Evacuated Tubes versus Flat Plate


Evacuated Tubes versus Flat Plate

Flat plate solar collectors vs Evacuated Tube Solar Collector's. An argument in the scale of Toyota Trucks versus GM Trucks. Each have their followers; each have advantages or disadvantages.

There are many points that are usually discussed. We will try to address some here.

Find out which type of solar collectors is the best in your climate. Evacuated Tube vs flat plate collectors. Use the test reports to work out which produce the lowest cost per BTU.

Which produces more heat?

In general, in warmer climates (i.e. Florida) the Flat Plates are more efficient, however in colder climates Evacuated Tubes work better, mainly because they are “a vacuum tube” and any heat they collect / trap, stays trapped due to the insulating vacuum. This is not always the case though, there are hundreds of manufactures of all types of collector all over the world, all have different sizes and efficiencies. How do you determine which is for you?

You need to look at the test reports for the collectors - it tells you what you need to know.......We wrote an article showing the relative heat outputs of both Evacuated Tubes and Flat Plates Collectors in this article. It will help you understand how they work.

Real life experience - Evacuated tubes produce more heat

The Canadian Government ecoENERGY program for commercial solar water heating ended in March 2011. This program was set up to promote commercial solar water heating projects in Canada.

There were 16 solar water heating projects in Canada between 400 m2 in size, up to 840 m2 in size approved under this grant. These were the largest solar water heating projects in Canada.

Of these 16 projects...
....14 projects used Evacuated Tubes
.... the other 2 used Flat Plate collectors.

Draw your own conclusions from this, commercial projects want heat, lots of it, and 88% of all the biggest projects in Canada used Evacuated tubes! as these produce more heat in cold and cloudy conditions that are typical in Canada.

Fact - in cold, cloudy conditions, Evacuated tube collectors can put out 1100% more heat that even the best flat plate collectors. (no 1100% is not a misprint)

The test reports for the better quality evacuated tube collectors show that the heat output by the tubes in Cold and Cloudy climates is about 12 times the heat produced by Flat Plate collectors. Click here for the full details. Marketing brochures by some flat panel companies have been quoting heat outputs based on warm climates. This is great if you live in Florida, not so great if you live in Canada or Northern USA!

Breaking Glass - How strong are the collectors?

There is a misconception that the first hail storm you get in Canada will smash your solar system to pieces.

This is a video (see link) of a hail storm in Calgary in summer 2010. None of our solar collectors were broken. Even if they do break, no fluid enters the tubes anyway and the system does not need to be drained. You just replace the tubes when you get chance. The tubes are cheap and easy to replace.

If a flat plate collector breaks the whole system needs to be drained down and you will likely need several people or a crane to remove the old flat plate collector and replace it with a new one. Not so a broken tube in a vacuum tube system.

However of course they can break, trees and branches can fall, people throw rocks but this applies to any collectors. The system with normally covered under your home insurance policy anyway. Read this "how strong are evacuated tubes".

Snow collecting on the solar collectors

Both Evacuated Tubes and Flat plate collector will at some point have snow on them. See here for photos and details. The best way to minimize snow load is a vertical installation. The vacuum tubes have the advantage that there is spacing between each tub for wind to blow the snow through so generally they don't accumulate as much snow. However because flat plates are less efficient in cold temperatures they loose heat energy through the collector and this heat energy will melt snow away sooner than an evacuated tube.

Installing the collectors

When it comes to installing the collectors the evacuated tube system is easier to install as they are put together in pieces and the heaviest part of the entire system would be the manifold which weighs about 40 lbs. Each tube is individually added once the frame is assembled. A flat plate system is usually hoisted onto a roof using a frame as it is large and very heavy as it is one solid piece. Installing a flat plate on a windy day can be very challenging.

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