More Batteries or More Solar?

[Naughty Cal]

Thank you all for your help with the toilet questions.

 

Next question for you is a more batteries vs more solar question.

 

The motorhome we intend to buy only has the one leisure battery as standard but does come with a 150w solar panel and associated charge controller.

 

We have had no real dealings wit solar power with the boat so have no idea how much output a 150w panel will generate. So the first question I guess would be how much output would be expected from a single 150w panel?

 

We know that they are next to useless in the winter and won't generate anything worthwhile then but what is a good guesstimate of what it might produce in Spring, Summer and Autumn?

 

The next question is would we be better adding a second battery or would adding a second solar panel be more beneficial?

 

There really isn't much run off the battery. It will be the usual LED lights and water pumps, TV, stereo and fans for the gas heater but the fridge is 3 way and will be running on gas when we are "moored up" for the night away from hook up. So power consumption will be fairly minimal. We expect it will be a lot less than we used on the boat with the fridge being the main power consumer on that.

[Alan de Enfield]

21 minutes ago, Naughty Cal said:

We have had no real dealings wit solar power with the boat so have no idea how much output a 150w panel will generate. So the first question I guess would be how much output would be expected from a single 150w panel?

 

For summer time I work on 50% of the rated output for 50% of the daylight hours.

 

Take it as being 75 watts (say) 6Ah,

For a 14 hour day of sunlight (allowing for any clouds and odd days of rain) assume 7 hours.

 

6 Ah for 7 hours = 42Ah per day.

 

Autumn and Spring with (say) 10 hours of sunlight would be ~ 30Ah per day (but you do stand a higher chance of clouds and rain in Spring and Autumn.

 

My estimate is normally 'not far off' and, if anything' will be slightly on the low / conservative side, but better than relying on more and it fails to perform.

 

The only time solar performs anywhere near its rated values is midday, on the equator, with the panel facing directly upwards.

 

You will get much less 'Sun' in our latitudes of typically ~53 degrees North.

I purchased panels from Bimble which were built for Scandinavia and were rated as 'low light' panels. (Not that they worked in semi-darkness, but that they were designed for sunlight hitting them at lower angles of incidence as found at 55-60 degrees N)

Edited February 17, 2021 by Alan de Enfield

[Bigtwin]

2 hours ago, Naughty Cal said:

Next question for you is a more batteries vs more solar question.

 

The motorhome we intend to buy only has the one leisure battery as standard but does come with a 150w solar panel and associated charge controller.

 

Have you signed up here:

 

Motorhome Fun

 

Lots of experience on there too.

 

Ian

 

[frangar]

19 minutes ago, Bigtwin said:

 

Have you signed up here:

 

Motorhome Fun

 

Lots of experience on there too.

 

Ian

 

And if you pay for a subscription you did get a discount at Midsummer Energy for solar kit....It paid me to subscribe with the discount i got off my panels!...its made interesting reading for the last year comparing motorhomes to boats!

[Naughty Cal]

29 minutes ago, Bigtwin said:

 

Have you signed up here:

 

Motorhome Fun

 

Lots of experience on there too.

 

Ian

 

No I have joined a couple of sites but not that one.

 

Motorhomeists don't seem to be quite so on the ball with solar installations as narrowboatsists though. 

 

I have seen that much so far!

[peterboat]

Add another battery, my mate Dave has done the same thing and has with his limited use this year found it works out ok [his is a caravan now but did the same in his motorhome] When I get around to it I am going to do the same in my Type 3, my solar is 180 watts so not so different to yours

[doratheexplorer]

If you're mainly using it from April to September, and you intend to spend multiple nights in one location, get the solar panel.  A second battery is pointless is you're not producing enough power to charge both up.  You'll gradually knacker both batteries and be forking out £200ish every couple of years.  Another 150w panel will last 20 odd years and it will mean you don't need to worry about power any more, you'll be putting circa 80ah into the battery which is more than the usable capacity of the battery, rather than 40ah into two batteries with a combined usuable capacity of about 100ah.  So there's a fair chance that you'll be needing to run your engine of a genny.  The only downside for you only having 1 battery would be if you work it too hard with high powered appliances, like a hairdrier.  It doesn't sound like you're planning to do that, so get the panel.

