Solar-water drive steaming ahead

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Slash your electricity bill
In April 2010 President Jacob Zuma launched the National Solar Water Heating programme in Winterveldt, north-west of Pretoria, where some 270 solar-water heating units have already been installed. The plan is to spread this campaign countrywide and get one million solar-water heaters set up in homes across South Africa by 2014.

Achieving this will also go a long way towards meeting another national target of ensuring that, by 2013, 10 000 gigawatt-hours of final energy consumption is supplied by renewable energy.

State utility Eskom, which runs the programme, is offering attractive rebates to households that replace their conventional, electric geysers with approved solar-powered equivalents. This could slash an average family’s water-heating bill by 50% to 70%, according to Eskom.

The utility has also calculated that, by switching to solar water heating, each household could drastically help reduce carbon emissions.

A 150-litre solar-water heater, which is adequate for two to three people, can save 4.5 kilowatt-hours of electricity per day, or 1.6 tons of carbon dioxide per year!

At the moment, most solar-heating units are imported due to a shortage of locally produced equipment, however, Minister of Energy Dipuo Peters says she is confident that our manufacturing base for such systems will grow rapidly and, by next year, more locally produced units will be available.


What is a solar-water heater?


Solar-water heating systems generally consist of a solar collector, a storage vessel, and a heat-exchanger in the case of indirect systems, and a pump in the case of a pumped system.

Indirect systems use a heat-transfer fluid called glycol to move the heat from the solar collector to the tank, which heats the potable water indirectly. Indirect systems are freeze-resistant, but require maintenance because the glycol may evaporate over time.

Direct systems are more susceptible to extreme cold and could actually burst in sub-zero temperatures. For this reason, they should only be installed in frost-free areas. There are, however, devices that can be added onto these systems to make them frost-resistant. Because of the absence of the heat-exchanger, direct systems are simple and reliable, and do not require regular servicing.

Solar-water heaters can be divided into two main categories: the flat-plate collector or evacuated-tube collector. The former consists of a simple, glass-topped insulated box with a flat absorber made of metal, which is attached to metallic pipes. The absorber is painted black to maximise the amount of energy from the sun.

The evacuated-tube type comprises copper pipes surrounded by a glass vacuum cylinder. This type of collector is very efficient at capturing the sun’s energy. Both flat-plate and evacuated-tube heaters work well in South African conditions.


What happens when there’s not enough sun to heat the water?


Solar-water vessels are far better insulated than conventional geysers, meaning the water stays hotter for longer. Like electric geysers, most solar ones operate with a thermostat so, if the water temperature does drop below the desired level, a backup electrical element switches on automatically.

To qualify for a rebate from Eskom, you must have a timer on the element so it doesn’t switch on during periods of peak electricity consumption or when the sun is available to heat the water.


How long will a solar-water heating system last?


Flat-plate direct systems can last for almost 30 years, if installed inland where there’s little chance of corrosion. Indirect systems are as hardy, but require more maintenance. However, good maintenance will prolong the lives of both systems.


Overview of how the process works

The first step is to visit the Eskom website and find a list of accredited suppliers in your area. You can also get advice by emailing the help desk at solar@eskom.co.za, or by calling the helpline on (011) 800 4744.

Once you have got the relevant supplier contact details, phone the person up and ask to be given a quote. It’s best for the supplier to come out to your home and assess your particular needs and set-up before a particular system is recommended. You will not receive the Eskom rebate if you do not use an Eskom-accredited supplier.

Once you have signed off the quote and paid your deposit, you will probably have to wait for about a week until the system can be installed, as there may be delays in sourcing the equipment.

When the supplier has all he or she needs, the job can be done in four to five hours. The maximum turnaround time from quote to installation is about 10 days depending on the supplier’s order book.

If you decide to buy a system that is not yet on the Eskom list, you must thoroughly research the track record of the product, and talk to several owners of such systems before you take the plunge. If the system is not accredited by the South African Bureau of Standards (SABS), it contravenes the SABS standards and will probably not be covered by your insurer.

For an average family of four, a 250- to 300-litre system (direct or indirect) is recommended. This will cost about R27 000 and the rebate will be between R7 000 and R9 000. A slightly smaller system of 200 litres will cost between R19 000 to R20 000 and the rebate will be about R4 800.

