Comparison of flat solar collector and vacuum tube collector

Is a flat solar collector or a vacuum tube solar collector better?

Both have advantageous properties over the other. Let’s see what these are:

Operating in winter

  • The vacuum tube solar collector has less power loss in winter, but we have fewer hours of sunshine in winter, so this advantage is less realized.
  • Due to the weaker thermal insulation of the flat plate collector, winter operation is limited, only preheating is possible.


  • The vacuum tube solar collector gives the house a slight futuristic character.
  • The flat plate collector can be aesthetically integrated into the roof or wall, although this increases the cost remarkably.


  • According to some, the vacuum escapes from the vacuum tube solar collector over time, there is no such danger with a flat solar collector.
    Damaged vacuum tube
    Damaged vacuum tube
  • The heat-dissipating head of a heat-pipe solar tube collector heats up during summer downtime and as a result it can crack due to the sudden cooling that occurs when circulation restarts. Unfortunately, I was askesd to repair a vacuum tube collector that is about ten years old, where the ovner has complained that performance has declined over the years. Theoretically, the packaged tube can be judged to be good, but I didn’t succeed in practice. In one place, I unpacked all the tubes and exposed them one by one on the roof for to the sunshine. I grabbed the heat pipe at their ends, but found no noticeable difference between them. However, the repair can only be solved by replacing all the pipes or by replacing the panels completely.
  • The vacuum tubes may brake.
    Broken vacuum tubes
    Broken vacuum tubes
  • The glass tubes of some vacuum tube solar collectors are sealed with a silicone ring, which can age in a few years. The flat plate collector does not have such a part.


During the summer, especially if the system is left alone when you go for holydays, the system can overheat. The flat plate collector is suitable for recooling the system at night, but the loss of the vacuum tube collector is so small that it cannot be cooled much with this process. You can read more about this here .
Due to the extreme overheating in the summer, the elements of the system are subject to increased stress. This results in the following problems:

  • the vacuum tube system is prone to acidification, so the antifreeze needs to be replaced more often (possibly annually).
  • If this is not done, the acid antifreeze will break through the system components from the inside and sooner or later something may puncture
  • The solar temperature sensor can also overheat and break down. The Pt1000 type probe is usually used here. If they are installed that have a temperature of only 180 ° C, they can easily overheat and break down in some cases. However, a Pt1000 probe that can be used up to 250 ° C is much more expensive.
  • Solar air valves are normally suitable up to 180 ° C, so it is practically impossible to install an automatic air valve.
  • Due to the low heat loss of the vacuum tube collector, the cooling functions built into the controllers hardly work, so if you go on holiday for a week in the summer, the temperature will rise adversely.
  • The flat plate collector can also be left alone in the summer, there is no need to worry about overheating while we are on holiday. This requires the controller to cool the system.
  • The flat plate collector is not characterized by summer overheating.


A flat solar collector is cheaper.

System pressure

In some cases, the vacuum tube solar collector cannot be pressurized. Hot water flows gravitationally from a tank placed on the roof to the taps. Therefore, hot water flows only slowly and there is a risk of frost in winter.

Operating costs

  • The flat plate collector is not characterized by summer overheating, the system is not prone to acidification, the antifreeze needs to be replaced infrequently.
  • In the vacuum tube collector, the antifreeze, especially if the control does not provide cooling, becomes acidic quickly, the antifreeze can be replaced even annually.

You can read about checking the antifreeze here.

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