You will be billed every quarter for all the electricity and any gas or heating oil you have used in the business (if you have any business premises).
Until you have been trading for a few months you will not know exactly how much energy the business will use. You could base your estimate on your energy consumption at home, perhaps increased by, say, 25%. You can adjust the figures once you have been in the premises for a few months.
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.
You're quite likely to have fairly large premises, such as an old warehouse, a converted church or similar. Buildings like this are often draughty and poorly insulated, so you'll want to make sure your heating bills aren't excessive. Think about which bits of your premises need to be heated and which don't. Think too about lighting - choosing an energy-efficient option can save you a considerable amount of money over the years.
You'll need to make sure that your premises are sufficiently well heated to prevent stock degrading as a result of things like damp and mildew.