A Project

We have a demonstration fleet of plug-ins at our headquarters in Mountain View and make publicly available the statistics on the performance of those cars. Our vision is that one day millions of cars will be plugging into a greener grid.

Since the inception of RechargeIT in 2007, we’ve been pleased to see great progress in this field:

* In our controlled Driving Experiment, Google plug-ins achieved 93+ MPG
* Almost every large automaker is putting out a plug-in in the next 2 – 4 years
* Recently-passed federal stimulus legislation contains $2 billion for plug-ins
* The stimulus bill also includes a U.S. tax credit of up to $7,500 per vehicle intended to spark the sale of up to 1.5 million plug-ins

RechargeIT Driving Experiment

We’ve had our RechargeIT plug-ins on the road for over two years, collecting data when driven by Google employees in our free car-share program. But we wanted to see how they would perform in a controlled test. The results of our seven-week driving experiment are in – and the plug-ins did great, getting as much as 93 MPG average across all trips, and 115 MPG for city trips!

As part of our mission to fully evaluate the usefulness of plug-in hybrid technology, RechargeIT has created a test fleet of cars. We collect and make publicly available data on the performance of these vehicles. The fleet currently consists of standard hybrid Prius cars as well as eight Priuses that have been retrofitted to become plug-in hybrid vehicles. You can see how the test fleet is performing below under real world conditions, with hundreds of different drivers in a variety of driving conditions. Read more about our methodology and the numbers behind the calculations.

The plug-in hybrid vehicles currently in the fleet are using the Hymotion/A123 production plug-in hybrid kit. Prior to October 2008, we were testing earlier prototype versions of the Hymotion system in both the Toyota Prius Hybrid and the Ford Escape Hybrid.

Please note that the data for specific vehicles can be significantly different even for vehicles of the same type. In particular, those vehicles that were part of the RechargeIT Driving Experiment will show significantly higher MPG numbers than the other fleet vehicles due to differences in drive cycles compared to GFleet driving. For more information, please see this FAQ.

For reference, the vehicles used in the RechargeIT driving experiment were Makalu (Escape); Tikal (Escape plug-in); Kilimanjaro (Prius); and Comoe & Great Barrier Reef (Prius plug-ins).


All of these cars are outfitted with data recording devices that track technical and environmental performance, use patterns and charging history. Above, you can see the actual data which is uploaded from the vehicles. Both electricity and gasoline consumption data is being used to calculate the total energy use for each vehicle to get "real world" performance data on these cars. In order to compare this data to other cars under similar conditions, we have equipped existing conventional hybrids with the same data recording devices. With this data, we are be able to measure more realistic MPG efficiency of plug-ins over conventional hybrid vehicles.

The system to collect data from our fleet consists of an embedded computer running Linux, a wireless data card, a GPS and an AC power monitoring device to monitor charge power. The embedded computer is connected to the vehicle’s CANbus (a data bus present in all new vehicles), and collects relevant data such as speed, distance driven, fuel use, and the vehicle’s high voltage battery parameters. Information from the extended hybrid battery, such as voltage, current, charge state and battery temperature, is also accessed and archived for data analysis.

During charging, the system monitors and records the AC charge power. GPS is used by the fleet manager to track the vehicle’s location, and in the future may be used to plot vehicle data against altitude. All this data is periodically uploaded to our servers via a wireless connection where it is further post-processed and used to refresh the data displayed on our website. In addition to the data collected on board, we use a fleet fueling card that accurately records the amount of fuel used by each car which is then uploaded to our servers and used for the miles-per-gallon calculation.

Once all the data is uploaded to our servers, any necessary calculations are done (such as calculating CO2), and the data is graphed and displayed on our website. Data is available at the fleet level, individual car level and charging event/trip level.


Why do the MPG numbers for the Driving Experiment differ from the observed MPG for the GFleet cars?

We think that the numbers reported in the Driving Experiment are closer to the numbers drivers of plug-ins would experience but still want to publish the data from our GFleet cars. There are many factors that affect the MPG achieved by our plug-in hybrids, some rather dramatically:

1. Our plug-in vehicles are plug-in conversions, and use a hybrid system that was not designed for plug-in use. We anticipate that clean-sheet plug-in hybrid vehicles like the upcoming Chevy Volt and Toyota Prius will deliver higher overall efficiency and less variability in fuel consumption.
2. Driving patterns for a corporate car that is driven by several different people a day is not always representative of "normal driving patterns." A disproportionate number of GFleet vehicle trips are very short. Although these trips could be driven with little use of the gas engine, the gas engine automatically starts to warm up the emissions equipment, lowering fuel economy.
3. The effect of differences in driving style is quite noticeable in plug-in vehicles. Google employees driving the GFleet cars are not familiar with how best to drive the car to maximize fuel efficiency. The Driving Experiment employed professional drivers who tended to drive the vehicles more conservatively. We think that individual owners of plug-in vehicles will have the incentive to learn how to drive their car in a way that is most fuel efficient.
4. The GFleet vehicles are sometimes not sufficiently charged before a trip, either because the drivers forgot to plug in the vehicle or there was insufficient time to fully charge the battery between trips.
5. We recently swapped out the Hymotion package in the GFleet cars. While this brought the vehicles into compliance with CARB emissions standards, it also led to an overall reduction in the fuel economy of the fleet.

