The conversation about solar on water treatment plants has shifted decisively. Three years ago, the argument was about resilience — staying online through load-shedding. The numbers favoured solar only on remote, off-grid or mission-critical sites. Today the argument is also financial: solar PV at R7–R10/Wp installed (2026 ground-mount lodge-scale) combined with Eskom + municipal water-utility tariffs at R2.20–R3.10/kWh (2026) produces a payback inside four years on most lodge water plants we model (IRENA, 2024).
What loads make sense to put on PV
Water plants are advantageous solar loads because they run during daylight. The largest load on a lodge water plant is typically the wastewater blower (continuous duty, 60–75% of plant kWh), followed by booster pumps (demand-driven, peaks during guest activity), followed by RO high-pressure pumps (intermittent, scheduled). The blower especially is a daylight-friendly load and the easiest to PV-cover.
The hybrid that wins
A direct-coupled solar array on the submersible borehole pump (using a VFD with PV input) covers a meaningful daytime load without a battery — the pump moves water into storage, the storage acts as the battery. This is the highest IRR configuration we model. Add a smaller battery for nighttime safety loads (telemetry, UV, control panel) and the site achieves grid-independence on the water plant without the cost of a full off-grid battery bank.
What to ignore
Two configurations look attractive in glossy brochures and fail in spreadsheets: (1) solar covering RO high-pressure pumps directly — RO needs constant pressure to run efficiently and a partial-power state damages membranes; (2) solar on the booster pressure set — boosters run almost entirely at night during shower hours, when the PV is gone. Both can be done — both need a substantial battery and the IRR collapses.
Engineering precedes finance. Map the load curve of the plant, then map the PV production curve, then size the overlap. The solar conversation has matured beyond "should we?" It is now "where, and how much?"
