Solar pannels

[dailew]

We have a new caravan and with a phantom tracker and alarm and are finding we are getting a call to say battery is flat while its stored during winter .So we have thought of a solar pannel but would not want to fit it permanently
so thought of a briefcase type one.Ques is what would i need size wise and part wise to go with it .also best place and way to site it

 

[JTQ]

As we are talking about covering the winter months the available solar energy will be low, and whilst solar is very practical it will require quite a bit of care in arranging.
The sun angle is low so shadows can decimate performance; site the cell as clear of passing tree etc shadows as practical; it needs to face due south and be tilted quite vertical, about 50 deg to the ground. Ensure its base is up out of any grass shadows. Behind a van window will result in very reduced performance, it really needs to be outside.
Size wise is much like a bit of string but it can't sensibly be too big.
I helped somebody do what you wish, he actually kept the van in the shed. On his set up I thought he needed about a 60Watt panel; when he priced things up the cost from ebay of a 100 Watt panel was relatively not much more than a made up 60 Watt unit so he got that and a cheap controller. This has proved to be doing the job very well through all of last winter and this one so far.