Module-Level Rapid Shutdown for Commercial Applications: Page 5 of 6

What is less clear is whether commercially available MLPE can have the same success in nonresidential applications. Two charts from the “US Solar Market Insight Report: 2015 Year in Review,” published by GTM Research and SEIA, put  the challenge in stark contrast. The first chart compares average system costs by market segment (residential, nonresidential and utility). According to these data, average costs in the residential market segment were roughly $3.50 per watt in both Q4 2014 and Q4 2015, suggesting that it may be difficult for system integrators to drive costs out of residential systems while transitioning from string inverter–based to MLPE-based designs. In contrast, average costs in the nonresidential segment have steadily declined quarter over quarter, from roughly $2.20 per watt in Q4 2014 to about $2.00 per watt in Q4 2015. The gap between $3.50 per watt and holding, and $2.00 per watt and falling, is substantial.

The second chart compares installed PV capacity by market segment over time. These data show that the residential PV market is the fastest-growing market segment in the US, with more than 50% annual growth for 4 years running. By comparison, GTM Research describes the nonresidential solar market as “essentially flat for the third year in a row.” Here again, the gap between these two markets—one growing at a record pace and the other stagnant—is substantial.

When one considers these two data sets side by side, as shown in Figure 2, it seems fair to wonder whether the nonresidential PV market might contract, at least initially, under the cost burden of an MLPE mandate. While that mandate would undoubtedly prove good for some—perhaps paving the way for integrated ac PV modules, smart modules and other junction box– or cell string–level disconnection devices—it could be a net loss for the industry at large, especially for commercial project developers and EPC firms working in states that will adopt NEC 2017 early, such as Massachusetts and Colorado.

Supply bottlenecks are another concern. Today, commercial project developers have access to multiple product lines and vendors. If one of these vendors exits the market (as happened with Advanced Energy) or has supply-chain issues, system integrators can substitute compatible product platforms from other vendors prior to construction or even during operations. Though MLPE vendors have made great strides in recent years, this is nevertheless a relatively immature market, largely populated with vendors who offer mutually exclusive products. Innovation and proprietary interfaces, rather than substitutability and cross-compatibility, characterize the sector.

If an MLPE mandate went into effect today, project developers would likely be forced to either put all of their eggs into one of two baskets—Enphase Energy or SolarEdge (which dominate in terms of market share)—or qualify an alternative solution with a limited track record. This is not a recipe for resilience, but rather a precarious situation susceptible to market distortion. SMA’s partnership with Tigo, which the companies announced in April 2016, suggests that supply chain could be strategically important under an MLPE mandate. In exchange for acquiring a 27% stake in Tigo Energy, SMA obtains exclusive worldwide sales rights, for a period of 30 months, to Tigo’s TS4 R product platform, which is a retrofit solution designed to add MLPE functionality to conventional PV modules.

TECHNICAL VIABILITY

Many in the industry, myself included, believe that MLPE are inevitable and perhaps necessary in the long term. In spite of the technological hurdles, the vendors pioneering this space have largely proven their doubters and naysayers wrong. If we could fast-forward into the future, we would likely see that module-level and perhaps even cell string–level power electronics will prove the norm, perhaps sooner rather than later. Some industry experts even predict the eventual rise of cell-level power electronics. While today’s products work well, tomorrow’s more advanced products will work even better and more reliably.

What remains to be proven is whether MLPE are the most effective way to reduce shock hazards for emergency responders within the array boundary. Do MLPE perform better in this regard than other hazard mitigation methods? While solar and fire service stakeholders agree that rapid shutdown outside the array boundary reduces risks for firefighters, initial fire research and engineering evaluations suggest that current product safety standards do not eliminate shock hazards within a damaged PV array.

Fire research. In 2011, UL conducted the first experimental investigation of the impact fielded PV systems have on fire suppression, ventilation and overhaul activities. UL’s research engineers started by reviewing the literature and standards associated with electric shock, impedance of the human body, touch-safe voltage levels, and safe distances between water hoses and live electrical equipment. They then developed electrical and fire performance experiments that would identify and quantify the electrical shock hazard associated with specific PV-involved firefighting scenarios. UL published its findings in the report “Firefighter Safety and Photovoltaic Installations Research Project” (see Resources).

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