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Electrical Load-curve
Coverage
Proceedings of the Symposium on Load-curve Coverage in Future
Electric Power Generating Systems, organized by the Committee
on Electric Power, United Nations Economic Commission for
Europe, Rome, Italy, 24 - 28 October 1977
Published for the
UNITED NATIONS
by
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First edition 1979
British Library Cataloguing in Publication Data
Symposium on Load-curve Coverage in Future
Electric Power Generating Systems, Rome, 1977
Electrical load-curve coverage.
1. Electric power-plants - Load - Congresses
I. Title II. Economic Commission for Europe.
Committee on Electric Power
621.31Ό42 TK1191 78-40342
ISBN 0-08-022422-9
In order to make this volume available as economically
and as rapidly as possible the authors' typescripts have
been reproduced in their original forms. This method
unfortunately has its typographical limitations but it is
hoped that they in no way distract the reader.
Printed in Great Britain by Page Bros. (Norwich) Ltd.
Introduction
The Symposium on Load-Curve Coverage in Future Electric Power Generating Sys-
tems provided the opportunity for an international exchange of economic and
technical information on problems connected with the coverage of the full load
curve. In their recommendations, the participants in the symposium made pro-
posals for the strengthening of international exchanges of information and
studies on load curve coverage.
Twenty-two countries* were represented at the symposium with, in addition, the
International Atomic Energy Agency (IAEA), the European Economic Community (EEC),
the International Union of Producers and Distributors of Electrical Energy
(UNIPEDE) and the Union for Coordinating Production and Distribution of Electri-
city (UCPTE).
The symposium was organised by the Committee on Electric Power of the United
Nations Economic Commission for Europe (ECE); at the invitation of the Italian
Government, it was held in Rome, at the headquarters of the Italian National
Electricity Board (Ente Nazionale per I'energia elettrica - ENEL) from 24 to 28
October, 1977.
The subject matter of the symposium was dealt with under five main topics:
1. Optimum composition of the generating system
2. Means of electricity generation for the variable part of the load curve
3. Means of storage at producer level
4. Means of storage at user level
5. Natural characteristics of energy demand (load curves)
Forty-two expert papers were contributed to the symposium. In the consolidated
report prepared by a general rapporteur for each subject-group, papers are
referred to by numbers which are provided in the table of contents of these
proceedings.
The chairman of the symposium was Mr. A. Angelini, President of ENEL- Five
vice-chairmen - Mr. A. Loeffler (German Democratic Republic), Mr. E. Sovary
(Hungary), Mr. A. di Perna (Italy), Mr. F. Willekens (Netherlands), and
Mr. A. Plumpton (United Kingdom) - were elected as vice-chairmen. Each vice-
chairman presided over the discussions on a subject-group. Mr. M. Penel (France)
and Mr. J. Tuma (Czechoslovakia) were appointed as rapporteurs.
♦Austria, Belgium, Bulgaria, Byelorussian SSR, Czechoslovakia, Finland,France,
German Democratic Republic, Federal Republic of Germany, Greece, Hungary,
Ireland, Italy, Netherlands, Poland, Spain, Sweden, Switzerland, Ukrainian
SSR, USSR, United Kingdom, and Yugoslavia.
ix
X Introduction
Mr. G. Colamarino, of Italy, chairman of the ECE Committee on Electric Power,,
declared the symposium open. Participants were welcomed on behalf of the Italian
Government by the Under-Secretary of State for Industry, Commerce and Small
Business, Mr. E. Erminero, and on behalf of ENEL by Mr. Angelini. Mr. Edmond
Janssens, Director of the Energy Division of the ECE secretariat, spoke at the
opening ceremony on behalf of the Executive Secretary of ECE.
The chairman of the organising committee was Mr. P. Peiser, of ENEL.
CONCLUSIONS AND RECOMMENDATIONS
Optimum Composition of the Generating System
Comparison of present methods. It appeared that, with regard to static charac-
ters, a number of methods of investigation and calculation were available to
planners and operators who were concerned with the optimum composition of the
generating system with a view to determining capacity, including the reserve
required to ensure reliable and economic supplies. In particular, methods
were available for studying the introduction of new units in an existing system
within the context of short-term planning. Those methods were at present
applied in decision-making processes. A set of models supplying mutually
relevant information was often used. There were different approaches to the
problem, but the experience of planners and operators who used them certainly
permitted the best possible application of results of their particular power
generating systems. An exchange of different experiences would be desirable
in order to be able to make comprehensive appraisal.
