The scientists compared the carbon, land, and water footprints per driven kilometer in midsize cars – ones using conventional gasoline, biofuel blends, bioelectricity, solar electricity and solar-based hydrogen. The resulting paper, authored by Bunyod Holmatov and professor Arjen Hoekstra (1967 – 2019), was published in the latest issue of Earth’s Future.
‘We try to switch to renewable energy to lower our carbon footprint, but we forget that renewable energy production also requires resources,’ says Holmatov. ‘For instance, solar panels require water to be produced and land to be placed on. Which is why we need to assess the trade-offs and see how different renewable energy technologies compare.’
Biofuels are ‘the worst’
According to the findings, biofuel-driven cars have by far the largest footprints. ‘By biofuels we mean liquid fuels from crops, in our research specifically biodiesel made of rapeseed and bioethanol made of sugar beet,’ clarifies Holmatov. ‘EU is increasing their use, but the question is whether that is a good idea. To grow them, you need land and a lot of inputs: water, fertilizers and pesticides. Emissions from the soil management, for example, lead to a very high carbon footprint.’
Solar power
On the other end of the spectrum, the ‘award’ for the smallest environmental footprint goes to solar‐powered electric cars. ‘Solar panels generate a lot of energy per square meter. They have essentially no carbon footprint and yes, you need water to produce them, but afterwards no water is needed, while biofuels production constantly needs water,’ says the scientist.
‘Gasoline cars have the smallest land footprint’
Where does gasoline stand? ‘Interestingly, gasoline cars have the smallest land footprint per driven km and the second smallest water footprint,’ answers Holmatov. ‘On the other hand, they have the second biggest carbon footprint. They are still better than biodiesel blends, though.’
What to do?
According to the researcher, the results show ‘it would be logical to use solar-powered electricity to power vehicles’. It is a complex issue, however. ‘There are always trade-offs. If we switch from gasoline to renewable sources, we need more land. Moreover, electric vehicles are very costly. As an average person, you can hardly afford an electric car fueled by solar energy. And the infrastructure gap is still very large. That is something that could be addressed in order to decrease the environmental footprint of car transport.’
Below you can find the overview of footprints per fuel source.
Table 1. Carbon, Land and Water Footprint per km and per Capita Year of Driving a Car Fueled by Conventional Gasoline, Biodiesel Blend B20, Bio‐Ethanol Blend E85, Bio‐Electricity, Solar Electricity or Solar‐Based Hydrogen
|
Gasoline |
Biofuel blend |
Electricity |
Hydrogen |
|||
|---|---|---|---|---|---|---|
|
B20¹ |
E85² |
Bio³ |
Solar (PV) |
|||
|
Carbon footprint (g CO2eq/km) |
165 |
185 |
80.2 |
7.3 |
0 |
0 |
|
Land footprint (m2/km) |
0 |
0.37 |
0.21 |
0.028 |
0.00091 |
0.0023 |
|
Water footprint (L/km) |
0.25 |
170 |
163 |
40 |
0.12 |
0.39 |
|
Carbon footprint (kg CO2eq/driver/year) |
3579 |
4010 |
1739 |
158 |
0 |
0 |
|
Land footprint (m2/driver/year) |
0 |
7977 |
4463 |
611 |
20 |
50 |
|
Water footprint (m3/driver/year) |
5 |
3685 |
3534 |
859 |
3 |
8 |
Notes:
1. 20% biodiesel from rapeseed and 80% conventional diesel;
2. 85% bioethanol from sugar beet and 15% conventional gasoline;
3. from sugarcane's biomass;
Source of table: The Environmental Footprint of Transport by Car Using Renewable Energy (Earth’s Future) by Bunyod Holmatov & Arjen Y. Hoekstra. First published: 31 January 2020 https://doi.org/10.1029/2019EF001428
