Getting Down to Basics: AC Modules and DC Modules
One of the newest technologies on the solar market are AC modules (or AC panels). These are solar modules with microinverters already mounted on the back. Although they cost more, AC modules can be a great solar option for sites with shading and/or irregularly shaped roofs.
Here's how it works: Standard DC modules are connected in series to make one or more strings that feed into one or more inverters. Shading on one panel can affect the production of other unshaded panels in the same string. With AC modules, however, an inverter is mounted on each module, so shading on one module will not affect the output of other unshaded modules. For example, a tree might create shade on a single panel, and typically that obstruction would affect the output of the entire series-string of panels. With AC modules, the shade would reduce solar output for only the shaded panel(s).
Since AC modules are not constrained to stringing requirements, they can be added in any number to improve aesthetics and fully utilize roof space.
AC panels use what is called Maximum Power Point Tracking (MPPT) on a panel level, whereas string inverters use MPPT at the string level. Panel level MPPT extracts the maximum power from each module in the array and provides energy production insight that was once previously unavailable. Online monitoring with AC modules allows us to monitor the output production of each panel.
Sharp and SunPower AC modules come with 25 year warranties, versus the typical 10 year warranty for string inverters. Other advantages include a reduction of hardware and installation time. One drawback is that there are more units to fail. The part is warrantied, but the service would be an additional cost to the system owner.
"AC modules make a lot of sense in some situations," says solar sales consultant JP Plumlee. "It's an advanced technology that is made for roofs with less than ideal solar conditions."
LightWave Solar currently has three customers who have chosen to use AC panels, and their installations are underway.