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Third Phase of SDG&E In-Use Study Shows PHEVs Excel on Fuel Economy and GHG Emissions Reductions Compared to Gasoline ICE and Hybrid-Electric Vehicles

One of SDG&E’s converted PHEVs. Click to enlarge.

The third phase of a SDG&E multi-year in-use study on plug-in hybrid electric vehicles showed that plug-in hybrids offer significant improvements in gas mileage and reductions in emissions when compared with standard hybrid-electric and gasoline internal combustion engine (ICE) vehicles. (Earlier post.) SDG&E is a regulated public utility that services San Diego and southern Orange counties.

SDG&E tested the performance of two 2007-model Prius hybrids and then converted them into plug-in hybrids, using a Hymotion 5 kWh lithium-ion battery conversion kit. In the most recent study, the prototype battery was replaced with a production-model battery. The same pool of drivers was used during vehicle evaluation.

When compared with the standard hybrid, the plug-in hybrid, at 68 mpg US (3.5 L/100km), achieved a 58% increase in gas mileage, a 37% decrease in carbon dioxide tailpipe emissions, and a 10% reduction in fuel costs.

When compared with a conventional gasoline-fueled vehicle that averages 22 mpg US, the plug-in hybrid achieved a 68% reduction in tailpipe emissions and a 54% reduction in overall fuel costs.

SDG&E announced the findings as state regulators and utilities met in San Francisco to discuss the role of utilities in advancing the electric and natural gas vehicle marketplace and fueling infrastructure.

California’s electricity capacity could recharge as many as 4 million plug-in hybrids when charged during off-peak hours when electricity use is low. The plug-in hybrid’s fuel-cost savings over traditional gasoline-powered vehicles would save these 4 million consumers approximately $4.2 billion a year at today’s average gasoline price of $3 per gallon when compared to 15 cents per kilowatt-hour of electricity for 14,400 miles driven annually.

With SDG&E’s deployment of smart meter technology, the interface with these vehicles in the future will allow customers to schedule charging time and select the lowest rate for charging.

SDG&E said the study results confirm the viability of electricity as a clean and low-cost transportation fuel and validate the increased efficiencies of plug-in hybrid technology.

California has the most aggressive greenhouse-gas reduction goals in the nation, with nearly 40 percent of those emissions coming from transportation. Integrating clean transportation alternatives, like plug-in hybrid and all-electric vehicles, will be critical to achieving the state’s goals. SDG&E will do its part to help ensure the San Diego region is “plug-in” ready when electric vehicles hit the road.

—Hal Snyder, vice president of customer solutions for SDG&E

SDG&E expects the OEM plug-in hybrids and all-electric vehicles due on the market in late 2010 will exhibit efficiencies higher than those demonstrated in SDG&E’s study.

The converted plug-in hybrids recharge their batteries through a standard 110-volt household outlet and charge in five to six hours for a 5 kWh lithium-ion battery. In the future, plug-in electric vehicles will primarily charge off of 220-volt for faster charge time on larger batteries, SDG&E projected.

SDG&E is part of a 48-utility coalition with the Electric Power Research Institute (EPRI) and General Motors to advance the deployment of plug-in hybrid electric vehicles. The collaborative is working to accelerate large-scale deployment of plug-in hybrid electric vehicles and create a blueprint for an electric fuel infrastructure. The collaborative also is addressing issues that ensure safe and convenient vehicle charging, public education, and public policy requirements to enable a smooth introduction of plug-in hybrid electric vehicles as a transportation alternative to conventional vehicles.

In March, SDG&E announced it would partner with Nissan Motor Co. to help develop the market for zero-emission electric vehicles and charging infrastructure in the San Diego region. Under the partnership, SDG&&E is serving as the local San Diego coordinator to help assemble a critical mass of regional electric vehicle fleets that municipalities, universities, the military , the port, private fleets and others use daily. The public-private collaborative is working to further develop and fine-tune the charging infrastructure, which is the critical link in making the vehicles commercially viable. (Earlier post.)


  • US Department of Energy, Vehicle Technologies Program, Advanced Vehicle Testing Activity (AVTA) Plug-in Hybrid Electric Vehicles (PHEVs) Overview (May 2009)



In the book Plug In Hybrids, the author shows how many converging interests are promoting this. They range from environmentalists, to government people, to evangelicals. When you can bring that diverse a group together for one issue, you may have a success.

J Maxwell

Note the "38% reduction in TAILPIPE carbon dioxide emissions" compared to a regular Prius.

They should do a well-to-wheels comparison, and count the emissions from the electricity.


Producing massive amount of electricity for PHEVs and BEVs does not have to pollute. Sun, wind, hydro, geothermal, nuclear power etc don't create much air pollution.

However, liquid fuel production and usage does.


