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BASIC SOLAR KNOWLEDGE – PART 2

HomeNewsBASIC SOLAR KNOWLEDGE – PART 2
29Jan

BASIC SOLAR KNOWLEDGE – PART 2

In Part 1 we touched on Solar geysers and Solar for electrical uses. 
I’m now going to touch on two types of heating used for Solar geysers.

Two types: Flat plate collector solar panels and Vacuum tube system

There are the flat plate collector solar panels that have been around for 50 years or so.  How they work is water travels inside pipes that are laid inside a casing that has a sealed glass front. As the sun heats this panel the water inside the pipes gets extremely hot.  This hot water enters the geyser while cooler water from the geyser enters the panel.  This rotates around 40 to 50 times in a day.  A pump is required.  This water is circulated by a pump when the geyser is lower than the solar panel, for example when the geyser is in the roof space and when the panel is up on the roof.  Not all installations require a pump.  If the geyser is mounted on your roof and the panel is below the geyser the cold water from the geyser drops down to the panel.  This water heats up and as you know hot water rises causing the of water to circulate. This installation is called a Thermosiphon system.

More and more installers are moving away from the standard pump that is fed by Eskoms Electricity because Eskom is unreliable which means the hot water in the panel never reached the geyser because the pump does not run.  All our installations are done with a Solar powered pump.  There are no controllers or timers to worry about. The simple concept is when the sun reaches the solar panel for the geyser our pump starts up.  When the sun disappears our pump stops.

The downside of these flat plate collectors is that with the great big surface area of glass it collects leaves and dust that need cleaning.  They are heavy and in areas where it freezers they can burst if the water in the panel freezes.  A whole new panel is then required.  To combat this a specific type of geyser is needed called an “Indirect geyser”.  How this works is that instead of all the water circulating through the solar panel, the manufacturer installs a grid type radiator inside the geyser. This radiator and solar panel is then filled with a type of anti-freeze called Glycol.  As the Glycol gets hot it travels to the radiator which in turn transfers this heat to the water of the geyser.

The other type of solar system used for heating water in solar geysers is the vacuum tube system.  I’m going to talk about the tubes that don’t have water flowing down them as in low pressure geysers.  How these work is the glass tube is in a vacuum, this means the refrigerant in the thin copper tube in the centre of the thick glass tube starts boiling at a temperature of 40°C.  This is achieved because of the vacuum.  As the refrigerant heats up it rises to the top of the probe and as it cools it shoots to the bottom.  This movement causes friction.  The probe of this tube reaches 230°C so I have been told. This tip is inserted into what’s known as a collector or header box.  Water from the geyser flows in this collector and with between 16 to 32 tubes all inserted into one header box the water gets extremely hot.  This hot water is circulated into the geyser.  By the way it’s the infrared and ultra violet rays from the sun that heats the vacuum tube.

We prefer this type of system as it’s so much lighter, if one tube breaks the system carries on working and you don’t lose any water. Its far cheaper to replace one tube than a complete flat Solar panel.  It also does not collect leaves and dust like the flat plate does.  Another advantage is that it does not freeze or burst and does not need Glycol.

With this type of system it’s easy to connect it to your existing high pressure geyser.  In other words you don’t need to change your geyser for an indirect geyser as freezing can’t occur which you would need to do in the case of using a flat plate in colder regions.

There is a new idea in the market where we install an electrical PV solar panel on your roof.  We remove your existing geyser element and replace it with a double element one being 230 volts as normal and the other element is rated at 12 volts.  The idea is that the panel on the roof producing 12 V power during the day.  That does most of the heating.  At night you can top up the heat by switching to Eskom 230V power.  It’s quite a new concept so I don’t know how well it works.

The different types of solar panels and invertors will be dealt with in a future article followed up by a discussion on generators, gas geysers and heat pumps.

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