When selecting an off-grid [inverter]{.underline}, the following technical parameters are critical: system voltage, output power, peak power, conversion efficiency, switching time, etc. These parameters significantly impact the electrical demand of connected loads.

System Voltage

This refers to the voltage of the battery bank. The input voltage of the off-grid inverter must match the output voltage of the [controller]{.underline}. Consistency between the inverter and controller is essential during design and selection.

Output Power

Off-grid inverters specify output power in two ways:

Apparent Power (VA): Commonly referenced from UPS standards. The actual active power output is calculated by multiplying the apparent power by the power factor. For example, a 500VA off-grid inverter with a [power factor]{.underline} of 0.8 provides 400W of active power, suitable for resistive loads like lights or electric stoves.

Active Power (W): Directly specifies the usable power. A 5000W off-grid inverter delivers 5000W of active power.

Peak Power

In photovoltaic (PV) off-grid systems, components like solar panels, batteries, inverters, and loads form an [electrical]{.underline} system. The inverter’s output power depends on the load. Inductive loads (e.g., air conditioners, water pumps) with motors require 3-5 times their rated power during startup. Peak power defines the inverter’s overload capability.

The inverter supplies startup energy from batteries or solar panels. Excess energy is provided by internal energy storage components—[capacitors]{.underline} and inductors. Capacitors store energy in an electric field, with capacity determining stored charge. Inductors store energy in a magnetic field, where the [inductor]{.underline} core’s permeability and inductance dictate energy storage capacity.

Conversion Efficiency

Off-grid system efficiency includes two aspects:

Inverter Efficiency: Off-grid inverters involve multi-stage power conversion, resulting in lower efficiency (80-90%) compared to grid-tied inverters. Higher power ratings, high-frequency isolation, and higher system voltages improve efficiency.

Battery Charge/Discharge Efficiency: Depends on battery type. When solar generation aligns with load demand, energy bypasses the battery, reducing conversion losses.

Switching Time

Off-grid systems operate in three modes: solar, battery, and grid. When switching from battery to grid due to low charge, the transition time matters:

Electronic Switching: Completes within 10ms, preventing desktop [computers]{.underline} from shutting down or lights from flickering.

Relay Switching: May exceed 20ms, risking computer shutdowns or restarts.