Our photovoltaic system – a blessing in many ways
The technology works – the mills of bureaucracy grind slowly
I had actually planned to write this blog once everything to do with our photovoltaic system had been completed. However, it seems that we still need to be patient with the City of Cape Town. First, we waited forever for our application for connection and feed-in to be processed. Since more than two years we have been feeding in diligently – because everything else is in fact finished – and are still waiting for this to be reflected in our monthly bill.
But let’s go back to the beginning: our main intention with electricity – as with water – was, on the one hand, to be sustainable and, on the other hand, to be independent of the public supply.
What needs to be considered during planning
During the planning phase, I tried to calculate our electricity requirements and the necessary size of the system based on information available on the internet. There is a lot of reliable information on this subject in Germany, but it was only of limited use for our project in Cape Town. I found data on per capita consumption with and without hot water production. This gave me a figure of approximately 1,700 KWh per month. But of course, this did not take into account that the entire energy supply was to be provided by the system. Consumption by the pool, water treatment (you have no idea how many pumps you need for this), air conditioning, etc. were not included. But in fact, at around 1,800 kWh per month, we are only slightly above my initial estimate.
The other side of the coin is the capacity of the system. There is a simple rule of thumb for this in Germany: 1 KWp (kilowatt peak – the maximum achievable output) can generate approximately 1,000 KWh per year. I translated this based on information on so-called global radiation that I found for the Western Cape and other parameters for Cape Town and came up with 1,670 KWh per year. Based on my above consumption estimate and considering the assumed seasonality I thought 15 KWp for our system would be good.
The installers we asked for a quote didn’t want to know about any of my considerations. They had their own experience and recommended a configuration of panels, inverters and batteries – everything from Golf to Mercedes. We opted for a solid middle ground. The system consists of 48 panels, each with 455 Wp, covering the two roofs facing the sun – i.e. approx. 22 KWp. The controllers and inverters are from Victron and Fronius respectively and are working great. On good days in midsummer, we produce a peak of around 20 kW and 170 kWh in total. Per year we produce approximately 33,000 kWh in total.
Load shedding was a key factor in the configuration
Energy supply in South Africa is organised by a state monopoly, the energy supplier Eskom, which is responsible for generation, grids and distribution. Corruption has spread here, especially during the years of former President Jacob Zuma. As a result, new power plant projects have been delayed and made more expensive, and the maintenance of existing plants has been neglected, meaning that sufficient capacity is not and was not available. To prevent the grid from collapsing in situations of low generation and causing a blackout, the power is switched off several times a day for several hours, depending on available capacity. This is called “load shedding,” and we wanted to become independent of it.
Since the end of 2024, the load shedding situation has improved significantly and only occurs occasionally for a few days at and no longer on a permanent basis. Nevertheless, power cuts still occur from time to time due to maintenance work on the grid or other events. Our guests do not need to worry about this.
During the day, we produce an abundance of energy as described above and feed about half of it into the grid from spring to autumn (and we are eager to see when we will receive payment for this). At night, we rely on our batteries, whose capacity of 28 kW is sufficient for this purpose. We only discharge them to a minimum capacity so that there is always enough energy available
What else we had to learn…
We were, of course, used to electricity simply coming out of the socket and had not given any further thought to the details behind it. This changed with our own generation and desire for independence, because we initially realised that our battery capacity was not sufficient. Our consumption cycle did not match the cycle of the sun. For example, there are a number of devices that run unnoticed “in the background” when they are needed and consume a lot of electricity, such as heat pumps or the pool filter system. However, they do not necessarily run when the sun is shining. We solved this problem with timers. We also make sure that energy-intensive tasks, such as washing and drying laundry, are completed while the sun is still shining. This way, our consumption pattern matches our generation pattern quite well and we are always on the safe side.