Are vaccum-tube water-heating solar panels still a thing?

[Vortex2]

All I seem to see nowadays are PV panels on roofs.

Are those older (?) & cheaper (?) vaccuum-tube water-heating panels still promoted?

[adam2]

They are AFAIK still available but are much less popular than in years gone by.

PV is now very much cheaper than in the recent past, and electric water heating from PV is now becoming economic. Electric water is certainly simpler and probably more reliable than any type of solar thermal equipment.
Fewer opportunities for leaks, freezing, or boiling over.

[PS_RalphW]

I fitted flat panel (not vacuum tube) solar hot water to my previous house. I worked well for the 8
years I lived there. When we rented out the house the pump died and I found it almost impossible to get it fixed - an engineer failed to turn up 3 times, to the inconvenience of the tenants. I recently sold the house and I expect the new owners will have ripped the system out as part of their renovation and extension work.

[Stumuz2]

Vortex,

I feel a bit of déjà vu coming on!

We (you,I, rest of the forum) had this conversation about the advantages and disadvantages of hot water panels, I think about 17 years ago!!

You are right, the debate was between flat plate and evacuated tube. I went for the flat plate (home made CAT design)

Still going strong after 17 years of faultless service. Best investment I have ever made. I would not know where to begin trying to work out the RoI.

[adam2]

The economics have shifted in 17 years.
Solar thermal collectors are about the same price in real terms as they were decades ago.
PV by contrast is now much cheaper than it was.

I can remember when a 40 watt PV module cost a weeks wages, a weeks wages now will purchase in the region of 500 watts of PV.

[Vortex2]

>> I think about 17 years ago!!

Gosh, the good old days when I was a well paid executive at a mobile phone manufacturer.

I miss the salary ... but not the 24/7 work and endless air travel.

[BritDownUnder]

I got my vacuum tubes hot water system in 2010 and they have not had a day out of service so far. I also heat the hot water via an immersion heater that uses mostly excess solar PV generated electricity and some night time controlled tariff. There is some parasitic demand from the motor but in the Australian sun it works well.

I would probably get a system without a motor where the vacuum tubes go straight into a small tank, maybe 150 to 300 litres and heat it without a circulation motor. This tank would be a pre heater to a main tank in the house. Such systems exist in Australia although they must be very heavy when filled and put on the roof.

I recall when the system was being fitted all the tubes came in cardboard boxes individually and the installer showed how hot the end got by having water boil off the metal part at the end of the tube that fitted into the manifold.

Main problem has been the insulation on the pipes going off the roof to the hot water tank and motor losing their insulation by the actions of birds pecking it off and the sun perishing it.

I would guess that vacuum tube collectors are a bit more efficient in collecting energy per square metre than PV and for a small roof they are maybe more desirable. I think also from experience mine are better at heating water from 20 degC to 40 degC than water from 60 degC to 80 degC. There are no frost issues where I am and it has never boiled over though the tank did get up to 87 degC once after returning from holiday it just seems to not go higher than that due to heat losses presumably.