New Micro-Inverter Technology for 2012

As a Product Manager here at altE, I recently had the opportunity to attend an Enphase training and chat with their reps regarding their plans for new products in 2012. Enphase Energy has become the first company to successfully manufacture, market, and sell the “micro-inverter”. For the past three years they have modified and changed their hardware numerous times in an effort to streamline the micro-inverter system.

If you’re not familiar with the Enphase micro-inverter and why it is special, here is a quick run down. In the past, grid-tied solar electric systems (also known as photovoltaic or PV systems) have had the same general layout. The system has a single DC to AC inverter, which converts the DC voltage being generated by the solar modules to AC voltage that is fed back into the power grid. The micro-inverter changes this layout, by attaching a small inverter near each solar module (generally they are attached to the module racking system). The micro-inverter’s attachment cables connect to the solar module and it converts the DC voltage being generated to AC voltage right there at the module. The AC output can be combined with the outputs of other modules into a single circuit and fed back to the power grid.

There are benefits to having a system layout with many small inverters instead of a single large inverter. First, it gives the system reliability by not having a single point of failure. If a module or an inverter is having an issue, it only affects the output of one module, as opposed to the entire system. In a single large inverter system, if one solar module is being shaded, it negatively affects the output of other modules in the system. The micro-inverter decentralizes this so that if one module is being shaded, the output of that particular module is the only one that will drop. A multiple inverter system also gives the flexibility to start small, maybe with just a few inverters, and then grow piece by piece.

Enphase has changed their systems a little bit each year, and 2012 will be no exception. They are calling their next line of technology the AC Module, “ACM” for short. The ACM micro-inverter will actually be attached directly to the junction box on the back of the solar module. The Enphase reps also referred to this setup as a “back sheet mounted inverter”. Now this won’t work with just any old solar panel! Enphase has been working with manufacturers like Sharp, Yingli and Trina Solar to create a specialized junction box on the back of the solar module that will plug right into the ACM directly. There has been discussion on whether or not the ACM will be sold already pre-installed with the solar module, or if the two components will be sold separately. Based on export charges for AC vs. DC products out of China, they seemed to be leaning towards the specialized solar module and the ACM micro-inverter being sold separately.

Enphase is still in the process of ironing out some minor design details. They’ve had to tweak their passive cooling system to keep things from getting too hot underneath the module and are still solidifying design plans with module manufacturers for the specialized junction boxes. It will be exciting to see this new step in micro-inverter technology. A back sheet mounted inverter could be the next sweet thing to streamline solar installations. Enphase says they are on track to have these out the first part of next year, so hopefully we’ll see the ACM sooner rather than later in 2012.

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11 Responses to New Micro-Inverter Technology for 2012

  1. Bill says:

    Dear Joey,

    Can the A.C. output of Enphase micro-inverters be connected to the A.C. output of 2 Outback 3000W FX3048T 48VDC/120VAC Inverters stacked in series?

    Note: This system would NOT be grid-tied.

    This system would be more efficient than if no micro-inverters were used.

    • Joey says:

      Hi Bill,

      The answer is no, micro-inverters cannot function in off grid systems. In order for an enphase micro-inverter to work, it must sense the 120VAC power grid present on the AC connection side.

      In the event that the power grid shuts down, all grid-tie inverters have "anti-islanding protection" which keeps the inverter from electrifying the power grid when it's possible someone could be working on it. Due to this built in protection, the inverter automatically shuts down if the grid connection is not present.

      On the other side of this connection, the Outback inverter would require a steady AC supply at the AC input (like a generator). The enphase inverters provide short "bursts" of AC power, but nothing that would be able to run an AC charger or loads.

      Thanks, Joey

  2. Seems like an obvious evolution of the solar panel. I'm surprised that it hasn't been done sooner and integrated into the panel. The start small and grow with your needs options seems compelling. I've upgraded my panels 4 times in six years. So I have several different briads and sizes of panels - and the innefficiencies that go with such an approach. It sounds like this approach (assuming I don't pay the price in DC/AC conversion efficiency) would eliminte the probles of peicmeneal growth.

  3. John says:

    I think Enphase should be talking with Tyco and come up with a junction box that can be used on all modules. Or perhaps come up with a way for us to pre install the inverters to the back of the modules ourselves ie; to the frame. That would be a small step toward speeding up the installation, and it would still allow for better cooling.

  4. Aaron Scholten says:

    Wouldn't it be so much easier to just have an A/C power cord coming out of the panel, just like there would be for any other electrical appliance? No inter panel wires to mess with, or other string connecting issues to worry about. I would imagine installation would be a lot easier and cheaper as you essentially eliminate the whole DC side of it because it's 'self contained'. Sending A/C down the line is going to help a ton with line losses and the expense of huge copper wires to minimize the line loss too.

    With a system such as this no longer would you have to worry so much about panel matching, sizing, array voltage or any of that. As you want to grow, you just buy more panels, plug them in and go! Throw some MPPT into each 'module' and each panel is operating at it's own unique peak efficiency and you truly have a versatile system designed for maximum output under all conditions. This would truly be a huge leap in system design I believe.

  5. Harold Davis says:

    I am an electrical inspector and am now inspecting quite a few PV systems with micr-processors

    There is no information on these installations in the NEC ( National Electrical Code )

    Would it be possible to get some information on this new installation

  6. Rahul says:

    Do we need to Ground these ACM Microinverters when they are released in the future. Now they are using Wiley WEEB for grounding right?

  7. Joey says:

    Hi Rahul,

    The grounding of the module will be specific to the model/brand that you are working with. If the ACM is a true AC Module (with an attached AC junction box that is a permanent part of the module itself), it should be wired with an AC grounding cable that will come directly from the junction box itself. However, the frame of each module and each rail in the system will still need to be grounded as well.

    Some of the ACMs coming out have an integrated grounding wire running from the module frame and tied into the module ground in the AC junction box. This would allow an installer to use a WEEB clip that is essentially "upside down" and biting into the module frame and rail. In this setup, the rail would be grounded to the module frame, which is already grounded to the internal AC junction box ground.

    The modules that do not have the "built in" frame grounding can be grounded with a standard grounding lug (using a lug on each rail too), running a grounding conductor through the lugs, and then combining this "module frame ground" with the "module output ground" from the array's AC circuit to have a single system grounding conductor from the roof.

    The moral of the story is to always READ THE MANUAL for the specific AC module that you are installing. Each manufacturer will most likely have specific instructions for grounding their modules safely.

    Kind Regards,

  8. Joey says:

    Hi Harold,

    John Wiles has written a great article on AC Modules for the International Association of Electrical Inspectors. I've included a link to the article on their website, hopefully it can help clarify some of their details regarding the NEC.

    Kind Regards,

  9. Actually micro-inverters have long made sense specially for rooftop captive solar power plants. The only problem is that thus far they have been an unreliable technology, but that's changing very fast and soon the big old box inverters will be replaced even in MW size projects. It just makes sense

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