What size Solar panel?

[DL42846]

I'm thinking of adding another hab battery. I currently have a new 110 amp and I am thinking of adding another to give me 220 amps. I currently have a small solar panel, I think its 75W Any suggestions as to what size I would need for 220 amp batteries. ( They are GEL batteries) I don't think that makes any difference.

 

[Just smiffy]

The most you can get up on the roof is the best option....

 

[Just smiffy]

But seriously.... try and get as much Power up there as you can and look at getting a better panel to replace the one you have... I have two 95a AGM’s with 300w of solar on the roof, when my agm’s die which I’m told will be soon I’m going to buy 3 gel batteries to replace the two originals.... I have 3 victron controllers, one for each 100w panel...

I haven’t run out of power yet but the Mrs is power hungry (aren’t they all ) and I was a bit worried when the sun wasn’t shining for some time...

If your going to be off grid for any length of time it’s better to have too much then run out, because as you’ll probably know it’ll happen at the worst time...

I also think gels take longer to put the power back into them so the quicker it gets back in there the longer the batteries will last..

 

[Lenny HB]

If you are going to spend a lot of time off grid as Garry says get as much as you can get on the roof and pair them with a decent MPPT regulator such as a Votronic or Victron.

 

[DaveandJen]

We have a 200 watt solar panel on the roof parked up facing south during the winter months and it just about keeps the engine and habitation battery topped up with a small draw from the alarm and tracker.

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[Lenny HB]

I also think gels take longer to put the power back into them so the quicker it gets back in there the longer the batteries will last..

Yes Gels do take longer to charge but having more panels won't have as much effect as you think.
With a normal flooded cell they are almost fully charged when they reach 14 .2 -14.3 v decent chargers or solar regulators will then go into an absorption phase which with hold the voltage at 14.3 with the current limited to 1 or 2 amps for an hour to fully charge them.

With a Gel battery when the voltage reaches 14.3 it is only 80% charged and it needs a long absorption phase of at least 4 hours to fully charge, preferably longer.
Also Gel can't take as high charge rate as flooded cells but you are unlikely to charge them too fast with the amount of solar panels you can get on a Motorhome roof.

 

[tonyidle]

The correct amount of solar for any size of battery is the most you can squeeze into the available space on the roof and is only limited by that and the depth of your pocket .

 

[autorouter]

The ideal is to get enough solar power to top up the batteries every day, in the climate you are likely to experience. 100 watts of solar panel on a good summer day will produce 6 amps for 8 hours, possibly a bit more if you are lucky. That's 48 amp-hours.

Your 220 amp-hour gel batteries have a maximum useful capacity of 80% of that, ie 176 Ah. To recharge them in one day from the 20% level will need 176/48 = 3.7 100 watt panels, in other words 370 watts of solar.

It depends on what you use your batteries for. For example, are you getting an extra battery because one isn't enough for one day, or to give yourself more days at the same useage. Output from solar panels is extremely variable, and is nearly zero on a dull winter day.

 

[DL42846]

The ideal is to get enough solar power to top up the batteries every day, in the climate you are likely to experience. 100 watts of solar panel on a good summer day will produce 6 amps for 8 hours, possibly a bit more if you are lucky. That's 48 amp-hours.

Your 220 amp-hour gel batteries have a maximum useful capacity of 80% of that, ie 176 Ah. To recharge them in one day from the 20% level will need 176/48 = 3.7 100 watt panels, in other words 370 watts of solar.

It depends on what you use your batteries for. For example, are you getting an extra battery because one isn't enough for one day, or to give yourself more days at the same useage. Output from solar panels is extremely variable, and is nearly zero on a dull winter day.

On our previous MH we had one 110 amp GEL battery and a 120 w solar panel which worked fine. We rarely go on EHU, Aires or wild camp most of the time. We had a TV which we would use occasionally. With our newer van we have a satellite system which seems to draw more power and a smaller solar panel. We have woken up in the morning with a flat battery. I'm also about to install a Eberspacher type heater in our MH so I want to make sure we have sufficient battery power to run it over night. Nearly all out trips in the MH are here in France where we do have long sunny days. My thinking at the moment is to go for a larger solar panel, possibly one that would be able to charge two 110 amp GEL batteries if I decide to go for a second one.