Trystan Lea

What might a Zero Carbon Wales look like?

Published: 7th September, 2022

Updated July 2023.

The following tries to answer this question by looking at Wales within the context of the UK wide ZeroCarbonBritain scenario developed by The Centre for Alternative Technology in Machynlleth. It looks at energy use in Wales today, how much energy we generate from renewable energy and how much we would need to build in order to supply projected energy needs.

The analysis here is based on the three summarised data tables below:

Energy and carbon in Wales today

GHG Emissions 38.5 MtCO2e [1]
Electricity 14.7 TWh [2] (4.9 TWh domestic, ~3520 kWh/household), 50% from renewables *
Gas 24.0 TWh (14.7 TWh domestic) [2]
Oil 38.4 TWh (23.8 TWh road transport) [2]
Coal & Manufactured Fuels 10 TWh (9 TWh industrial) [2]
Bioenergy 5.3 TWh (0.8 TWh domestic) [2]
Total final energy 92.4 TWh/yr [2]
Total primary energy estimate 125.7 TWh/yr *

* Electricity supply on a UK wide basis is currently about 21% from wind, solar and hydro, 19% from nuclear, 11% from bioenergy (of which about half comes from drax wood chip’s). The remaining 49% is mostly gas power stations, plus a little from oil and coal.

* Primary energy estimate based on 1.36x factor difference between national primary and final energy figures. This covers thermal power station losses, grid losses, other conversion losses and energy industry own use [3].

These figures give us an idea for how much energy we use today, the exact figures and units are less important than the overall relative changes. We use a lot of energy today, we can save a lot of energy just by switching to more efficient technology such as heat pumps and electric vehicles. 50% of our electricity consumption is currently generated by renewable energy in Wales but electricity is only 16% of final energy demand.

Energy demand in a future ZeroCarbonWales scenario

The following is based on a proportional share (by number of households, 1.38 million) of the national ZeroCarbonBritain scenario, modelled using the open source ZeroCarbonBritain scenario tool.

ZCB [3]
Lighting, Appliances and Cooking 5.2 TWh/yr (More efficient appliances)
Space and Water heat, fuel demand 5.9 TWh/yr (Retrofit & heat pumps)
Transport demand 7.2 GWh/yr (Electrification & modal shifts)
Industry demand 13.3 GWh/yr (Increased by onshoring and economic growth)
Total final energy demand 31.6 TWh/yr
Losses & conversion 10.5 TWh/yr
Excess / curtailment 6.7 TWh/yr
Total primary energy supply 48.8 TWh/yr
Renewable electricity supply 35.9 TWh/yr
Bio-energy supply 11.0 TWh/yr
Geothermal & solar thermal 1.9 TWh/yr

Like most energy scenarios, ZeroCarbonBritain is a combination of changes on both the demand side and supply side of the energy system. It includes almost full electrification of heat and ground transport in order to make the most efficient use of zero carbon electricity. It is also particularly ambitious compared to other scenarios in reducing demand with building retrofit and behaviour change, it includes:

Total primary energy demand is reduced by almost 50% compared to our energy use today.

Other scenarios such as the recently published 100% Renewable UK scenario are much less ambitious on reducing demand and compensate by building more supply. ZeroCarbonBritain also sources a relatively large share (23%) of it's energy supply from biomass energy, this uses 18% of total UK land area. It might be better to build more wind, solar and associated power-to-gas and liquid fuels infrastructure (with carbon recycling or direct air capture) so that we can free up more land for biodiversity.

The 100% Renewable UK with inter-annual storage (IAS) scenario has a primary renewable energy demand of 1361 TWh/yr, of which renewable electricity supply is 1344 TWh/yr, it has a projected population for Wales in 2050 as 3.263 million and projected population for the UK & Ireland as a whole at 80.939 million. The Wales share of renewable electricity supply is therefore 1344 x 3.263 / 80.939 = 54.2 TWh/yr.

Electrification progress

While electrification of heat, transport and industry are key parts of both the ZeroCarbonBritain and 100% Renewable scenarios we are still only at the first few % points of the transition on the demand side.

