You will be billed every quarter for all the electricity and any gas you have used in the business.
Until you have been trading for a few months you will not know exactly how much energy the business will use. Your energy supplier may be able to give you some guidance, based on the size of your premises and the nature of any equipment you will be using. You can adjust the figures once you have been in the premises for a few months.
You premises will probably be quite large, so it's well worth making sure that they are as efficient as possible to heat. Think about which parts of the premises need to be heated and which don't. Try to make sure that the areas you heat have low ceilings and are well insulated and draft proof.
It's worth shopping around the different energy companies to get the best deal for your business, particularly if you're going to be a heavy energy user.