Energy storage facility comprising: a photovoltaic system, energy production means other than the photovoltaic system, and a water heating device intended for supplying a room with hot water, the water heating device comprising: a water heater including: - a heating member for heating water contained in the water heater, - a thermometer for measuring a temperature of the water Teau contained in the water heater; and a regulating board connected to the heating member and to the thermometer, the regulating board being suitable for regulating the heating member according to energy received by the photovoltaic system and energy received by the means other than the photovoltaic system, the regulating board being suitable for determining a heating power to be controlled from the heating member according to a temperature setpoint, the temperature setpoint having a base value Tbas, and a surplus value Tsur greater than or equal to the base value Tbas; the facility being characterized in that it comprises an energy manager connected to the regulating board and to the photovoltaic system, the energy manager being suitable for communicating to the regulating board that a surplus of energy produced by the photovoltaic system is available, and in addition when the temperature of the water contained in the water heater is lower than the surplus value Tsur of the temperature setpoint, the regulating board being suitable for determining from the available surplus a heating power to be controlled from the heating member in order to store at least a portion of the surplus in the form of hot water available in the water heater, and the regulating board controlling the heating member to heat the water of the water heater using the surplus photovoltaic energy as long as the water temperature is lower than the surplus value Tsur. a photovoltaic system, energy production means other than the photovoltaic system, and a water heating device intended for supplying a room with hot water, the water heating device comprising: a water heater including: - a heating member for heating water contained in the water heater, - a thermometer for measuring a temperature of the water Teau contained in the water heater; and a regulating board connected to the heating member and to the thermometer, the regulating board being suitable for regulating the heating member according to energy received by the photovoltaic system and energy received by the means other than the photovoltaic system, the regulating board being suitable for determining a heating power to be controlled from the heating member according to a temperature setpoint, the temperature setpoint having a base value Tbas, and a surplus value Tsur greater than or equal to the base value Tbas; the facility being characterized in that it comprises an energy manager connected to the regulating board and to the photovoltaic system, the energy manager being suitable for communicating to the regulating board that a surplus of energy produced by the photovoltaic system is available, and in addition when the temperature of the water contained in the water heater is lower than the surplus value Tsur of the temperature setpoint, the regulating board being suitable for determining from the available surplus a heating power to be controlled from the heating member in order to store at least a portion of the surplus in the form of hot water available in the water heater, and the regulating board controlling the heating member to heat the water of the water heater using the surplus photovoltaic energy as long as the water temperature is lower than the surplus value Tsur. a water heater including: - a heating member for heating water contained in the water heater, - a thermometer for measuring a temperature of the water Teau contained in the water heater; and - a heating member for heating water contained in the water heater, - a thermometer for measuring a temperature of the water Teau contained in the water heater; and a regulating board connected to the heating member and to the thermometer, the regulating board being suitable for regulating the heating member according to energy received by the photovoltaic system and energy received by the means other than the photovoltaic system, the regulating board being suitable for determining a heating power to be controlled from the heating member according to a temperature setpoint, the temperature setpoint having a base value Tbas, and a surplus value Tsur greater than or equal to the base value Tbas; the facility being characterized in that it comprises an energy manager connected to the regulating board and to the photovoltaic system, the energy manager being suitable for communicating to the regulating board that a surplus of energy produced by the photovoltaic system is available, and in addition when the temperature of the water contained in the water heater is lower than the surplus value Tsur of the temperature setpoint, the regulating board being suitable for determining from the available surplus a heating power to be controlled from the heating member in order to store at least a portion of the surplus in the form of hot water available in the water heater, and the regulating board controlling the heating member to heat the water of the water heater using the surplus photovoltaic energy as long as the water temperature is lower than the surplus value Tsur.