If you had 4 you could have up to 12 watts. I doubt that it would charge much at all but if your bank is small it might keep it up while in storage. It really depends on bank size and type.
Of course the advantage is no need for a regulator. I have a 30watt that is so small for my bank that I do not need a regulator for it, even in florida but then I always have something on.
Have faith that the oceans are going to rise and flood the world, that plague and pestilence brought on by Climate Change is going to punish us for not believing. Please do as they say it is our only hope. :P