Methodological improvements to be considered. An important aspect of the op-
timization of the generating system, namely optimization of the ability to
follow the continuously variable load (generating system flexibility), would
require more detailed consideration, but there were insufficient data and
completely developed models to be able to simulate the operating conditions
of a power system in respect of flexibility requirements. The data collected
did not seem to be either coherent or complete. They must therefore be arran-
ged on a common clearly-defined basis and efforts made continuously to keep
them up to date. The consideration of the load curve as a reference model
seemed to be the simplest approach to a study of the coverage of energy demand
by different types of generating units. When peak plant structure had to be
defined (such plant accounts for a substantial proportion of total installed
capacity), the contribution of this plant to peak load coverage and to reserve
capacity must be considered. This joint function had assumed greater rele-
vance and importance with the increasing size of generating units.
Means of electricity generation for the variable part of the load curve. At
present, two methods were widely favoured as means of peak generation: pumped
storage hydroelectric stations and gas turbine stations. Neither system
offered clear-cut advantages since their economic performance depended to a
large extent on various local conditions. A technical or economic evaluation
should always be considered.
Coverage of the intermediate power levels between base-load and peak-load
was at present provided by base-load stations whose capacity was reduced
Introduction X1
during off-peak hours. Would it not thus be preferable to develop conven-
tional equipment specifically adapted for such a function and to consider
questions relating to the use of base-load nuclear stations to cover the
peaks ?
Means of Storage at Producer Level
Storage means in use and prospects. Pumping was at present the only energy
storage method used by electricity producers. Experience in this technique
was of long standing, and advanced technology had been developed. Prospects
in the field of storage means in general seemed to suggest that the other
options mentioned in the consolidated report should be studied very closely,
since none of them could be dismissed out of hand: thermal storage, elastic
(compressed air) storage, inertia storage, electrochemical storage and elec-
tromagnetic storage. Prototypes were being developed in the fields of elastic,
thermal and inertia storage. Hydrogen, touched upon during the discussions,
deserved special mention since the research to be undertaken in that area
required cooperation between widely differing disciplines (chemistry, fuels,
etc.).
Methodology. A broad exchange of views enabled the group to compare methods,
some of which were extremely elaborate and others purposely simplified. The
range of methods available was therefore extremely wide.
The Symposium nevertheless considered that pumping stations could not always
be justified from an economic point of view, under present conditions, exclu-
sively on the basis of their "static" advantages, i.e. essentially the advan-
tage offered by the difference in energy costs between the pumping and gene-
rating operations. Those kinetic advantages - load variation flexibility,
frequency regulation, rapid intervention possibilities - today substantially
enhanced the value of pumping stations. New methods which had made it possible
for that type of advantage to be appreciated in quantitative terms were consi-
dered to be of interest, and it was felt that extensions and improvements in
that methodological field would be very useful.
In that connexion, a certain contradiction was found in the development of
multistage reversible hydraulic units in which the non-existence of a distri-
butor eliminated any possibility of finely regulating their capacity.
Development of storage methods from now until the end of the century. The
prospects for the widespread development of nuclear energy and increases in
the size of individual sets left little room for doubt as to the increasingly
important role that storage would be called on to play in the future. Other
reasons, including the long-term need to regularize non-conventional fluctua-
ting energy sources such as the sun or the wind, and a number of environmental
constraints, would seem to confirm that view.
That impression was further confirmed by the extent of the programmes described
by various countries for the period 1985-1990. An average estimate of the
pumping power needed until then represented some 10 per cent of the generating
systems' installed capacity.
In the long run, pumping would be restored to its former economically advan-
xü Introduction
tageous position from the standpoint of energy transfer, and the development
of its "kinetic" qualities would undoubtedly continue.
Exchange of experiences. In addition to a number of excellent reports, various
statements provided a wealth of valuable information on the operating criteria
of pumped storage power stations.
