Solar Water Heating

In an average household in South Africa, water heating is the greatest expense when it comes to energy costs. Obviously, the more hot water you use, the more electricity you use and the greater your monthly bill will be.

1.Research your requirements

  • Find out the best type of hot water system for your household - either a solar, gas or heat pump hot water system. Consider your household size, available energy sources, your climate, space and access, and your existing system.
  • You should also consider purchase and installation costs, as well as running costs for different systems. Don’t forget to include potential long term energy savings and reduced greenhouse gas emissions in your decision making.
  • Make sure you understand what electricity tariff will apply to your new hot water service.
  • If you decide on a solar hot water system, it’s important to choose the most appropriate one for your needs as there are many different types available. You will need to consider your house type, roof characteristics, available space and visual appearance.
  • Talk to your installer or supplier about Small-scale Technology Certificates (STCs), An STC is a measure of renewable energy which can be traded for cash or a discount on the purchase price of solar or heat pump hot water systems.
  • If you are looking at particular systems or models, you will often be able to research them online.
  • For further details and resources about the different types of systems available and how they work, see ‘Further information’ below.

2.Contact installers

  • Seek expert advice about your options and get several written quotes to make sure you get the best system for your needs at the best price. You can speak to installers, building information centres, designers or retailers for advice.
  • Check your installer is accredited. Qualified installers will be aware of safety issues and will install systems correctly.
  • Ask installers about any additional costs that may not be included in the quote.
  • If you are in a frost-prone climate, make sure your system is appropriate for the conditions.
  • Ask about the warranty and after-sales service and what help you'll get if you have questions about your installation in the future.

3.Install your solar hot water system

  • Talk to your installer about the best place to locate your system. In Australia, for the most efficiency, solar hot water systems should face north. The best tilt angle of the solar collectors will depend on where you live. Make sure the solar collectors (usually flats panels or evacuated tubes) are not shaded by trees or nearby buildings, particularly in winter.
  • Some solar hot water systems have a storage tank located on the roof. A complete system when full of water can weigh several hundred kilograms. Most roofs can support a storage tank without reinforcement but talk to a builder, designer or engineer to check yours.
  • If you have a booster control, make sure it’s in an accessible location and has an indicator light you can see from inside to remind you to turn it off when not needed. (Most solar hot water systems will need a booster to guarantee hot water when sunshine is low and to make sure that the water is heated enough to prevent growth of bacteria.)
  • If your system has an electric booster, the person doing the electrical work must be licensed to undertake this work.
  • If you have a booster control, make sure it has a timer to ensure that you are only heating water when you need it.
  • Make sure your pipes are insulated.
  • While your installer is on site, make sure you have all the information and paperwork necessary to lodge application for any rebates you may be eligible for and renewable energy certificates.
  • Request a Certificate of Compliance from your installer so you can be confident your new water heater meets all regulatory requirements.

4.Operate and maintain your system

  • Before your installer leaves, make sure you have clear instructions on how to operate your system and what maintenance is required. Follow the manufacturer’s maintenance recommendations.
  • Talk to your installer about having your hot water system regularly inspected and serviced.
  • Set the temperature of your booster thermostat to a minimum of 60°C. This is to prevent growth of harmful bacteria. Don’t overheat the water as this wastes energy.
  • Use hot water early in the day if possible so that the water left in the tank will be heated by the sun, ready for use at night.
  • If you have a booster, make sure you turn it off when going on holidays. Consider turning it off during summer if conditions are favourable.

 

By reading this, you will come to realize that implementing solar water heat in your home or business is not as complicated and intimidating as you initially thought.

This buying Guide will cover the following topics:

  • How does solar water heating work?
  • Types of Solar water heating systems
  • Types of solar collectors
  • Determining how much water your household uses (what size system you require)

 

How does a Solar Geyser Work?

Solar Geyser Direct relies on warm water rising, a phenomenon known as natural convection, to circulate water through the flat plate collector and to the tank. The hot water storage tank is located above the flat plate or in the roof. As water in the plate heats, it becomes lighter and naturally rises into the tank above. Meanwhile, cooler water in the tank flows downwards into the absorber, thus causing circulation throughout the system.

On very sunny days Solar Geyser Direct can bring water to boiling point.

Internal Workings of a Solar Geyser




How a Solar Geyser is connected to your existing geyser

 

How an indirect Solar Geyser is connected to your property

Solar water heating is an entirely different technology to solar powered electricity generation. Whereas solar power uses the suns energy to create electricity, solar water heating uses the radiating heat from the sun to physically heat water up.

