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This article describes a method for increasing the solar heat energy share in the heating of a dwelling. Solar irradiation is high in summer, in early autumn, and in spring, but during that same time, the heat demand of dwellings is low. This article describes a solution for storing solar heat energy in summertime as well as the calculations of the heat energy balance of such a storage system. The solar heat energy is stored in a thermally insulated water tank and used in the heating period. The heat is also stored in the ground if necessary, using the ground loop of the heat pump if the water tank’s temperature rises above a certain threshold. The stored heat energy is used directly for heating if the heat carrier temperature inside the tank is sufficient. If the temperature is too low for direct heating, then the heat pump can be used to extract the stored energy. The calculations are based on the solar irradiation measurements and heating demand data of a sample dwelling. The seasonal storing of solar heat energy can increase the solar heat energy usage and decrease the heat pump working time. The long-term storage tank capacity of 15 m3 can increase the direct heating from solar by 41%. The direct heating system efficiency is 51%.

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The main task of the energy system is to supply the consumers with high-quality electric and heat energy. As possibilities for accumulation of the energy and especially electrical energy in Estonia are very limited, one of the main energy parameters is its uninterrupted supply. The needs of consumers are characterized by the demand curve-the variation of load for a given time period (day, month, year). It is necessary to stress the difference between load and demand curves for the producer and consumer. Up to the recent time the producer load curve consisted of the individual consumers' demand curves sum plus losses in the distribution elements (in electric networks). Nowadays when by economical and ecological reasons the renewable energy sources are more intensively used, the part of the energy producers using wind and solar energy is constantly rising, and they are increasingly influencing the work of the whole energy system. That complicates significantly the work of the high-powered electric energy generators (with large inertia) at power stations as, in addition to the load variations depending on demand, they have to compensate extremely stochastic production of wind turbines. In this paper the problem is discussed on the basis of load and demand curves of the Energy system of Estonia and Pakri wind farm. It is shown that these curves are not suitable for mutual compensation and that may disturb the stability of the energy system at the wind park maximum power. The result is that the Energy system dispatcher is forced to limit the production of the wind park.