Seriously, do the maths. You have 4.8w (not a chance you do BTW) assuming your in the med.
4.8w /12v (A=W/V) is 0.3 amps per hour. Indeed it is something for nothing.
Without getting too technical here and factoring in resistance of a flat battery,charging inefficiency etc. Most fixed VHF's use about 25w for emergency to get range. It will be in your manual should you need it and dont have the means to test it.
25/12 (A=W/V) is 2.03 amps.
So, in Lehman's terms, to get enough power to make that emergency call would take circa 8 hours if you were in the brightest of sunshine and you actually did get the rated wattage, realistically it is about half what they say.
The moral of the story is this, dont leave home with anything but good batts as solar power won't bail you out.
They will help keep topped up though if left on in storage.
Personally I'd take the money they cost and give it to shell and have a day out instead.