Solar geysers and how solar hot water heaters work

Solar Thermal Flat Panels

Solar thermal panels

Solar geysers and thermal energy panels. Next time you receive a high costing electricity bill, you might start to think about alternative energy solutions. One of the most popular and effective alternative solutions, is solar energy. Won’t you feel good if you are independent from Eskom and can generate electricity and thermal energy directly from the sun? Many people all around South Africa and around the world, already converted to solar energy as their main source of power. Most of the solar energy gets received in the form of heat rather than electricity. Solar PV panels or photovoltaic cells, converts sunlight to electricity are becoming more popular presently around South Africa. However, solar thermal panels which are used to generate hot water by using the sun, have been a popular implementation in South Africa for the past decades.

Save on bills even during winter with a solar geyser

South Africa is a very sunny country and solar thermal panels hugely benefit from this factor. However, some parts around the country can get very cold during winter times. But apart from the cold, solar geysers or solar thermal hot water collectors, can still produce enough hot water for your home. Thus, you will still be saving great amounts on your electrical bills with a solar geyser. Most solar geyser systems can produce up to 90% of your hot water. Therefore, allowing the solar geyser system to pay for itself in about 10 years, just from the savings made.

Save Money With Solar Geysers
"... One of the most effective and efficient steps the government can take is to encourage the use of solar hot-water systems—a well-developed and relatively low-tech method for using the sun's energy."
Larry Hunter
The New York Times (Op Ed), 2009
Build Solar Geyser

How to build a solar geyser system

In the most basic form, you can create your own solar water heater system at your home. Although, water can take a long time to heat up by using the sun. However, water has a good and high heat capacity and that is why water or liquid is used to transfer thermal energy. So, how can you construct a solar geyser system by yourself by the means of only using water?

Simple solar thermal example

This is just a simple example which aims to also explain how a solar geyser system works. If you take a plastic or glass bottle filled with water, leave it in the sun for a long period, the water will be warm as time passed. But, there’s a problem with this scenario. A jar of water won’t provide your home with sufficient hot water. You can use hundreds of water jars to generate hot water through solar thermal energy. But this will also be an impractical solar thermal solution. Another way is if you take the water bottle and use it as a solar thermal collector by making a hole at the top and bottle of the bottle and connect pipes to each end. Connect the pipes to the houses hot water storage tank to create a water circuit. A pump can now be fitted somewhere in the system to circulate the water. As the sun produces solar energy and the thermal energy gets trapped inside the bottle, the water in the storage tank will heat up as time goes by. However, water bottles are not a real solution as they can’t trap enough solar heat as solar geyser systems can. But, in theory, you just created a solar hot water heating system.

Solar Geyser Components Diagram

Solar Geyser system components

As for using water bottles to generate thermal energy, solar geysers make use of more sophisticated components to produce larger amounts of thermal radiation. Here is a list of the main components that allow a solar geyser to function.

Evacuated Tube And Flat Plate Solar Geysers

Solar collectors

A solar collector is also known as a flat panel which is usually black in colour. This panel black solar collector panel usually gets installed on a roof. In South Africa, we receive lots of sunlight, therefore, many people can install a smaller sized solar collector. In colder areas and people living in large homes, will usually require a larger solar collector installed on their roofs. A solar collector needs to be installed on a roof which does not have shading, ensuring the sun can reach the collector without obstructions. There are two types of solar collectors used for solar geyser systems. A common type of collector known as a solar flat panel or flat plate collector and also evacuated solar tube collector.

Solar flat-plate collectors

Also commonly known as flat panel collectors, are one of the simplest types of solar collectors on the market in South Africa. A solar flat plate collector is connected to water pipes which goes through the collector which is coated with a thick black glass. The glass on the flat panel absorbs the sunlight and traps the thermal energy inside. This is much like a greenhouse effect. The water inside the pipes connected to the flat plate collector, transfer the heat to the hot water storage tank.

