## 3 Energy Balance Results and Discussion
### FCEV2G Usage and Electricity Balance Discussion and Results  
Figure 6 provides further insight into seasonal and hourly FCEV2G usage. The FCEVs needed for producing V2G electricity (# cars left \(y\)-axis, % of car fleet right \(y\)-axis) are shown by means of boxplots for every hour of the day. For both locations and scenarios, usage is shown separately for both the colder winter period (in blue, left, 1 October-31 March) and the warmer summer period (in orange, right, 1 April-30 September).  
* _Reliable electricity supply can be realized at all hours of the day_, as extreme FCEV2G peaks never exceed 50% of the total car fleet. The number of cars needed to balance the system peaks in the morning (06:00-09:00) and the late afternoon/early evening (16:00-20:00) and correspond to driving rush hours. These peaks are extreme outliers, and values close to these occur for only a small number of hours per year (Figure A1).
* _In Murcia, virtually no cars are required during daylight hours_. This is valid in all scenarios and seasons, except for some moments. In Hamburg, this is only the case in the summer period, for both scenarios.
* _Hamburg faces a greater seasonal, and Murcia a greater day-night storage challenge_, particularly in the Mid Century scenario. In Hamburg, peak FCEV2G electricity production occurs in the winter period, whereas, in Murcia, the production is highest in both the summer and the winter period (see also Figure A2).
* _On average, less than 22% and 13% of all cars are required during peak hours (17:00-19:00)_, in, respectively, the Near Future and the Mid Century scenario (black crosses).
* _In Murcia, the mean FCEV2G usage is highest in summer. In Hamburg, the mean FCEV2G usage is highest in winter_. Electricity demand in Murcia is dominated by space cooling, whereas, in Hamburg, it is dominated by space heating. In the Mid Century scenario, the mean daily FCEV2G usage in the winter period in Hamburg is 7.3% of all cars, whereas, in Murcia, the figure is 4.6%. In summer, this is 3% of all cars in Murcia and 2.7% of all cars in Hamburg.
* _Relatively more FCEV2G electricity is produced outside regular driving hours_ (20:00-06:00) [129] than during regular driving hours (06:00-20:00). In the Mid Century scenario, up to 60% of all FCEV2G electricity production in Murcia takes place during the 10 night hours (20:00-06:00); the remaining 40% FCEV2G electricity is produced during the 14 regular driving hours (06:00-20:00). In Hamburg, in the Mid Century scenario, the figures are 50% during the 10 regular driving hours and 50% during the 14 regular driving hours.  
Figure 6: Boxplots showing the hourly average FCEVs needed for producing V2G electricity (# left \(y\)-axis, % of all cars right \(y\)-axis) throughout the day during the colder winter period (in blue, left, 1 October-31 March) and the warmer “summer” period (in orange, right, 1 April-30 September) in the Near Future and Mid Century scenarios for, respectively, Hamburg and Murcia. The black crosses represent the mean values, the red lines represent the medians, and the green triangles represent the maxima. Based on a normal distribution, the bars represent the interquartile range, IQR, the difference between the first and third quartiles (Q1 and Q3), approximately 50%. The upper and lower whiskers represent the data points within the ranges [Q1–(Q1-1.5\(\times\)IQR)] and [Q3+(Q3+1.5\(\times\)IQR)], approximately 44%. Dots indicate outliers, outside aforementioned ranges, the remaining approx. 1%.