Winter Sun, Smarter Solar: How Seasonal Adjustments Boost Solar Efficiency
Many solar users are discovering, blue skies don’t always guarantee peak performance and without seasonal optimisation, solar systems may deliver less-than-expected efficiency during the colder months.
16/07/2025
While South African winters are known for their crisp, clear days, many homeowners are discovering that their solar panels are underperforming during this season. This drop in performance is often subtle, but avoidable with a few key tweaks.
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.”