Nine Months Monitored, 73% Solar — The Longest-Running Dataset in the Series

Danie and Lize Erasmus were early adopters. Their 1.6 kWp system went live in September 2024, making their installation the longest-running monitored case study in this series at nine months. Their Roodepoort home is modest — three bedrooms, a 150-litre geyser, a family of three with a seven-year-old who, in Lize’s words, “treats the bath like a swimming pool.”

The system was sized conservatively. At 1.6 kWp, it’s the smallest array in this batch, feeding a household that’s also the lightest on hot water demand. The question was whether a budget-friendly installation could still make a meaningful dent.

Nine months of data says yes. The system averaged 112 kWh of solar energy per month against 41 kWh from the grid — a 73% overall solar fraction. Cumulatively, the panels have delivered 1,116 kWh of solar energy, with 406 kWh drawn from the grid. Monthly savings sit at an estimated R575.

The financial picture here is different from the high-demand households. The Erasmus family wasn’t spending R1,000+ on water heating to begin with. Their monthly grid cost has dropped to R156, and the R575 total saving represents a proportionally huge reduction in their overall electricity spend.

Danie sees it as a no-brainer investment: “We spent less than any of our friends on the installation because we went small. And it still covers almost three-quarters of our hot water. The payback period was under two years.”

This case study matters because it represents the entry-level scenario. Not every household needs or can afford a large array. The Erasmus data proves that even the most conservative installation delivers meaningful, sustained returns — and nine months of monitoring through both summer and winter leaves little room for doubt.