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. You could contact your energy supplier who may be able to give you an idea of likely consumption, based on the area of your premises and the nature of the business. 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.
If you are refurbishing your premises or equipping them from scratch then it's a good idea to consider building in energy saving and efficiency measures. Even some simple measures, like installing low energy lighting, can make a big difference to bills.