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

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.The study showed that disregarding the NZEB requirements and primarily focusing on the PV systems, a higher profitability can be achieved. The first step is to optimize the PV system size, and then adjust the energy renovation ambitions to reach Net-Zero Energy Balance. If economic profitability is desired, the Swedish NZEB definition showed to be somewhat contradictory. The passive energy renovations towards passive house standard (required by the Swedish NZEB definition) were not profitable compared to installing a PV system. If aiming for maximum profitability, a suitable strategy for achieving a net-zero energy balance between energy load and production is to maximize the use of the highest yielding roof surfaces for PV. Thereafter, adjust the level of ambition of the passive energy renovation measures to reach an annual balance between energy need and production. The results are shown as Life-cycle profitability which is the difference in cash flow before and after the investment. Furthermore, using energy storing batteries in PV systems will result in even higher profitability, particularly in cases where the tax reduction for sold electricity is removed. More specifically, the added profitability of implementing batteries showed, on average, an additional 25 % while including the tax reduction and 108 % while excluding it. With varying economical parameters, the results showed that the current battery prices is, in most cases, low enough to ensure a profitable PV system. Depending on the economic scenario the battery prices may vary from 1 100 – 6 000 SEK/kWh with tax reduction and 2 000 – 10 000 SEK/kWh without tax reduction. To further assess these conclusions however, future studies might include the added value in terms of increased indoor climate and market value that is generally brought while renovating to passive house. Additionally, looking at a longer period, more suitable for an energy renovation might also affect the results as energy renovation measures generally have a longer life span than a PV system. The motivation for this study roots in the current green house gas emissions and energy use, brought by the building industry. This is mainly caused by heating of the buildings and is therefore an indication that energy related measures must be taken to reach the future energy goals. As 80 % of the buildings that will exist in 2050 have already been built, the greatest potential for these measures lies in the existing building stock, as opposed to new construction. Using energy simulation software, previously measured data, and guidelines from the industry, one single-family building and one multi-family building were modelled and assessed regarding their potential of energy renovation. Furthermore, the potential of implementing PV systems with energy storing batteries was evaluated and designed to reach the Swedish Net-Zero Energy Building definitio