With the goal of carbon neutrality, low carbon transition is necessary in China. it is a common sense that there will be more RES(renewable energy sources) and thermal power will quit the main stage of power supply. RES will bring volatility to power system and threaten its reliability. Thermal power with flexibility modification and BESS(battery energy storage system) are two ways to ensure the safety of power system. This study provides a model on level of hour to calculate and analyze cost of power system in different penetration rates of RES. A province in China is taken as an example to compare flexible thermal power with BESS in five scenarios. It is found that thermal power with flexibility modification has an obvious advantage over BESS in short term while BESS is more potential in long term. An opinion for future of power system is given: thermal power still has a lot of things to do and it will quit by stepwise decreasing available hours instead of abandon of existing units in short term, BESS will play a more important role in long term.
Keywords thermal power, flexibility modification, BESS,penetration rates of RES, available hours