How much power does solar panels actually generate?

What I stated is true. Aceis' question was about different types of panels, not whether there would be a need for independent controllers.
I simply answered the question in that different types of panels can be mixed. Its not misleading, it is a fact, they can be mixed.

Hi acei,

8 years is possible with six volt jars. Capacity does initially increase (mostly in the first five cycles) and then slowly sinks into the sunset. If you are full time in the RV the life span may be shorter than the 8 year time frame. 500 cycles to 50% state of charge. At that point 80% of the capacity remains. With a larger amperage bank the number of cycles increases because the depth of discharge is smaller.



I'm one of the lucky ones who got 9.5 years from a pair of 12 volt marine batteries (I credit the 30 watt solar system on the previous RV for that).

pianotuna wrote:
Hi Harold,

The output curves between amorphous and mono crystal and poly crystal are different. Therefore, to work in an optimum manner, they would each require their own controller. I don't know why I bother replying to you. I guess it is to protect others.

This was what I had in mind before, but I think I will just simplify the setup and go with Panny(Sanyo) HIT 240S 240w x 3 setup. I read up more on the efficiency on these HIT setup, and they seem quite decent on shady conditions as well.

Hi Harold,

The output curves between amorphous and mono crystal and poly crystal are different. Therefore, to work in an optimum manner, they would each require their own controller. I don't know why I bother replying to you. I guess it is to protect others.

pianotuna wrote:
Hi harold,

All the specs have to be the same and different types of panels would have different voltages under the same conditions. Please stop misleading folks.

Excuse me !!!!! Are you implying the voltage of a panel engineered to produce 12 volts somehow changes its voltage? :E
Or is it that a 12 volt panel made by Sanyo produces a different 12 volts than one made by Sharp? :S

Acei wrote:

harold1946 wrote:
Just as an example and by no means the only solar set up, but works well for us.
We are full timers and camp off grid 90% of the time. We have an Amana 18.5 cu.ft. residential refer with icemaker and run it on a MSW inverter.
Our batteries are 3- Deka 8D 12 volt AGMsw totaling 735 AH. We have 645 watts of solar.
My advice is that if you go with around 100 watts of solar for each 100 amp hours of storage capacity, you will be safely in the ballpark under most conditions, but there will be times when conditions will require some form of generating power other than solar.

This seems to be pretty close to my end-goal. Why did you go with 3x12V setup instead of 6V setup?

Also, that's a 3-panel setup, correct? What sized trailer do you own that accommodated these panels?

Thanks for the advises.

My battery compartment had the room for the large 8D,s and I am partial to AGMs. Other than that, just my choice.
Yes its a 3 panel set up and the motorhome is a 35 footer.

It gets hot here in Montana as well typically 15 or so days a year over 100F
At those temps no way do we get the full rated wattage

Being further north with a properly designed system and quality components you should easily see the full rated wattage of your PV array. For us to see the full wattage heavy loads drawing lots power are needed - since the batteries are typically sitting at 100% SOC by mid morning and do not need much if any.


PS - GC 6 VDC batteries last me 8 to 10 years of use in the RV

pianotuna wrote:
Hi acei,

The two volt cells have a life span of up to twenty years.

Cell failure, statistically speaking is more likely with a greater number of cells.

Six volt batteries have 3 cells each. 6 x 3 = 18 cells to possibly fail, or three times the risk of failure.

I see... What would be the lifespan of 6V (say Trojan) batteries? Is it significantly shorter? As I mentioned before, my goal is to own this future rig for about 8 years or may be a bit longer. Would a good 6V battery last this long?

Hi acei,

Are you custom ordering an RV? What are you planning on purchasing?

The two volt cells have a life span of up to twenty years.

Cell failure, statistically speaking is more likely with a greater number of cells.

Six volt batteries have 3 cells each. 6 x 3 = 18 cells to possibly fail, or three times the risk of failure.

sunfrost refrigerator

As to sizing a solar system, in some ways it is a u shaped curve. The lower the amount of storage the greater the importance of having enough watts to get recharged quickly.

The bare minimum may be about 60 watts per 100 amp-hours. That is enough to allow equalization to be done.

Above 85% state of charge only about 12.5 amps of charging are accepted by the battery--and that number drops as the battery gets closer and closer to fully charged. 12.5 amps translates to 150 watts of panels per 100 amp-hours of storage.

Assuming you go with six six volt jars or 696 amp-hours the range of size the range of wattage would be about 420 to 1050 watts of panels.

My charging day starts at 30 minutes after sunrise and continues to sunset. By one hour after first light I harvest enough to meet the parasitic loads in the RV. Solar system "rule of thumb" is five hours per day at the rated panel output if the panels can be tilted. I chose to not tilt.

I added a 2nd bank of 500 amp-hours and have barely enough solar to equalize it. Without bank switching I'd be too low to do so. When boondocking I run out of grey water tank room before I run out of power, but I don't run a residential fridge either. In summer time I do run my water heater on electric.

There is an argument to be made for a 24, 36 or even a 48 volt battery bank.

Once you have decided on the wattage of panels and the voltage of the battery bank, look for a fully featured charge controller. If cost is not an object MPPT will wring move watts from the solar array than PWM. Try to find a controller that allows diversion loads, so that once the battery bank is full (or above 85% of full) the solar panels can be used for electric water heating or other loads.

My favorite controller under 500 watts (for non tilt installation) is the MPPT Rogue 3048 (made in USA)

Rogue 3048

Over 500 watts the Tristar 60amp PWM controller is a great unit.

Over 800 watts consider a 24 volt battery bank.

What ever controller is decided on should include a temperature sensor on the battery. That will optimize the charging voltage. For the climate I live in (-40 to +42 C; -40 to 107 F) it is essential.

I do not think there is much difference between the cheapest panels available (as low as 68 cents per watt, from time to time) and the most expensive ones. I know of only one person who had a failure--and that was on a "name brand" panel of high reputation and quality. Save on the panels and buy a "top of the line" charge controller.

KJINTF wrote:
For us the current supplied by our 550 watt PV array has on many occasions produced 40amps (the full 550 rated wattage, Battery voltage sitting at 13.6 )to the loads. Every once in a while 43 amps ( A bit more than the rated wattage) as seen on the TS-RM-2 is being produced by the array. That said we live in a cool climate, hot panels drop in efficiency quite a bit (Arizona in August = VERY HOT). The above is during the middle of the day with cool weather and direct sunshine while I am loading the system with the on board 12 Volt powered compressed air system.

One of the reason for going full-time is to avoid extreme temperatures, so I doubt we will face really hot temperatures. During the winter, we will be in southern states, and during the summer we will be in Ontario, but probably up in the north side. It might still get hot here but not Arizona-hot.