Solar Water Heating Systems (SWH) are a renewable energy technology that heats cold water using the sun’s energy. The solar energy is absorbed by the panels or collectors, usually installed on top of the roof, and heats cold water.
Solar water heaters are a form of thermal heating, which relies on the direct energy emitted by the sun.
This is in contrast to other Solar Photovoltaic (PV) systems which convert the sun’s energy into electricity.
Solar Water Heating Systems are a good investment, especially for households with a monthly electricity bill exceeding R1200.
A household that installs a solar water heater will significantly reduce its monthly electricity bill as it will not always need to use City of Cape Town / Eskom supplied electricity to heat water but will instead rely on the solar water heater system to provide the bulk of the hot water.
Components of a Solar Water Heating System and movement of water
A typical solar water heating system has three major components: A solar collector (also known as a solar panel), a transfer medium and a storage container (also known as a geyser).
The solar collector absorbs solar radiation and transfers the energy in a form of heat, to the fluid within the collector.
The collector is often made up of a simple glass-topped insulated box with a flat solar absorber made of sheet metal attached to copper pipes and painted black (flat plate collectors), or a set of glass tubes surrounded by an evacuated (near-vacuum) glass cylinder (evacuated tube collectors).
Once the water has been heated by the collector it needs to be moved into a storage tank. The storage tank should be well-insulated to ensure the water remains hot for as long as possible.
The volume of the tank needs to be large enough to allow for bad weather days when the collector is unable to heat water.
When installing a new solar water heater system, households with existing Kwikot geysers in good condition less than 5 years old can save money by using the existing geysers as the storage tank by means of installing a retrofit kit.
Water moves around a solar water heater system either by natural convection (known as thermo syphon systems - thermosiphon solar water heater) or through the use of electrical pumps (known as pumped systems).
In a system using natural convection the water heats up in the collector and rises naturally into the storage container above it, while the cooler water in the storage container flows down, to the bottom of the collector creating an unaided circulation.
For a natural convection system the solar geyser used for storing the water needs to be located above the solar collector. In cases where the water is stored below the collector, an electrical or solar PV pump is used to circulate water.
Direct and indirect systems
Residential SWHs fall into two groups, direct and indirect systems.
Direct SWH systems, generally used in coastal applications, provide heat generated in the panel directly to the geyser, where it is then utilized by the home owner.
The indirect system, designed to overcome problems associated with frost in colder areas as well as poor quality water issues, uses a food grade antifreeze (Glycol) that is circulated through the panel into either an outer jacket or element in the geyser where the heat is then transferred into the water that is in the tank.
With indirect systems there is an additional step to the process of heat exchange.
Most of the solar water heater installations around the Western Cape are direct SWHs, which means that the hot water is directly heated by the sun.
Direct systems are commonly found in coastal parts of South Africa where frost and cold weather are not an issue and there is a good supply of sunlight.
However, the colder areas situated inland use indirect systems where the water in the panels is replaced by the anti-freeze solution.
Electrical Backup
The majority of solar water heaters include a backup electrical element in the geyser.
The electric element is used to heat water in the tank when it falls below a minimum temperature setting.
The backup system is normally required in cases where there is constant cloud cover and not enough sunlight to heat the panels.
This ensures that the users will always have hot water regardless of the weather conditions. The volume of water held in reserve will determine how long a system can last without electrical support.
Maintenance
Solar Water Heating Systems are fairly cheap and easy to maintain. The solar collectors need to be dusted off and cleaned from time to time to allow for maximum solar output.
To do this you can use soapy water and a sponge once every quarter depending on your area or hose and mop depending on your installation. However, owners are advised against using detergents.
The rain in the Western Cape is generally enough to keep the panels or tubes clean during winter. The inclination of the panels also helps the rain water to keep them clean. During the long hot Cape Town summer months, periodic cleaning and preventive maintenance is advised.
The benefits of installing a Solar Water Heating System
There are multiple benefits of installing solar water heaters in Cape Town, these include
• Saving money on your monthly electricity bill • Reduced demand of electricity and pressure on Eskom and the Municipality • Reduced greenhouse gas emissions • Reduced dependency on ever decreasing fossil fuels • SWHs are a sustainable renewable energy method with easy installation and maintenance
However, like most technologies solar water heater installations have had their share of challenges.
Some of the clients have uninformed and unrealistic expectations of what solar can do and in some cases do not take advice about which installations are suitable to their particular circumstances.
This has led to unwarranted criticism of the systems. An example is where residential clients are sold heat pump water heater systems where these are clearly will have no economic benefit for the quantities of hot water involved.
The big challenge is to get the reality of the savings across, moving away from “going solar” to understanding the financial impact of a reduced bill and using the correctly specified system.
There are currently rebates available on the Eskom Water Heating Rebate Programme which can reduce the capital outlay of the investment by between R5 000 and R10 000. It is for this main reason that a DIY solar water heating system is not advisable.
For further information please go to the Condor Solar Water Heating FAQ - Or contact us for a free Solar Water Heating quote
Get the latest updates in your email box automatically.
Your nickname:
Email address:
Subscribe