Solar Hot Water Choices: Difference between FPC and ETC Solar Water Heaters

Solar hot water is a water heating system that has come a long way in the past decade. In this blog post, I am going to discuss key components of any solar water heating system such as collectors. The hot waters are solar energy products and important as resellers often classify solar water heaters based on collectors.

Now a question arises, what is called a solar collector? A solar collector is a key device and used in the solar hot water system, which collects heat by absorbing sunlight to heat the water. The solar Flat Plate Collectors (FPC) and solar Evacuated Tube Collectors (ETC) are the two type’s collectors.


Solar flat plate collectors are one of the commonly used devices (of flat plate solar water heater) where a glazed Flat Plate Solar Collector gets mounted on insulated, weatherproofed boxes fitted with a dark absorber plate under one or more plastic or glass covers (known as glazing). On the other hand, solar Evacuated Tube Collectors contain rows of tubes that are constructed by enclosing metal absorber tubes inside transparent glass tubes. And, the air in the space between the two tubes is removed to create a vacuum, which prevents convective, or conductive heat loss.

What is the difference between FPC and ETC solar water heaters                                                          (Image Source:

Have a look at the comparison between ETC (evacuated tube solar collector) and FPC for solar water heating!

S.No Evacuated Tube Collector (ETC) Flat Plate Collector (FPC)
1 Quickly heat water Slowly heat water
2 The efficiency of the collector on higher temperature is high The efficiency of the collector on higher temperature is low
3 Negligible heat loss in the tubes during the daytime (evacuated tube solar water heater) Higher heat loss (due to convection) in the collector & tank during the day-time
4 Convection and Convecting losses are low Convection and Convecting losses are high
5 Low emissivity High emissivity
6 Satisfactory performance (-18 deg. C) even in extreme cold condition Freezing of water will take place at high altitude can cause damage to the collector
7 Temperature range (heat water) from 60degrees to 120 degrees Temperature range (heat water)from 60 degrees to 80 degrees
8 Easy to replace glass tube Difficult as well as expensive to replace glass sheet
9 Negligible scaling of tubes which can be cleaned manually (inner tube dia. Is 37mm) hence, loss of efficiency consequently is minimal Heavy scaling of the copper/aluminum tubes which cannot be cleaned manually as the bore dia. is 12.50 mm hence, giving rise to a substantial loss inefficiency of the system.
10 In locations with an average availability of solar energy over-sizing of the system glass tube collectors are not required Higher system sizing is required to get the desired result and therefore added extra cost
11 Heat exchanger not required Heat exchanger required
12 Advanced technology at competitive price Old technology at higher prices
13 Provision of a hot water facility for 350 days a year Provision of a hot water facility for 300 days in a year
14 System life above 5-11 years System life over 25 years
15 Water quality does not affect the system Water quality affects the heating system forming scale over a metal tube
16 Low maintenance High maintenance
17 Grouting of Collectors not required Grouting of collectors are required
18 The collector glass tube absorbers (being cylindrical the incident) absorbs the sun’s rays on the tubes is at 90 degrees throughout the day. Hence peak heat absorption as always The collector fins & tubes (being flat the incident) absorbs sun’s rays is at 90 degrees at noon only for peak absorption
19 System hot water tank only is insulated using polyurethane insulation material, which does not absorb water or moisture Collector & tank insulated with glass wool/ rock wool absorbs moisture & gets wet during monsoons reducing the efficiency of the system

Final Say

This table for comparison between ETC and FPC collector or ETC solar water heater and FPC solar water heater is conveying a general idea of how the two systems differ. However, you should consult your manufacturer for additional information on your specific solar water heater. HAPPY BUYING!!


Please spread the word 🙂

6 thoughts on “Solar Hot Water Choices: Difference between FPC and ETC Solar Water Heaters

  • 23/01/2020 at 8:25 pm

    Awesome post! Keep up the great work! 🙂

    • 25/01/2020 at 7:13 am

      Thank you for your appreciation.

    • 10/04/2020 at 7:12 am


      Thanks for your appreciation!

  • 20/06/2020 at 5:07 pm

    Like!! Great article post.Really thank you! Really Cool.

    • 24/06/2020 at 11:48 am


      Thanks for your appreciation.


Leave a Reply

Your email address will not be published. Required fields are marked *


Enjoy this blog? Please spread the word :)