The Scottish Government

« Previous | Contents | Next »

Listen

Introduction

This report was prepared by the Institute for Energy Systems in the School of Engineering and Electronics at The University of Edinburgh. It was commissioned in May 2004 as an academic study by the Scottish Executive, Meridian Court, Glasgow, under reference QLC11/1. The subject of the report is an appraisal of the extent to which Scotland could meet forty-percent of its demand for electricity in the year 2020 from renewable resources.

1.1 Context

Scotland has extensive renewable energy resources that might be developed to reduce carbon dioxide (CO2) production by future electricity generation. The resources are geographically dispersed and variable. Demand for electricity is also variable and largely remote from the resources. This report describes the method and findings of a study that explored the extent, location and availability of onshore-wind, offshore-wind, wave, and tidal-current energy relative to the timing, location and extent of demand for electricity.

1.1.1 Scotland's Future Demand for Electricity

In March 2003, the Scottish Executive aspired to the target of Scotland generating forty-percent of its electricity from renewable sources by the year 2020 (Scottish Executive 2003). Demand for electricity is forecast to increase slowly in the period up to that time. Based on a predicted one-percent annual increase from 32.4 TWh in 2003, demand could exceed 38.4 TWh by 2020. Supplying forty-percent of this demand from existing hydro-generation, consented and new renewable sources would require an annual production of over 15.3 TWh.

Allowing for the consequences of changing rainfall patterns and hydrology over the next fifteen years, the plant capacity factor of the existing 1.3 GW of hydro generation could be as low as 25%. There is potential for another 200 MW of large and small-hydro capacity. Total annual hydro contribution might then be 3.3 TWh, leaving nearly 12 TWh to come from new renewable sources such as wind, wave, tidal-current and biomass. Based on an assumed average plant capacity factor of 30%, this would require the development of over 4.5 GW of new renewable energy capacity by 2020. By the end of 2005, there was about 500 MW of existing wind capacity at stations accredited by Ofgem under the Renewables Obligation (Scotland) Order. In addition the Scottish Executive has consented more than 1 GW of onshore-wind, offshore-wind, hydro and biomass plant which is planned or under construction. Some further capacity has been consented by local authorities. With the assumed 30% plant capacity factor another 3 GW of new renewable energy-generating capacity would need to be identified, consented and constructed.

This broadly accords with estimates from the FREDS Future Generation Group report "Scotland's Renewable Energy Potential: Realising the 2020 Target" (Scottish Executive 2005). In that report Scottish demand in 2003 was taken as 35 TWh, increasing to about 43 TWh in 2020 based on an annual increase of one percent. The figures used in this study were somewhat lower as they are based on the information published in the Seven Year Statements and are slightly offset by embedded generation satisfying local demand and not using the transmission system. Historical demand time-series and scaling factors used in this study led to an average annual demand of about 41 TWh which endorses the projections in the FREDS report.

1.1.2 Scotland's Renewable Energy Resources

Scotland is at the end of long wind-fetches over the Atlantic Ocean and therefore has some of the best wind and wave energy resources in Europe. Its landmass separates the basins of the Atlantic Ocean from the North Sea and consequently has good tidal-current resources around its headlands and coastal channels. At present, the major renewable-energy sources in Scotland are hydro and onshore-wind. In the future, these could be joined by offshore-wind, wave tidal-current and biomass.

Onshore- and offshore-wind, waves and tidal-currents were selected for the study as they have significant potential for growth and could considerably broaden the mix of energy sources used in Scotland. Garrad Hassan (2001a) predicted an exploitable capacity in Scotland by 2025 as shown in Table 1.1. The figures were based on lifetime production costs ( LPC) below seven pence per kilowatt-hour. In the case of onshore-wind the exploitable capacity was additionally constrained by a socially acceptable limit which was based on experience in Denmark. This set a maximum average density of wind-generation at 150 kW per square kilometre in any planning authority's area.

Table 1.1 Exploitable renewable energy capacity in Scotland by 2025.

Notes: ¹ Figures are taken from Garrad Hassan (2001a); ² Includes forestry residues, energy crops and agricultural wastes; ³ Scottish Executive (2005) assumes a potential of 450 MW.

Data for hydro-power has been added to Table 1.1 for comparison and assumes a small growth from the currently installed capacity of around 1.3 GW. Large hydro power and biomass can generally be considered to be dispatchable while the other sources in the table are variable. Tidal-currents have the benefit of being fully predictable with some secondary influence from weather conditions. Hydro and waves can be forecast from weeks to days ahead, whilst for wind detailed forecasts are, as yet, generally shorter-term.

1.1.3 Matching Renewable Electricity Generation with Demand

The figures in Table 1.1 suggested at the time that forty-percent of Scotland's electricity demand could be met from any of the first four renewable energy sources considered, or from a combination of them. However, such a conclusion would have been based solely on installed-capacity.

