Well-to-Tank

Zemo Partnership assesses the impact of vehicles on a Well-to-Wheel basis. The reason for this is to ensure that both tailpipe emissions and the emissions associated with generating a fuel or energy vector are fully captured to enable a fair comparison of all technologies and fuels. e.g. an electric bus has no tailpipe emissions, but there are emissions produced in the generation and transmission of that electricity and so we must include the well-to-tank emissions to truly understand the greenhouse gas impact of that electric bus.

A Well-to-Tank emissions factor, also known as upstream or indirect emissions, is an average of all the GHG emissions released into the atmosphere from the production, processing and delivery of a fuel or energy vector.

To ensure a fair comparison of all technologies, the Low Emission Bus and Ultra-Low Emission Bus Schemes use the UK national carbon conversion factors that are produced annually by the Department for Business, Energy and Industrial Strategy. These factors are published annually and emission factors will vary depending on the origin, production process and feedstocks of various energy vectors and fuels.

The only fuel not to have a UK average factor is hydrogen (as there is no hydrogen grid) and so each operation will be assessed independently on a case by case basis. Hydrogen must be produced from renewable sources in order to have a strong case to reduce greenhouse gas emissions from transport operations.

Zemo Partnership will publish the latest factors below as well as list the factors used on each LEB/ULEB certificate to ensure transparency and consistency. We will also aim to use these emission factors across all projects to enable fair comparison of greenhous gas performance of different vehicle types.

This page was last updated on 14th June 2021.

2021 Well-to-Tank Conversion Factors

Liquid Fuels
g CO2e/Litre
g CO2e/MJ
(Net CV)
% change from 2020- 2021
Pump Petrol (average biofuel blend)¹
613.28
18.82
+2.43%
Pump Diesel (average biofuel blend)¹
609.86
16.97
-0.30%
Bioethanol ¹
544.88
25.61
+3.33%
Biodiesel (RTFO average)¹
419.26
12.66
+12.16%
Hydrogenated Vegetable Oil (HVO)²
213.20 6.21
-21.56%
Biodiesel (UCO)¹
349.01
10.54
+20.47%
Gaseous Fuels
g CO2e/ kg
g CO2e/MJ
(Net CV)
% change from 2020- 2021
CNG¹
542.11
12.04
11%
LNG¹
882.35
19.60
0%
LPG¹
347.01
7.55
-3%
Biomethane (Compressed)²
855.13
17.45
+11%
Other
g CO2e/kWh
g CO2e/MJ
(Net CV)

% change from 2020- 2021

UK Grid Electricity¹
291.3
80.92
1%
Hydrogen (Thermal)³
31.7- 854.3
8.8 - 237.3
-
Hydrogen (Electrolysis)³
15.1 - 1776.6
4.2 - 493.5
-
  1. Figure has been sourced from DBEIS 'Government emission conversion factors for company greenhouse gas reporting' - conversion factors for 2021. Available here. 
  2. Figure has been sourced from the Renewable Fuel Statistics 2020: Fourth Provisional Report. Available here. 
  3. Range sourced from JEC “Well-to-Tank Appendix 4 – Version 4a: Description, results and input data per pathway” from “Well-to-Wheels Analysis of Future Automotive Fuels and Powertrains in the European Context” (2014). Available here.

The UK Grid Electricity factor for 2021 is broken down in the table below:

Source
Emission Value
Unit
% change from 2020-2021
Generation
212.33
g CO2e / kWh
-9%
Transmission & Distribution Losses (T&D)
18.79
g CO2e / kWh
-6%
WTT from Generation
55.29
g CO2e / kWh
72%
WTT from T&D
4.89
g CO2e / kWh
77%
Total emissions
291.3
g CO2e / kWh
1%

2020 Well-to-Tank Conversion Factors

Liquid Fuels
g CO2e/Litre
g CO2e/MJ
(Net CV)
% change from 2019- 2020

 

Pump Petrol (average biofuel blend)¹

593.44

18.37

- 0.8%

Pump Diesel (average biofuel blend)¹

610.15

17.02

- 1.0%

Bioethanol ¹

527.19

24.78

- 13.7%

Biodiesel (RTFO average)¹

373.81

11.29

+ 1.9%

Hydrogenated Vegetable Oil (HVO)²

271.77

7.92

+13.1%

Biodiesel (UCO)¹

289.77

8.75

+9.4%

Gaseous Fuels
g CO2e/ kg
g CO2e/MJ
(Net CV)
% change from 2019- 2020

 

CNG¹

486.62

10.87

- 0.3%

LNG¹

877.9

19.59

0%

LPG¹

369.3

7.822

-2.8%

Biomethane (Compressed)²

770.71

15.73

+19.7%

Other
g CO2e/kWh
g CO2e/MJ
(Net CV)

% change from 2019- 2020

UK Grid Electricity¹

288.13

80.04

-10%

Hydrogen (Thermal)³

31.7- 854.3

8.8 - 237.3

-

Hydrogen (Electrolysis)³

15.1 - 1776.6

4.2 - 493.5

-

  1. Figure has been sourced from DBEIS 'Government emission conversion factors for company greenhouse gas reporting' - conversion factors for 2020. Available here.
  2. Figure has been sourced from the Renewable Fuel Statistics 2019: Fifth Provisional Report. Available here.
  3. Range sourced from JEC “Well-to-Tank Appendix 4 – Version 4a: Description, results and input data per pathway” from “Well-to-Wheels Analysis of Future Automotive Fuels and Powertrains in the European Context” (2014). Available here.

