Time-of-Use Tariff Billing Example
As an example of the use of local processing, Project Hydra has written a time-of-use billing demonstration.
The demonstration takes real energy consumption data from a smart meter and processes it in two ways:
- Conventional billing with processing done at the server. Here we export 30-minute consumption data from a smart meter, apply a notional time-of-use tariff on the server, and display the bill on a web page.
- Billing processing performed at the meter. A secure microcontroller runs a Java Card applet in the electricity meter. The applet applies the same tariff and returns only the total bill to the server, where this bill is displayed on a web page.
Of course, the results are identical.
This shows that the energy supplier can receive the information that they are enititled to – in this case the amount that they should bill the customer – without needing to access the 30-minute data.
There is no additional security issue here: if the energy supplier can trust the meter to export accurate raw data then it can also trust that the meter can process the same data locally and export just the total. In both cases the data is encrypted and cryptographically signed before leaving the meter. It is a characteristc of the Java Card security model that the digital signature added by the applet proves that the billing calculation could only have been performed by that particular applet. The applet’s source code could be published to allow all to see that it is applying the tariff fairly.