Selecting a quality solar inverter is important; if an inverter fails 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%. Investing in an expensive inverter will be money well spent; higher quality inverters produce more yield of AC electricity and will last longer.
There are two types of inverters on the market today, string inverters and micro-inverters.
String inverters have been around a lot longer than micro-inverters. For a residential solar power system, a string inverter can be mounted on a garage wall or close to a switchboard. Cables 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%)
3 phase power demand is possible
Offer monitoring access at the inverter and remote access
Micro-inverters (much smaller inverters) have been on the market since the 1990's, but only became competitive with string inverters in early 2010. One micro inverter is attached to the back of every solar panel installed 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.
Solar panels can be individually monitored for performance
Most string inverters have a warranty of 5 years. Paying more for a 10-year warranty is highly recommended. Micro-inverter warranties range from 10 years to 25 years.
An oversized inverter makes sense if additional solar panels are going to be added onto a system in the future. For example, you might install 3kW of solar panels and a 6kW inverter, allowing double the amount of solar panels to be added at a later date.
Be sure that the inverter is oversized within the inverter manufacturers recommendations. If not, the warranty will be considered invalid.
Some solar 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 amount, as optimal solar generation conditions do not occur frequently. Inverter efficiency is low when operating at low power levels, so you might be better suited with a smaller inverter. Because the output of solar panels will decrease slightly over their lifetime, a smaller inverter will operate more efficiently than a large one (once the panel output begins to decrease).
Due their reliability and consistent build quality, European brands are favoured amongst solar engineers. Having said that, Chinese manufactured inverters are gaining ground and many Chinese brand inverters are becoming just as reliable as their European counterparts.
Quality European Brands Include:
Quality Chinese Brands:
Quality New Zealand Inverter Brands:
Quality North American Inverter Brands: