Wireless and Low-Power Technologies Drive New Opportunities in Smart Grid Devices

Smart grid product innovations will be driven by technology trends that include ultra low-power electronics, innovative power sources, miniaturization and integration, and a range of wireless communication protocols. To get a sense for what’s happening in these areas, EE Catalog caught up with Steven C. Grady, VP of marketing at Cymbet Corporation; Tyler Smith, marketing manager, Wireless Products Division and Clayton Pillion, business unit leader, Smart-Energy Solutions Group at Microchip Technology, Inc.; Øyvind Janbu, chief technology officer, Energy Micro; and Dennis McCain, director of marketing, Murata Wireless Solutions. These experts offer insight on how smart grid device developers can take advantage of new technologies and standards, and some pitfalls to watch out for.

EE Catalog: As the smart grid extends out to homes and businesses, wireless sensors and mobile control devices become important elements in monitoring and managing energy use. What are challenges that developers of these systems need to be aware of?

Dennis McCain, Murata Wireless Solutions: There are several challenges of which smart energy system designers need to be aware. One challenge is the fragmentation of the home area network (HAN) market. There are several wireless standards that are currently used in HANs including WiFi, ZigBee, Z-Wave and Bluetooth/Bluetooth Low Energy (BLE), but for nearly all deployed smart meters, ZigBee Smart Energy is the wireless standard chosen by utilities for communicating with the HAN.

In terms of the smart grid extending to homes and businesses, the real challenge is how to design a system that bridges this gap, thereby ensuring interoperability between devices. Another challenge is selecting the optimal wireless standard for the application, as each has its advantages and disadvantages. WiFi is proven, fairly ubiquitous and is the easiest to integrate with current IT systems; however, it has significantly higher power consumption compared to ZigBee and BT/BLE, making it problematic for battery-powered devices. Bluetooth and, more specifically, Bluetooth LE offers the lowest power consumption but is primarily used in point-to-point communication as opposed to any type of wireless networking. ZigBee is also lowpower, offers mesh networking functionality and is the wireless standard chosen for all smart meters; however, it is fairly new and does not have the chip volumes of WiFi and Bluetooth, making it temporarily more expensive. The bottom line is that there will continue to be many wireless standards used in the HAN with no clear winner, so it is up to the system designers to select a wireless technology that best fits their application while addressing the potential problem of interoperability with other HAN devices.

Steven Grady, Cymbet Corporation: There are many challenges to extending the smart grid into homes and businesses. The returnon- investment (ROI) for deploying energy management systems must be identified and quantified. The ROI from these systems must be great enough to stimulate purchase and use. This is especially true for homeowners who might balk at a $200 initial cost for an energy-management system. The costs go up from there if appliance-specific monitoring devices are added to the system. In addition, home energy-management systems that access the main AC feed from the utility company may require professional installation, which increases the costs of home deployment.

Incumbent building energy management suppliers have an embedded customer base and market share to protect. Most of these vendors’ systems use proprietary equipment and protocols. The ideal solution of an open energy management system, where monitoring and control devices can be plugged in from other vendors, is not attractive to the incumbent suppliers.

Øyvind Janbu, Energy Micro: When working on sensor systems with limited or random energy sources it is important that the hardware and software can efficiently perform tasks and shut down in a safe way. Such redundancy can be implemented with some care, but developers need to choose efficient hardware and make sure the application code is energy optimized. The latest microcontrollers and tools support such energy-aware designs.

Smith and Pillion, Microchip: Challenges include regional requirements or restrictions that may dictate radio usage and implementation. Additionally, customers need to decide which technology they will support with their smart-energy device. Many technologies are being discussed and proposed for the smart-energy market. Maintaining flexibility is a key attribute of today’s implementations.

EE Catalog: What are the pros and cons of the various wireless protocols in embedded smart energy applications?

