MSc Energy Engineering with Environmental Management
ENG-7003B – Wind Energy Engineering
Ex1 Team-based Coursework
Supporting Summary:
“Examine the role that pumped storage power stations play in
supporting the UK grid. If a catastrophic failure occurred that put
Dinorwig power station out of action for 3 years from December 2017,
what impact is that likely to have on the way the grid could supply UK
peaks in demand?”
by
Project Team B
(Catalina Igoa, Andy Cossey, James Eastman, Manuel Manrique Castañeda)
University of East Anglia
Faculty of Science
School of Mathematics
Norwich Research Park
Norwich
NR4 7TJ
United Kingdom
20/02/2017
1. Introduction
1.1 Brief
The aim of the presentation and this report is to analyse the role pumped storage stations play in
supporting the United Kingdom’s (UK) National Grid, particularly the main pumped storage station:
Dinorwig Power Station. To help determine Dinorwigs’ importance, and what may happen if it were
out of action until 2020, current and future electricity generation was examined.
1.2 Current electricity generation
Figure 1. Shares of Electricity Generation (BEIS,2016a)
1.3 Future Targets
The UK has compromised itself by the Renewable Energy Directive 2009/28/EC on Promotion of the
use of energy from renewable sources (2009) to achieve 15% of energy production from renewable
resources by 2020. One of three targets set to help achieve this objective is the aim to produce 30%
of electricity from renewables by 2020 (DECC,2010). Most of this supply will come from wind farms.
Another objective of the Directive is to reduce carbon dioxide emissions. The UK's objective is to
reduce approximately 75% of the emissions from electricity generation by 2030 (DECC,2015). To
achieve this reduction cost-effectively, whilst ensuring the stability of electricity supply, the UK’s
strategy is based upon an increase of gas, nuclear and offshore wind power generation (House of
Common, 2016).
Figure 2. Change in the percentage of electricity generation (Vaughan, 2017)
2. Consequences from the use of Gas, Nuclear and Offshore
Wind Energy Supplies
As shown (Figure 2), the decrease in the use of coal from 2009 is somewhat compensated by
increased use of gas and wind energy sources, which is aligned with the strategy to reduce CO2
emissions.
The use of gas, nuclear and offshore wind as sources of energy each have their advantages and
disadvantages, but it can be concluded that extra storage capacity is needed to support this change;
the reasons for this will be explained throughout the document.
2.1 Gas
On average, each gigawatt-year of electricity generation switched from coal to natural gas reduces
CO2 emissions by 59 percent (Lafrancois, B., 2012). However, burning gas is still not a renewable
source of energy and it is not as clean as renewable energy; although it has the advantage of being a
relatively flexible source of energy. Gas Turbines can be powered during peak hours, although they
cannot respond quickly to sudden demand spikes (for example, over a thirty-minute period).
The total UK electricity demand in 2016 was approximately 330 TWh (GridWatch,2017). Per Figure 2,
40% (132 TWh) of production in this period came from gas. This output is close to the maximum
generation that the UK’s Combined Cycle Gas Turbines (CCGT) can currently deliver. Calculations
supporting this statement can be found in Annexe 1. Furthermore, as shown in Figure 3, the UK relies
upon imports for more than 50% of its total gas consumption.
Figure 3. UK gas (The Source, 2016)
Upon consideration, gas is certainly a cleaner energy source than coal and helps towards providing a
stable baseload of supply to meet with the constant electricity demand; however, it is unable to react
quickly to sudden demand spikes, indeed, current gas-powered stations are already working close to
capacity. Furthermore, the requirement for gas imports reduces energy self-reliability in the UK.
2.2 Nuclear
As seen (Figure 2), electricity generation from nuclear energy has been very consistent throughout
the eight-year period; 2009-2016. Similarly, as with gas-powered stations, nuclear power plants are
operated continuously at full load and therefore are unable to provide additional power during demand
spikes. Although additional capacity is planned, this will not be operational in the relevant period and
there is significant worldwide political pressure against the building of nuclear fission power stations,
primarily due to security concerns following the Fukushima accident along with potential terrorist
activity.
2.3 Wind power
Wind power has seen an exponential increase since 2009, as wind energy has been seen as the key
factor to achieving the 30% target of electricity from renewables by 2020. Installed wind power
capacity in January 2017 was 14.5 GW; 9.395 GW from onshore capacity and 5.098 GW from
offshore capacity (RenewableUK, 2017). However, wind power is an inconsistent and somewhat
unpredictable source of power, its efficiency depends upon the hour, day, and season of the year
along with daily weather patterns.
