The　incorporation　of　energy　storing　units　into　hybrid　systems　reallocates　the　excess　electricity　to　meet　demand　requirements　in　the　deficiency　periods.　This　study　seeks　to　determine　the　optimal　size　of　a　Photovoltaic　(PV)/wind/biomass　hybrid　system　with　and　without　energy　storage　built　on　the　base　of　boosting　the　demand–supply　fraction　(DSF)　and　the　renewable　energy　fraction　(FR)　with　a　net　present　value　larger　than　or　equals　to　zero.　The　Generalized　Reduced　Gradient　algorithm　has　been　utilized　in　this　study　to　evaluate　the　optimal　components’　capacities　of　the　proposed　system.　Middle　East　Technical　University　Northern　Cyprus　Campus　was　used　as　a　case　study.　The　proposed　system　consists　of　1.79　MW　PV,　2　MW　wind　and　0.92　MW　biomass　systems　with　24.39　MWh　pumped　hydro　storage　system　and　148.64　kWh　batteries　achieving　FR　of　99.59%,　DSF　of　98.86%,　and　a　cost　of　electricity　equals　to　0.1626　$/kWh.　The　simulations　results　proved　that　the　integration　of　a　hybrid　energy　storage　system　with　the　PV/wind/biomass　system　ensures　very　high　autonomy　approaching　almost　99%.　Finally,　considering　the　significant　excess　energy　produced　by　the　tri-hybrid　system,　this　excess　could　also　be　allocated　towards　meeting　the　campus＇s　thermal　and　domestic　hot　water　demands　creating　a　polygeneration　power　system.　©　2021　Elsevier　Ltd