ZigBee—A Key Enabler for Residential Demand Response

By Bob Gohn, Ember Corporation

The old adage “work smarter, not harder” has become a suitable mantra for utility system planners as the gap between electric supply and peak demand continues to grow. The use of advanced metering infrastructure (AMI) systems to address these supply and demand issues is well-known, and new capabilities now exist that bring the “smart” in the “smart grid” right down to the ordinary consumer.

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The emergence of home area networks (HANs) that connect various power-consuming devices with smart meters or other “energy services portals” enables consumers to participate–directly or indirectly–in powerful residential demand response systems. And ZigBee, the curiously named wireless networking standard, has emerged as the key to robust, reliable, and secure HAN deployments.

Enter ZigBee

The emergence of home area networks for energy management comes at a time when wireless home automation products that control entertainment, lighting, climate and security systems are taking hold, driven by the emergence of standards-based wireless solutions. Whole-house automation systems are becoming standard in upscale homes and are forecast to make significant inroads even in average homes as device and installation costs drop. Various broadband and wireless telecom service providers are beginning to offer “home awareness” services that can access and control connected home systems over the Internet or via cell phones.

Smart meters serve as the home area network gateway for devices such as ZigBee thermostats, load control devices, in-home displays and smart appliances.Click here to enlarge image

Enter ZigBee: an ultra-low-power wireless networking technology that is making it practical to embed wireless communications into virtually any home/building automation product–from lighting ballasts to climate controls to smoke and security alarms–all without the prohibitive cost and disruption of installing hard wiring. ZigBee enables devices to self-assemble into robust wireless mesh networks that automatically configure and heal themselves and allow individual devices to work for years on battery power. ZigBee has become the standard wireless control technology for home automation, commercial building automation, and a variety of other sensing and monitoring applications, and has emerged as the preferred standard for HAN/AMI applications as well.

Wireless networking–rather than wired technologies–is a key enabler for HANs not only because of dramatically lower installation costs, but because it allows the use of battery-powered devices not directly connected to home power lines, such as thermostats, security sensors, and various remote controls and displays. Perhaps most importantly, wireless can also integrate gas and/or water metering systems, which in any case require the use of wireless, battery-operated communications.

These are among the reasons the analyst group ON World estimates that utilities will spend $1.6 billion on wireless sensor network technologies–predominantly ZigBee–for smart metering and demand response by 2011.

How ZigBee Works

Just as Wi-Fi grew to meet the demand for wireless data networking and Bluetooth did the same for wireless head-set connectivity, ZigBee has emerged as the dominant standard for wireless automation networks. ZigBee is designed specifically for highly reliable, low-power and low-cost control and monitoring applications. Similar to the way Wi-Fi specifications leverage the IEEE 802.11 standards, ZigBee is built on top of the IEEE 802.15.4 radio standard, which defines the physical and MAC layers, typically operating at 250 kbps on one of 16 selectable channels in the 2.4 GHz band, which is uniquely unlicensed in most of the world.

But ZigBee is quite different from Wi-Fi or Bluetooth in its use of a self-configuring mesh topology rather than a “star” topology that requires each device to be within range of a central access point. ZigBee devices automatically route messages through other ZigBee devices if the destination is not in direct connectivity with the sending device. Hence, the reach of a ZigBee network can be much greater than the range of the individual radios themselves, and can adapt to challenging and/or changing conditions within a home or commercial environment.

ZigBee enables devices to self-assemble into robust wireless mesh networks that automatically configure and heal themselves.Click here to enlarge image

ZigBee is simple to use and easily incorporated into a wide range of devices, but this does not mean ZigBee is a simplistic protocol. In comparison to earlier proprietary solutions aimed at home networking, the ZigBee protocol stack is highly scalable, capable of supporting thousands of devices in a single network. ZigBee also provides strong security capabilities with built-in encryption capabilities. And, ZigBee is extremely tolerant of interference from other radio devices, including Wi-Fi and Bluetooth. In fact, typical home automation products often build both Wi-Fi and ZigBee into the same device.

Even though the ZigBee protocols are quite sophisticated, ZigBee can be fully implemented within a single silicon “system-on-chip” that integrates the radio, access controller, CPU processor core, encryption engine, various peripherals, and RAM and flash memories. This allows very simple and low-cost system designs. The ZigBee protocol stack runs as software on the embedded CPU and is stored in the integrated flash memory, enabling remote updating of the protocol firmware at any time in future. The device application (such as a wireless light switch, temperature sensor, load switch, etc.) may also be implemented as software within the embedded CPU, allowing complete systems to be implemented within the single ZigBee chip. ZigBee platform vendors provide complete ZigBee solutions, including chips, software and development tools, to the various vendors building AMI systems.

