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Fraunhofer, KIT study finds CO2 mitigation potential of higher-range PHEVs greater than expected

In an open-access paper published in Scientific Reports, a team from Fraunhofer ISI and KIT (Karlsruhe Institute of Technology) has presented the first systematic overview of empirical findings on the electrification of vehicle mileage based on on actual PHEV (plug-in hybrid) and BEV (battery-electric vehicle) usage for the US and Germany. The team found that, contrary to common belief, a PHEV with about 60  km (37 miles) of real-world range currently electrifies as many annual vehicles kilometers as a BEV, despite having a much smaller battery.

Further, they found that when the higher CO2eq emissions generated during the production phase of BEVs compared to PHEVs (due to the much larger BEV battery) are included in the analysis, a PHEV today shows higher CO2eq savings then BEVs compared to conventional vehicles. For significant ongoing CO2eq improvements of PHEVs—and particularly of BEVs—the decarbonization of the electricity system needs to continue, the researchers said.

For the study, the team compared the performance of 49,000 BEVs and 73,000 PHEVs in Germany and the US. The data are taken from fleet trials and automobile manufacturers as well as websites used by drivers to manage and monitor their own vehicles.

Average electrified annual kilometres for different PHEV (green) and BEV (red) models from the US (squares) and Germany (circles). The shaded areas are sample size weighted local smoothers (95% confidence bands). © Fraunhofer ISI. Click to enlarge.

Analyzing the data showed that plug-in hybrids with a real-world electrical range of about 60 kilometers drive the same number of kilometers electrically as battery electric vehicles—up to 15,000 kilometers (9,321 miles) each year. Their CO2 reduction potential is therefore just as large as battery electric cars, the researchers said.

Overall distribution of daily VKT for a large daily driving data set. Also shown are the annual electrified VKT by BEV and PHEV with typical ranges as shaded areas under the curve. Click to enlarge. Plötz et al.

In the paper, the authors observed that when more fast charging stations become available, BEVs will increase their electrified VKT significantly as more trips will become feasible with intermediate charging. This implies that more long range trips could be electrified by a BEV. Although, in principle, a PHEV could also recharge during long-distance trips, the small relectric range would require many breaks for recharging and users might prefer to refuel their fuel tank instead.

Plug-in hybrid vehicles represent a good addition to battery electric cars in order to meet the goal of reducing greenhouse gases. They have often been judged too critically in the past based on insufficient empirical data. However, it is important that they have a sufficiently large battery with a real electrical range of more than 50 kilometers and, in addition, that the decarbonization of the electricity system continues to be advanced.

—Dr. Patrick Plötz, who leads the study at Fraunhofer ISI

On the lifecycle analysis side, the researchers pointed out that today, one kWh of battery capacity results in about 100 kg CO2eq emissions during its construction phase. Thus, the additional construction phase emissions for the battery are smaller for a PHEV (on average 0.6 t of CO2eq) than for BEV (on average 2.6 t of CO2eq). However, PHEVs also include internal combustion engines and complex gear boxes, which lead to additional emissions of about 0.6 t of CO2eq per vehicle during the construction phase.

Thus, currently the overall CO2eq emissions from vehicle construction are about 1.4 t higher for BEV than for PHEV. Learning effects in battery production together with an improved electricity mix might even decrease this disadvantage in the future.

—Plötz et al.

According to the study, the decreasing CO2 emissions during battery production and the increasing diffusion of rapid charging points will shift this advantage more and more in the direction of battery-electric vehicles in the coming years.

The study was conducted within the framework of the “Profilregion Mobilitätssysteme Karlsruhe” (Profile Region Mobility Systems Karlsruhe). Fraunhofer ISI and regional research partners are pooling their expertise in this think tank to develop efficient, intelligent and integrated mobility solutions.


  • P. Plötz, S. A. Funke, P. Jochem & M. Wietschel (2017) “CO2 Mitigation Potential of Plug-in Hybrid Electric Vehicles larger than expected” Scientific Reports 7, Article number: 16493 (2017) doi: 10.1038/s41598-017-16684-9



The figures given are for the current average battery size for BEVs.

When one considers the long range BEVS, with 60, 80 or 100kWh packs they will have far higher embodied GHG in production, and on a lifetime emission basis will be way behind a PHEV.

The rationale given for long range BEVs does not make sense.


This all makes sense - larger batteries make the system heavier and take up more space.
Once you have a PHEV system set up, you can size the battery as you wish, but you can size it to a normal day's driving, rather than a hypothetical long run, and let the ICE engine handle the long runs.
So 60 Km (12 KwH?) seems about optimal.
The only problem I can see is that of gasoline going stale, which means that you have to keep using it, or they need to find a better tank sealing mechanism so all the volatiles don't evaporate off.

