With increasing energy production from renewable sources in China the power system must be operated more flexible in order to integrate the variable energy production from wind and solar. The capability to operate the existing coal-fired power plants in a flexible way is one of the most cost-efficient ways to ensure power system flexibility as this will exploit the potential of an already existing infrastructure to its maximum.
The Danish coal-fired power plants are among the most flexible power production units in the world as described in this article. But can the Danish experiences be used in China? The Danish Energy Agency has together with the Danish TSO, Energinet.dk and the power plant experts from the Danish company “Added Values” looked more into this question through a dialogue with Chinese power plant experts.
Modern Chinese power plants current flexibility
By comparing key technical design parameters relevant for operation flexibility (low minimum production load, high ramping rates, quick start-up time, bypass potential, full independence of simultaneous heat and power production at CHP plants etc.) between Danish and Chinese power plants the potential for operational flexibility enhancement of a typical Chinese coal-fired power plant has been estimated. In the table below four important power plant flexibility parameters are presented. The presented values presented are approximated and rough averages.
The capability to reduce minimum load and ramp production up or down fast is highly valuable in periods where power demand to a large extend – and sometime very fast for short periods – are being met by renewable energy production. This is especially true as the alternative to reducing load is a time consuming and costly start-stop of a power plant. As Danish power plants may have as many as 20-40 start-stops pr. year a fast start-up time also becomes valuable in order to provide flexible production. Finally, optimizing high efficiency through all load ranges becomes important in order to minimise fuel usage and keep OPEX (operational expenditure) at lowest possible level.
Modern Chinese and Danish power plants have similar technical design
The typical Danish coal-fired power plant is about half the size of the Chinese power plants but the technical design features are almost identical. A comparison between the technical design of the power plants shows that many design values with key relevance for the enhancement of the operational flexibility are identical. Therefore, the potential for enhancing the operational flexibility of the thermal power plants with respect to minimum load, load ramping, start-up time and efficiency will be the same in China as in Denmark. And since the average age of the Chinese power plants is much lower than the Danish power plants it is highly probable that the starting potential is even better.
Danish experience with decoupling of simultaneous heat and power production for combined Heat and Power (CHP) plants using large heat storages shows that this is an excellent starting point for increasing operational flexibility. Further, flexibility can often be improved without additional hardware investment by operating the existing equipment in a different manner.
During the process of enhancing the flexibility of Danish power plants a number of technical obstacles were removed through a multidisciplinary process where all power engineering disciplines were involved, among others materials, thermodynamics and control technology as the obstacle characteristics are interdisciplinary. The experiences from this “process” aproach would be valuable input to a similar Chinese flexibility improvement process.
Economic incentives needed
The main challenge for increasing Chinese power plant flexibility appears not to be technical. However, a big barrier for more flexibility is the lack of economic incentives for flexibility. Chinese power plants have a fixed feed-in tariff above the current marginal production costs together with a minimum number of full load hours and as such have no incentive at present to increase their operational flexibility and thus partake in the needed development of the energy system towards more renewable energy. It will be necessary either to introduce new regulatory interventions to create proper incentives or to introduce a power market with time dynamic power prices and production set by the market based on a least cost merit order.
The analyses are further documented in the report “Flexibility in the power system”. The report will be published in October as part of the “Boosting RE as part of China’s energy system revolution” program.