Figure 4 shows the average wind power capacity factor by season in the UK:
Figure 4. Average Daily Variability in UK Wind Power Capacity Factor (Sinden, 2007)
However, the data in Figure 4. is averaged, and there is no security than in any certain day these
values will be achieved. Figures 5 & 6 aim to show the intermittency of wind by comparing the
contribution of wind energy recorded over two days, with a two-week interval between each day.
Additionally, the data in Figure 5 was recorded upon the day with the greatest demand during the
2015/2016 period; it is apparent that the contribution from wind energy this day was very low
(relatively), measured in megawatts.
300
Wind (MW)
250
200
150
100
50
0
0:00:00 4:48:00 9:36:00 14:24:00 19:12:00 0:00:00
Time
Figure 5. Wind Contribution for triad day 19.01.2016 (GridWatch,2017)
7000
Wind (MW)
6000
5000
4000
3000
2000
1000
0
0:00:00 4:48:00 9:36:00 14:24:00 19:12:00 0:00:00
Time
Figure 6. Wind Contribution for 01.02.2016 (GridWatch,2017)
Research estimates that, as wind power capacity increases, by 2020, 27% of our wind electricity will
be wasted unless it can be stored and released when needed to help balance peak supply and peak
demand. Additional storage capacity is therefore the key factor for ensuring that increased power
generation is not wasted.
3. Pumped Storage Power Stations
Pumped storage stations operate using two water reservoirs, one lower than the other, to create an
energy potential. During periods of low demand and cheaper energy, water is pumped to the upper
reservoir; this water then is released through a turbine to generate electricity during times of peak
demand.
Pumped storage is a net user of power, but, when used in conjunction with other renewable energy
methods to pump water back to the upper reservoir, it can help to resolve problems with intermittency
issues associated with renewable technologies (BHA,2017).
3.1 Pumped Storage Stations in the UK
The UK has four pumped storage facilities: Festiniog, Cruachan, Foyers and Dinorwig.
The maximum amount of energy stored by the four facilities is 30GWh. Dinorwig is the main supplier
to the National Grid, with a capacity of 1.8 GW. It can be switched on and providing 1.3 GW of power
within 12 seconds (MacKay,2009). With all four facilities operating simultaneously, they can produce
2.8 GW of power. Compared with other sources of electricity, this amount may not seem particularly
significant, however the main advantage is it can be switched on and providing very quickly, helping
the Grid to cope with sudden demand or lulls in wind activity.
4. Triad Days
4.1 Definition
The Triad Days are three half hour periods of peak power demand across the National Grid in the
period from November to February, when energy demand is at its most intensive. They need to be 10
days apart to avoid adversely affecting industry and business within consecutive half-hours.
Triads are used to calibrate the transmission costs, which are then passed to heavy consumers of
energy. Although there is no way of knowing in advance when a Triad may occur, companies can sign
for a Triad warning service, and if they have an efficient energy strategy, they may escape from Triad
payments (SSE Business Energy, 2016).
Table 1 shows the Triad days of the last three years. It can be seen how the maximum demand is
always around 17:30 and between Monday to Friday. This is due to high domestic demand coinciding
with industry/business demand.
Table 1 Triad days from 2013 to 2016 (National Grid, 2017a)
DATE
2015 - 2016
Wednesday 25 - 12 - 2015
Tuesday 19 - 01 - 2016
Monday 15 - 03 - 2016
HALF HOUR ENDING
DEMAND (MW)
17:30
17:30
18:30
47,601
50,596
47,982
2014 - 2015
Thursday 04 - 12 - 2014
Monday 19 - 01 - 2015
Monday 02 - 02 - 2015
17:30
17:30
18:00
49,655
51,276
50,859
2013-2014
Monday 25 - 11 - 2013
Friday 06 - 12 - 2013
Thursday 30 - 01 - 2014
17:30
17:30
17:30
50,694
49,927
49,947
4.2 Triad day: 19.01.2016, maximum demand for the 2015/2016 Period
The importance of pumped storage on the 19th January 2016 triad can be seen in Figure 7 below. In
the hour where demand peaked, the pumped storage contribution reached its maximum, because of
its ability to reach full capacity within seconds.
As previously stated, the total capacity of pumped storage is 2800 MW, while average efficiency is
0.75 (MacKay,2009). Therefore, with all of them operating together, output would be 2100 MW. At
17:30, the contribution was 1815 MW, close to the total maximum output.
