I have a lot of stuff shipped to me for my business. If I order something overnight, and it doesn't arrive overnight, I have received a full refund on all shipping charges, on more than one occasion.
You don't have the item yet right? Call Wholesale Solar and ask them to refund the whole shipping amount, since they screwed up. They will likely do that for you. If not, you can always refuse to sign for the package and they get to eat shipping both ways, and make no sale, instead of eating it one way and making a sale. I bet you can get free shipping out of this fiasco for your inconvenience.