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In the know

Grid-tie Inverter or Hybrid Inverter – what’s the difference?

Solar power is more affordable than ever, making it an attractive option for many homeowners. If you’re considering installing solar power in your home (and you should, as it’s one of the most efficient and environmentally friendly power sources available anywhere), you may be wondering what type of solar system to choose.  There are two basic types of residential home solar setups to consider:

  • Grid-Tie Inverter system
  • Hybrid Inverter system

Grid-Tie Solar PV system – provides NO BATTERY back-up

A grid-tied solar system is still dependent upon your municipality’s electrical grid. The DC electricity generated by the photovoltaic (PV) panels is sent through a grid-tie inverter, which converts it to AC power that’s compatible with the grid.  While grid-tie solar is the cheapest option available, as the PV panels and inverter (along with fuses, disconnect switches, breakers, grounding equipment and surge protection) are the only equipment necessary, it is important to understand that your grid-tie system is only designed to supplement your day-time electricity usage by producing solar electricity while the sun is shining.

The downside to grid-tie systems is that you’re still at the mercy of the grid – when Eskom goes down due to a power outage or load shedding, your grid-tie solar system also goes down as there is no battery back-up provided for.  In other words, grid-tie solar PV is only designed to supplement your daytime electricity usage and save you money – it provides no back-up during a power outage.  It’s typically a better solution for commercial applications where the bulk of energy is used during the day and where the cost of a large battery-back up does not make sense for an energy intensive operation.

Hybrid Solar PV system – BACK-UP when the grid goes down

A hybrid inverter system gives you the best of both worlds.  With a hybrid setup, the solar battery is used as a backup in the event that the grid goes down.  Since it’s being used as a backup instead of full-time dependence, the battery discharges less frequently, which extends its life. This also means the battery needs to be replaced less often and saves you a packet.

Keep in mind though that the battery bank isn’t charged during a power outage – so it’s important to work with a renewable partner who will correctly configure your back-up system for you and ensure that only your critical loads are included on the battery back-up.  Other energy-draining and non-critical power loads like elements (geyser, kettle) are usually taken off the back-up load to protect your batteries.

Big energy guzzlers like electric element geysers should be converted to solar geysers which is a much more efficient and affordable solution, slashing around 30%-40% off your total electricity bill.

Once grid-electricity is restored or sun shines again on the panels, the batteries are recharged first if they were used for back-up, so that they are ready to provide back-up again at night or during power outages and load shedding.

While a hybrid inverter system is more expensive than a grid-tie system as you need to purchase a battery bank, it’s still much cheaper than buying your electricity from Eskom. It’s an ideal solution that ensures you have backup power in the event the grid stops working and with the great improvements in solar and battery technology – you’ll hedge your costs at R1/kWh and less for the next 15-20 years, rather than being at the mercy of outrageous Eskom increases and power outages.

The second reason why a hybrid solution (capable of handling power storage) should be considered is that all indications are that, in the medium term at least, Eskom’s ability to provide cost effective and reliable electricity is severely compromised. Hybrid systems can easily become off grid solutions, without the addition of more (costly) system components, provided that the initial system was installed with this as a possible future requirement in mind.  Solar power is already cheaper on a decentralised basis than Eskom can provide with centralised power generation.