Today ZCB
Electrification of heat with heat pumps 0.7% [4] 90%
Electrification of transport ~2% [5] 90%

Renewable Energy in Wales today vs a future ZeroCarbonWales scenario

Current ZCB Progress
Renewable Electricity 7.3 TWh/yr 35.9 TWh/yr 20.4%
Offshore Wind 0.726 GW (2.226 TWh) 6.45 GW (24.42 TWh) 11% (9.1%)
Onshore Wind 1.273 GW (3.070 TWh) 1.38 GW (3.53 TWh) 92% (87%)
Solar PV 1.016 GW (0.963 TWh) 4.15 GW (3.43 TWh) 25% (28%)
Tidal 0 MW 922 MW (1.93 TWh) 0%
Wave 0 MW 461 MW (1.14 TWh) 0%
Geo Thermal Electricity ? 138 MW (1.1 TWh) 0%
Hydro 184 MW (0.365 TWh) 138 MW (0.364 TWh) 133% (100.3%)
CHP elec from biomass 131 MW (0.686 TWh) 0 TWh
Renewable Heat 2.07 TWh/yr 3.6 TWh/yr 57.5%
Solar Thermal 0.013 GW (0.008 TWh) 1.5 GW (1.14 TWh) 0.9% (0.7%)
Geo Thermal Heat (Mine water heat feasibility study in progress) 92 MW (0.73 TWh) 0%
Biomass for direct heat (457 MW, 3468 projects) 1.4 TWh 1.76 TWh 80%
CHP heat from biomass 120 MW (0.663 TWh) 0 TWh
Renewable Fuels 9.2 TWh/yr
Biomass for biogas 0.658 TWh [6] 4.24 TWh 9.6%
Biomass for liquid fuels ? 5.0 TWh
Total Supply 10.04 TWh 48.8 TWh 20.6%

Additional storage infrastructure is required to provide a complete working energy system that matches demand for every hour of every day. Wales's share of national storage requirements based on the ZeroCarbonBritain model would very roughly be: 9.2 GWh high efficiency electricity storage, 1.24 GW of electrolysis, 922 GWh of hydrogen storage, 2996 GWh of e-methane storage, 2.8 GW of backup gas turbine capacity (800 GWh/yr). These are indicative figures to provide a more complete picture of what the model suggests is required. We do already have two large pump hydro storage schemes: Dinorwig and Ffestiniog which have a combined storage capacity of 10.5 GWh and there is another proposed project at Glyn Rhonwy.

How far are we on the path to a zero carbon future?
We have so far built enough renewable energy to provide just over 20% of the energy required for our portion of the ZeroCarbonBritain energy scenario demand, or 13.5% of the higher demand scenario. In terms of zero carbon electricity supply, ZeroCarbonBritain suggests a need for 35.9 TWh/yr, or another 28.6 TWh/yr above current generation levels. The higher demand scenario would require 47 TWh/yr above current generation levels.

New offshore wind projects

Total offshore wind: 4.6 GW (17.9 TWh) by 2035:

Type Project Name Capacity Annual generation Construction start Final commisioning
Offshore wind Awel y mor 0.6 GW ~2.1 TWh ~2026 ~2030
Offshore wind Mona 1.5 GW ~5.9 TWh ~2027 ~2028
Floating offshore wind Erebus 0.1 GW ~0.4 TWh ~2026 ~2027
Floating offshore wind Valorous 0.3 GW ~1.2 TWh ~2026 ~2029
Floating offshore wind Dylan 0.3 GW ~1.2 TWh ~2027 ~2028
Floating offshore wind Dylan Extension 0.6 GW? ~2.4 TWh? ? ~Early 2030's
Floating offshore wind Myrddin 1.0 GW? ~3.9 TWh? ? ~Before 2035
Floating offshore wind Llyr 1 0.1 GW ~0.4 TWh? ? ~2026/27
Floating offshore wind Llyr 2 0.1 GW ~0.4 TWh? ? ~2026/27

While floating offshore wind maybe considered an early pilot stage technology, the world first floating offshore wind farm; Hywind in Scotland is out-performing all other wind farms in the UK:

These projects together with existing renewable energy could take us to 70% of the low demand scenario or 46% of the high demand scenario.

The resource potential for offshore wind around Wales is much larger than the projects listed above. An ITP Energised estimate suggested that 15-50 GW of floating offshore wind could realistically be developed in the Celtic Sea region [7]. Offshore wind alone and only in the Celtic sea could therefore in theory at least produce enough for both a low and high demand scenario if it was all built out. Some argue that we should build only offshore wind in place of more onshore wind, but caution is needed here as it's not yet certain if all the projects above let alone further significant projects will reach completion. There are also other benefits to onshore wind that make a combined approach worthwhile.

