Jack W Ponton, FREng - 13 August 2014
The Scottish Government’s aim of having the capacity to produce “100% of Scotland’s electricity” from renewable sources now seems likely to be met
well before the target date of 2020. Existing and consented developments now represent more than 98% of this target with a large additional capacity already awaiting determination. There is a significant risk of overprovision.
Generation Output Target
The primary target is formulated in terms of generation output required. This will be taken as equal to Scottish gross electricity consumption in 2012, the last year for which full figures are available.
This was 36.6TWh . Consumption has shown a general declining trend from over 40TWh in 2000 and there is no reason to expect it to increase. Renewables generation in 2013  was 17.0TWh. To meet the target thus requires an additional
19.6TWh of output.
The Table below shows the status of renewables generation projects from Scottish Government figures  in July 2014 as operational, consented, or awaiting determination. The first part of the table lists generation
capacities in gigawatts (GW). The second part of the table lists annual generation outputs in terawatt hours (TWh). For operational capacity these are taken directly from below. For other output they are estimated for an 8,760 hour year
from generation capacity figures in the top part of the table and DECC load factors.
The sum of outputs from existing capacity (17TWh) and consented capacity (18.9TWh) is 35.9TWh, representing 98% of the target requirement.
To meet the remaining 2% would require only 0.7TWh, 700GWh, of additional output.
Generation Capacity Target
Generation output, rather than generation capacity, is the appropriate measure of target fulfilment.
This is because the generation capacity required will depend on the load factor of the generation technology. For example, 1GW of nuclear generation capacity which can run at a 90% load factor would produce the same output as 10GW of solar with a load
factor of around 9%. The measure of approach to the 100% target is the requirement to generate an additional 0.7TWh.
A conservative estimate of the generation capacity required to produce this can be obtained by assuming that all
further consented renewables will have the load factor of onshore wind. This has the lowest load factor other than that of solar which would make no significant contribution. UK rolling average load factor for onshore wind is 27.9% but we use the lower
DECC figure of 26%.
80MW operating for an 8,760 hour year would generate 700MWh or 0.7TWh. Applying a load factor of 26% implies an actual capacity of 308MW.
To produce 36.6TWh annually would require
an estimated additional capacity of 308MW.
This implies a total installed capacity of 13.8GW (6.8GW operational, 6.7GW consented and 0.3GW additional). This is close to the lower end of the 14-16GW Audit Scotland
estimate of required capacity .
1. Renewable Energy Statistics for Scotland, June 2014, Scottish Government
2. Audit Scotland report on Renewable Energy Sept 2013
Table 6.1c Renewable electricity capacity and generation: Scotland
3. Includes four schemes consented since June 2014: Kype Muir Wind Farm 104MW; Harburnhead 66MW; Clyde Extension 171MW; Dersalloch 69MW
4. Load factors derived from DECC, Digest of United Kingdom Energy Statistics (2013) Table
5. www.scotland.gov.uk/Topics/Statistics/Browse/Business/Energy/energysumjun2014 Table 1
annual output from plant operating 365 days, 24 h per day, at the respective load factor.