I'm also in the business of SWH.
Go for a good brand, Kwikot, Solarhart and have it installed properly or do it yourself properly. There is a lot of energy in 200 litre of water at 65 degrees C, so follow plumbing regulations, the regulations gave been learnt the hard way. I have seen 3 holes blown in house's roofs from botched geyser installations, not to mention rejected insurance claims because of DIY jobs, so please be careful. Replacing roofs, ceilings, cupboards, carpets etc can get pricey.
Water temps over 65 simply reduce the life span of the tank, I always laugh when installers brag about how hot their systems get.
Vacuum tubes are fine for Europe, but not suited to SA condition, they are TOO EFFICIENT. Geysers are designed to vent at certain a temp and pressure, so if the water in the system gets too hot (usually at about 14h30) the safety valve opens and vents basically half of the tank, so you get home to a tank of caold water in the evening. Currently the SESSA ombudsman is facing several hundred complaints almost all of which are vacuum tube systems, so be careful.
Flat plate collectors look like skylights, 25 year lifespan, ideal for our climate. In three years I have done several dozen installations where the client has requested NO electrical backup and 60 - 65 degree water has been no problem. Don't get confused by the whole efficiency of EVT vs Flat plate debate. EVT IS MORE EFFICIENT, but flate plate is better, we are certified to install both so I am totally unbiased. EVT is better for industrial/commercial applications, hotels and guesthouses where hot water is constantly used. Residential application always go for flat plate collectors, at least 1m2 per 100 litres, you won't be sorry.
Budget on R16 000 for 150L, R22 000 for 200L and about R26 000 for 250L. Rebate of about R2 000 for 150L, R3 900 for 200L and R4 700 for 250L.
Go to Eskom website, look under DSM for a pdf list of all accredited installers.
CSIR figures put energy spent on water heating at 43%, generally (almost 400 SWH installations experience) 30% - 40% saving residential and 55% - 60% saving B&B/guesthouse application. Payback is under 4 years, depending on usage. Yet to have a dissatisfied client! My house of 4 runs off a 200L Kwikot direct system, installed by myself when I started my business. It only uses electrical backup on rainy days (I got fancy and installed a rain sensor, from a wrecked Merc), cloudy days, winter days - no problem.
There is a lot of distrust about the solar industry, SWH prices are not going to drop much further and it is the biggest saving you can make per Rand spent. To the clever arse punting RA's, show me an investment of R22 000 that can give you GUARANTEED monthly income of R500 AND SAVE THE PLANET from day one!!!!!! I know, I have installed systems on 4 stock brokers houses, challenge me, I dare you, I double dare you.
Photovoltaics are still exorbitantly priced with enormous ROI timeframes. Wind turbines are only truly efficient on towers 15 - 20 metres high, EIA's and departures from immediate neighbours required in residential applications, so good luck (I currently have 16 clients going through the motions of wind turbine applications). Solar batteries are very expensive, standard deep cycle batteries are reasonable, but require replacement every 5 - 8 years depending on maintenance and charger/monitoring equipment quality.
All I can say is do your homework. Talk to people. Most of my time is spent educating people, I am a treehugger so I don't mind. Call me, PM me, I don't mind.