math challenge. In fact, it’s a subspecialty within the electrical trade, with installers trained to use “string calculators” that determine how many modules can be placed on a roof depending on factors like roof pitch and shading.
“The calculator might say you can put up three strings of four modules each,” says Nahi. “But then you superimpose that on the roof and you figure out there is no room. Then you go back and see if you can do two rows of five, and that fits, but then there’s a chimney that will shade one module for three hours a day, which you can’t have, because of hypersensitivity to shade. The process iterates. It’s all very unique to solar, and the calculations and the high voltages are the only reasons installers need to be specialists.”
With microinverters, all of those problems go away. Installers can put as few or as many modules on a roof as they want. If one module is partially shaded, that’s okay, since it won’t affect the others. “The traditional installers benefit because their job is now easier and faster, and there is an entire class of electricians and general contractors who can now participate in solar without hiring huge design teams and specialty electricians,” says Nahi.
Ben Kortlang says his firm wanted to fund Enphase mainly because the startup’s technology squares with Kleiner Perkins’ emphasis on easing deployment in cleantech. “Our thesis has been that rather than investing in the panel itself, we should invest in cheaper ways of getting systems in place to allow higher energy generation,” Kortlang says. “We think that the solar installer community needs to expand, and for that to happen, it needs to be easier for electricians and roofers and general contractors to become solar installers.”
But there’s a second feature to Enphase’s technology that gives its microinverters a lot more sex appeal than central inverters. It’s that each microinverter is also a tiny computer, churning out data that shows homeowners how their solar arrays are performing.
Using powerline communications, meaning there are no separate data cables or wireless connections, Enphase’s microinverters send data to a small white box the company calls the Envoy. It resembles an electronic thermostat and has a display showing an array’s energy output in watts and kilowatt-hours. The Envoy plugs into a home’s existing broadband router, and every five minutes, it sends a burst of data over the Internet to Enphase’s network operations center in Virginia. There, the company analyzes the data and prepares reports on the health of the modules, the inverters, and the surrounding grid at each installation site. Installers and customers can access these personalized reports at a website that Enphase calls Enlighten (the startup is big on the “En” prefix). Graphics and animations at the Enlighten site illustrate an array’s output over time, down to the level of individual modules—as the video below illustrates. If the Enlighten system diagnoses a problem, it sends customers or installers an alert by e-mail.
With a central inverter, there wouldn’t be much point in collecting and visualizing all this data. “It wouldn’t tell you anything—the sun comes up, the sun goes down, and if the output should be higher or lower you wouldn’t know,” says Nahi. “With us, every module is a data point.”
Now, while there’s real utility in this setup, there’s also a certain amount of eye candy. In my interview with Nahi, I compared Enlighten to the energy monitor display in the dashboard of the hybrid Toyota Prius, which shows how much power is coming from