[Naughty Cal]

13 minutes ago, doratheexplorer said:

If you're mainly using it from April to September, and you intend to spend multiple nights in one location, get the solar panel.  A second battery is pointless is you're not producing enough power to charge both up.  You'll gradually knacker both batteries and be forking out £200ish every couple of years.  Another 150w panel will last 20 odd years and it will mean you don't need to worry about power any more, you'll be putting circa 80ah into the battery which is more than the usable capacity of the battery, rather than 40ah into two batteries with a combined usuable capacity of about 100ah.  So there's a fair chance that you'll be needing to run your engine of a genny.  The only downside for you only having 1 battery would be if you work it too hard with high powered appliances, like a hairdrier.  It doesn't sound like you're planning to do that, so get the panel.

There will be no high powered appliances involved. We intend to be fully 12v or gas this time for off grid use.

 

I can't see us staying in one place for more than a couple of days max. We never did with the boat. The whole point of having the motorhome is to hop around from place to place.

 

I do think we will use it in the winter as well but that is likely to just be weekend use and a night here and there at a local Britstop. Our main use will most likely be March through to October or November. 

[Bigtwin]

1 hour ago, Naughty Cal said:

No I have joined a couple of sites but not that one.

 

Motorhomeists don't seem to be quite so on the ball with solar installations as narrowboatsists though. 

 

I have seen that much so far!

 

It is, by far, the biggest one.

 

The trick with all fora though is sorting the wheat from the chaff in terms of which members know their onions.

 

Ian

[peterboat]

52 minutes ago, Naughty Cal said:

There will be no high powered appliances involved. We intend to be fully 12v or gas this time for off grid use.

 

I can't see us staying in one place for more than a couple of days max. We never did with the boat. The whole point of having the motorhome is to hop around from place to place.

 

I do think we will use it in the winter as well but that is likely to just be weekend use and a night here and there at a local Britstop. Our main use will most likely be March through to October or November. 

Defo for the extra battery then, your driving will charge it and the solar will keep it topped up nicely 

[Bigtwin]

2 hours ago, peterboat said:

Defo for the extra battery then, your driving will charge it and the solar will keep it topped up nicely 

 

Driving puts very little into the leisure batteries unless you fit a B2B and, perhaps, could be part of the solution.

 

Ian

[peterboat]

1 minute ago, Bigtwin said:

 

Driving puts very little into the leisure batteries unless you fit a B2B and, perhaps, could be part of the solution.

 

Ian

Seems to work ok on my VW, never have a flat battery anyway, 100 amp relay i think and big wiring works fine and way cheaper than a B2B

[Tony Brooks]

4 minutes ago, Bigtwin said:

 

Driving puts very little into the leisure batteries unless you fit a B2B and, perhaps, could be part of the solution.

 

Ian

 

Upon what do you base that statement?

 

The engine battery will spend most of its time all but fully charged as long as the engine is in reasonable fettle. It only takes a few Ah to start the engine. A lot of amps but for a very short time.  The domestic battery(ies) will normally be far more discharged after a night's use with no charge. This means that if you have a split charge relay or a VSR the current flow into the batteries will be proportional to their state of discharge  so the domestic battery will take more of the available alternator output. If you use a passive split charge diode it will degrade the charge to both banks.

 

I think that to give a sensible answer we need to have a lot more information about exactly how the caravan will be used. Without that information I would tend to go with @peterboat . If the intention is to stay on site with no hookup for days then I may well go for more solar.

 

 

[Bigtwin]

1 minute ago, Tony Brooks said:

 

Upon what do you base that statement?