2000
Pumped (MW)
1816
1500
1000
500
0
0:00:00 4:48:00 9:36:00 14:24:00 19:12:00 0:00:00
Time
Figure 7. Pumped Storage output 19th January, 2017 (GridWatch, 2017)
Another important contribution towards satisfying peak demand is the imported electricity from the
UK's interconnections with France, Northern Ireland, Netherlands and with the East-West (South
Ireland).
Table 2. Interconnectors in the GB electricity system (Moore, 2010)
Project Name
Company
Location
Capacity
(GW)
Start year
Interconnexion
France Angleterre (IFA)
Moyle
National Grid and RTE
(French transmission
system operator)
Mutual Energy
Between Folkestone,
Kent and Calais, France
2
1986
Between Auchencrosh,
Ayrshire, Scotland and
Ballycronan More, Co.
Antrim, Northern Ireland
Between Isle of Grain,
Kent and Rotterdam,
Netherlands
0.5
2001
BritNed
National Grid and
TenneT (Dutch TSO)
1
Between Shotton, Wales
and Rush North, Co.
Dublin
0.5
Operational since
2009, at full
capacity since
2010
2012
East-West
EirGrid
However, as can be seen in Figure 8, during peak demand they are already working almost to their
full capacity. There could still be 500 MW left from the Dutch interconnector, but this would not be
enough to replace the contribution of Dinorwig (1800 MW) if it were non-operational.
4000
2000
ew_ict
irish_ict
1000
dutch_ict
french_ict
0
-1000
0:00:00
1:10:00
2:20:00
3:30:00
4:40:00
5:50:00
7:00:00
8:10:00
9:20:00
10:30:00
11:40:00
12:50:00
14:00:00
15:10:00
16:20:00
17:30:00
18:40:00
19:50:00
21:00:00
22:10:00
23:20:00
Imported (MW)
3000
-2000
Figure 8. Imported electricity 19.01.2016 (GridWatch, 2017)
Furthermore, analysis (Ofgem, 2014) shows that the risk of supply to each of the countries
interconnected with the UK is expected to increase in future. Therefore, unless we become more selfreliant, there is a potential to lose import availability.
5. Mitigating Actions to Manage Supply Shortfalls
If electricity demand exceeds market supply the first mitigating action to be used by the National Grid
would be the SBR and DSBR services (Ofgem, 2015):


Supplemental Balancing Reserve (SBR): the service is aimed at generators who are either
closed, mothballed or generally unavailable to the market. They would only be required after
all actions within the normal operations have been taken (National Grid, 2017b). Through
SBR, coal power stations are paid to be available if needed.
Demand Side Balancing Reserve (DSBR): the service is targeted at commercial and
industrial consumers who volunteer to decrease their demand of energy between 4 and 8 pm
on winter weekday evening in return for a payment (National Grid, 2017c). For example: a
fridge-freezer draws around 18 W power; the estimated number of refrigerators is
approximately 30 million. The ability to switch off all the nation’s fridges for a few minutes
would be equivalent to 0.54 GW of automatic adjustable power (MacKay, 2009).
If these measures are not enough, other actions that can be implemented prior to a controlled
disconnection are: voltage reduction; maximum generation; and emergency services from
interconnectors.
Furthermore, National Grid concluded the T-4 Capacity Auction for 2020/21 delivery on December
2016, to secure electricity supplies for the 2020/2021 winter period (National Grid, 2017d). The
auction secured over 52GW capacity; remarkable excerpts:
●
New gas generation, including two new power stations, will be built
●
500 MW of new battery storage – agreements won for the first time in market auctions.
6. Storage Technologies
Dinorwig installed capacity is 1800 MW and works at an average efficiency of 75%. Therefore, the
output is approximately 1350 MW. Annexe 2 shows an estimated cost of replacing Dinorwig’s 1350
MW output with different storage technologies. Other factors that should be considered when
choosing an alternative, for instance, the technological maturity and economy of the solution. As
previously stated, in the National Grid 2016 auction, low-carbon battery storage has been agreed
upon.
7. Conclusions
Pumped storage generation, particularly at Dinorwig, is already key to satisfy peak demand and is
working close to maximum operating output.
If Dinorwig power station was inoperative for three years from 2017, although the National Grid would
have several courses of mitigating action before any disconnection is suffered by the customers, the
loss would have a large impact, more so in triad days. As Dinorwig contribution is 1800 MW at 75%
efficiency, reachable within 12 seconds.
