Solar Panel Size To Battery Bank Size

Plan is fine.

"Sizing" to me is "how many panels can I get on my roof?"

Hi Roy;

What do you mean by " When it tapers back after about an hour of charge running then generator then I will be able switch to the solar panels."?

I have two solar systems(TT and TV) and the solar is never disconnected. Genny charging is done in parallel. The genny is shut down when it drops to idle.

HTH;
John

RoyB - great going on planning for that much solar on a popup. Ground mount solar panel means you can adjust angle to get maximum insolation. Ours are all roof mounted on 34' 5th wheel, but we have sufficient panels to mount flat.

Reed and Elaine

34' Open Range 337RLS 5th wheel (cheap but quite nice)
2006 Chevie 4x4 diesel (dualie) w/50 gallon Transferflo auxilliary tank
1.4 kW of panels (6 x 235 W): 2 sets of 3 x 235 W in series then parallel to
controller at 90 V
8.7 kW-hr (at 48 V nominal) LFP battery suite (7 kW-hr usable)
4.0 kW Magnum PSWI
1 kW Honda (only turn on every month or so to make sure it still works)

reed - The 50AMPS plus is coming from my on board Converter/charger unit run by the generator. When it tapers back after about an hour of charge running then generator then I will be able switch to the solar panels. I will only be getting just alittle over 20AMPS of DC CURRENT from the solar panels in high sun. I haven't added the panels yet but planning on putting two 120WATT Panels on the front on both sides of the Fantastic fan and then a 240WATT Panel across the rear of the roof between the Air Conditioner and the rear edge. That adds up to 460WATTS.

The 240WATT panel should be easy to move to the ground if needed. I may run into a weight problems adding these panels to roof and try to raise the electric roof when setting up. I may have to add the 240WATT PANEL after I raise the roof.

Some of the experts tell me I can almost make getting my batteries from 50% to 90% charge just using the solar panels for 5-6 hours of high sun. I'm glad I have the generator along me as I know that works every time rain or shine... During a typical day/night run I am pulling the usually 1-2AMPS parasitic loads an around 20AMPs load from 6PM to 11PM to run all the home entertainment, lights, and ham radio stuff. This drops my 255Ah battery bank down to around the 50% charge state by 8Am each morning.

All still in the planning stage here for solar - waiting for money to fall out of the sky hehe...

I've been camping off the power grid with my 255AH battery bank for 5-6 years now so know what to expect to keeping the batteries giving me great performance.

Adding solar panels will be a big help.

We also mostly camp off-road here on the East side of the US and have to live with all the generator run time rules everywhere. Adding solar panels should drop my daily generator run time down to around one hour hopefully.

Roy Ken

CT_WANDERER wrote:
When you pro's talk, having solar panels sized to battery amp size, are you referring to total battery capacity or the 50% useable battery capacity? I am working on my Solar system, I have a total house bank of switch-able 410AH on Bank#1(GC2) and 170AH Bank#2 (Group24). I plan on installing 5 X 120watt panels. I figure this should work good. Is my plan good? Thanks Gary

(I understand the question even though I do not agree with those who do relate their solar wattage to battery bank size as the way to do it.)

The answer is they use the full rated AH capacity of the bank, not just half of it.

Second question is whether 600w is enough for 580AH of bank. Answer is "It depends" on:
-how many AH you need to replace daily with the solar (as a side note, if you do some of that with the generator/charger, that would be less solar needed)
- how the panels are mounted flat or tilted
-your latitude, and time of year for how much sun you can expect. "Just enough" solar for summer is "not enough" for winter.

That AH replacement amount is the same no matter how many batteries you have. How many batteries you need is also related to your AH usage of course.

If the solar is doing some of the AH usage as "extra" as well as recharging the batts, then you won't need as many batts to stay above 50% .

But if some of that AH is high draw like microwave inverter then you might want more batteries to stay above the inverter's 11v shut off during the high draw times, even though for straight AH count, you don't need that many batteries to stay above 50% resting.

Solar amount and battery amount requirements are two separate calculations, but each is based on your daily AH usage.

Watch out for shade. Four panels in full sun probably produce more than 5 panels with one or two in partial shade.

CT Wanderer

"...When you pro's talk, having solar panels sized to battery amp size, are you referring to total battery capacity or the 50% useable battery capacity..."

Not a pro but a delighted user of solar. I believe that people are referring to total battery capacity and not the 50% usable capacity. Unfortunately, a lot of folks do not know the difference. I guess that your 580 AH battery suite is composed of 12 V batteries or about 7 kW-h total or 3.5 kW-h usable. You do have a 36' motorhome so you could easily install over 1 kW of panels. I think that there seems to be a rule-of-thumb of about 8 to 10 times total battery capacity to maximum solar power. Your planned ratio is about 11 so you are in the ball paark, but another one or two panels would not be a bad idea. Your panels are 12 V (more or less) and probably will be in parallel so that you have 12 V to 12 V which simplifies things.

We run 90 V from panels to battery suite since it reduces power loss, can use smaller cabling, and a smaller conroller (TriStar 45). Our battery bank is 48 V nominal.

Roy B

How do you get 600 W of solar on your popup or is that 50 amp charge rate from the generator. Absolutely agree with running generator in early morning to get the battery suite up and then let solar top off. This is what we did with earlier systems; however, we have a 34' 5th wheel with sufficient solar to top off the battery suite fairly early in the day.

Reed and Elaine

Plan is good.

For me, my planning is how much solar power I can get in the 5-6 hours of HIGH SUN to get my batteries back to at least their 90% charge state so I can make it through the next day/night run off my batteries.

My camping off the batteries is planned to not drop my batteries below 50% charge by 8AM the next morning when I can either start recharging them by running my 2KW generator to use the on-board smart mode charging from my converter/charger unit or depend on the solar panels being in high sun all day long.

To recharge my battery bank I see over 50AMP of DC charge at the initial re-charge state that starts tapering off to around 8AMPs of DC charge after an hour or so. Then i need to provide the 8AMPS charge state for an additional 2-3 hours to get my batteries back up to their 90% charge state. If I can't get to the 90% charge state I will not be able to make it through the night off my battery banks. My goal is to never drop below the 50% charge state over night.

It will take alot of solar panels if no generator is planned to be used. Consider a 120WATT Solar setup will only produce 5-6AMPS of DC Charge in high sun.

This is my game plan at any rate when camping off the power grid. Generator first for the short time running and then switch to solar for the long term charging. What ever it takes to get to 90% charge or more before the high sun goes away.

Roy Ken