I am seeing an uptick in requests about Alternating Current Photovoltaic (ACPV) Modules. ACPV solar panels are traditional solar electric panels that have an inverter affixed to the back. The module assembly is UL listed as a complete assembly, and is essentially an appliance. Rather than output DC power that needs to be converted to AC for use in your home, the appliance puts out AC energy that can be connected directly to your home’s wiring system.
Despite what manufacturer’s may say, these are not the same as the “plug-and-play” solar panel concept, which doesn’t really exist. ACPV modules are still required to be connected to dedicated branch circuit wiring and fall under many of the same National Electric Code (NEC) requirements found under Chapter 690 of the NEC. They require a qualified professional to install, and are no less dangerous than a typical solar photovoltaic module. Some have argued that ACPV panels are the next evolution from the current microinverter revolution. Microinverters convert each solar panel’s energy to usable AC energy, but are not integral with the panel. They mount beneath the panel on rails or to the module frame in some cases.
So what are the pros and cons of ACPV solar panels?
- Simplified installation wiring – no DC disconnects required or DC combiner boxes.
- Simplified installation mounting – no microinverter to mount on rails or central inverter to mount on wall.
- Elimination of many NEC grounding requirements.
- Per-panel maximum power point tracking eliminates module mismatch losses, increasing energy harvest over string inverters.
- Reduces impact of shading on solar arrays. Allows installation on multiple orientations and pitches.
- No high-voltage DC electricity on roof, reducing shock hazard and potentially increasing firefighter safety.
- No high-voltage DC conductors run through attics and walls, possibly reducing arc-fault potential and severity and fire risk.
- Reduced chance for DC ground faults.
- Easy identification of under-performing and failed components.
- Per-module performance monitoring.
- Inverter warranty length typically exceeds string inverters (but not traditional microinverters).
- Failure of the PV module or attached inverter requires replacement of complete assembly, increasing shipping costs and complexity of service.
- Proprietary connectors on inverters – questions about long-term serviceability and availability of components.
At first glance it would seem that the pros greatly outweigh the cons. However, many of the pros are achievable with traditional DC solar modules with “traditional” microinverters (the word “traditional” is in quotes because microinverters are in their product life-cycle infancy, but this pair is essentially the same thing as a disassembled ACPV module). More importantly the cons offer significant questions about what happens down the road if warranty service is required.
While the DC component of an ACPV module is generally very reliable, there are still questions by many about the long-term failure rate of the microinverter component. With traditional microinverters, the inverter component can be replaced separately from the module. Furthermore, a DC module is likely to work with future technology iterations and can always be converted for use in different systems. The proprietary nature of an ACPV module requires that a matching replacement component be installed. Technically an ACPV module could be converted to a traditional DC module, but it’s unclear if it would be properly listed for that intended use and thus be code compliant for any installation other than an ACPV system.
Since the panel and the associated microinverter are manufactured by different companies, if the inverter manufacturer goes out of business, I assume the panel manufacture would be on the hook to produce replacement parts for warranty service. This could be difficult to do, but I assume that manufacturers have thought that through (I hope). Remember, you would presumably have to return the entire ~38″ x 65″, 50 pound solar module for warranty service to the solar panel manufacturer.
Conceptually, I love the idea of the ACPV module. It is one step closer to “plug-and-play” solar. It makes the job of solar installers very easy. Many of the great advantages of microinverters are incorporated, because ACPV modules are essentially microinverters permanently mounted to the panel. Unfortunately, I cannot recommend ACPV modules at this time due to questions about future serviceability and availability. Some of my colleagues will make the same argument against “traditional” microinverters, but I am convinced that a separate solar panel and inverter makes more sense at this time than an ACPV appliance. If the future of microinverters is bleak, and I don’t think it is, then at least there will be better options for servicing existing microinverter systems. The few cons of ACPV modules outweigh the many pros in my opinion when there are microinverter options available.
If you are convinced about the benefits of microinverters over central/string inverters, I would recommend going the microinverter route and avoiding ACPV solutions at this time.