Solar, Hybrid, ESS (Smart Hybrid), Off grid inverters - What to use were and whats the difference?

Different types of inverters do different things and have limitations on what there able to do. Thus making sure you have the correct one for your situation is critical otherwise your going to get rather disappointed on it's capability.

Note: This blog is about how they work, sizing of the inverters will be in another blog.

Grid Tie Solar Inverter

A grid tie solar inverter takes high voltage DC power from your solar array and converts it to AC 230 V (in NZ) to power your home. Any excess of power at any given time will export through your export meter to the grid. A solar inverter is an appliance and therefor is measured in kW. It produces active power (see Link to understand active power).

Note: A solar inverter does have a row of capacitors to mitigate reactive power but at a very low level.

When attached to the grid - A solar inverter will match the sign wave of the grid (AC 230 V in NZ) and sync with it. It will supply active power to your home or excess is exported to the grid. High reactive power required for your home will be draw from the grid and any active power above it's rating. ( See Link to understand reactive power).

When there's a power outage - A solar inverter will disconnect from the grid when there's a power cut, thus won't power your home. This is due to safety reasons. A solar inverter can't isolate it's self, thus could potentially shock a work person fixing the lines if it was exporting power.

Grid Tie Hybrid Inverter

A grid tie hybrid inverter works pretty much the same as a solar inverter but with the main difference of having 2 DC sources to power your home. One being the solar array and the other from high voltage battery's. Excess of power will charge the battery's first then export through your export meter to the grid. A hybrid inverter is an appliance and therefor is measured in kW. It produces active power.

Note: A hybrid inverter does have a row of capacitors to mitigate reactive power but at a very low level.

When attached to the grid - A hybrid inverter will match the sign wave of the grid (AC 230 V in NZ) and sync with it. It will supply active power to your home from the solar array or battery's or both and any excess power is exported to the grid. High reactive power required for your home will be draw from the grid and active above it's rating.

When there's a power outage - A hybrid inverter has the ability to be used as a "back up". It will disconnect from the grid then isolate it's self from the grid (Fronius is about 15 to 20 seconds to do this). Then it can be used to power your home from both the solar array and battery's. There are limitations of "back up". Hybrid produces active power thus any high reactive power required it will overload and shut down. In GB around 80% of homes have a water pump which is a high reactive load thus a hybrid would not be Fit For Purpose for most of GB. Hybrid inverters are excellent in city's were very little reactive power is used, but in rural areas this is not the case.

Note: Hybrid inverters are designed only to run in "back up" for a short period of time, as most power outages are in the hours not days. Run them in "back up" for to long they will fail. Also if your wanting to use induction hobs or any electrical motor appliance (water pump) in a "back up" situation you will need ESS (Smart Hybrid) system.

Example - Fronius 5KW hybrid inverter with correct battery storage peeks @ 5.17 kW

NEVER USE A HYBRID INVERTER OFF GRID - There not designed for it, warranty's will be invalid to do so, and it will die in a short period of time.

ESS (Smart Hybrid) Inverters

ESS or Smart Hybrids inverters are common know as transformer inverters. These inverters have a transformer inside. Transformer inverters are attached to low voltage DC battery's. It can take it's solar energy from either a solar inverter (AC Couple) or a low volt MPPT (Solar Controller). A transformer inverter is an power generator and therefor is measured in kVA. It produces active and reactive power.

When attached to the grid - A transformer inverter will match the sign wave of the grid (AC 230 V in NZ) and sync with it. It will supply active and reactive power to your home from the solar array or battery's or both and any excess power is exported to the grid. No power is taken from the grid within it's rating.

When there's a power outage - A transformer inverter has the ability to be used as a "On going back up". It will disconnect from the grid then isolate it's self from the grid (Victron energy is about 15 ms to do this, you won't even see a light flicker). Then it can be used to power your home from both the solar array and battery's. There are no limitations of " On going back up" you can run pretty much anything within its power rating. There is also no limiting time for a transformer inverter, as a power generator it can run in "On going back up" for days, weeks or months at a time.

Example - Victron Energy MultiPlus 2 5 kVA transformer inverter with correct battery storage peeks @ 9 kW.

Off Grid Inverters

Off grid inverter works pretty much the same as a ESS (Smart Hybrid) inverter. It has a transformer inside, attached to low voltage battery's has the ability to get energy from a solar inverter (AC Couple) or low voltage MPPT (Solar Controller). The main difference is it's rated for much higher peek loads / high reactive power. A transformer inverter is an power generator and therefor is measured in kVA. It produces active and reactive power.

As there's no grid a off grid inverter will make power 24/7 to the limits of amount of battery / solar power it has and it's rating. Most off grid power system require a 2nd source of power as a back up. This is normally a generator (petrol / diesel / hydro) or now days a EV car can also be used to charge the battery's.

Example - Victron Energy MultiPlus 5 kVA transformer inverter with correct battery storage peeks @ 10 kW.

Conclusion

Pending on what your situation is, you need to be mindful of the type of inverter you require to do everything you expect of it.

Keep it - Fit For Purpose.