Clearing Up The Confusion About Solar Water Heater Systems

Investing in a solar water heater is the best investment you will ever make, but you need to start investing sooner than later! There are a couple of deciding factors on the type of system you’ll need, which brand or what capacity etc. and this can be confusing and overwhelming.

The South African National Standards 10400XA that was Gazetted by government as law in 2011, makes it compulsory to fit a renewable form of water heating on your newly built home or extension of your existing home, to bring down the carbon footprint of your household. 

We often make costly but important decisions based simply on the advice from friends, family, neighbors and in most cases based on whatever the salesperson of a brand tells us we use to form a decision.

When you consider purchasing a solar water heating system one must bear in mind it consists of a collector system (flat plate or evacuated tubes) and a water storage tank. The hot water tank in a solar water heater is the most critical part of the system and generally consists of an inner tank and an outer wrap. The inner tank contains the heated water and is insulated to keep the water hot. The outer envelope protects the insulation material and provides a foundation for mechanical fitment to your roof.

Some Of The Key Factors To Consider Before Purchasing A Solar Water Heater 

What is the application of the solar water heater?

Solar water heating can be used for household applications and industrial applications – the size of the systems will differ as well as the temperature needed – on industrial installation, the correct way to specify the size is 1 tube per ten liters or 1 x 1sqm flat plate collector per 100 Liters.

Solar water heaters are designed to collect the energy from the sun during the day, for the water to be utilized in the evening.  Most solar water heaters do have an electric back up as the main objective remains to have hot water on demand but according to SANS, the electrical back up element is fitted in the middle of the tank and not in the bottom of the tank as per the normal electrical geyser, resulting in a solar water heater only heating half the tank with electricity.

How many people will be using the system?

One of the most important factors to consider when choosing the size of the solar water heater are to make use of the stats provided by the SABS.  The SABS regulations states that with a solar water heater, the storage vessel is specified at 75L of hot water per person per day thus a household of 4 people need a minimum of 300L to have a proper saving, as you are looking at a solar water heater with an electrical back up and not an electrical water heater with a solar back up!

How far is the point of installation from the point of draw-off in the home?

It is always ideal to have the solar water heater as close as possible to the point of draw off, either being the kitchen, bathroom etc.  If possible, the solar water heater must not be further than seven meters from the point of draw off, as the efficiency of the solar water heater will be affected by the distance of the pipe work that transports the hot water from the storage vessel to the taps.

Is the house roof suited to have a solar water heater installed?

It is of utmost importance to inspect the roof structure prior to the installation of a solar water heater. First of all, the house roof must point in the direction of North, North West or West. The ideal angle of the solar water heater installation must be between 21 and 34 degrees for optimum heat exchange between the panels and the storage unit. The roof structure needs to be supported properly under the point of the installation.
 

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.