Meeting the power surge is not for feint hearts (nor wind turbines)

Meeting the power surge is not for feint hearts (nor wind turbines)

by Paul Spare
article from Wednesday 28, November, 2018

NEW YORK, in the words of the popular song, is the city that never sleeps - life there continues around the clock.  To some extent, in 2018, London, Manchester, Glasgow and other large UK cities might feel on a par with the Big Apple, but not so.  Our lives are still dominated by the bulk of activities occurring in the 9.00 am to 5.00 pm (or 6.00 or 7.00) working day.  The evidence can be seen in our electricity consumption records.  A much greater range is encountered each day than would be found in a 24-hour society.  

The lowest consumption occurs in the small hours.  This is typically 20–25,000 MW.  From about 6.00 am however, there is a dramatic change as activities begin in the working day.  Over the following three hours, power demand surges and consumption can almost double. Kettles, lights, showers, cookers, computers and businesses fire up in a totally uncoordinated programme but with a regular, predictable pattern.  It normally remains quite steady at this high level before tailing off in the late evening.

Although this morning surge in demand is the aggregate impact of millions of individual decisions, its pattern is very predictable.  Indeed if the grid engineers and generating companies could not forecast the daily movement in electricity consumption within a percent or so, there would be severe problems with grid frequency/voltage and even regular power cuts.  

Demand also shows a distinct pattern of change through the seasons, as our activities respond to weather conditions and temperatures.  Forearmed with decades of records and knowledge, the engineers can anticipate the changes.  They can prepare to start up the Combined Cycle Gas Turbine (CCGT) plants and coal-fired stations, imports and hydro plants to match the increasing electricity demand.  The nuclear stations are not involved because they function as permanent base-load to operate at maximum continuous rating, month after month because their fuel costs are very low.  [Pressurised Water Reactors (PWRs) such as Sizewell B can ‘load-follow’ but we have only one.]

At certain times of the year and in very cold weather, electricity demand increases even further around 5.30–6.00 pm, when the working population returns home and more electrical appliances are turned on.  This system is however so predictable and well managed that security of supply exceeds 99.95 per cent so that there is a loss of supply for only about one hour per year.  

There are also more infrequent and less predictable surges in demand that have to be accommodated. Large sporting events, royal weddings, TV specials and even solar eclipses can involve increases of several thousand MW (needing three or four large power stations) arising in only a matter of minutes.  Since this is more than the turbine governors can control, pumped storage and gas turbines may have to brought into action to stabilise the electricity grid at such times. Electricity – unlike water and gas, cannot be stored.  It has to be available the instant it is required.

The observant reader may have noticed that in the above analysis, there is no reference to the main renewable power supplies – wind turbines and solar panels.  This is not an oversight, but reflects the reality and physics of the wholesale supply of electricity.  There are times when renewable sources contribute significant quantities of power to the grid system.  The wind contribution can exceed 25 per cent and the solar exceed 15 per cent but, they are not controllable to meet the surges in demand and therefore have a lower intrinsic value than the other power stations.  On certain summer days, solar power increases very rapidly as the sun rises, peaking around mid-day so that other power plants can be shut down.  Our highest power demands however occur in the winter. During January, from 6.00 to 9.00 am when demand goes up by 10,000 MW, the solar contribution may be too small to be measured accurately.  It can be said to be superfluous because it is not available when needed most.

Wind turbines are similarly vulnerable to unhelpful variations in output.  Their increased output can vary in line with national demand but sometimes they worsen the situation.  On 24th October 2018, electricity from wind turbines was almost 9000 MW in the early hours – close to its peak value.  However there was a steady decline down to about 7000 at 9.00 am. The main thermal generators had therefore not only to increase output for the usual morning surge, but also an additional 2000 MW to compensate for the reducing wind turbine performance as the breeze abated. At midday on 21 November, wind power was almost 9000MW, but it declined steadily to 2400 MW over the next 24 hours so that coal-fired stations had to increase to almost 9000MW to make up the shortfall and were still generating over 7000 MW on 26th November when wind power was down to only 2 per cent of supply. 

There is also a second problem because short term variations in wind output as much as 700 MW, can occur in an hour and these have to be smoothed out by gas and coal fired stations – mostly by automatic governor control.  The fossil fuel plants however, will not be able to balance the erratic output from wind turbines vary far into the future. As the coal fired plants are closed over the next few years to meet EU commitments and wind turbine numbers increase, the remaining turbo-generators will not have the capacity to compensate for the variations in wind power.  Steam turbines cannot increase power rapidly like a car engine, but are constrained from exceeding a certain rate of power increase – perhaps 200 MW per hour. In simple terms – loss of power quality or blackouts will ensue.

To compound this progressive deterioration in reliable generation capacity, HM Government is proposing a series of measures that will increases stresses on the electricity grid eg:

  • To replace small private cars by electric vehicles EVs;
  • the electrification of further rail lines to reduce diesel use; and,
  • the elimination of gas heating in domestic properties.

 

Let us consider the first. If EVs are bought in large numbers, additional electricity will be needed for battery charging.  When cars are driven to the place of work, they will most probably be connected without delay to the charging network, aggravating the morning surge.  At the end of the day, on arrival at home, the same vehicles will be plugged in to the home charging point to coincide with the second daily demand peak.

It is the third point however that shows the most formidable challenge – exemplified by a day during the ‘Beast from the East’ cold period earlier in the year.  Between 5.00 am and 8.00 am on 28th February, there was an increase in gas demand of 116,000 MW.  For comparison, the peak electrical demand over the winter was 53,000 MW. Put at its simplest, power generation equipment and the electricity networks would have to be tripled to replace domestic gas central heating.  Only someone with the capacity to envisage the most sublime fantasies could ever believe that such a scheme would be manageable with renewable power or affordable.

In fact a high proportion of the measures that are proposed to reduce our CO2emissions involve additional electrical and electronic controls and hence the increased use of electricity.  It is criminal lunacy of the first order to incentivise the proportion of unreliable, weather-dependent, renewable power systems over the more secure nuclear and hydro generators that are low carbon, but take longer to recover the capital investment.  Pressure groups and our politicians appear to believe that all electricity generators are equal and that they can be mixed up like basket of vegetables.  Their ignorance of electricity generation and power control is leading to catastrophe.

Paul Spare CEng FEI FIMechE

 

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