Solar panel tilt and trackers for water pumping

Tilt by season

These are rules of thumb, not optimums. NRCS's pumping plant standard puts it the same way: base panel tilt on the location's latitude and the time of year power is needed, and change the tilt seasonally if the system runs all year. Our sun hours by state are computed for a fixed 20 degree tilt, so a well-tilted winter array can do a little better than the December figure there.

Trackers and direct drive

A direct-drive pump only pumps when the panels make enough power to turn it. On a fixed array that threshold is crossed late in the morning and lost early in the afternoon. A single-axis tracker that follows the sun east to west holds the array square to the sun for longer, so the pump runs more hours at a steadier flow. That benefit is largest in summer and at low latitudes, and smallest in a northern winter.

The cost is moving parts in a pasture. A tracker needs its own maintenance and a sturdy mount. Often, adding one or two panels to a fixed array buys the same water for less. Run both options in PVWatts (fixed vs 1-axis tracking) for your location and compare the months you care about.

Mounting details that matter

• Face true south, not magnetic south, in the northern hemisphere.
• No shade on any cell from mid-morning to mid-afternoon. One shaded cell can drag a whole series string down below the pump's start voltage.
• Fence the array in livestock country and mount it high enough that animals cannot rub on it.
• Portable arrays on a trailer or skid suit rotational grazing; NRCS lists mobile panels as a design consideration for livestock watering.