Select Committee on Innovation, Universities, Science and Skills Written Evidence

Memorandum 9

Submission from Alan Shaw, Retired Chartered Engineer



  This brief paper summarises the UK context for introduction of new electricity generation sources based only on the Great Britain (GB) sector of the UK public electricity supply system, being some 97% of the UK total.

  The second part of the paper discusses the fundamental differences between the pattern of GB electricity demand as shown in the National Grid Seven Year Statement. This pattern arises from British habits of life and work combined with seasonal and climatic influences, The largely predictable historic shape of this pattern, day by day and year by year, is not matched in achievable supply patterns from most forms of renewable energy. Instead lunar, solar and other cyclic bases are typically the the governing factors.The need to safeguard the integrity of National Grid's demand Balancing Mechanism (BM) is underlined.


1.  Introduction

  1.1  Successful large scale development of any renewable energy depends on its ability to fit in controllably to the overall demand pattern of the national electricity supply system , hour by hour, day by day and annually. The overall pattern of demand varies with the season of the year, weather and special events but by and large is predictable from past records and the expert knowledge of daily events of the Great Britain System Operator (GBSO)—National Grid Electricity Transmission plc.(NGET)

  1.2  The UK electricity system in England, Scotland and Wales (GB) together forms a system separate from Northern Ireland (NI) but interconnected with the NI system by the Moyle high voltage direct current (HVDC) submarine interconnector between Northern Ireland and south west Scotland The direct current feature of the Moyle interconnector means that the two systems, which can exchange power in either direction by planned mutual consent and are both of 50 cycle alternating current frequency, are not synchronised with each other.

  1.3  The NI system maximum power demand MW (megawatts) and its total distributed energy MWh (megawatt hours) are similar in demand profile to, but less than 3% of, the GB system. I will for simplicity therefore take the GB system operated by NGET as representative, bearing in mind that, based mainly on 2005-06 figures * it is around 97% of the UK total.

  1.4  It should be noted that although revenues from electricity ( and fuel or renewable energy used in generation) are energy (MWh) based, the continuous balancing of demand with supply is carried out entirely by frequency sensitive control of the overall generation power rate (MW). Excess of demand over generation causes frequency to fall, excess of generation causes it to rise. Frequency maintenance at an average of 50 cycles per second is a statutory requirement for system stability. Instantaneously demanded power in MW must be continuously matched by instantaneously supplied generation in MW. In practice the balance is recorded half hourly. Electricity on a national scale can NOT be stored. The four pumped storage stations in Wales and Scotland have a total capacity of only 2,290 MW or about 2.7% of current annual maximum demand **. Not all of this may be available at any given moment as it is subject to normal pumping/generation profiles imposed by system requirements.

  1.5  Until the recognition some 10 years ago of the necessity for greenhouse gas (GHG) control the entire electricity system was supplied by fully controllable forms of energy generation—coal, oil, natural gas, nuclear power and a small percentage (about 1%) of hydro-electric generation. Hydro power is of course a renewable energy but dependent on a variable rainfall. As rainfall is to some extent predictable, visible once it falls, and some can be stored, the small and variable percentage of total generation it represented at any given time is normally able to be accommodated by the national grid system, but not always. In 1955 the North of Scotland Hydro-Electric Board (NSHEB) contracted to supply annually to the then South of Scotland Electricity Board 280 GWh. In the event, in that year an unprecedented and prolonged drought reduced the figure to 167.5GWh or only 60% of the contractual amount. The shortfall had to be made good from the England and Wales system.*** Although such extreme shortfalls are rare this event was a sharp reminder that hydro power under UK weather conditions is not completely predictable.

2.  Fundamental differences between pattern of UK electricity demand and various renewable energies ability to match with supply

  2.1  The following Figure 2.2 and explanations extracted from NatGrid GB Seven Year Statement 2007 shows how the seasonal demand profiles follow a characteristic shape determined entirely by the British habits of life and work, some determined by the weather and climate.

  Figure 2.2 below presents demand profiles for the days of maximum and minimum demand on the GB transmission system in 2006-07 and for days of typical winter and summer weekday demand. These demands are shown exclusive of station transformer, pumping demand and interconnector exports.

