Choosing the Right Solar Heating- Panels

Solar thermal panel is also called with other different names such as solar heating panel or solar thermal collector. However, the most often name for it, is solar thermal collector. This is the name that any manufacturer mentioned in their product brochures as well as it is the name that they mentioned in their catalogues.

Solar thermal collector is actually the most important component in any solar heating system. This is the place where heat energy is absorbed or accumulated before sending it to our home. It is a very important subject to be understood. By understanding the process, we could differentiate easily which type is for cold, mid or warm climate.

Previous articles:

  1. Choosing the Right Solar Heating- Passive, Active & Open Loop (Part 1)
  2. Choosing the Right Solar Heating- ICS & Close Loop Basics (Part 2)
  3. Choosing the Right Solar Heating- Freeze Protection in Closed Loop (Part 3)

How it Collects Heat Energy?

In order to give a clearer picture, the best explanation is only with physics. There are three methods or process of how a solar thermal collector could absorb or gain heat energy from the sun.

  1. Through radiation from the sun – which means through sunrays or in physics is through energetic wave. Light is a very special creation where it has a wave-particle duality property which behaves either wave or particle.
  2. Through thermal conduction – conduction is occurred between two solid bodies due to temperature gradient. From hotter area of solid to colder area of solid. This is not occurred in gas or liquid.
  3. Through thermal convection – convection is occurred only on fluid (liquid or gas). The process is almost similar to conduction except the media is liquid or gas.

Flat Plate Solar Collector

Flat Plate Solar Collector

Flat Plate Solar Collector

Flat plate collector is suitable for all climates. However it could not collect much heat energy during winter or snowing. Heat may loss through conduction and convection.

For warm and moderate temperature, flat plate is perfect because it provides reliable heating as well as the cost is cheaper. Although flat plate’s efficiency is lower than the rest, however for warm and moderate temperature heat collected is adequate.

 

Radiation

Conduction

Convection

Warm climate Gain Gain Gain
Moderate climate Gain Gain None
Cold climate Gain Loss Loss

 Solar Evacuated Tube

Solar Evacuated Tube

Solar Evacuated Tube


Solar evacuated tube is not suitable for warm temperature since it will overheat as well as no need to invest for more expensive heater. Evacuated tube collectors are very efficient collectors. The way it works is similar to a thermos in principle. A glass or metal tube containing water or heat transfer fluid is enclosed by a larger glass tube. The space between them is a vacuum, thus very little heat is lost from the fluid.

These collectors can even work well in gloomy conditions and operate in temperatures as low as -40°F (4 to 5 °C). Individual tubes could be replaced as needed.

 

Radiation

Conduction

Convection

Warm climate
Moderate climate Gain None None
Cold climate Gain None None

The efficiency of a solar evacuated tube water heater is strongly related to the intensity of the solar radiation or known as insolation. The reason is the tube is designed to collect solar heat energy radiation and not from conduction or convection. Below is the map for insolation of the world.

Solar insolation Worlwide

Solar insolation Worlwide

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