Why Plug-in Vehicles?

Transportation related greenhouse gas emissions are responsible for roughly one-third of greenhouse gas emissions in the United States and at least 20% globally. In the US, over 60% of the transportation emissions result from gasoline consumption for personal vehicle use. We believe that plug-in vehicles capable of running on biofuels, in the form of pure battery electric vehicles and plug-in hybrids, are the best near term option for significantly reducing greenhouse gas emissions from the transportation sector and reducing our dependency on fossil fuels.

Plug-in hybrid vehicles can achieve 70 -100 miles per gallon, quadrupling the fuel economy of the average car on the road today (~20 mpg) and doubling the fuel economy of a regular hybrid car such as a Prius (~45 mpg). For pure battery electric vehicles using no gas, it has been shown that they can deliver a miles-per-gallon equivalent (MPGe) of well over 100 MPG (see post on computing MPGe). A plug-in hybrid is different from today’s hybrid because it has a higher capacity battery and the car can be plugged into a regular 120-volt outlet for charging. Because it is operating primarily on electricity for the first 20-40 miles, the car operates much more efficiently and uses dramatically less gasoline. Since more than 70% of Americans drive fewer than 33 miles per day, many plug-in hybrid drivers will not use any gasoline in their daily commutes — but they will retain the flexibility of using the hybrid gas engine for longer trips. In addition, plug-in vehicles will often recharge at night using excess power from base-load power plants that are already running, so they won’t generally add to peak electricity demand. Plug-in vehicles could also contribute to overall grid stability and help the penetration of renewable energy resources, as noted in this blogpost.

People often ask whether this won’t just shift pollution from cars to power plants, but even without adding any new power plants, the existing U.S. electrical grid has sufficient capacity to fully fuel three quarters of the nation’s 217 million passenger vehicles, assuming the average car drives 33 miles per day. This integration of hybrid cars with the electric power grid could reduce gasoline consumption by 85 billion gallons per year. That’s equal to a 27% reduction in total U.S. greenhouse gases, 52% displacement potential of U.S. oil imports, and $270 billion avoided in gasoline expenses (see

What has RechargeIT focused on?

RechargeIT is an effort within aimed at accelerating the adoption of plug-in electric vehicles and intelligent integration of these vehicles into the electric grid (for example, through smart charging applications).

Plug-in Hybrid Demonstration Fleet at Google: We have created the GFleet, a free car-sharing program for Google employees on the Mountain View campus, which includes eight hybrid Priuses converted to plug-ins with a Hymotion conversion module. is demonstrating the capabilities of this technology while collecting and publishing actual data on the performance of these vehicles. (For information about plug-in performance, please see the RechargeIT driving experiment). This program encourages alternate forms of commuting by providing employees who come to work by carpooling, taking public transport, riding the Google shuttle, or self-powered commuting (bicycling, walking, etc.) with the ability to use a car during the day. This corporate car-sharing program enables employees who need to go to business meetings or run errands to avoid driving to work in a single occupant vehicle. This program is based on a partnership with Enterprise Rent-A-Car who manages the fleet.

Solar Charging at Google: We have connected Google’s fleet of cars to solar charging stations on campus to demonstrate the role that renewable electricity can play in replacing gasoline and other fossil fuels in the transportation sector.Learn more about the solar panels at Google.

Strategic Grant-Making and Investments: has made modest investments in companies and projects which will accelerate the commercialization of alternative transportation that reduces vehicle fossil fuel use and climate emissions. Check out our grantees and investees here.

What has RechargeIT accomplished?

There has been great progress in the area of plug-ins during the last several years, not the least of which is the fact that plug-in vehicles have entered the national discussion as part of the future of transportation. Almost every large OEM plans to bring a plug-in to the market in the next 2-4 years. Recently-passed federal stimulus legislation contains $2 billion for plug-ins and includes a U.S. tax credit of up to $7,500 per vehicle which is intended to spark the sale of up to 1.5 million plug-ins.

Where can I buy a plug-in vehicle?

Though there are currently very few plug-in vehicles available commercially, almost all major vehicle manufacturers have announced plans to produce fully featured plug-in vehicles within the next few years. A good resource for information on the status of plug-in vehicle production is available from Plug In America. Examples of upcoming plug-in hybrids include an offering from GM which is currently developing the Chevrolet Volt, a range-extended plug-in vehicle that will be in production in 2010. Toyota has also publicly stated that they will bring an extended-range plug-in Prius to market by the end of 2009. If you’re looking for a nearer term solution, one option is to retrofit an existing hybrid vehicle using a plug-in module installed by a conversion company.

Understanding the Calculations

1. US Fleet Average MPG

The average combined MPG for all US cars and light trucks on the road today is 19.8 MPG. (Source: 2005 Highway Statistics from the U.S. Department of Transportation, Federal Highway Division).