Both figures are useful (tailpipe and total), but in practical terms, tailpipe emissions are what we can measure and what is useful for emission comparison purposes. We control power plant emissions at the plant, and that is declining towards zero. When you consider the question of how to reduce total emissions, we have to act separately on each source. That we can cut tailpipe emissions by electrifying cars is a very good thing and in a world of declining power plant emissions, it is fair to compare plug-in hybrid emissions with traditional ICE emissions.
I've been getting 73 mpg overall average on my commute with my Hymotion-equipped Prius, and that would be closer to 90 if I could charge at work. Plug-ins really DO work, and they are a great way to reduce emissions. Here in CA, we're aggressively driving down our power plant emissions, and so plug-ins are especially valuable in CA for promoting air quality.


"We control power plant emissions at the plant, and that is declining towards zero."

The emissions from gasoline production OTOH have been going up; what with America's increasing reliance on Canadian tarsands. Add in plans to get oil from shale and CTL and it doesn't look good.



Thanks for your real world experience. The PHEV upgrades may become more popular over time as prices of conversions go down and gasoline prices go up.

George K

J.A. Turner,
Well put! I'm enjoying my Hymotion Plug-in as well.

I live closer to work, and can drive round trip and still have a few bars (of energy) left upon return. I'm showing 99.9 mpg on the current tank with about 750 miles, and just over 1\2 full. The Prius tank is about 11 gal.

edit - Ok, I'll just say it: This car is so cool!!!


Why are they comparing this to "a conventional gasoline-fueled vehicle that averages 22 mpg US"? They should compare it to a car of similar size like the Corolla that averages 30 mpg.

It's also a bit suspicious that they exclude smokestack emissions. It's not like our lungs can tell the difference. If anything, the air coming out of a 2010 PZEV car is much cleaner than what comes out of your typical coal power plant. I realize that future power plants should be cleaner in theory, but decades will pass before they are the rule rather than the exception. What matters is the performance of power plants in use during the expected lifespan of the car.

Al Roderick

A Corolla or Cobalt or something is definitely a better comparison for capacity and capabilities, but 22 MPG is the average of all personal transport vehicles in America, and so they went that way. It's not just SUVs throwing it off, the number of big pickup trucks used for combined business and personal transportation by trades and contractors tends to wreck the curve a bit.

As for the smokestack issue, a million electric cars powered by a coal plant still produce less CO2 than a million ICE cars; big engines are more efficient than small, and get more usable energy per carbon atom released. Steam engines like those found in coal plants burn their fuel more completely and emit less unburned fuel into the waste stream. The reason why they're not in cars and trains anymore is that they have a lousy power-to-weight ratio; it sucks for a vehicle, but is of no consequence for a building.

For the particulates and other noxious chemicals, there are technologies for reducing and recapturing those, many of which have been in service for years, and they're easier to implement on one giant tailpipe that never moves than on a million little ones with weight limits. And don't forget, electricity doesn't need to be trucked to market.


22 mpg is no doubt the current average, however a Prius-size vehicle can not be compared to a pickup truck. Is anybody making a plug-in conversion for GM's hybrid SUVs? That would be a fair comparison to a regular pickup.

I don't doubt the actual numbers that this study came up with for plug-ins, just the fact that they doped the emissions improvement figures by comparing them to much larger cars and trucks. They should have compared like to like, in terms of cabin space, load capacity and performance.

A family with two adults and three adult-sized teenagers can't even fit into a Prius, so it's not like that car is a reasonable alternative to a larger car.


" family with two adults and three adult-sized teenagers can't even fit into a Prius"

Have you ever tried to get 3 teenagers to agree to go anywhere with their parents? Getting them into the back seat is never going to be a problem you'll ever face, trust me.

Stan Peterson

Did you know that California has ZERO coal powered electric plants? And no Oil powered electric plants either. Its only California generated power comes from renewbles like hydro; and Natural Gas and one nuclear plant. And yes, a tiny percentage of extremely expensive and inefficient Wind and Solar electric generation as well.

So native California electric generation is extremely clean.

But then there is the hidden Truth. Its all a Potempkin Village for the Tree-huggers, that could end, any day.


AI Vin's point about gasoline production getting dirtier just means PHEVs will get more and more attractive as compared to conventionally-fueled cars.

The real truth about CA power generation is that SoCal gets lots of dirty power from out of state. As we make more of our own from renewables (or buy more renewables) that will reduce the percentage of dirty power CA uses. On the bright side, we can support millions of PHEVs and BEVs charging at night with no more pollution that is being generated now, so that means comparing tailpipe emissions with conventional cars is quite fair.

Since the average passenger load in the U.S. is about 1.3 (2 out of three cars having only the driver), all cars pretty much are on an equal footing. Solo driving still dominates. So, comparing the average car's mileage to a PHEV's mileage really is pretty fair. Solo driving a Hummer 50 miles a day pollutes a lot more than solo driving a PHEV-equipped Prius the same distance.

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