*3.2. Multi-Generation for Coupled Power and Resources*

Smart energy networks (SNE) integrate electricity, gas and heat under common Information and Communications Technology (ICT) with power-to-gas technology (PtG) [77]. An 850-kW rooftop solar installation generating 3.5 MWh per day for an electrolyzer system of five 30-Nm<sup>3</sup> /h units would be expected to produce 54 kg of hydrogen per day [78]. Two tonnes of adsorption material (sorbent) in an AWG system could be used to capture the approximately 500 L per day of water required for this electrolysis [52].

Theoretically, this size system could also produce 427 kg of oxygen per day, enough for approximately 45 medium-concentration oxygen therapy devices or 60 percent of the anticipated demand. Low-cost energy from grid connected solar or wind during periods of excess supply could power additional electrolysis to increase this to 80 or 120 percent of the demand. Efficient on-site oxygen concentrators could fill any supply gaps with cylinder backup [50]. Excess oxygen can feed hydrogen peroxide synthesis for disinfectant supply, as discussed in Section 2.

Excess hydrogen surplus to the hospital's energy storage requirements could be fed into the gas network. Existing methane infrastructure could accept up to 10 or 20 percent hydrogen [79,80], or more as synthetic methane after being combined with carbon dioxide extracted from the atmosphere [81]. Hydrogen could, alternatively, replace natural gas altogether. In addition to its use as fuel for electricity generation, hydrogen can be used in industry as a chemical feedstock and to supplement thermal energy primarily provided by heat pumps.

Hydrogen could also be used for vehicles, either in its pure molecular form for cars and commercial vehicles or as a feedstock for synthetic fuel [82] to support aeromedical services. A hospital campus of this size may have thousands of parking spaces [83]. Just 50 medium size EVs represent over 3 MWh of energy storage and at least 500 kW of two-way power with vehicle-to-grid connections. Covering the car park with solar PVs could provide a much larger on-site solar precinct.

Figure 6 shows how all these systems interact to meet hospital requirements. In addition to redundancy, all these systems would be backed up independently from an infrastructure network and/or by road transport. *Sustainability* **2020**, *12*, x FOR PEER REVIEW 11 of 17

**Figure 6.** Multi-generation hospital precinct energy system concept diagram, with energy and resource flows for coupled energy and resource demands. **Figure 6.** Multi-generation hospital precinct energy system concept diagram, with energy and resource flows for coupled energy and resource demands.

This high-level system design meets the goals outlined in Section 2.4 of this article, namely 'sustainably provisioning for reliable on-site power requirements to improve outcomes for the community'. Future work would need to examine specific site requirements in more detail. This would include techno-economic optimization of system components and could also explore other opportunities, such as wastewater treatment and mobile installations for field hospitals. Detailed engineering design would consider other applicable standards and regulation, including the location of gas storage. Hydrogen is not inherently more hazardous than conventional fuels but it must be managed appropriately [84–86]. The positioning of technology in this hybrid clean energy system presents an opportunity to engage the public with the vision presented here, particularly with less well known vanadium systems. This high-level system design meets the goals outlined in Section 2.4 of this article, namely 'sustainably provisioning for reliable on-site power requirements to improve outcomes for the community'. Future work would need to examine specific site requirements in more detail. This would include techno-economic optimization of system components and could also explore other opportunities, such as wastewater treatment and mobile installations for field hospitals. Detailed engineering design would consider other applicable standards and regulation, including the location of gas storage. Hydrogen is not inherently more hazardous than conventional fuels but it must be managed appropriately [84–86]. The positioning of technology in this hybrid clean energy system presents an opportunity to engage the public with the vision presented here, particularly with less well known vanadium systems.
