Has the micro-inverter revolution begun?

About 10 per cent of inverters sold in Australia are micro inverters compared to 40 per cent in California. The likely switch to AC solar modules brings benefits, but won't be a silver bullet.

A glance through recent solar trade publications reveals a proliferation of advertisements from micro inverter suppliers. Micro inverters, which are embedded into PV modules or, directly adjacent on the roof top are clearly gaining popularity, but has an AC photovoltaics revolution begun, or is this just hype?

Micro inverters are not a new phenomenon to Australia. Back in the late 1990s, Pacific Solar were embedding micro-inverters into “Plug’n’Power” systems using BP Solar panels and although it was early days for roof mounted electronics. Although many are still operational today, it’s true that the heat stress caused an unsatisfactory failure rate and since Pacific Solar’s (unrelated) closure not long afterwards, micro inverters have been virtually unheard of.

Fast forward 10 years.

Micro inverters started emerging again, particularly in US markets and soon afterwards, several innovators in Australia started supplying them locally into a tiny market niche. With the benefits of hindsight and rapid advances in electronics, micro inverter manufacturers around the world ramped up production, convinced they had overcome the reliability and cost issues, and extolling the virtues of the product. Even the incumbent string inverter kings (SMA and PowerOne) launched micro inverter products.

Just three years later, it is estimated that around 10 per cent of all inverters sold in Australia this year will be micro inverters, hence the burst of advertising activity. Compared to an estimated market share of 40 per cent in California, it seems Australia could be on the cusp of a micro inverter boom.

Why?

Talking to solar integrators around the country it’s clear that with the dramatic fall in PV cost, balance of systems and installation costs are an area of increasingly intense scrutiny. Despite a higher cost per watt for micro inverters, many integrators are suggesting that the final installed cost of micro inverter based systems are equal and in some cases lower than string based systems. Data from US studies confirms this potential. Berkeley Lab released a report in July as part of the US SunShot program analysing data from PV systems installed between 1998-2012. Among many fascinating findings, the report noted that “among larger systems sizes (>10kW), no appreciable difference in installed price is evident between those with micro inverters and those with central inverters”.

A second issue is, of course, the eternal challenge of optimising system yield. Micro inverters have a natural advantage here because they provide module level maximum power point tracking; every single solar module gets individually optimised inversion, overcoming mismatch and variations in output caused by soiling, different degradation levels, and other real world variables including the solar killer – shading.

A 2012 National Renewable Energy Laboratory report quantified this in its own testing suggesting yield benefits of 3.7 per cent to 12.3 per cent were likely from micro inverter based systems, validating the claims of manufacturers. Local testing facilities and pilot sites in Australia have found similar results.

This provides another clue as to why solar integrators are increasing selecting micro inverter based systems. With rapidly rising roof penetration rates (around 20 per cent nationally) the proportion of shaded, or non-optimal, multi-faceted roofs is increasing. Surveys conducted of installers over the last month confirmed this with suggestions that between 30-40 per cent of all sales enquires have shading of non-optimal roofs. This provides an ideal opportunity to use micro inverters as an alternative to a lost sale or, complex multi string installations using traditional inverters.

Lastly, there are the issues of safety and upgradeability. An AC based system has inherent Arc fault detection built into the inverter and reduces DC system voltages to 30-40V; a huge advantage. In the event of a module or AC system fault, micro inverters isolate each and every solar module and don’t technically require DC isolators (although the standards still require string isolation). In addition, the complete modularity of ACPV allows system owners to add panels one at a time, of differing types without the worry of string voltage or exceeding inverter power ratings.

The majority of micro inverter manufacturers sell their products as a retrofit option to suit any solar module. One company SolarBridge supplies to PV manufacturers only, preferring to embed their products into PV modules at the factory.

International and local solar market analysts predict that micro inverter market share will continue to grow as the price gap decreases, improvements occur and confidence builds in the technology; estimates are consistently for around 30 per cent of total inverter sales by 2017 on a global basis with some markets even higher.

Micro inverters and ACPV are not a silver bullet, but it seems that the market has figured out it’s an increasingly good option in a wider array of circumstances; and Australia has those circumstances in spades. Welcome to the ACPV Revolution.

Nigel Morris is the director of SolarBusinessServices.

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