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.

Interval pricing represents just the beginning of where AMI and Smart Energy can both save money and have a positive effect on our environment. To take optimizing consumption one step further, Smart Energy also supports the scheduling of events and external control of smart appliances which can be power cycled (in the case of an HVAC system), or switched off (in the case of a pool pump) based on time-of-day pricing. On the Smart Energy side, this includes load control devices that can be controlled remotely by either a user or utility company directly. Smart Energy also extends out to a bigger picture concept that is referred to as the OpenHAN.

OpenHAN focuses on supporting two-way communications between the utility and the home area network (HAN). In proposed usage cases (no final decisions have been made at this point), utilities will maintain a proprietary communication backbone to the electric meter, which will serve as a gateway to the ZigBee Smart Energy network. This network will comprise devices like those already discussed, and support a load and energy management system that includes load controllers on the Smart Energy network, as well as bridge to a separately maintained home automation (HA) network.

Figure 2: ZigBee Smart Energy Home Network

The entire system provides direct access to usage data and pricing, and supports load control integration and secure two-way communications for on-demand load shedding. Furthermore, it ensures a future path to augmenting the functionality of the OpenHAN with future products and devices capable of leveraging data sent from the utility company. In this scenario the Smart Energy network is essentially controlled by the utility company, while the HA network remains open to the customer. New devices can be integrated into the system and registered with the utility based on what the service provider offers.

While not part of initial trial deployments or the core of Smart Energy, the infrastructure put in place by the utilities will serve as a launching point for future "smart energy" technology. We can envision a not too distant future where our washer and dryer, dishwasher, refrigerator, pool pump, lights, HVAC, TV, other electronics and a myriad of other devices in and around the home connect into the network, turn on and off automatically based on time of day, and shut down or power cycle during times when the cost of electricity is especially high.

In this scenario some devices will be controlled by the home owner, some by the utilities, and others could be controlled via an optional service where the utility is given control but the home owner has override control and an opt-out feature for certain critical devices such as medical equipment.

To put the scope of this effort into perspective, Chartwell AMR Report, November 2006[1], stated AMI technology is projected to double purchases of automated meters in the next four years. With over 100 million housing units in the United States, there is a large market for this technology. Significant energy and money can be saved through the deployment of AMI and smart metering.

Although initially focused on the U.S. market, Smart Energy promises to become a global standard as well, being initially considered as a solution in both Europe and Asia markets. With oil prices and electricity costs hitting record highs almost daily, and with an increasing concern for carbon emissions and the environment, we are likely to see an increasing demand for AMI and other forms of smart energy-efficient technologies in the near future. ZigBee is one technology that is making this all possible.

References:

[1] The Chartwell AMR Report 2006, 11th Edition, November 2006

For more information about ZigBee solutions, visit: www.ti.com/zigbee

About the author:
Brian M. Blum is a ZigBee product marketing engineer with Texas Instruments where he is responsible for 802.15.4 and ZigBee Low Power RF product line. He received his Master's of Computer Science with a focus on Wireless Sensor Networking from the University of Virginia. He can be reached at lpw-pme-zigbee@list.ti.com