Solar Flat Plate Versus Evacuated Tubes

When you read the endless sites that profess how much better one type of collectors is better than another you need to learn how to compare the performance of various solar collectors for yourself.

This applies not just to the Flat plate vs evacuated tube debate, but also to any other solar collectors.

No one collector performs the same in every climate. It all depends on where you live and what the climate is where you live.  This article will help you make that decision for yourself.

The info in this article is to help you understand how to compare various solar collector test reports and how to interpret the some of the data. The info on this page looks at test reports made by the SRCC. Please note however that not all collectors are tested by the SRCC, there are many other testing facilities around the world that also test Solar Collectors which are also accepted in Canada under the ecoENERGY for renewable heat program that runs until the 31st March 2011. See this article for more background info on the various test reports.

 Anyway.... onto the information - Flat plate vs Evacuated Tubes.

This article was inspired by very well know flat plate manufacture who sent out one of their flyers calling it something like "the Flat out truth". They say look our collectors produce 31 700 BTU/Day. Initially you think, that's not bad, however one look at the charts below show they are being very selective with the information. The saying goes when looking at statistics, its possible to prove almost anything to show your point of view by manipulating the data and statistics.....

Technically they are telling "the Flat out truth", it depends on if you live in Hawaii or Canada. They are using the test data from "Image 1, Section C - Water Heating, Clear Day, WARM CLIMATE"

As you can see from the images below, in warmer climates (Section A Pool heating in a warm climate then the Flat Plate Collector (Image 1) has better heat output than the Evacuated Tube Collectors - only just though!!!

In general the climate in Canada is not Warm, and you need to look at the data for the Cool Climate (sections D)

The images below are taken from the SRCC test reports.

How to read this..... Look at Section D of the image below - this is the Section for "D-Water Heating Cool Climate" - read text along the bottom of the table.

Solar collector Power Output on a clear day = Thousands of BTU per Panel Per Day

  • IMAGE No1 - Flat plate Collector - 18,000 BTU/ft2/Day
  • IMAGE No2 - Evacuated Tube Collector - 30,000 BTU/ft2/Day

Now Look at the Cloudy Day data

  • IMAGE No2 - Evacuated Tube Collector- 12,000 BTU/ft2/Day
  • IMAGE No1 - Flat plate Collector - 1,000 BTU/ft2/Day - 12 times LESS heat in cool and cloudy conditions.!!!!!!

This alone tell you that these Evacuated Tube Collectors produce more heat in Canadian Climates than this Flat Plate Collectors will.......

Well known, Flat Plate Collector SRCC Data

Flat PLate Solar Collector SRCC Data

IMAGE No.1

Evacuated Tube Test Data

Apricus SRCC data

IMAGE No.2

The only way to compare one collector with another impartially is to use the Government Program RETSCREEN.

Retscreen - Read here to find out how to do this. This article shows you the output of the main collectors you will find in Canada (both Evacuated Tubes and Flat Plates) and compares the output in different cities.

Does Size Matter!

When comparing the collectors, there is a minefield of information, which often looks confusing, but one good thing about the SRCC test reports is that they try to simplify the data so anyone can read it. In this example if you take the number from the same section for each collector, for example....

IMAGE No1 - Flat plate Collector - 18,000 BTU/ft2/Day (just over half the power output)

IMAGE No2 - Evacuated Tube Collector - 30,000 BTU/ft2/Day

You need to look at the cost for each collector to work out the cost per BTU.

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