Having suffered from a flat battery on a couple of occasions when we had a Euro6 standard diesel which didn’t charge the battery very well during a journey, I decided that some sort of supplementary charger was required.

There was also the problem of maintaining the battery during winter storage to consider, something which had previously resulted in the destruction of a battery.

I investigate ways of prevention. One way was to remove the battery for the winter period and bring it home for periodic charging. This seemed a simple thing to do but was a bit of a hassle, it also meant that there was no back-up for the caravan’s alarm battery, if indeed that was necessary. I also thought that taking a 20 kg lump on a 90-mile round trip was something to avoid if at all possible.

Another possibility advocated was the installation of a small solar panel somehow connected to the battery, this solution had appeal to the ex-electrician that still resides somewhere in my inner recess.

On reflection the idea of erecting and removing an internal panel did not appeal, so, a decision was taken to plonk a solar panel on the roof!

This raised the next questions of what size would I require to maintain the battery through the winter gloom and how to fix it in position when I had no idea where the timber stiffeners were located in the roof?  The practical, but not necessarily the most economical answer to that of size seems to be to fit the largest panel possible. Fixing the thing was solved when I discovered a supplier of flexible panels that could be glued directly to the roof, which added a bonus of a considerable weight saving; I get quite excited by weight savings. 

Now one could be forgiven for thinking that there is plenty of roof on a caravan roof for a solar panel, especially on a large unit such as our Lunar Clubman.

Sticking my head up through one of the roof lights revelled that there isn’t, for it’s quite cluttered with roof light and vents.

One has also to consider the inconvenient fact that a couple of wires have to be routed through the roof and down to the battery in some way, and I didn’t fancy them dangling from the middle of the ceiling.

The solution seemed to be to mount the panel close to the edge of the roof and route the cables into one of the overhead lockers. This would also have the practical benefit of making installation and maintenance simpler as the panel could then be reached from steps placed at side of the van.

Taking a measurement of the room available and comparing that to panel sizes lead my to select a 100 watt panel, a selection influenced greatly by that size being on special offer at the time bundled with most of the other bits required. I purchased a Biard 100w semi-flexible mono-crystalline panel, 10A charge controller, cables and gland box. In addition I ordered from another source a tube of SikaFlex 552 white adhesive and Sika 205 cleaner. 

After scrubbing the selected area of the roof clean I put down the zig-zag bead of SikaFlex as instructed by Biard and laid the panel on to it, one only gets one attempt at this and a few weights placed on the panel to encourage it to follow the undulations of the roof. I then left it for 24 hrs for the glue to cure enough to retain the panel, even though this adhesive does remain flexible. Drilling through the roff, installing the cables through the roof gland box and sealing it with lashings of SikaFlex was straightforward. Less straight forward was the routing of the cables through to the batter box. I used a couple of metres of white electrical mini-trunking to conceal the cable at a couple of points. 

The controller was installed in an overhead locker where I could easily check its operation but also where the various flashing lights would not disturb our sleep. 

I thought it advisable to fit a fuse in the circuit between the controller and the battery, but where, close to the controller or the battery? After a little thought it seems that as I had to protect the interconnecting cables against a short circuit drawing from the battery as well as, an admittedly lower current from the panel! After further thought I decided that a 10 amp fuse at each end of the cable would cover both scenarios, so two are installed.

Now that I am confident that the installation is working as it should I intend moving the controlled out of the locker and installing it close to the battery where it will be less visible. 

The combined weight of all the components was just under 5 kg.

It’s now a year since I installed the panel and it has performed faultlessly. The battery was kept fully charged during the winter period and quickly recharged when is use off-grid.

I consider it a good investment of both my time and money.


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