In view of the interest shown in this type of hydroelectric scheme, the Sympo-
sium noted that it would be useful to take measures to encourage exchanges of
ideas or experience in that field between member countries.
Means of Storage at User Level
The role of storage in the optimization of the energy system. Certain uses
of electricity, such as heating or lighting, occurred only in certain seasons
or at particular times of the day. Coverage of these uses by means of a storage
process might prove beneficial as part of efforts to improve the aggregate pro-
ductivity of the generating system, a concept closely linked to that of the
interest of the community as a whole. In itself, storage might be applied at
all levels of the electricity system from generation to distribution, throughout
all the intermediate stages of the network. Solutions must therefore be sought
without starting from a priori concepts of centralization or decentralization,
since on that basis the decisions reached would be non-optimal or less than
optimal.
Storage at user level could thus be considered as one aspect of a very broad
problem.
The technical procedures for introducing storage at the user level, mentioned
in the general report, were potentially very varied (mechanical, chemical,
thermal storage), and should be examined in each individual case.
Present situation at the user level. Among all the options offered, the Sympo-
sium placed particular emphasis on storage heating, which for the moment was
the only widespread form in current use, together with hot water production.
It should be noted that the advantages offered by this techique derived princi-
pally from the improved use of the networks which it permitted. The Symposium
also noted the limitations of the technique:
Quantitative limitations: in many countries, the markets were at present
relatively small; and
Qualitative limitations: because of the importance of unit capacity in relation
to demand reflecting other consumer uses, and the inflexibility of the tech-
nique, which, once installed, could not be adapted in response to changes in
the situation.
Prospects
Promising solutions for the future were discussed: chemical storage by means
of batteries, electric vehicles, combined electric energy and heat production
by thermal motors, enabling the user's "electricity" or "heat" load curve to
be smoothed. The variety of possible solutions suggested that specialists
should endeavour to acquire as much information as possible on all new disco-
Introduction χιιι
veries. The user himself must help in the compilation of such data, since his
participation in that activity could determine its success or failure: the
user, in effect, had to decide between changing old habits and benefiting from
favourable prices, and that he would be able to do objectively only if he was
sufficiently well informed. A certain saturation point as regards heat storage
already seemed to have been reached at the user level, so that a broad inves-
tigation should be made of the optimum distribution of storage between the
various levels of the system, a distribution which must not, of course, be
arbitrary. Indeed, it was no coincidence that, while daily storage had some
interesting applications at the decentralized user level, seasonal storage
was, on the contrary, selectively applied only at the generating level (to-
day's hydroelectric storage). That problem obviously required further study,
taking into account the possible development of new techniques, such as those
mentioned at the Symposium.
Finally, tariffs, themselves should be capable of playing a more effective
part in modulating load curves, especially by extending the range of products
available to the consumer. At the moment the consumer was attracted princi-
pally by guaranteed supplies, which were consequently quite expensive without
necessarily corresponding to his needs. Proposals for cheaper non-guaranteed
supplies could be made to the advantage of all concerned. Indeed the Sympo-
sium emphasized the understanding reached between producers and users, and
considered that it might constitute a possible solution.
Natural Characteristics of Energy Demand (Load Curves)
Data relevant to the problem. The producer-distributor did not control the
flow of electric energy to the consumer, for it was the consumer himself
who drew on the energy as and when he needed it, according to the nature of
his activities and the climatic conditions prevailing at the moment.
The producer-distributor could, however, intervene either to encourage the
user to change his habits through intelligent tariff structures or to offset
the effects of load variations by installing appropriate operational systems
such as pumping.
The analysis of load curves in order to determine the influence of each type
of appliance on the energy supply, was discussed at length. Such analysis
had called for sustained and costly efforts and sometimes the use of sophis-
ticated data processing techniques. In that connexion, particular mention
should be made of the remarkable work done by UNIPEDE, an organization with
which many countries were associated.
Those analyses resulted in forecasting methods which could be classified under
two headings:
Those based on an overall forecast of consumption;
Those based on all the forecasts made in respect of different sectors.
