Energy self-sufficient households with photovoltaics and electric vehicles are feasible in temperate climate

• Which factors influence the technological and economic feasibility of self-sufficiency? • How would energy costs for self-sufficient households compare to those still relying on fossil fuels and grid-based electricity by 2050? The more densely populated an area, the more difficult it will be to generate enough elec- tricity for that area with solar PV only. Single-family buildings therefore achieve self-suffi- ciency most easily. However, with technological improvement leading to more efficient PV panels, even some multi-family buildings can be self-sufficient. In all cases, cost driven by stor- age needs is a key issue, and implementing fully built-out rooftop PV on fully electrified build- ings while remaining connected to the grid is the most cost-attractive solution under almost all assumptions. Methods Definition of cases We define sixteen cases through which we examine energy self-sufficiency, aiming to represent expected state-of-the-art technologies available by 2050. The cases are constructed by varying four dimensions which each represent a binary choice on key assumptions for stylized housing types, as shown in Fig 1. Dimension 1 (household type) defines energy requirements of single-family households (SFHs) in single-family buildings (SFBs) and multi-family households (MFHs) in multi-family buildings (MFBs). Dimension 2 (building type) distinguishes between new and retrofitted buildings, with a focus on their differing energy requirements for space heating. Dimension 3 (electricity demand) is defined by behavioral changes and technology developments which

may lead to lower energy demand. Because future electricity demand cannot be predicted we differentiate between two stylized cases: a profound electricity reduction and a scenario with a conventional electricity use. This only affects electricity demand not already included in space heating and electric mobility (covered by dimensions 2 and 4, respectively). Dimension 4 assumes a complete electrification of passenger cars in both cases, with differentiation of mobility behavior based on a typical urban or rural household. This is an important dimension because driving behavior and developments in the car industry will profoundly influence elec- tricity demand [20–22]. We only consider battery electric vehicles (BEVs) here. Fuel cell elec- tric vehicles (FCEVs) can be seen as an alternative provider of electric mobility, but we do not Table 1. (Continued) Source Aim and methods Results Differences to our study Lang, Ammann (17) The creation of a model to simulate the performance of rooftop PV for different building types to assess the techno-economic potential of PV self- consumption. In the small residential sector, 40% of the produced electricity is self-consumed. In the large residential sector 80%. Furthermore, the internal rate of return is calculated to measure profitability. • The aim is not to be self- sufficient • No facade PV • Connected to the grid • No storage of electricity Prognos (18) The aim is to build a quantitative basis for political and societal discussions. This is done by modelling three scenarios to investigate the effect of framework

conditions, influencing factors, political interventions, and climate and energy goals. Quantitative data of the three scenarios until 2050. • Modelling of the entire Swiss energy landscape • No statement regarding self- sufficiency • Diverse technologies are modelled SFOE (19) Different heating systems are simulated with the aim to find the most efficient combination of heat pumps and solar energy solutions. Different advantages and disadvantages are mentioned. The most economical system is composed of an air-to-water heat pump and solar PV. • Special case of a single-family building with a fixed energy consumption • Only heating system is of interest • No storage of electricity https://doi.org/10.1371/journal.pone.0227368.t001 Energy self-sufficient households with photovoltaics and electric vehicles are feasible in temperate climate PLOS ONE | https://doi.org/10.1371/journal.pone.0227368 March 4, 2020 4 / 25