# The Role of Smart Meters in Enabling Real-Time Energy Services for Households: The Italian Case
## 2 Smart Meter Overview  
A smart meter (SM) is a device able to measure the physical quantities flowing through its boundary, record events (e.g., outages or changes in contractual rated power), and digitalize and transfer such information to a central acquisition system. An electric SM is in charge of collecting data on not only energy flows, but also power and voltage levels at the customer's premises, and then sending those measurements to the DSO. In turn, the DSO uses the acquired information for both managing the network (e.g., controlling network losses) and providing retailers with validated data to be used mainly for billing reasons but also for customer management. In this article we only consider the electricity value chain and we refer to electric SMs as simply SM. Given the crucial role of the SM in the electricity value chain, various regulatory authorities have defined its main characteristics. According to Directive 2004/22/EC of the European Commission regarding measuring instruments (MID), SM must show the results of the metering process directly at the customer's premises at least through a display or other more sophisticated system. It has to be user-friendly and long-lived, ensuring a future-proof nature. More than one physical quantity can be collected (e.g., active energy, reactive energy, power usage, and voltage) and even stored within the SM registers for many days in order to cope with the possible unavailability of the communications channel used for data exchange with the HES. Metering data exchanged between SM and the DSO's HES usually travel across two hops. In the most common architecture of smart metering systems, the first link connects the SM with the so-called \"data concentrator\" (usually situated in a Secondary Substation where the MV/LV transformer is located), while the second link enables the acquisition of the measurements from the concentrators to the HES. The data concentrator is an intelligent station that receives hundreds of measurements coming from different SMs, processes and repackages the data before sending them to the HES. It can also ask for a new data acquisition should the communication with some SMs fail. The SMs, the concentrators, and the HES required for a smart metering system belong to the so-called Advance Metering Infrastructure (AMI) [19]. Communications within an AMI can in theory enable data acquisition from SMs to HES but, in almost all cases, can be used both ways (upward from the SM to HES and downward from HES to SM); of course, this requires a more complex infrastructure that allows DSOs to execute several actions through the SM such as remote customer disconnection for unpaid bills. The former architecture is called Advanced Metering Reading (AMR), while the latter implies the upgrade from AMR to Advance Metering Management (AMM). For communicating metering data to the data concentrator, different technologies can be used. Usually, Power Line Communications (PLC) is the preferred solution since it does not require a dedicated infrastructure (as coverage is provided by the existing electrical system); it ensures good reachability even in deep-indoor installations and can be managed directly by the utilities, reducing the need for the DSO to procure telecommunication services (although these services are commonly used for the second link from the data concentrator to HES). Wireless technologies operating at sub-GHz frequencies, such as the Wireless Meter-bus (wM-Bus) protocol, are popular alternatives for collecting data from the SM, ensuring long-distance communications. The main drawback is that they require the installation of a dedicated communications network and frequency planning to ensure low interference. At the HES, raw measurements are analyzed in the so-called validation process, which checks if the collected data are complete and valid or, failing that, uses advanced algorithms for missing-data reconstruction. Finally, the validated measurements can be forwarded upstream for the billing phase managed by retailers.