The inverter pad is the central location where all AC and DC circuits cross paths in a ground mount solar farm. The incoming DC circuits are protected and are able to be safely isolated at the inverter pad. Similarly, the AC circuits are protected and have an isolation capability at the inverter pad. Plus, there is often a meteorological measurement station, SCADA controls, energy metering, communications, tracker power and station power at the inverter pad. In short, there is a lot going on at the inverter location. In some cases, on larger solar farms, a preengineered inverter pad is replaced with an inverter skid which contains the equipment and most of the prewiring completed. Whether the inverter equipment is placed on a concrete pad, on a skid, or in a container there should be substantial solar design and engineering considerations at this focal point in the solar farm.
The incoming DC conductors from the solar array will require a large amount of volume underneath the inverters. Not only is the volume large, the bend radii required by the National Electrical Code requires significant space. Proper planning for the incoming DC conductors to the overcurrent protection device is important.
The outgoing AC Conductors will often travel a short distance from the inverter output to a step-up transformer or a piece of switchgear. This short distance provides a challenge for the electrician to plan for the conductor’s path and potential obstructions from other solar farm conductors.
There has to be a lot of consideration ahead of time to provide power to the various pieces of equipment at the pad. If the solar farm is using single axis trackers, each tracker motor or actuator has a controller which allocates control commands and power to the drive units. The distribution of power under the pad and to the individual pieces and parts can be confusing unless carefully planned.
Meterological Station and SCADA
The measurement and controls associated with a utility scale solar farm or commercial solar farm can be the last 5% of work that takes 95% of the effort. Many of the control wires will run between various pieces of electrical gear and communications equipment. Also, a Supervisoary Control and Data Acquisition (SCADA) system requires at least one phone line and one data line. This is the spaghetti mess of detailed wiring that if, properly planned, can save your precious brain cells.
The Full Picture
Many solar installations are completed with minimal solar engineering and planning services from a professional because this is a budget-driven adolescent industry. However, we have witnessed more than once that the sweet taste of a low price is long forgotten after the bitter results of an unplanned inverter pad.