The UK Grid Electricity factor for 2020 is broken down in the table below:

Source
Emission Value
Unit

% change from from 2019- 2020

 

Generation

233.14

g CO2e / kWh

-9%

Transmission & Distribution Losses (T&D)

20.05

g CO2e / kWh

-8%

WTT from Generation

32.17

g CO2e / kWh

-10%

WTT from T&D

2.77

g CO2e / kWh

-9%

Total emissions

288.13

g CO2e / kWh

-9%

2019 Well-to-Tank Conversion Factors

Liquid Fuels g CO2e/Litre g CO2e/MJ (Net CV) % change from 2018-2019
Pump Petrol (average biofuel blend)¹ 598.52 18.52 - 0.1%
Pump Diesel (average biofuel blend)¹ 617.09 17.20 - 0.2%
Bioethanol ¹ 610.98 28.70 - 0.5%
Biodiesel (RTFO average)¹ 367.95 11.08 + 17.2%
Hydrogenated Vegetable Oil (HVO)² 200.21 7.00 -75.0%
Biodiesel (UCO)¹ 264.77 8.00 -9.8%
Gaseous Fuels g CO2e/kg g CO2e/MJ (Net CV) % change from 2018-2019
CNG¹ 488.0 10.89 - 4.5%
LNG¹ 877.9 19.59 0%
LPG¹ 369.3 8.04 0%
Biomethane (Compressed)² 643.16 13.13 +6.6%
Other g CO2e/kWh g CO2e/MJ (Net CV) % change from 2018-2019
UK Grid Electricity¹ 315.98 87.77 -10%
Hydrogen (Thermal)³ 31.7- 854.3 8.8 - 237.3 -
Hydrogen (Electrolysis)³ 15.1 - 1776.6 4.2 - 493.5 -
  1. Figure has been sourced from DBEIS 'Government emission conversion factors for company greenhouse gas reporting' - conversion factors for 2019.
  2. Figure has been sourced from the RTFO 2017/18 Year 10 - report 6
  3. Range sourced from JEC “Well-to-Tank Appendix 4 – Version 4a: Description, results and input data per pathway” from “Well-to-Wheels Analysis of Future Automotive Fuels and Powertrains in the European Context” (2014). 

The UK Grid Electricity factor for 2019 is broken down in the table below:

Source Emission Value Unit % change from 2017-2018
Generation 255.56 g CO2e / kWh -10%
Transmission & Distribution Losses (T&D) 21.70 g CO2e / kWh -10%
WTT from Generation 35.65 g CO2e / kWh -15%
WTT from T&D 3.03 g CO2e / kWh -15%
Total emissions 315.98 g CO2e / kWh -21%

2018 Well-to-Tank Conversion Factors

Liquid Fuels g CO2e/Litre g CO2e/MJ (Net CV) % change from 2017 -2018
Pump Petrol (average biofuel blend)¹ 596.65 18.51 + 0%
Pump Diesel (average biofuel blend)¹ 618.46 17.23 - 0.24%
Bioethanol ¹ 613.77 28.83 - 5%
Biodiesel (RTFO average)¹ 312.95 9.45 - 23%
Hydrogenated Vegetable Oil (HVO)² 980.87 28.58 n/a
Biodiesel (UCO)¹ 293.60 8.87 - 23%
Gaseous Fuels g CO2e/kg g CO2e/MJ (Net CV) % change from 2017-2018
CNG¹ 551.8 11.41 -6%
LNG¹ 948.2 19.59 -2%
LPG¹ 369.4 8.04 0%
Biomethane (Compressed)² 615.93 12.31 +23%
Other g CO2e/kWh g CO2e/MJ (Net CV) % change from 2017-2018
UK Grid Electricity¹ 352.76 97.99 -21%
Hydrogen (Thermal)³ 31.7- 854.3 8.8 - 237.3 -
Hydrogen (Electrolysis)³ 15.1 - 1776.6 4.2 - 493.5 -
  1. Figure has been sourced from DBEIS 'Government emission conversion factors for company greenhouse gas reporting' - conversion factors for 2018 energy (for energy supply 2016/17). 
  2. Figure has been sourced from the RTFO 2016/17 Year 9 - report 6.
  3. Range sourced from JEC “Well-to-Tank Appendix 4 – Version 4a: Description, results and input data per pathway” from “Well-to-Wheels Analysis of Future Automotive Fuels and Powertrains in the European Context” (2014).

