Energy Renovation Towards Net-Zero Energy Buildings using Photovoltaic Systems and Batteries in Residential Buildings

Abstract: As the future energy goals of the building industry involve reducing the energy intensity in buildings as well as increasing the share of renewable energy sources, a suitable approach would be energy renovating existing buildings and further utilizing renewable energy production technology to reach Net-Zero Energy Building (NZEB) standard. This study is therefore investigating the economic feasibility of energy renovating buildings built during the Swedish Million program towards NZEB. The primary goals include finding suitable energy renovation- and PV system design strategies as well as assessing the economic impact in the scenario of removing the tax reduction for sold electricity. In line with the Swedish NZEB standard, the buildings were initially renovated to passive house standard. From an economic perspective, numerous scenarios were then evaluated in terms of optimal battery and PV array size, optimal battery dispatch strategies, effects of removing the tax reduction for sold electricity, as well as variations in economical parameters such as interest rate and electricity price change. By utilizing well established energy- and PV simulation software, the evaluated buildings and PV systems were modelled to accurately resemble realistic conditions. With the results obtained from the simulations, the economic feasibility was assessed using life cycle cost calculations. It was found that ambitious energy renovations, such as passive house renovations required by the Swedish NZEB standard, were not profitable in most cases. The evaluated PV systems with battery storage did however show profitability even in the least desired economical scenarios, indicating a low risk investment. By going beyond the requirements for NZEB and maximizing the PV output on the suitable surfaces, an even higher profitability was achieved. It was therefore concluded that, from an economic perspective, maximizing the possible PV output on suitable roof surfaces is preferable as an initial step. According to the PV energy output, the ambitions of renovation should then be adjusted to reach NZEB. This may however mean that the renovation measures might not fulfill the Swedish NZEB standard, indicating it is not primarily promoting economic profitability. It was moreover found that a discontinuation of the tax reduction for sold electricity will significantly increase the value of utilizing battery storage in a PV system while, in the case of the tax reduction being continued, implementation of batteries might not always be the optimal strategy as it does not entail a significant increased profit.