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Old 11-12-2015, 08:26 AM   #21
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You will manage to spend a bit more at an auto part store or similar to put 20 or 30 amps blade fuses on both the solar array side and the lead to the battery. You ought to order 10 ga wire as an option with the kit which comes with 12 ga by default. You will also want some crimp on loops to take the Positive to the Battery post and the Negative to the a frame ground or the battery post. I have done or helped on several installs and you may well need a roll of 10ga stranded copper wire for your run from controller to battery and wire ties as well as some inch or inch and a quarter #14 stainless sheet metal screws to mount the panels to the roof as well as a tube of self leveling Dicor or similar to caulk every point that you penetrate the roof. Some blue or red loctite to make sure the screws holding the panels to the mounting brackets never back out might not hurt.

Its a KIT but you still need shop supplies to install it
You have hit on every point I saw with the exception of upgrading the 20 amp controller to 40 amp in the event I want to add panels in the future. Additionally rule of thumb is to measure current of panel by 1.25 when sizing the controller. Two 100 watt panels would put this at 20.8 amps. That runs the 20 amp controller a little hot for my liking.
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Old 11-12-2015, 08:30 AM   #22
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Most good controllers will take a "12v or 24V" input two in parallel is 12 v two in series is 24 v. At 24 volt you can carry more on thinner wire. Some controllers start working in lower light at 24 input than on 12 input but we did some tests on the drive way and it did not seem to make too much difference.
I was thinking panels wired as 24 volts with an MPPT controller would be better on a cloudy day??? Any thoughts
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Old 11-12-2015, 09:11 AM   #23
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Solar Panel Strength

One question I have is how strong are solar panels, ie how easily damaged? My reason for asking is I live in the north east. There may be a heavy snow load on the panels in the winter. In addition I park under Oak trees. In the Fall the acorns drop from as high as 50 feet above the coach (yes I have had the trees trimmed to the tune of $1300). If in the coach when an acorn hits the roof it sounds like a gun shot. I wonder if the panel would sustain this or if I would need to cover in the fall or perhaps cover the panels with Plexiglas. I have looked at panel specs and see they are made with tempered glass but no comment as to strength. Any thoughts?
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Old 11-12-2015, 09:25 AM   #24
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I also live in the northeast. Snow has not been a problem nor acorns hitting the panels. Have had small branches hit them in bad storms. Good so far. One other thing I found with mine, last winter, with 3 inches of snow on the panels, they were putting out 2 amps of power to the bats. Bright sunny day.
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Old 11-12-2015, 09:59 AM   #25
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Check Solar Electric Power Systems For On & Off Grid | Panels and More | NAWS

Once you decide on the total wattage of panels you want to use, double that when choosing a controller. For a small added cost, you will have expansion capability. Buying a second controller or larger controller later on will be much more expensive.
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Old 11-12-2015, 10:51 AM   #26
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I was thinking panels wired as 24 volts with an MPPT controller would be better on a cloudy day??? Any thoughts
That is what they say, but we did not see a notable difference in "driveway tests" Maybe we had a lousy MPPT and a really good PWM.
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Old 11-12-2015, 11:01 AM   #27
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To the question about 24V vs. 12V. The differences are in the gauge of wire required on the down runs and the type of panels you can choose. You can use lighter wire as the voltage drop will not be as great at the higher voltage and lower current. You can choose to use the less expensive per watt larger panels on the roof. There is a rather technical argument about the efficiency and gains you might see if using MPPT. For large systems (many many panels) the cost of MPPT will be offset by the gains acquired. For small systems that cost is not easily made up. All of it boils down to cost per watt of the entire system: more expensive 12V watts less expensive controller or less expensive 24V watts and more expensive controller. Simple arithmetic. Also, the 24V panels are often much larger and will not fit on many smaller RV roofs. If they will fit and cost isn't an object then overkill the system with many panels and MPPT. Never worry about charged batteries again!
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Old 11-12-2015, 11:15 AM   #28
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You have hit on every point I saw with the exception of upgrading the 20 amp controller to 40 amp in the event I want to add panels in the future. Additionally rule of thumb is to measure current of panel by 1.25 when sizing the controller. Two 100 watt panels would put this at 20.8 amps. That runs the 20 amp controller a little hot for my liking.
The output specs on the panel are MAXIMUM POSSIBLE. Efficiency is never more than about 80%. I have the higher priced WindyNation.com 30 amp PWM controller, which shows rate of charge, voltage and state of charge in the Batteries. As a practical matter, it will handle 4-100 watt panels. In fact, my two 100 watt "12v" panels (wired parallel) seldom push over 10 amps, but that may just be because by HIGH NOON my batteries are already full. Often by the time I check my charge rate after breakfast and morning chores, I am only charging 3-4 amps, which is little more than trickle rate plus the static load of our trailer, because my three Group 24 batteries are already full.
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Old 11-12-2015, 12:12 PM   #29
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Exactly: we don't often find ourselves in a situation where the MPPT advantages will come into play. And even if MPPT were 20% more efficient (which is a huge stretch) the raw numbers don't work. I am not saying don't by MPPT! If your cost per watt makes more sense using 24V panels and MPPT (to reduce the 24V to 12V for you battery charging) then use it! Otherwise don't get hooked on the hype. Remember: the manufacturer makes more money on MPPT. You spend more, they make more...
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Old 11-12-2015, 12:17 PM   #30
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I have 305 watts of panels(2), on a bright sunny day with out shore power, I can run 2 exhaust fans and an inverter running a 42 inch flat screen TV for six hours and see over 13 amps from the panels and 98% charge in bats.
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