The microinverters were mounted on a horizontal cross-piece of Unistrut that also serves as wire management for AC and DC wiring and the equipment-ground wire. This required extending the wires from the modules with custom MC4 extensions. The modules help shade the inverters, allowing them to operate more efficiently. Each inverter is connected to the equipment-grounding conductor through the manufacturer-supplied grounding point. The microinverters greatly simplified the DC wiring, which would have been rather complex if we had to series-wire between the tracking pivot arms.
The two branch circuits from the microinverters were combined on the tracker rack using a standard outdoor air-conditioning disconnect that had two 15 A, 240 VAC breakers combined into one 30 A disconnect output circuit. This allows the system to be disconnected on the roof for commissioning tests and maintenance, and allows troubleshooting of each branch circuit. This circuit then passes through the production meter and is interconnected on the load side of a 240 V subpanel with a 30 A breaker in the building. A separate circuit powers the tracker actuator and control electronics.
DH Solar is new to the PV industry but has had a long-standing business making satellite trackers. The system was lightweight, but very strong because of additional cross-bracing. The tracker has to be manually programmed for seasonal variations. With 32 programmable positions per day, it is not as accurate as a tracker using astronomical data for a specific latitude and season.
The system has been operating for only five months, so it is too soon to see how well it is performing compared to the SAM predictions. The first month had only three weeks of production and we had an unseasonably cold and wet summer. The last month was also poor, since smoke from nearby forest fires significantly impacted PV production.
Bill Hoffer has worked in the solar industry in the Pacific Northwest for more than 16 years. He is a NABCEP Certified Solar PV Installer and a professional mechanical engineer in Washington state. He lives in a straw bale home he designed and built himself, and is an avid gardener and skier.
PV System Equipment:
APS • solaraps.com • Microinverters
DH Solar • dhsolar.net • Single-axis tracker
Itek Energy • itekenergy.com • Modules