This Is What Tesla Owners Are Doing While You Sleep

By day electric vehicles are taking the world by storm: their sales are doubling every year, their fuel efficiency is off the charts, and some of them can even accelerate from 0-60 mph about as fast as you can say Elon Musk.

By night the electric vehicle (EV) community continues to make waves. While you are in bed dreaming about how some day you too might own an electric car, many EV owners are doing something dramatic; something unusual; something that is reshaping the energy landscape.

They are using gobs of electricity.

Today we once again crack open Opower’s energy data storehouse (the world’s largest, spanning more than 50 million households worldwide) – this time to examine the energy usage behavior of an increasingly important segment of utility customers: electric car owners who charge their car in the wee hours of the night.

To fuel our analysis, we evaluated anonymous data from about 2,000 night-charging EV owners in the western U.S. (see Methodology below) — a region where Teslas, Nissan Leafs, and other plug-in electric cars abound.

Our statistical findings suggest how vastly EV owners’ energy profiles can deviate from normal; why the timing of EV charging is so important; how solar panels fit into the picture; and what it all means for utilities, their customers, and the future of the electric grid.

After a Long Day, It’s Time for a Good Night’s Charge

The wee hours have in recent years gained traction as a popular time for EV owners to recharge their vehicles.

In the hourly usage curves below, you can see that the EV owners in our dataset (light blue) exhibit a massive spike in electricity use beginning at midnight, shooting up to around 4 times the average level.

Why the huge usage bump at midnight sharp? The answer hinges on incentives and utilities’ ability to shape consumer behavior.

Specifically, many EV owners in the western region (upwards of 60 percent, according to one California study) — and all the EV owners considered in our analysis — have signed up with their utility to get highly discounted electricity between midnight and 7am, in exchange for a daytime price hike. The sudden surge on the right side of the graph above suggests the behavioral effectiveness of this framework: when EV owners enroll in a time-of-use rate plan, they operate in alignment with it.

Offering an off-peak rate plan tends to be a savvy move by utilities: it helps them prevent power-hungry electric cars from overtaxing the electric grid during the day, when system-wide demand is already on the high side. As we’ve previously examined on this blog, high electric demand in the afternoon hours is notorious for destabilizing the power grid.

That’s why utilities in numerous states — ranging from California to Texas to Georgia — have been quick to introduce targeted customer engagement programs and off-peak charging incentives that help smooth the integration of EV’s into their territory. Last month, Minnesota became the first state to roll out a statewide approach for promoting night-time EV charging.

We’ve seen above that EV owners who have an incentive to charge their car at night understandably exhibit abnormal electricity usage during those hours. What may be more surprising is what happens after the sun rises…

After the Sun Rises, Electric Car Owners Are Still Different

It’s morning, around 7:00 a.m. Teslas have been charged, the time-of-use electricity price for participating EV households has cranked up, and the hourly electric usage from those households has diminished.


Despite the marked reduction in usage however, EV rate plan subscribers continue to out-consume their peers even during the waking hours. Between 7:00 a.m. and midnight, they use an average of 21 percent more electricity from the grid than the typical single-family household.

EV owners’ outsized grid electricity consumption during the waking hours appears to register at specific times of day, namely in the morning and evening. For a visual perspective, look at the hourly usage curves from earlier, which show that EV rate subscribers’ grid electric usage during the edges of the day (i.e. 7:00 a.m.-9:00 a.m. and 5:00 p.m.-midnight) are relatively high, but usage during midday is actually below normal.

Why? Consider a couple key factors that may help explain EV owners’ distinctive usage pattern during the waking hours:

1) EV owners appear to have larger electricity needs, especially when at home. 

People are more likely to be home in the morning and evening; EV owners may be especially likely to use more power at those times because they have bigger homes as well as bigger amenities (see below); it’s also entirely plausible that some EV owners may occasionally charge their EV during those times, even though their time-of-use rate plan discourages this kind of behavior.

2) EV owners are much more likely than their peers to own solar panels.

One recent survey among west-region utility customers found that 32 percent of EV owners had installed rooftop solar, which drastically reduces their grid electric consumption during the sunny middle of the day. Likewise, we discovered that many EV households’ afternoon solar generation routinely exceeds their own needs: our regional analysis shows that 1 in 13 EV rate plan subscribers regularly spin their electric meter backwards via solar, compared to just 1 in 86 typical households.

Thanks to their surplus solar generation, EV owners who are also solar super-users actually consume a tad less total daily grid electricity than the typical utility customer.

In light of EV rate plan subscribers’ unique behavioral and household profile, it’s striking that having a sufficiently large solar rooftop can make them — from the perspective of total daily grid electric usage — look pretty darn normal.

More After-midnight Action Is on the Way

EV rate plan subscribers — with their huge night-time charging spike, bigger and fancier homes, and elevated grid electric consumption in the morning and evening — are a distinctive sort of energy user.

And it appears that there are many more of them on the way. Last month, eight U.S. states announced a market development plan to put 3.3 million zero-emission vehicles on their roads by 2025. This month, Tesla CEO Elon Musk released his company’s patents to catalyze the growth of the broader EV industry. Meanwhile, states and utilities are taking bold steps to support off-peak charging options that play nicely with the power grid and make EV fueling more affordable.

Utilities will play a central role in shaping how the EV landscape unfolds in the coming decades. As an increasing number of EV owners begin to plug in, utilities are in an important position to advise them and guide their behavior (e.g. toward night-time charging) in a way that helps smoothly integrate electric vehicles into the modern electric grid – in parallel with other critical trends like distributed solar generation, changes in energy prices, and new controls on power plant emissions.

As for what more and more Tesla owners will be doing while you sleep, just remember: it’s happening in the garage.


Data used for this analysis stems from single-family residences with hourly electric meters, located in a western U.S. region characterized by high penetration of plug-in electric vehicles.

All utility service points fall within a common area bounded by a 100-kilometer radius. Usage statistics are annual per-household averages based on hourly electricity consumption data measured between May 1st, 2013 and May 1st, 2014.

Electric Vehicle, or “EV” households (n=1,996) are defined as utility customers enrolled in an electric vehicle rate plan that promotes night-time charging commencing at 12:00 a.m. Among these customers, the mean start month for rate plan enrollment is October 2012. Energy data for these households specifically reflects usage following the date of their enrollment in the EV rate plan.

Solar EV Households evaluated for this analysis are defined as customers who exhibit an annual average negative usage read (i.e. routinely spin their electric meter backwards by generating solar electricity in excess of on-site demand) for the 12:00 p.m.-1:00 p.m. measurement interval.

Typical Households (n=996,465) are defined as customers enrolled in a standard rate plan with no time-of-use component. This group is certain to contain EV owners who are not enrolled in an electric vehicle rate plan. However, the relative scarcity of EV’s within the broader population at this time implies that their usage patterns have a negligible impact on baseline group statistics.

This blog was co-written by Ben Harack and Barry Fischer.

Graphics by: Waleed Al-Alami

Special thanks to: Meggie Bonner, Emily Bailey, Alessandro Orfei, Aaron Tinjum, and Casey Davis-Van Atta

Data Privacy: All data analyzed here are anonymous and treated in strict adherence to Opower’s Data Principles.

Author’s note: The analysis and commentary presented above solely reflect the views of the author(s) and do not reflect the views of Opower’s utility partners.

This blog was originally published on Opower and was republished with permission.

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Former editor of I hold a MA in Professional Writing and BA in English from the University of Massachusetts and a certificate in Professional Communications: Writing from Emerson College.

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