Choosing a Solar Power Inverter

Selecting a quality solar inverter is important; if your inverter fails, inevitably the whole system will shut down.

An inverter converts electricity from solar panels, DC through to AC. A small amount of loss can occur during this process. Inverter manufacturers specify a percentage of DC electricity that they can convert to AC electricity, often around 94%.

Paying for a slightly more expensive inverter will be money well spent, higher quality inverters produce more yield of AC electricity.

There are two types of inverters on the market today, string inverters and micro-inverters.

String Inverters

String inverters have existed longer than micro-inverters. For a residential solar power system, a unit can be mounted on a garage wall or close to a switchboard. Wires connected to the solar panels run through wall cavities through to the inverter.

The advantages of string inverters:

  • They allow for flexible solar panel configuration
  • They are Highly efficient (94% to 97.8%)
  • Economical
  • They allow 3 phase power demand
  • Offer monitoring access at the inverter and remote access

Micro Inverter

Micro Inverters (much smaller string inverters) have been on the market since the 1990's, only to become competitive with string inverters in early 2008.  One micro inverter is attached to the back of every solar panel you install and they perform the same function as string inverters. The main difference is that they convert DC electricity from just one panel into AC. An AC cable connects all the panels and sends the electricity through to your switchboard.

The advantages of micro inverters:

  • Inverter efficiency ranges from 95 to 96.5%.
  • They run silent.
  • The micro inverter will maximize each solar panels output, therefore panels will not need to be adjust to lower levels if other panels in the system are not performing. Therefore shading is less of an issue.  See how each panel is optimised with micro-inverters in the video below.

Inverter Warranties

Most string inverters will have a warranty of 5 years. You may have to pay more for a 10-year warranty, but this is highly recommended.

Micro inverter warranties range from 10 years to 25 years.

Over-Sizing Inverters

The reason you would oversize an inverter is if you are going to add more solar panels onto the system in the near future. For example, you might install 5kW of solar panels matched with a 6kW inverter, allowing you to add more when you need to.

Hint: Adding micro inverter panels to your system in the future means not having to worry about sourcing the right components for an older system, a consideration worth thinking about.

You want to make sure that the inverter is oversized within the inverter manufacturers recommendations. If not, the warranty will be considered void.

Under-sizing Inverters

Some engineers may select an inverter that could be up to 15% smaller than your solar panel array size. For example, you have 5.5kW of solar panels and a 5kW inverter.

Reasons for under-sizing an inverter could include the fact that smaller inverters cost less, therefore you could save money with an undersized inverter, and performance may not be compromised.

Solar panels often operate below the nominal rated power. Nominal rated power is the output of the module, however, these conditions are not always met under standard test conditions. Inverter efficiency is low when it operates at low power levels, so you might be better suited with a smaller inverter. Also because the output of the solar panels will decrease slightly over the lifetime of the panels, the smaller inverter will operate more efficiently than a large one once the panel output begins to decrease.

Chinese Vs European Solar Inverters

European brands are favored amongst solar engineers due their reliability and consistent build quality. Having said that, Chinese manufactured inverters are gaining ground and many Chinese brand inverters are becoming just as reliable as their European counterparts.

Some high quality European brands include:

  • SMA
  • Powerone Aurora
  • Xantrex
  • Fronious
  • Delta

Quality Chinese brands:

  • Samil Power
  • Grow Watt
  • Eversolar
  • Goodwe

High Quality New Zealand Inverter brands:

  • Enasolar

High Quality North American Inverter brands:

  • Enphase (micro-inverters)