Thinking About A Solar Panel? Look At This.....

[Pete C]

Thanks both.

I see where I got confused as I was using A and Ah interchangeably to work out my max current for cable sizing which hopefully is correct as 45A is 45A regardless of how long it takes to flow.

So I have calculated my total Amps over a 24 hour period on the basis that it gives me a max Ah for battery and solar power sizing. i.e. 0.5A per hour for 3 hours gives me 1.5A over 3 hours. Presumably this would equate to 1.5/3 = 0.5Ah.

I think that what the fridge has been hard to calculate as the documents read on it have 1.73A/h over 24 hours, which I took to mean 1.73Ah per hour for 24 hr and hence 40 odd amps per day.

Cheers,

Not quite - you are still mixing the units up.

0.5A for 3 hours is 1.5Ah

1.73Ah over 24 hours means an average of 1.73A in each hour. So over 24 hrs it will use 24*1.73 = 41.52 Ah in a day

Pete

 

[Sniggib]

Sniggib, you are so of correct in that yes the total amps drawing from device will say 1.73Ah per hour MAX, but that is if it is cooling down stuff added. Once the fridge reaches max -temp it will start to withdrawn less amps from battery. So...... may drop down to less than 1amp............. until you open lid to remove or add something.
I would say (do have my van yet) that if used on battery 24hrs a day the draw on battery would be closer to 24amps across the whole period. I have owned until last week a motorhome for the passed 12 years and have a good understanding of batteries. My last bank for 300amps worth of batteries lasted for 7 years before failing.
I intend to add solar power to my van as I had with old motorhome. I have 300watts of solar good sunny day in Spain would have battery fully charged (not topped up) by midday. This was whilst watching TV and charging phones, iPads etc. If your not going to use EHU then solar is the way ahead.

Thanks, yes I have found fridges the hardest thing to calculate so far. Partly because as you say I imagine the 1.73Ah is a maximum, but it then states an average over 24 hours which makes the 41.52Ah total in a day, which seems a lot for a fridge which is considered 'low power'! I am planning for the worst i.e max amps and hoping for the best!

Going for solar and split charge set up rather than relying on EHU. Working on my amp draw (using max with fridge) then its approx. 50Ah per day. So will be using two batteries and the 200W solar to keep things topped up. In winter, we wont have the fridge on so will drop the Ah to approx. 10 Ah per day so should last us a lot longer and get charged up as we drive around every few days or so.

Cheers

 

[Qnapper]

Remember that to draw 50Ah you will need a 100amp hr battery and even then that's getting close to killing the battery or worst shorting the life of the battery as no battery should be discharged below 50% of the total amps, unless you are using lithium to replace AGM's and that is a whole other story.............
So in your case you will need 2 x 100amp batteries which will give you 100amps of usable power to take out of the batteries. Then there is the solar panels to charge NOT top up the batteries you will need 300/400 watts of panel power, however in the UK sun....... on a good day you might not get enough to charge the batteries back up only top them up. The batteries need charging every few days and most people fail to understand this thinking that solar will do it all. If you were living in Spain (as I do) then yes 4/5 hours and my batteries were fully charged and ready for whatever I took out.
Then there is the charging system used by VW. My understanding so far reading the forum is that VW charging system only charges the batteries to 80% to allow for driving time and regen (chargers whilst breaking) so again you are not getting a 100% after driving from A to B.
When I get my van I will be adding solar on roof and Ctek charger as well as an inverter to ensure I get the best out of the batteries. It's all a black art..............

 

[Sniggib]

Remember that to draw 50Ah you will need a 100apm hr battery and even then that's getting close to killing the battery or worst shorting the life of the battery as no battery should be discharged below 50% of the total amps, unless you are using lithium to replace AGM's and that is a whole other story.............
So in your case you will need 2 x 100amp batteries which will give you 100amps of usable power to take out of the batteries. Then there is the solar panels to change NOT top up the batteries you will need 300/400 watts of panel power, however in the UK sun....... on a good day you might not get enough to charge the batteries back up only top them up. The batteries need charging every few days and most people fail to understand this thinking that solar will do it all. If you were living in Spain (as I do) then yes 4/5 hours and my batteries were fully charged and ready for whatever I took out.
Then there is the charging system used by VW. My understanding so far reading the forum is that VW charging system only charges the batteries to 80% to allow for driving time and regen (chargers whilst breaking) so again you are not getting a 100% after driving from A to B.
When I get my van I will be adding solar on roof and Ctek charger as well as an inverter to ensure I get the best out of the batteries. It's all a black art..............

Thanks.

Yes, batteries are next on the research list!

Looking at 2x batteries, likely 2x 80Ah - 100Ah, to give me a capacity of 80Ah, to 100Ah. Depends what will fit where id like them to go, might have to be a compromise haha!

Yes it does indeed seem a black art! I've gone for the CTEK, which is why I'm trying to keep solar in line with that. My hope is that the 200W solar in summer will top the batteries up enough to keep things happy, and then trips in the day will also top up via split charge. Worst case is I will get a portable EHU (already on the cards for occasional EHU sites) and a battery charger. Saves on having the EHU kit taking up space all the time and another hole in the van side (don't really like the look of the EHU ports for occasional use).

In winter, the solar is really just to be used to trickle in to top the batteries up when the Van is on the drive, and will have to monitor more closely when using it in winter.

Just getting my wiring diagram drawn up and then ill start a build thread I think!

