A hot water storage-type hot water supply device comprising: a hot water storage tank; a heat pump unit that heats water in the hot water storage tank; and a control unit that controls the heat pump unit, wherein the device is configured to: perform, in a first time zone, a first heating-up operation in which water in the hot water storage tank is heated at a first heating capacity, using electric power supplied from a commercial power supply, and perform, in a second time zone which is a time zone other than the first time zone, a second heating-up operation in which water in the hot water storage tank is heated using surplus electric power obtained by subtracting electric power consumed by other appliances from electric power supplied from a renewable energy power generation device, characterized in that: the control unit configured to determine whether the surplus electric power is less than electric power that exhibits the first heating capacity, and in the second heating-up operation, when it is determined that the surplus electric power is less than the electric power that exhibits the first heating capacity, the control unit controls the heat pump unit to heat water in the hot water storage tank using the surplus electric power at a second heating capacity less than the first heating capacity. a hot water storage tank; a heat pump unit that heats water in the hot water storage tank; and a control unit that controls the heat pump unit, wherein the device is configured to: perform, in a first time zone, a first heating-up operation in which water in the hot water storage tank is heated at a first heating capacity, using electric power supplied from a commercial power supply, and perform, in a second time zone which is a time zone other than the first time zone, a second heating-up operation in which water in the hot water storage tank is heated using surplus electric power obtained by subtracting electric power consumed by other appliances from electric power supplied from a renewable energy power generation device, characterized in that: the control unit configured to determine whether the surplus electric power is less than electric power that exhibits the first heating capacity, and in the second heating-up operation, when it is determined that the surplus electric power is less than the electric power that exhibits the first heating capacity, the control unit controls the heat pump unit to heat water in the hot water storage tank using the surplus electric power at a second heating capacity less than the first heating capacity. perform, in a first time zone, a first heating-up operation in which water in the hot water storage tank is heated at a first heating capacity, using electric power supplied from a commercial power supply, and perform, in a second time zone which is a time zone other than the first time zone, a second heating-up operation in which water in the hot water storage tank is heated using surplus electric power obtained by subtracting electric power consumed by other appliances from electric power supplied from a renewable energy power generation device, characterized in that: the control unit configured to determine whether the surplus electric power is less than electric power that exhibits the first heating capacity, and in the second heating-up operation, when it is determined that the surplus electric power is less than the electric power that exhibits the first heating capacity, the control unit controls the heat pump unit to heat water in the hot water storage tank using the surplus electric power at a second heating capacity less than the first heating capacity. the control unit configured to determine whether the surplus electric power is less than electric power that exhibits the first heating capacity, and in the second heating-up operation, when it is determined that the surplus electric power is less than the electric power that exhibits the first heating capacity, the control unit controls the heat pump unit to heat water in the hot water storage tank using the surplus electric power at a second heating capacity less than the first heating capacity.