What Are AC Solar Panels?

| 9/11/2009 12:00:00 AM

What are AC solar panels? I always thought solar panels had to be DC, but now I’m hearing about new AC products. How well do these work? Are there any benefits to using them?

AC (alternating current) solar panels are a promising new idea on the photovoltaic (PV) market. The panels themselves still produce DC (direct current), but each panel would come with its own attached micro-inverter, which converts the DC to AC. The inverters also synchronize the output with the grid, allowing the modules to be grid-intertied. The micro-inverters replace the need for the single, centralized inverter currently used in solar-electric systems.

AC solar panels with integrated micro-inverters are under development by several companies, but are not yet in widespread use, so there’s no performance data from the field. Bob-O Schultze of Electron Connection, an installing dealer in northern California and southern Oregon says, “No one that I’m aware of is marketing AC panels at this time. What is available is something called an Enphase inverter. These are designed for use with individual 24-volt (nominal) PVs. You parallel as many inverters as you have PV modules.”

Solar modules with preassembled micro-inverters will be easy to install once they are available. The AC panels in production are touted as “plug-and-play” products, so installation costs should be considerably less. The installation process seems easy enough, but we are not aware of plans for making them available to DIYers. The modules connect together to form an AC branch circuit, which is wired to a breaker in your house’s main panel. The micro-inverters eliminate the need to calculate inverter string sizing, but installers will need to stay within circuit breaker and service entrance limitations.

The advantages for having individual micro-inverters, whether integrated with the solar modules or not, are several.

  • Increased performance. Each individual micro-inverter performs Maximum Power Point Tracking (MPPT) to optimize its panel’s performance under conditions of varying sunlight and temperature. While centralized inverters also have MPPT capabilities, they average the performance of an entire “series string” of connected PV modules. This means that if one panel in the group is shaded, dirty or not working, it degrades the performance of the entire string. In conditions that are less than ideal, the micro-inverter may increase performance of the overall array.
  • Problems with solar module mismatches or differing orientations are eliminated. Because the micro-inverters optimize output independently, you can use mismatched panels of varying watts, ages or types. With a centralized inverter, using mismatched panels is not recommended because they limit the performance of the series string to the lowest common denominator — the smallest or lowest performing panel in the group. Likewise, placing modules in differing orientations, for example some panels facing south, and others facing southwest, will no longer be a system design issue.
  • Incremental system installation. Another great benefit to the end-user is that you can start with as many panels as you can easily afford, and add to the system over time. You won’t need to worry about finding matching panels later on or having to buy a larger centralized inverter as your system grows.
  • No single point of failure in the system. When a centralized inverter fails, your whole system shuts down. With the distributed nature of the micro-inverters, if one of them fails, the others continue to operate. The Enphase micro-inverter has a 15-year warranty, and an operating efficiency of 95.5 percent, both of which are comparable or better than traditional inverters on the market.
  • Safer to install. Having a series of micro-inverters with AC output eliminates the dangers of working with high DC voltages (up to 600 V) on the rooftop.

As with any technology, there are many potential downsides. Here are several questions to consider.

Kelvin park
7/29/2011 4:21:58 AM

B Green Solar Power is dedicated to providing affordable alternatives which help eliminate our country's dependence on foreign supplied oil, contribute to a cleaner healthier environment and alleviate the effects of rising energy costs. Our goal is to educate individuals and businesses about today's pressing energy and environmental issues, and to offer them the opportunity to participate in making a positive impact on the world. http://bgreensolarpower.com/

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