Differences Between Grid Tied/Off Grid And Hybrid Inverters

OFF GRID SYSTEM

OFF-GRID INVERTERS: (Standalone system) do not have to match phase with the utility sine wave as opposed to grid-tie inverters. Electrical current flows from the solar panels through the solar charge controller and the bank battery bank before it is finally converted into AC by the off-grid-inverter.

NOTE: There`s no need for an inverter if you`re only setting up solar panels for equipment that runs on DC current. You will need an inverter to convert DC to AC for all other electrical appliances.’

OFF-GRID: Operating totally off the grid requires a large capacity battery array capable of powering the property during night time and periods of low irradiance in winter and an inverter capable of supplying the maximum load ever required at one time.

This requires a significant investment in PV modules, inverters and especially batteries which cannot normally be justified if there is a good quality grid connection available at the property. An off-grid system is well suited to rural areas with little or no grid connection but is unlikely to be a viable solution in a well-connected urban area.

Should however fixed connection charges for electricity become more common and higher then disconnecting from the grid may become a more viable option in the future.

GRID TIED SYSTEM

GRID-TIED INVERTER (GTI): What is the job of a solar inverter? They regulate the voltage and current received from your solar panels. Direct current (DC) from your solar panels is converted into alternating current (AC), which is the type of current that is utilized by the majority of electrical appliances.

In addition to this, grid-tie inverters, also known as grid-interactive or synchronous inverters, synchronize the phase and frequency of the current to fit the utility grid (nominally 50Hz). The output voltage is also adjusted slightly higher than the grid voltage in order for excess electricity to flow outwards to the grid.

Typical Grid-Tied Inverter System

GRID-TIED:  A pure grid-tied system with no storage or load management for a user with fixed rate power charge is a viable option for South Africa but the system will need to be significantly under sized to minimise the wasted energy generation as typically no surplus power can be exported.

Essentially the PV system has to be sized to generate only sufficient power for the base load during the day, i.e. the fridge, freezer, pool pump and other permanently on devices.

The low investment cost of a small PV system with a high self-consumption rate should make them quite attractive especially for households with family at home during the day.

HYBRID SYSTEMS

HYBRID INVERTERS: A Hybrid solar system combines the best from grid-tied and off-grid solar systems. These systems can either be described as off-grid solar with utility backup power, or grid-tied solar with extra battery storage during night time, low irradiance (overcast) or winter seasons. You don`t really need a backup generator, and the capacity of your battery bank can be downsized. Off-peak electricity from the utility company is cheaper than diesel.

Typical Equipment for New Hybrid Solar Systems

Typical hybrid solar systems are based on the following additional components:

• Solar Panels
• Charge Controller
• DC Disconnect (additional)
• Battery-Based (Hybrid) Grid-Tie Inverter Battery Bank