Low-carbon day-ahead joint market clearing for integrated energy systems with high renewable energy penetration

Driven by carbon-neutrality targets and the rapid growth of renewable generation, improving wind and photovoltaic (PV) accommodation has become a central requirement for integrated energy systems (IESs). This paper proposes a low-carbon day-ahead joint electricity-heat market-clearing model that coordinates combined heat and power (CHP) units, gas boilers, wind power, PV generation, grid transactions, and shiftable demand. The model minimizes total operating cost and monetized direct-emission cost while satisfying fixed electricity and heat demand. Electricity and heat balances, unit operating and ramping limits, tie-line capacity, energy-neutral demand shifting, and fixed-load requirements are represented within a linear-programming framework. A 96-period numerical case is constructed from publicly available electricity-demand, renewable-generation, electricity-price, and heat-demand profiles. The results show that the renewable-curtailment rate in Scenario 1 is 12.70% under a 350 kW tie-line and a 1000 kWh/day shiftable-energy limit. Increasing shiftable energy to 2000 kWh/day reduces curtailment to 9.96%, whereas increasing tie-line capacity to 800 kW enables complete renewable accommodation. At the reference carbon price of 505 yuan/tCO2, emissions are monetized but the physical dispatch remains unchanged because the heat balance and tie-line constraint are binding. At 1500 yuan/tCO2, curtailment decreases to 0% and direct emissions decline from 13.873 to 13.333 tCO2. Increasing the CHP heat-to-power ratio from 1.0 to 1.6 further reduces curtailment from 33.10% to 1.23%. These results show that carbon pricing, demand flexibility, CHP coupling, and tie-line capacity jointly determine renewable accommodation and should therefore be coordinated in day-ahead market design.