Difficulties encountered: the foreseeable increase in such difficulties
In the light of the studies mentioned above, knowledge of load-curve shapes
had made considerable progress. The Symposium nevertheless emphasized the
major difficulty inherent in forecasting, namely, determination of the peak
xiv Introduction
load of the system as an absolute value, a criterion on which depended all
the forward planning and management of the electricity enterprises. That
difficulty was a real one, because the numerous factors involved in the deter-
mination of the peak load were for the most part totally beyond any control:
distribution of the social product, the political environment and the interde-
pendence of different forms of energy were all factors reflecting structural
changes which were impossible to forecast. Knowledge of the load curve never-
theless remained an essential basic element, even though it was insufficient
in itself.
In view of those constraints, the best course of action was to acquire a deeper
knowledge of the consumer structure in order to ascertain more precisely indi-
vidual cost responsibilities, and thus to be able to determine tariff measures
which might influence consumer habits. Such measures might be very far-reaching,
ranging from conventional guaranteed tariffs to interruption of supplies - an
extreme case, and covering all sorts of more subtle provisions (supplies with
possibility of interruption, non-guaranteed supplies, etc.). Obviously all
those measures, except of course in the case of complete interruption, should
be taken with the aim of producing as little impact as possible on the quality
of life of consumers.
Conclusion
The Symposium expressed appreciation of the numerous efforts made to acquire a
better understanding of the natural characteristics of demand. Those efforts
were essential as a guide to planning equipment and improving management. In
that connexion, the progress recently made in data collection and processing
augured well for the fruitful continuation of that work. The structural
changes which had occurred in numerous fields, as well as the environmental
constraints encountered in relation to the installation of new plant, contri-
buted significantly to uncertainty concerning the future.
Undoubtedly, however, the meetings between experts in different disciplines
which had taken place at the Symposium could give rise to measures that might,
to a certain extent lessen the difficulties inevitably encountered in fore-
casting.
The following recommendations were adopted by the Symposium:
All the various energy storage methods which offered the producer of
electricity an alternative to hydroelectric pumping: thermal storage,
elastic (compressed air) storage, electrochemical storage and electromagne-
tic storage. All the principal ECE subsidiary bodies concerned should be
associated with the study pertaining to hydrogen.
A methodology capable of identifying the "kinetic" advantages of hydroelec-
tric pumping more objectively than present methods: possibility of rapid
intervention, rapid load variation, frequency regulation. That methodology
should constitute a basis for data on precise definitions.
- Possibilities offered by the use of combined heat/power cycles to improve
the economic performance of gas turbines. Recommendations to be addressed
to manufacturers.
Introduction xv
- Minimum load operation and possibilities of modulating the load of conven-
tional and nuclear thermal power stations with a view to using them as
intermediate load stations between base and peak.
- Analysis of the problem of storage in the general framework of the electri-
city system, as part of the energy economy, without a priori concepts of
decentralization or centralization.
The ECE Committee on Electric Power was requested to take any measures it
deemed necessary to promote exchanges of ideas and experience in member coun-
tries on various methodological approaches to the optimum composition of an
electric energy generating system, in the area of the operation of hydroelec-
tric pumping stations.
The Committee should also organise activities relating to the role of infor-
mation in the development of storage procedures:
Exchanges of operating experience among member countries;
Promotion of broad interdisciplinary dissemination of discoveries
and the results of research and development;
Promotion of cooperation between all partners in storage procedures;
Expansion of consumer information services, especially with regard
to tariff procedures, which might become more complex (e.g. non-guaran-
teed supplies.)
The Committee was also requested to organize, within two to three years, a
meeting of experts to take stock of documentation relating to the characte-
ristics of demand for electric energy, and to consider what measures the pro-
ducer-distribution could take to deal with new problems.
The Symposium recommended that the Seminar on the Combined Production of Elec-
tric Power and Heat, which was to be held in 1978 under the auspices of ECE,
should include the following subject in its work programme: "Possible contri-
bution of combined production to the smoothing of the variable part of the
load curve".
In view of the particular value of the work of the Symposium for many experts
on the subject from different countries, the secretariat was requested to find
means of publishing, for broad general distribution all the documentation of
the Symposium, including the memoranda, consolidated reports, summaries of
debates and conclusions adopted.
