Solar Panel one large or 2 small

[emjga]

Folks

T5 2011 with Pop up Top , Live in Scotland , 2 X 100Ah AGM batteries

Looking to get some solar for off grid which is my main reason for having the Van

Looking for some advise on whether to get one large panel or 2 / 3 smaller panels

The large panel is 270W as example
Solar panel specifications:

Peak power: 230W
Maximum power voltage: 25V
Maximum power current: 9.8A
Open circuit voltage: 34.9V
Short circuit current: 9.7A


The small panel is 100W as example
Solar panel specifications:

Peak power: 100W
Maximum power voltage: 18.2V
Maximum power current: 5.49A
Open circuit voltage: 21.4V
Short circuit current: 5.82A

So for the single panel on a good sunny day could produce 25Volts
However on a cloudy day this could drop by 50% to say 12.5Volts which is not enough to charge the AGM batteries ~14.4Volts

For the 2 x single panels wired in series on a good sunny day could produce 36Volts
However on a cloudy day this could drop by 50% to say 18Volts which is still enough to charge the AGM batteries ~14.4Volts

I think I have answered my own question , i.e 2 X 100W
However does anybody have any thoughts on not doing 2 X 100W


The only way I can see a single panel would work is a very large and expensive panel like this one 360W
Solar panel specifications:

Peak power: 360W
Maximum power voltage: 39.1V
Maximum power current: 9A
Open circuit voltage: 47.7V
Short circuit current: 9.0A

Thanks

Matt

 

[Deaky]

That’s not quite how it works. You will need an MPPT controller that will step up or down the voltage to the correct charging voltage and the current will vary according

 

[emjga]

That’s not quite how it works. You will need an MPPT controller that will step up or down the voltage to the correct charging voltage and the current will vary according

I know I will need a MPPT controller.
So from what you are saying it does not matter if the large panel is only producing half its output due to cloud etc.

The single 270W panel and MPPT will still charge the AGM batteries , or have I completely misunderstood (Properly)

 

[t0mb0]

Your voltage logic doesn't really hold, as it's the current that is strongly dependent on the levels of sun, and, as @Deaky says, the voltage is regulated by your MPPT anyway. However, both solutions will produce strongly diminishing current (and therefore power) as sunlight reduces. All other things being equal, you'll get slightly more out of the single panel simply because it's higher rated but with two panels you get some redundancy against failure (if wired in parallel), and possibly some marginally increased protection against shading if only one panel is shaded (although it likely is an extremely marginal benefit).

For what it's worth, I've got one which looks very much like your 270w option from photonics universe (although mine was quoted at 250w) and it's been excellent.

 

[Salty Spuds]

I know I will need a MPPT controller.
So from what you are saying it does not matter if the large panel is only producing half its output due to cloud etc.

The single 270W panel and MPPT will still charge the AGM batteries , or have I completely misunderstood (Properly)

If the panels are semi-flexible, go for the 2 smaller panels in parallel. This means that when one fails, as it inevitably will, you’ll have some redundancy.

 

[emjga]

Folks

Thanks , looks like I have dived opinion on One large or two small panels

On re-reading my original post and my notes , realized I should have said in Parallel for Two panels , Thanks Salty Spuds / T0mb0

It is going to be easer just to fit one panel , but more expensive I think
Will have to do some more costings and see what stacks up.

 

[DXX]

What @Salty Spuds said.

 

[Deaky]

It's the current that's important rather than the voltage, although the two are linked, but not linearly. Half the sunlight doesn't equate to half the voltage. The wattage of the panels is more important. Simply put, a 200w panel is two 100w panels on the same board. 2 separate 100w panels will give you redundancy if one fails but it's really swings and roundabouts. I've no doubt that there are theoretical gains form doing one or the other but in the real world you'll never notice them. In the real world a 200w panel will never produce 200w. Here is a screen shot of my 250w panel this morning totally overcast and parked up against the house but it's still producing 27v. Personally I'd go with what ever is easiest to fit and gives the most watts.

 

[t0mb0]

On the redundancy point of using two panels, the impact of having a failure is clearly reduced in the sense that you'd hopefully still have one functioning panel but the likelihood of having any single failure obviously increases - along with the associated hassle of having to replace it.

In any case, a good tip would be to apply a section of wrap to the roof you're putting the panel on - this will hugely reduce the hassle of changing a panel.

 

[emjga]

On the redundancy point of using two panels, the impact of having a failure is clearly reduced in the sense that you'd hopefully still have one functioning panel but the likelihood of having any single failure obviously increases - along with the associated hassle of having to replace it.

