Solar Water Heating Systems.

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Solar Water Heating Buyer's Guide

If after reading this guide you still have any unanswered questions, please do not hesitate to contact us for further information. At first glance the purchase of a solar water heating system might seem a little intimidating, enough so to often deter potential buyers from following through on their decision to save money and help save the environment. This buying guide takes you through some of the key factors you need to consider when purchasing a solar water heating system. 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)

1. How does solar water heating work?

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.
  
• 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.
  

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:

• The Flat-Plate Collector System is the traditional solar system comprising of a solar panel which is approx 80mm thick and ranges in size anywhere from 1.5 sq. m to 4 sq. m. The solar panel is mounted on the roof and is connected to a solar geyser which can also be installed on top of the roof (above the panel) or inside the ceiling. Flat-plate collector panels have been around since the 1950's and whilst the materials used in the manufacture of the solar panels have improved over time, the technology within the system is largely the same. The system utilizes the thermosyphon principle whereby cold water is fed into the bottom of the solar panel, and as the panel is heated by the sun the water in turn is heated and automatically starts to rise to the top of the solar panel from where it is then fed into the solar geyser. The Flat-Plate Collector System is a tried and tested system which has provided thousands of people with solar-heated water for decades.

• The Evacuated Tube Collector System is a much newer system which has been available in South Africa for around 10 years. With this system a series of cylindrical glass tubes are attached to a frame and installed on top of a roof. Each tube is approx 1.8m long and inside each tube is a copper rod (copper heat pipe) which extends from the bottom to the top of the tube and then into a manifold. A special chemical formula inside each tube starts to boil between 30 and 40 degrees celsius. This quickly heats up the copper rods in each tube which in turns heats the water which passes through the manifold. The manifold in turn is connected to a geyser (some evacuated tube systems are connected directly to a geyser instead of a manifold / close coupled).
  

• Which Solar Geyser Should I purchase?

        

  There are two main technologies on the market, namely Flat Plate Collectors and Vacuum Tube Collectors. There are advantages and disadvantages to both systems, and the debate over which technology to use has been going on for many years. It is important that the sales person you are speaking to understands both technologies and can offer you both options depending on your budget, geographical area, water quality and number of people that will be utilizing the hot water from the solar geyser.

• Table courtesy of eskomdsm.co.za