Integrating the existing coal-fired, solar, wind power plants, and high-temperature thermal energy storage can simultaneously increase the portion of renewables and enhance the flexibility of electricity supply in a power grid. In this paper, a four-tank cascade heat storage scheme based on the combination of solar salt and Hitec salt is proposed under protective gas, a techno-economical analysis is performed. The results show that the unit energy cost of the proposed cascade heat storage with four tanks accounts 49% of that of traditional two-tank solar salt storage system. At a charging price of 3 cents/kWh, the levelized cost of electricity of the four-tank cascade heat storage scheme is about 2.2 cents/kWh less than the traditional two tanks of solar salt scheme. The levelized cost of electricity of the proposed cascaded system is significantly lower than systems integrated with other energy storage technologies with discharging duration is less than 9 hours, due to the reduction in initial investment utilizing existing infrastructures of coal-fired power plants. After investigating the distribution of wind, photovoltaic, and coal-fired power plants in China, Inner Mongolia, Gansu, and Shandong provinces are suitable to push the integrated systems. Taking Inner Mongolia as am example, Ordos and Ulanqab cities are particularly fit for the scheme implementation.