01 / Direct answerChoose inverter power from the maximum simultaneous load and the largest starting surge.
Add the appliances that may run at the same time to obtain the required continuous AC power. Then identify the largest motor, pump, compressor or air-conditioner starting event and confirm that the inverter's surge rating supports both the magnitude and required duration.
For example, a site with 5 kW of simultaneous load and a 7 kW short starting peak needs at least 5 kW continuous output and a surge capability that explicitly supports 7 kW for the relevant duration. Capacity should not be selected from daily kWh consumption alone.
Continuous power
Total watts or kilowatts of equipment expected to operate at the same time.
Starting surge
Short-duration peak from motors, pumps, compressors and other inductive loads.
Design allowance
Allow for temperature, future loads and operating uncertainty without assuming a universal percentage.
Match the site's AC phase, voltage and frequency before comparing power ratings.
Confirm whether the site is single phase or three phase and document the required line voltage and frequency. A three-phase site also needs phase-balance information and identification of any critical single-phase loads.
Single phase
Common for homes and smaller commercial loads, subject to local service limits.
Three phase
Often required for larger motors, workshops, commercial buildings and balanced multi-phase loads.
Grid conditions
Record weak-grid voltage, outage behavior, export restrictions and generator use.
Check solar-array voltage, current and MPPT limits separately from AC output power.
The PV array must remain within the inverter's maximum DC voltage, MPPT operating range, start voltage, input-current limit and string rules under the site's expected temperatures. A larger permitted PV input does not increase the inverter's rated AC output.
Cold-condition voltage
Use module temperature coefficients to keep open-circuit string voltage below the inverter limit.
Operating window
Keep normal string voltage inside the applicable MPPT range.
Input current
Confirm string current and parallel-string count for every MPPT input.
Verify battery voltage, DC current and communication for the selected inverter power.
Approximate battery-side current rises as inverter power increases. A planning calculation is DC current ≈ AC power divided by battery voltage and conversion efficiency, but the final design must use the inverter and battery manufacturers' published limits.
Confirm the full battery operating-voltage range, continuous and peak charge or discharge current, BMS limits, CAN or RS485 protocol, firmware, cable size, protection and any parallel-battery requirements.
Voltage platform
Match the inverter's supported battery range, not only the nominal 48 V or 51.2 V label.
Current capacity
The battery bank and BMS must support required continuous power and surge current.
BMS protocol
Obtain written confirmation for the exact inverter and battery model combination.
Send measured project data for a defensible model recommendation.
Provide destination country, AC phase, voltage and frequency, a load list with starting surges, operating hours, required backup time, grid and generator information, proposed PV modules, battery model, installation environment and expected future expansion.
Loads
Running power, starting power, simultaneous operation and essential-versus-nonessential classification.
Energy
Daily kWh consumption and backup hours for battery sizing.
Site
Temperature, dust, humidity, altitude, indoor or outdoor location and applicable local 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.