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Since the first published specification in 2004, the ZigBee standard has now matured to the point of global acceptance and is starting to make some real traction in the market. ZigBee provides a cost-effective, standards-based wireless networking solution that supports technology focused on low-data rate, low-power mesh communication.
Although most ZigBee products and deployments to date still remain somewhat proprietary, in the sense that they are sold as systems and not devices that link into a public network, a recent focus on advanced metering infrastructure (AMI) or more specifically, Smart Energy, is well positioned to open up ZigBee to become the truly interoperable global standard that has been claimed all these years.
Figure 1: ZigBee Mesh Network
So what is AMI and how will ZigBee provide a solution?
Advanced metering infrastructure (AMI) is defined by Wikipedia as "systems that measure, collect and analyze energy usage, from advanced devices such as electricity meters, gas meters, and/or water meters, through various communication media on request or on a pre-defined schedule. The infrastructure includes hardware, software, communications, customer associated systems and meter data management software."
The AMI initiative came about as state and local governments push utilities to develop business models that will support dynamic pricing, push for reductions in energy consumption and cost, and decrease the peak energy demand on the system by utilizing load control and demand response. The basic idea is to provide information and incentive to the customer, enabling them to be more responsible for how they consume energy in the home. Obviously, this AMI initiative goes well beyond simply deploying ZigBee, but for the sake of this article, I will focus on the role of ZigBee in AMI.
As a standard, ZigBee and the 802.15.4 PHY and MAC protocol on which it is defined, specifies the details of the network over which application messaging takes place. This means that ZigBee provides the backbone, but doesn't specify or limit the details of what is being communicated. All ZigBee devices participating in the AMI network will follow the same rules for network discovery, joining, security and establishing links (binding) on a peer-to-peer basis. However, simply adhering to the same networking standard is not enough for full interoperability. To ensure that devices all speak the same language, conformance must be achieved at the application layer. In ZigBee, this is what is referred to as a public profile.
ZigBee Smart Energy
To support AMI, the ZigBee Alliance has defined and ratified the Smart Energy profile. The details were debated and finalized in a committee made up of meter and thermostat vendors, utility companies and other interested parties. ZigBee Smart Energy offers utility companies a secure mechanism for communicating with "smart" devices and appliances, allowing energy management in the home.
By way of a voting majority, the Smart Energy profile defines metering, demand response and load control, pricing, text messaging and notification, security and a list of supported devices. More specifically, the profile defines which devices will be allowed into the AMI network (e.g., gateway, electric, water and gas meter, thermostat, load control device, in home display), and the required and optional messaging that must be supported between these devices. One major component of AMI is the support for real-time pricing so that billing can be achieved on an interval (e.g., 15-minute window) basis.
The cost of producing energy rises significantly during peak demand times (it costs significantly more money to squeeze out extra electricity when power plants are running at close to maximum efficiency). Therefore, the ability to establish and offer pricing on a per-interval basis as compared to the current flat rate pricing offered today provides benefits to both the utility company and the consumer. Interval pricing means that a consumers' electric bill will reflect their actual usage cost.
For those who are looking to save money, interval pricing will reward people who make an effort to turn off lights, unplug unused appliances, adjust their thermostats when they're not home, and use non-essential appliances like the dishwasher and washing machine when it is cheaper (and greener) to produce energy. This change in behavior also benefits utility companies. The concerted effort of their customers can actually shave peak consumption and avoid the need for producing electricity when it is expensive (and less profitable) to do so.
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