Solar Panels: How many watts?

profdant139 wrote:
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.

My semi-portable solution:



I can lift the panels off by pulling two pins in each panel and set them out in the sun. If that side of the coach is in the sun, I can leave them in place and tilt them up. I also have a panel permanently installed on the roof. For a total of 385 watts.

hedgehopper wrote:

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?

I forget the exact amp hour rating on my batteries. Grp 24 are usually in the range of 70-85 amp hours each. So lets say 80 amp hours each, 12V are run in parallel so the amp hours are added together for 160 amp hours.

With two GC2 batteries, 6V run in series to add the voltage to 12V and you maintain your amp hours rating which is usually around 225 amp hours. So a significant increase in amp hours by just changing the batteries.

There is a very minor footprint change from Grp 24 to GC2, mainly the height impacts most. Some general dimensions:

Grp 24: 11.13" 6.60" 9.25" LxWxH
GC2: 10.38" 7.13" 10.88" LxWxH

batterystuff.com - List of Common Battery Case Sizes by BCI Group Number

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?

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.

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.

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.

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.

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

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.

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.