Design Con 2015

Robust design principles for home smart grid metering

Vamshi Kandalla

October 11, 2010

Vamshi KandallaOctober 11, 2010

A worldwide trend toward more efficient energy utilization is extending so-called Smart Grid technology into the home. This is creating a demand for new energy meters that can serve as a two-way communication hub between the home and the utility, and have the ability to measure, verify, dispatch, and enable demand response for power usage within the home.

To meet this demand, developers must address key design goals such as small size, low cost, and integration of metrology, control, and communications. As the cost of energy keeps rising, the need to manage energy more efficiently is becoming more evident. Utilities, for instance, must find a way to address growing demand by building new generation capacity or better utilizing the capacity they already have.

Energy generation capacity is typically sized to meet peak demand, which results in much of that capacity remaining unneeded much of the time. In Pennsylvania, New Jersey, and Maryland utility (PJM) area studies, it has been shown that generation needs to run at only 85% of full capacity 98% of the time.

If the utilities had a way to moderate that peak demand, they could reduce their need for capital investment. According to the California Energy Commission, implementing a demand response system to reduce peak energy demands is one-sixth the cost of adding new capacity

Governments are also interested in curtailing demand by managing energy consumption more efficiently. Reduced energy demand improves both national security and trade balances by lowering dependence on an uninterrupted supply of imported fossil fuels.

Implementing a smart grid to manage energy can also improve national security by providing more effective ways to prevent or mitigate attacks on a nation’s energy infrastructure. Increasingly, governments are also interested in reducing energy demand to lower carbon emissions that may be contributing to climate change.

Consumers, too, will benefit from the development of a smart utility grid for energy management. At the very least, they would see more accurate billing. More importantly, however, a smart grid will give consumers the tools to lower their energy costs.

One such tool is time-of-use pricing, which charges consumers less for the energy they use outside of peak demand periods. The cost differential encourages consumers to change their energy use patterns to make capacity utilization more uniform, as trials by Puget Sound Energy have demonstrated. The implementation of time-related pricing yielded a 6% reduction in peak demand and a 5% reduction in energy use overall.

Smart Grid Needs Smarter Meters

But to make time-of-use pricing possible, as well as provide other energy management tools to create the smart grid, there need to be smart energy meters. The traditional energy meter has remained essentially unchanged for more than a century.

It only measures accumulated power usage, providing a single point of information without any inherent time history. To learn what energy has been used over a time period requires reading of the meter at the beginning and the end of the period.

Further, these readings have to be made by a human being. This creates several problems. One is the labor costs involved in making repeated readings in order to determine billing. Another is that such manual readings are prone to errors, which can affect cash flow or create customer dissatisfaction depending on the error type.

In addition, residential energy meters can often become inaccessible for reading without customer involvement due to the construction of fences or other barriers, aggravating both cost and error concerns.

Utilities began addressing these problems by introducing automated meter reading (AMR) in the 1990s. AMR utilized energy meters that had an ability to communicate unidirectionally with a handheld reader unit, vehicle-mounted unit, or to a central office using powerline or wireless communications.

This one-way link allowed reading of the meter electronically, eliminating the need for visual inspection. Although not eliminating human involvement completely, AMR yielded significant reductions in billing cost and improvements in accuracy.

In some cases, AMR also supports time-of-use metering, with the meter recording energy usage over preset time intervals. This additional information allows the utility to engage in time-of-use pricing, but only in a static fashion. Time intervals are pre-set with limited or no flexibility and the consumer has no access to the information to help guide their energy use in real time.

Utilities are now engaged in deploying the Advanced Metering Infrastructure (AMI) to allow full automation of the billing process and add flexibility to time-of-use billing. AMI meters maintain continual two-way communications with the utility, eliminating even the need for drive-by readings. Instead, the utility’s billing system can automatically read any AMI meter remotely, either on a schedule or on demand.

This automated remote reading capability not only streamlines billing, it provides an opportunity for the utility to perform real-time system analysis and gather feedback on power utilization.

Such analysis can help utilities apply their resources more efficiently. A block-by-block analysis, for instance, can help a utility choose transformers of the optimum size for a given area, preventing the expense of too large and the reliability issues of too small a transformer.

The AMI meters also support dynamic time-of-use metering. The meters record power usage based on time intervals and they can change the definition of those intervals. The communications link is bidirectional, so the utility simply downloads new timetables to the meter as needed.

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