Next-Generation Grid-Tied Inverters


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Inverter technology is progressing with the growing needs of the market. This SolarEdge HD Wave unit is listed to UL 1741-SA and has an integrated electric vehicle charger.
SMA was one of the early leaders in the batteryless GT inverter market and has continued to adapt to new requirements, with products like this UL 1741-SA listed Sunny Boy inverter.
Enphase Energy was an early adopter of microinverter technology and continues to develop next-generation GT inverters, such as this Rule 21-compliant IQ 6 microinverter.
AP Systems
Magnum Energy
Darfon Solar
Enphase Energy
OutBack Power
As battery storage becomes popular again, either for load management or backup, some companies like Darfon are offering integrated battery packages.

Before 1998, when a generous grid-tied PV rebate program was launched in California, the off-grid (battery-based) market dominated renewable energy installations, because they were often cost-competitive with bringing in utility power to remote sites. However, with the establishment of incentive programs for on-grid RE systems that tied into utility power and eliminated the need for batteries, a new market for batteryless grid-tied (GT) inverters emerged.

The first residential batteryless GT inverters were bulky (~200 pounds) and used low-voltage DC input. In 2001, German-owned SMA entered the U.S. market with its 600 VDC Sunny Boy inverters. Higher DC voltage inverters cut costs by allowing longer series module strings, fewer fuses, (sometimes) no combiner boxes, smaller-gauge wires, smaller and lighter inverter boxes, and higher efficiency. Soon DC and AC disconnects were integrated into inverter packages, again reducing installation time and equipment needed. The next evolution was integrating combiner boxes into DC disconnects and adding remote system monitoring.

Two decades later, new influences—such as more PV grid penetration (and thus the need to better support the grid), changes to net-metering programs, and renewed interest in backup power—are driving the latest developments in GT inverters.

Adapting to Greater Grid Penetration

Previously, with such a small amount of PV capacity on the grid, inverters were designed to simply shut down anytime there was a utility disturbance to ensure lineworkers’ safety. With U.S. PV installations now reaching more than 47 gigawatts of capacity, having PV systems go offline due to brief fluctuations in grid power isn’t desirable—it decreases grid stability. In some places with high concentrations of PV systems, such as California and Hawaii, new rules about how PV systems need to work with those grids have been established.

”Smart” PV inverters are designed to support the grid, including benefits like voltage and frequency “ride-through” (which allows PV systems to stay online during brief power fluctuations) and regulation; specified power factor; and soft-start ramp control. Rule 21 has been under development for California (and HECO Rule 14H for Hawaii) to address these smart inverter designs.

The first requirements address minor utility issues, such as voltage and frequency fluctuations that normally cause inverters to trip offline. Large-scale PV arrays can exacerbate the problem, affecting voltage and frequency even more. Voltage and frequency “ride-through,” which allow PV systems to stay online during brief fluctuations, is on the list of grid-support functions included in Phase 1 of Rule 21.


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