New onshore wind projects

The 2020 Energy Generation in Wales report suggests that there are over 20 onshore wind projects with capacities greater than 1 MW.
I have been able to identify:

Note: Only 2 projects out of 39 are currently under construction, 9 have were granted planning permission more than 5 years ago. It would be good to evaluate in a bit more detail the likely-hood of completion for each project and monitor the status of these projects over time. It may be that many listed are not built, while others not yet listed end up completing faster.

Wales's proportional share of the ZeroCarbonBritain national target for Onshore wind would be 1.38 GW (3.53 TWh/yr). A proportional share here may not be the correct allocation of course given our much better wind resource in Wales than England. We may want to generate proportionally more from Onshore wind given our good resource. The combined capacity of existing onshore wind 1.273 GW (3.070 TWh) and identified projects 1.7 GW (4.5 TWh/yr) could take us to a total of 3.0 GW (7.6 TWh/yr).

In generation output terms the combination of planned onshore and offshore wind projects could provide an additional 22.4 TWh/yr of generation above our existing 7.3 TWh/yr of generation, enough to take us from our current 20% all the way to 79% of the lower demand renewable electricity supply requirement, or 48% of the higher demand target.

Solar PV

We currently have just over 1 GW of solar pv capacity and 0.013 GW of solar thermal. The ZCB scenario proposes building 4.15 GW of PV and 1.5 GW of solar thermal. We have so far delivered an average of 0.07 GW of additional solar PV capacity per year in the period 2006-2020. Reaching 4.15 GW by 2050 would require a doubling of this installation rate.

There are 71 Solar PV projects in the Renewable Energy Planning Database that could total 0.684 GW of capacity. Like wind, further projects are likely at the pre-application stage. Only 3 out of 71 projects are currently under construction, 4 have had planning permission granted for 5 years or more.

The 100% RE UK report suggests an upper resource bound of 1% of land area for solar PV and assumes an installation power density of 75 MW/km2. Wales has a land area of 20,779 km2 x 1% = 208 km2. At an installation power density of 75 MW/km2 this might suggest an 15.6 GW (15 TWh/yr) potential. If we look at the 5 largest solar farms in Wales, the power densities are Shotwick: 81 MW/km2, Llanwern: 75 MW/km2, Fenton Farm: 63 MW/km2, Tiers Cross 56 MW/km2, Caeremlyn: 64 MW/km2. An average power density of 70 MW/km2. These power densities include land areas for tracks & hedgerows between fields of solar. These examples suggest 14.6 GW (14.1 TWh/yr) at 1% of land area.

It's worth noting that 14.6 GW is solar at scale! Equivalent of building an additional 180x 75MW Llanwern solar farms, each covering 1 hectare or 260 acres. Yet still only 1% of land area. The 100% RE UK report that suggests the 1% of land area figure is more optimistic on solar than most/all other scenarios, this surprising outcome is based on a detailed least cost analysis. Caution is again required here given the large gap between current and planned projects and a high end potential capacity such as this.

Wave and Tidal

There is work being done to develop tidal and wave energy in Wales. These projects are in the early development / pilot stage but could deliver significant energy in future. The Morlais project near Holyhead aims to develop around 240 MW which would deliver ~0.55 TWh/yr at a 26% capacity factor. Another proposal by North Wales Tidal Energy proposes a 2-2.5GW scheme that could generate 4.0 TWh/yr.

The ZCB figures suggest building a combined 1.4 GW of wave and tidal, generating 3.1 TWh/yr. The morlais project could deliver ~18% of this. A larger lagoon such as the North Wales Tidal Energy scheme could more than make up the rest. Alternatively a number of smaller lagoons or extensions of projects like Morlais could contribute to this target. The Swansea Bay tidal lagoon was also projected to generate 0.5 TWh/yr.

Wave and tidal projects are still more expensive than wind and solar and have been struggling to get out of the pilot stage, suggesting caution in relying on the development of this sector alone as an alternative to more mature technologies.


There does not appear to be any active geothermal generation currently in Wales and we dont seem to have any obvious high temperature resource. There are feasibility studies into utilising mine water heat though these are really variations on heat pump heating rather than direct geothermal heat in the traditional sense. The ZCB scenario suggests that our share of national capacity would be 138 MW of geothermal electricity and 92 MW of geothermal heat, generating a total of 1.8 TWh/yr. These projects are more likely to be focused around high temperature sites elsewhere in the UK, that is unless next generation geothermal technology opens up a wider resource.


