Solar Panels: How many watts?

My scenario is about the same as above except my trailer is not 3 season.
I have 200 watts of solar with 2 GC2 batteries (225 AH total). They are usually at 70% in the morning and fully charged by mid afternoon.

I know everyone wants you to do complicated formulas. And even after you do that, the answer will still be different for each individual situation. Nothing wrong with doing the surveys, but you just want some point of reference to get your planning started. The geeks just love to overcomplicate stuff.

So here is my suggestion. Go with a minimum of 1 watt solar panel per 1 AH battery capacity. And figure a maximum of 2 watts solar panel per 1 AH battery capacity. Lean toward the smaller side if budget is important to you. Lean toward the larger side if you like a little overkill, and if you want a good charge on a less than good solar day.

But whatever you do, make sure you have a plan for adding more panels in the future.

400w solar is doing a great job on my 230AH battery bank, which is a pair of 6V. I could add another 200 to 400, because I planned the layout that way, but I've found that I don't need any more. At least not unless I add more batteries.

BFL13 wrote:

red31 wrote:
corrective equalization requires current, 60w/100ah maybe on the low side.

Assumes solar is the only charging method he has. For a weekend warrior it is valid to lose capacity every day with solar just slowing down how much you lose, then charge to full on shore power at home.

How much solar you need is all about scenario.

understood, what beside solar would they need to buy?

Well a wfco won't equalize, solar can so no need for additional charger.

hedgehopper wrote:

RedRocket204 wrote:
200W will get me by with limited usage of 12V items in the CO mountains, late fall boondocking. That includes 2-3 hours of some LED lighting, USB phone charging, CO detector, fridge running on propane, some water pump usage and the big one, heater fan kicking on with the thermostat set at 52f and outside temps dropping into the teens f. My TT is considered a 3-season trailer with decent insulation but I don't have separate tank heaters. With two Group 24 12V batteries, I do get pretty close to 50% discharge rate by the time the sun comes up.

This pretty well describes our situation except that we have a truck camper not a trailer.

Chances are then the "big one" of heater fan will be somewhat reduced for you since your TC is heating a smaller space than my 26' cabin with a slide-out. I also carry a 2000W Champion generator with me as a backup but you probably know that at 9,500', the generator doesn't produce the same amps as if I were camping thousands of feet lower. I did use it one day last fall when it was raining in the mtns, fired up the Plex server and TV and watched a couple movies. Per the mention of my preference for mounted panels, I am usually gone all day and return early evening so I like the security of having the panels bolted on top. I would not be around during the day to follow the sun with portable panels so it is of no benefit.

I still feel 200W of solar gets me by just fine and really believe two GC2 6V batteries will make a nice difference for my intended use. I will need to see if my battery usage will fully charge with the 200W solar and then make a choice. My charge controller can handle 400W which was intentional in the event I want to add some panels. If planed right, these systems can be somewhat modular so you don't have to go all out at first.

Boon Docker wrote:
My scenario is about the same as above except my trailer is not 3 season.
I have 200 watts of solar with 2 GC2 batteries (225 AH total). They are usually at 70% in the morning and fully charged by mid afternoon.

Yep, I really feel a couple of GC2 batteries will make a nice difference for my setup. My current Grp 24 batteries are getting on in age so time to replace this year. Actually just checked pricing for GC2 batteries at Costco today but will hold off until the season officially starts for me.

Hi 2112,

Since the battery is rated at 100 amp-hours (yeah only 50% you can use) then 60 watts is the bare minimum to equalize. 150 watts hits the 85% acceptance level of 12.5 amps for 100 amp-hours. I.E. more than 150 watts is only going to get you to 85% a tiny bit faster.

The 60 watts is only going to able equalize when the RV is in storage.

I was invited write a series of articles at freecampsites.net

https://freecampsites.net/adding-solar/

2112 wrote:

pianotuna wrote:
Some where between 60 and 150 watts per 100 amp-hours of storage.

Don

Can you clarify this? I have a 100Ah battery but 50 usable Ah. Would I consider 50 or 100 as my "storage"?

The question of 'how much solar' comes up in my circle from time to time.

I agree with performing a realistic audit

Thanks

As can be seen, size and number of panels can vary by your usage.
If you move around much, remember that roof mounted panels can charge while you travel, portables will be stowed away.
For a TC your limited on rooftop space, so try a single 100-160 watt panel, leaving yourself a space for a second one or even a third to be added later if needed. Run wire large enough to allow for as many panels as you can hold, and upsize the controller by the same amount.
The differences in 20 to 30 amp controllers and the associated wiring is minimal so upsize them to start with.

You can energy audit some things , but life changes, a cold snap may increase your need beyond what you allowed for, so start with one or two panels, and plan the layout to allow for a future increase if you have to.

time2roll wrote:
Kinda like asking how long is a rope.

... and how thick.
Not only he didn't tell the scenario (usage vs storage), he didn't tell the batteries capacity either.

To elaborate further - he didn't specify for how long, if this is a usage scenario. Short-term you could get away by increasing the bank to 3*110 AH . No solar. Not that a solar would hurt, though.

Just to add to your data set, here are our numbers -- we have two group 31 batteries with 110 amp hours each. We are minimalists when it comes to energy usage -- very little furnace usage. We can camp for a week at a time with our 120 watt portable panel, as long as there is about four hours of sunshine during the day.

The advantage of portable solar is that it is tilted properly and can be moved into the sun, while you are parked in the shade. The disadvantage is that you have to deploy it on arrival and pack it up when you leave.

red31 wrote:

BFL13 wrote:

red31 wrote:
corrective equalization requires current, 60w/100ah maybe on the low side.

Assumes solar is the only charging method he has. For a weekend warrior it is valid to lose capacity every day with solar just slowing down how much you lose, then charge to full on shore power at home.

How much solar you need is all about scenario.

understood, what beside solar would they need to buy?

Well a wfco won't equalize, solar can so no need for additional charger.

Solar equalizing is a special technique that requires a controller that can do 16.2 volts (for Trojan specs) in a controlled manner. You can also do it by-passing the controller and go direct, but have to watch it carefully and it might go too high before the equalizing is done, so you have to stop.

Also you are still camping, so you have to split the bank to ensure the batts being equalized are full before you start--that means take them off line and use the other part of the bank. Put the solar on the disconnected batts and get them to full at 14.8v then go to equalize at 16.2v needs to be enough sun that day to get it all done.

I have been through all that and it is a lot of bother and no certainty of getting it done in the spotty weather we have.

So, that means having a charger that can do it when you are on shore power and not using the batteries - not while camping-- and you need one that can do 16.2 volts on command. (example is PowerMax LK that is adjustable from 13-16.5 volts-there are others that could do it)

It is not easy to organize all that, so most folks will accept buying batteries more often instead, and consider that worth the extra money, since batteries are fairly cheap compared with a lot of other things to do with RVing.

RedRocket204 wrote:
With two Group 24 12V batteries, I do get pretty close to 50% discharge rate by the time the sun comes up.

I...will be changing up to (2) GC2 6V batteries

How much will that improve your battery capacity?