Why South African solar power systems can underperform in winter
South African homes and businesses with solar power systems may experience a significant dip in generation performance during winter, AWPower has told MyBroadband.
Although South Africa gets copious amounts of sunshine for much of the year, it is not immune to the impact of winter on solar power efficiency.
During this period, the Earth’s Southern Hemisphere is tilted away from the Sun, which means its rays don’t shine on solar panels as directly as they would during the summer.
According to AWPower, Capetonians are more significantly impacted by the change of the seasons than households in Gauteng.
There are two main reasons for this — fewer overall hours of sunshine and inclement weather during the winter.
To illustrate this, one can compare the amount of sunshine that Cape Town and Pretoria got on the shortest day of the year — the winter solstice.
On 21 June 2022, sunrise in Cape Town happened at 07:51 and sunset at 17:45. Therefore, the Sun was out for roughly nine hours and 53 minutes.
On the same day in Pretoria, the Sun rose at 06:53 and set at 17:25, meaning it had sunshine for about 10 hours and 32 minutes.
In addition, the Western Cape has its rainy season during the winter and more overcast weather, while Gauteng has its dry season.
Solar energy specialists AWPower recently spoke to MyBroadband about the realities of generating solar power during the winter.
AWPower managing director Christiaan Hattingh said the company often receives customer queries in winter with claims that their systems were not working correctly.
For example, one of AWPower’s Cape Town-based customers had a massive solar system that generated 1MWh (1,000kWh) of electricity during a peak summer month.
However, at one point during winter, that was cut to around 300kWh, less than a third of his peak generation.
Hattingh said in most instances, systems like this perform within the bounds estimated during the planning process and are communicated to the customers.
AWPower provided the graph below to show how solar generation could vary monthly, with peak production in the year’s hottest months and a dropoff in the colder months.
It shows the solar energy production of a 4.095kW PV installation site with a 5kW inverter in Durbanville near Cape Town.
The picture is radically different when looking at solar production in the northern part of the country.
The graph below shows the production for a site in Johannesburg with the exact same specifications as above.
Interestingly, the production was much more consistent in each month of the year.
However, the peak month of production did not come close to Cape Town, as the latter tends to get more sunshine than Johannesburg over the summer because it does not experience rainy weather.
But Johannesburg’s worst month had much higher production than Cape Town’s worst because it had clearer skies during its colder months.
Joburg site solar production over a year
Hattingh advised consumers to oversize their panel array if they can afford to instead of overspending on battery storage to compensate as much as possible for the natural losses in efficiency.
The global prices of solar panels have decreased significantly in recent years and are among the cheapest parts of the self-generating system.
While some energy storage would be required in cases where consumers want their excess electricity available for dispatch in the evening, they can upgrade batteries at a later stage with moderate effort.
On the other hand, expanding your solar array could require further certification and approval processes by the relevant municipality.
Hattingh provided these tips for ensuring the best possible efficiency on your solar panels:
- Technology improvements — Use an inverter that supports individual optimisers on solar panels to manage generation on a per-panel basis, lowering the impact of shade.
- Limit shade — Trim trees as frequently as necessary to avoid as much as possible shade from hitting the panels during the day.
- Clean panels regularly — Give your panels a proper wipe down several times a year. This is particularly important for solar users with homes located on farms, where dust from gravel roads can settle on panels.
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