In any case, a good tip would be to apply a section of wrap to the roof you're putting the panel on - this will hugely reduce the hassle of changing a panel.

Never thought about Wrapping the roof.
Is it something that could be done as DIY

Would you have to wrap the whole roof or just the bit where the panel(s) is going to go plus a decent overlap

If so any suggestion on where to get the wrap from.

If it makes any difference it is a T5 Pop up top which is fiberglass in White
I dont have any photo's of the roof but over the weekend will take some and upload just in case.

 

[t0mb0]

Never thought about Wrapping the roof.
Is it something that could be done as DIY

Would you have to wrap the whole roof or just the bit where the panel(s) is going to go plus a decent overlap

If so any suggestion on where to get the wrap from.

If it makes any difference it is a T5 Pop up top which is fiberglass in White
I dont have any photo's of the roof but over the weekend will take some and upload just in case.

Just the bit the panels occupy, plus some overlap I guess.

 

[John7612]

Afternoon. I also live in Scotland and opted to have a panel put on to my camper 2 weeks ago. I opted for a 320w fixed non flexible panel. I want to a company called solar shack in Ashington. Colin who installed it is very passionate about all things solar and installed the panel etc once I added a replacement battery and Bluetooth etc it all came Inc fitting to £1k. Took around 5 hours to install. Just need to get out and about now.

 

[emjga]

Afternoon. I also live in Scotland and opted to have a panel put on to my camper 2 weeks ago. I opted for a 320w fixed non flexible panel. I want to a company called solar shack in Ashington. Colin who installed it is very passionate about all things solar and installed the panel etc once I added a replacement battery and Bluetooth etc it all came Inc fitting to £1k. Took around 5 hours to install. Just need to get out and about now.

Interesting

A Long way from Aberdeen but some of there pictures looked interesting
With what seems to be a 345W on a Pop up Top (VW Transporter) 345W Gray

I thought having a fixed panel would be a lot heaver and may effect the Pop Up Top
It would increase the Hight as well (Mind you I can NOT squeeze under a 2M barrier any way)

Might give them a call

 

[John7612]

Interesting

A Long way from Aberdeen but some of there pictures looked interesting
With what seems to be a 345W on a Pop up Top (VW Transporter) 345W Gray

I thought having a fixed panel would be a lot heaver and may effect the Pop Up Top
It would increase the Hight as well (Mind you I can NOT squeeze under a 2M barrier any way)

Might give them a call

I went from St Andrews (not as far as you) and used it as an opportunity to spend the night out in my van. There is a nature reserve type area where you can go for free. It’s a little walk around a lake which was nice and a place where you can grab breakfast in the morning. My pop top has a 60kg load limit. The panel including fixtures etc is around 20kg. There is just a little more resistance when you put the roof up. In terms of height it adds a little I would say no more than if you had roof rails and bars, just depends on were height sits in your priority that’s all.

 

[John7612]

My bad it was the 345w that I opted for (not sure where I got 310w from) and have the same roof as in the pic.

 

[John7612]

320w, need to stop doing this off my phone.

 

[Salty Spuds]

Interesting

A Long way from Aberdeen but some of there pictures looked interesting
With what seems to be a 345W on a Pop up Top (VW Transporter) 345W Gray

I thought having a fixed panel would be a lot heaver and may effect the Pop Up Top
It would increase the Hight as well (Mind you I can NOT squeeze under a 2M barrier any way)

Might give them a call

Having gone through 2 flexible panels & now on a rigid panel (on a poptop) I would go for a rigid panel from the get go.

 

[emjga]

Having gone through 2 flexible panels & now on a rigid panel (on a poptop) I would go for a rigid panel from the get go.

If you don't mind me asking.

Over what sort of time frame have you gone through 2 flexible panels

If say 10 years then not to bad I guess
If say 5 years then would give me some concern

 

[Salty Spuds]

If you don't mind me asking.

Over what sort of time frame have you gone through 2 flexible panels

If say 10 years then not to bad I guess
If say 5 years then would give me some concern

6 years/3 panels. The first lasted 18months & this was a “quality” Reimo factory fit on the poptop. The second was a replacement under warranty that lasted 2 years. I’m now on a rigid & won’t go back. The forum is full of tales of dead flexys.

 

[t0mb0]

They certainly fail enough to crop up on the forum but it's like all these things - people are rarely incentivised to create posts on how things haven't failed. I'd love to see hard data on the actual failure rate of flexible panels, especially by type and installation style.

I'm certainly not looking forward to the day if/when mine does fail though - will be a right PITA to replace as it was installed six years ago (probably one of the very first 250w photonics universe ones I think), before sticking a wrap on first was the done thing and they didn't skimp on the adhesive!