## 1 Introduction
The proposed system can work as a stand-alone Bio-HRES, generating about 31 MWh per annum electric power, together with providing the thermal energy, and hydrogen at a LCOE of 0.793 USD/kWh. [PERSON] et al. discussed the optimal design of a hydrogen-based HRES, using the particle swarm optimization (PSO) method, in order to minimize the total cost of the system and CO\({}_{2}\) emissions [11]. Their proposed system consists of a solar water electrolyzer coupled with a wind turbine, a diesel generator, a battery bank, and a fuel cell. The total cost of the system was estimated at EUR 93,487 over 25 years lifespan of the system. Table 1 shows a summary of the recent hydrogen-based HRES studies with the different modeling approaches used in their techno-economic analysis. \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline  & & & & \multicolumn{4}{c}{**System Components**} & & \\ \cline{6-10} \multirow{2}{*}{WT} & \multirow{2}{*}{PV} & \multirow{2}{*}{FC} & \multirow{2}{*}{Biomass} & \multirow{2}{*}{Battery} & \multicolumn{2}{c}{H2} & \multirow{2}{*}{Electrolyzer} & \multirow{2}{*}{Diesel} & \multirow{2}{*}{ \begin{tabular}{c} **Objective** \\ **Function** \\ \end{tabular}  } & \multirow{2}{*}{**Method**} & \multirow{2}{*}{**Ref**} \\  & & & & & & **Tank** & & & **Other** & & \\ \hline \(\boldsymbol{\check{\
u}}\) & \(\boldsymbol{\check{\
u}}\) & Total Cost/CO\({}_{2}\) Emission/unmet load & PSO 1 [12] \\ \(\  
The combination of biomass gasification with hybrid systems is gaining significant attention from the scientific community. All these studies focus on the gasification of relatively dry biomass combined with fuel cell hybrid systems [19; 20; 21; 22; 23; 24; 25]. The combination of SCWG and fuel cells is a new concept. However, research has been absent into integrated SCWG fuel cells in the literature, forming the basis of this study. Following the previous studies, this paper aimed to optimally design a hydrogen-based HRES, consisting of a combination of the solar water electrolysis process, as the conventional method of hydrogen production, with the SCWG, as a more recent hydrogen production technology. The main electric power generators in the proposed HRES are solar panels and the fuel cell. Surplus power generated by the solar panels is consumed by an electrolyzer to produce hydrogen through the water decomposition process. The hydrogen is then stored in a hydrogen tank. The fuel cell performs as the backup system to generate electricity from the hydrogen when sunshine is not available. The SCWG is used to produce extra hydrogen in order to offset hydrogen deficiency in the hydrogen tank, using supercritical water as the reaction medium for the hydrothermal dissociation of the wet biomass feedstock. Residential food waste, with moisture content up to 40%, was considered as the possible feedstock to be used in the SCWG. In this study, hydrogen is considered as functioning as an energy storage medium by storing renewable energies until the fuel cell converts it to electricity. Hydrogen can be provided from two sources: (1) a solar water electrolyzer and (2) a SCWG, which generates hydrogen from biomass gasification via hydrothermal conversion route. The SCWG uses water as the gasifying agent at its supercritical condition to decompose the organic biomass such as kitchen waste and organic biomass to hydrogen, carbon dioxide, carbon monoxide, and methane gas, allowing for the achievement of a very high volumetric hydrogen ratio. Moreover, SCWG can resolve some problems facing conventional biomass gasification. Among many hydrogen production methods, eco-friendly and high purity of hydrogen can be obtained by water electrolysis. Solar hydrogen production by alkaline water electrolysis was considered in this study as a most promising technique for high pure, efficient hydrogen production from renewable energy sources, which only emits oxygen as a byproduct without any carbon emissions.