Primary energy storage vessel suitable for heating water from solar circuits and other renewable energy heating sources like heat pumps and geothermal sources. It needs to be connected in a closed heating loop.     Through the storage of large quantities of heated primary water, SolarTank combined with an instantaneous tap water system, such as SolarFlow, meets the power peaks that occur at high tap water flow rates and reduces the use of fossil energy of the boiler.   SolarTank is the ideal solution where sudden high demands occur on a fairly regular basis such as in : • Apartment blocks • Hospitals • Schools • Hotels