Winter Sun, Smarter Solar - How Seasonal Adjustments Boost Solar Efficiency

South African winters are often crisp, clear, and full of sunlight, which are ideal conditions for solar panels - or so it seems. But as many solar users are discovering, blue skies don’t always guarantee peak performance. Without seasonal optimisation, solar systems may deliver less-than-expected efficiency during the colder months.

“Mid-year sunlight reaches rooftops from a lower angle, daylight hours are shorter, and night-time temperatures regularly dip into single digits,” explains Rein Snoeck Henkemans, CEO of Alumo Energy.

“These factors impact panel output, often in ways that go unnoticed until your system begins struggling to meet even basic power demands.”

Offsetting for winter’s lower sun angle

Researchers at the Vaal University of Technology found that panels produced solid power for about 4.7 hours per day, or just under 20% of the day in April, and only 4.4 hours on average by mid-July. This is because photovoltaic systems only ‘come alive’ when sunlight is strong enough to push the panel-and-inverter pair past a set minimum voltage.

Protecting battery capacity during colder nights

Lithium-ion batteries operate less efficiently in very cold conditions. When cell temperature drops below 0 degrees, electrochemical reactions slow down, usable capacity decreases, and the pack begins the next discharge cycle at a disadvantage. Snoeck Henkemans recommends conducting a dawn temperature check – if the cabinet sensor reads in single digits, the enclosure should be insulated or fitted with active heating, however this highly unlikely in our South African climates.

Then, schedule charging when the day is at its warmest – usually in the early afternoon. Finally, end each day with around 40% charge left on the system to ensure all systems continue functioning uninterrupted throughout the night.

Firmware and load scheduling: small changes, big results

An inverter’s firmware determines how fast a battery charges and how low it can safely go. Installer-providers such as Alumo Energy can update or reconfigure systems to optimise battery charge and discharge rates. These updates are typically included in the solar maintenance package, can be performed remotely, and are completed quickly.

Load timing also matters more in winter. Pool pumps, dishwashers, and washing machines should run between late morning and early afternoon when panels still supply surplus watts. Heating water in that same window spares the battery a heavy draw at dusk. Running these appliances during the optimal charging window, typically between 10am and 3pm, preserves reserve energy for when it’s needed later in the evening.

Snoeck Henkemans recommends that homeowners run geysers, washing machines, and pool pumps before 2pm. “This frees up roughly a quarter of the battery reserves for lights, television, and phone charging after sunset. The system’s components also last longer because the pack avoids deep-cycle strain, and you need to buy fewer kilowatt-hours from the grid during peak hours.

“If you have a solid maintenance plan backed by a trusted solar installer, your solar system will be a set-it and forget-it setup. But if you truly want to get the most out of your array, making small adjustments as the seasons change can help you achieve additional savings, increase efficiency, and extend your system’s lifespan over the long-term.”