Chapter 3
Introduction | Discussion of Chapter 1 | Chapter 2 | Chapter 3 | Chapter 4 | Chapter 5 | Chapter 6 | Chapter 7 | Chapter 8 | Chapter 9 | Chapter 10 | Chapter 11 | Chapter 12 | Conclusion | Appendix
Chapter 3: No wind, low wind – intermittent generation. Etherington defines ‘intermittent as ‘unpredictably variable and intermittently available generation’. Thus he emphasises his complete omission of wind speed prediction and hence wind power prediction. Obviously, if there is lack of wind, there is lack of wind power. The nature of wind speed variation and wind turbine dispersal means that the correct word for this problem is ‘variable power’ (as for demand), and not ‘intermittent power’ (as for a central power station). Yes, a problem is presented, but this fact can be accommodated easily for wind grid-connected capacity as now and for the next few years in the UK. As wind capacity increases, especially of large offshore windfarms, gradual change of the transmission network and control method will be needed. But such change is no more unexpected or different in scale from the past connection of nuclear power stations and other significant plant. All plant ages and has to be replaced, back-up and reserve power strategies change, demand-side action is always possible, tariff options alter and technology advances. Etherington presents such change as harm rather than challenge, so exposing his ignorance of the history of technology and the motivation for applied science. His fear of change is compounded by his misunderstanding of grid connection of wind power, for he states* ‘individual wind farms, even with sufficient wind, are not themselves abler to restore power to the network after failure because of this problem of matching synchronisation… when the “wind engine” stops, there is no recovery without outside help’. One can only gasp at such erroneous statements, which plant fear in the mind of the reader.
Evidence is given of days when wind speed was insufficient for wind power over whole regions, with separate uncoordinated examples from Ireland, Wales, most of the UK, and Denmark. One does not argue that such examples do not happen, but Etherington offers no information on the frequency of such occurrences, or of their meteorological predictability.
Within the context of national supplies, Etherington makes gross errors by giving national spatially-averaged wind power generation the characteristics of a single turbine. He states** ‘(wind) generation can be entirely lost and must be replaced by instantly available capacity from another source …backup”; “ available (wind generated) MW can vary rapidly and unpredictability between zero and maximum…so fossil fuelled backup must…cope with such fast variation of demand”. Here the averaging of widely separated wind turbines and the meteorological prediction of wind speeds are ignored. Demand is muddled with supply. Yet Etherington fails to spot that grid controllers do indeed cope with the normal variations of demand by adjusting supply. He continues*** ‘there is no way of knowing whether there will be (wind) electricity tomorrow morning or even this evening’, which is erroneous with even elementary weather forecasting, yet alone with modern meteorology prediction.
Although nowhere in his book does Etherington consider the vital probability distribution functions of wind speed**** and hence wind power, he does discuss load/capacity factors of turbines and capacity credit of assemblies of turbines. He rightly defines the capacity credit of wind power as the reduction in the total controllable capacity needed on a national network for plant margin. Because such networks already have backup capacity to cover outages from large central plant and unexpected increases in demand, initial wind capacity needs no extra backup capacity. Etherington is loath to admit that such backup is a shared resource for all generation on the grid, stating that ‘the reserve generation which our wind fleet [sic] uses as backup [is] stolen from the backup power intended to secure conventional supply’.***** His use of the word ‘stolen’ is totally inappropriate.
A more detailed analysis of ‘backup’, capacity credit etc and windpower is given in the Appendix below.
As wind capacity increases, the need for extra operational reserve capacity increases, since there are times when even widely separated windfarms are all becalmed****** and the established reserve capacity and load management methods provide insufficient margin. The analysis of such situations is becoming established knowledge******* and is based on the statistical chance of reserve capacity being actually needed. The crossover when wind power noticeably causes the need for extra operational reserve capacity and load management, as distinct from sharing reserve capacity with other plant on the system, occurs for the UK when wind capacity becomes about 15% of total capacity, i.e. about 12 GW. UK wind capacity now totals about 4GW, with an expectation of about 26 GW installed capacity by 2015.
In addition to the short-term operating reserve capacity, the vague term ‘back up’ includes the firm capacity within the whole-system plant margin. Having wind power on the system increases the statistically derived plant margin according to the wind power’s capacity credit. 26 GW of wind power would have a capacity credit of about 5 GW******** in the UK system.
For costs, we must distinguish between the capital costs of plant and of the fuel used. Wind power always displaces fuel costs on the system and also reduces the capital costs of plant margin. By concentrating on ‘backup capacity’ rather than on the utilisation of that capacity, Etherington ignores the fact that the import of wind power into the grid always displaces and abates electricity from other generation. In the UK the displaced fuel is overwhelmingly fossil-fuel, with associated abatement of carbon dioxide and other pollutant emissions.
Etherington’s discussion of national wind power capacity credit, which is definitely a small proportion, is not unreasonable. He is right to raise the subject. However he fails to distinguish between short-term reserve capacity and plant margin. He also fails to explain that national power systems constantly upgrade and replace power plant and transmission systems, from historic beginnings to ever-advanced cooperative and integrated technology. What he sees as doom, others see as challenge.
*Chapter 3, page 55, paragraph 3.
****Weibull, Raleigh functions etc
******Meteorological forecasting gives several days warning of such possibilities
*******See publications by D. Milborrow
********See Fig 6 of D. Milborrow ‘Quantifying the impacts of wind variability’, Energy, vol 162 pp 105-112, Proc Institute of Civil Engineers, UK