The Cost Implications of Cycling Coal-fired Power Stations to Support Increased Renewable Energy Generation

The ambitious penetration of renewable energy into the future energy mix compels coal-fired power stations to operate under a cycling regime. Therefore, the financial implications of this operation must be seamlessly incorporated into future energy planning. This study used the calculated costs incurred by Majuba Power Station due to cycling operations in 2016. It projected the total cycling costs for the Eskom coal-fired fleet in 2035. The cost of cycling operations per scenario of the energy mix as per Wright and Calitz’s (2020) systems analysis report was calculated, comparing the relative costs of two-shifting and load-following. The study also estimated the two-shifting events for each coal-fired plant operational in 2035. This paper projects differential costs for cycling operations in 2035, influenced by primary energy resource consumption rates and costs. Considering the cost of load-following and the cost of two-shifting, the annual cost of cycling the coal-fired fleet is expected to range between R25.5 million and R695.1 million in 2035. Majuba Power Station is estimated to incur the most cost of two-shifting for the fleet in all four scenarios, projected to be approaching R500 million, while other stations are below R100 million.

I. Introduction

There has been an increase in the penetration of renewable energy sources, such as wind and solar power, into the South African power system in recent years [1], leading to a need for flexible operation and management of conventional coal-fired power plants. One approach to meeting the fluctuating electricity demand and accommodating intermittent renewable energy generation is to cycle coal-fired power plants [2]. Cycling takes the form of two-shifting and load-following and is adopted to curtail energy when electricity demand is low. Typically, baseload plants will load-follow or two-shift in order to accommodate the load deviation [3]. The difference between two-shifting and load-following is that while both are forms of cycling operation, load-following is the potential for a power plant to adjust its power output as electricity demand fluctuates throughout the day [4]. Two-shifting is the ability to shut down a generating unit off-peak and start up to support peak periods within a day.