The rebate is a scam. The BEE supliers that are eligible to give the discount charge way more than skipping it altogether. The only real option is either get a plumber to do it and buy everything from a plumbing supply shop - the kwikot vacuum tube collectors are reasonably priced. Another option is to get someone from ITS to install it. From itssolar.co.za you can contact them and they will put you in touch with the nearest franchise. A retrofit is more complex than a standalone unit, and it costs about the same. It will look better, though and you have better control over the temperature with a proper controller.
A very important thing to consider is the q factor. That is basically how much energy you can collect from the sun. I have 24 tubes with a 200l geyser, it is a bit much, and my system is properly isolated, so it is also more efficient than most. I get about 10kWh worth of energy per day after losses. Wich means that I never use any electricity except when the sun doesn't come out for more than a day. It also means that the geyser would boil everyday if two people only shower or one bathes and one shower.
If you look at the list of approved systems on the eskom website, you will see that many have only enough energy to overcome the daily standing losses of the geyser, which is pretty useless. (Q factor around 10MJ, mine is >40MJ).
Another consideration is that you need double the capacity geyser for solar than for electric, since you cannot reheat the water in the night, so budget 100l per person, unless you are prepared to heat it to 80degC+.
For an 18 tube system, it should cost about R15k installed with a controller from ITS, which should be sufficient for a 150l geyser, all the cheaper options are not worth it, they either do not add enough energy to ever pay themselves off, or are low pressure type systems that are a real pain.
