COULD LOAD SHEDDING REOCCUR?

Transcription

1 COULD LOAD SHEDDING REOCCUR? ROBBIE VAN HEERDEN GM SYSTEM OPERATOR MAY 2012 AFRICAN UTILITY WEEK

2 MANAGING THE RISK OF LOAD SHEDDING At all times there must be a balance between supply and demand The expected demand is forecast based on a number of assumptions and for specific time periods the accuracy of the forecast is critical for optimising the power system. To ensure adequate supply there must be sufficient plant on line and sufficient fuel (e.g. coal) to run this plant. There will always be plant out of service this may be for planned outages (maintenance) or unplanned outages (failures). It is necessary to ensure that sufficient reserves are made available to cater for the unexpected events on the power system on a daily basis. Planned maintenance must be provided for, both network and generation equipment, to ensure the sustainability of the plant. If insufficient planned maintenance occurs it will result in a backlog which will affect the reliability of the power system.

3 TYPICAL SEASONAL LOAD PROFILES Winter peak is substantially higher but for a shorter period of time Summer load profile is much flatter, peak of GW, so if there is a constraint, the system is constrained for the entire day Most planned maintenance is done in summer, when demand is lower, so that the maximum capacity is available for winter peak. A colder-than-expected winter puts added pressure on the system: for every 1 degree Centigrade decrease in winter temperature, electricity demand increases by MW during the evening peak; a warmer than expected summer increases air-conditioning load and demand can increase by up to 400 MW.

4 SUMMARY OF THE STATE OF THE SYSTEM South Africa s power system will be tight for the next few years: the next two years are critical We have kept the lights on since 2008 but balancing supply and demand has been a challenge Most power stations are in their mid-life and require increased maintenance; however, maintenance has constantly been shifted in order to ensure we can meet demand Strategy of shifting maintenance outages can no longer be sustained. Summer is typically maintenance season in Eskom while limited maintenance is done in winter. The system is presently run at higher levels of risk,to tackle backlog and keep up with maintenance while at the same time meeting demand Energy demand year to date has been lower than originally forecast, but early summer peaks were higher than expected This year has seen a significantly increase in the usage of open cycle gas turbines and other reserves to balance supply and demand.

5 SUMMARY OF THE STATE OF THE SYSTEM

6 SYSTEM OVERVIEW

7 RECOVERING FROM 2008

8 FORECAST OF ANNUAL ENERGY SUPPLY GAP 9 TWh is equivalent to ~ 1 000MW of base load capacity 1 TWh is approximately equivalent to the annual energy consumption of households Source: Medium Term Risk Mitigation Plan (2009) Analysis was done to determine the expected shortfall to meet demand for a 7 year period. The load experienced in 2011 was lower than that earlier forecast. This forecast assumed that all planned supply and demand levers were put in place

9 GENERATION PERFORMANCE 3600 MW target * * The 3600 MW load loss allowance includes 600MW for the Duvha unit 4 which is unavailable Eskom uses a 3 600MW allowance for unplanned outages and production losses in its generation fleet, to cushion the system. Unplanned outages have however sometimes run at higher levels for some periods of time. Coal-related load losses have decreased over the past few months but still remain a concern at 3 power stations

10 SYSTEM OVERVIEW

11 PREVENTATIVE MAINTENANCE A typical coal fired generating unit requires certain necessary routine maintenance to ensure that it accedes in its technical performance requirements, is safe to operate and does not violate any environmental laws. Activity Cycle time (years) Duration (days) General Overhaul (GO) Interim Repairs (IR) Mini General Overhaul (MGO) 6 28 Boiler Inspection (BI) Statutory inspection and test (ST) 6 35 Main steam pipe work months 18 months 18 months 18 months 18 months 6 months

12 2012 MAINTENANCE CHALLENGE The planned outage requirements exceed the capacity available for maintenance and so liquid-fuel open cycle gas turbine usage and demand-side management become critical. Planned outages are ranked on scope and risk, to enable prioritisation of outages within the available capacity.