While conducting O&M on a Satcon 250kW central inverter, we noticed this fan with an object lodged between the blades.
After inquiring with the owner, we learned another O&M company was called in to repair a squealing fan bearing. Apparently, rather than replacing the fan they opted to stop the noise by stuffing cardboard inside the fan which preventing it from spinning. While that stopped the noise, it put the inverter at risk of overheating. We have seen a lot of corners cut over the years, but this may be the most egregious offense yet.
Learn from this owner’s mistake and only hire qualified technicians to repair your solar PV system!
During O&M we often find combiner boxes and disconnect switches with water inside them, despite the box being NEMA 4 and fully gasketed, no top or side penetrations, and weather tight connectors properly installed.
Where is the water coming from?
The water enters the enclosure as moisture in the air, which later condenses into water. During the day, the bus bars heat up and warm the air in the enclosure. When air warms, the amount of moisture it can hold increases. At night, the air in the conduit or enclosure cools, and the water vapor in the air condenses. Each daily cycle only generates a tiny drop of water, but after several months this begins to add up.
Water may only travel downwards due to gravity, but moist warm air can enter and travel through a conduit and enter the enclosure from any direction. This is how water enters an enclosure even when there is no apparent way for water to run down and into the cabinet.
The solution is to seal the conduits where they enter the enclosure to prevent fresh air from getting inside the box. Traditional duct seal is effective and readily available. Expanding foam sealants area also available and very effective, however they must be approved for direct contact with the electrical cables.
Here are two examples of enclosures with only bottom entry conduits, but ground water entered the underground conduit, evaporated up the conduit into the enclosure, then condensed.
At this site, the intermodule wiring is zip-tied to the rails but the string homeruns are laying loose on the roof, which is poor workmanship. Over time the rough shingles will wear away on the insulation compromising its integrity and putting the system at risk for faults. In the winter, snow and ice will surround this wiring, and as the frozen ice tries to slide down the roof it will pull on the conductors. Wire must be kept up off the roof and secured to the rails.
A roof drain clogged causing the water to rise in the surrounding area. This installation has poor wire management, as shown by a connector sitting loose on a ballast block. Once the water rose and got in the connector, it began to short out (burn marks visible on the ballast block). The connector exploded and fell completely the water below where the modules continued to feed short circuit current right into the water, causing more damage and creating an extreme safety hazard for workers. Scary!
On our first operation and maintenance trip to this site, we discovered an old broken module stashed under a HVAC unit. This module was not secured, and would surely have become airborne during a hurricane or tropical storm. This module could have smashed up the surrounding modules, or even worse damage to people and property. Make sure all equipment are always fully secured and the roof is free of debris!
Two things went wrong here. First, the vegetation was not maintained, allowing it to grow tall enough to shade the modules and cover the modules in lots of pollen. The second mistake is improper seeding. If the site has proper low-growing ground cover, the weeds would not grow tall like this!
This installer gets full points for creativity, but fails miserably for inappropriate construction means and methods. These cables are not protected from physical damage, and they are not outdoor rated so the UV rays will deteriorate the cables causing premature failure.
NEMA 3R and 4 inverters and outdoor cabinets may be rated for outdoor use, but any scratches in the paint will expose the metal to rusting. Once the rust gets a foothold, it will quickly spread. In this case, the corrosion should be sanded, primed, and painted.