A solar water heating system is made up of three primary elements:

  • Solar collector: This is an energy device which has been specifically designed to absorb solar heat radiation and transport that energy into the transfer medium or liquid passing through the collector.
  • Energy transfer medium: This is a medium that via the process of conduction or convection, transfers the heat that has been absorbed by the solar collector, into the water to heat it up.
  • Thermally insulated hot water storage vessel or geyser: Usually consisting of an inner lining made up of copper, steel or a polymer, this is the storage vessel, or more commonly, the geyser in which your water is stored and kept warm. Different geysers with different pressure systems are used in various circumstances, depending on the overall system design.

Solar water heating geysers are usually larger than your average household geyser as they are required to store the ENTIRE water allocation for each day.

Depending on your requirements, you can either use your solar water heating system to supplement the amount of heated water required from your conventional electric geyser, or you can use it to completely replace your electric geyser and provide your total hot water allocation for each day (recommended).

As far as the positioning of your solar water heating system is concerned, it can be stored on the roof, in the ceiling or in a regular closet as with a regular electric geyser. Ideally, you want to store your water storage vessel vertically, but if this is not a possibility, it can also be mounted horizontally without too much of an effect on the performance of the geyser.

2.    Types of Solar Water Heating Systems:

There are two main types of solar water heating systems, namely:

·         Open circuit or direct systems: These types of systems circulate water directly to the geyser from the solar collector. Unfortunately, these systems aren’t anti-freeze resistant and therefore often not eligible for an Eskom solar water heating rebate if you reside in an area of the country that is susceptible to extremely cold temperatures. 

 

·         Closed circuit or indirect systems: These are systems that contain a heat transfer medium that is circulated through the pipes within the system to heat the water and then returned to the solar collector for re-heating. These systems are more resistant against colder temperatures and are therefore recommended for use in the South African inland where frosty conditions are often experienced.

 

3.    Types of Solar Collectors:

As mentioned before, Solar Collectors are the actual solar water heating panels that absorb the heat from the sun and supply the heat to be used in the remainder of the system. There are two main types of solar collectors:

  • Flat panel collectors: These types of collectors tend to be a little more versatile as far as their positioning and placement goes. They can be mounted on the roof, inside the roof or even separate from the roof if need be.
  •  Vacuum (Heat pipe) / Evacuated tubes: These tubes function similarly to the way in which a hot water (coffee) flask does; by creating a complete vacuum inside the parallel pipes that make up the collector, which results in the water staying hot once heated.

Evacuated Tube Collector

Both the above systems are equally effective as long as they are used in the correct type of system. Have a look at some of the pros and cons of each system and then decide which will best suit you and your domestic solar water heating needs.

 

4.    Selecting the correct size solar water heating system:

The two variables that come in to play when determining the size of the solar water heating system that you require are the size of the total collector area and the size of the geyser/storage vessel that you require.

The general rule of thumb for calculating the size of your solar hot water heating system is that on average, each person in the house requires approximately 50 litres of solar heated water per day. Obviously, this can fluctuate depending on different people’s habits, but one should aim to use on average this amount of water.

Remember though, that different household tasks and appliances also utilize hot water. Below is a table that illustrates the average daily hot water consumption for a family of four:

Sizing example for a household of four people:

Daily hot water requirement

50 litres per person (200 litres)

Hand basins

5 litres per person per day (20 litres)

Dishwashing

3 litres per meal, assume 2 meals at home daily (24 litres)

Add compensation for heat loss due to cold water mixing

244 litres x 20% (48.8 litres)

No washing machine added

 

Total hot water requirement

292.8 litres per day

Table courtesy of eskomdsm.co.za

You see, it’s not that complicated

As you can see, the process of selecting a solar water heating system need not be any reason to deter you from actually going through with purchasing one. Your biggest considerations are what type and size of collector to utilize, and what size storage vessel/geyser to use.

At savenergy.co.za, we realize that purchasing a solar water heating system such as this can be intimidating, which is why we have put together solar water heating kits which contain all the necessary equipment that you require in order to start saving money on your electricity bill whilst at the same time reducing your carbon footprint on the environment.

If you require any further assistance, please do not hesitate to contact us. We have professional consultants at hand to advise you on exactly what you require and what type of system will create maximum benefits for you.