You'll be billed every quarter for any electricity (and perhaps gas) you have used at your business premises.
Until you've been trading for a few months you won't know exactly how much energy the business will use. However, you could contact energy suppliers who may be able to give you an idea of likely consumption based on the size of your premises and the type of equipment you'll be using. You can adjust your estimated figures once you have been in business for a few months.
You're quite likely to have fairly large premises, such as an old warehouse, 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 time.