## Materials and Methods
### Location Selection, System Design and Dimensioning, System Components, and Scenarios
#### 2.2.2 System Design and Dimensioning
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Label** & **Components** & **Label** & **Components** \\ \hline
**S** & **Local solar electricity and hydrogen production** & **TT** & **Hydrogen tube trailer transportation** \\ S1 & Solar electricity system & TT1 & Tube trailers \\ S2 & Water purification (reverse osmosis) & TT2 & Trailer tractors \\ S3 & Pure-water tank & **FCEV** & **Fuel cell electric vehicle-to-grid (V2G)** \\ S4 & Electrolyzer & FCEV1 & Fuel cell in fuel cell electric vehicle (FCEV) \\ S5 & Hydrogen purifier & FCEV2 & V2G infrastructure \\ S6 & Low-pressure compressor & & **Energy and water flows** \\
**W** & **Large-scale and shared wind hydrogen** & & **Electricity** \\
**W** & **production** & **E** & **Electricity** \\ W1 & Shared wind turbine park & E\({}_{\text{W}}\) & Electricity from wind \\ W2 & Water purification (reverse osmosis) & E\({}_{\text{S}}\) & Electricity from solar \\ W3 & Pure water tank & E\({}_{\text{DC}}\) & Direct consumption solar electricity \\ W4 & Electrolyzer & E\({}_{\text{surp}}\) & Surplus solar electricity \\ W5 & Hydrogen purifier & E\({}_{\text{B}}\) & Electricity consumption in buildings \\ W6 & Low-pressure compressor to SHS & E\({}_{\text{V2G}}\) & Electricity from hydrogen via V2G \\
**HFS** & **Hydrogen fueling station (HFS)** & E\({}_{\text{HFS}}\) & Electricity consumption HFS \\ HFS1 & High-pressure compressor & E\({}_{\text{SHS}}\) & Electricity consumption SHS \\ HFS2 & High-pressure stationary storage & **H** & **Hydrogen** \\ HFS3 & Chillers & H\({}_{\text{W}}\) & Hydrogen from wind electricity \\ HFS4 & Dispensers & H\({}_{\text{S}}\) & Hydrogen from surplus solar electricity \\
**SHS** & **Large-scale and shared seasonal hydrogen** & & \\  & **storage (SHS)** & H\({}_{\text{HFS}}\) & Dispensed hydrogen at HFS \\ SHS1 & Shared seasonal hydrogen storage (SHS) & H\({}_{\text{Boad}}\) & Hydrogen consumed by road vehicles \\ SHS2 & Low-pressure compressor & H\({}_{\text{V2G}}\) & Hydrogen consumed for V2G electricity \\  & & **H\({}_{\text{B}}\)O** & **Water** \\  & & H\({}_{\text{G}}\)O\({}_{\text{W}}\) & Water for hydrogen production via wind \\  & & H\({}_{\text{2}}\)O\({}_{\text{S}}\) & Water for hydrogen production via solar \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Components, energy, and water flow in the smart city area (Figure 2). Figure 2: Smart city area components, electricity, water, hydrogen flows, and transportation. fuel cell electric vehicles (FCEV), fuel cell electric vehicle; V2G, vehicle-to-grid. On average, 2000 households in Germany and Spain correspond to, respectively, 4310 and 5083 people, with 2364 and 1846 passenger cars and 156 and 410 other vehicles, according to German and Spanish national statistical data [55; 57; 113; 118; 119; 120]. See Table 2 (local parameters). The floor area of residential and services buildings is derived from national statistical data and scaled to 2000 households: German and Spanish average household floor area S-hh is, respectively, 91.60 and 91.78 m\({}^{2}\)[54; 55]. Residential and service sector roofs will be used for solar electricity systems and rainwater collection [121; 122; 123]. Solar electricity systems are installed on all technically suitable roof areas: 9 m\({}^{2}\) per person on residential buildings and 4 m\({}^{2}\) per person on service sector buildings area [125; 126]. Facades are not considered. For ease of comparison between Hamburg and Murcia, the roof area available for solar electric modules and rainwater collection in Murcia is based on the Hamburg parameters.