The UK Grid Electricity factor for 2018 is broken down in the table below:

Source Emission Value Unit % change from 2017-2018
Generation 283.07 g CO2e / kWh -19%
Transmission & Distribution Losses (T&D) 24.13 g CO2e / kWh -27%
WTT from Generation 41.98 g CO2e / kWh -25%
WTT from T&D 3.58 g CO2e / kWh -32%
Total emissions 352.76 g CO2e / kWh -21%

2017 Conversion Factors

Liquid Fuels g CO2e/Litre g CO2e/MJ (Net CV) % change from 2016-2017
Pump Petrol (average biofuel blend)¹ 597.72 18.56 + 30%
Pump Diesel (average biofuel blend)¹ 619.77 17.27 + 12%
Bioethanol ¹ 645.35 30.65 - 6%
Biodiesel (RTFO average)¹ 408.02 12.32 - 34%
Biodiesel (UCO)¹ 382.69 11.56 - 34%
Gaseous Fuels g CO2e/kg g CO2e/MJ (Net CV) % change from 2016-2017
CNG¹ 599.4 12.11 +10%
LNG¹ 1006.7 19.59 7%
LPG¹ 369.7 8.04 0%
Biomethane (Compressed)² 615.93 10.00 0%
Other g CO2e/kWh g CO2e/MJ (Net CV) % change from 2016-2017
UK Grid Electricity¹ 445.72 123.5 -14%
Hydrogen (Thermal)³ 31.7- 854.3 8.8 - 237.3 -
Hydrogen (Electrolysis)³ 15.1 - 1776.6 4.2 - 493.5 -
  1. Figure has been sourced from DBEIS 'Government emission conversion factors for company greenhouse gas reporting' - conversion factors for 2017 energy (for energy supply 2015/16).
  2. Figure has been sourced from the RTFO 2015/16 Year 8 - report 6. 
  3. Range sourced from JEC “Well-to-Tank Appendix 4 – Version 4a: Description, results and input data per pathway” from “Well-to-Wheels Analysis of Future Automotive Fuels and Powertrains in the European Context” (2014).

The UK Grid Electricity factor for 2017 is broken down in the table below:

Source Emission Value Unit % change from 2016-2017
Generation 351.56 g CO2e / kWh -15%
Transmission & Distribution Losses (T&D) 32.87 g CO2e / kWh -12%
WTT from Generation 56.05 g CO2e / kWh -9%
WTT from T&D 5.2 g CO2e / kWh -6%
Total emissions 445.72 g CO2e / kWh -14%

2016 Conversion Factors

Liquid Fuels g CO2e/Litre g CO2e/MJ (Net CV)
Pump Petrol (average biofuel blend)¹ 461.3 14.32
Pump Diesel (average biofuel blend)¹ 554.3 15.42
Bioethanol ¹ 687.7 32.28
Biodiesel (RTFO average)¹ 621.8 18.78
Biodiesel (UCO)¹ 475.3 14.36
Gaseous Fuels g CO2e/kg g CO2e/MJ (Net CV)
CNG¹ 543.8 11.37
LNG¹ 1006.7 21.05
LPG¹ 369.7 8.04
Compressed Biomethane Gas³ -2,205 - 725.2 -45.0 – 14.8
Liquefied Biomethane² 0.49 10.00
Other g CO2e/kWh g CO2e/MJ (Net CV)
UK Grid Electricity¹ 516.8† 143.5
Hydrogen (Thermal)³ 31.7- 854.3 8.8 - 237.3
Hydrogen (Electrolysis)³ 15.1 - 1776.6 4.2 - 493.5

Bus Operators intending to use compressed hydrogen should contact their fuel provider to determine the pathway used in producing and distributing the fuel to determine the appropriate WTT GHG emission factor. The ranges provided in the above table are indicative figures.

1. Figure has been sourced from DECC's UK greenhouse gas inventory - conversion factors for 2014/15 energy

The UK Grid Electricity factor for 2016 is explained in the table below:

Source Emission Value Unit
Generation 412.05 g CO2e / kWh
Transmission & Distribution Losses (T&D) 37.27 g CO2e / kWh
WTT from Generation 61.88 g CO2e / kWh
WTT from T&D 5.6 g CO2e / kWh
Total emissions 516.8 g CO2e / kWh

2 Figure has been sourced from the RTFO 2014/15 Year 7-report 6. 

3 Range sourced from JEC “Well-to-Tank Appendix 4 – Version 4a: Description, results and input data per pathway” from “Well-to-Wheels Analysis of Future Automotive Fuels and Powertrains in the European Context” (2014). 

*Liquefied Biomethane is produced by capturing biogas released from organic municipal waste disposed at landfill. Compressed Biomethane Gas is produced from biogenic waste e.g. animal slurry, using anaerobic digestion.