The terms demand and generation are used in the electricity industry to describe consumers and producers of electricity.
Electrical demand, or consumption, includes lighting, heating, running fridges and freezers, power tools, import for battery schemes – the list is almost endless.
Electrical generation, or production, includes older fossil fuel generators like coal and gas, newer renewable types of generation, like solar and wind, as well as nuclear.
Every part of the network has a certain capacity, or rating often different for demand and generation. You can read our article ‘What is reverse power flow?’ for an explanation of headroom for generation. This article explores the rating of the network for demand, or more importantly (for developers) the headroom for new demand connections.
Electrical demand changes incrementally over time. For most of the time since the electricity network has been established, electrical demand has increased year on year. Interestingly, from 2005 to 2020 electrical demand in Great Britain dropped, due to the introduction of more efficient products (like compact fluorescents and LEDs for lighting). Demand is expected to increase significantly over the next ten years and beyond with the introduction of electric vehicles and electric heating.
Every piece of equipment on the electrical network has a rating, a maximum level of power to prevent them from getting too hot. If the electrical demand in a particular part of the network increases too much, then reinforcement is required to increase the capacity.
Demand headroom is the gap between the rating of the network to supply demand, and the actual demand in that part of the network. A typical example is below.
Figure 1. How demand headroom works on the network using a simplified substation diagram.
A bulk supply point (BSP) substation might have 2x 90MVA 132/33kV transformers. The substation needs to be able to supply all the demand fed from it if one of the two transformers is switched out (this is sometimes referred to as N-1, i.e. the number of transformers at the substation minus one of them).
In this case, only having one transformer gives the substation a capacity of 90MVA to supply the demand. The demand is 70MVA, which means that the headroom is 90-70 = 20MVA.