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Old 07-31-2015, 05:26 PM   #1
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Solar amp hours in real life

How many amp hours a day can I expect from each 100 watt solar panel.
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Old 07-31-2015, 05:42 PM   #2
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A rule of thumb is: Solar watt output divided by charging volts X peak sunlight hours.


So 100 watts / 13.5 volts = 7.4 AH X 5.5 hours of peak sun = 40.7 AH per day.


I built a system using that formula 6 years ago and it seems close.
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Old 07-31-2015, 05:44 PM   #3
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I believe there are simply to many and varied factors involved to give any meaningful answer other than to restate the specs of the panel, which is always given in consideration of optimum conditions and efficiency, but that's just my opinion, I could be wrong.
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Old 07-31-2015, 06:15 PM   #4
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Yeah, and you have to have good orientation and good sun.
twinboats, my system bulk charges at 14.7 volts and up to 40 amps.
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Old 07-31-2015, 06:23 PM   #5
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Quote:
Originally Posted by twinboat View Post
A rule of thumb is: Solar watt output divided by charging volts X peak sunlight hours.


So 100 watts / 13.5 volts = 7.4 AH X 5.5 hours of peak sun = 40.7 AH per day.


I built a system using that formula 6 years ago and it seems close.
X-2 on that!
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Old 07-31-2015, 07:41 PM   #6
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Yeah, and you have to have good orientation and good sun.
twinboats, my system bulk charges at 14.7 volts and up to 40 amps.
My system bulks at 14.7 also. As a matter of fact I can equalize at 15.5.

The OP was looking for a rough guide, per 100 watts. The 13.5 volts is the minimum volts needed to push a charge into 12.6 volt batteries.


I have 3, 225 watt, 36 volt panels wired in series to a Morningstar MPPT 60 amp controller, charging an 8 piece 6 volt GC2 bank configured to 12 volts, monitored by a Trimetric 2020 battery monitor. It supplies a Xantrex PS2000 inverter.
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Old 08-01-2015, 02:21 PM   #7
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I believe there are simply to many and varied factors involved to give any meaningful answer ...
There is too much truth in this statement, IMO.
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Old 08-05-2015, 11:59 AM   #8
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I have learned that the most favorable answer to how many watts/panels to install on an RV is "Fill the roof with all the panels that you are able to install".

By doing that, it's possible to fill your matched battery bank even on cloudy days. More is better than just enough!

The cost to do this used to be cost prohibitive in the days of five bucks a watt, but solar panels are down to around a buck a watt. 24 volt panels with a MPPT controller is great!

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Old 08-05-2015, 01:26 PM   #9
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Agree with Ed "..."Fill the roof with all the panels that you are able to install.." and use a good MPPT for maximum charging efficiency. Determine which size panels to use and set them up in parallel or series, or a couple of series then in parallel. We have 235 W which are 30 V.

There are definite advantages to using higher voltage battery bank: 24, 36, or 48 V as well as the higher voltage run from panels to MPPT. Higher voltage battery suite does then require a converter from the higher voltage to 12 V but these are inexpensive (Mean Well makes them in all types of flavors: 48, 36, and 24 to 12 V).

We left the Dometic fridge on AC overnight and we were down - 3.1 kW-hrs this morning. We knew it would be a very sunny day today (always check weather report before leaving the fridge on AC overnight) and are charging at 1221 W (to MPPT) at the moment. This is only 14 amps to the MPPT and 22 amps from MPPT to battery suite. The battery is only charging at 700 W due to running fridge on AC and the two Fantastic Fans. It is 95 outside but only 85 inside. May run air conditioning later today if it gets above 90 or 95 inside. That takes 1750 W from the battery suite/solar panel combo

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Old 08-06-2015, 08:59 PM   #10
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All I know is that my 200 watts of 24 volts panels and the MPPT controler is way better then running my power plant above 5 hrs per day.
Since I am fully charged by noon I allow my friends to hook on to my system after lunch.
I do not expect to run the microwave or toaster but do enjoy normal living in our RV when electricity not available.
Batteries are great after 3 years compared to ruined after 2 years while using the stock converter and power plant.
I see no need for more even though I mostly do my boondocking between November to May. The few times in the summer have been for weeks at ba time.
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Old 08-07-2015, 08:41 AM   #11
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I think we've hit a sort of "sweet spot" with the size of our solar system. The only time we ever have to run the generator is when we want to run the ac's or there is no sun & the batteries need to be charged. We cook with propane, the battery bank and inverter runs everything else.

So we are in that spot where adding a little more makes no sense because it would provide no further capability. We would have to add a lot more to make a difference & really the only difference we could make is to be able to run the ac's.

As for cost. When I decided to install solar I knew nothing about it other than general knowledge of what it is. I checked with local RV shops and even called a few local solar company places but could find nobody that knew much about or installed solar on RV's. Because of that I decided to go with a kit that had everything, including good instructions, and do it myself. Between those instructions and YouTube videos I was able to install the Go Power 480 watt kit that came with a 75 amp 4 stage smart converter/charger that replaced the stock 45 amp model that came with the coach in 2004, a 3000 watt PSW inverter, and switch. After I had everything installed I called a local electrician to hook the included switch to the coach's power panel. Including the battery bank cost of my system, start to finish including the electrician, was within cents of $5000 on the nose. I could probably do it for less knowing what I know now, on the other hand there is something to be said for receiving a big box with everything you need in it and it all works as advertised

One thing we have learned from having solar is that on our next, and final, motorhome we want more of it. Lots more!!
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Old 08-07-2015, 03:44 PM   #12
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Sounds like you up with what you want and need.

Reed and Elaine
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Old 08-08-2015, 08:03 AM   #13
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Always easier to see what you did incorrectly after posting.

Sounds like you wound up with what you want and need.

Reed and Elaine
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Old 08-08-2015, 10:15 PM   #14
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Most of a solar install is straight forward. Personally the biggest issue to get right is the panel mounting. There are so many things on the roof it can make it difficult to get the panels place well.

I've always thought the best side for panels is the road side. That way when you boondocks you keep the curb side toward the north so it's shaded. the ACs, antennas and other tall items are also toward the north. All of this keeps shadows off the panels. It also allows one to stack panels so they can extend out the road or south side. Of course your fighting the floor plan placement of vents and skylights. It's so much fun figuring this stuff out.
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