Editor's Note: Scientific American's George Musser will be chronicling his experiences installing solar panels in Solar at Home (formerly 60-Second Solar). Read his introduction here and see all posts here.
Just last week, I blogged about how the future would bring solar panels with built-in electrical inverters, greatly simplifying the design and installation of solar arrays. Well, the future is here already. Two days after my post, California installer Akeena Solar announced that Lowes's California stores would begin selling Andalay solar panels that, because they incorporate an inverter, output AC power rather than DC. “AC modules will be one of those technologies that change things,” says Andrew McCalla, CEO of Meridian Solar, the leading installer in Texas.
Most solar installations today consist of a string of solar panels wired in electrical series to a centralized inverter. Cables carry DC power from the roof down to the basement, where the inverter converts the current to AC and feeds it into the service panel. But as I discussed in an earlier post, this setup is very restrictive: to avoid an electrical mismatch, the panels must all have the same orientation with respect to the sun. The situation is analogous to old-style holiday lights wired in series. Either all of them light up, or none.
In my case, I can fit put 15 panels on my roof in such a way that they have the same orientation, even though there is room for another six at a different orientation. You might think that I could wire those six to a separate inverter, but six panels would not produce a high enough voltage for a centralized inverter to convert to household current.
The solution is to give each panel its own inverter, known as a microinverter. The Andalay panels produce 208 or 240 volts AC (depending on the model) and you wire them together in electrical parallel, which lessens their sensitivity to one another's output. Each inverter optimizes the power output of its panel. "These microinverters are great because they allow you to max-power-track by the module," says Chris Anderson of Borrego Solar, a large commercial installer.
You can stick each panel on at whatever orientation you want. You can have an array of one panel or as many as 21. Not only does this let you fill out your roof, it allows you to install panels incrementally as your budget permits and as technology improves. Because precision alignment is less important, advanced DIYers could install panels on their own. Loosely speaking, AC panels are to DC panels what window air-conditioners are to central a/c.
To be sure, there are risks, too. Good design is still crucial to ensuring the best performance, and most people should still leave it to the pros. Anderson says that a pilot project in Mill Valley found that microinverters had a higher failure rate than centralized inverters. For a large commercial installation, their maintenance costs could outweigh the benefits. But homeowners should investigate these new devices, whether by Akeena or another company. I plan to use them myself in a few years to expand my system.
Andalay AC panels on a Habitat for Humanity installation, courtesy of Akeena Solar