DID GEOMAGNETIC ACTIVITY CHALLENGE ELECTRIC POWER RELIABILITY
DURING SOLAR CYCLE 23? EVIDENCE FROM THE BALANCING MARKET IN
ENGLAND AND WALES
Kevin F. Forbes, School of Business and Economics, The Catholic University of America
Washington, DC, 20064, USA, Forbes@cua.edu
O. C. St. Cyr,NASA-Goddard Space Flight Center,Greenbelt, Maryland, 20771, USA and
Department of Physics, Catholic University of America, Washington, DC, 20064 USA, Chris.StCyr@nasa.gov
Overview
Solar activity has an approximately 11 year cycle. It is well established that activity at the peak of the cycle can give rise to
geomagnetic storms that are harmful to communications, GPS, and electric power systems located in mid to high latitudes
[National Research Council, 2008; Royal Academy of Engineering, 2013]. Consistent with this assessment, during the 22th solar
cycle since 1755, a very intense geomagnetic storm on 13 March 1989 contributed to the collapse of the Hydro-Quebec power
system in Canada [Bolduc, et al, 1998].
This paper addresses whether geomagnetic activity challenged power system reliability during Solar Cycle 23. Operations by
National Grid (http://www.nationalgrid.com/uk ) in the United Kingdom are examined over the period 11 March 2003 through 31
December 2004. During this time period National Grid coordinated generation and transmission in England and Wales. This paper
examines the relationship between a proxy for geomagnetically induced currents (GICs) and a metric of challenged reliability. The
research follows from Forbes and St Cyr [2008] who found evidence of a relationship between GICs and real-time operational
metrics in 12 geographically disparate power systems.
The context of this research is that unexpected interruptions in electricity supply, i.e. blackouts, have very high societal costs.
Joskow [2012, p 38] has reported that typical estimates of the value of lost load, i.e. the amount that consumers would pay to avoid
an outage, are in the range of USD $5,000 to $10,000 per MWh of electricity that is lost even though the average wholesale price
of electricity is less than 50 USD. Keeping the lights on requires adhering to very stringent stability conditions in terms of system
frequency, i.e. the level of voltage and current oscillations each second. System frequency falls when demand exceeds supply
and rises when demand is less than supply. In either case, reliability is compromised. National Grid attempts to offset these
electricity imbalances by dispatching balancing power. A key measure of the electricity imbalance in the United Kingdom is
known as the net imbalance volume (NIV). It equals the total net amount of energy that National Grid purchased in order to
balance the system.
A positive NIV value indicates that the overall market position was short in terms of electricity while a negative value indicates
that there was excess quantity of electricity. The distribution of NIV is approximately Gaussian (normal). NIV is highly variable
as evidenced by the absolute value of the coefficient of variation in NIV exceeding 100 percent. Large NIV outcomes in absolute
value represent instances in which the reliability of the system is challenged. There were numerous instances of large NIV
outcomes (in absolute value) during the period 1 October – 30 November 2003. Modeled GIC levels were very high in many of the
transformers during the peak of the large geomagnetic storms that occurred over this period [Royal Academy of Engineering,
2013, p. 23 ]
Methods
It is hypothesized that NIV can be modelled as a function of ambient temperature, the GIC proxy, and explanatory variables that
reflect expected operating conditions. These latter variables include the forecasted load, the coefficient of variation in the
forecasted load for the day, the skewness in the forecasted load for the day, the forecasted imbalance, the day-ahead spot price of
electricity relative to the price of coal, the day-ahead spot price relative to the price of natural gas, the coefficient of variation in
day-ahead spot price, the skewness in the day-ahead spot price, the level of commercially scheduled electricity imports from
Scotland, the level of commercially scheduled exports to Scotland, the level of commercially scheduled imports from France, the
level of commercially scheduled exports to France, the level of balancing offers by market participants, and the level of balancing
bids by market participants. The study also makes use of binary variables for the hour of the day and the day of the week. It is
further hypothesized that the effects of both GICs and temperature may be directly related with other variables such as the
forecasted electricity imbalance.
A two-step time-series estimation approach is employed. In the first step, the functional form is identified. In the second step, an
Autoregressive-Moving Average (ARMA) process is modelled. The purpose of this second step is to obtain parameter estimates
and standard errors that are untainted by serial correlation in the residual error terms.
Results
The findings are consistent with the hypothesis that GICs contribute to electricity market imbalances. The results indicate that the
effect of GICs on the imbalances is highly dependent on system conditions at the time of the geomagnetic storm. Specifically, the
findings indicate that the effect of GICs is contingent on the forecasted imbalance. The estimated GIC induced effect on NIV
ranges from 8 to 462 MWh per market period. The median estimated effect is approximately 122 MWh.
Using the estimated parameters, an out-of-sample forecast of NIV was generated for the period 1 January 2005 – 31 March 2005, a
period of nontrivial NIV variability (Figure 1). There is a high degree of correspondence between the predicted and actual NIVs
(Figure 2). Specifically, the correlation between the predicted and actual NIV is approximately 0.92.
Figure 1. The Net Imbalance Volumes in England and Wales, 1 January 2005 – 31 March 2005
1500
Net Imbalance Volume (MWh)
1000
500
0
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-1000
-1500
-2000
-1500
-1000
-500
0
500
1000
Figure 2. Predicted and Actual Net Imbalance Volumes in England and Wales, 1 January – 31 March
2005
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0
500
1000
Predicted NIV (MWh)
Conclusion
While there is no evidence of a space weather induced blackout in England and Wales during solar cycle 23, the analysis of this
paper indicates that National Grid’s operations were nevertheless challenged by geomagnetic activity. The findings are consistent
with previous literature. The findings also indicate that the operational uncertainty faced by the system operator can be reduced by
improved forecasting.