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Smawgunner
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# Posted: 30 Jun 2013 16:02
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I'm just getting my feet wet researching solar power for the cabin. "IF" I do go this route, I think I may have to cut down LOTS of trees around the cabin but I'm not 100% sure how many hours of daylight I really need. To be worthwhile, what is the recommended hours of direct sunlight needed? Also,...can a solar set up be efficient with partial or indirect sunlight?
Thanks!
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VC_fan
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# Posted: 30 Jun 2013 17:25
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Not sure this will help, but I've just started experimenting. I bought the HF set of three 15 watt panels off Craigslist. My cabin is directly under a huge 100+ year old oak and shaded by others nearby. I watched the voltage coming off the solar panels when I was over last weekend. By 9:00, with the panel sitting inside the cabin (i.e., sun coming through a window and screen) and with the light filtered by the canopy the panel was already at over 20 V, so it was charging the battery. Optimum efficiency? Maximized output? Neither - far from both of them, but it was producing. Others can be more specific but the technology has really advanced and they are considerably more tolerant of partial shade than they had been a decade ago.
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VC_fan
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# Posted: 30 Jun 2013 17:26
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I should have also said that this is in Southeast Ohio and not optimally angled or even pointed in the correct direction to maximize insolation.
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ICC
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# Posted: 30 Jun 2013 18:09 - Edited by: ICC
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Quoting: VC_fan at over 20 V
What were the amps or better yet, the watts? The amps is what charges, the volts are just pushing the amps into the battery and yes batteries need at least 14 VDC to get charging.
Quoting: Smawgunner not 100% sure how many hours of daylight I really need.
You need the maximum that is average for your location. That is not a cop-out or smart-ass answer, it is simple truth. No sense telling someone in OH they need 6 hours of good sun a day if the area average is only 4, which it is in OH on an annual average. Less in winter, more in summer.
It means that for a given use as person in ND will need more PV panels than a person in AZ.
First you need to know the quantity of power wanted to use daily. Then you figure the battery capacity. Finally the number and size of PV panels for the location conditions. Google "solar insolation map" to find more about the hours of good sun in any particular place. Wikipedia has an article.
And yes, you want as little shadowing as possible. Shadows kill performance. Sometimes the panels can be located farther from the cabin than ideal if there is a clearing. Before panels got cheap the best solution to maximizing the sun was to use a tracker. We have one old one. The trackers cost so much ($2000 plus) though that today you may be better just buying more panels. Sometimes splitting them in groups so some get more early sun and others get more late sun works well. That will usually mean more than one charge controller is needed though.
So, IMO if the proposed installation area can not provide the average hours as per the insolation data without being shaded it is time to cut trees or move the panels.
If the panels can be placed a few hundred feet away then you are best with a high end controller like the Midnight Solar units that can accept very high PV input voltages. Panels in series provide higher voltages and higher voltages means smaller gauge wire can be used to save some money. Long runs of wire are not ideal, but better than shade for certain. We have some 400 feet from the batteries.
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Dillio187
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# Posted: 30 Jun 2013 21:50
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without direct sunlight you are largely going to be frustrated and disappointed. You probably are going to want at least 2-3 hours (and preferably much more) to charge much of anything, and it really depends on how much you need to put into the batteries.
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Truecabin
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# Posted: 1 Jul 2013 13:02
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if you are a young fella you can put the panels up in the tree then maybe you can get 4 hours from 10 to 2
more panels may be cheaper than climbing up in a tree you can set one panel for morning sun and another for afternoon sun
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GomerPile
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# Posted: 1 Jul 2013 14:01 - Edited by: GomerPile
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I have a lot of trees on my lot but I also have a wetlands area that gets about 4-5 hours of sun. Its about 200ft from my cabin, so I strung wires up in the trees, but my panels are pole mounted on the ground.
I used 2 pairs of landscape light wire. Its waaay too small and I lose a good bit of voltage as a result. That said it does work.
I have 140 watts of PV panel and harvest between 6 and 12 amp hours per day depending on the season. I use a 12V power system.
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ICC
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# Posted: 1 Jul 2013 19:17 - Edited by: ICC
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Quoting: GomerPile landscape light wire. Its waaay too small and I lose a good bit of voltage
Wow! It sure will be costing you a lot of power. I guess that your 140 watt panel may be putting out 8 amps maximum. If that is correct using the fact of a 12 VDC system if we wanted to keep the voltage drop to 3% the 200 feet run would need 2/0 wire. Whoa!! Just for your info.
If that wire is equivalent to 10 ga wire the drop is about 33%. 8 ga. = about 20%
Distances are best done with panels in series for higher volts and with an MPPT charge controller. Again, just for info and education. . No criticism intended.
