Historically I believe that it's been the other way round. When I monitored electricity use for a previous employer they paid around 70% of my domestic rate, and I was on the lowest tariff I could find. It's the same as any bulk purchase, businesses generally use much more than domestic dwellings so there is more competition for their business, hence their rate tends to be lower. It's a little different at the moment. As it was pointed out earlier, the energy price cap doesn't apply to commercial property but a quick Google shows that the average commercial rate has been broadly similar to the domestic rate this year.
It leads to an interesting question though. A caravan site can't charge you more than they pay for electricity (unless they are licenced as a supplier or distributer), but how could you check what they were paying? I doubt that asking to see their bills would be favourably received.