OPTIMAL WIND/SOLAR ENERGY MIX FOR RESIDENTIAL NET ZERO-ENERGY BUILDINGS

The article is concentrated on the energy storage problems arising from microgeneration in private households. The case study involves a small-scale wind and solar electricity production set in a net zero-energy building. Both the net zero-energy building and the microgeneration units are connected to an utility grid. The current article serves to confirm the hypothesis, that the self consumption is at its maximum with the annual 70/30 wind and solar energy mix of in favour of the wind. The maximal self consumption at no additional energy storage in a net zero-energy building is studied as well. Produced and consumed energies are equal, which satisfies the requirements for a net zero-energy building with the utility grid acting as an energy buffer. The consumed energy is used to operate a heat pump, heat up ventilation supply air, run ventilation fans, supplying non-shiftable loads (white goods, TV, lighting etc), heat up domestic hot water via heat pump. To express self consumption, we use the term of supply cover factor, which describes optimally the directly consumed energy in relationship to net consumption or production. In annual scale, the cover factors for a net zero-energy building are equal as the production and consumption are equal as well. Also, seasonal variations in self consumption are studied. According to study results, the annual maximal supply cover factor in a net zero-energy building is 0.375 with 70/30 wind/solar mix. Seasonally, the self consumption is at its maximum in summer when the supply cover factor equals to 0.49.