Since　the　renewable　energy　generation　output　is　unstable,　some　measures　are　needed　to　maintain　the　stability　of　the　power　grid　with　the　increasing　proportion　of　them.　Integrating　thermal　energy　storage　(TES)　system　into　coal-fired　power　unit　(CFPU)　to　increase　its　flexibility　is　a　simple　and　promising　solution.　This　work　proposed　a　novel　two-stage　three-tank　molten　salt　TES　system.　A　600　MW　subcritical　CFPU　was　utilized　to　analyze　the　effect　of　main　steam　extraction　on　the　thermal　performance　and　peak　shaving　capacity　under　different　cases.　40　%　turbine　heat　acceptance　(THA)　was　selected　as　peaking　shaving　condition　of　charging　process.　Results　show　that　with　the　increase　of　THA　in　the　discharging　process,　thermal　efficiency,　exergy　efficiency,　and　output　electric　load　of　the　flexible　CFPU　increased,　while　comprehensive　coal　consumption　rate　and　peak　shaving　time　decreased.　Additionally,　due　to　the　increment　of　output　electric　load　being　greater　than　the　decrease　in　peak　shaving　time,　the　highest　generation　increment　is　obtained　when　discharging　at　100　%THA　(137.43　MWh).　Lastly,　the　efficiency　of　TES　is　38.1–48.04　%,　which　increases　with　the　electrical　load　output　of　the　discharging　increases.　Overall,　this　work　provides　an　effective　and　feasible　integration　method　between　TES　and　CFPU.　©　2025