What can you do with solar?
Hi, Please reply with what your solar system can do to enhance your RV'ing experience. Please list the number of watts, Charge controller, inverter (if any) and amp-hours of battery bank 256 ...
Forum Discussion
I tried to make a guide to what to expect from how many watts solar.
(You can print this)
It turns out there is a fairly good ratio for watts vs max amps and it is approx the same whether you have PWM or MPPT--just use the watts.
The trouble arose from the location and timing in the year when using solar. I thought what works here in summer would be the same down south in winter. Nope, winter is winter--a lot less sun time and sun not high enough.
Still, you need some sort of way to WAG how much solar you need, assuming the sun gets high enough for long enough where and when you are doing it.
Part 1
The magic formula is that 130w gets 8.2 amps (same as Isc) and that will get you approx 56AH/day flat, 70AH /day tilted pointing South. (actuals for May at 49N)
So if you need 100AH/day to get by, and your panels will be flat, you can go 100/56 x 130w = 232w
Doesn't matter if that is one 230w panel with MPPT or a collection of 12v panels with PWM, same answer. (close enough) Just use the watts.
Another wrinkle that showed up is those dratted DM panels that have high Voc and low Isc compared with most poly panels. That screws up using my ratio method comparing them with "normal" Isc per watts panels.
Anyway, the method does work, sort of, and you need a way to figure that. Or else just get "some solar" and find out what it does afterwards--luck of the draw sort of deal.
EDIT- adding:
Part 2
How to pick the controller size in amps you need. Going with the "rule" you need a 20% margin, and getting Isc amps at noon, use the ratio above for estimating your amps, then pick the controller amps.
eg, 250w will get 250/130 x 8.2a = 16a so you need a 20a controller.
Doesn't matter if that is PWM or MPPT, amps is amps. Note that we have reports that a single 230w panel with MPPT gets about 15a so it all works out. The other thing with controllers is voltage limit, which is different. I don't have a system for that--check the specs on their voltage limits before you buy once you have the amps right.
(You can print this)
It turns out there is a fairly good ratio for watts vs max amps and it is approx the same whether you have PWM or MPPT--just use the watts.
The trouble arose from the location and timing in the year when using solar. I thought what works here in summer would be the same down south in winter. Nope, winter is winter--a lot less sun time and sun not high enough.
Still, you need some sort of way to WAG how much solar you need, assuming the sun gets high enough for long enough where and when you are doing it.
Part 1
The magic formula is that 130w gets 8.2 amps (same as Isc) and that will get you approx 56AH/day flat, 70AH /day tilted pointing South. (actuals for May at 49N)
So if you need 100AH/day to get by, and your panels will be flat, you can go 100/56 x 130w = 232w
Doesn't matter if that is one 230w panel with MPPT or a collection of 12v panels with PWM, same answer. (close enough) Just use the watts.
Another wrinkle that showed up is those dratted DM panels that have high Voc and low Isc compared with most poly panels. That screws up using my ratio method comparing them with "normal" Isc per watts panels.
Anyway, the method does work, sort of, and you need a way to figure that. Or else just get "some solar" and find out what it does afterwards--luck of the draw sort of deal.
EDIT- adding:
Part 2
How to pick the controller size in amps you need. Going with the "rule" you need a 20% margin, and getting Isc amps at noon, use the ratio above for estimating your amps, then pick the controller amps.
eg, 250w will get 250/130 x 8.2a = 16a so you need a 20a controller.
Doesn't matter if that is PWM or MPPT, amps is amps. Note that we have reports that a single 230w panel with MPPT gets about 15a so it all works out. The other thing with controllers is voltage limit, which is different. I don't have a system for that--check the specs on their voltage limits before you buy once you have the amps right.
