To be able to display the energy mix and carbon intensity for a user via the app, the Carbon Tracer has to carry out the following broad tasks:
The information displayed by the app is based around a large electricity distribution supply substation called a Bulk Supply Point, or BSP. The app has to work out two things, each of which is constantly changing: The current total demand (or load) for all customers on the customer’s substation, and the mix (and carbon intensity) of the different forms of generation which try to meet that load. The electricity is actually supplied from two main places: locally attached generation and where that is insufficient to meet demand, by taking electricity from the National Grid. Some locations in the country are well provided with local generation plants of various types while others are not.
Once the customer’s location has been traced to the supply point on our network, the amount of local generation of each type can then be determined from our data. Each attached generation source has a declared maximum capacity but this is seldom achieved because of factors such as the season, time of day and weather all of which act to change what can actually be generated given the prevailing conditions. Individual generation sites may also be unavailable at intervals due to specific operating cycles, planned maintenance or faults. The app therefore takes capacity information and then in a process that we call scaling, applies the necessary environmental and time based corrections to determine the actual generation levels.
In the same way that the level of generated electricity is constantly changing, the load at the substation also changes through the day as the households and other premises which it serves all do different things. Additionally, the seasons, time of day and weather are all changing. For example, more lighting and heating is needed on winter evenings than in the summer and more generally, less electricity is used though the night when very few people and appliances are active.
Solar photovoltaic output can be modelled very accurately given appropriate input information. Similarly wind farms only operate efficiently when there is air flow available to move the turbine blades. The generation output level is then dependent on the amount of wind, up to a point where there is too much and the blades have to be stopped to protect them from damage. In such conditions you may therefore see minimal wind generation even though there is a howling gale outside.
Solar and wind are by far the most common forms of generation, but there are several others and there is considerable variation in which forms are present at a given location. Solar and wind are also the easiest to model since many different factors come into play with some of the other forms. For example biomass incinerators will all have individual operating timetables and these may also change from what has been planned.