How long untill I get my money back

What about financial payback?
Approximately 5 years

A typical 200L geyser uses an average of approximately 11-13 kWh per day to maintain the temperature at 60 degrees. At the current 39c/kWh this resolves to R4.29 per day or 1565.85 per annum.

With projected Eskom tariff increases of 30% per annum the recovery point for a system delivering 9.23kWh into a 200L tank will be reached between 5 and 6 years based on the installed price of the 9.23kWh product of R17, 300

Anything less powerful than 9.23kWh into 200L will take correspondingly longer to recover.

kWh Cost Annual Saving
Year 1 R 0.39 R 1,575.89
Year 2 R 0.51 R 2,048.65
Year 3 R 0.66 R 2,663.25
Year 4 R 0.86 R 3,462.22
Year 5 R 1.12 R 4,500.89
Year 6 R 1.46 R 5,851.16
Total R 20,102.07

See the Sky Power Payback Calculator: -
http://www.skypower.co.za/content/calculators/power_demand.asp

Any 200L product with a lower Q factor forecasting a shorter payback will be overly optimistic.