Hybrids are 14 times better than battery electric vehicles at reducing real-world carbon dioxide emissions
Why a multi-pronged approach to electrification is needed
Battery production capacity for motor vehicles is currently scarce, expensive and suffering supply lags and challenges. This may change over time, but for some period securing an economic supply of battery production capacity will be pivotal to the successful commercialisation of electrified vehicles, and to the relative fortunes of individual auto makers. At the same time, electrification is a proven route to tailpipe carbon dioxide (CO2) reduction, or elimination. Therefore, the efficient deployment of available battery capacity between competing applications is critical to maximising fleet CO2 reduction.
So long as this scarcity remains, a major concern is that the push to pure battery electric vehicles (BEVs) will crowd out a more effective programme of mass hybridisation. Put another way, given the urgency of the need to reduce CO2, paradoxically BEVs may not be the best way to achieve it with their supply chain, production capacity, infrastructure and customer acceptance challenges. The assertion that BEVs are required to solve air quality problems is confusing the argument – cities in Europe can be brought into compliance with conventional internal combustion engines, with technology on the market today. Electrification is first and foremost a CO2 reduction technology, but what strategy mix represents the correct path?
This newsletter is inspired by recent insightful articles by Kevin Brown: https://bit.ly/30j50Ed and https://bit.ly/30oC1yM. His insights on the efficiency of carbon reduction can be put together with the Emissions Analytics’ database of real-world testing over almost 100 hybrids vehicles to see in more detail the most efficient options for electrification and CO2 reduction.
As with tailpipe pollutant reduction, CO2 reduction comes down to how to achieve it as cost-efficiently and quickly as possible. Emissions fell during the financial crisis, but at the significant price of sharply reduced economic activity – not desirable. So, how best to deliver road transportation’s part in meeting the Paris climate change targets? The apparent consensus is to transition to pure electric vehicles as rapidly as possible. But is this singular focus better than a combined strategy employing a wide variety of hybrid electric vehicles?
The problem with the pure electric vehicle approach is that the transition will be slow, BEVs need disproportionately large batteries to give acceptable consumer utility, just as battery capacity is currently a scarce resource. As cumulative CO2 emissions are important for climate change – due to the long life of the gas in the atmosphere – a smaller reduction per vehicle now, but across many more hybrid vehicles, would eliminate a far greater volume of CO2 than applying the scarce battery resource to a smaller number of BEVs. This approach also helps mitigate naturally slow fleet turnover, with the average age of cars on the road being over twelve years.
So, what does the real-world performance data of hybrids look like?
The following analysis takes the mild, full and plug-in hybrid vehicles tested by Emissions Analytics in both Europe and the United States. Each hybrid is paired with its nearest equivalent internal-combustion-engine-only vehicle, often the same make and model with a similar engine size. The difference in average CO2 emissions over Emissions Analytics’ standard on-road cycle between the hybrid and its conventional-engined pair is then calculated.
The first table focuses on mild and full hybrids, excluding plug-ins, and shows the average tailpipe CO2 reductions that are achievable with models that are currently on the market, or that have been sold over the last seven years since Emissions Analytics started its test programme.
The average US reduction is larger than in Europe due to the typically higher CO2 emissions starting point of US vehicles, and often the latest hybrid technology is launched in the US market earlier. Of these 95 hybrids, five are diesels.
To put this 30% reduction in context, the EU’s post-2021 CO2 reduction target for passenger cars is 37.5% by 2030. Therefore, widespread non-plug-in hybridisation with currently available technology would achieve over three-quarters of that target. Moreover, with fourth generation hybrids now entering the market, the benefits of hybrids will improve further, as illustrated at https://bit.ly/2KhDlhh. Together with plug-in hybridisation and other design innovations, it is plausible that the target could be met without the need for full electric vehicles.
The results from the first table are then combined with results from plug-in hybrids and a representative BEV, with the difference in CO2 being divided by the battery size of the electrified vehicle. The result measures the efficiency of CO2 reduction in return for the deployment of the scarce battery resource. The results are shown below, with three different illustrative scenarios for plug-ins depending on varying battery utilisation.
* Typical battery size across models currently on the market. The CO2 reduction from BEVs is based on switching from an average internal combustion engine emissions to a zero-emissions BEV.
The table above shows that mild hybrids are clearly the most efficient method of CO2 reduction, followed by full hybrids, given scarce battery production capacity. Plug-in hybrids are the next most effective after that, but only if they are operated entirely on battery, which is hard to enforce in practice. BEVs have the lowest efficiency, primarily due to requiring disproportionately large batteries to accommodate relatively infrequent, extreme usage cases where the driver will otherwise suffer range anxiety.
This analysis ignores the upstream CO2 in fuel extraction, refining and transportation, as well as in the production and distribution of electricity. Some studies suggest the upstream CO2 of the electricity is greater than for gasoline, but the relative efficiency calculations here implicitly assume they are equal.
Showing the distribution of performance by individual model, the chart below relates the efficiency of CO2 reduction by battery size. Mild and full hybrids are the most efficient on average, but there is significant variation within the class – demonstrating that individual vehicle selection remains at least as important as generic powertrain. The same chart also demonstrates the advantage in CO2 reduction that the US currently holds.
In terms of the trajectory to total CO2 reduction, a transition from gasoline internal combustion engine to full gasoline hybrid can reduce emissions by 34%. As it will take time to increase the supply of full hybrids, there are two routes to short-term CO2 reduction that are viable more quickly. First, a switch from gasoline to diesel internal combustion engine in practice reduces CO2 emissions by 11% at the tailpipe. A second step then to a diesel mild hybrid delivers a further 6% reduction. The final swap to full hybrid delivers another 16%, making 34% in total. Alternatively, a direct switch from gasoline to gasoline mild hybrid can deliver 11%, followed by a further 23% in moving to full hybrid. Therefore, there are immediate-term options for significant CO2 reduction, involving both gasoline and diesel powertrains – the former more suitable in the European market, the latter in the US due to the current mix of fuel utilisation.
It is at any regulatory stages beyond the 37.5% fleet reduction that fuller electrification would be required, as there are limits to the total CO2 reduction that hybrids can deliver. However, by 2030 the EU and US would have had more time to develop expanded, cleaner electricity generation capacity, enhanced distribution grid, and addressed the supply chain issues around the scarce materials in batteries. Not neglecting also that consumer education and acceptance are required to remove barriers to adoption. An alternative scenario by 2030 is that the availability and price of renewable electricity may have fallen to a level at which hydrogen fuel cell vehicles become economic viable, which avoid some of the environmental and geopolitical issues created by largescale battery production.
In summary, this data strongly suggests that policy unilaterally favouring one technology solution may be deeply inefficient and perhaps even the wrong eventual solution. A better approach would be to use real-world data to allow competing technologies to flourish as they can evidence genuine CO2 reductions, delivered as soon as possible.