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

self-sufficient with a realistic PV generation profile: PDneg � PDpos � 38:3% ð4Þ Where Dneg are days where DCaseX > CCaseX and Dpos are days where DCaseX < CCaseX. We also examine the sensitivity of results to both technical and cost uncertainties. The effi- ciency of PV modules is a key parameter due to the exclusive reliance on PV to generate elec- tricity. We assume that our rooftop PV systems are sc-Si modules. Other work has shown that an efficiency of 27.2% can be reached by 2050 with a yearly increase by 0.3% [24]. We examine a range of PV efficiencies from the current efficiency of 17% to 27.2% [24, 25], focusing in par- ticular on two cases: 22.1% (assuming an annual increase by 0.15% until 2050) and 27.2% (annual increase by 0.3%). According to Mu¨ller, Folini [77], the average yearly increase in effi- ciency of sc-Si cells over the last decade was 0.17%, so our assumptions are within a realistic range. We assume that CdTe thin-film modules are used for facade electricity production as they are more suited for difficult light conditions or when PV modules should be integrated into building parts with a heterogenous structure [23]. Efficiency of CdTe thin-film cells are assumed to be 0.787 times that of sc-Si cells, based on their relative efficiencies under standard conditions from [78]. Other technical parameters as detailed in the results below are varied while PV efficiency is kept at 27.2%. A final component of our sensitivity analyses are the cost of key components, to examine their effect on the economic feasibility of the self-sufficient

cases. This includes costs in the alternative (fossil fuel and grid connected) cases. Their total costs are strongly influenced by the energy prices for electricity, gas, and gasoline. Finally, dis- count rate also affects total costs, so we vary it from its default of 4% to 0% and 6%. Results Feasibility of self-sufficiency The composition of the end-use demand for electricity we use based on the assumptions laid out above is shown in Fig 2. It consists of domestic hot water (DHW), space heating, general Table 4. Cost assumptions for the alternative cases exchanging energy with the grid and using fossil fuels. All costs are in 2019 CHF. Price in 2050 [CHF2019] Source Lifetime [years] Source Gas heating system New installation—SFH 20,000.- [72] 20 [11] Replacement—SFH 14,000.- [72] 20 [11] New installation—MFH 76,000.- [72], own assumptions 20 [11] Replacement—MFH 70,000.- [72], own assumptions 20 [11] O&M costs [CHF/year] 650.- [72] - - Air conditioning Price–SFB 6000.- [73] 20 Own Assumptions Price–MFB 10,000.- [73] 20 Own Assumptions O&M costs [CHF/system] 150.- [73] - - Energy prices Change 2020–2050 Electricity price [CHF/kWh] 0.262 [11] +24% [18] Gas price [CHF/kWh] 0.175 [18] +43% [18] Gasoline price� [CHF/kWh] 0.29 [18] +29% [18] � with a density of 0.775 kg/l and a heating value of 11.6 kWh/kg https://doi.org/10.1371/journal.pone.0227368.t004 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 10 / 25