Solar Flat Panel Collector
Solar Evacuated Tube Collector

Evacuated tube solar collector

Evacuated tube solar collectors could look like a bunch of pipes or tubes connected to a metal frame. It goes beyond that. Evacuated solar tube collectors are a very efficient type of solar collector because each tube work almost the same as a vacuum flask. All the tubes are empty or evacuated, however, they collect the sun’s heat and also effectively traps the thermal energy inside. The trapped heat is transferred to the manifold which is usually at the top of the evacuated tubes. In the manifold, heat transfer liquid or fluid, heats up and transfers the heat to the hot water storage tank. What makes evacuated tube collectors more efficient? Heat does not escape as easily from evacuated solar tube collectors, unlike flat panel collectors. The only downside about evacuated tube collectors are, flat panel collectors are much more affordable than these evacuated tube collectors.

Hot water storage tank

Collecting heat from the sun for hot water is amazing, but you will need some place to store all this heated water. If you already have an electrical geyser in your home, a solar geyser conversion can be implemented which will use your current electrical geyser as a storage tank for hot water. Also, you can have an electrical backup element which will allow you to fall back on electricity if you really require it. This is mostly at times when you receive guests at your home and you need to accommodate everyone with hot baths or showers. However, if you don’t have any water storage tank or geyser installed at your home, you will need to install an additional storage tank. The most common hot water storage tanks for solar geysers are 150 Liters and 200 Liters.

Solar Hot Water Storage Tanks

Solar collector types in more detail

Integrated Solar Geyser Systems

Integrated Solar Collector-Storage systems

Water is usually heated in evacuated solar tubes inside an insulated box and is stored until it gets used. If the hot water is not used over a period, it will remain hot but also, the water temperature will keep rising as it receives thermal radiation. Using a tampering valve, you protect yourself from the very hot water when using your faucets. A tampering valve allows for the mixing of cold water with the very hot water, to decrease the temperature of the water you receive at the faucet. Integrated Collector-Storage systems is not a recommended solar geyser solution if you’re living in a very cold environment.

Flat panel solar collectors

Flat panel solar collectors are constructed by copper tubes placed within flat absorbing plates. Usually, there will be a series of parallel tubes connected at each end of the flat panel by two pipes.  One pipe is for the inlet and the other the outlet manifolds. All the components which makes up a flat panel solar collector, is fitted inside an insulated box which is covered by thick and dark tempered glass. By using two flat panel collectors, you can provide enough hot water suitable for 4 people in a home.

Flat Plate Solar Geyser Collectors
Evacuated Solar Tube Collector Working Graphic

Solar evacuated tube collectors

Solar evacuated tube collectors are one of the best and efficient solar collectors available in South Africa. Solar evacuated tube collectors consist of glass or metal tubes which contains water or heat transfer fluids and are surrounded by another bigger glass tube. The area between the tubes, are known as a vacuum. Therefore, preventing thermal energy or heat, to escape. Solar evacuated tube collectors can produce hot water although it might be cloudy. Also, they can function in temperatures as low as 4 degrees Celsius. However, Solar evacuated tube collectors might come at a higher price tag. We still recommend them as a solar conversion or investment due to their efficiencies or producing hot water.

Circulation loops for solar geyser systems

Indirect Solar Geyser System

Indirect solar geyser systems

Uses an anti-freeze type of liquid to transfer the heat generated from the sun into the storage tank. The fluid receives their heat in the form of thermal energy which is directly obtained from the sun. The heated fluid flows to the heat exchanger where it transfers heat to the water. If the transfer is complete, the heat transfer fluid gets circulated to return to the solar collector. However, the heat transfer fluid never makes contact directly with the storage water.

Direct solar geyser systems

Direct solar geyser systems use circulation of water in the solar collectors which directly allows the water to heat up by the sun.  A storage tank is used to store the heated water or the water can also be used directly if required. Direct solar geyser systems are ideal in locations where there is not freezing climates.

Direct Solar Geyser System
Active Solar Geyser System

Active solar geyser systems

An active solar geyser system makes use of electric pumps, valves and controllers to transfer water from the solar collector, to a storage tank.

Passive solar geyser systems

Passive solar geyser systems do not require pumps for water circulations. Instead, Passive solar geyser systems make use of natural convection which allow the water to move from the solar collector, to the water storage tank as the water heats up.

Passive Solar Geyser System

Solar geyser products

JC Solar Panels offer high-quality SABS-approved solar geyser systems for your home to always benefit from having hot water independently from Eskom. 

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