by Russell French, Australia Sales Director, Enphase Energy
Solar technology should be simple and affordable; however, homeowners and businesses often find themselves facing high costs and lengthy timelines during both the design and the installation process. Microinverters present a solution.
Typically, solar systems are custom-designed following a detailed site visit that analyses the impact of shade at different times of the day and year, as well as the planar orientation of roof surfaces and general climatic conditions. Additionally, the direct-current (DC) wiring found in central inverter systems requires a variety of speciality electrical components such as combiner boxes, large wire sizes and conduits. This can result in an overly complicated and laborious design and installation process.
It was exactly this combination of cost and complexity that faced Enphase Energy’s co-founder, Martin Fornage, when he bought a photovoltaic (PV) solar system for his home in 2006. After seeing how the string inverter system worked, Mr Fornage decided there must be a way of building a more efficient and more effective solution.
This was the catalyst for creation of the world’s first commercially-available microinverter, which was launched by United States-based Enphase in 2008.
Desperately seeking: an easier design and installation process
Microinverters simplify the solar experience, because the microinverter design process is as simple as dividing the available roof space by the size of a solar panel and ordering the same number of microinverters. Installers using this system do not have to spend time designing around shade, different roof orientations or multiple string sizes.
Microinverters require fewer electrical components than traditional inverters, and they are not limited by perfectly-matched solar panels. As a result, installers have stated that microinverter systems can reduce system design time by more than 40 per cent.
The installation process is reasonably simple; microinverters are bolted on to the same racking that is in place for the solar panels. Microinverters remove the need to find a place to install a central inverter, which in larger installations can require pouring a concrete pad and building an air-conditioned hut with a chain-link fence surrounding it.
Advancing performance, reliability and safety
Microinverters are the first technology to transform low-voltage DC to higher alternating-current (AC) voltages. Every module is connected in parallel and operates as an independent power producer.
Designed to optimise the power conversion process, microinverters attempt to ensure that if one panel suffers from environmental interference or failure – from shading, dust and debris, non-uniform temperatures or sub-optimal irradiance angles – it doesn’t affect the entire array.
DC circuits used within a central inverter solar system can generate and sustain electrical arc faults of considerable intensity, presenting shock and fire risks. This is because the solar panels continue to produce high-voltage electricity even when the circuit breaker has been shut off.
Microinverters, on the other hand, enable an all-AC system that eliminates the risk of DC arc faults. Each microinverter is utility-interactive, meaning the disconnection from utility power by shutting off the circuit breaker automatically results in the complete shutdown of every solar panel.
The evolution of AC modules
The logical next step is to integrate microinverter technology directly into solar panels; AC panels further simplify the design and installation of solar systems, reducing the overall cost of solar.
Even though AC panels seem a natural evolution of microinverters, it’s crucial that technology is tested and proven as a stand-alone solution before integration into a solar panel.
Whether it’s a stand-alone microinverter or module-integrated, the trend toward microinverter technology is happening today in the global solar market. In the United States, for example, microinverters have increased their market share over the past few years.
Russell French has 17 years’ experience and full qualifications in the Australian solar power and electrical industries. Prior to joining Enphase, Mr French was Managing Director for Sun Empire Solar Systems, where he was responsible for company management and business operations.
A microinverter installation case study from the United States
When the St Louis Cardinals baseball team in the United States decided to install a photovoltaic (PV) system at its home base, Busch Stadium, it requested a solar system that would provide detailed performance reporting. Module-level monitoring was also a necessity for the stadium’s operations staff, who would be responsible for the system’s long-term performance.
Additionally, safety was a major consideration during the install; Busch Stadium, with a seating capacity of nearly 48,000, hosts baseball games, concerts and other events that attract large audiences. The three solar arrays for the project were to be located in high-traffic areas within close proximity to the public; this meant that a PV system incorporating high-voltage direct-current would not be an option.
Project manager Microgrid Solar says that there was a need for multiple arrays within the stadium, with different azimuths and tilts, necessitating the use of microinverters. Eighty-eight 240 watt (W) modules placed on the roof of the stadium’s ticket building required zero tilt; eighteen 235 W modules on top of the concession stand canopy are tilted 10 degrees. In addition, there are four modules positioned with 33-degree tilt on an awning over an interpretive display.