You could use an even smaller battery if you could recharge at work. You might have to redesign the car so there is still space in the boot (trunk), perhaps putting the battery under the floor.
The other problem is the cost of a PHEV which requires two full size engines, but I am sure mass production will solve that.

Bernard Harper

This study seems to assume long range (future) BEVs will have batteries manufactured with the same inefficiencies as today. But is that possible to predict, or even likely? If a BEV is charged mostly by renewables, surely that would tip the balance back in their favour? Also, BEVs have usable lifespans that are many times longer than ICE-engined vehicles. When you factor in their innate longevity and ability to be fueled mostly with renewable energy over a greatly extended lifetime, surely the BEV would win the lifetime emissions comparison?



Hydrogen does not go stale, and FCEVs are an obvious follow on to PHEVs and ICE hybrids.

Maybe batteries will improve in production enough and costs drop enough to make BEVs competitive, but they are the ones with it all to prove.


The joke/saying goes that those that can predict the future are called futurists, those that can say when are called billionaires.

Absolutely batteries will improve but to what extent and the timing is less clear. The ongoing research efforts and commitment to battery development is absolutely returning substantial outcomes.

The reference to "contrary to common belief" is over egging the level of belief in the scant studies that exist which could be expected as part of either statistically insignificant investigation unsupported opinion or even the lobbying and nay saying by interest and industry based opposition.


I believe that what is underestimated or not talked about is the cost of building out a fast charging network, cost of power (demand charges) and cost for electrical service to the charging stations. Until fast charge stations are ubiquitous, plentiful and fully charge a battery in 5-15 min there will be only a limited number used for long range travel, most will use there ICV. Also, with a limited number of charging stations, imagine the waiting line to recharge a long range BEV on a highly traveled national holiday weekend. On the other hand, consider the number of unused charging stations, there to handle the peak travel days, resulting in very poor utilization of some very expensive charging infrastructure.

Because of the limitations of the BEV fast charging infrastructure, only limited number of single car buyers will purchase a BEV and households with two plus cars, one is likely a BEV and the other an ICV. A two car household with a BEV and ICV, from an emissions perspective, is the equivalent of a PHEV, might actually worse if there two drivers. It would be reasonable to expect that there would be more buyers for a 40-50 mile PHEV and the overall net affect on a nationwide basis would result in more electric miles because there would be more PHEVs sold than with an all BEV offering.


EV driver.

Your reasoning and writing style is a welcome and novel contribution.

The two points I take are the affect that the rate of change in the transport mix can affect the contribution to emissions reduction from EV's.
The other point being the high cost of charging infrastructure.

My observation of the many new or startup industries pricing structures suggests that once mass deployment and production hits a 'critical' rate we see the cost of supply drop year on year to a point where the competition is so strong and margins so low that many suppliers leave the industry while the rest scale up.

Electrical services has always been a skilled industry and while the cost structures are often high the real costs of manufacture at scale are low.

It could come back to purchasing power with larger contracts having the potential to drastically cut the unit price while small lot suppliers and purchasers will necessarily remain relatively high.

Once these chargers become standard in new connections as opposed to retrofits - houses buildings etc the added cost could become very minor.


In my view this information on relative lifetimes emissions ties in well with the latest news on highly efficient wireless charging:

this is massive news for PHEVs, particularly shorter range ones, as opportunity charging will greatly increase their average yearly AER.

11kW wireless charging will not make much difference to BEVs, but one heck of a lot if your AER is 25 miles.

If a BEV is charged mostly by renewables, surely that would tip the balance back in their favour?

No.  The low capacity factor of the scalable RE sources (wind and PV) means they are unavailable in sufficient quantity much of the time EVs need to charge.  This goes double for PHEVs.  This requires fallback to fossil fuels, which is why the FF industry is pushing them and away from nuclear.

Also, BEVs have usable lifespans that are many times longer than ICE-engined vehicles.

The powertrain is usually one of the last parts of a vehicle to wear out.

I believe that what is underestimated or not talked about is the cost of building out a fast charging network, cost of power (demand charges) and cost for electrical service to the charging stations.

This is why the PHEV is at the sweet spot now, and will be for some time.  You drive around town on electricity, with predictable charging times and consumption.  Long-range travel uses liquid fuel, which is storable for the long term.  In the near term the fuel will remain petroleum, but for the long term I hope that this fuel can come from byproducts and waste of various types.

11kW wireless charging will not make much difference to BEVs, but one heck of a lot if your AER is 25 miles.

Why bother with wireless?  The Combo Connector is good for 80 kW.

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