Energy efficiency has become a very topical issue that has been discussed throughout the European Union for preventing negative environmental impacts that have been associated with the consumption of energy. In the residential sector have mainly municipalities set strict requirements for the reduction of energy consumption while the renewable energy has been asked. Different concepts of low-energy buildings have been developed to reduce the cost of operation and maintenance in existing buildings such as in new ones.This thesis has aimed to minimize the energy cost of a large building which has had low energy consumption features originally. Energy reviews has been initiated in order to be able for showing how the house electricity could be carried out even more efficiently.The work was initiated through a literature study to clearly increase the reliability on the energy subject. Different concepts of low-energy buildings have been treated in connection with its specifications, afterward those have been compared with the obtained results.

This master?s degree project concerns the combination of a multi dwelling passive house with solar energy for the generation of electricity and domestic hot water (DHW). Different alternatives with either solar thermal systems or photovoltaic (PV) systems are compared with two reference alternatives producing DHW from electricity or district heating. The economical comparison uses a life cycle cost (LCC) perspective based on the present value of expenditures for investment, energy and annual operating and maintenance.The energy yields from the solar energy systems were calculated by hand and with simulation software. Calculation and dimensioning of PV systems were carried out with a software called PVSYST.