02. November 2020, 10:32 Uhr | Tobias Schlichtmeier
Since January 2020 it is now signed and sealed – every household and industrial consumer has to fit their electrical connection box with a digital meter. But what can these meters do, and what do things look like for the user?
The »smart home«, the dream of many. From a smart TV through Amazon Alexa to intelligent control of shutters. It has long been possible to control many things through a smartphone or tablet. But not only things in daily use are becoming smart, our electricity meters too. Looked at perhaps once a year to read off consumption, the good old analog electricity meters (Ferraris meters) keep turning untiringly. That is due to change however — although installation of modern metering devices is supposed to have been under way for a number of years.
From 2017 the Federal Law on Metering Point Operation  foresaw the installation of intelligent metering systems in private households. But it has not really happened. Electricity supplier E.ON, for example, did not install the first smart meter for a private customer until the end of 2018. But in January 2020 the legal situation changed. The Federal Office for Information Security (BSI) issued the socalled market declaration. This was the start for the official rollout of intelligent metering systems. Metering point operators started to replace old analog meters by digital ones.
There are two kinds of digital meter: the socalled modern metering device and the intelligent metering system, also called a smart meter. A smart meter consists of two components: the digital electricity meter and a communication module for data transmission (Fig. 1). But who gets which meter? All German households will have a modern metering device by 2032 at the latest. Utilities started installing them in February 2020. Customers receive notification of installation from their utility, proposing a first date. But at the moment there are only the following three groups of smart meters:
Fig. 2. This shows how a smart meter is integrated into the electricity grid and the benefit for the consumer.
But what actually is the reason for changing from an analog to a digital meter? With the socalled energy transition that is planned, more and more installations generating from regenerative sources are feeding electricity into the grid. But because regenerative sources do not deliver electricity constantly, that leads to strong fluctuations in the grid that are difficult to compensate. Further development of the grid is unavoidable and already being implemented. But to better predict fluctuations in the grid and compensate them it takes data on power generation and use. Smart meters support communication of users in the grid. In that way utilities can ensure more easily that electricity gets to where it is consumed. That leads to better utilization of electricity generating installations and by consumers in the grid, and thus to lower costs for both utility and end consumer (Fig. 2).
Modern metering devices work electronically — by different principles. A magnetic field is built up in what are called Rogowski coils. This inducts a voltage, from the level of which the current flow and thus power consumption can be derived. Rogowski coils are regarded as very robust, although investigations by the Dutch University Twente have shown that in certain conditions they can deliver false readings.
The situation is different with shunt resistors. When a current flows across such a resistor, a certain voltage drops. How high this is depends directly on the amperage, thus allowing accurate conclusion of the amount of electricity consumed. The third common electronic method of metering uses a Hall sensor, working with magnetic fields like the Rogowski coil.
In addition to coil, resistor or sensor, each metering system includes further electronic components — so a meter needs energy to operate. According to meter supplier Discovergy that accounts for about 120 Wh a day (about 44 kWh/year). If a modern metering device is extended by a smart meter gateway, making it an intelligent electricity meter, the power for the minicomputer is added. The power of a smart meter is thus about 240 Wh per day (about 8 kWh/year).
A direct comparison shows that modern metering devices require little more power than a conventional Ferraris meter. Calculated for a year, the extra cost at an electricity price of 25 cents/kWh is just €3 — that corresponds to less than 1 cent per day. With smart meters it is a little different. Here the price for the energy from the utility is about €14 over the old Ferraris meters, i.e. about 4 cents per day. By comparison: the German Energy Agency (dena) has calculated that a DVD recorder with harddisk in standby mode also costs about €14/year .
There are digital meters proverbially wherever you look. Distributor Conrad alone offers about 200 different models . But it takes a communication module or smart meter gateway to turn a digital meter into a smart meter measuring device. To date the BSI has only certified three communication modules. The reason is partly that only a few manufacturers have ventured into the development of such a module; the high security requirements and lengthy certification processes have deterred many. The other reason not to produce such a module is not trivial technically. Last year the Handelsblatt business newspaper wrote that the Department of Works network Trianel, of which more than 100 departments in Germany and neighboring countries are a member, wanted to cease its smart metering activities until the end of the year out of annoyance at the sluggish approval procedures .
But what exactly must a communication module be able to do, why do so many manufacturers founder in their attempts to develop a gateway? The smart meter gateway (SMGW) with integrated security module is the central component that receives and stores data from meters, conditioning it for market players. It communicates to transmit the data and for administration with different components and market players (Fig. 3). Thus it connects the electronic metering devices in the local metrological network (LMN) with the different market players like the distribution network operator in the wide area network (WAN) and the local home area network (HAN) .
In the WAN the gateway communicates with external market players and the SMGW administrator, while in the LMN it exchanges data with the linked meters of one or more end consumers and vice versa. In the HAN of the end consumer the information from the SMGW is passed to the controllable energy consumers or generators like smart household appliances or photovoltaic installations and vice versa. The gateway also produces data for the end consumer or a service technician. So there are many communication paths, many interfaces and thus many potential gateways for risks. That deterred many to date from developing an SMGW. Nevertheless, three manufacturers have managed to obtain certification from the BSI. Another six modules from different manufacturers are in the certification process . While those certified and able for official installation are: