Computer Laboratory

Introduction to Joule

Sankey Diagrams

Tree Map Diagrams

File Formats

Recovering Carbon Information

Grid Carbon Intensity Data

At different times of the day and year the energy mix used to generate electricity varies, and therefore so does the amount of CO2 emitted per unit of electrical energy produced. Joule can display CO2 emission rather than power consumption. To do this Joule reads carbon emission data.

Carbon information is held files available on the Computer Laboratory website at

http://www.cl.cam.ac.uk/meters/carbon/CarbonIntYYYY.json

and Joule can be configured to read these (specified in the configuration file). Here are the contents of CarbonInt2014.json (you will need to scroll to see all of it):

The fields at the beginning are intended to be helpful in understanding what the data is and where it came from (and are ignored by Joule - the file name contains the year which is the only meta-information that Joule needs). The information that Joule does use is the data object in the file. The data object has three components:

  • a start time as a JavaScript time stamp, i.e. milliseconds since 1 January 1970
  • a step time in milliseconds between readings (so in the example above the samples are at hourly intervals)
  • an array of readings in grams of C02 per kilowatt-hr (Joule's only non-SI unit!), the first being for the time denoted by the start time.

There is information here on how this information is produced (and what to do if it isn't)