U.S. Electrical Grid Undergoes Massive Transition to Connect to Renewables

The U.S. electrical grid is the largest interconnected machine on Earth: 200,000 miles of high-voltage transmission lines and 5.5 million miles of local distribution lines, linking thousands of generating plants to factories, homes and businesses. The National Academy of Engineering ranks it as the greatest engineering achievement of the 20th century. What it cannot do is support the massive shift to low-carbon power that scientists warn will be needed to avoid catastrophic climate change impacts.

To shrink the electricity sector's carbon footprint, experts say, the nation needs to build thousands of miles of new transmission lines over the next 20 years to connect more renewable resources to electricity demand centers. A 21st-century grid will also have to balance fluctuating power flows from wind and solar generation, small-scale distributed sources, and plug-in electric vehicles. And it must be interactive so that customers can manage their electricity use.

The transition is already under way, although it means different things for different companies. Firms that operate long-distance transmission lines, such as the Independent System Operators that manage regional grids in New York, New England and the Midwest, are adding sensors, phasors, and other devices invisible to non-engineers, that give them much more precise control over the system. Better control will help utilities add more renewable power, a challenge now because wind and solar energy are intermittent sources, and grid operators can't always react quickly when their output fluctuates.

"The whole power system is engineered to balance demand and supply at every second, which means that control over generators is really important," said energy consultant Peter Fox-Penner, a principal with The Brattle Group and author of Smart Power: Climate Change, the Smart Grid, and the Future of Electric Utilities (Island Press, 2010). "But if you have really up-to-date information on all the flows on your grid, you can tolerate a little more variability. The smart grid will monitor everything at a very, very fine level of detail and reacts really fast, so operators will have time to fire up another plant if wind speed drops or a big cloud formation reduces solar output."

Suppliers such as utilities that deliver power directly to homes and businesses are focusing on a more visible element of the smart grid: meters. Today the grid transmits information one way - from utility to customer - and most meters only show power usage for the current billing period. What's more, power companies charge the same rate for every kilowatt-hour of electricity that's consumed, even though the cost of generating electricity can change dramatically during the day. Since users don't see how much power they are using or how much it costs in real time to generate it, they have little incentive to conserve energy or shift their use to off-peak hours.

To crack this problem retail power suppliers are installing advanced metering systems (smart meters and wireless communications systems and databases to support them). Advanced metering lets utilities show customers how much electricity they use at different times of day and how much that power costs. With regulators' approval, power companies can also use time-based pricing, charging customers based on the actual cost of power. There are many ways to structure time-based pricing: some suppliers charge more for certain blocks of time when demand is typically high, like weekday afternoons, while others raise prices sharply on selected days when the grid is under heavy stress, as on the hottest days of summer. But all of these programs aim to shift consumption away from high-demand periods. ...

The main reason for peak-shifting is economic, Fox-Penner said: It reduces the utility's cost to provide power at high-demand times. But peak-shifting can also reduce carbon emissions, although the climate impact depends on what kind of plants utilities would otherwise call into service to meet peak demand. BGE's peak reductions, for instance, will reduce the need to call on old and relatively dirty coal plants, eliminating significant carbon emissions, Case said.

The bigger climate payoff from smart metering comes as customers reduce electricity consumption throughout the year. Studies in the U.S., Canada and Australia have shown that providing real-time information about electricity use and costs can reduce energy use, although some customers are more receptive than others to smart metering and time-based pricing.