Distributed Generation and Utility Lineman Safety

The concern with distributed generation (renewable or otherwise) is that the safety technology, such as the inverter, designed to prevent back-feeding a distribution line when the grid goes down may fail and a utility lineman could get hurt not realizing there is electricity where there shouldn't be. The most common distributed generation (DG) technologies are gasoline and diesel generators, which are common after a storm event when the grid is down, but renewable energy systems that operate continuously are also part of the DG mix. I'll focus on PV systems and issues specifically, however.

First, the good news. To date, I don't know of a single PV/lineman incident. Safety should be a continued priority. Second, there are three operational levels of safety for a utility lineperson (lineman) working on any distribution line:

1. Always follow safety procedures. Utility distribution line work occurs during either routine maintenance, where a line is purposefully turned off, or during an unexpected event, where repairs are necessary. In either case, a utility lineman should always follow basic safety procedures to test a line and make sure it is not energized with electricity. Linemen can work on lines that are either "hot" (energized) or "cold" (not energized) and there are different safety requirements for each circumstance. Standard requirements for working on a "cold" line include isolate, measure and ground. If linemen find an energized line where one shouldn't be, they won't get physically hurt, but the repair might be delayed while they track down the source of the electricity.

2. UL/IEEE Inverters. All grid-connected PV systems are required to use listed inverters that have been evaluated according the UL/IEEE anti-islanding requirements and that can quickly sense when the grid is down and consequently shut down the PV system. The only way these inverters turn back on is if they measure stable and normal grid voltage and frequency for a minimum amount of time. It's interesting to note that there are cases where the inverter shut-down set-points are so sensitive that minor grid voltage fluctuations affect PV system performance because the inverters turns the system off and on.

3. External Disconnect Switch (EDS). The third safety level is the use of an external disconnect switch, which is essentially a lever that a utility lineman can use to shut down a homeowner's PV system and physically isolate it from the grid while he/she does maintenance or repair work. When the work is done, linemen then turn the EDS switch back on. From a practical standpoint, not many EDS's are actually ever used — driving around to various homes, businesses or farms to turn off the DG systems in the area delays repairs. PG&E and SMUD announced earlier this year that they weren't requiring an EDS for inverter-based systems served by self-contained meters. Not only do both utilities trust that inverter technology works as it should, but also the practicality of physically going to each PV system (PG&E has over 20,000 PV systems in its service territory) led to this change in requirements. The self-contained meter provides a back-up means for isolating the DG by pulling the meter. As another side note, advanced meters, i.e. smart meters, which many utilities are now installing may have the ability to disconnect the house and/or PV system remotely, saving time and resources. However, these devices would need to be approved for this purpose.

Finally, while not a safety aspect, many states or utilities require PV system owners to have a minimum amount of liability insurance, and for small systems, this is often just homeowners insurance. Most insurers don't "exclude" PV systems from insurance policies, an indication of the safety record.

It should also be noted that first responders (a.k.a. the fire department) should also be aware of PV systems during any incident — cutting through PV wires with axes or chainsaws presents an obvious danger. Designing PV with first responders in mind, i.e. clearances and walkways, and educating first responders about working around PV is an important effort. The California Solar Energy Industries Association (CalSEIA) and the California State Fire Marshall's office have been working on this issue and produced draft design guidelines and educational materials earlier this year.

Safety should be #1 at all times for both utilities and the industry — one incident and the image is tarnished.