Micro-inverters…Lots of Them

Enphase Energy spoke with the solar coaster about their groundbreaking micro-inverter system technology.

Many solar PV breakthroughs have been achieved by increasing solar conversion efficiencies of solar cells. One of the themes I have previously touched on in achieving grid parity solar power is the reduction of the balance of systems and installations costs. In Enphase Energy’s Micro-inverter system, launched yesterday, we might just be seeing a significant breakthrough in increasing solar system efficiency (which is really what matters, rather than just solar cell efficiency).

The Single Large or Several Small (SLOSS) debate is a well-known battle of ideas in the field of conservation biology. Enphase is seeking to prove that when in comes to solar power inverters, there is no debate, and that several small is the way to go.

An inverter is a necessary component of any solar system. It converts the direct current (DC) generated from a PV system into alternating current (AC) to make it compatible with the grid and usage of electrical appliances. Typically, a solar installation will rely on a single large inverter. With Enphase’s novel Micro-inverter System, each solar panel gets its own micro-inverter. Each micro-inverter is connected to a communications gateway that feeds solar power generation data to a monitoring data center that can be assessed by the solar user by the internet. Check out this cool video which take a closer look at the micro-inverters and how they are installed.

The Micro-inverters represent a remarkable technological advancement for a variety of reasons:

1. Increased energy harvest—According to Enphase’s CEO, Paul Nahi, its 1,000 or so pilot Micro-inverter systems currently deployed have experienced a 5 to 25% increase in energy harvest over traditional single inverter systems. The reason is two-fold. First, its inverters are the first to achieve 94.5% inversion efficiency. Second, and perhaps more significantly, the phenomenon where multiple solar panels arranged in series and connected to a single large inverter perform only as well as the worst performing solar panel is avoided. Because each panel now has its one micro-inverter, a poorly-performing panel (for whatever reason such as shade or damage) will not affect the efficiency of the other panels.

2. Increased reliability—The obvious advantage to having “several small” over “single large” is that the system is no longer vulnerable to the failure of the single large inverter. Additionally, Enphase’s Micro-inverters have a MBTF (mean time before failure) of 119 years, as compared to 15-20 years of regular large inverters. Another dimension to increased system reliability is that because each panel now has its own inverter feeding data to the monitoring center, a user is now able to, in the event of suboptimal performance, pinpoint the malfunctioning panel by acessing such data on the internet through Enphase's web-based monitoring software (see screenshot on right showing panel by panel performance data of a typical solar array) and resolve the problem more promptly.

3. Increased ease of installation—Enphase’s Micro-inverter system radically simplifies the installation process by eliminating installation complexities (e.g. string design, marginal designs, co-planarity, and matched modules) associated with installing a high voltage inverter. There is no need to make space for a large centralized inverter and wiring time is reduced. The result, says Nahi, is that the balance-of-systems costs can be reduced by 13 to 15% by using Enphase’s systems.

All this means is that the return on investment in a solar system is greatly enhanced in multiple ways, and none of them have to do with increasing solar cell technology. According to Nahi, not only are there life cycle savings to the Enphase Micro-inverter system, but the up-front economics of the system also compare favorably to traditional single inverter systems.

Enphase has raised $6.5 million since its inception in 2006 from investors such as Third Point Management and Applied Ventures. According to Greentech Media, Enphase is selling its products and services through installers and distributors such as AEE Solar, DC Power Systems, Focused Energy, Solar Depot and SunWize.

Balance of system and installation breakthroughs are just the kind of stories I’d like to focus more on. As this excellent article on Enphase’s corporate background observes:

In the fast-growing solar industry, most of the venture capital to date has flowed into developing newer and better photovoltaic cells, while the inverter has largely been overlooked, Nahi said. "There are all kinds of new panels coming out . . . and it's thrilling to watch," he said. "But very little investment has been made in the inverter space."

Hopefully, this new technology byEnphase and the news by Xantrex that is has received $1.9 million in orders from OptiSolar are signs of change.