Existing thermal power plants must be adapted to cooperate with wind farms and other renewable energy sources by improving their flexibility. The paper analyzes the improvement of the 200MWe block's flexibility by installing hot water storage tanks. The maximum increase in the block output resulting from the shut-off of low-pressure steam bleeds is calculated. During this period, the hot water from water storage tanks is supplied to the boiler. Hot water is accumulated in pressure water tanks during the low-load period of the unit. Water with design temperature in the feed water tank flows into the water pressure tanks to reduce the electric power of the unit in the off-peak night hours. The hot water accumulated during the night in storage tanks is used to feed the boiler during the period of peak demand for electricity. The reduction in the block electric power was calculated for various volumes and charging periods of the water storage tanks. A cost analysis was carried out to demonstrate the economic profitability of installation of pressure water accumulators. It is worth mentioning that hot water tanks may also be applied to fill the boiler evaporator with hot water before the start-up of the power unit from the cold state. (C) 2019 Elsevier Ltd. All rights reserved.