Figure 2.2


  Key points of interest are:

  (i)  Maximum & Typical Winter Profiles (Weekday)

  (ii)  Typical Summer Profile (Weekday)

  (iii)  Minimum Summer Profile (Sunday)

  2.2  The various types of renewable energies produce annual daily and annual availability profiles quite unrelated to the electricity demand pattern produced by the British way of life and work—tidal power is governed by sea level which varies approximately with a 12.4 hour period, the diurnal ebb and flow cycle, superimposed upon a longer sinusoid with a period of 353 hours, the springs-neap cycle. The largest tidal barrage in operation is the Rance estuary scheme in France. The tides follow a two week cycle throughout the year. The Rance output is computer controlled and optimised to match the needs of the French grid. The nominal average output of this 240 MW project is between 50 and 65 MW and is thus not the maximum that could be obtained, but it contributes maximum savings to the grid. While La Rance electricity is the cheapest electricity on the French national grid Electricity de France say that it would be too expensive to build any further power stations. Studies have shown that the method of operation that results in the lowest unit cost of energy is either simple ebb generation, or ebb generation with pumping at high tide. As the generation period is about an hour later each day the generation (and pumping if used) needs to be planned in advance to integrate with the needs of the French national grid.

  2.3  Studies have shown that the method of operation that results in the lowest unit cost of energy is either simple ebb generation, or ebb generation with pumping at high tide. ****

  2.4 Solar energy in the UK is of course dependent on time of day, season and cloud cover. Wave energy is affected by "fetch" ie, distance of wave travel, on strength and direction of wind and in some cases tidal conditions.

  2.5  Such influences tend to produce renewable energies which are intermittent, uncontrollable and unsuitable for the national grid's continual need for firm, responsively controllable power. This is the function of the NGET's "Balancing Mechanism" (BM). From the point of view of economic electricity generation the most valuable sources of energy are those which, in instantaneous rate of electrical production are "firm " ie, reliable, fully controllable and quickly responsive. *****

  2.6  To have large MW capacities of uncontrollable non-firm power running loose risks the stability of the entire national grid system and can greatly increase the stress under which grid controllers work. Also of growing concern are the costs of generation coupled with the annual capital charges of Supergrid transmission reinforcements to generate and convey the renewably sourced electricity from the favoured generation sites (in the Highlands and Islands of Scotland and offshore) to satisfy competitively the dominant demands in the Midlands and south of England. These must be very carefully considered before even greater expenditures are incurred, all of which must eventually percolate down to consumers and taxpayers.

  2.7  The full extent of the potential problems which would be presented to central grid control by, for example , the realisation of leading Scottish politicians' aspirations in past months, quoting 40% and even as high as 100% of Scottish electricity MWh from renewable energy is obviously politically uncomprehended. The basic reason is the uncontrollability and unpredictable intermittency of wind energy together with its overall average annual load factor making both its generation and Supergrid high voltage transmission to its supposed markets in the Midlands and South of England economically unattractive except for the entrepeneurial purpose of earning quite unjustified subsidies.

  2.8  Even at present levels of installed windpower MW capacity the growing total UK burden of fully controllable standby plant capacity is not publicly understood. To bring up from near zero load to full load on-line standby plant at the MW per minute rate ("response time") at which large scale windpower can disappear only to unload it similarly rapidly risks damage to high temperature thermal plant such as gas and steam turbines. In extreme circumstances only large pumped storage hydro turbines can start up "from dry" and pick up load shed by renewable energy sources rapidly and safely enough. As footnoted in ** below the existence of such plant nationally is very limited and largely already spoken for by normal operational contingencies.

  2.9  I would earnestly recommend the Select Committee to study, with NGET assistance, the latter's excellent Seven Year Statement 2007 (and previous years) produced annually as a condition of its Transmission Licence and downloadable on the internet.

  I am sirs, yours most faithfully,

  Alan Shaw BSc CEng MIET

  (Retired ex National Nuclear Corporation Limited (1955-81) and author and co-author of energy papers to World Power, United Nations and other international engineering conferences.)


*  Electricity Industry Review 11 (EIR11) June 2007 pps 7, 9 and 10.(published by Electrica Services Limited and sponsored by NationalGrid).

**  Dinorwig 2,200MW, Festiniog 350MW, Foyers 300MW, Cruachan 440MW ( Source: EIR 11).

***  "The Hydro" by Professor Peter L Payne pub Aberdeen University Press 1988.

****  Section 21 of "Kelvin to Weir and on to GB SYS 2005" by Alan Shaw: Royal Society of Edinburgh Inquiry into Scotland's Energy Issues 2005.

*****  Please note that Capacity Factor, a partial synonym for Load Factor often appearing in the press nowadays, is an Americanism and a term not recognised by the IEC/ International Electrotechnical Vocabulary (see "Electropedia" on the internet.)

July 2007

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