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

subtracting the electricity demand from the produced electricity. The algorithm computes the optimal area of solar PV, considering a surplus production for hydrogen storage, and by taking restrictions on the rooftop and facade sizes into account. An optimal solar PV area can be reached when the energy balance is exactly equilibrated at zero. The objective is to produce a sufficient amount of energy with the given parameters of Table 2 while minimizing the panel Table 2. Assumptions for all cases. Dimension 1 determines the dimensioning of SFBs and MFBs with their electricity consumption and domestic hot water (DHW) demand. Dimension 2 determines usable rooftop share and yearly space heating energy demand of newly built SFHs and MFHs today and in 2050 with the individual reduction potential and the projected SPF of air-to-water heat pumps in 2050. Dimension 3 determines changing electricity demand with the consideration of cooling and lighting demand, and dimension 4 considers the required electricity for transportation, per house unit and month, derived by estimating in passenger kilometers per per- son in both a rural and urban setting. All cases Overall assumptions Sources Inverter efficiency 99% [23] Performance ratio 0.9 [24] Solar irradiation, rooftop 1,000 kWh/m2/year [25] Solar irradiation, facade 800 kWh/m2/year [10], [26], [25] Dimension 1: building type SFBs MFBs Occupancy rate per household 4 4 [10], [27] Occupancy rate per building 4 20 [10] Stories 3 5 [10], own assumptions Floor area 200 m2 900 m2 [10], [28], [29], [30], [31]

Rooftop slope 35˚ 35˚ [32], [33] Rooftop area 81.4 m2 219.7 m2 Own assumptions Facade area for PV production (33% of one facade side) 25.5 m2 67.7 m2 Own assumptions Current electricity consumption of each house unit 5,200 kWh/year 19,250 kWh/year [34] DHW demand in 2050 10.9 kWh/m2; -26% compared to 2020 [18] 12.6 kWh/m2; -26% compared to 2020 [18] [14], [19], [29], [30], [31], [35] DHW efficiency factor in 2050 3.5; +22% compared to 2020 [18] 3.5; +22% compared to 2020 [18] [18], [36] Dimension 2: building age New buildings Retrofitted buildings Usable rooftop area 100% 70% [37] Yearly energy demand of SFHs–now 16.0 kWh/m2 22.5 kWh/m2 [14], [19], [29], [30], [31], [35], [38] Reduction potential -53% -56% [18] Yearly energy demand of SFHs–in 2050 7.5 kWh/m2 9.9 kWh/m2 [14], [18], [19], [29], [30], [31], [35], [38] Yearly energy demand of MFHs–now 18.2 kWh/m2 20.9 kWh/m2 [14], [19], [29], [30], [31], [35], [38] Reduction Potential -34% -39% [18] Yearly energy demand of MFHs–in 2050 12.0 kWh/m2 12.7 kWh/m2 [14], [18], [19], [29], [30], [31], [35], [38] SPF of air-to-water heat pumps–in 2050 4.8; +46% compared to 2018 [18] 4.4; -9% compared to new buildings [39] [18], [36], [39], [40], [41] Dimension 3: demand Profound reduction Conventional use Decrease of electricity reduction compared to [34] -29% -7% [18] Climate change impact on cooling electricity demand +2.5% of today’s electricity consumption [34] +2.5% of today’s electricity consumption [34] [42], [43] Share of lighting of the entire electricity demand 13.3% 13.3% [38]

Dimension 4: mobility Urban SFBs Rural SFBs Urban MFBs Rural MFBs Passenger km (pkm) in 2050 per person times occupancy rate 4,814 7,554 4,201 6,439 [44], [45] Pkm in 2050 per house unit 19,255 30,215 84,021 128,785 [45], [46] Required kWh/100 km in 2050 12 12 12 12 [47], [48], [49] Required kWh in 2050 per house unit 2,311 3,626 10,082 15,454 Calculation based on above sources Required kWh in 2050 per house unit and month 193 302 840 1,288 Calculation based on above sources https://doi.org/10.1371/journal.pone.0227368.t002 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 6 / 25