Off-Grid PV Power Generation:-
Stand-alone PV power plants are not connected to the grid and consist of PV panels as power generators and a storage system which will guarantee electric energy supply when lighting is poor or is dark. Since the current delivered by the PV generators is DC (direct current) we will need an AC inverter. This Off Grid Inverter becomes the core of the BOS (Base of System) and in most of the installations works as a charger for the battery bank. In an Off Grid configuration the PV array it is over-dimensioned in such, during the high irradiation hours both the power supply to load as well as the recharge of the storing batteries can be guaranteed. Off grid inverters are designed to handle battery banks and external conventional generators (petrol base) at the same time.
Common functions build into Off Grid Inverters:
Charges Batteries While Supplying;
Cleans and Regulates Power Output;
Correlating with an External Petrol Generator Set;
Efficiently Handles Surge Requirements of Electric Motors and Pumps;
Choosing an Off Grid Inverter requests some of the Inverter specific values to be correlated to the PV array output, to the battery bank and even to the petrol based power generator set. Here is a list of Off Grid Inverter parameters:
Waveform (sine wave vs. modified square wave):-
Off-grid inverters are sold with two wave form options: sine wave and modified square wave (sometimes called “modified sine wave”). Sine wave output, has low total harmonic and are the most common used for residential systems. Modified square wave are used in budget type of installations (remote cabins and observation posts). They do not run some types of loads optimal and they may harm those appliances.
Total Harmonic Distortion (THD):-
Is the measure of how closely the wave form matches a perfect sine wave. A THD of 0% is a perfect sine wave, and the larger the percentage, the farther it deviates from a sinusoidal waveform. Sine wave inverters typically show a THD of 5% or less, while the THD of modified square wave inverters may range from 10% to 40%.
Rated Continuous Output Power:-
An off-grid inverter must supply enough power to meet the needs of all the appliances running simultaneously.
Nominal Battery Voltage(s):-
Each inverter has a nominal battery voltage where it can be connected to. Common off-grid inverter battery voltage options are 12, 24, or 48 volts. Exeltech’s line of inverters, for example, includes models that can connect to 32, 66, or even 108 volts battery banks.
United States based Off Grid Inverters are designed for 60Hz at 120V or 120/240V appliance (electrical load) voltage. So called export inverters are designed for 50Hz at 240V or 240V/380V.
Some loads (like motors) require significantly more power during startup than they need to run. To start these loads, inverters will briefly “surge” or run at higher than their continuous power rating. Surge ratings include the maximum amperage and a time period that the inverter can run at that high power level without sustaining damage or turning off to protect itself. Good number are in a range of 50Amps to 120Amps for 1sec.
Inverter Peak Efficiency:-
Efficiency is measured as the ratio of the inverter’s AC power output to the DC power input from the batteries. Higher efficiency means that the inverter wastes less power while converting DC into AC. Common values are in the range 90% up to 95% ( Xantrex - XW4024 works with 95% efficiency).
Some off-grid inverters include the capability to connect several units to operate as a single, larger unit. Stacking options allow 120 V inverters to work together to power 240 V loads.
The information posted herein has been compiled by Clean Energy Brands from OEM product data and reputable publications. All rights reserved!