## 5 Discussion
### Other Balancing Methods  
* _Using a mix of FCEVs, BEVs, or fuel cell plug-in hybrid electric vehicle (FCPHEV) and stationary batteries_[84; 87; 178; 179; 180]. Instead of only using hydrogen and FCEV2G for both daily and seasonal energy balancing, other technologies could be used in parallel. For example, batteries in BEVs or FCPHEV, as well as stationary batteries, could be used for storing or releasing peak surplus or shortage of electricity [181] for day-to-day storage. Especially in Murcia, this could result in lower total system costs, as the day-to-day storage is more prevalent in Murcia [182]. Capacity factors of electrolyzers could be improved, and so decrease costs. FCEVs and hydrogen production and storage could subsequently be used for energy balancing for longer periods, up to entire seasons [182].
* _Using other \(CO_{2}\)-free hydrogen carriers for energy transportation, short and long-term energy storage._ There are several other proven and available carriers today, such as liquefied hydrogen [183; 184; 185; 186; 187], ammonia (NH\({}_{3}\)) [188], or liquid organic hydrogen carriers (LOHC) [189; 190]. Transporting liquid hydrogen can be less costly compared to compressed hydrogen when volumes and distances are larger. Ammonia storage and LOHC storage are becoming commercial applications at scale, and both represent reasonable alternatives in the absence of salt caverns.
* _Increase passenger car FCEV2G power output, use other FCEVs and stationary fuel cells for combined heat and power._ At the moment, only passenger cars with an output of 10 kW/car while having a 100 kW fuel cell system on-board are used for FCEV2G electricity. This limitation is mainly because of potential insufficient cooling radiator capacity when parked and providing FCEV2G electricity [38]. If V2G output could be increased by enhancing cooling capacity, then proportionally fewer passenger cars would be needed. Cooling capacity could be enhanced by installing, for example, a bigger radiator and cooling fans, or by using two-phase cooling fluids with a higher cooling capacity [191]. Commercial vehicles (vans, trucks, buses) are more widely used than passenger cars, although often not during the night. By also using commercial for V2G purposes [192], the number of passenger cars would be reduced. In the case of an underground hydrogen pipeline network, stationary fuel cells [193; 194; 195; 196; 197; 198] could provide heat and power to buildings, and when necessary, FCEV2 Gs could provide peak power.
* _Internet Technology (IT) usage for demand response forecasting, scheduling, virtual power plants, and autonomous driving._ Weather and electricity demand forecasting [199; 200; 201; 202; 203; 204; 205; 206; 207; 208] in combination with demand response [209; 21; 210; 211] could potentially avert peaks in temporal surplus or shortage of electricity. This would reduce installed capacity cost. Combining the output of thousands of grid-connected FCEVs would create so-called virtual power plants [212; 213] with potentially large capacities. Similar to mobility as a service (MaaS) [214; 215; 216; 217; 218], power or electricity as a service (PaaSor EaaS) could be introduced. To create these markets, additional pricing structures, contract types, and aggregators scheduling and operating the cars will be required [219; 220; 221]. Upcoming technologies could facilitate the scheduling of cars, for example, self-driving, free-floating, cloud-connected car-sharing fleets [223; 224; 225], together with inductive (wireless) self-connecting V2G infrastructure [226; 227; 228; 229; 230]. As mentioned earlier, most FCEV2G electricity is required at night, whereas most people travel and work during the day. So, even if car-sharing spreads widely and the total number of cars decreases, at night, car-sharing fleets will be used less and, therefore, will be available to provide power.