Some Of The Key Factors To Consider Before Purchasing A Solar Water Heater
Shade is a determining factor
Shade on the collector of a solar water heater is the number one enemy of the efficiency of the solar water heating system, as any shade will cause the rays of the sun not to penetrate the panel to be converted into energy to heat the water. The biggest cause of shade are trees, buildings, chimneys, roof structures on the Northern or Western side of the solar water heater.
What is the thickness of the insulating foam around the inner tank?
According to the new VC specification that was Gazetted for implementation on 12 September 2017, the insulation foam around the inner tank must be thick enough to ensure the correct energy grading as per the new standard. Solar water heaters must at least have a 50mm insulation between the inner tank and the outer wrap of the storage vessel to ensure that the water is insulated to stay hot over a 24hour period. Please keep in mind that the sun doesn’t shine at night, so if all the hot water is depleted at night, the water will not be able to be hot in the morning unless the back-up element heats half the storage vessel for the morning use.
The quality of the inner tank
Stainless steel is commonly used in the manufacture of cutlery, pots and pans, water tanks and many other industrial applications due to the longevity of the product. With solar water heating systems, various grades of stainless steel are used to manufacture the inner tanks. The best quality inner tanks for hot water applications, are manufactured from type 444 stainless steel because of its corrosion resistance properties at elevated temperatures.
Why does the grade of stainless-steel matter?
The different stainless-steel grades are high-alloy steel that have excellent corrosion resistant properties when compared with other steels. One property common to all stainless-steel grades is that they contain chromium and this provides corrosion resistance.
Many years ago, producers of electric hot water tanks all over the world started replacing the traditional enameled-steel water tanks with stainless steel tanks. The corrosion-resistance of stainless steel meant that the tanks had a far greater lifespan.
Flat-plate or evacuated tube collectors?
The choice between a flat-plate and evacuated tube solar water heating system is usually a personal choice based on cost. The main difference actually comes down to the efficiency. With evacuated tubes, the vacuum drawn on the product, provides almost perfect insulation and also increases the efficiency, as a product with a vacuum drawn, operates at 50% better efficiency, compared to a non-vacuum product as a flat plate.
A flat-plat panel has insulation at the back and sides, with glass on top and is subject to heat loss. Generally during the summer months, there’s very little difference in performance between the two. However, in winter when we have cold days and lower light levels, the evacuated tubes will perform better.
Flat plate solar collectors can be used in most climates, but are significantly more suitable to warmer, sunnier climates, where freezing and solar angles are less likely to impact on the solar water heating system (which are coastal areas in South Africa) . When a portion of a flat plate collector fails, the entire flat plate collector must be shut down and replaced. Flat plates in frost sensitive regions normally use a glycol heat transfer fluid which requires replacement every two years.
Evacuated tubes require no maintenance (with a 15-year design life on the selective coating) and is very affordable to replace, should the need arise. Evacuated tubes capture sunlight better as they have a greater surface area exposed to sun at any time. If one tube becomes damaged, only that tube needs to be replaced. Depending on the type of tube system used, there is no need to shut down the entire system and no water wastage occurs. The vacuum tubes are also resistant to damage from adverse weather conditions and are tested according to SANS 1307 to withstand a 32mm hail stone at 10MJ close range.
Ensure you invest in a system made from high-quality materials – cheap is nasty
When you invest in a solar water heater, make sure you select a system that is manufactured from high-quality materials. Avoid the cheap units and rather choose a locally manufactured system that provides you with local backup and support.
Units with longer warranties usually are of higher quality, but so often – as with everything else – the least expensive option you purchase is the most expensive option in the long run. Remember, the purpose of a solar geyser is to collect energy from the sun in the most efficient way to prohibit electrical backup and the resultant costs.