Given that the UK electricity generation strategy to reduce CO2 emissions and to achieve the target of
30% of electricity from renewables is based upon the increase of gas, nuclear and wind energy,
pumped storage becomes even more important. A problem in Dinorwig in 2020 would be even worse
that if it happened today.
8. Recommendation
Increasing energy storage would be an answer to:





intermittency issues associated with renewable technologies
fixed output of nuclear plants
making the UK more energy self-reliant by not depending so heavily on imported electricity
and gas
reducing CO2 emissions by further reducing use of gas, or coal, powered stations
any problem that may potentially put Dinorwig power station out of action.
The most mature storage technology is pumped storage, but other technologies will become more
important in future as technology matures and associated costs reduce.
Annexes
Annexe 1
Electricity from gas is primarily delivered from CCGT power plants as shown in Table 3. The total
capacity of CCGT at the end of 2015 was 31,741 MW, compared with 1,333 MW for the sum of gas
turbines and oil engine power plants.
For the following calculation, the total capacity of 2016 for CCGT will be considered using 2015 data,
as 2016 data is currently unavailable. The values used can be found in Table 3 and Table 4.
CCGT Output =
330×40%
(24×365)×106
=15,069 MW
CCGT Capacity (2016): 31,741 MW
CCGT Thermal Efficiency: 48%
Maximum Output 2016: 31,741 * 48% = 15,236MW
CCGT in 2016 worked almost to its full capacity. On average, there was 168 MW capacity remaining.
Table 1 Plant Capacity United Kingdom (BEIS,2016b)
MW
2011
2012
2013
2014
end December
2015
89,031
89,299
84,598r
83,543r
80,820
Conventional steam stations (8)
34,164
30,988
25,230r
23,392r
20,794
Combined cycle gas turbine stations
32,395
35,357
34,872r
33,807r
31,741
Nuclear stations
10,663
9,946
9,906
9,937
9,487
1,706
1,651
1,639r
1,643r
1,333
Natural flow (4)
1,550
1,556
1,561
1,569r
1,580
Pumped storage
2,744
2,744
2,744
2,744
2,744
Wind (4)
2,781
3,827
4,821r
5,606r
6,145
Solar (4)
-
-
488
922
1,561
3,027
3,231
3,337r
3,923r
5,435
Major power producers (1)
Total capacity
Of which:
Gas turbines and oil engines
Hydro-electric stations:
Renewables other than hydro and wind (4)
Table 4 Thermal Efficiency (BEIS,2016b)
2011
2012
2013
2014
end
December
2015
Combined cycle gas turbine station:
Per cent
48.1
47.2
47.7
48.0
Coal fired stations
Per cent
35.7
35.8
35.9
35.6
Nuclear stations
Per cent
38.0
39.8
39.6
39.1
Thermal efficiency
(gross valorific value basis)
Annexe 2
Table 5. Storage technologies (REA, 2016)
Technology
Maturity
Cost (2010
US
dollars/kW)
Efficiency
Response
Time
Average
cost
Average
efficiency
Necessary
installed
capacity
(MW)
Total Cost
(2010 US
dollars)
Pumped Hydro
Mature
1,5002,700
80–82%
Seconds to
Minutes
2100
81%
1666.7
3,500,000,000
Compressed Air
(Underground)
Demo to
Mature
960-1,250
60-70%
Seconds to
Minutes
1105
65%
2076.9
2,295,000,000
Compressed Air
(Above-ground)
Demo to
Deploy
1,9502,150
60-70%
Seconds to
Minutes
2050
65%
2076.9
4,257,692,308
Flywheels
Deployed
to Mature
1,9502,200
85-87%
Instantaneous
2075
86%
1569.8
3,257,267,442
Lead Acid
Batteries
Demo to
Mature
950-5,800
75-90%
Milliseconds
3375
83%
1636.4
5,522,727,273
Lithium-ion
Batteries
Demo to
Mature
1,0854,100
87-94%
Milliseconds
2592.5
91%
1491.7
3,867,265,193
Flow Batteries
(Vanadium Redox)
Develop
to Demo
3,0003,700
65-75%
Milliseconds
3350
70%
1928.6
6,460,714,286
Flow Batteries
(Zinc Bromide)
Demo to
Deploy
1,4502,420
60-65%
Milliseconds
1935
63%
2160.0
4,179,600,000
Sodium Sulphur
(NAS)
Demo to
Deploy
3,1004,000
75%
Milliseconds
3550
75%
1800.0
6,390,000,000
Power to Gas
Demo
1,3702,740
30-45%
10 Minutes
2055
38%
3600.0
7,398,000,000
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