2. What is CO2e?

CO2e is a measure that expresses the amount of greenhouse gases produced in terms of the amount of carbon dioxide (CO2) that would have the same global warming potential. This allows a single value to encompass the effects of many gases, such as methane, perflouorocarbons, and nitrous oxide, in addition to just carbon dioxide.

3. CO2e Emissions for US Fleet Average

CO2e benefits shown in the calculator are derived relative to the US fleet average. The US fleet average is 14,303 pounds/year CO2e for 12,000 miles or 1.192 pound CO2e per mile. The calculation is:

12,000 miles ÷ 19.8 mpg = 606.1 gallons
606.1 gallons x 23.6 pounds CO2e/gallon = 14,303 pounds CO2e/year
23.6 pounds CO2e/gallon ÷ 19.8 MPG = 1.192 pounds CO2e/mile

Each gallon of gasoline burned includes 19 pounds CO2e/gallon for tank-to-wheels fuel use and 4.6 pounds CO2e/gallon for upstream well-to-tank emissions. The source of the gasoline CO2e emission factor is chemical mass balance for converting gasoline to CO2 and Technology and Cost Assessment for Proposed Regulations to Reduce Vehicle Climate Change Emissions Pursuant to Assembly Bill 1493, California Air Resources Board, 4/1/2004.

4. CO2e Emissions for Conventional Prius

CO2e emissions for the conventional Prius in our fleet (without the plug-in conversion) is 6,924 pounds/year for 12,000 miles or 0.577 pounds CO2e/mile. This number is based on the 49.0 MPG observed (as of 7/18/2008) from real use data from our data acquisition system as described in the methodology section. The calculation is as shown above for the US fleet average, except that it uses the actual mileage driven and the observed MPG.

The percentage of reduced CO2e emissions is calculated as for the US fleet average, above, except that it uses the 6,924 pounds CO2e/year computed for the Prius.

5. CO2e Emissions for Prius Plug-ins

CO2e emissions for the plug-in hybrids in our fleet (as of 7/18/2008) are 4,860 pounds CO2e/year for 12,000 miles or 0.405 pounds CO2e/mile. Total CO2e emissions are the sum of CO2e emissions from gasoline use and electricity use. Gasoline use CO2e emissions are calculated using the methodology previously described above for the conventional Prius.

Electricity emissions are calculated by the following equation:

Total kWh/mile x state-level emission factor (pounds CO2e/kWh) = pounds CO2e per mile electricity use.

The percentage of reduced CO2e emissions is calculated as for the US fleet average, above, except that it uses the 4,860 pounds CO2e/year (as of 7/18/2008) computed for the plug-in Prius.

6. Gallons of Gasoline Saved Per Year

We compare gasoline used for the comparison cars (conventional Prius, plug-in Prius, and your car) to the average US fleet vehicle for a 12,000 mile annual driving cycle. The calculation is:

average gallons used = 12,000 / average MPG
comparison gallons used = 12,000 / comparison MPG
gallons saved = comparison gallons used – average gallons used

7. Barrels of Oil Saved

One barrel of oil yields approximately 20 gallons of gasoline. To calculate barrels of oil saved, we compare gasoline used for the comparison cars (conventional Prius, plug-in Prius, and your car) to the average US fleet vehicle for a 12,000 mile annual driving cycle. The calculation is:

average barrels used = 12,000 / (20 * average MPG)
comparison barrels used = 12,000 / (20 * comparison MPG)
percentage saved = 100 * (1 – comparison barrels used / average barrels used)

8. Percent of US Fleet to Halve CO2e emissions

The average car in the US gets 19.8 MPG and produces 1.192 pounds of CO2e per mile. Given the reduced emissions of hybrid and plug-in hybrid vehicles, we calculate the percentage of such cars we’d need to reduce overall CO2e emissions by half.

As calculated above (as of 7/18/2008), a Prius plug-in gets 69.2 MPG and uses 129.7 Wh/mile. Overall it produces 0.405 pounds CO2e per mile. To halve average emissions, we want:

P x 0.405 + (1 – P) x 1.192 = 1.192 ÷ 2

where P is the percentage of Prius plug-ins. In this case, P is 0.76, or 76%.

The calculation is similar for a conventional Prius, except that it generates 0.481 pounds CO2e per mile (as of 7/18/2008).
9. Cost Savings

This calculation assumes that gasoline costs $4.15 per gallon, and that electricity costs $0.10 per kWh. Assuming a 12,000 mile yearly driving cycle, the yearly fuel cost to operate a gasoline vehicle or conventional hybrid is:

cost = 4.15 x 12,000 ÷ MPG

So, for example, the average US car that gets 19.8 MPG would cost 4.15 x 12,000 ÷ 19.8 = $2525.15 per year for fuel.

For a plug-in hybrid, we add the cost of electricity:

cost = 4.15 x 12,000 ÷ MPG + 0.10 x 12,000 x kWh/mile

A Prius plug-in that gets 69.2 MPG and uses 0.1297 kWh/mile (129.7 Wh/mile) would cost 4.15 x 12000 ÷ 69.2 + 0.10 x 12000 x 0.1297 = $875.29 per year, for a savings of $1649.86 per year when compared to the average car.