01 / Direct answerSize power and energy separately, then verify that every component works together.
A complete solar system is not selected from one kW number. Use maximum simultaneous load and starting surge to select inverter power; use essential-load energy and required backup time to select battery energy; and use daily energy, local solar resource and system losses to estimate the PV array.
After the first calculation, verify AC phase and voltage, inverter surge duration, battery discharge current and BMS communication, PV string voltage and current, protection, generator or grid behavior and local installation requirements.
Inverter power (kW)
Maximum simultaneous running load plus verified starting-surge capability.
Battery energy (kWh)
Required backup energy adjusted for the permitted usable fraction and conversion losses.
PV array (kWp)
Daily energy divided by peak sun hours and expected overall system yield.
Start with what must run, when it runs and how it starts.
List each appliance or machine, its running power, starting power, quantity and daily operating hours. Mark essential and nonessential loads and identify which loads may operate at the same time.
Daily energy is the sum of load power multiplied by operating hours. Inverter kW comes from simultaneous demand, not from the daily kWh total.
Continuous demand
Add the loads expected to run together under the intended operating schedule.
Starting events
Record pumps, compressors, motors, refrigerators and air conditioners separately.
Energy profile
Use measured bills, meters or interval data where available instead of relying only on nameplates.
Convert the essential backup load into nominal battery energy.
First calculate required backup energy: average essential load multiplied by backup hours. Then divide by the permitted usable battery fraction and expected discharge-path efficiency. Keep an operating reserve if the project requires it.
Illustration only: an 8 kWh essential-backup requirement, assuming an 80% usable battery fraction and 90% discharge-path efficiency, gives 8 ÷ (0.80 × 0.90) = 11.1 kWh of nominal battery energy. The final value depends on the selected battery, settings, temperature, aging allowance and required reserve.
Energy is not power
A larger kWh battery can extend runtime, but its BMS and cells must also supply the required kW.
Compatibility
Confirm voltage range, current, CAN or RS485 protocol, firmware, parallel limits and protection.
Runtime
Treat calculated runtime as a planning estimate, not a guarantee, because real loads and losses vary.
Estimate PV power from daily energy and the site's usable solar window.
A planning formula is PV array kWp = daily energy kWh ÷ (peak sun hours × total system yield). Use credible local monthly or seasonal solar data and account for module temperature, orientation, shading, wiring, inverter conversion and battery charging losses.
Illustration only: 12 kWh per day with 5 peak sun hours and an assumed 80% total yield gives 12 ÷ (5 × 0.80) = 3.0 kWp as a baseline. Additional array capacity may be needed for poor-season production, battery recovery, daytime loads and future expansion.
Seasonal design
Check the weakest relevant solar month, not only the annual average.
String design
Keep cold-condition open-circuit voltage, operating voltage and input current within each MPPT limit.
Recharge objective
Define how quickly the battery should recover after an outage or overnight discharge.
Keep the assumptions visible so the recommendation can be checked.
Consider a planning case with 4 kW maximum simultaneous running load, a 6 kW short starting event, 12 kWh daily consumption and 8 kWh of essential backup energy. The inverter must support at least the 4 kW continuous demand and an explicitly documented 6 kW surge for the required duration. The illustrative battery result above is 11.1 kWh nominal, and the illustrative PV baseline is 3.0 kWp.
This is not a final package. Phase, voltage, motor-start behavior, inverter derating, battery current, PV string limits, local solar data, backup scope and applicable electrical rules can all change the equipment selection.
Do not round down
Choose available equipment only after confirming continuous, surge and environmental limits.
Coordinate controls
Confirm grid charging, solar priority, generator input, export limits and load-shedding strategy.
Document the basis
Keep the load list, formulas, assumptions and selected datasheets with the proposal.
Send complete project inputs before requesting a final quotation.
Provide the destination country, phase, voltage, frequency, load list, starting surges, operating hours, daily kWh, required backup duration, local solar data, roof or ground area, grid and generator conditions, installation environment, quantity and delivery schedule.
Electrical
Single or three phase, voltage, frequency, grid quality, generator rating and essential-load circuits.
Site
Temperature, dust, humidity, altitude, shading, cable distances and indoor or outdoor location.
Commercial
Quantity, destination, documentation, certification, OEM, packing and delivery requirements.
Product data and related evidence.
Use these public sources to verify the model facts used in this guide. Final order specifications still require written confirmation.