We live in an age where the non-renewable resources on which we rely so much are fast depleting. We have Eskom’s load shedding threats hovering over our households. And the National Building Regulation now states that energy usage in new home is restricted. As a result, saving energy should be a key consideration in eco building and sustainable home building. Fix Shack explains the in and outs of solar water heating, allowing home owners to make informed decisions when it comes to their water heating needs.
Although solar water heaters have been available since the 1800s, today’s solar water heaters are much more effective in reducing energy bills in an environmentally-friendly way.
Solar water heating is the process of harnessing energy from the sun in order to heat water. Water is circulated into solar panels; solar energy is absorbed by a solar collector, heating the water; the hot water is then stored in a tank, ready to use.
Choices choices choices
1. Two types of solar systems are available: direct and indirect systems. Direct systems function by circulating water between the solar geyser and the solar collector. Usually, these systems are installed in environments that are not exposed to frost or snow. In contrast, indirect systems circulate glycol, a nontoxic antifreeze fluid, between the solar geyser and the solar collector. An indirect transfer of heat from the glycol to the water, using a heat exchange mechanism, allows the water to become hot. These systems are resistant to frost and snow, and they often have a longer lifespan when compared to direct systems.
2. There are also two ways in which the heat is circulated between the solar geyser and the solar collector: thermo siphon systems and pumped circulation. In thermo siphon systems, the solar geyser is placed above the solar collector. Because water rises when it becomes hot, the circulation is unassisted. In contrast, pumped circulation achieves just that: circulation by means of a pump. In these systems, the solar geyser is placed below the solar collector; therefore, it requires assistance in order to circulate. Because pumped circulation requires the installation of various mechanisms, there is a greater likelihood that the system will fail.
3. Collectors come with two options too. Solar flat plate panels are the most common types of collectors and better suit South African weather conditions. These panels are shaped as a rectangular box with an absorber plate inside them. The absorber plate transfers heat into a fluid (either water or glycol). This collector is often covered with a hail-resistance substance. Solar tube collectors have been developed for use in predominantly colder climates. There are various types; however, the heat rod type is most common. In this type, the solar water heaters are rows of parallel, glass tubes. These tubes collectors reach hotter temperatures than flat plate collectors.
4. During installation of the solar water heating system, the solar geyser is either positioned directly above the solar collector, or it is mounted a fair distance from the solar collector. In the former method, heat loss is minimized and the installation is much simpler. In the latter configuration, lengthy pipes are required which are costly and result in greater heat loss. Maintenance and installation is also much more complex.
Consider these installation guidelines before installing your solar water heating system
• In order to perform optimally, the collector must face the sun when the sun is at its highest and strongest, i.e. 12 noon. In order to accomplish this in the southern hemisphere, the collector should be placed to face the north.
• To make sure that the maximum amount of sunlight is falling at right angles on the solar collector, the solar collectors should be inclined upwards the same number of degrees as the angle of latitude. This will allow the collector to receive the sun’s radiation at right angles at midday, both in summer and winter.
• Roof structures have commonly been designed to support loads of approximately 80kg. However, when solar installation requires that the storage cylinder, weighing much more than 80kg, be mounted on the roof, roof strengthening will be a likely requirement.
• The size of a solar water system is based on the size of the hot water storage tank and the collector area, and is dependent on how much hot water is used in the household. It is advantageous to have two days of hot water usage in storage, in case the sun disappears for a day. The more household members, the more the household water consumption, and therefore the bigger the storage tank and collector area needed. In terms of collector sizes, an approximate rule of thumb is that a 1m2 area is required per person, as well as 1m2 for each appliance that uses hot water from the solar system.
When deciding to install a solar water heating system, take note
• The contractor installing your solar water heating system must be a qualified plumber, registered with the Plumbing Industry Registration Board, and with additional solar training. Solar plumbers must issue a Certificate of Compliance (COC) on completion of the installation. This is an assurance that the plumber has worked according to the national standards, and it also holds the plumber accountable for work done incorrectly.
• Eskom is currently running a rebate programme for solar water heating systems. In order to claim a rebate, the solar system must be accredited by and registered with Eskom, and the installer must be registered with Eskom too. Customers claim the full installation price and then claim the rebate back from Eskom. The monetary value of the rebate is dependent on the type of solar system installed, and therefore, it varies between R4 000 and R10 000 per solar water heating system.
• The solar system must be tested and approved by the South African Bureau of Standards.
• The solar system should have a warranty of at least five years.
• Ensure that post-installation maintenance as well as continuity of spares and replacement parts is available.
Solar systems, correctly installed will result in a 60% saving of water heating costs, making it an inexpensive eco-friendly water heating option. However, saving water heating costs is also dependent on users changing their water habits. Therefore, the optimum efficiency of the solar water heating system is dependent on its users’ lifestyle changes.
For more information, see Green Plumbing Advisory Centre’s page on Solar Water Heaters.