The Smart Meter Gateway Part I: The Basics

There is hardly any topic in the energy sector being discussed more than metering — and for good reason! Meters are the building blocks for almost any energy system. Without meters, there is no billing and no accounting — but even worse would be the lack of identity and trust. If we can´t track production and consumption values tied to specific entities for specific intervals, how is anyone — from small to large scale — supposed to use their energy assets efficiently?

In the context of a more volatile, dynamic, and complex energy system, meters will have take over an even more important role. Because renewables produce electricity intermittently, we have to put further care in orchestrating production and consumption — and also securely bill it accordingly.

Besides reducing the current standard interval for energy billing and accounting (yearly) to smaller timeframes (e.g. quarter-hourly) to further incentivize the actual matching of production and consumption, we also might want to add additional functionalities to the meter. Why? Because the Smart Meter is already interconnected to remote systems (or in other words: it has Internet or VPN access) and could also do multiple other things like getting specific sets of data from energy assets or device-control. Using a one-device-fits-all paradigm makes a lot of sense to avoid uncontrolled growth of non-interoperable solutions and to decrease investment, operation, and maintenance costs. And that´s exactly the way the German government was thinking — and started the development process of the SMGW (Smart Meter Gateway) framework.

In this article, a compact introduction to the SMGW framework is given.

Power Metering - A history that spans more than a century

Meters have undergone many changes over the years. Knowing the technical history of metering from past to present is helpful to understand the current scenario better.

Figure I: Ferraris Meter (left) and a modern metering unit (right) with a SMGW (Source: Verbraucherportal-BW)

Figure II: Modern modern metering units and an OLI BOX (Source: OLI Systems GmbH)

The analogue, electro-mechanical “Ferraris” meter with its rotating metal disc is probably the one most of us know. It is very sturdy, simple, accurate and can operate for decades. Depending on the country, they are being read out either by the resident of the building or grid-operator personnel on a monthly or yearly interval. The meter reading is then manually sent to the grid operator with a handwritten form, a letter or a digitally via a webpage.
The next generation consisted of a wildgrowth of digital meters. The power measurement changed from the electro-mechanical approach to purely electrical. Because there are no more turning components in the meter, a digital display is also needed to show the current readings. Depending on the individual regulation of the country, the meter might also have multiple local interfaces - optical, electrical, wireless, unidirectional and bidirectional - all sort of combinations are possible. Even though they are the product of a digitalization process they very often lack a critical component: the communication unit. While the data is all there - in the meter - there is often no way to securely transmit it to the grid and market operator, to retailers and other third parties.
Lastly, what we would like to call the third generation of meters, are the so-called ‘moderne Messeinrichtung’ (mMe or ‘modern metering unit’). These are standardized digital meters according to the demands of the German regulators and industry. They feature a fixed set of interfaces - for both local devices and humans to interact with. But similar to existing digital meters they also lack the communication component to transmit data from the meter to remote and external systems.

The mMe is designed in a way it can easily be combined with that missing communication component and form an intelligent metering system (iMSys). In Germany, the Smart Meter Gateway (SMGW) is that missing unit.

Law

In Germany, the “Gesetz zur Digitalisierung der Energiewende” (engl: law for the digitalization of the energy transition) was passed in 2016 to build-up the legal framework for the deployment of iMSys in Germany. Starting from 2020, consumers with more than 6,000 kWh annual consumption and prosumers with more than 7 kWp installed PV capacity will be required to have an iMSys installed. As a DENA study states, almost 16 million intelligent measurement systems are expected to be in use by 2032.

Balancing Transparency, Security, Privacy and Efficiency

When digitalizing any system, a number of design objectives are always apparent, that sometimes contradict each other:

• Transparency and Integrity: An maximum of information should be disclosed at all times for all possible stakeholders about static and dynamic information of the system in use. For example, if things get intransparent and the ‘end-customer’ becomes increasingly skeptical about who uses their data or what exactly it contains, the acceptance might diminish. But also grid-operators or retailers that want to use the data for various applications need a maximum of transparency about its origin and integrity. Of course, keeping everything transparent has its downsides.
• (Data) Security: The data measured by an iMSys should only be visible to a few participants in the system and should not be disclosed into a public domain. Therefore, security zones and a straightforward permissioning scheme have to be implemented and kept secure at all costs. Not only should we keep malicious actors away from the data as it enters the heights of B2B communication, but also every single iMSys is installed in an hostile environment. Basements, transformer stations and other locations like this are ideal places for trying to hack into a Smart Meter Gateway. Therefore also device-level security has to be implemented.
• Efficiency: Installing IoT devices, maintaining communication lines and keeping everything up-to-date is an expensive task in any possible context. While there should be no compromise on security, a poorly designed system can easily cost way more than necessary - and still bring no distinct advantage over an analogue implementation

