I discussed this very subject with some exhibitors at York,
Bascially, it's because they don't work well enough. As a couple of people ( and they were satellite sellers ) said, "If they worked, don't you think we'd use them at shows?"
I accept that in the right conditions, they would provide some power, but , like any natural source, how often do you get the right conditions? I had intended to have a hybrid solar/wind setup (when we eventually do get our MH), but have been convinced, at the moment I hasten to add, that it would be wiser to invest in additional solar panels, rather than my original intention. And no, I'm not associated in any way with any wholesaler or retailer of any goods, let alone solar panels.
However, "you pays your money and makes your choice." Personally, any green power is preferable in my opinion, so congrats on airing the subject. I hope that others will air their views too, as it will aid me in my final decision.