Hydro generation in Wales already meets the share of national capacity in the ZCB scenario. It may well be that there is scope to build further projects, though the total scale is likely limited, e.g even a doubling of current capacity would only deliver as much energy as a relatively small 100MW offshore wind farm.


Biomass energy provides a large component of the overall energy supply in the ZCB scenario. Our share in Wales of the national biomass energy requirement is ~11 TWh/yr. We currently produce about 20% of this amount, mostly in the form of biogas and biomass for direct heat. In terms of land area the ZeroCarbonBritain scenario suggests 54 kha for rotational grasses used for biogas, 74 kha of miscanthus for liquid biofuels and 70 kha of short rotation forestry and coppice for direct heat. A total of ~200 kha for biomass energy. This is about 10% of total land area in Wales.

Other scenarios such as the 100% RE UK IAS scenario use almost no biomass energy, producing e-fuels using direct air capture instead. Land use is likely better used for biodiversity and conservation rather than adding another industrial demand. Burning biomass for energy can also have significant air-quality health impacts.


Though not included in the 100% Renewable ZeroCarbonBritain scenario, new nuclear is being discussed for several sites in Wales:

A recent report by the European Commission's Joint Research Centre highlighted many of the environmental benefits of nuclear including a similar carbon intensity to wind [8]. Given challenges that the nuclear industry has had with building new projects it's hard to know how likely these projects are of being taken forward. While the UK Government appeared to be making a big commitment to nuclear in it's recent Great British Nuclear announcement, the final investment decision for new projects has been pushed back to 2029, suggesting that the original delivery dates for new plants for the early 2030s is less likely. There is a big question as to how the next generation of nuclear projects will fare, projects due for delivery before 2030 in Canada and the USA should start to give a clearer indication.


We currently generate 7.3 TWh/yr out of the 35.9 TWh/yr of non-biomass zero carbon energy supply suggested by the ZCB scenario (~20%), or 13.5% of the higher demand scenario.

The offshore and onshore wind projects at various stages of planning could get us to 79% (low demand) or 48% (high demand).

1.4 GW of additional Solar PV could produce 1.3 TWh/yr, getting us to 84% (low demand), 51% (high demand).

The full development of Morlais and either a single Swansea bay sized lagoon or further Morlais like schemes may contribute another 1 TWh/yr taking us to 87% (low demand) or 53% (high demand).

A 440 MW SMR at Trawsfynydd could bring us to 99% (low demand) or 61% (high demand). An additional 1 GW project at Wylfa could bring us to 127% (low demand) or 77% (high demand). An alternative 3 GW project at Wylfa could take us to 111% of the high demand scenario.

Alternatively for a 100% renewable scenario we would need between 3.7 TWh/yr and 22 TWh/yr of additional supply. 1 GW of offshore wind, onshore wind or solar PV could provide 3.8, 2.6 or 0.95 TWh/yr respectively. Meeting the low demand scenario would be relatively straightforward. The higher demand scenario would be a bit more challenging, requiring e.g 5.8 GW of additional offshore wind, or a mixture of offshore, onshore and solar.

We are still a long way from generating enough zero carbon supply to meet future energy needs and for now it looks like we need to build as much as we can if we are to reach a zero carbon future.


  1. Total CO2e emissions from CCC Progress Report, Reducing emissions in Wales, Supporting information, charts and data. There is a significant difference between total figures given here and those given in the UK local authority and regional greenhouse gas emissions national statistics. 38.5 MtCO2e vs 29.8 MtCO2e?
  2. Derived from Sub-national total final energy consumption data. Figures given in ktoe converted to TWh by multiplication with conversion factor x0.01163.
  3. ZeroCarbonBritain hourly energy model and scenario tool
  4. Heat from heat pumps 104 MW (173 GWh), target for 3% electrification of heat by 2025.
  5. 14,600 EV's 2021 (9100 BEV's, 5500 PHEV), 27 GWh electric demand.
  6. Current biomass for biogas estimated from current use of AD for 19 MW elec (100 GWh) & 8 MW heat (49 GWh). (100÷0.3)+(49÷0.8) = 395 GWh. Energy from waste (136 GWh), sewage gas (44 GWh) and landfill gas (83 GWh) is added to this to give 658 GWh.
  7. Floating Offshore Wind in Wales
  8. Technical assessment of nuclear energy with respect to the ‘do no significant harm’ criteria of Regulation (EU) 2020/852 (‘Taxonomy Regulation’)