We use our van for winter trips. Biathlon, Alpine all kinds of snow sports.
We have a built in genny and find its essential. Batteries can fail ( and did for us this winter...) and if you cannot move due to weather then no amount of engine charging is going to help you.
We are often without EHU for a week or so. We have solar panels too but when its chucking down the white stuff they are useless.
I assume Sarah(Salomon) is meaning after the batteries have failed.
Engine charging can be effective especially if one fits Battery-to-battery (B2B) charger e.g. a Sterling B2B - there are others. It is a bit of a misnomer, because what it does is to provide the alternator's full charging capacity to the leisure batteries at about 4 times the rate that they get from the alternator normally. This has two effects; firstly, even on a short journey, you arrive with full leisure batteries and secondly running the engine when parked will soon top-up the batteries and much quicker than the low output from a small generator, which means less annoyance for any neighbours.
Being able to ensure that you never let the batteries get below 12v should also prolong their useful life.
As Sarah said relying on solar for a skiing holiday not practical. - cloud, snow, mountain shadow, low sun and short days do not make for good solar performance.
A generator would do it for you but need hours of running and may cost more than a B2B. We fitted ours for about £250 I think but you may need to add fitting costs, maybe £150?
Once the B2B is fitted it is working for you on every trip and does not take up space and weight and need for lugging out of the locker - and the noise.
Sorry if I am starting to sound like a salesman, but I have been very pleased with our system thus the enthusiasm.