Forecasting NBP kWh

2025-11-08

We've had a run of NBP kWh related posts ( Calculating NBP and NBP Reconciliations, and this post rounds off the series by talking about forecasting NBP kWh.

Even though actual TLMs are specific to the GSP Group and the particular half-hour, estimated TLMs (ETLMs) apply to all GSP Groups and cover whole months and sometimes multiple months. You can see the ETLMs on an Elexon webpage, here's a screenshot:

Further down on that page is a link to a CSV download of the ETLMs.

As an aside, it's really frustrating that this link can't easily be automatically downloaded using a script, because it requires cookies, JavaScript etc and various protections to prevent automated access. Elexon do have a 'scriptable downloads' section on their portal, and I've written to them asking if they'd put the ETLMs there. In the meantime we download the file to the rate repository. Feel free to make use of this repository, it contains all the industry data that has to be manually downloaded, and can be accessed using the GitHub API.

Okay, back to ETLMs. When Chellow sees that a new ETLM file has been added to the rate repository, it downloads it and stores the ETLMs in its database. ETLMs are useful for two things, firstly they are used for forecasting, because as you can see they go out to the end of this financial year. We can run the virtual bills in Chellow for a time in the future and it will calculate the expected costs using the ETLMs and other rates that apply at that future time.

Secondly, ETLMs are useful as a basis for the (initial, before reconciliations) bill from the supplier. The first settlement run (with the code 'II') is 1 week after the time in question, and so suppliers might not be able to use this for all half-hours. What they can do instead is use the ETLMs, and then reconcile as updated actuals come in. The key thing is that the supplier should use a standard version for TLMs (either ETLMs, or one of the settlement runs). Otherwise, without knowing the TLM version we can't check that the bills are correct.

See you next time! ✨