How much wattage is enough? Also how long is a piece of string.....

L

LittleGreyCat

Joined
Feb 18, 2022
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Suffolk, UK
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MH
Rapido 9048DF 2016
I have been reading the discussions, and everyone seems to have a different opinion about how much wattage on a roof is enough.

The minimum seems to be 100W but some seem to have approaching a kilowatt on the roof.

Efficiency depends on the angle of the sun, so what is adequate for midsummer is not as effective in midwinter.

So how do you decide how much is enough?

One reason I am asking is because I am looking at a used motor home which comes with a 100W solar panel, and I'm wondering if this might need upgrading.

We aren't planning to camp off grid in the winter (but who knows?) but would like to be able to have the occasional off grid day or two in the summer.
No plans to run a hair drier or a microwave, mainly charging phones, running the heating.
 
It also depends a lot on what space there is available for additional panels on the roof and if you have space/ weight available for additional batteries Best to try with what you have first and see how it goes.
. (y)
 
We don't currently have any solar and a standard single leisure battery. But we manage perfectly OK parked up for 2 or 3 days during summer.

And if moving on reasonably regularly, again shouldn't have a problem.

So 100 watts of solar, although not the biggest, should make a useful contribution. (y)
 
Family of 4, I like it bright and kids have lots of tech. We use about 30amps a day in Summer off grid, perhaps 40 if we are wasteful with the inverter.

We have about 360 watts of solar, in full summer sun that gives 20 amps. Even a 100 watt panel will give you at least 4 amps. Say there is 5 hours of sun and a bit of cloud, I reckon you will put 30 amps back in. With good days, you will yield more than you will use in Summer even with 100 watt panel.

I think it’s more than enough.

Just to add, we have been off grid all this week in Scotland. We have travelled but stayed a couple of nights in places. Even with heating and all lights on plus inverter for laptop and toaster, we haven’t used more than 60amps a day.
 
Or the simple answer:- Twice as long as the middle to the end.
 
as much as you are willing to pay for.
Genuinely, going over kill as much as is reasonably possible physically and financially imho. If you're relying on it come Winter time / overcast days, a fraction of its sunny potential will be most welcome!

I have about 700W solar and still plan to add a little more. All depends on your own piece of string though obviously.
 
the answer is how much you want to use per day and work back why not fit a controller that will handle more than you think and less panels than you think as its easy to add panels if your not having to change controller each time
 
It's a law of diminishing returns.
100W was considered enough in the early days and, although modest by today's standards, is 'good enough'.
Clearly the length of your 'string' will depend on the size of what you want to wrap it around.
If you can replenish what 'leccy you use in a day with 100W, you don't need any more.
200W would recharge quicker but (Watts the point?-) the excess just goes to waste.
Fair weather sun-seekers will be fine with 100W and, if you move frequently, you may not need any at all.
Be aware that no matter how much you invest on solar, you won't get much return from it in Winter.
 
We've got 150 on the roof ,was going to add more but I've bought a free standing 100w which I think is better in winter because of the low sun.
 
cookie said:
We've got 150 on the roof ,was going to add more but I've bought a free standing 100w which I think is better in winter because of the low sun.
Click to expand...
Free standing would seem like a good idea for getting the light perpendicular to the sun and you can also keep it out of the shade.
Bear in mind that the amount of power from the sun is reduced by more of the atmosphere when low and it's around for much less time in Winter.
 
Thanks for all the replies.(y)(y)

For context, in our old 2002 Hymer B544 with a single leisure battery we ran out of juice the second day (I think) on an aire at Le Touquet.
MH next to us had a small Honda generator.

I doubled up the batteries, and eventually bought a small Honda generator, but was never off grid again for long enough to run out of juice.

Solar has always been something I would get around to soon.
Prompted by the 100W installation to think about getting another panel if the controller will take it.
Of course, I first have to buy the van.
 
Might be an idea to use it first, its a cart and horse situation. To get the benefits you need to balance batteries against solar. If one battery and 100 watts of solar That will keep you going in the summer with light use. If you have 200 watts of solar you could end up charging your 1 battery quickly but only have the same usable amount of storage. At best you will get 50 usable amps from a good 100 amp battery. If you have 2 100 amp batteries and 1 100 watt panel, you will have more capacity but longer to recharge.
 
LittleGreyCat said:
I have been reading the discussions, and everyone seems to have a different opinion about how much wattage on a roof is enough.

The minimum seems to be 100W but some seem to have approaching a kilowatt on the roof.

Efficiency depends on the angle of the sun, so what is adequate for midsummer is not as effective in midwinter.

So how do you decide how much is enough?

One reason I am asking is because I am looking at a used motor home which comes with a 100W solar panel, and I'm wondering if this might need upgrading.

We aren't planning to camp off grid in the winter (but who knows?) but would like to be able to have the occasional off grid day or two in the summer.
No plans to run a hair drier or a microwave, mainly charging phones, running the heating.
Click to expand...
For what you describe 100w is enough for you .


For me it's nowhere near enough .

Im fitting 600w tiltable to my self build , with the potential to double that if required.
 
We have 700 watts 200 amp lithium

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200w tilting on the roof and 150w freestanding...Serves me well..🌞🌞🌞🌞🌞
IMG_20220103_145641.jpg
 
If nobody above has mentioned it, might be worth looking at the style of solar controller you have. If it’s not a mppt then it would be a good upgrade to make.
 
It's a bit like asking how many BHP an engine ought to have. Some want loads and spend a fortune on tuning etc others manage in an old mini. If like us you have very little power requirements a 100w panel should be enough we managed the first 5 years without any panel and only got close to a flat battery once I only put the 100w panel on as it seemed like a good idea and I was bored in the first lockdown. If you get it and it's got plenty of space on the roof I would try with whats on there now and see if you need more or not. If like us you tend to use the MH mainly in the summer drive most days and stay mainly off grid you could be fine with just one panel as long as the battery is ok.
You could spend a lot on solar just in case you need it a weight upgrade just in case you need it a big battery bank b 2 b alarm e bikes etc etc but it depends how you feel.
 
First ten years we didn't have any solar and could easily last a week off grid without starting the engine with twin 110amp/hr batteries.
This can has an 85 watt panel on the roof and we've never needed any more.

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two said:
It's a law of diminishing returns.
100W was considered enough in the early days and, although modest by today's standards, is 'good enough'.
Clearly the length of your 'string' will depend on the size of what you want to wrap it around.
If you can replenish what 'leccy you use in a day with 100W, you don't need any more.
200W would recharge quicker but (Watts the point?-) the excess just goes to waste.
Fair weather sun-seekers will be fine with 100W and, if you move frequently, you may not need any at all.
Be aware that no matter how much you invest on solar, you won't get much return from it in Winter.
Click to expand...
i wouldnt call 45v / 10amps in Winter "not much"? Its certainly a fraction of its summer potential, but thats the point of getting as much as possible up there (so that in Winter you can still get by with it)
 
Calm Seas said:
i wouldnt call 45v / 10amps in Winter "not much"? Its certainly a fraction of its summer potential, but thats the point of getting as much as possible up there (so that in Winter you can still get by with it)
Click to expand...
Is that tilted? we have 540watts but still get next to nothing with them flat in winter.
 

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