Bristol net zero

Bristol net zero by 2030: The evidence base (December 2019) is a report prepared for Bristol City Council by the Centre for Sustainable Energy together with the consultancies Ricardo plc and Eunomia [1]. Some of the main points of the report will be summarised below, and its relevance to other local authorities will be briefly discussed.

Bristol’s ‘net zero’ target refers only to scope 1 and 2 emissions; these are defined in the Global Protocol for Community-Scale Greenhouse Gas Emission Inventories [2]. Scope 1 GHG emissions are those from sources located within a city boundary, and scope 2 GHG emissions occur as a consequence of  the use of grid-supplied electricity, heat, steam and/or cooling within the city boundary. Scope 3 GHG emissions are all those that occur outside the city boundary as a result of activities taking place inside it. (Examples might be emissions associated with purchased goods and services, business travel, transportation and distribution). Scope 3 emissions are to be the subject of a separate study for Bristol, however the Bristol net zero report includes waste, sometimes treated as scope 3.

The proposed route to net zero for Bristol includes “much better insulated buildings heated by heat networks and individual electric heat pumps to enable the end of using gas for heating; far smarter use of electricity across the city and growth in roof-top solar PV to support the decarbonisation of electricity generation nationally; a significant shift to public transport and active travel (walking and cycling) and a switch to electric vehicles (EVs) for the remaining fleet to accelerate the phasing out of petrol and diesel vehicles in the city; a significant reduction in waste, greater re-use and recycling, and the removal of plastics from residual waste” (p.6).

Among the assumptions made in the report are the following: Grid electricity will be zero-carbon by 2030;  Any bio-methane and zero-carbon hydrogen resources will not be distributed directly to buildings but used to fuel buses or heavy goods vehicles, industrial processes, peaking electricity plant or heat networks; In the city’s existing buildings most cavity walls and lofts have already been insulated, but fewer than 10% of the solid-walls have been insulated and energy saving retrofit would be justified;  All new buildings in the city will have a district heating connection or a heat pump to achieve zero carbon, and will be sufficiently well insulated to not require significant heat other than for hot water. In estimating the potential for solar energy generation in the city, assumptions on efficiency and cost have been made (p.51), and the transport scenarios discussed involve assumptions about population growth and the rate of change of car and commercial  vehicle mileage (e.g. p.64). One possible consequence of the changes proposed is a 50% increase in the city’s electricity demand by 2030 (p. 47 ff.).

The report recognises that at present the city does not have the powers, funding or capacity that it needs to achieve its target. Effective powers are needed to “set and enforce local planning policies and building standards” and it will be necessary to “present the city’s … case to national government for the granting of these powers and associated funding”. Further, there is the need for an “extensive skills and capacity development programme to enable delivery at scale and capture the jobs created for the city” (p.110).

The investment needed to achieve net zero carbon emissions in scopes 1 and 2 by 2030 is estimated to be at least £5 billion over the next decade. The capital breakdown is £1,950m on heating networks, £580m on heat pumps for individual buildings; £650m for insulation retrofits to improve the energy performance of buildings; up to £625m on roof-top solar PV; £1,000-2,100m on re-designing road layouts and expanding and improving the transport system, encouraging a shift away from private vehicles; £175m on electric vehicle charging infrastructure; up to £1,000m on smarter management and upgrade of the electricity network; expenditure on waste decarbonisation will depend on the approach taken.There will also be spending on delivery partnerships and governance structures, the seeking and securing of funding, and on cultural change programs to engage businesses and the public with the scale and nature of the net zero program.

Perhaps as much as half of the cost is not additional, but should be seen instead as reassignment of investment which would have been made in areas such as replacing old gas boilers with new, old petrol or diesel vehicles with new, refurbishing buildings without an energy upgrade, and improving roads to accommodate traffic growth.

Do the above figures provide any guidance to other local authorities in the UK seeking to estimate the cost of reaching net zero emissions? Setting aside the questions of whether the UK’s electricity supply will be completely decarbonised by 2030, and whether an increase in electricity demand such as that predicted for Bristol could be met elsewhere, can the figures simply be scaled to other areas by population? (The population of Bristol is estimated to be 463,400 [3]). There are several reasons why this might not be possible. The concentration of housing in a city such as Bristol can lend itself to district heating schemes which might not be feasible in less densely populated areas. The costs of improving the energy efficiency of buildings can vary considerably from region to region depending on building age, type and construction methods. A transport system efficient in a city environment might be unsuitable in a rural area of villages and small towns. The industrial, financial and academic capabilities of Bristol may enable it to attract the skilled workers and resources needed to implement its plan more easily than could be done by other regions, from which workers and resources might actually be drawn to the city. For all these reasons, some local authorities, while deriving useful information on the magnitude of the task of decarbonisation from Bristol net zero, will anticipate an even more difficult and expensive route than that outlined for the city.


[1] Bristol net zero by 2030: The evidence base (December 2019)

Centre for Sustainable Energy with Ricardo and Eunomia

[2] Global Protocol for Community-Scale Greenhouse Gas Emission Inventories

Greenhouse Gas Protocol

[3] The population of Bristol


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