Big isn't always better. Sometimes it makes more sense to start small and work your way up; buy what you can afford and add on incrementally as your financial prospects brighten. It's an idea that works great with coin collections, herds of livestock, and giant balls of string, but not so great with bicycles, cosmetic surgery or billion-dollar hydroelectric dams. Or, until recently, grid-tied solar-electric systems.

The problem—or part of it, anyway—has always been the inverter, which is the component that inputs direct current (DC) from a photovoltaic (PV, or solar electric) array and outputs grid-compatible alternating current (AC). Ever since grid-tied solar electric systems first became available to homeowners, people have been faced with the task of sizing their inverters to fit their PV arrays, or vice versa. Of course, at first glance it doesn't appear to be that big of a problem. If you want a 2,000 solar watt array, you pick an inverter that will handle that much input, plus a little extra. But how much extra?

It depends on how much PV you intend to add down the road. If you begin with a 2,000-watt array and an inverter that maxes out at 2,500-watts of array input, you're limited to an extra 500 watts of PV. If you want to add more than that, you'll have to buy another (or a bigger) inverter, at considerable expense. Conversely, if you super-size the inverter from the outset and never increase the size of the solar array, you've wasted a lot of money on idle capacity. It really kind of means you need to know what you're going to do before you know what you're going to do.

But even if we all had the prescience to peek into the future and see if, when, and how much PV we were going to want to add later on, it still wouldn't alleviate the problem of standard inverters coming in large preset chunks of wattage. Nor would it help those of modest means who truly want to get started in solar but simply can't afford the large initial investment that a full-blown PV system demands.

And what about the thousands of would-be solar enthusiasts who live in condos or apartments? Isn't there a simple way for those folks to install one or two PV modules (commonly known as panels) to reduce their carbon footprint and shave a few kilowatt hours off their electric bills each month?

Now there is. The component that makes it all possible is the Enphase micro-inverter from Enphase Energy, and it's really one of the cleverest ideas I've seen in my ten-plus years of solar living. Rather than routing the DC output from several PV modules to one or two inverters mounted on the side of the house, the Enphase micro-inverter system uses one small (4-pound) inverter for each module.

Enphase inverter. Photo courtesy of Enphase Energy Inc.

There are several advantages to this type of arrangement, not the least of which is the fact that the Enphase system greatly simplifies installation. All you have to do is mount an Enphase micro-inverter onto the rack beneath each individual PV module, then plug the module's DC output directly into it. From that point on the wiring is AC. All the micro-inverters in a given branch circuit are easily connected together in a simple parallel arrangement, like lights on a Christmas tree. There are no series-string sizing calculations to contend with, and no vexing problems of resizing when you want to add on later. Depending on the model of inverter and the voltage and wattage of the PV modules, it's possible to join as many as 24 modules on a single branch that terminates at a branch-circuit junction box. From there it's wired into an unused 15-amp house circuit, either 208-volt 3-phase, or 240-volt single-phase, depending on the type of electrical service your house, condo or apartment currently has.

In terms of performance, the Enphase micro-inverter can't be beat. Because the DC wiring is kept to an absolute minimum, there is no appreciable voltage loss due to long DC wire runs; the output from each module is converted into high-voltage AC the instant it reaches the inverter.

Nor is occasional or intermittent shading a problem. With a traditional inverter system, shading of one PV module—whether by windblown debris, nearby tree branches, chimneys, vent pipes, or the neighbor kid's missing Frisbee—will cause all the other modules in the series string to send a portion of their output to the affected module to try to "drive" it to a higher voltage. As commendable and altruistic as this may sound, the entire array can easily be compromised by one poorly performing module.

With the Enphase system, by contrast, every PV module operates independently from all the others, so the whole system doesn't suffer when one or more modules is temporarily shaded. This allows you to mount your array in places you wouldn't ordinarily be able to, such as near roof obstructions or even on the east or west sides of the roof, as you might do if your array incrementally outgrows the south-facing roof's holding capacity.

Enphase also makes it easy to monitor your system's performance. So easy, in fact, it's a little bit spooky. Once the system becomes operational, every micro-inverter in the array sends packets of information regarding that module's performance along the power line from the array to your house. To access this information all you need to do is plug the EMU (Energy Management Unit, colorfully dubbed the Envoy Communications Gateway) into any AC wall outlet and then connect an Ethernet cable from the EMU into a broadband router. The performance data will be transmitted at five-minute intervals to a proprietary website from which you can gain immediate access to each individual PV module's past and current performance information, complete with graphs and graphics that are really quite impressive. If no broadband router is available, you can access the real-time information directly from any computer with a standard web browser.

As you might expect, this degree of performance and flexibility comes at somewhat of a premium. So, even though there will be savings on material and installation costs with Enphase's streamlined system, in large systems you may have to pay a little more for the convenience and flexibility an Enphase micro-inverter system provides. Currently, Enphase micro-inverters can be found on the Internet for under $200. If mated with a 230-watt module, the inverter cost will amount to about a $.87 per watt. (Enphase micro-inverters are compatible with dozens of different PV modules, many in the 230-watt range.) By contrast, the popular Sunny Boy line of inverters from SMA America can be purchased for anywhere from $.46 to $.57 per watt, depending on the vendor and the model. Unfortunately, SMA's smallest inverter is currently an 84-pound, 3,000-watt affair capable of running arrays of up to 3,750 watts. Smaller inverters are available from other manufacturers but the cost for anything tailored for arrays of under 1,500 watts will set you back well over a dollar per watt, a fact that underscores the thriftiness of Enphase micro-inverters for small startup systems.

The Envoy EMU is currently running around $350, a reasonable price considering the wealth of information it provides access to, and it will continue to provide precise data on every module you add to your array, up to 240 modules. The cost for personalized Web based services is presently $2.00 per module per year. This is a whole lot less than many similar services provided by other companies. To learn more about the unique Enphase system, visit www.enphaseenergy.com.

The 30-percent federal income tax credit now in effect can be applied to the entire system, including installation, and other state-sponsored rebates may also apply. To discover what you're eligible for, check out the Database of State Incentives for Renewables & Efficiency at: www.dsireusa.com. Then start planning the simplest and most efficient direct grid-tied PV system money can buy.