To ensure the design objectives are met the BSI (German Federal Office for Information Security) and PTB (German National Metrology Institute) started working on a precise list of requirements and a system architecture which resulted in the technical documents (BSI TR-03109). The technical guideline has six main subdocuments which are focusing on “Gateway architecture”, “Safety module”, “Cryptographic specifications”, “Public-Key infrastructure” and “SMGW administration”.

The central design component of the SMGW ended up to be a three area/zone network.

Local areas and different parties of the framework

The SMGW itself has divided into three main security areas or zones:

1. Home Area Network - The HAN is its own network supposed to interconnect the energy devices (Inverters, batteries, electric-vehicles) with the smart meter gateway. It is highly restrictive and only permissions specific, pre-validated and pre-registered devices to route their communication through the other zones.
2. Wide Area Network: The WAN is supposed to connect the SMGW and the other zones to the administrator (SMGWA) and external market participants (EMP) that for example could represent the grid operator, a retailer or an aggregator. This network is highly restrictive, has specific rules and usually forms a VPN.
3. Local Metrological Network: The LMN connects the local modern metering units to the SMGW for a secure readout with high integrity.

Figure II: SMGW and its environment (Source: BSI)

Made out of three different zones, the SMGWs ‘central’ task is to route communication from one zone to another. Those zones represent basically a Smart Grid: The end-customer is connected to the HAN with the help of an certified installer to the HAN. The other participants (grid operator, retailer, aggregators) are connected to the SMGW via the WAN, while the local certified and secure meters all communicate through the LMN.

For the WAN, further levels of permissioning apply. The Smart Meter Gateway Administrator (SMGWA) for example has special rights in comparison to the External Market Participants (EMPs). Besides being able to update the SMGW with a new firmware, they can also configure it with new profiles in order to support an ever-changing set of EMPs. The EMP however, only can access the SMGW via the Administrators permission - and even then the SMGW itself will start the connection process (“bottom-up”).

The whole setup enables in first instance the quarterhourly readout of a meter installed at a SMGW. Besides that, external device-control by an EMT via the WAN is also possible, for example in the context of PV-curtailment.

That should be it for Part I!
Next time we will take a look at the WAN to HAN communication in greater detail, while Part III will report about how distributed ledger technologies (DLTs) can augment the SMGW architecture.

References

Bundesamt für Sicherheit in der Informationstechnik. Technische Richtlinie BSI TR-03109–1: Anforderungen an die Interoperabilität der Kommunikationseinheit eines intelligenten Messsystems; Bundesamt für Sicherheit in der Informationstechnik: Bonn, Germany, 2013. Source : https://www.bsi.bund.de/DE/Publikationen/TechnischeRichtlinien/tr03109/index_htm.html

Physikalisch-Technische Bundesanstalt (PTB) Anforderungen 50.8A Dezember 2014 https://oar.ptb.de/files/download/56d6a9e2ab9f3f76468b4618

Kroener, N., Förderer, K., Lösch, M., & Schmeck, H. (2020). State-of-the-art integration of decentralized energy management systems into the German smart meter gateway infrastructure. Karlsruhe. https://doi.org/10.5445/IR/1000120981

“Smart meter — Deutsche Energie-Agentur (dena).” [Online]. Available: https://www.dena.de/en/topics-projects/energy-systems/digitalisation/smart-meter/. [Accessed: 19-Sep-2020].

Messstellenbetriebsgesetz: https://www.gesetze-im-internet.de/messbg/BJNR203410016.html

Figure I:
https://www.verbraucherportal-bw.de/,Lde/Startseite/Verbraucherschutz/Smart+Meter
Figure III: https://www.bsi.bund.de/DE/Themen/DigitaleGesellschaft/SmartMeter/SmartMeterGateway/smartmetergateway_node.html