These solar systems pay themselves back, by off-setting the  electricity generated by the system, directly against the clients municipal electricity account. What this means , is that the clients electricity bill is reduced on a monthly basis , by the amount that the solar system generates. The ROI (Return on investment) is usually between 3,5 - 5 years, and thereafter the electricity generated is pure profit. IRR (Internal rate of return) is between 22 -25% per annum over a 10 year period. After 10 years the IRR exponentiates. The life expectancy of the system is excess of 20 years. There is a special tax incentive by SARS -12B allowing the client to write off the initial project costing at 100% in the first year.