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GomerPile
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# Posted: 1 Jul 2013 22:23
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Agreed, but its what I had on hand. Turns out that the panels produce 20v give or take which works in my favor. Kind of a trade off between a good location and bad wire run. I'm still getting 4 amps in good sun and I only use 10 amp hours per day so I only need 2.5 hours of sun to break even. Most days during summer months I do better.
When I get some spare cash, I have an underground run planned with big ass wire.
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ICC
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# Posted: 2 Jul 2013 00:59
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4 amps would make ideal wire size awg 2.
If the panel Vmp is rated 20 volts, in this case that would be a good thing. That is if you have a charge controller that is a "regular" type, a PWM and NOT an MPPT. Normally with panels and batteries close together anything over 17 - 18 volts is a waste with a 12 VDC battery system.
I managed to snare a very good deal on #2 wire a few years back by keeping an eye on prices. Wire (copper) follows the market and has been kinda high but I hit a dip and bought two 500 ft spools. Maybe you already know, but when it comes to do a long run of the heavy wire you only need a pos and a neg, no ground required on a long run if the panels and the distant equipment have their own 8 ft ground rods. Best is 2 rods per end with min 6 ft spacing. Lightning arrestor fitted at the panels for sure, connected to ground stake.
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soundandfurycabin
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# Posted: 2 Jul 2013 19:09
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For a far-away PV panel location you could also put the batteries and inverter in a shed or box near the panels then run AC to the cabin.
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ICC
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# Posted: 5 Jul 2013 14:33
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Do the math on the wire sizes. It seems to be a wash most times I've run the numbers for running AC vs DC. If the AC amperage wanted is fairly low, then maybe there is some savings. But when the AC inverter has an output of 2500 watts or more the AC wires also have to be quite large to avoid voltage drop. It's worth doing the math to know for sure.
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creeky
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# Posted: 6 Jul 2013 10:18
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the ac drop will be much lower. it's 120 volts. not 12v. of course one more reason why folks run high voltage dc to their controllers.
2500 watts AC is only 20 amps (12g) ... and amps is what requires heavy wire. Now, 2500 watts coming from a DC 12v battery!!! 200 amps. Get out the 2/0! But only to the inverter.
Smaw... with a PWM you're probably looking at 3 hrs of sun min. I have a pal who lives up by a lake surrounded by trees. he put in a mini tower (big pole) and mounted his panels up there. he gets by with 3 hrs of sun in the summer.
i've been hinting mppt might give him more power and he's getting there!
mppt is the way to go. you can run higher voltage (smaller wire/less voltage drop) you can use cheaper higher powered panels and mppt will improve poor light power generation.
gomer, your 140 volt panels should be generating 10 amps/hr. you say you have them ground mounted? is there shading from vegetation? what angle do you have them set at?
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ICC
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# Posted: 6 Jul 2013 14:09 - Edited by: ICC
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Quoting: creeky 2500 watts AC is only 20 amps (12g) ... and amps is what requires heavy wire.
Yes. My old place was perhaps odd, unique. 400 feet from PV to cabin. Because of that low voltage DC would have been stupid.
Run 120 VAC from PV, batteries, inverter with 26 amps as max draw. (3500 watt inverter. I have hit a high draw of 3200 watts a few times. Not for a long duration but maybe a minute or so a few times) The calculator says AWG 1 wire for 3% max voltage drop
Run 120 VDC from PV panels in series 400 feet to the batteries, inverter and cabin, with maximum amps being 12 and the wire is AWG 2. Smaller wire but close in size to what is needed for the AC.
That's why I said run the numbers and see what your own case would bring. The DC current is frequently less than the higher loads put on an AC circuit when there are things like standard size microwaves and toasters in the picture.
If I ran fewer series panels (lower voltage) the DC wire requirement would then be huge. If I had less demand on the AC side the AC wires could be smaller, but that is not the case.
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TheWildMan
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# Posted: 6 Jul 2013 15:53
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I'm on the 45th parrellel (US Canada boarder), my array was built by wiring 18 of the 15 watt pannels in parrallel (bought them as a single, or a 3 panel kit from harbor freight as i could afford more, piece by piece). i generate 270 watts an hour in full sun and my battery bank holds 550 watts at 12 volt. this is the power i live year round with for lights, 19 inch flatscreet tv with playstation 2, laptop and some other minor things. i never run out of power and my batteries get topped off every day. my array only gets about 3 hours full sun every day from 10 AM to 1 PM then gets partial shade the rest of the day. winter it gets almost full sun all day (when not cloudy)
the panels generate power in shade but not as much, you should be fine if you size your needs right
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