Japan is facing a severe challenge regarding the heavy dependence on fossil fuel after the Great East Japan Earthquake. Fossil fuels currently account for 89 % of the total energy consumption in Japan, which approaches the level of the oil shock in 1973. To tackle this challenge, the government of Japan needs to develop and utilize renewable energy sources to increase its energy self-sufficiency rate and reduce the environmental impacts of the increased use of fossil fuels. Since the renewable energies are from the natural environment, they are all-weather dependent, which makes them vulnerable in developing a stable power system. The hybridization of variable renewables can allow for smooth, durable, and reliable output to power grids to improve the safety, reliability, and stability of dispatched power, which is cheaper than investing in single renewable technologies. Therefore, Hybrid Renewable Energy System (HRES) can be considered as one possible solution which can combine two or more renewable energy sources to produce power continuously, without interruption. A hybrid renewable energy system (HRES) is defined as a combination of several renewable technologies which can operate as a self-sustaining power system with higher efficiency than a single renewable power generator such as solar or wind system. If the proposed HRES does not guarantee the production of energy during extended periods, energy storage requirements should be considered to bridge the lean times. Battery storage can be considered as a solution. However, the concerns with the battery storage include its cost and lifetime. Beyond battery storage, a feasible solution is adding a hydrogen-based storage system, including a hydrogen producer, storage tank, and hydrogen consumer such as a fuel cell. Currently, there are several hydrogen production technologies such as water electrolysis, natural gas reforming, photochemical and thermochemical splitting of water, and also a fermentation process which can be used as the hydrogen producer in a HRES. Biomass gasification via biochemical or thermochemical conversion processes are also the most practical technologies for HRES applications. However, the main concern with the gasification process is the formation of ash and tar, which causes severe technical problems such as fouling and slagging in the gasification process. As an alternative to the conventional gasification, the supercritical water gasification (SCWG) process uses water over 22 MPa and 374 C (critical point) as the gasifying agent to decompose the wet biomass feedstock, allowing to achieve a much higher ratio of gasification and hydrogen generation. In this study, Firstly, an innovative HRES will be introduced with specific emphasis on the integration of renewable generation into the power grid. The proposed HRES is based on the combination of hydrogen generation from two sources: (1) SCWG process of the residential kitchen waste and organic wastewater and (2) solar water electrolysis process which uses the surplus electric power generated by the solar cells. The fuel cell converts hydrogen into electrical power, which can be used during the periods when the sunlight is not available. So, the proposed HRES forms a composite energy system capable of all-weather conditions. Secondly, a detailed techno-economic-analysis of the proposed HRES is carried out to estimate the cost of electricity generation from the system to meet the electrical load requirements of a selected household area in a subject district around the Shinchi station which is located in Shinchi-machi in this prefecture. The techno-economic-analysis includes simulation and optimization models. The simulation model is based on the technical design of the system to evaluate the hourly power generation from the proposed HRES, using real meteorological data available in the selected residential area. The optimization model’s main goal is set to find the optimal configuration of the system subject to satisfying the required load (electricity) in the selected household area, based on introducing two different optimization criterions: 1) minimization of the total cost of the system and 2) maximization of the total profit obtained from using renewable electricity and selling surplus solar electricity to the grid, considering the Feed-in-Tariff (FiT) scheme in Japan. The optimization method is based on the PSO algorithm, which is one of the meta-heuristics methods to find out the pseudo solution. The model was employed to perform sensitivity analyses of the Levelized Cost of Energy (LCOE) with respect to three scenarios of: 1) cost minimization with unlimited biomass feedstock, 2) cost minimization with the limited biomass feedstock and 3) profit maximization with the limited biomass feedstock. As indicated by the model results, the proposed HRES can generate about 47.3 MWh of electricity in all scenario which is needed to meet the external load requirement in the selected study area. The LCOE of the system in scenario 1, 2 and 3 is estimated about 48.89 JPY/kWh, 55.92 JPY/kWh and 56.47 JPY/kWh, respectively. Comparison between scenario 1 and scenario 2 showed that the capacity of electrolyzer and PV module with limited biomass feedstock increases. The limited availability of biomass feedstock resulted in increasing the share of the PV panels from 45% to 90% in electricity generation mix and decreasing the share of the fuel cell from 55% to 10%. The major part of the generated electricity from the solar panels was consumed in the electrolyzer to support the required level of hydrogen consumption in the fuel cell. Comparison between scenario 2 and scenario 3 revealed the role of PV module in increasing the profit through selling back the surplus electricity to the grid, using the FiT mechanism. The model was employed to perform sensitivity analyses of the LCOE with respect to the size of solar-powered hydrogen generation system (Solar PV + electrolyzer). The result of the sensitivity analysis shows that the substitution of biomass hydrogen with solar hydrogen can significantly influence the LCOE of the system. By increasing the amount of hydrogen produced by the electrolyzer, the total cost of the system increases. Therefore, the reduction of the cost of the solar hydrogen system turns out to be by far the most important cost driver. However, under the profit maximization scenario with limited biomass feedstock, the capacity of the solar electricity increases under FiT mechanism.