• Energy conservation Agreement this was a key enabler in meeting the 80% target. Final energy demand from end users must stabilise, and preferably reduce, with the majority of scenarios suggesting a reduction of between 30% and 50% on current levels.
• Behavioural change Many scenarios made strong assumptions about the capacity to bring about the necessary demand reductions. There was also a general presumption that demand would be reduced without a corresponding reduction in energy service delivered. The role of energy efficiency across the board was essential, the range of efficiency assumptions varied with each scenario but the reliance on incremental improvements to deliver the same standard of energy service for less was consistent.
• Demand reduction Divergence and uncertainty around whether levels of demand reduction are actually achievable. Although all scenarios recognised that it was necessary, some models, particularly those with a forecasting approach, concluded that this level of demand reduction was not a feasible outcome, either because there are not suitable demand side technologies to make the reduction, or, because the behavioural element of technology use would lower the performance efficiency of end-use technologies.

• Decarbonisation of power Consensus on the need for rapid decarbonisation of power generation
• Electricity demand Divergence on the extent of increase in demand with the range varying from 10% to well above 100%.
• Generation Agreement on the main components of the power system in 2050, with centralised provision from nuclear, wind, fossil (mostly coal) with CCS taking a lead role, but there were variations in proportion of each major technology.
• Other technologies No consensus on the role for other low carbon generation technologies such as tidal, wave, energy from waste, bioenergy, solar photo-voltaic and concentrated solar power. Most studies picked out a small role for a wide range of other technologies but there were no obvious patterns in these conclusions.
• Intermittency Scenarios did not agree on how system control would evolve to resolve intermittency issues. A range of solutions were deployed by the models, from flexible conventional generation, to flexible demand, interconnection to mainland Europe and large scale storage solutions.
  • Forecasting studies cited gas as primary source of system flexibility, particularly in the short to medium term (out to 2030), although this was often coupled with failing to achieve the full 80% CO₂ reductions by 2050.
  • Back casting studies showed more of a role for interconnection and storage (e.g. pumped storage). The involvement of the demand side in treating flexibility was dependent on the electrification of heat and transport and assumptions around behaviour change and end-use technology capabilities (e.g. to enable vehicle to grid interaction).

• Effciency Efficiency gains in conventional vehicles and hybrids drove the bulk of emissions reductions in road transport up to 2020/2025. Post-2025 there was a diversity of fuels playing a role in both passenger and freight transport. Nevertheless, the table also shows there was a significant role for electric drive-train vehicles with some scenarios seeing electric vehicles dominating after 2025.
• Electrification General shift toward the large-scale electrification of transport (particularly domestic transport) after 2025. A limitation of many of the scenarios studied is that the modelling approaches used are not well adapted for representation or costing of infrastructure developments. So comparison of alternative transport options is limited to end-use technology.
• Technology Assumptions around the efficiency improvements (or lack of them) for electric, biofuel and fuel cell vehicles drove scenarios down various alternative paths.
• Bioenergy This was still quite unclear across the energy system with some scenarios seeing a strong role for biofuels in the post 2025 system. But again, highly dependent on assumptions around availability of biofuels and conflicting demands between modes of transport, from other energy services and from non-energy sectors.
• Infrastructure Assumptions around the feasibility and cost of infrastructure evolution also drove the interplay between biofuel, hydrogen and electric transport futures.

4. Heat supply

• Electrification Across scenarios there ws some diversity in the energy sources used for provision of heat but with a slight shift towards electrification away from gas-based heating. There was a general theme of heat supply being provided by multiple technologies (electric heat pumps, gas domestic-scale CHP, biomethane, district heating), so moving away from a single dominant technology (gas central heating).
• Demand The role of responsive demand (particularly use of low-grade heat as a storage device through heat pumps and domestic heat storage) in providing power system balancing services was a recurring feature of the scenarios. However, there was variation in assumptions regarding responsiveness of end users (caused by both technical and/or behavioural limitations).
• Technologies There was considerable uncertainty around deployment and acceptability of new (or alternative) heating technologies. Many of the solutions suggested would require a change in the way that domestic dwellings receive heat services, others require a completely different approach to installation that may not be compatible with retrofit into existing homes and many are susceptible to less than optimal running efficiencies through user behaviour.