries are of the flooded type. AGM batteries don't have that issue. Gel batteries are not generally recommended. The system runs through a charge cycle every day and ends up in float. The batteries we have use very little water over the winter season and are fully charged and ready to go any time. Fully charged batteries will not freeze.
The only AC systems that can be sensibly run off grid are the split mini systems.
Regarding DC outlets. It is correct that a switch designed for AC only use will rapidly burn the contacts when used with DC. However the NEC approves the use of receptacles and plugs that were designed for AC use, IF the receptacles used use a different pattern from that used for the AC power. Most folks will use plugs designed for 240 AC. The plug prongs have a pattern not used for any 120 VAC use. Note this is only approved for installations that have to 240 VAC power. I have a few of the 240VAC 20 amp pattern; look for units in the NEMA-6 series. Lowes carries them.
Best off grid systems will not draw the batteries down any more than 25% in one day, IMO. Many folks run their batteries down 50% regularly. That will shorten battery life a lot.
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