Integrator Perpectives on Module-Level Power Electronics

Integrators weigh in on equipment advances, market variables and NEC requirements that impact the sale and deployment of module-level power electronics systems in the US.

Seven years have elapsed since Enphase Energy released its first-generation microinverter system in July 2008, a launch that for practical purposes created the modern module-level power electronics (MLPE) product class. In the ensuing years, microinverter products from vendors including ABB, APS, Darfon, SMA America and SolarBridge Technologies (acquired by SunPower) have entered the US market, as well as module-level dc optimizer products that include systems from SolarEdge Technologies and Tigo Energy.

As the MLPE class has evolved, string inverter manufacturers have been hard at work refining and enhancing products with new features such as dual independent MPP trackers and wide voltage input windows. These upgrades make string inverters and their centralized, off-the-rooftop power conditioning and optimization more flexible in terms of array layout, and more competitive with some of the benefits MLPE has historically offered, such as shade mitigation and the ability to configure source circuits (ac or dc) with different numbers of modules.

Integrators have experienced the highs and the lows associated with the development and deployment of MLPE. I reached out to several integrators across the US to get their perspectives on the past, present and future of module-level systems.
 

How would you characterize your experience with MLPE systems?

Over the last 7 years, Sun Light & Power has dabbled in several MLPE products and deployed others in earnest. We had an early interest in microinverters, especially for residential projects, but we experienced a relatively high failure rate in the field. DC optimizers seem more reliable, with the inverting taking place off the roof and in a centralized device.

We have designed hundreds of systems with Ampt, Enphase Energy, HiQ Solar, Maxim, SolarBridge Technologies, SolarEdge Technologies and Tigo Energy module-level products. The majority of our recent experience has been with Tigo and HiQ, with about 100 systems built. We have become more interested in string-level MPPT devices such as Ampt String Optimizers and HiQ TrueString inverters for commercial systems and have been moving away from module-level devices for projects other than residential rooftops.

On my house I have Tigo optimizers on a 3 kW system that overproduces compared to modeled performance. It has two additional monitoring systems; as an engineer, I like to have all of the data. The PV system powering the Sun Light & Power headquarters uses the HiQ 208V Mini Inverter and HiQ Balancers. Since the HiQ Balancers provide MPPT for each module, we built the system from a medley of surplus modules without worrying about matching their electrical characteristics. Access to granular data from our rooftop array is very useful for testing.

The largest MLPE system we have designed and built is about 2,000 modules, just over 500 kW. In retrospect, the amount of data available is more overwhelming than useful.

—Blake Gleason, PE, director of engineering, Sun Light & Power, Berkeley, California

Technicians For Sustainability has installed more than 30 microinverter systems, the first in December 2008. Our experience is limited to Enphase and Power-One (ABB). We generally install microinverters in residential systems with less than 12 modules.

—Kevin Koch, president, Technicians For Sustainability, Tucson, Arizona

We have been installing systems using MLPE for about the last 5 years. We have projects with Enphase microinverters and SolarEdge optimizers and inverters, as well as LG and SunPower ac modules. We have roughly 400–500 MLPE systems installed, the majority of which are Enphase, although SolarEdge is quickly catching up. Our largest MLPE system is approximately 20 kW.

—Fortunat Mueller, co-founder, ReVision Energy, Portland, Maine

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