Energy meters with prepayment function are mainly working with the Standard Transfer Specification (STS). There are still some manufacturer specific proprietary solutions in the market.
Not only for security reasons, these solutions are not recommended.
Now there are more than 60 million STS payment meters installed worldwide. The IEC 62055-41 is the master document for STS operations. It’s the most advanced and secure system for prepayment.
Tokens are used to transfer information in a secure way. In STS terminology, a token is a 20-digit number. To illustrate how a token looks like, click the button below.
The STS association has defined token for various tasks. The end-user needs mainly credit-tokens to top-up his credit.
The Meter Manufacturer can not provide tokens
To make this better understandable, let’s take a look at a little graphic.
You get your token from the power company service, or vending station. The energy meter must be registered in their vending system upon first installation. The reason behind is clear: You can’t buy a token from power company A and use it for a meter supplied by power company B.
In addition, each power company has their own supply group code (SGC) with the matching encryption key. If the meter is registered, the security module generates a valid token (blue arrows). Then, you as user, get the token and punch it in at your meter key pad.
Tokens are for one time use only and have an expiry date. So you can’t buy credit for the next twenty years.
Advanced Token Operations
Up to now, many utilities are operating according to the graphic. It’s not very convenient for the user to go to the point of sales (POS) to join the queue for buying new credit.
With an AMI (Advanced Meter Infrastructure) solution together with bi-directional meter communication, it’s possible to buy credit online.
Sooner or later, all power companies will follow this trend. Still, the security is maintained with the encryption at the security module. The AMI-system transfers only the token, so there is no need to enter it manually.
The Token Poll
This article is pretty much simplified to make the end-user understanding, why meter manufacturers are not able to generate tokens.
The STS association is active in energy meter prepayment since 1993 and their concept hasn’t been compromised until now.
Thank you for reading, and don’t ask again for a token.