ZigBee Standards

ZigBee standards are specified by the ZigBee Alliance, which is made up of more than 250 member companies, including many well-known global brands. The alliance uses independent labs to test, verify and certify ZigBee platforms and products for conformance to the specifications. To assure protocol-level interoperability and to earn use of the ZigBee Alliance logo, designers must start with a “ZigBee Compliant Platform,” consisting of a silicon and software stack combination that has been tested by one of the alliance-designated test houses.

The ZigBee Alliance also specifies “public application profiles” that define the detailed messaging used within typical application scenarios. Vendors may have their products tested to one or more public application profiles to be designated as “ZigBee Certified Products.” In January 2008, the ZigBee Alliance unveiled its latest profile–the ZigBee “smart energy” public application profile–specifically to support demand response and AMI systems. The ZigBee standards process goes beyond defining “paper” specifications by including demonstration of true multi-vendor interoperability as part of the approval process. For example, dozens of leading AMI systems vendors are participating in the testing and finalization of the smart energy public application profile.

ZigBee has prevailed over earlier proprietary offerings not only for its technical superiority, but also because it is the only complete, mature, open, multi-vendor standard available today, allowing designers many different platforms to choose from.

Leveraging ZigBee in AMI

To connect the home area network to the energy provider, typical AMI networks consist of at least two tiers: the neighborhood area network connecting the meters within a local area to an aggregation point, and a backhaul network that connects the aggregation points to the utility’s back-end IT systems.

The AMI systems vendors offer a wide array of neighborhood area network solutions ranging from power line carrier technologies to RF-based mesh networking implementations. The underlying networking technology may be an optimized proprietary protocol or an adaptation of the Internet Protocol (IP). Utilities will choose the optimum solution based on the specific characteristics (urban, suburban, rural or a mix) of their service area. The backhaul network connecting the various neighborhood area network access points may use existing wired broadband network connections, wireless cellular data connections, or emerging fixed wireless systems such as WiMAX.

In a typical AMI system, the electric meter serves as the “energy services portal,” the gateway between the ZigBee-based HAN and the energy provider’s neighborhood area network. In some instances, especially in deregulated environments, the energy services portal may be a separate gateway that connects to the energy provider through a local broadband connection or local cellular network. The meter may still participate in the HAN, but might not be the energy services portal. In any case, the portal communicates with a variety of ZigBee-enabled devices, such as programmable communicating thermostats, load control devices, in-home displays and energy management consoles. Load control devices are generic plug-in devices for monitoring and controlling high-current appliances in the home, primarily air conditioners and pool pumps. In the near future, consumer appliance manufacturers will offer next generation “smart appliances” embedded with ZigBee technology to extend AMI device control even deeper into the home. For example, LG is integrating ZigBee chips and software into its HomNet home networking-based products, which feature the ability to check and control appliances and home automation devices throughout the house and manage utility usage.

Because of the type of data and control within AMI networks, application security is imperative. Energy providers desire to commission HAN-based devices explicitly through the energy services portal using strong public key cryptography to authenticate devices that are part of the HAN, as well as communications between the HAN devices. In this way, energy providers can distinguish between HAN devices directly under their control as part of a formal demand response program, and other consumer devices that might exist in the home. For example, all devices–such as a complete, integrated home automation system–may desire to receive public pricing information and messages from the energy provider and take pre-programmed actions based on current pricing levels. But only specific authenticated devices may be permitted to participate directly in provider-initiated direct demand response actions.

It is critical that the means of authenticating and securing demand response device communication be a well-established industry standard to allow consumers to purchase approved devices through normal retail channels. The ZigBee Smart Energy Profile provides the basis for such standards.

ZigBee Deployment Examples

One of the most anticipated AMI system rollouts is Southern California Edison’s (SCE) SmartConnect program, which begins deployment this year. The utility expects the program can reduce peak power consumption by as much as 1,000 megawatts. SCE is also working on a more advanced AMI program to provide customers with time-differentiated rates and demand response options. SCE is replacing approximately 5 million electric meters for homes and businesses with new ZigBee-enabled smart meters.

Zigbee is the wireless networking technology that makes it practical to embed wireless communications into virtually any home/building automation product.Click here to enlarge image

Metering vendors such as Itron, which is supplying SCE, have integrated ZigBee-certified technology into their products to provide a two-way communication pathway to the home for energy load control and demand response. Itron’s OpenWay AMI platform enables homeowners to make more informed decisions about their energy usage and promotes energy conservation. The smart meters serve as the HAN gateway for devices such as ZigBee thermostats, load control devices, in-home displays, and smart appliances, and also support load-limiting remote disconnect switch, positive power outage detection and restoration notification, voltage monitoring, theft detection, and the ability to reprogram the meter remotely.

