Solar panels UNDER roof rack!?

[Slunkie]

Any thoughts on fitting solar panels under a roof rack, a rhino in my case which has quite narrow cross bars?



Yes I know, it's daft. There will be shading. But....I sometimes need the whole roof rack for kayaks/sailing dinghy although most of the time it's empty, so I'm looking for a compromise.

My power usage isn't massive, a small fridge and charging the phone/laptop when camping. I already have a Renogy 50ah lifepo4 battery and 50 amp DC-DC MPPT charger. I was thinking if I got 2x200w panels, even if there is a bit of shade from the cross bars there would still be a reasonable area unshaded for my power requirements? It's a LWB so I might even fit more than 400w.

I've read that shading can make a huge difference which is obvious really, but it's not clear in what context that is meant i.e. clouds filtering all light Vs intermittent obstructions.

Thoughts please.

Cheers

 

[Kind of Blue]

Under a rack or bars, is something that I considered. Out of the way, some protection and still able to carry freight!

 

[JumpShip]

I had also thought about this but thought the shading would be too much of an issue....unlike you I didn't ask the question though
Best of both worlds really if it'll work

 

[soldas]

I'd expect pretty poor performance. But as you say if you get say 400w in panels you might be able to expect 100w through on a good day.

I have seen some videos online where people have had really poor performance with just a little bit of shadowing.

I don't think there is a set formula. 200w panel, 25% shaded gives you 150w kind of thing. I think the performance is worse than that when the full panel isn't exposed.

But if are looking for a little trickle change kind if thing then you might be able to get enough...in the summer!

 

[Dellmassive]

the shading from that rack will servierly reduce the output power. . . if your happy with 10-20% output then fine.

if not id say look at adding a mobile panel or beef up your dc-dc charger.

 

[TallPaul_S]

the shading from that rack will servierly reduce the output power. . . if your happy with 10-20% output then fine.

if not id say look at adding a mobile panel or beef up your dc-dc charger.

This, wot 'e said.

Just one bit of shade on a panel over a few cells can reduce the outout by 40% easily, so that roof rack with shade over multiple bits of the whole panel, at a guess I'd say you'll maybe get 25-50w (maybe less) from the 400w on a perfect day when you would be betting 350+w.

Some panels do cope better with shading that others but it's not going to be great.

See this video as an example: 150w panel, 90w with no shadows, 60w with one roof bar across the panel.

To find a better solution, firstly - your power usage and battery: a fridge if left on all day with use 25Ah per day. You've only got a 50Ah LifePO4 which is quite small - so the fridge will drain half the battery a day. So if you'll need a decent sized solar panel to keep you going.

How do your kayak etc mount to the rack? Could you mount it on one side of the rack, leaving the other side for a long, slim panel? Like this:


Or you could possibly use mounting pads etc that would have the kayak sit over the top of the solar panel.

 

[Stay Frosty]

Two 200 watt panels might be a bit ambitious too as the Transporter roof is tiny as soon as you wave a solar panel near it, this is two Renogy 175 watt flexy panels...

 

[TallPaul_S]

Just some ideas, I've mounted a 305w rigid panel to my rack, and left a space at the side and back. The rear space is for my bag which has my chairs/table/windscreen cover/leveling ramps inside it. And the space to the side I'd use with either a vertical surfboard rack, or bike fork mount if I needed to carry a surfboard or (an)other bike on the roof.




I could probably fashion up some pads to mount a surfboard over the panel without too much issue, too.

 

[ginkster]

As mentioned it’ll have a big impact on output, far more than a simple ratio of the area covered. I tried my panel (200w Renogy Flexible) by shading a single cell and the output dropped from 200w to just under 60w. Shade another cell and it went to about 20w. CIGS panels are meant to perform better with shading but there will still be an impact. I’d suggest mounting on top as TallPaul shows or just getting a bigger battery that will cover your whole trip (if that’s doable).

 

[Slunkie]

Some very helpful insight above, thanks.

My original plan was to put one or two panels on top of the rack, one in front of the other so leaving a strip free down one side. This is fine for 1 kayak but doesn't work for 2 or with my dinghy which pretty much takes up the whole rack.

I've come across a panel Renogy sell called the ShadowFlux Anti-Shading N-Type. It supposedly uses lots of diodes to bypass shaded cells. I may get a couple of these (2x200W) and try above and below the roof rack, see what I can get away with. A larger battery is definately on my list too.

 

[JumpShip]

What about a demountable panel that could be stored under the rack when it's needed to be ?

 

[drinfinity]

There was a pic on here a while ago of a flex panel on the bonnet…

 

[AussieMick]

I've actually seen a panel mounted on the bonnet of a vehicle and the reflection from the sun while driving was terrible and unsafe. Not recommended.

 

[Slunkie]

What about a demountable panel that could be stored under the rack when it's needed to be ?

Is there an 'off the shelf' solution to this?

 

[Kind of Blue]

If the panels where suspended between transverse roof bars that surely would not cause too much shade?

 

[drinfinity]

I have 100W behind my roof bars, and a Karitek rack for the kayak and canoe. Works fine in this arrangement.

 

[JOG]

I have 100W behind my roof bars, and a Karitek rack for the kayak and canoe. Works fine in this arrangement.

View attachment 274489

Any chance of a couple of close up pics of how you routed the cables?

 

[JumpShip]

Is there an 'off the shelf' solution to this?

Not that I'm aware of ....but it wouldn't be rocket science designing and building something .

 

[TallPaul_S]

Not that I'm aware of ....but it wouldn't be rocket science designing and building something .

Only issues would be that rigid panels are heavy and flexible panels really shouldn't be flexed much - so you'd need some sort of system to slide it off the rack then back under...

 

[drinfinity]

Any chance of a couple of close up pics of how you routed the cables?

Alongside the panel, through the poptop outside the canvas, and then into the back of the van. Along the roof beam and down the B pillar inside if I remember right.

I had to take the plugs off to get them through the pop-top.

Rubber grommets going through each panel.
The housing for the entry to the van is glued on with Sikaflex. Since this picture, I glued on some cable guides with Sika.