I currently have 2 renogy 100 watt solar panels and a 20 amp charge controller and very happy with equipment and output. Plan on doing more boondocking this year so am going to install another 100 watt panel. I know my controller can handle up to 400 watts. I have 2 -100 amp deep cycle house batteries. My question is with the increased output am I better off keeping just the 2 batts or adding another house battery. Thanks New York Newbie

“More” boondocking isn’t the criteria for an additional battery. An adequate solar system recharges fully your batteries almost every day. Adequate batteries supply all the reasonable power you need each day. With 300 solar watts and an anticipated 300 battery amp hours, you meet the minimum on panels.

I had 300 watts on my other mh and added 2 mote deep cycle batterys. I had plenty of power and used the gen set rarely. I now have a newer mh and will be putting 680 watts and 2 extra batterys on it with a 30 amp controller

A possible 680 solar watts running through a 30 amp solar controller? That isn’t wise IMO. At 5.6 amps per 100 watts...38 or so possible amps. Yes, some controller manufacturers say the controller won’t be harmed but I wouldn’t try it.

I think you are looking at this wrong. To start with you should have a big enough battery bank to last a couple days in case you have a very cloudy day. Then you need enough solar to charge your battery bank. I have 1 watt of solar for each amp of battery, some will say that you need 1.5 or 2 watts per amp.

so according to your formula if solar panels are 300 watts then 2 100 amp batts would be 1.5 watts per amp which tells me not to add another battery.

solar add on and batteries | Good Sam Community

Lwiddis
Explorer II
Jun 21, 2020
“More” boondocking isn’t the criteria for an additional battery. An adequate solar system recharges fully your batteries almost every day. Adequate batteries supply all the reasonable power you need each day. With 300 solar watts and an anticipated 300 battery amp hours, you meet the minimum on panels.
madjack60
Explorer
Jun 21, 2020
I had 300 watts on my other mh and added 2 mote deep cycle batterys. I had plenty of power and used the gen set rarely. I now have a newer mh and will be putting 680 watts and 2 extra batterys on it with a 30 amp controller
Lwiddis
Explorer II
Jun 21, 2020
A possible 680 solar watts running through a 30 amp solar controller? That isn’t wise IMO. At 5.6 amps per 100 watts...38 or so possible amps. Yes, some controller manufacturers say the controller won’t be harmed but I wouldn’t try it.
corvettekent
Explorer
Jun 21, 2020
I think you are looking at this wrong. To start with you should have a big enough battery bank to last a couple days in case you have a very cloudy day. Then you need enough solar to charge your battery bank.

I have 1 watt of solar for each amp of battery, some will say that you need 1.5 or 2 watts per amp.
JR51
Explorer
Jun 21, 2020
so according to your formula if solar panels are 300 watts then 2 100 amp batts would be 1.5 watts per amp which tells me not to add another battery.
Flyfasteddie
Explorer
Jun 21, 2020
I think 300w and 200a capacity is perfect. I have 1.5 to 1 and it works terrific for me.
BFL13
Explorer II
Jun 21, 2020
I wish you guys would stop saying "amp" instead of "amp-hour". It suggests you are clueless and won't understand any answers you get to your questions. Since that is probably not the case, just use proper terms. Thank you.
pauldub
Explorer
Jun 21, 2020
How do you know your controller can handle up to 400 watts? 20a X 12v = 240 watts.
MEXICOWANDERER
Explorer
Jun 21, 2020
Overthinking this will surely lead to disappointment. It depends exactly where you live

THEN start calculating

Coastal fog and cloudiness along the Pacific coast for instance, may allow for a three-hour charging window. Central plains, afternoon thunderstorms may limit a charging window to a few hours. September sunlight is quite a bit shorter than summer solstice time. Use wisdom.
corvettekent
Explorer
Jun 21, 2020
JR51 wrote:
so according to your formula if solar panels are 300 watts then 2 100 amp batts would be 1.5 watts per amp which tells me not to add another battery.

Your system will work fine with 200 amp hrs of batteries but if you feel that you need more battery capacity 300 amp hrs would just as well and you would have some reserve for a cloudy day.