 

The engine battery will spend most of its time all but fully charged as long as the engine is in reasonable fettle. It only takes a few Ah to start the engine. A lot of amps but for a very short time.  The domestic battery(ies) will normally be far more discharged after a night's use with no charge. This means that if you have a split charge relay or a VSR the current flow into the batteries will be proportional to their state of discharge  so the domestic battery will take more of the available alternator output. If you use a passive split charge diode it will degrade the charge to both banks.

 

I think that to give a sensible answer we need to have a lot more information about exactly how the caravan will be used. Without that information I would tend to go with @peterboat . If the intention is to stay on site with no hookup for days then I may well go for more solar.

 

 

 

I understood that the alternator output was, essentially, governed by the vehicle battery which, as you say, is discharged very little so the alternator ’throttles back’ relatively quickly and, consequently, very little charge ends up going into the leisure batteries.

 

Have I got that wrong or is that why @peterboat uses the workaround that he does?

 

Ian

[Tony Brooks]

13 minutes ago, Bigtwin said:

 

I understood that the alternator output was, essentially, governed by the vehicle battery which, as you say, is discharged very little so the alternator ’throttles back’ relatively quickly and, consequently, very little charge ends up going into the leisure batteries.

 

Have I got that wrong or is that why @peterboat uses the workaround that he does?

 

Ian

 

It all depends upon exactly what charge splitter you are using and how its wired. In any case for maximum life of the splitter the alternator should be rewired to charge the domestic bank and the SCR or VSR used to charge the engine battery. Be aware that on a modern vehicle with the alternator controlled by the engine ECU you may need more complex and expensive equipment.

 

Taking basic 9 diode alternators and common 6 diode ones. The charging voltage is inversely proportional to the charging voltage and the batteries basically control the current that can flow at any given voltage. As the current starts to approach the alternator's maximum output the charging voltage automatically falls. As the batteries (all of them) charge the current they will accept falls and as it does so the voltage rises until it gets close to the alternator's regulated voltage and at that point the regulator start to control the charging voltage to the regulated voltage. All the alternator sees is just one large battery so  it has no idea if it's an engine battery, domestic battery, or all of them. Each bank will take the charge it wants (providing in total it less than the alternator's rated output) in proportion to the degree of battery discharge.

 

You may need a B2B on an ECU controlled alternator though. I don't know enough about how they sense and work to be sure.

 

Peter is just employing best practice that I fear many commercial builders will not on grounds of cost. In fact as you can get 140 amp relays I would use one of those. Any cause of volt drop on the charging circuit will adversely affect the charging.

Edited February 17, 2021 by Tony Brooks

[LadyG]

Slim Potatohead on youtube has a truck and trailer, he is very good at innovative ideas. 

[peterboat]

21 minutes ago, LadyG said:

Slim Potatohead on youtube has a truck and trailer, he is very good at innovative ideas. 

Their is an issue the motorhome will be brand new with a warranty, so whatever NC does can't invalidate the warranty.

[nicknorman]

The other thing to consider with a new vehicle is the start stop system and how that affects charging. The alternator is controlled by the engine ECU and most of the time, keeps the battery well below 100%, so it can be topped up under regenerative braking. I suspect this will mean a bolt on leisure battery won’t get well charged. But of course it is quite possible the motor home builders have thought of that and fitted a B2B etc. But I would be asking the question.

[Richard10002]

Assuming you aren’t short of the odd hundred quid here and there, I would get the extra solar and a second battery. I would worry that one battery wouldn’t provide enough power for a day or two of use, and one solar panel won’t provide enough power to keep two batteries topped up.

[Naughty Cal]

6 hours ago, Richard10002 said:

Assuming you aren’t short of the odd hundred quid here and there, I would get the extra solar and a second battery. I would worry that one battery wouldn’t provide enough power for a day or two of use, and one solar panel won’t provide enough power to keep two batteries topped up.

Ideally we would do that but we only have a 520kg payload to play with so we need to keep the weight down. 

 

One or the other would be better.

