CARBON FOOTPRINT STUDY
The template was issued to the members of the Interest Group to complete. The Interest Group also conducted a preliminary carbon footprint estimate for an alternative to concrete gravity foundations, namely a steel jacket solution based upon the steel jackets used in the Beatrice wind Farm for a 5MW turbine in 42m deep water.
RESULTS – FOUNDATION ONLY The ‘foundation only’ results include raw materials and other resources to be used in the construction of the foundation but exclude the manufacturing facility, bespoke vessels, installation, maintenance and deconstruction.
The average carbon footprint for six different CgF solutions was estimated
to be 1,190 tonnes CO²e per 5MW unit (with a range of 708-1,597 tonnes CO²e per 5MW unit). This compared with an
estimated carbon footprint for a steel jacket
solution of 2,770 tonnes of CO²e per 5MW unit.
Average for CGF Solutions (5MW turbine)
Steel Jacket (5MW turbine)
Table 1:
Comparison of CO²e per 5MW unit for materials and manufacturing only.
The key driver for the difference in the carbon footprints was the quantum and type of steel within the different solutions. The concrete foundations incorporate significantly less steel than the steel jacket solution. Moreover, reinforcement steel is used in the concrete solutions, which in Europe is produced almost entirely from recycled materials, whilst this study assumed that steel plate would be used for a steel jacket.
Steel plate is manufactured principally from virgin materials. The assumed carbon factors for the two materials, as derived from the Inventory of Carbon and Energy, are…
• Steel (bar and rod based on UK avg recycled content) 0.45 kg CO²e /kg
• Steel (plate based on world avg recycled content) 2.21 kg CO²e /kg
Some of the concrete solutions also included a significant proportion of cement replacement products such as ground granulated blast furnace slag (GGBS). Cement is a significant contributor to the carbon footprint of concrete and hence
1,190 tonnes CO2e per unit
2,770 tonnes CO2e per unit
237 tonnes CO2e/MW
554 tonnes CO2e/MW
replacement of cement with recycled materials such as fly ash and ggBS is a potential means of lowering the carbon footprint of concrete.
The findings are plotted in Figure 1, together with other data that has been sourced, but unfortunately is not otherwise in the public domain.
RESULTS – TOTAL CARBON FOOTPRINT The total carbon footprint results include raw materials and other resources to be used in the construction of the foundation AND the manufacturing facility, bespoke vessels, installation, maintenance and deconstruction.
Combining all the resources used in the manufacture, installation, maintenance and deconstruction of concrete foundations gave an estimated average carbon footprint for four different concrete gravity foundation
solutions of 2,480 tonnes CO²e per 5MW unit.
Some of these aspects are more uncertain than the raw materials used in the foundations themselves and hence the estimated total carbon footprint
of 2,480 tonnes CO²e should be considered as an indicative figure only. CONCLUSION
This preliminary study conducted by the Interest Group indicates that concrete solutions are not likely to be any worse than a steel jacket solution in terms of its carbon footprint. Indeed, concrete solutions appear to have a significantly lower carbon footprint compared with a steel jacket.
The Interest Group would like to thank all those organisations who provided information in support of this study.
MPA The Concrete Centre Click to view more info
www.windenergynetwork.co.uk
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