Communications is a core component of any smart-grid business case since each part of the smart-grid value chain is based on it. Multiple communications technologies can coexist within a sole smart-grid project depending on many key factors (applications requirements, urbanism, existing grid infrastructures, …).
This article focus on technologies used in the last mile (FAN) for Utilities AMI applications. Past and running smart-meters rollout all over the world already show strong Regional disparities in term of communications technologies selection. Where does these differences come from ? What are the main technologies and vendors available and what criteria to select of the best solution ?
Three main technologies are sharing the AMI market
Many communications technologies can answer the technical requirements of smart-metering applications. The choice is usually a combination of several technologies rather than just one to take into account every characteristics of customers (urban vs. rural, ground topography, meters accessibility, radio cover, …). For some customers, manual metering remain the most economic solution.
Today, three main technologies are sharing most of the AMI market : low data-rate PLC, RF Mesh and cellular.
Main technologies used into smart-grid project
Source : BearingPoint
Power Line Communication (PLC)
This technology consists in using the power lines as data transmission supports. This is a very well-known technology which has been used for years for home automation, multimedia or electrical grids applications, indoor and outdoor, in low or high data-rate. AMI applications are usually based on low data rate technologies (few hundreds of kilobits/sec max). It allows a bi-directional communication between the meter and a concentrator usually located in a transformer. This is a mature technologies with several open standards and many vendors. Last evolutions include the OFDM (Orthogonal frequency-division multiplexing) technology (IEEE P1901.2) which make the signal more robust and reduce the amount of concentrators required (the signal can go through the transformer). The “PLC-G3” Alliance led by ERDF (French DSO) and “Prime” Alliance led by Iberdrola (Spanish Utilities) are among the main promoters of this technology.
Depending on the grid architecture (number of meters by transformer), this solution can prove to be very expensive in term of concentrators and the bandwidth too short for some applications.
Its range (several kms), its ability to reach meters difficult to access (basements, high building, …) and its installation easiness are its main advantages.
Radio-Frequency Mesh (RF Mesh)
This technology is based on the unlicensed RF spectrum using a mesh topology. Smart-meters have a role of transmitters/receivers and are communicating with each-others. Data are collected by concentrators with help of repeaters. Frequencies used are usually located around 900 MHz (between 902 and 928 MHz in USA) or 2,4 GHz (shorter range).
This technology is well adapted to urban areas, for areas with few obstacles and easy to access meters (outdoor preferred). Utilities need to acquire new communications networks management skills.
A good bandwidth, its independence of electrical grid (keep working in case of grid outage in contrary to PLC) and its economic competitiveness in certain grid architectures compare to PLC (few number of meters by transformer) are its main advantages.
Most of the solutions available are proprietary and raise interoperability questions. Standardization works are ongoing within the IEEE 802.15.4g workgroup.
Silver Spring Networks, Itron, Landis & Gyr, Elster, GE are among the main vendors.
Some projects are also based on cellular networks (GPRS or 3G) for field area network (in addition of the WAN). This choice requires to contract with one or several telecom operators. This solutions is very well suited for areas where the use of PLC and RF Mesh is technically impossible or too expensive. It allows a quick service activation with very low investment cost et offer very good performance. Its main drawback is its dependence to a telecom operator which can make service quality and cost management complex. Subscription costs for each equipments may also limit its use on a large scale.
Moreover, most of telecom operators plan to shut down their GPRS network to replace it with 3G and 4G/LTE. Technical obsolescence must be take into account when it comes to rollout meters for 15 to 20 years.
Main communications technologies comparison
Source : BearingPoint
A fourth technology hold a significant market share in the US : long range point to poit/multipoint RF in a licenced spectrum. Sensus is the main vendor. This solution has a higher investment cost but offer better performance than RF Mesh. Its use remain limited since few countries have authorized a dedicated licensed spectrum for Utilities applications. However UK has recently selected Sensus to provide part of its AMI communications infrastructure.
USA vs. Europe
Until now, smart-meters projects were mainly based on PLC in Europe with cellular for certain areas. It is the case for Italy, France and Sweden for example.
In the US, Utilities have widely adopted RF Mesh solutions.
These differences can be explained by :
- A very strict regulation of RF spectrum in Europe which limit the access to frequencies used for RF Mesh (especially those lower than 1 GHz).
- The European Architectural characteristics (high buildings, meters in basement, building materials …) which are less favorable for wireless uses.
- The American electric grid characteristics (number of meters by transformers much lower than in Europe) which tend to make PLC too extensive (with a technology that does not go through transformers).
Discussions are ongoing at European level to soften RF spectrum regulation and open dedicated bands. Meanwhile, new RF Mesh standards aim to improve adaptation to others areas than US. This should accelerate wireless solutions penetration in Europe and open new markets for vendors. As mentioned before UK has chosen to base its AMI communications infrastructure mainly on RF solutions (Cellular and Sensus) while using PLC for some flat blocks.
Main technologies used for AMI projects in Europe and North America (September 2013)
Source : BearingPoint
Adrien Mathieu, Manager