The level of demand for electricity in Scotland varies hourly, daily and seasonally as well as regionally. To meet the aspirational forty-percent target, renewable energy resources that vary with time and that are geographically dispersed over land and sea must be able to concurrently match or exceed that portion of demand for electricity at each moment in time. The timing and location of these resources is important, both in absolute terms and in relation to the timing and location of the demand. The objective of the study was to provide a detailed exploration of the temporal and spatial factors that govern the match between renewable electricity generation and demand for electricity. The degree of matching was considered at two timescales: long-term and hour-by-hour.

The four renewable energy resources and technologies studied in this context were onshore-wind, offshore-wind, wave and tidal-current, as they are the most variable and the most abundant. A Geographical Information System ( GIS) was used as the database within which the renewable resources, along with most of the physical constraints on their development, were mapped. This allowed the visualisation and representation of statistically averaged wind, wave and tidal-current resources by location. The extents and locations of each of the four resources that were left after exclusion of all constrained areas were set in rough economic merit order by area. Farms and arrays of generators were located at suitable development sites and the time-series of their electricity production were estimated on an hourly basis over three years. This permitted regional and national comparison with demand, and allowed exploration by scenario of the extent to which forty-percent of Scotland's demand for electricity could be met by renewable resources.

1.1.4 Electricity Supply Infrastructure

The energy resources must either be near to the load demand or, if remote, there must be corresponding capacity in the electricity network to accept and deliver the energy. Without any constraints imposed by the electricity distribution and transmission systems, Scotland could be considered as a single land and sea area with a broad portfolio of renewable resources that could meet local and remote demand for electricity. At the time of writing however, the network is heavily constrained by existing power flows, and future access to the network in geographically remote areas will be expensive to secure. The location and volume of the renewable energy capacity identified in this study to be necessary to provide 40% of Scotland's 2020 demand for electricity would require network reinforcement at the levels recognised in numerous studies (see for example: DTI 2003b, DTI 2003c & Sinclair Knight Merz 2004). Future investment may release much of the network constraint through upgrades of identified sections of the transmission system, to allow accommodation of up to 4.8 GW of additional consented generation (Scottish Executive 2005). Evolution of the thermal plant mix in Scotland and operation of the Scottish electricity system within the context of BETTA and new network rules are not expected to reduce this capacity.

During the course of the present study, transmission and distribution network models were completed that allowed scenario analysis of network power flows within the existing system. Their modification to reflect future reinforcements was agreed to be too speculative and may be the subject of a separate and later study. The present study therefore concentrated on analysis of the location and availability of the renewable resources relative to the location and timing of demand, as if the network would impose no restriction. This provides the most fundamental appraisal of the extent to which the renewable resource can provide 40% of demand, but it must be emphasised that progress towards this goal will require release of current constraints through network reinforcement.

1.2 Report Structure

After this introduction, the study and its results are presented in six further sections and an appendix, as detailed below.

Section 2 - Analysis

Describes the general methodology adopted for the study, the analysis models that were developed and the input data that was used. The data describes the renewable resources themselves, the many constraints that affect generating plant location, and the parameters used in the relative financial analysis.

Section 3 - Electricity Generation

Separate sub-sections are presented for onshore-wind, offshore-wind, wave and tidal-current energies. For each of the four technologies, the nature, location and extent of the available resource is described and quantified. The characteristics of generic energy converters are discussed and the constraints that affect placement philosophy are identified.

Section 4 - Electricity Demand

The creation of disaggregated demand profiles at regional grid supply points is described. Data was derived from half-hourly system demand of the years 2001, 2002 and 2003 and scaled to anticipated levels in 2020. The future demand profiles take account of daily and seasonal variation.

Section 5 - Energy Delivery Scenarios

A scenario based methodology was used as a means of concisely specifying various mixes of renewable-energy sources. Eleven scenarios were modelled based on resource time series from 2001, 2002 and 2003. Six technology scenarios explored the development of the resource in combinations of up to 6 GW of onshore-wind, 3 GW of offshore-wind, 3 GW of wave and 0.75 GW of tidal-current devices. The selection of each resource was based on the nationally most cost-effective or energetic sites. Five geographical or area scenarios tested the nature of the resources in each of ten regions by allocating capacities of each technology evenly in each area. The balance or match between generated and consumed electrical energy was calculated nationally and disaggregated by area. This section of the report describes the analysis methodology in detail and defines the key figures for each scenario.

Section 6 - Results and Discussion

This section contains the results that are tabulated as spreadsheets and shown as graphs. The resources were appraised in a number of ways and are reported in terms of the plant capacity factors that they would bring about; their long-term local matching to demand; their hour-by-hour matching to demand; and coincident hours between their production and demand levels. Graphical results are presented for each of the technology and plant-mix scenarios and the implications of the results are discussed. Furthermore, geographical, physical, resource and time-series limitations are identified.

Section 7 - Conclusions

The report concludes with an appraisal of the extent to which Scotland's renewable resources can individually, or in combination, supply forty-percent of demand for electricity in 2020.

Appendix

The Appendix contains eleven A4-sized maps covering the study area at a scale of approximately 1:3,150,000. The main GIS datasets are displayed together with information which illustrates the approach taken in the study.

« Previous | Contents | Next »