John Gwynn

Not infrequently one of my many dear friends will tell me, “You’re toast man. They’re selling do-it-yourself solar systems at Lowe’s. Who’s going to pay you to plug something in?” Okay, thank you for that…but plugs can be tricky.

Then there’s my buddy at Bandwagon Solar (formerly Bandwagon Oil Shale PC) who lured me onto one of his roof installs, where we basked in mid-afternoon shade. “Darkness at noon. This is going to give you trouble,” says I, because photovoltaic (PV) solar modules need sun like a tanorexic. His smile alone was almost enough to fire up one of his shaded panels. “We’re talking Enphase baby, micro-inverters (“Texas T”), 240 AC all the way to the panel! Now who’s afraid of a little shade? And I hope I never see a string sizing program again!”

I won’t go so far as to call this blasphemy – “string sizing” is the holy liturgy of the high solar priesthood – but it certainly brought up some interesting issues.

This fellow, and the Lowe’s shopper, is all abuzz about a new product from a California start-up called Enphase Energy that promises (or threatens) to revolutionize the way solar systems are designed and installed. It’s called a “micro-inverter” because it’s tiny compared with the hardware it replaces. (Note to “dear friends” above: It actually looks more like a Panini maker than a toaster.)

Don’t touch the remote while we do a little background. When the Goddess of Electricity came up with the otherwise magical “photoelectric effect,” She neglected one thing: the juice we get from solar is Direct Current (DC), which is generally incompatible with the flat screen American Dream powered by Alternating Current (AC) ( and also supplied in deceptively cheap abundance by coal-burning PNM.)

In the “Olden Days” (or B.E., Before Enphase), the business of converting DC to AC was handled exclusively by large ground-based inverters that collected the combined outputs of all the solar panels on the roof and rendered them home and grid feed-back ready.

We called them “Sunny Boys” (one of several prominent brands), which may sound wimpy, but we always knew they were Real Men’s Inverters. For one thing they weigh more than a keg. Just getting them to stay on the wall presents anchoring challenges. They’re bombproof machines for sure, and they have big voltage appetites to go along. They like to make current at a point called the MPP where power (wattage) is maximized and voltage is a toasty 400 volts. But since each PV module only operates at around 30 volts, the modules need to be wired together in series on the roof (as in 13x 30 =390 volts).

Determining the size of those strings is a bit of an art; too many modules in series can produce too much voltage on a cold day (not a typo: PV loves cold as it loves sun), too few and on a hot day DC input drops below the operational window. Then there’s also that tricky little bit about getting this combined voltage safely off the roof without killing anybody.

So, in the heroic days of the big strings, when large DC voltages could cause arc flashes and fires, and polarity miscues could blow otherwise bombproof inverters off the wall, and sizing mistakes could cripple a system’s output on a summer day, only the well qualified (and those willing to buy Personal Protective Equipment safety gear) dared sally forth.

Now we have the Bandwagon Boys. Enphase has changed the game. No more scary DC voltages with their attendant expensive disconnects. No more string sizing headaches. With a baby inverter on its back, each module is a string unto itself with it’s own MPPT (Maximum Power Point Tracking), thereby alleviating the fatal flaw of a multi-module string: just like with those old Christmas lights, if one module in a string goes off-line (and it takes a ridiculously small amount of shading to do that), the output of the entire string is compromised. With Enphase, the shadow of a chimney, for instance, can mosey across an array all day but only affect one module at a time. And now modules don’t have to be matched sets by brand, orientation, age or even temperature for optimum power. No longer constrained by string sizing (usually 8 to 13 modules each), you can start building a PV system as small as one panel, then add one a year, like contributing to an IRA. In fact, an Enphase solar array can be a crazy quilt of oddball panels picked up at the Restore and slammed up all over a roof by some weekend warrior. You can make your house look like a solar armadillo. Who needs friendly neighbors?
Not everyone likes this picture. No doubt there is still a place (a sunny, unshaded place where qualified technicians cater to clients who can afford their ideal system) for the tested technology of traditional inverters. You’ve still got to have installers who can get most of those modules pointing in the right direction (that would be south) and get them to stay put on the roof for 30 years. And that’s the kind of experience that usually goes with string inverter expertise.

So maybe part of the unease among solar professionals is guild mentality: the string theorists want to protect their turf. It’s like when a seasoned skier sees a novice snowboarder flash by and thinks: that’s too darn easy. There are legitimate aesthetic (armadillo) and accountability (yahoo) issues. After what went down with solar thermal in the seventies, the industry wisemen say we can ill afford another black eye.

On the technical score sheet, Enphase has defused the old efficiency bugaboo by announcing a 95.5 % efficiency rating right up there with the big boys. Then they pointed out enhanced system efficiency (plus 5 to 25%) by eliminating string shading effects. On price, micro-inverters add 50 cents per watt but save on hiring more expert personnel for the install. Enphase has a great website that let’s you keep tabs on each individual module, but it costs $10 per month, roughly the output of two panels.

Skeptics usually fall back on longevity concerns. Enphase hasn’t been around long enough, and by that they mean not only the hardware but also the company itself. Will they be able to honor their 15-year warranty? Or will the rash of failures at year five sink the whole enterprise? That said, if Enphase builds on its early success, it may be the Sunnyboys (can’t help thinking: big like dinosaurs, or mainframes) that adapt or die. SMA, German parent of Sunnyboy, recently purchased a micro-inverter firm of its own. A few years back this might have set off alarms of a General Motors buying up battery technology in order to kill it, but in this case it seems more like running to catch up. Enphase is already here. You can get it at Lowe’s. You plug it in. Of course, you might want to call in qualified personnel: 240 Volt AC can still toast you good.

John Gwynn is a NABCEP certified solar installer (“string theorist”) and a managing partner of Bellasolar.net in Santa Fe. He has both Enphase and Sunnyboy on his home. Cont