Tyler Smith and Clayton Pillion, Microchip: There are three primary wireless communication protocols—proprietary (user-defined), ZigBee and WiFi (TCP/IP). Determining which communication protocol stack is appropriate for a given application is a key decision factor. Do you need to provide interoperability with a standard? Do you need to support a mesh network topology? Do you need to connect to the Internet? Do you have regional limitations, as well as range and reach requirements?

The ZigBee protocol is an interoperability standard for lowpower and low data-rate wireless mesh networks. The advantage is that it is a standard and products from multiple vendors can interoperate on a defined ZigBee network. The ZigBee protocol involves a fairly large stack, so it requires a larger microcontroller. The ZigBee protocol also supports large networks, and therefore requires more wireless networking experience and expertise.

The WiFi (TCP/IP) protocol is an established interoperability standard, as well. The WiFi protocol has one key advantage in that it allows products to get onto or be accessed from the Internet, which the ZigBee protocol does not. WiFi typically uses more power than ZigBee, but it supports higher throughput or data rates. WiFi only supports point-to-point communication and, today, does not support mesh networking or routing.

Proprietary protocols are cost-effective communication protocol stacks, but they are not interoperable or standards-based. Proprietary networks can operate over multiple radio frequencies and data rates. They also operate at some of the lowest power levels and are some of the lowest cost solutions. Microchip’s MiWi proprietary protocol stack supports mesh and pointto- point networking. There is more flexibility in proprietary wireless networks, but they will not talk with third-party solutions or access the Internet.

EE Catalog: What trade-offs should developers address in deciding on power management/energy harvesting options for smart energy applications?

Janbu, Energy Micro: From a microcontroller perspective, it is important to address the amount of autonomous and energy-friendly peripherals available for the sensor tasks. Most operations might actually be solved without using the CPU, and by choosing the right feature set, even a limited energy source can actually power a system with a MCU, a specific sensor and radio transmission.

Grady, Cymbet: Energy harvesting for microelectronics is primarily used to replace a coin cell battery or supercapacitor. Often times the energy storage devices (especially batteries) do not last the life of the product. The cost of changing a battery can be very expensive depending on where the device is located. So the first trade-off is the cost of using energy harvesting circuitry vs. the cost of changing batteries. The next big design trade-off is what energy source to harvest: light, thermal gradients, vibration, electromagnetic, RF induction, etc. The choice of energy harvesting transducer drives the entire design of the EH-based device. Another key trade-off for EH-based wireless sensors is the choice of wireless interface and protocols. There are many choices to be made – Wireless Hart, ISA-100, ZigBee, Bluetooth, WiFi, etc. All of these wireless interfaces have different electrical and power characteristics that must be taken into account in the power management design.

EE Catalog: What types of smart energy applications are most appropriate for energy harvesting? What are some key considerations designers need to make in these decisions?

Grady, Cymbet: The most appropriate applications for energy harvesting (EH) are EH-based wireless sensor nodes for building energy management systems; EH-based wireless sensor nodes for industrial process monitoring; structural monitoring for roads, bridges and buildings; data logging equipment for transportation vehicles; and rechargeable medical devices. The key considerations are power budget, ultra-low power electronics and utilizing energy-efficient design techniques. Applications where a battery cannot be used due to transportation safety or disposal issues are excellent candidates for energy harvesting.

Janbu, Energy Micro: Energy Micro and Linear Technology have already demonstrated how tiny vibrations from, for instance, a motor can be harvested and used to run an application with a 32-bit microcontroller, an LCD screen, a motion and temperature sensor and a radio interface. With this in mind, designers should trust that they can achieve almost anything with only limited energy, and learn how to really utilize their new hardware and software tools. The smart energy applications have barely started, and the future will show us many smart energy harvesting applications.

Cheryl Berglund Coupé is Editor of EECatalog.com. Her articles have appeared in EE Times, Electronic Business, Microsoft Embedded Review and Windows Developer’s Journal and she has developed presentations for the Embedded Systems Conference and ICSPAT. She has held a variety of production, technical marketing and writing positions within technology companies and agencies in the Northwest.