Cold-climate dwellings can face coincident electricity and domestic hot-water shortfalls in winter, when solar availability is at its lowest. This study evaluates an integrated residential system for Aomori, Japan, combining photovoltaics, evacuated-tube solar water heating, and battery storage with electrolysis, compressed-hydrogen storage, and a PEM fuel cell operated in combined-heat-and-power mode. Building on a screening-level annual-balance analysis, a coupled annual TRNSYS simulation with a 0.125 h time step resolved battery dispatch, electrolyzer part-load operation, hydrogen compression and finite storage, seasonal fuel-cell operation, and heat recovery. The results show that the principal value of seasonal hydrogen lies in improving winter supply adequacy, dispatchability, and heat recovery rather than annual conversion efficiency. Fuel-cell heat recovery increased the number of days satisfying the hot-water screening indicator—a daily mean tank temperature of at least 43 °C—from 221 to 332. A reserve-aware criterion identified a 225 W electrolyzer operating-power cap as the positive-reserve case; 205 W was near-cyclic with a negligible margin, whereas the original 475 W cap was substantially oversized. The hydrogen pathway remained markedly less efficient than direct photovoltaic and solar-thermal use, and the estimated storage hardware’s lower bound substantially exceeded the break-even capital ceiling supported by the annual operating value. Seasonal hydrogen can therefore strengthen winter energy adequacy and heat recovery but is not yet cost-effective at the single-dwelling scale under the investigated conditions.

Residential fuel cell cogeneration is usually credited with all its recovered heat, although that heat is useful only if a coincident demand absorbs it. Hourly TRNSYS 18 simulations of an off-grid dwelling in Aomori City, Japan, with a 700 W proton exchange membrane fuel cell running on self-produced hydrogen, compared four dispatch rules, two thermal services and several electrolyzer and store sizes over a periodic year. With space heating, residual heat demand was 12.6 times the electrical deficit after photovoltaic and battery supply. The unit was potentially heat-rich in 88.7–92.3% of deficit hours with hot water alone and 2.2–3.7% with space heating. Against a run without hydrogen, 25–61% of the heat an immersed coil delivered to the store reduced unmet thermal demand where the cycle closed; 22–54% displaced solar heat and 15–22% raised tank losses. Under calendar dispatch with hot water alone, 75% of recovered heat could not pass the coil. Load following raised self-sufficiency from 88.9% to 96.3%, whereas calendar dispatch, and thermally led dispatch with space heating, needed 2.8–5.0 times the producible hydrogen. Electrode areas of 40–110 cm² gave identical service; each Nm³ of storage was below the seasonal swing of 76.7 Nm³ cost 1.77 kWh of output.