Posted by: Yes Solar Cape (Cape Town, South Africa) – 29 October 2010
When purchasing a solar water heating system consider the following 12 points, and evaluate each one before committing to a system.
1. Certification – what kind of certification does the system have? First prize is SABS Mark Approval. This is a higher form of certification than just an SABS Test Report. Mark Approval means that the entire supply chain of the product has been inspected and that SABS are confident that the product will consistently meet their standards.
2. Also look out for Solar Keymark certification (EU), and the German TUV standard.
3. Direct versus Indirect systems – basically, if you live near the coast you can install a direct system (no intermediate heat transfer fluid), but if you live somewhere that is prone to frost (i.e. temperatures drop below 4 deg), then you have to go for an indirect system. Where possible, go for a direct system, the heat loss between panel and geyser is lower.
4. Evacuated Tube versus Flat Plate collector – the respective suppliers / manufacturers of these systems place too much emphasis on this question. Rather look at the build quality, efficiency and durability of the collector, regardless of the type of technology it employs. Pay special attention to corrosion resistance – low quality stainless steel and shoddily galvanized metals will start to rust after a couple of years.
5. A quick way to measure efficiency is to look at the rebate a system enjoys. The rebate is simply a multiple of the Q factor of the system (which is a measure of its efficiency). But be careful to compare systems of the same size, e.g. a 200 litre system with a 200 litre system.
6. Thermosiphon versus Pumped – I won’t install an evacuated tube system in a thermosiphon configuration (this is where the geyser is higher than the panel and the water circulates by convection) because evacuated tubes can produce extremely high temperatures, and a pump/controller configuration is better able to regulate these high temperatures.
7. A flat plate in a thermosiphon configuration has the advantage of simplicity, but is only possible if you put the geyser on the outside of your roof, or if you have a very steeply pitched roof and mount your geyser in the apex of that roof (higher than the top of the panel outside).
8. Bigger is better with solar – choose a geyser size that’s bigger than your current geyser. Your savings will be maximised if you have a big tank which can store your solar heated water through periods of no or low sunshine. A 300 litre tank may sound excessive, but for four or more people in a house it’s recommended.
9. Geyser quality is important – in a solar configuration your geyser needs to be able to withstand high temperatures and it needs to be well insulated to retain that heat. There are a number of cheap geysers (hot water cylinders/storage tanks) on the market, made of materials such as fibreglass. Be wary of companies that do not have a long track record of making geysers that last. Look for at least a 10 year warranty on your geyser.
10. Eskom accreditation – check that the system, the supplier of the system and the installer of the system are all accredited by Eskom, or you won’t be able to claim your rebate.
11. Backup and support – check the details on the warranty – not just how long it is, but under what conditions it is effective. Are there any exclusions? Also consider how long the supplier has been around, and ask them for customer references so that you can find out what their level of backup service is like.
12. The manufacturing location of the product could be a factor for you, but bear in mind that the entire world buys their evacuated tubes from China (bar a few manufacturers in Southern Europe), so don’t expect to get a South African made evacuated tube system. That being said, there are some good flat plate manufacturers in SA, and buying from them has the additional benefit of being transport emissions free.