This is our best documented ground mounted PV installation so far. We installed Gary’s 4.5 KW system in two group work days, plus work Gary had done by other contractors. This series of photos documents the entire process.
The advantages of a ground-mounted PV system (if you have the room on your lot) is it can be located with perfect orientation to the sun, and it is easily accessible for maintenance. We prefer an in-ground ballasted framework, where the posts supporting the array are anchored in concrete blocks in the ground. The first step is to measure and locate where the trenches will be dug for the concrete.
Gary had the trenches dug with a small backhoe. The trenches are typically 16 inches wide, 10-12 feet long, and 24-30 inches deep and hold about 1.3 yards of concrete weighing about 6500 pounds.
Completed trenches. Used three-inch pipe is used for the posts of the frame.
The next step is to build three rebar cages to go into the trenches. The cages reinforce the concrete and help hold the posts in place.
A rebar cage placed in a trench.
We purchase used 3-inch well pipe from a yard in Farmington, NM, and have a one-inch hole drilled through the base of each post to hold a length of 1-inch re-bar that connects the two posts in each trench. From an engineering standpoint, this provides tremendous resistance to uplift.
Lowering the two posts + 1-inch re-bar unit into a trench. This sits inside the re-bar cage that is already in the trench.
After everything is in the trench, we place a homemade post-holder on each post, which sits on top of some boards to support it across the trench.
The next step is the tedious task of aligning and spacing the posts. The 3 North posts and 3 South posts need to align perfectly and be at the correct height, and the North line of posts needs to be parallel with the South line of posts.
Our homemade Christmas Tree stand post holders hold the posts in place.
Here’s the finished post placement. The North and South lines of posts are straight and the posts are held solidly in place so they don’t move. The next step is to complete wiring the cages to the posts, install a grounding rod in each trench that extends above the surface, and order cement. Each trench takes about one yard of concrete (weighing about 5000 pounds). The holes are simply filled with concrete, no need to construct a frame.
The trenches are filled with concrete. Each trench requires about 1.3 yards of concrete.
Completed in-ground ballasts with posts in place.
A welder attaches the North and South horizontal pipes to the vertical posts. Optionally, top caps are available to attach the horizontal pipes to the posts.
The next step is to bolt specialized aluminum rails onto the pipe frame. The rails will hold the PV modules.
Mounting the PV modules.
Completed PV array. A 4.5 KW system has 18 modules.
The final steps are the electrical connections, which was done by an electrician hired by Gary. The modules, connected in series, lead to an inverter which converts direct current from the modules to alternating current to feed into the grid.
An AC disconnect is required so the system can be shut down in the event of an emergency.
After everything is connected, an electrical inspection is required, then an inspection by the local utility to approve and turn on the system.