Solar photovoltaic (PV) systems are some of the safest types of ways to generate electricity. Once installed, there are few (if any) moving parts, no need for extracting fossil fuels from the earth, no danger of meltdowns or spills…the array just sits there soaking up the sun. As with any type of electrical system, though, there is always the danger of dealing with high voltage going somewhere it wasn’t intended.
The biggest risk for PV is a ground fault, which under certain circumstances could potentially start a fire. It is, however, extremely rare. A 2010 study by the National Fire Prevention Association found only a handful of incidents over more than 30 years of data, and concluded “there are very few incidents of fires originating with or directly involving solar power systems. This implies that the solar power industry has a relatively good record when it comes to their equipment and components contributing to the source of ignition.”
Earlier this year, SEM’s solar team came up with a design improvement for large-scale systems that we believe can minimize solar PV fire risks even more. It doesn’t add significant cost, and allows for systems to essentially police themselves in the event of a problem. For full details, click here to request our white paper on the subject.
The "Bakersfield" solar fire caused significant damage to a PV system and building in California.
The basic premise of our findings is that typical systems 100 kW and larger can be code compliant but still be unable to detect certain types of ground faults. One of the most famous solar PV fires in the country was likely a result of this exact problem. That 2009 fire in California was on a system that had an undetected single fault for a while, but didn’t have any major issues until there was a second fault at a conduit expansion joint. The resulting “Bakersfield” solar PV fire, as it became known, caused significant damage on a commercial building and sent waves throughout the entire solar industry. SEM didn’t work on that system, and there is no evidence the installers did anything drastically wrong at the time — but we think we can recommend a plan that would have prevented the fire.
Our solution is to add a device called a differential current tester with contactor combiner boxes to all large scale PV systems. This might sound overly technical, but I’ll try to keep it simple. These instruments can easily detect ground faults on both hot and neutral conductors; more importantly, they will also automatically open the contacts for all of the combiners serving a specific inverter if they detect a ground fault. That means as soon as it senses a problem with any single wire, it stops power to all the wires feeding into the same inverter.
Additionally, this setup allows the system to sound a local alarm and notify its owner. By then it has already prevented the system from doing any more damage. This provides an added layer of protection that allows Operations & Maintenence experts to come in and fix the problem before it gets really bad.
We’re excited to offer a solution; it’s making our systems safer, and we hope it makes other systems safer, too. The last thing anyone in the industry needs is a catastrophe, and we’re optimistic that this is a strategy that could become part of best practices for installers around the country. I understand this is a complicated topic, so if you have any questions, please leave a comment below.
Request our white paper on solar PV fire prevention by clicking here.
Chuck Ladd is an Engineer and Architect at Southern Energy Management. Read more about him here.
Tags: commercial pv, solar pv fire
So, if I understand correctly, this will operate like a GFCI, and stop power from going past the combiner box as soon as it detects a ground fault, sounding an alarm?
Bob,
What you said is correct. The differential current monitor functions similarly to a standard GFI wall receptacle – it will detect a ground fault by detecting a difference in current flow between the hot and neutral conductors. The monitor can detect a differential current of as low as 50 mA for a circuit that would carry 150 amps or more at full power. The isolation function will isolate all faults to the combiner level.