Cheers

 

[Phil_G]

I see where I got confused as I was using A and Ah interchangeably .... So I have calculated my total Amps over a 24 hour period

You're still not quite there, theres no such animal as "total amps over a 24 hr period", an amp is an instantaneous value, it has no time factor. You could calculate the 'total amps' when all your appliances are switched on, again thats an instantaneous measurement, the sum of all the individual currents drawn by your appliances at any moment. For fridge calculations, or any other non-constant drain, you need to work out its amp/hour usage over a long period of time, ie several duty cycles. Say for example a fridge uses 5 amps when its running, and it happens to have a twelve minute cycle, 2 minutes on and 10 minutes off. Thats 1:5 duty cycle so over any long period of time it will average one-fifth of its instantaneous current, which in this example would be one amp. In 24 hours this average current equates to 24 amp hours (average current x time) and that is what you use in your calculations

Its also good advice from Pete & Qnapper, when doing theses calculations assume your batteries have at best 50% of their claimed capacity.

To continue the example, say you have a 96Ah battery. 'Safe' capacity is 48Ah. If your fridge is using 24Ah per day, then it will last 2 days, assuming no solar input and ignoring any other current draw such as lights etc.

Cheers
Phil

 

[Phil_G]

Sorry just realised Pete had already picked this up

 

[Sniggib]

Questions on solar fuses if I may.

Do you need to put a fuse between the solar panels and the controller (in my case the CTEK DC-DC with MPPT).

Cheers,

 

[Phil_G]

Theres no need, they're inherently current-limiting since their equivalent series resistance is high compared to a battery.
Short a battery and its fireworks. Short a panel and nothing happens, thats what the Isc spec means.

 

[KtmDuke]

Solar panels are the way forward. I haven’t used mains hook up since installing one. I’m not even sure I really need leisure battery charging from the alternator.

Is that CTEK gizmo just measuring voltage though across the battery though? If so, how on earth is it measuring accurate charge during charge/discharge cycles?

Hello, I'm Sandi and I am new to your forum. Actually any forum!!
So I hope it is ok to ask a question here.
I want to put a solar panel on the roof of my T6 hightop. My concern is whether it would cause damage to the roof whilst traveling, due to the vibrations.
I thank everyone for any advice you can give..

 

[t0mb0]

Hello, I'm Sandi and I am new to your forum. Actually any forum!!
So I hope it is ok to ask a question here.
I want to put a solar panel on the roof of my T6 hightop. My concern is whether it would cause damage to the roof whilst traveling, due to the vibrations.
I thank everyone for any advice you can give..

No, a correctly installed solar panel would be fine. Most people use a semi-flexible panel and stick them to the roof.

 

[KtmDuke]

Thank you for your reply.. I am thinking of a 300w rigid panel, bonded to the roof by the corner mounts.

 

[Skyliner33]

Thank you for your reply.. I am thinking of a 300w rigid panel, bonded to the roof by the corner mounts.

Bare in mind the roof isnt flat and for a panel that size the curvature might some onto play.

 

[KtmDuke]

Thank you. Yes that is certainly something I will need to think about..
Whatever panel I get, I will mount on corner brackets so hopefully any curvature would just go under the panel.
So long as it doesn't vibrate whilst travelling, thus causing damage. As I will be driving a lot of miles with it. But I wi use a lot of sealant to keep it in place..

 

[Skyliner33]

Thank you. Yes that is certainly something I will need to think about..
Whatever panel I get, I will mount on corner brackets so hopefully any curvature would just go under the panel.
So long as it doesn't vibrate whilst travelling, thus causing damage. As I will be driving a lot of miles with it. But I wi use a lot of sealant to keep it in place..

The corner brackets that the panels sit on are not that thick, Are you planing to bond the rigid panel to the roof with sealant? Why not put one of the semi flexible ones on then?

 

[KtmDuke]

I haven't looked I to the semi rigid ones yet. I will rectify that and have a browse. I think the last panel I fitted on my caravan, had about a 2" clearance, do you think the roof curvature would be more than that? The only reason I raised the question was because the garage that I'm purchasing the van from, said I couldn't out panels on it, because it would damage the fibreglass roof. But several good points have been raised, so I will do a bit more research.
Thanks to all that are helping me here..

 

[Skyliner33]

I haven't looked I to the semi rigid ones yet. I will rectify that and have a browse. I think the last panel I fitted on my caravan, had about a 2" clearance, do you think the roof curvature would be more than that? The only reason I raised the question was because the garage that I'm purchasing the van from, said I couldn't out panels on it, because it would damage the fibreglass roof. But several good points have been raised, so I will do a bit more research.
Thanks to all that are helping me here..

Ah, I didn’t realise it wasn’t a standard roof. Pics might be useful for people to help.

 

[KtmDuke]

Ah, I didn’t realise it wasn’t a standard roof. Pics might be useful for people to help.

I hadn't realised either until the garage told me last night. I haven't collected the van yet. But will definitely post some pics once I do..

 

[Big.mac]

I hadn't realised either until the garage told me last night. I haven't collected the van yet. But will definitely post some pics once I do..

This is a semi flexible panel stuck down onto my roof. Mine is the standard van roof not a pop top. My local converter fits these same panels onto pop tops fairly regularly. I’d be surprised if you can’t do the same thing.

 

[KtmDuke]

Skyliner, thank you that is really handy. Where do the cables run??

 

[Big.mac]

The cable is rear entry on this particular panel so on my van it goes through the roof under the panel and is then routed down the B Pillar to my DC-DC MPPT charger which is under the drivers seat.
I robbed a few pictures showing these same panels on pop tops for you. There is also a picture showing where the cable attaches to the panel which may help.
I bought mine here:

12V solar panels charging kits for caravans, motorhomes, boats, yachts, marine

12V solar panel solar charging kits for motorhome caravan boat campervan yacht marine off-grid

www.photonicuniverse.com

Mine is actually a 180 Watt version.