Electronic Design

The Smart Grid Meets White Spaces

Before the Smart Grid can be implemented, designers need to determine which wireless technologies and frequency spectrum are best for use inside the utility as well as from the home to the utility. Many options are under consideration. Now, another alternative could be a serious contender: low-cost frequency shift keying (FSK) radios in the white-space spectrum.

White spaces are open TV channels in the VHF and UHF regions. A designated 6-MHz TV channel that isn’t being used would be white space. There are lots of white spaces across the U.S., but the available channels vary widely from area to area. White spaces are easy to identify thanks to a unique database developed by Spectrum Bridge Inc.

Because of the lower frequencies involved, white-space radios inherently have a longer range and a greater link reliability, even without a line-of-sight (LOS) path, than Wi-Fi, ZigBee, and other radios operating in the microwave bands. This makes them attractive for robust control links in the utility industry as well as for providing a solid consumer-to-utility connection.

Now, Spectrum Bridge, Plumas-Sierra Rural Electric Cooperative & Telecommunications (PSREC), and Google have launched the nation’s first wireless network trial using TV white spaces to test their viability in the Smart Grid. The test is underway in Plumas-Sierra County in California.

Since white spaces provide outstanding propagation characteristics, the ability to penetrate foliage, and non-LOS connectivity, PSREC chose them to enable Smart Grid technologies and investigate more efficient ways to manage its supply of and demand for electricity, improve system control and data acquisition (SCADA) with PSREC substations, and provide broadband Internet access to underserved areas.

“Plumas, Lassen, and Sierra counties are located in the Sierra Nevada Mountains and present some very technical challenges with respect to wireless coverage,” said Lori Rice, chief operating officer at PSREC. “The ability to use white space has proven to be an effective option for dealing with difficult terrain and offers another option for wireless connectivity.”

TV white spaces are unused TV broadcast channels made available by the recent transition from analog to digital TV. As part of the National Broadband Plan, the Federal Communications Commission (FCC) has declared that TV white spaces are well suited for wireless data networks and can be used to deliver cost-effective broadband connectivity for a wide variety of consumer, business, and government applications.

By The Numbers
White-space radio modems can deliver a data rate of 1 to 3 Mbits/s in a 6-MHz channel at a range up to 4 miles reliably in a non-LOS environment. Basestations can run up to 4 W. TV channels 2 through 51 include the VHF frequencies in the 54- to 216-MHz range and UHF frequencies in the 470- to 698-MHz range. The PSREC application uses a channel in the 550-MHz range. The range is exceptional at these frequencies, with even more range possible with higher antennas. The only downside is that these low frequencies require longer antennas.

PSREC currently employs a wide variety of wireless solutions across multiple frequency bands, but still faces challenges in some areas due to challenging terrain. The applications deployed for the Plumas-Sierra Smart Grid wireless network (see the figure) trial deliver real-time broadband connectivity to remote substations and switchgear, allowing PSREC system operators to manage the electrical system remotely, request critical data from substations, manage power flow, and protect the system and employees while maintaining the local grid.

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The wireless network is also providing broadband access to an underserved community. In addition, PSREC has deployed Google Power Meter technology, an energy monitoring tool that helps consumers save energy and money using information provided by a smart meter. With the white-spaces network and Google Power Meter, consumers can view real-time detailed energy consumption data from anywhere online.

The PSREC test system deploys a device called the Energy Detective (TED) made by Energy Inc. to measure power usage. It uses small current transformers that clip on to the utility wiring in the home electrical entrance box and measures current, voltage, and power factor. That data gets transmitted over the ac line to an LCD monitor inside the house. Real-time updates are provided every second with the energy calculated and displayed with 1-W resolution. When used with the Google Power Meter software on a PC, a consumer can easily get a handle on energy usage and how to control it.

To prevent the TV white-spaces network from interfering with licensed television broadcasts and other protected TV band users, the system operates under the control of Spectrum Bridge’s intelligent TV White Spaces database. The basestation radios link to the database via the Internet. The database dynamically assigns non-interfering frequencies to the white-spaces transceiver, which then adapts in real time to new TV broadcasts as well as other protected TV band users operating in the area.

“The Plumas-Sierra white-spaces trial is further proof that TV White Spaces is a great tool to extend broadband connectivity to underserved areas and make possible applications like the Smart Grid in ways that couldn’t be done cost-effectively before,” said Jeff Schmidt, director of engineering at Spectrum Bridge.

Spectrum Bridge’s database technology underlies the TV White Spaces trial network and allows it to operate efficiently and without causing interference. TV white-spaces availability can be determined for any location in the U.S. by using the free search tool at www.spectrumbridge.com or by downloading the free Spectrum Bridge TV White Space application from smart-phone application stores.

Spectrum Bridge has completed other successful white space trials in Claudeville, Va., Wilmington, N.C., and Lake Mary, Fla. These successes were recently reported to the FCC, which is in the final stages of devising formal rules for white spaces that could be announced by September or October of this year.

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