Towards the nearly zero and the plus energy building: primary energy balances and economic evaluations

In the construction sector, responsible for the greatest amounts of energy consumption and greenhouse gas emissions, nowadays a significant turning point in the current scenario that qualifies building approach is taking place. In recent years, the ambitious nZEB (nearly Zero Energy Building), a building with very high energy per- formance, in which energy saving, cost-optimal vision and user well-being are assessed in a comprehensive way, has found legislative and operational implementation. Moreover, the adoption of increasingly challenging en- ergy targets today offers important opportunities for the energy requalification and improvement of the overall quality of the building stock, particularly in the field of renewable plants. Within this frame in the paper, as a contribution to the analysis of benefits deriving from the use of RES (Renewable Energy Sources) plants in buildings, in terms of primary energy, cost, and greenhouse gas emissions, an intervention aimed at the satisfaction of the electric demand of a residential building through a photovoltaic plant, in different configurations (grid connected, stand-alone and storage on grid) has been analysed. For each configuration, balances between energy rates (production, load, grid exchange and/or battery store/withdrawal) have been hourly assessed in order to evaluate the Net Present Cost at the end of plant life. Moreover, a yearly primary energy balance has been determined, taking into account also thermal energy required to guarantee thermal needs (provided by a methane boiler), together with produced CO2 emissions.