What is an AC solar panel?

Solar panels generate DC electricity, but more companies are selling AC solar modules. In this article, we’ll explain what these are.

Example of an AC module (Courtesy Panasonic)
Example of an AC solar panel (Panasonic HIT)

Solar panels are magical things that turn sunlight into electricity. The electrons that flow out of a solar panel move in a steady stream, known as direct current (DC).

But because Nikola Tesla and George Westinghouse triumphed over Thomas Edison in what is now called The War of the Currents (they even made a movie out of it!) we use alternating current (AC) in our homes instead of DC. This means that the DC electricity generated by solar panels needs to be converted into AC before your home can make use of it.

These days, you’ll find some manufacturers selling AC solar modules (aka solar panels), and more and more are jumping on the bandwagon. But what does that mean?

An AC solar panel is one that has a microinverter built-in. The microinverter converts the DC power generated by the solar cells into AC power. Because this conversion happens immediately at the module, an array that uses AC solar panels will send AC power into your home rather than DC. This saves time and labor costs, because the installer doesn’t need to handle the inverter installation.

If you’ve read our guide to solar inverters, you’ll know that the inverter is a critical piece of hardware in a home solar system. If you’re not familiar with how these work, you should read the full article, but here’s a quick explainer on the different types.

Crash course on solar inverters

There are different types of solar inverters, and choosing the best one for your home is one of the key decisions you’ll need to make when designing a system with your contractor.

There are three main types to consider:

  • String inverters are centralized inverters that handle the output for a group of solar panels. Large systems may need more than one inverter. The main advantage of a string inverter is lower cost, but the tradeoffs are that a string inverter-based system can have trouble with shaded roofs, and you’re unable to monitor the output of individual solar panels.
  • Power optimizers are based around a central string inverter, but with this type of system each solar panel is paired with a small electronics module called a power optimizer. The optimizer allows the system to better handle shading, and lets the system monitor each panel individually.
  • Microinverters do away with the central string inverter entirely. Instead, each solar panel is paired with a miniatured inverter that handles the output for that panel. This makes for the most flexible system available, but at a higher cost.

With either a power optimizer or microinverter system, an electronics package is mounted on the rear of each panel by the installer. While this adds some cost, for many situations the payback in higher efficiency is worth it.

Here’s a summary:

string inverter• Least cost• Least effective in shade
• Single point of failure
• May limit future system expansion
power optimizers• Handles shading well
• Panel-level monitoring
• Expansion limited by string inverter
• String inverter is single point of failure
• Some components are exposed to the elements
microinverters• Handles shading well
• Panel-level monitoring
• Single failures do not impact system
• Easiest to expand in the future
• Highest cost
• Units are exposed to the elements

So what is an AC solar module?

An AC solar module - also known as a solar panel (the terms are used interchangeably) - is simply a solar panel with a microinverter mounted at the factory. This means that if you go with AC solar modules, there’s no need to choose an inverter system, as the inverter choice is already made.

In most cases, the solar panel manufacturer isn’t making their own microinverter, but instead partnering with an inverter company. For all AC modules currently on the market that we know about, the microinverter is supplied by Enphase, which is the leading company in this segment. The one exception is LG, which is producing their own microinverter for their NeON R ACe panel.

List of AC solar modules on the market

Enphase is the largest microinverter company, and they’re currently partnering with three solar panel companies to jointly produce AC modules. These include:

  • SunPower. The SunPower Equinox panel combines a panel based on SunPower Maxeon cells with an Enphase IQ 7XS microinverter.
  • Panasonic. The Panasonic N330E HIT AC panel pairs a 330 watt heterojunction panel with an Enphase IQ 7X microinverter.
  • Solaria. Solaria is a lesser known American solar panel manufacturer, but they make excellent panels that compete with SunPower products and others in the high performance end of the market. Solaria’s PowerXT AC Module comes with the Enphase IQ7+ microinverter.

Finally, LG Solar makes the NeON R ACe series, which pairs their excellent NeON R panel with a custom LG microinverter. The highest wattage for this series is 375 watts, placing it at the high end of efficiency.

Pros and cons of AC solar modules

There’s some potential advantages with the modules. First, because the solar manufacturer is purchasing the microinverter in large volumes, they can get the equipment at a lower price than the average consumer or solar installer.

The other big advantage is labor savings at installation time. Because the panel leaves the factory with the microinverter pre-installed and wired, there is less work for your solar installer to do. This means faster installation time which, in theory, should result in lower labor costs that are passed onto you.

Finally, the warranty that comes with an AC solar module is often better than what you’ll find with a conventional solar panel. While Enphase microinverters normally come with 25 year product warranties, most solar panels have separate product and power warranties.

The power warranty for a solar panel guarantees a certain power output, but only if the product is still working. An actual failure of the panel is covered by a separate product warranty, which in some cases can be as short as 10 years.

However, every AC solar module that is currently on the market (that we know about) comes with a 25 year product and power warranty. This means that if either the microinverter or the panel fails after 24 years, that failure will be covered by the warranty.

Disadvantages of AC solar modules

The downsides of AC solar modules are really the same as any microinverter system. Microinverters cost more than a central string inverter. And while Enphase microinverters have long warranties and should give trouble-free operation for up to 25 years, earlier Enphase products (mainly the M-series) had a reputation for early failures. While reports from solar installers seem to indicate that the newest Enphase products are much more reliable, it’s hard to predict whether they will continue to hold up through a couple decades of operation.

Finally, there’s a special consideration with the LG NeON R AC module. LG previously partnered with Enphase on LG’s AC module - you might find older versions of this panel on the market that used the Enphase IQ6+ microinverter - but it looks like that partnership has ended. With their latest AC module, LG has seemingly decided to develop their own custom microinverter and monitoring software.

There’s risks to this approach. Enphase has been in business for many years and has gone through several product iterations, giving them a chance to work out the bugs in their microinverters. While LG is a massive consumer electronics company and there’s no doubt that they know how to make electronics, engineering a quality microinverter involves some special considerations.

Unlike a television or kitchen appliance, a microinverter needs to operate trouble-free for 25 years or more. It needs to withstand extreme weather conditions: high heat, freezing cold, high winds, and soaking rains. While many installed microinverters do benefit from being sheltered between the panel and a rooftop, microinverters on ground mounted panels don’t receive the same benefit, and will experience high winds and driven rain.

If this is the first iteration of LG’s microinverter, there’s a higher risk that they won’t have figured out how to build a 25 year product on their first attempt.

Basically, what I’m saying is that you might not want to take a risk by going with the LG AC module series. (That said, the LG NeON R is an excellent panel, so you could think about having your installer pair it with an Enphase inverter.)

AC modules: maybe a good way to save money?

Solar panel manufacturers struggle to find ways to differentiate their products, so it’s great to see them bring new products like AC modules to the market.

For the homeowner, the main potential benefit is cost savings compared to purchasing solar panels and microinverters independently, and lower installation costs.

Whether these theoretical cost savings actually materialize for you will depend on your solar installer. Shopping tip: have your installer quote you an installation using AC modules and also with conventional panels and inverters. If your installer doesn’t pass any savings onto you, then there’s less of a reason to choose AC modules (or you should get quotes from another installer).

#Panel Technology #Microinverters

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