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7 Conclusions
This study was commissioned to determine whether Scotland could meet 40% of its 2020 demand for electricity from renewable resources. By then annual demand for electrical energy in Scotland could be around 41 TWh with a peak power demand of around 7.3 GW. Supplying 40% (16.4 TWh) of the electricity required over the year from renewable resources suggests the need for around 6 GW of renewable capacity.
Current and planned hydro capacity in Scotland will contribute 1.5 GW to the 2020 energy mix. Onshore wind projects built to date, and consented but not yet operational, should contribute at least a further 1.5 GW. The balance of around 3 GW could be met by a range of technologies. Biomass has been assessed to have the potential to contribute up to 0.45 GW using existing technology. Information available before this study suggested that wave and tidal power, between them, have the potential to deliver over 1 GW, but that these are nascent technologies which need to be developed commercially. Onshore and offshore wind have potential to contribute significantly more.
Generated power must match demand for power on a second-by-second basis. Demand varies with time and with location across Scotland and so does renewable energy. This is particularly true for time-varying resources like wind, wave and tidal-current. Historical demand data was available for the study, but hourly production time-series were not available for existing renewable plant and could not be synthesised for consented or planned plant without detailed siting information. Instead a Geographical Information System and industry standard software were used to provide a consistent generic approach. This study has:
- mapped the location of onshore and offshore-wind, wave and tidal-current resources and the physical, environmental and planning constraints for their development;
- estimated connection costs between renewable plant and grid supply points;
- used an unconstrained electricity network as a basis;
- predicted the lifetime production costs of electricity generation which enabled the economic ranking of locations feasible for development;
- assembled and analysed resource time-series;
- converted the renewable energy resources to calculate hourly time-series of power levels by location for a consecutive period of three years;
- forecast hourly time-series of demand in 2020;
- developed individual and combined renewable technology scenarios to derive seasonal and annual key figures;
- calculated plant capacity factors and long-term matching data which describe the ability to meet, on average, the 40% target;
- estimated the extent to which portfolios of plant can meet the 40% target on an hour-by-hour basis by calculating hours of shortfall and hours of coincidence between production and demand.
Each of these steps is necessary to characterise the selected renewable resources, to increase confidence in them and to derive maximum benefit from the minimum number of developments.
Results in this summary are tabulated for generation from onshore and offshore-wind, wave and tidal-current generation, both individually and in a combined scenario with 75%, 10%, 10% and 5% respectively from each resource. To illustrate trends the scenarios are based on capacities of 3 and 6 GW where there was sufficient technically viable resource. The results do not imply that a combination of modelled with existing, consented or planned capacity will necessarily result in the same average and hour-by-hour figures. Hydro in particular could reduce the overall plant capacity factor and the long-term matching, but has the advantage of being dispatchable and offering storage.
1. After application of constraints it could be possible to develop renewable resources to capacities reaching or exceeding 6 GW for onshore wind, 3 GW for offshore wind, 3 GW for wave and 1 GW for tidal current, or any combination of these technologies. However, none of the resources studied is ultimately limited to the totals identified. There is significant additional onshore wind capacity available at less energetic sites. Offshore wind, wave and tidal current could be further developed in deeper waters.
2. The annual plant capacity factors derived from production time-series all exceed 30% and are in line with working experience. Generally they reduce as the capacity increases by adding sites of higher cost which are often less energetic. Seasonal values for the capacity factor indicate strong variations of wind and wave power over a year with significantly higher output in winter than in summer. |  |
| 3. The long-term local matching is the best assessment of the extent to which renewable resources could meet 40% of annual demand for electricity in 2020, taking account of their time variation and that of the load. In the case of onshore wind, offshore wind and wave a 3 GW capacity of any one of these resources would on average match at least half of the 40% target demand. Extending onshore wind and the mixed technology portfolio up to 6 GW demonstrates that such a capacity would be able to supply, on average, at least 40% of the electricity demand in 2020. |
4. This illustrates that Scotland could, in 2020, meet on average 40% of its demand for electricity from renewable resources with a total renewable capacity of around 6 GW. It does not mean that the aspirational demand target is reached during each hour of a year. There will be periods of shortfall and periods of excess. The remainder of the study has quantified this.
5. Due to the variability of the renewable energy output, 40% of the actual demand level will only be met or exceeded for a fraction of the hours in a year. With 3 GW of renewable capacity this would happen between 12 and 18% of the total time. An increased capacity of 6 GW of onshore wind or the technology mix could meet or exceed 40% of demand for electricity for around 45% of time. |  |
| 6. The ongoing hourly match between renewably produced electricity and demand can be described by a histogram of coincident hours when production (arranged in 10% bins up to installed capacity) matches demand (arranged in 10% bins up to peak demand). At times of high production and low demand the excess energy would be exported or constrained off. At times of peak demand and insufficient production the shortfall in energy would need to be imported or sourced from balancing plant. |
7. Diversification of energy sources and their geographical dispersion improves the hour-by-hour matching with demand. Nevertheless there will be many hours in a year when renewable output from wind, waves and tidal currents falls below demand targets and balancing plant would be needed. A strong interconnected transmission system will reduce the need for local balancing plant and increase security of supply. Full development of the more remote onshore and most of the offshore resource would require completion of planned network upgrades in northern and western Scotland.
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