Posts Tagged ‘evacuated tube collectors’

7 April

Solar Water Heater-How It Works (3)


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Dear friends and readers, let’s continue to look into the workings of Solar Water Heater.  The simplest approach to heat water with solar energy is to simply mount a metal tank filled with water in a sunny place.  The heat from the sun would then heat the metal tank and the water inside and this is how the very first Solar Water Heating systems worked more than a century ago.  But the inefficiency in this system is: once the tank and water has started to be heated, the heat gained would be lost back into the environment until the water in the tank would assume the ambient (surrounding environment) temperature.  Therefore, the challenge is to limit the heat loss from the tank and delaying the time until thermal equilibrium is reached. To meet this challenge, there are three types of solar collectors most commonly used in the solar water heating systems, described below:

An ICS (Integrated Collector Storage) system or batch collector

  1. ICS (Integrated Collector-Storage) systems or batch collectors:to limit the heat loss from the tank back into the environment, water tank is encased in a glass-topped box that allows heat from the sun to reach the water tank, while the other walls of the box are thermally insulated, reducing convection as well as radiation to the environment.  Furthermore, the box can also have a reflective surface on the inside. This reflects heat lost from the tank back towards the tank. (think of an ICS solar water heater as a water tank that has been enclosed in a type of “oven” that retains heat from the sun as well as heat of the water in the tank.  Variations of this basic design may be composed of several smaller water containers and even including evacuated glass tube technology.  Since the amount of heat that a tank can absorb from the sun is largely dependent on the surface of the tank directly exposed to the sun, it follows that a small surface would limit the degree to which the water can be heated by the sun.  Therefore most modern collectors attempt to increase the efficiency warming of the water in the tank by increasing the surface-to-volume ratioThe ICS systems are often installed in areas where the temperature is very low and heating from solar energy is not sufficient. So cold water is first heated in the solar collector, then to the insulated tank, and finally passed to the conventional water heater that ensures the heating of the water to required temperature levels.

    Flat Plate Collectors for Solar Water Heating System (Source: Wikimedia Commons)

  2. Flat plate collectors: these collectors are flat in shape and oriented towards the sun, enclosing a network of piping, applying the basic idea of “oven”-like box.  Here a  pipe is connected to the water tank and the water is circulated through this pipe and back into the tank.  The water tank is now outside the collector that only contains the pipes.  Most of these flat plate collectors’ pipes have diameters less than 1 cm in order to increase the surface-to-volume ratio (recall this would help to increase the efficiency of the warming process of the water).  At the top there is one or more layers of glass or plastic cover on which the sunlight falls. The light is then absorbed by the absorber plate (metal plate such as aluminum). There are piping of water absorbing the heat from the absorber plate.  The most commonly used solar water heating system is the flat plate collectors, which are usually insulated and weather shielded.
  3. Evacuated tube collectors: these collectors are comprised of parallel rows of the glass tubes which are exposed directly to the sunlight.  The water piping in an evacuated tube collector is surrounded by two concentric tubes of glass with a vacuum  in between that admits heat from the sun (to heat the pipe) but also limits the heat loss back to the environment.  The inner tube is coated with a thermal absorbent. These solar collectors are usually used for commercial applications where maximum amount of heat to be absorbed and the losses due to radiations have to be reduced.

    Evacuated Tube Collectors (Source: Wikimedia Commons)

    Flat plate collectors are generally more efficient than evacuated tube collectors in full sunshine conditions, but energy output of flat plate collectors drops off rapidly in cloudy or cool conditions compared to the output of evacuated tube collectors that decreases less rapidly.


For better understanding of these systems, please stay tuned in my next episode of Solar Water Heater-How It Works (4).  There will be a rather enlightening clip waiting for you.

posted by sunisthefuture-Susan Sun Nunamaker,


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