You do not need a full specification to begin. A rough outline of your site, how it is used, and what you are looking into is enough to get things moving.
Some people send detailed figures. Others just describe the building and their energy concerns. Both approaches work.
Anything that gives context is useful. That might include your type of site, approximate electricity usage, operating hours, or any recent changes that have affected costs.
If something is missing, it can be picked up afterwards. The aim here is simply to understand where to start.
The details are reviewed in the context of how your site may actually operate. That can include timing of usage, demand peaks, and any obvious constraints.
If needed, a follow-up question may be sent before anything more detailed is outlined. From there, the next step may be a more detailed assessment or survey.