Enphase micros in commercial?

NOTE: THIS ARTICLE WAS WRITTEN BEFORE THE RELEASE OF THE ENPHASE IQ8P-3P AND IQ8H-3P. THIS ARTICLE IS BASED ON THE IQ7+ COMMERCIAL USECASE.

When it comes to residential and even small commercial installations, Enphase micro-inverters are still the go-to for many installers. It offers one of the most flexible and modular system in the market as of today, the IQ lineup of micro-inverters allow for panel-level optimization and monitoring, as well as a modular design that makes system modifications and troubleshooting easy tasks.

However when it comes to large commercial installations is not so popular, in this article I would like to review the "Why" as well as giving you some design considerations for your future projects.

Can Enphase micro-inverters work in a 3-phase system?

The short answer is YES, all of the IQ micro-inverters can be connected to a 3-phase electrical system. Even though the nominal voltage is in single phase (208V or 240V), each branch of micros can be connected to 2 of the 3 phases of a 120/208 3P-4W supply, as long as the branches are distributed in a way that the 3 phases have closely the same amount of micros (and very similar current). The goal is to avoid unbalancing the phases too much (check with your local AHJ and utility for specifics). but if done properly this should not be a problem.

What happens if the building uses 480/277V?

For anything different that 120/208V, a transformer must be used. This transformer should be a dry-type, general purpose and high-efficiency for example a 480DELTA:208Y/120V, a transformer will also provide some level of power-line filtering, as well as cost savings for long wire runs and the ability to make minor adjustments to the utility voltage using adjustable taps. The transformer must be sized based on the combined inverter output power and any derating factors that might be applicable. Enphase recommends using a DELTA configuration in the primary side of the transformer (utility side), even if it is a Wye configuration, this would reduce wire costs (no neutral), improves performance and reduce harmonics.

Where do the Enphase IQ micro-inverters struggle?

For large systems, specially for those with PV modules spread over a large area, micro-inverts that function at a single-phase, low voltage like 208V, struggle to keep voltage rise low. The Enphase Q Cable, designed with an aluminum #12 AWG wire, can introduce a voltage rise that can go from 0.1% all the way to 1.3% in the Q cable alone, this is important since the TOTAL voltage rise from the Point of common coupling (PCC) to the last micro-inverter at the end of the Q cable should no be more than 2% (and never more than 3%). This will force the designer to upsize the Inverter output circuit wire from #10 to #8 or even to #6 CU AWG. this usually also requires conduit upsizing from 3/4" to 1" or even to 1-1/4".

Another constraint to consider when installing a photovoltaic system is the maximum number of microinverters per branch. For example, in the case of IQ7 microinverters connected to a 120/208V system, the maximum number of IQ7s in a single branch is 13. This means that every 13 microinverters, a new set of wires must be run to an accumulation or combiner panel and protected by a 20A double-pole breaker.

For large commercial systems, the number of wire runs and conduits might be double compared to a system working with a higher voltage (400V+). In such cases, multiple accumulation panels might be required due to the large number of 20A, double-pole breakers needed. This helps to ensure proper protection and electrical distribution for the system. The use of multiple accumulation panels also helps to avoid overloading a single panel, which can result in malfunctions or failures in the system.

The IQ Commercial Gateway is a communication device that acts as an interface between different components in a photovoltaic system and the Enphase Enlighten platform. It processes and transmits information from the components to the platform. However, it imposes a limit on the number of microinverters that can be connected, with a maximum limit of 249 micros per Gateway. This means that systems larger than 249 micros will require multiple IQ Commercial Gateways.

When multiple IQ Commercial Gateways are used in a single installation site, it becomes necessary to segregate the microinverters and Gateway into a single accumulation panel and to add a Power Line Filter to prevent cross-domain communications between the units. The segregation of microinverters and the Gateway helps to maintain proper communication between the components and the platform, while the Power Line Filter is used to eliminate any interference or cross-talk between the IQ Commercial Gateways. This helps to ensure the accuracy and reliability of the information transmitted to the Enphase Enlighten platform.

When working with lower voltage systems like 208/120V, the current is higher compared to higher voltage systems like 480/277V. This results in the need for larger AC panels and disconnects, which can be both expensive and take up more physical space. The higher current also means that the electrical system components must be capable of handling the increased load, which can also contribute to increased costs. Additionally, the need for larger components and increased physical space may not always be feasible, depending on the availability of space and budget constraints.

What are the advantages of using Enphase micro-inverters over other systems?

The advantages of using Enphase micro-inverters in photovoltaic systems are substantial and far-reaching, particularly when considering the system over its entire life cycle.

In terms of safety, the use of lower voltage AC wiring in Enphase micro-inverters significantly reduces the risk of arc-fault fires when compared to DC wiring. This is a crucial safety consideration, especially in residential and commercial installations.

Moreover, the built-in rapid shutdown technology in Enphase micro-inverters allows for immediate compliance with National Electric Code (NEC) 690.12, without the need for a separate third-party rapid shutdown system. This feature helps to ensure the safety of personnel and equipment in case of an emergency or maintenance requirement, and helps to minimize damage in the event of an incident.

Another major advantage of using Enphase micro-inverters is the module-level electronics and conversion that provides maximum energy extraction and monitoring capabilities. This not only makes the system easier to troubleshoot and maintain, but also helps to reduce the overall cost of the system over its 25-year lifetime.

Finally, the distributed architecture of Enphase micro-inverters eliminates the risk of single point of failure, further improving the reliability and longevity of the system. This, combined with the 25-year warranty, provides customers with peace of mind and a sense of security when investing in a photovoltaic system.

Conclusion:

In conclusion, Enphase micro-inverters offer a flexible and modular system for residential and small commercial installations. However, for large commercial systems, there are a number of design considerations that must be taken into account. Firstly, the Enphase IQ micro-inverters can be connected to 3-phase electrical systems, but the nominal voltage is single phase (208V or 240V). The system may require a transformer for voltages other than 120/208V, which must be sized based on the combined inverter output power and any derating factors that may be applicable. Secondly, the Enphase IQ micro-inverters can struggle in large systems with PV modules spread over a large area, as the low voltage single-phase design may result in a high voltage rise. This can result in the need for larger circuit wires and conduits, which may require multiple accumulation panels and increase costs. Furthermore, the number of microinverters that can be connected to a single IQ Commercial Gateway is limited to 249, which means larger systems will require multiple IQ Commercial Gateways. Segregating the microinverters and Gateway into a single accumulation panel and adding a Power Line Filter is necessary to prevent cross-domain communications and ensure accurate and reliable information transmission. Finally, lower voltage systems like 208/120V result in higher currents and may require larger AC panels and disconnects, which can contribute to increased costs and take up more physical space. These design considerations must be carefully evaluated when installing a photovoltaic system with Enphase IQ micro-inverters in large commercial installations.