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Calculating ROI & payback
The payback on a PV system depends on the cost savings on electricity by the system.
The electricity generated will only amount to a direct cost savings, if you utilise it as it is produced, store it and use it later or feed in to the grid using a feed-in tariff or net-metering. An optimally There are a number of online calculators that allow you to calculate the yield of a PV system at specific coordinates based on orientation and angle. This can give you a good indication of the maximum savings that you can achieve with your system.
Alternatively using the above solar resource map and assuming an ideal orientation we can calculate the yields for Gauteng for a 5 kWp system as follows:
5 kWh/kWp × 5 kWp × 365 = 9,125 kWh
At an electricity cost of R2 per kWh that will amount to a maximum of R18,300 of savings per year.
However, it is vital to note that these savings can only be achieved through net-metering or total self-consumption. In general, a residential home will not be able to use the power as it is produced unless PV capacity is small compared to the overall consumption.
This can be overcome by storing the electricity for later use.
For example – (using the same illustrative system as above):
Size of System (kWp)
Size of Storage (kWh)
Cost Including Installation (Illustrative approx.)
Approximate Payback Period