Generally, a plumber will install the system and then recommend a qualified electrician who will connect the solar water geyser up to the distribution board for back-up, fit a timer to the system and issue a safety certificate. Once you have the plumber and electrician’s input on the rebate claim form, you can drop if off at a collection point near you or post it to the facilitating auditors, Deloitte & Touche. More information on this process follows below. See “useful addresses” box for the relevant details.

Before a system is installed, you must decide on the following:

Will I get a direct or an indirect system?
In short, direct systems mean exactly that – water is heated directly by the sun. With indirect systems, water is heated up via a heat-exchanger. Generally, indirect systems are suitable for all areas and water types.

Go for a direct system if:

  • You live in a low-lying area or at the coast where you don’t get any frost. Places on the Highveld, such as Johannesburg, are not ideal for direct systems. A good indication of being in a frost-prone area is if your ambient temperature drops below 4°C. If this is ever the case, you need a freeze-resistant system

  • The water in your area does not have a high mineral or chemical content. An easy way to determine this is by checking for an accumulation of lime scale inside your kettle. If there is such a build-up, your water probably has a high mineral or chemical content and is therefore not suited to a direct system

Go for an indirect system if:

  • You live on the Highveld or any other region above sea level

  • Your area is prone to frost, and temperatures drop below 4°C

  • The water in your area has a high mineral content and calcium build-up occurs

What size do I need?
The size of the system depends on your household’s hot-water requirements. The system should be capable of meeting these requirements so you don’t have to rely on electrical back-up.

To work out how big your system should be:

  • Allocate 50 litres of hot water per person in your household. For example: four people = 200 litres

  • Then add an extra 50 litres to cover general domestic hot water usage. For example: 200 litres + 50 litres = 250 litres

  • Use this total as the minimum holding capacity of your solar water heater

Consider the climate you live in when choosing your system. If you live in an area that gets a lot of rain or cloud cover, a lower-cost system with smaller panels won’t meet your household’s hot-water needs. This means the electrical element will kick in to make up for the shortfall, so you won’t save much electricity.

Likewise, if you live in an area that gets lots of sunshine every day, a big system with big panels will produce more hot water than you need. This can cause the system to produce water that is too hot, which could be a safety risk.

What type of water storage do I need?
You have two choices: pumped storage, where water is forcibly moved by a pump, or thermosyphon, where the tank is placed above the solar panel, usually on the roof, and water moves by natural convection.
Choose pumped storage if:

  • You want the tank to be located away from the panel and hidden from view in a cupboard or in the ceiling

Choose thermosyphon if:

  • You don’t mind having the tank in view on the roof

  • Your roof structure can handle the weight of the tank

  • You want to reduce the chance of water damage from a burst geyser

What type of installation do I need?
There are three tank configurations to choose from:

  • A standard installation, which uses a new solar tank – this is the most common and recommended installation

  • A pre-feed installation, where a solar tank and panels are used to pre-feed an existing electrical geyser

  • A retrofit system, where just the solar panels are fitted on an existing electrical geyser

Choose a standard installation if:

  • You want to replace your existing electric geyser

  • You want to optimise the use of solar energy and not rely on electrical backup

  • You want to save as much electricity as you can

Choose a pre-feed installation if:

  • You want to feed solar-heated water into an existing electrical tank. This type of installation is only recommended when extra hot water capacity is required

Choose a retrofit system if:

  • You want to save on the cost of buying a new solar tank. Your existing tank must be suitable for this type of application and must be in good condition. A supplier will tell you if your tank is suitable or not

Once you have made these choices, and had the system installed, claim your rebate!

  • Ask your accredited supplier for your claim form, which should have the details of the electrician and supplier already filled in – and have the Eskom rebate structure on it

  • Fill in your personal details

  • Attach the original invoice, a copy of your ID and a copy of your utility bill as proof of residence

  • Post or drop off your claim at the facilitating auditors, Deloitte & Touche, within six months of the installation. See “useful addresses” box for the relevant details

  • You will receive an SMS notification when the auditors receive your application, when your application is processed and queued for electronic payment, or if your application is incomplete. The rebate is paid within eight weeks of receiving the correctly completed form

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