The Dangerous Resurgence of Guerrilla Solar

A new wave of do-it-yourself grid-tie solar products is hitting the DIY circuits. This author has seen a few examples of this at recent Maker Faire events and other green or solar events in the last several months. The systems are generally very simple and utilize the new generation of commercially available micro-inverters or hacked small in-vehicle inverters connected to a three prong plug end with instruction for the user to plug it in to their wall outlet. Unfortunately, what many of these DIY-ers may not realize is the risk associated with plugging a solar panel into an outlet in their homes as these DIY systems suggest. Guerrilla Solar, as the term coined by the Home Power team over a decade ago, is just as dangerous now as it was then.

In The Beginning, It Was All Guerrilla

In the later half of 1999, Home Power Magazine editors began featuring a "Guerrilla Solar" column in each issue in which an anonymized homeowner would explain and show off their illegally grid-tied PV system. The rise of guerrilla solar activity was in direct response to the stonewall homeowners were receiving from utility companies as they attempted to legitimately navigate a net metering system that was not set up to accommodate small-scale backfeeds. In California around the early 2000's, the rolling blackouts began to hit after the electrical markets deregulated. The first was on June 14, 2000 and the next round rolled in just a few months later at the beginning of 2001. Suddenly, there was a surge of interest in energy-saving PV systems that would help homeowners keep the lights on.

The ability to easily grid-tie and net meter a code-compliant energy-saving PV systems has helped create a viable solar PV industry that now supports hundreds of thousands of workers and has attracted the attention of investment dollars. The industry continues to grow, the National Electric Code Article 690 covering photovoltaic system installations continues to evolve, and the regulation and inspection processes have become more streamlined. In many states, in order to receive cash incentives from rebate programs, homeowners must work through a licensed installer. Even so, many handy homeowners would still chose to install their own PV system if given the chance- some for the challenge, some for the costs savings.

The New Guerrilla Solar

Many of the DIY solar products available are very small-scale and are composed of usually one 200 - 300 watt PV panel, a microinverter or modified in-vehicle inverter, and a 120VAC plug. Many of the products in their marketing literature or websites even instruct that you plug it in directly to a wall outlet. Perhaps the most obvious place where this interconnection would occur would be in an outdoor GFCI outlet conveniently located next to the panel, where it could be tilted against the exterior wall of the home in a sunny place in easy reach of an outlet. Here is where the problems arise.

The Problem of "Just Plug It In"

There are problems present in many of these DIY designs:

  1. Suggested backfeed is inappropriate. Unless on a dedicated circuit, you should not backfeed electrical outlets- especially GFCI. GFCI outlets are especially vulnerable and will trip open and remain energized until the inverter ceases to operate. See W. Bower & J. Wiles "Investigations of Ground-Fault Protection Devices for Photovoltaic Power Systems Applications" for a great analysis of what happens in this situation.
  2. The inverters might not be UL 1741 compliant. Inverters that are not listed for use with PV or lacking grid-synching capabilities per UL 1741 leave stray voltages on the line if the grid goes down. Inverters intended for in-vehicle use are inappropriate for grid-tie applications since they do not conform to UL 1741, they do not produce the quality of power necessary for grid-tie, and they require after market modification to plug in to an outlet.
  3. No net metering agreement, no buyback. If for whatever reason a guerrilla-installed PV system is producing more power than the home is consuming, the utility will not buy back excess power. Only with a pre-existing net metering agreement and a properly listed UL 1741 grid-tie inverter will the utility enter a net metering agreement and pay for excess power production.
  4. These systems do not provide backup power. For the systems that use UL 1741 listed inverters, they will disconnect if they cannot synchronize to the grid in the case of a power failure. For systems that do not have UL 1741 inverters, the power produced will be so small and so low quality that it was not be capable of running any emergency household loads.

Consumers should exercise caution when investigating the potential purchase of any energy generating products. Look for whole-product UL listings for any product that claims to be plug-and-play as if it were an appliance. Currently, none of the plug-and-play PV products are commercially available and none have a UL listing as an appliance. A licensed electricial should install any system that produces electricity in an NEC-compliant installation.

And if it seems too good to be true, it probably is.