The article describes a concept of Dynamic Thermal Storage (DTS) characterised by the ability to switch rapidly between heating/cooling and charging. The DTS is part of an integrated system serving a building, where the temperature drop required for transport of heat is used also for thermal storage. Charging is optimised based on weather forecasts (obtained via Internet), in effect turning natural variation in outdoor temperature into a renewable energy source. A DTS is built like a well, some 3 – 4 m deep, lined with polymer sheet and filled with fired, expanded clay spheres. These carry weight and allow parking or lawns/greenery atop, and stabilises the storage. The DTS operates as a two-phase system similar to chemical chromatographic analysis, with warm and cold zones separated by stagnant water some 0.6 – 0.8 m thick. The filling is ordinary, lightweight construction material (about €40/m³) filled with water, with a specific heat of 3000 kJ/m³. Maximum effect is 0.3 kW/°C m². Cross sections of 2 – 4 m² and volumes of 5 – 10 m³ fit single homes when optimised over 48 hour time spans. The concept appears economically promising particularly in areas with low installation costs and with large differences in day/night temperature, to give substantially reduced consumption of electric power for air conditioning. Heat pumps may be avoided where/when night-temperatures go below about 17 °C.