[Bacchus]

It all depends on how you use the vehicle. I would be tempted to see whether it's a problem first. Either do a full power audit, or just use the thing - suck it and see.

 

On my old Hymer I had a gas fridge, a single 80AH house battery (you don't say what size yours will be, size does make a difference whatever you've been told...), old fashioned split-charge relay, incandescent lights, and no solar; never had an issue, but we used to use it for touring. Never free-camped anywhere for more than one or two nights - if it was going to be longer than that we would generally use a site for the facilities so had hook-up. The only draw really was the lights. Laptops, cameras, phones etc. charged during the day's driving.

 

On the mighty Nissan I have two 120AH AGMs (deeper cycle), LED lighting, but a 12v fridge (mobicool cold box - c. 30AH/day in hot weather). Again I will rarely stay for more than one or two nights in one place and have never dropped below 50% SOC even using a laptop all day whilst parked up.

 

I fitted a Ring B2B charger in the Nissan (because it has a "smart" alternator) which is a brilliant bit of kit - fit and forget (fit, test, and forget...) - and has a separate input for solar/other. I have just bought a 200W panel from eBay, but that will go in the boot rather than permanently on the roof so I can top up if necessary (and put the panel in the sun but park in the shade!)

 

I genuinely suspect that you will have enough for "leisure" use and wouldn't worry about it. Your payload is really small (two adults, pots and pans, 70l of water, 70l of diesel, a couple of mountain bikes... soon adds up!), and batteries are heavy. If you go away in winter it is unlikely that you will be free-camping without facilities for long, even skiing a lot of the aires have hook-up (and solar doesn't work under a foot of snow)

 

Also second Motorhome Fun. Don't call anyone a knob however much of a knob they're being because you will get banned for life (ask me how I know...), but I had a lot of fun there and learned a hell of a lot. The sister site diymotorhome.co.uk is great for techie stuff and is free, but the owner is a bit precious -- he tends to use it as a sandbox for software upgrades etc. and did shut it down for a while after an argument with one of the regulars (not me)

 

Look forward to hearing how you get on.

 

 

[peterboat]

1 hour ago, Naughty Cal said:

Ideally we would do that but we only have a 520kg payload to play with so we need to keep the weight down. 

 

One or the other would be better.

Then as i said at the beginning the extra battery will work best as you are moving so it will charge up then. Solar will keep it topped up

[Alan de Enfield]

2 hours ago, Naughty Cal said:

Ideally we would do that but we only have a 520kg payload to play with so we need to keep the weight down. 

 

Do you have a 3.5 tonne licence or are you old enough to have a 7.5 tonne licence ?

I sold this last year for my Brother In Law, it was 'huge' with loads of stuff, including a 7.5KVA built in generator.

 

We were both driving this on a 'car' licence.

 

Amazing machine - no need for a wheel jack - it had hydraulic levellers on each corner which dropped down and you could 'lift it off the ground' with them.

 

 

Edited February 18, 2021 by Alan de Enfield

[doratheexplorer]

16 hours ago, Naughty Cal said:

There will be no high powered appliances involved. We intend to be fully 12v or gas this time for off grid use.

 

I can't see us staying in one place for more than a couple of days max. We never did with the boat. The whole point of having the motorhome is to hop around from place to place.

 

I do think we will use it in the winter as well but that is likely to just be weekend use and a night here and there at a local Britstop. Our main use will most likely be March through to October or November. 

Then you don't need either.  Spend the money on booze.

[Guest]

I would definitely be tempted just to see how things go.

 

We dont 'wild camp' but we used to rally with no 240v hook up with the caravan club. A single battery would regularly get us through a weekend, sometimes longer. That was just running water pump, TV and lights. Back then the lights were not LED and we had no solar as it was virtually unknown.

 

Your heating will draw for the pump if its wet central heating or the blower if its blown air so winter with lower solar input might prove a challenge but I wouldnt rush to do anything untill youve tried it a few times or as has been suggested doing a power audit.