Some AMI vendors are extending ZigBee’s capabilities beyond the HAN by using ZigBee standard technology for the neighborhood area network implementation as well. In Europe, the city of Gothenburg, Sweden, is in the process of deploying the world’s largest ZigBee-based AMI network for its 270,000 homes. Gàƒ¶teborg Energi AB is using the AiMiR AMM System from Korea’s NURI Telecom, making it the world’s first company to cover a whole city with a wireless ZigBee infrastructure for the metering services of tomorrow. Gàƒ¶teborg Energi AB plans to save millions of euros by eliminating manual meter reading and being able to bill the actual usage to the customers. Future plans include extending the technology into the home via HANs for demand response applications as well as home monitoring services.

ZigBee: A Critical Element of Demand Response

Energy providers (and their regulating agencies) are turning toward AMI/HAN systems as part of larger “smart grid” initiatives to meet energy conservation and demand response challenges. ZigBee wireless standards are a critical element of these systems, providing the robustness and reliability, low cost, security, and ease-of-deployment required to indeed allow the grid to “work smarter, not harder.”

Bob Gohn has more than 20 years experience in the communications industry, working in both semiconductor and networking equipment companies. Bob is vice president of marketing at ZigBee wireless networking company Ember Corporation. Bob holds an MSEE from Polytechnic University and a BEEE from Stony Brook University.

ZigBee “ËœSmart Energy Profile’ Delivers Efficiency And Savings

At DistribuTECH 2008 in late January, the ZigBee Alliance announced completion of its ZigBee Smart Energy public application profile. ZigBee Smart Energy offers utility companies a global open standard for implementing secure, easy-to-use wireless home area networks (HANs) for managing energy. The profile also helps product manufacturers by establishing a standards-based technology for new products designed to enhance consumer energy management and efficiency.

The ZigBee Alliance is an association of companies working together to enable reliable, cost-effective, low-power, wirelessly networked monitoring and control products based on an open global standard. The ZigBee Alliance membership comprises technology providers and manufacturers worldwide.

The ZigBee Smart Energy profile enables wireless communication between utility companies and common household devices such as smart thermostats and appliances. Its goal is to improve energy efficiency by allowing consumers to choose interoperable products from different manufacturers, giving them the means to manage their energy consumption more precisely using automation and near real-time information. It also helps utility companies implement new advanced metering and demand response programs to drive greater energy management and efficiency, while responding to changing government requirements.

ZigBee Smart Energy offers electric, gas and water utilities support for advanced metering, demand response, load control, pricing and customer messaging programs. It provides communication and control for devices such as in-home displays, programmable communicating thermostats, water heaters, lighting, smart appliances, plug-in hybrid electric vehicles, plus energy service portals and energy management systems. For a more detailed list of features, see http://zigbee.org/imwp/download.asp?ContentID=12484.

Many countries are facing energy supply and demand imbalances that will require alternative energy management and efficiency solutions like ZigBee Smart Energy. For example, the North American Electric Reliability Corporation (NERC) reported that electricity demand in the United States is expected to increase by 135,000 MW in the next decade yet only 77,000 MW of new resources have been identified, creating a shortfall of 58,000 MW–an amount equivalent to 110 large power plants.

Energy management and efficiency solutions can bridge the gap, according to the ZigBee Alliance. For example, the U.S. Department of Energy’s Pacific Northwest National Laboratory recently released the results of a yearlong study showing that households with digital tools controlling temperature and price preferences saved an average of 10 percent on utility bills. The study also showed that if households have digital tools to control temperature and price preferences, peak loads on utility grids can be cut by up to 15 percent, which translates into $70 billion dollars saved over a 20-year period on new power plants and infrastructure expenditures.

“ZigBee Smart Energy was the result of a powerful collaboration between leading utility companies, product manufacturers, and technology suppliers, ensuring the latest features are built in to meet current market demands,” said Bob Heile, ZigBee Alliance chairman. “ZigBee Smart Energy provides a critical piece to many energy management and efficiency programs under way today because it creates a global, open standard allowing energy consumers information and control over their energy use and helps utility companies expand relations with their customers while planning for a greener future.”

A number of alliance members are currently building products that will be certified by the alliance to support ZigBee Smart Energy. These companies include: Cellnet+Hunt, Ember, Freescale Semiconductor, Itron, Tendril and Texas Instruments, who are ZigBee Alliance promoter member companies and members of the Board of Directors which is responsible for setting the alliance’s direction in the energy sector. Some of the other members building ZigBee Smart Energy products include: Alektrona, Computime, Comverge, Control4, Corporate Systems Engineering, Daintree Networks, Digi International, Elster, Energate, Frontline Test Equipment, Golden Power, Greenbox Technology, LS Research, PRI Limited, Radio Thermostat Company of America, Riga Development, Trilliant Networks and Wireless Glue Networks.

Additional information about the ZigBee Alliance is available at www.zigbee.org.

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The Clarion Energy Content Team is made up of editors from various publications, including POWERGRID International, Power Engineering, Renewable Energy World, Hydro Review, Smart Energy International, and Power Engineering International. Contact the content lead for this publication at Jennifer.Runyon@ClarionEvents.com.

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