WattTime, the Tool That Tells You When to Charge Your EV to Keep It Green

Analytics from Berkeley-based WattTime precisely match new loads on a grid to the power plant that will serve them, providing estimates of carbon intensity that are up to 45 percent more accurate than regional averages. Such tools can guide cleaner charging by electric vehicles, and yield a bigger carbon reduction bang from energy efficiency measures and renewable power projects.

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WattTime feeds EV chargers real-time intel on a power grid's ever-shifting carbon footprint
WattTime feeds EV chargers real-time intel on a power grid's ever-shifting carbon footprint.
Photo: Electric Motor Werks

Gavin McCormick’s attendance at an EcoHack in San Francisco ultimately sidetracked his doctoral studies at the University of California, Berkeley, but for a clean cause: software initiated at the 2013 event has transformed the budding economist’s nascent research into a potent tool for squeezing the cleanest performance out of power grids. Real-time algorithms from WattTime, the Berkeley-based nonprofit that McCormick cofounded and runs, are telling electric vehicle owners when to charge to minimize their carbon footprints and predicting which renewable power projects will deliver the biggest CO2 emissions reductions. 

WattTime tracks swings in carbon dioxide emissions as a grid’s power supply mix shifts from minute to minute. Its intelligence, explains McCormick, comes from mining two datasets. The first is power market data. Algorithms trained on that data enable WattTime to predict what power plant will ramp up to meet new electrical demand at any moment in 106 markets across the United States. 

WattTime turns that ‘marginal’ power supply prediction into an estimate of ‘marginal’ carbon impact by plumbing an underused database from EPA’s Air Markets Program. That database contains hourly records of pollution and fuel consumption for every U.S. power plant. “It’s been around for about 40 years and no one was paying attention to it,” says McCormick.

The resulting estimate of CO2 per kilowatt-hour can be strikingly different from a grid’s average emissions intensity—the most commonly used metric for evaluating power consumption. A grid delivering 90 percent nuclear or renewable power, for example, will have very low average emissions. But WattTime can spot when such a grid is ramping up a carbon-spewing coal plant to meet additional demand, and thus has very high marginal intensity.

WattTime is partnering with manufacturers to empower consumers to make cleaner choices. For example, a line of EV chargers from San Carlos, Calif.–based Electric Motor Werks communicates with WattTime when a car is plugged into the charger and then schedules charging to deliver the greenest fill possible.

eMotorWerks claims its JuiceBox Green can cut CO2 emissions by up to 60 percent relative to conventional EV chargers. In fact, analysis by WattTime suggests that chargers designed to optimize for price, rather than emissions, can actually increase carbon emissions (see graph).

Shifting power demand based on cost can drive up CO2 emissions, as the negative carbon savings in this WattTime analysis of New England's power grid showsScheduling power consumption based on cost can drive up CO2 emissions, as the negative carbon savings in this WattTime analysis of New England's power grid shows.Graph: WattTime

Canadian smart thermostat provider Energate, meanwhile, is looping in WattTime’s intelligence to time electric heating and air conditioning for minimum carbon emissions. A pilot of the devices is underway in Chicago. Two more partnerships are in place and “many others are kicking the tires” says McCormick, including energy storage system firm Advanced Microgrid Solutions.

These devices turn the tables on power supply, enabling consumers to essentially game the grid and help keep the highest carbon power sources from ramping up—or even from turning on in the first place. WattTime guarantees at least a 5 percent reduction in emissions. But McCormick says it can deliver up to a 100 percent reduction in some locations such as Hawaii, where curtailed solar power is often the marginal power supply.

WattTime’s next big play is targeting the installation of clean energy. Their algorithms can predict where deploying solar and wind farms to regions are likely to displace the dirtiest fossil fuelled power plants.

WattTime is already providing such advice to corporations investing in renewable power, via the Rocky Mountain Institute, a Boulder, Colo.–based energy think tank. However, McCormick says dramatically shifting investment trends will require an overhaul of carbon accounting schemes, which mostly certify carbon reductions based on grid averages. 

Within six months they hope to achieve a first breakthrough, gaining acceptance for marginal intensity accounting by the Greenhouse Gas Protocol—the leading global carbon accounting standard. McCormick says their petition is, like his nonprofit’s mission, about leveraging marginal emissions data to drive cleaner use of electricity, rather than advancing their proprietary system: “We want them to accept anyone with technology like ours.”

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