Begin with heat demand and electrical input separately
A heat pump moves heat rather than converting electricity directly into heat, so its thermal output can be several times its electrical input under suitable conditions. Do not size solar or batteries from the advertised heating capacity alone. Record the exact unit’s electrical input range, seasonal performance data, auxiliary-heater rating and climate design conditions.
Winter is usually the hardest solar match
Heating demand often rises when solar production is seasonally lower and daylight is shorter. A summer solar surplus should not be projected directly into winter autonomy. Use local monthly production estimates and realistic heating profiles. Battery storage can shift energy within a day, but it does not normally solve a multi-week seasonal mismatch without a much larger energy source.
Backup resistance heat can dominate electrical demand
Many heat-pump systems include electric resistance backup or crankcase/defrost loads. If those stages can operate during a battery outage, they may exceed the inverter power budget quickly. Decide whether backup heat should be shed, limited or supported and verify the control strategy. The appliance-load calculator can start the load inventory, but final design needs exact nameplates and controls.
Battery energy and battery power solve different constraints
Enough kilowatt-hours for an overnight heating period does not guarantee enough kilowatts for compressor starts, pumps and simultaneous household loads. Conversely, a high-power battery may still have too little stored energy for a cold night. Review Melnti’s battery capacity versus power guide and model both dimensions.
Smart scheduling can improve self-consumption
Where comfort and tariffs allow, pre-heating or pre-cooling during solar-rich hours can store useful energy in the building itself. Battery charging can then be reserved for evening loads or expensive tariff periods. The control plan should avoid creating a new coincident peak by starting the heat pump, EV charger and battery charging at once.
Use measured data after the first season
Weather, insulation, occupancy and thermostat behaviour make heat-pump demand highly site-specific. After installation, compare measured electricity use and indoor comfort with the design assumptions. Adjust schedules and reserve settings before concluding that more battery capacity is necessary.