This section gives an overview of metering technology, from the point of data acquisition to data analysis and sharing. A typical flow diagram for smart metering data looks as follows:
The steps in detail:
(1) Data Acquisition
Smart metering typically applies to electricity, which is also the most commonly metered resource. However, a wide range of resources and fuels can be metered in a smart way.
- Electricity: measured as power draw (in W / Watt) or consumption (in Wh / Watthours); in addition, a number of additional metrics can be measured such as voltage (V), current (amps), powerfactor (PF) etc.
- Gas/Fuel: measured typically as volume in m3 or ft3, or litres for other fuels; in order to determine a kWh value from gas consumption, it is necessary to know its calorific value (in MJ/m3) – this value depends on the exact composition of natural gas, and can be obtained from the energy supplier.
- Heat: measured in joules (J), British thermal units (Btu) or Wh (the metric unit)
- Environmental metrics: e.g. temperature (degrees C or F), humidity (often measured as relative humidity in %), illuminance (lux), windspeed (m/s) and so on
- Other metrics, including (related to buildings) occupancy, footfall, etc.
In addition to the sensing module, meters are equipped with a communications module that often come with a (small) local data storage. The modules connect to the concentrator or gateway (step 2) and send reading data in regular intervals. These typically range from real time to half hourly, hourly or daily (with readings at the same or higher frequencies).
Meters are powered by mains electricity or via batteries. For some low power devices, it is possible to use light or energy harvesting in the form of small solar PV modules integrated or connected to the meters, or induction or heat transfer based modules.
(2) Data Concentration
Data is sent from meters to the concentrator either wirelessly or via a wireline connection. Wireless has the advantage that devices can be easily retrofit, and moved, in existing buildings. Wireline connections on the other hand offer higher data transfer speeds (although the difference has shrunk in recent years with higher bandwidth wireless transfer technologies). In some operating contexts it is preferable to have wireline communications as these generate less interference with other sources of wireless communications – e.g. WiFi, cellular and so on.
Typical standards for wireless communication between meters and gateways are Zigbee (commonly used in residential environments) and proprietary technologies working in the 400MHz and 833 MHz bands. These allow the transmission of signals across distances of several tens of meters, sometimes more. A trade-off has to be made between signal strength and power consumption of meters and other devices. More recent transmission technologies such as Sigfox provide long range capabilities at low power consumption, but require larger network to be rolled out.
The concentrator or gateway is in general composed of three levels:
- Data processing and possibly storage units
The concentrator aggregates data from multiple meters – up to tens and even hundreds of meters (metering channels) are possible. The data is then processed locally to convert it into a single data stream. Gateways can typically store a certain amount of data locally, which is required in case there are problems with the transmission to the server.
The gateway typically sits in the same building as the meters, or just outside where multiple residential dwellings are monitored. The ratio of meters to gateways is often determined by the spacing of the meters and how well the signal can travel. In a typical setting the limiting factor can be walls or floors between meters and gateways, which might require multiple gateways to be placed around the building to ensure a reliable collection of meter signals.
(3) Data Transmission and (4) Data Management Server
The data is then transferred at regular intervals (e.g. daily) to the data management server, also called meter data management (MDM) system. The server is often offsite and sites in the “cloud”, i.e. in the central office or datacenter of the meter operator (MOp). In this case, the transmission occurs via mobile networks (GPRS or 3G/4G technologies), or Ethernet / broadband.
There are cases where the gateway is integrated with a data server, that is then connected to the world wide web via Ethernet. This is useful if the gateway captures data from a large number of meters and the building operator wants to forgo meter data management fees. It is possible to install repeaters to ensure the meter signals can reach the gateway.
The server performs a certain level of data validation and cleansing, e.g. where meter records show gaps it could flag these, or interpolate values to provide “complete” readings. It can also format data in different ways so that it can be exported to a variety of systems for data analysis and validation.
(5) Data Upload to EDMS (Energy Data Management System)
From the meter data server (or servers), data can then be made directly accessible to the user, e.g. via a web interface to the server, or transferred to a third party system for energy data management. This transfer occurs via the WWW and uses one of the following methods:
These methods and the type of files and formats that are being transferred are discussed in more detail in the section on Metering Standards and Protocols.
(6) Data Analysis & Visualisation
Data Analysis & Visualisation is often provided by third party systems that are hosted in the cloud, and accessed by the user through a web browser. The section on Data Analysis treats this topic in more detail.