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 having suffered from a battery going flat during a winter, which resulted in the destruction of that 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. I also thought that taking a 23 kg lump on a 90-mile round trip between our home and our caravan storage was something to avoid if at all possible.
Another solution advocated was the installation of a small solar panel behind a window somehow connected to the battery, this solution had appeal to the ex-electrician that still resides somewhere in my inner recess. However the idea of erecting and removing an internal solar panel did not appeal, so, a decision was made 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. The question of how to fix it was solved when I discovered a supplier of flexible panels that could be glued directly to the roof. That was a solution with an 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 room 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 revealed that there isn’t, for it’s quite cluttered with roof lights, vents and an aerial. One has also to consider the inconvenient fact that a couple of wires have to be routed from the panel, 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 caravan’s 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 led me to select a 100 watt panel, a decision influenced greatly by that size being on special offer at the time, and bundled with most of the other bits required. I purchased a 100w semi-flexible mono-crystalline panel, 10A charge controller, cables and gland box. In addition I ordered a tube of SikaFlex 552 white flexible adhesive and Sika 205 cleaner.
After scrubbing the selected area of the roof clean I put down a zig-zag 6mm bead of SikaFlex as instructed by the panel manufacturer and carefully laid the panel on to it, one only gets one attempt at this! I then placed a few weights around the panel to encourage it to follow the slight undulations of the roof. The idea apparently is to leave a small air ventilation gap under the panel to discourage heat build-up.
I then left it for 24 hrs for the glue to cure sufficiently to retain the panel, even though this adhesive does remain flexible. Drilling through the roof, installing the cables through the roof gland box and sealing it with lashings of SikaFlex was straightforward. Less so was the routing of the cables through to the battery box. I used a couple of metres of white electrical mini-trunking to conceal the cable in the lockers and down the wall in a of our bedroom area corner. From there it was a case of threading it through the low-level kitchen fittings and appliances to a point adjacent to the battery box under the front seats.
Initially 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.
Subsequently I decided to move the controller to a point close to the battery when I realised that it would operate a little more efficiently in the new position.
I thought it advisable to fit a fuse in the circuit between the controller and the battery, but where, close to the controller or to the battery? After a little thought it seems that as I had to protect the interconnecting cables against a potential short circuit drawing power from the battery as well as, an admittedly lower fault 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 in-line fuses were installed.
It’s now more than a year since I installed the panel and I’m pleased to report that it has performed faultlessly. The battery has been kept fully charged during two winter periods and quickly recharges when it is used off-grid.
I consider it a very good investment of both my time and money, the overall cost being about £150. Apart from an occasional panel clean, and a visual check of the charge controller that all is well, it is very much a fit and forget system.
Update July 2019
Following an extended period off-grid in variable weather I was pleased to find that our battery was fully recharged before noon each day. Admittedly the sun rises quite early, but for most of this period it was quite cloudy.