Rooftop Solar and the Great Debate: Microinverters vs. String Inverters

Microinverters are said to be disrupting the industry by promising a 5-25% increase in output efficiency, however their greatest competitor, the ever reliable string inverter continues to dominate the market internationally.

The type of inverter you end up choosing is one of the most important decisions to make when looking to get solar, so it’s important to get it right and understand the pros and cons of both options.

What exactly is the inverter responsible for?

Firstly, before we get into string length and power optimisation, it’s important to understand exactly why inverters are important to your system. A solar inverter is often referred to as the ‘brains’ of a solar system due to the fact it is able to detect power input and output and subsequently guide electricity to your home, the grid or your battery storage.

They also are responsible for ‘inverting’ the DC (direct current) into grid compatible AC (alternating current). This allows for the electricity from your solar panels to become usable, as well as exportable to the grid.

Fronius Inverter

The Popular Choice: String Inverters

The first inverter to gain popularity was the central, or string inverter, which inverts all your electricity at a single point. The image above shows a Fronius inverter, as you can see, they are about the size of a meter box, if not bigger.

When a system uses a central inverter, the solar panels are arranged in ‘strings’, hence the name string inverter. This means that a number of panels are arranged in tandem, and direct power to the inverter using the same cables and circuitry.

For example, a 20 panel system will usually be arranged into 2 strings each containing 10 panels each.

The main issue people have with central or string inverters is that the entire array of panels usually have to be installed under similar conditions. This means that if a string of panels is partly shaded, the entire system will be compromised.

An easy way to understand this is to think about having a kink in a hose, it slows down the flow of water entirely. Similarly, if the array of panels is installed on multiple roof panels, this can have a negative effect on the system’s efficiency.

Another issue is being able to monitor the health of individual panels, as the inverter is usually responsible for providing system reports and feedback, as well as measuring the system’s overall output. However, central inverters can’t determine how each panel might be functioning as it receives power from each string simultaneously.

Many companies have begun producing monitoring equipment which allow for not only each panel to be checked up on, but optimised so that a system requires less strings. In fact, Tigo (a leading monitoring company) claims that it is able to increase string length by 20%.

This means that if Tigo monitoring equipment is installed alongside their respective panels, your system will require less “...combiners, fuses, disconnects, and copper home-runs per installed kW of solar”. Meaning you will save money on your system installation cost.

The New Kid on the Block: Microinverters

Microinverters have gained a lot of popularity in Europe and the US however have still not surpassed string inverters as the popular choice among consumers. The main reason for this being the cost, which is around 40-50% more expensive than your average inverter.

Couple that with the fact that microinverters are not as efficient as a standard inverter, it's easy to see why microinverters have not yet taken off in this sun rich country.

While there are many advantages to microinverters, it seems that the price point still outweighs the possible pros for a lot of people.

Firstly, microinverters minimise the chance of fire, and therefore are considered safer in many ways, however it's important to mention that monitoring systems allow for safety optimisation of string inverters for anybody worried about the possible hazard of a solar system.

More importantly, it is rarely mentioned that in the Australian climate, microinverters, which are positioned directly behind a systems panels, can often be destroyed by heat, despite minimizing fire risk.

While microinverters don't suffer the same fate in European climates, many dissapointed customers in Australia will end up having to replace system parts after a couple of years.

Microinverters are also capable of measuring the output of individual panels, meaning that monitoring software is not required. On top of this, microinverters are modular, meaning that additional panels can be more easily installed.

Another benefit of modularity is that if one panel is shaded or damaged, the entire system will not be compromised.

The Conclusion

In many ways microinverters are in a similar place to energy storage. They present a lot of benefits, however their price seems to much to ask. Standard inverters on the other hand are still a reliable and efficient option, and continue to be the favourite of new and existing solar owners.

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