«RESEARCH MONOGRAPHS ON ENERGY PAUL-FREDERIK BACH The Variability of Wind Power Collected Papers 2009–2010 With a preface by Michael Laughton ...»
of Wind Power
Collected Papers 2009–2010
With a preface by Michael Laughton
THE VARIABILITY OF WIND POWER
Paul-Frederik Bach has more than 40 years’ experience in power system planning.
He worked with grid and generation planning at ELSAM, the coordinating ofﬁce for West Danish power stations, until 1997. As planning director at Eltra, Transmission System Operator in West Denmark, he was in charge of West Denmark’s afﬁliation to the Nordic spot market for electricity, Nord Pool, in 1999. Until retirement in 2005 his main responsibility was the integration of large amounts of wind power into the power grid in Denmark. He is still active as a consultant with interest in safe and efﬁcient integration of wind power, particularly prevention of disturbances by advanced system control measures.
Professor Michael Laughton Michael Laughton is Emeritus Professor of Electrical Engineering at the University of London. He has served as Specialist Advisor to parliamentary committees on alternative energy and energy efﬁciency and published on energy policy and electrical power systems. He is a member of the energy policy advisory committees of the Royal Academy of Engineering and the Royal Society.
RESEARCH MONOGRAPHS ON ENERGY The Renewable Energy Foundation’s Research Monographs on Energy are a new series publishing technical analysis and information relating to the energy sector, with a particular emphasis on renewable and alternative energy.
The series is edited by Dr John Constable, Director of Policy & Research at REF, and published by the Foundation as part of its effort to improve understanding of the provision of energy, and in pursuit of its charitable objectives.
PAUL-FREDERIK BACHThe Variability of Wind Power Collected Papers 2009–2010 With a preface by Michael Laughton The Variability of Wind Power was ﬁrst published in 2010 by The Renewable Energy Foundation 21 John Adam Street London WC2N 6JG www.ref.org.uk email@example.com The Variability of Wind Power copyright © Paul-Frederik Bach 2010 A version of “Wind Power and Spot Prices in Denmark and Germany: Statistical Survey 2009” was previously published by the Renewable Energy Foundation under the title Wind Power and Spot Prices: German and Danish Experience 2006–2008 in 2009.
“Wind Power Variability: Observations and Analysis” was ﬁrst published in New Power 14 (March 2010), 7–10.
Printed by Peach Print, Impressions House, 3–7 Mowlem Street, London E2 9HE Contents Preface
Wind Power and Spot Prices in Denmark and Germany: Statistical Survey 2009..........1 Wind Power Variability: Observations and Analysis
Wind Power Variations Are Exported
Geographical Distribution and Wind Power Smoothing
The European Wind Integration Study Final Report
Preface The electricity supply of the future will become ever more dependent on renewable energy sources. That much is clear from consideration of many global requirements and factors, such as the need to reduce greenhouse gas emissions, the inevitably ﬁnite nature of oil, gas and coal deposits, and – although this is not often mentioned – the moral responsibility to conserve hydrocarbon resources for the various chemical, as distinct from energy, needs of future generations. Most prominently, of course, growing environmental awareness and in particular the determination to limit carbon dioxide emissions has led to national and international legislation and agreements that either directly or indirectly focus on the development of sources of renewable or alternative energy.
Generally speaking, and whatever its original form, renewable energy is converted most easily into electricity, so the direct connection of such sources to the electricity supply system has appeared as the obvious ﬁrst solution to seek, though other possibilities will probably emerge in due course. While national policies have been formulated and enacted, a widespread misunderstanding of the scientiﬁc and technical nature of the requirements of electrical power system operation has unfortunately resulted in targets and time-scales being set without reference to reality, at least as seen from the engineer’s perspective.
As a result, it is possible and perhaps likely that environmental and political idealism combined with technical naivety will come into conﬂict with the more complex realities of electrical power supply, resulting in disappointment and consequent damage to the perceived need for more renewable generation. Notably, high economic costs to the consumer, caused by excess generation capacity and operational subsidies, could be paradoxically combined with an increasingly weak security of supply, leading to political disenchantment. This should be avoided, but doing so will require candour and courage.
In practice, electricity is supplied as two commodities: energy, that has a clear and well understood market value; and power, that does not, but nevertheless ‘keeps the lights on’. It is the absence of proper consideration of ‘power’, strictu sensu, in current energy policies that is at the root of much difﬁculty.
The present work by Paul-Frederik Bach works towards rectifying this deﬁcit by offering a detailed examination of power output from wind powered generators in Denmark.
Mr Bach frequently emphasizes the importance of having ﬁne-grained publicly available data for the actual performance of wind generation, for without such information debate concerning the contribution of wind, or any other renewable source of energy, it is not possible at present to evaluate the effects of policies and, importantly for wind, to open the discussion as to how best to compensate for its variability.
The development and use of renewable energy depends inescapably on geography, and this study foregrounds the special nature of the Danish situation. Denmark has only been able to achieve a proportionately high penetration of wind power on its system due, The Variability of Wind Power vii Michael Laughton ﬁrstly, to the relatively small size of the Danish power system compared to the larger power systems with which it is linked, and, secondly, to the strong transmission links to surrounding countries, namely the HVDC undersea cables to Norway and Sweden, and especially the 400 kV AC interconnection between West Denmark and Germany. (At the time of writing there is no fully operational link between East and West Denmark, though a new connection is undergoing testing and scheduled for opening in September 2010.) With a strong grid, plus responsive power plants – in this case Norway and Sweden’s hydroelectric plants (and Norway is 99% and Sweden 40% hydro), able to balance the stochastic variations in wind power – the task of integration is made much easier. In their absence it becomes harder.
The outstanding major concern in the work reported here, and one with very serious implications – especially for the United Kingdom with its predominantly island system with inadequate international interconnection capacity – is the extent to which subsidized wind power can, in practice, be used within the system without needing to be constrained off: in other words wasted, or exported at whatever market prices, perhaps disadvantageous ones, prevail elsewhere.
There has been much discussion of the export question in Denmark, and in 2009 a report was commissioned from the Danish think tank CEPOS by the Washingtonbased Institute for Energy Research, a not-for-proﬁt organization that conducts intensive research and analysis on the functions, operations and government regulation of global energy markets. Among other conclusions the report, Wind Energy – The Case of Denmark,1 established that on average wind power production in Denmark converts to just over 19 per cent of electrical energy consumption in Denmark, but that variations in wind power output lead to signiﬁcant variations in power exports, primarily to Norway and Sweden and also to Germany.
Matching these variations in wind power and export power, the report concluded that signiﬁcant quantities of Denmark’s wind power output are transmitted to other systems.
Indeed, on average over the past ﬁve years just under 10 per cent of electric power consumption in Denmark actually came from wind power, a much smaller quantity than is superﬁcially apparent.
If true, the implications are highly signiﬁcant, both economically and politically. A reasonable concern, at least within Denmark, is the degree to which governmentmandated subsidies paid for by Danish consumers end up simply lowering prices in neighbouring countries. The CEPOS report suggested that subsidy is exported along with wind power to the tune of about 110 billion euros per year. While the report doesn’t give full details for the calculation – and it is hard to assess its reliability – the topic raised is an important one, and cannot easily be dismissed.
The CEPOS report is, for the most part, serious and methodical, and it certainly contributes to an understanding of wind power in Denmark. However, electricity ﬂow is not 1 http://www.cepos.dk/ﬁleadmin/user_upload/Arkiv/PDF/ Wind_energy_-_the_case_of_Denmark.pdf
a traceable commodity, so the work inevitably provoked controversial reaction, for example, the recent report Danish Wind Power – Export and Cost,2 published by Aalborg University and partly ﬁnanced by the CEESA (Coherent Energy and Environmental System Analysis) Research Project. This response maintained that wind energy replaces energy from Danish thermal power stations in the Danish market and that, depending on the market situation, these thermal power plants in Denmark are either closed down or choose to produce for export.
In his analysis of the nature of Danish wind power Mr Bach, however, remarks that:
While the amount of exported wind energy is a matter of interpretational deﬁnition, and is dependent on perspective, it is clearly evident from the data that the irregular variations of Danish wind power are reﬂected in the exchange of electricity with the neighboring countries. This much cannot be denied; the facts are clear.
In turn, he considers the assumptions and conclusions in the CEESA report; these are analysed and found to be incorrect, and negated by the examination of actual Time Series data rather than the use of a general economic theory of merit order scheduling.
In particular, he notes that the electricity output from thermal power plants in Denmark depends mainly on the demand for heat for district heating and on market prices.
Thermal power plants are also used for system regulation and as operating reserves. If high wind power output causes lower spot prices in Denmark then the thermal production will be lower. From the data revealed in the Time Series describing plant output, on the other hand, Danish wind power has normally only a little inﬂuence on spot prices;
thus, this indicates that thermal power plants in Denmark, with few exceptions, are operated practically independently of wind power output.
It follows that the levels of power exported vary directly with the levels of wind power, a conclusion in good agreement with the observed power exchanges. Thus, to assume that that all or most wind-produced Danish electrical energy is used within Denmark is mistaken, and it is therefore erroneous to conclude that the Danish development of
wind power is a leading example for other countries. As noted in the text:
Maintaining the myth of the successful Danish integration of wind power may be good public relations, but refusing to face realities is self-deception.
Mr Bach correctly emphasizes, however, that this is more than a fault-ﬁnding analysis. The principal concern is to understand what is required if wind is to be integrated successfully into the Danish power system, and the author’s qualiﬁcations are excellent. Until retirement Paul-Frederik’s main responsility at Eltra was the integration of substantial quantities of wind power into the Danish electricity grid, and he has unparalleled ﬁrst-hand experience and knowledge of the practical problems faced. The results published here, and the associated methods used to obtain them, are a valuable contrihttp://www.energyplanning.aau.dk/Publications/DanishWindPower.pdf
bution to a subject where so much is obscured by idealism or vested interests both intellectual and ﬁnancial.
The Renewable Energy Foundation – a charity founded to publish data, including performance records, in the public interest, for those wishing to invest in the renewables industry, including wind – is to be commended for supporting the investigation recorded in this book.
There is much in this report of interest and value relevant to the future UK situation if the planned wind generation capacity both on and offshore materializes. It appears that the United Kingdom must consider signiﬁcant regulatory and technical changes to grid operation if security of supply is to be guaranteed and costs to the consumer kept under reasonable control.
First and foremost, however, this study’s use of large publicly available databanks concerning the operation of the European grid shows that there is a pressing need for similar energy sector data transparency in the United Kingdom. Bluntly, at present we could not attempt to replicate Mr Bach’s work here; the data is simply not available. That has to change.
M. A. Laughton, FREng.
1. Preface This text is both an update and extension of my previous study, Wind Power and Spot Prices: German and Danish Experience 2006–2008.1 Comprehensive data survey for the calendar year 2009 is provided, and the study now covers hourly wind data from all four German control areas.
The data employed is published by Energinet.dk, and by the four German transmission
system operators, the sources being identiﬁed by the following abbreviations:
EEX European Energy Exchange DKE Denmark East DE Germany NP Nord Pool N Norway ENDK Energinet.dk DKW Denmark West S Sweden