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3 different generations of Solar Vacuum Hot Water Systems

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It will probably surprise many people to find out that there are different generations of Solar Vacuum Hot Water Systems and ALL are still being sold today. You may have just bought one but which generation is it ?

This is why you see HUGE differences between performance of solar vacuum systems and why there is so much confusion. We have many requests from people who have just bought Solar Vacuum systems and they can’t understand how our customers systems are producing so much more energy than them.


NOTE: This is the first time you have probably heard anything about the different generations of Solar Vacuum Technology anywhere.

FIRST Generation Solar Vacuum Systems, (about 35 years old), still being sold on the market, always compared to flat plates due to their low performance.

How to recognise one ?, simple, it has a single wall (not double skinned vacuum) clear glass tube and a strip of absorber inside.

solar heat pipe generation 1

Fig: First Generation Solar Vacuum System – (approx 35 years old)

Whilst they are still available to buy in very well known BRAND NAMES, they are quite old at this stage. How did they come about. Simple, a bright Engineer about 35 years ago looked at flat plates in sunny climates and made an assumption that if he put the strips of a flat plate absorber into glass tubes, he would improve on the output of flat plate collectors in cloudy climates. Here is a picture of a flat plate solar collector with its covers off.

solar absorber

He simply decided to split the absorber and put it in glass tubes. A new version of this has a direct flow pipe instead of a heat-pipe. THIS IS FIRST GENERATION SOLAR VACUUM HOT WATER TECHNOLOGY.


SECOND Generation Solar Vacuum System’s, (about 25 years old), still being sold on the market, noted for their lack of performance in poor weather and over-heating problems in sunshine. THIS IS THE MAJORITY OF SOLAR VACUUM SYSTEMS BEING SOLD ON THE MARKET TODAY AS THE COLLECTORS CAN BE SHIPPED BROKEN UP IN LONG BOXES.

You will always hear about sizing to only do 90% of your hot water in case of overheating (of course this makes it poor performing in winter), the adding of dump radiators, etc. with this technology. Here is a picture of this type of solar heat-pipe. There is a condensing heat-pipe running into a twin walled vacuum tube with a sealing cap to hold in the heat. The tube always carries a selective coating so it looks black on the outside. The heat pipe then plugs into the manifold and heats up the manifold. When the manifold gets heated, it transfers the heat to the water passing through. This process is fairly inefficient.

solar heat pipe

Fig: Second Generation Solar Vacuum System – (approx 25 years old)



THIRD Generation Solar Vacuum Systems, (about 8 years old), still being sold on the market BUT only a few suppliers make this generation of system, it is noted for more stable performance than Heat Pipes and has reduced the overheating issues on really hot days. It is more expensive to produce and unless it is shipped in one piece, it has to have rubber seals and run at low pressure. THIS IS TYPICALLY CALLED  A U-TUBE OR DIRECT FLOW COLLECTOR.

Here is what it looks like:

solar u tube

You can see that the circulating water runs into the glass tube via copper pipes unlike any of the 1st and 2nd generations where the water only runs in the manifold. The tubes are twin walled and have a selective coating and appear black on the outside.

ONE MAJOR DRAWBACK (and it is a biggie): If this type of collector comes as a kit (and not in one piece out of the box) and has to be assembled at the installation site, then it will cost a significant amount of money to change a tube. The system will need to be drained down, tube changed and then refilled, this is in effect a FULL SERVICE every time you want to change a tube. Typically the new tube will come with all the pipework so can be over £120 a tube ON TOP of the full service cost.

If the collector is one piece and can’t be broken down, then this does not apply, the changing of a glass tube takes seconds, like changing a light bulb and is a few quid at most. THIS IS THIRD GENERATION SOLAR VACUUM HOT WATER TECHNOLOGY.


FOURTH Generation Solar Vacuum Sytems, (about 4 years old), this is proprietary technology to Surface Power. It involves a system wide science called TDLF (thermodynamic laminar flow technology) coupled with MPPTt, (Maximum Power Point Tracking – thermal). Several patents cover this technology which has been developed to create high powered solar air conditioning and solar central heating systems.

You can see its performance in the samples of our live systems 24/7.

The key thing to notice is the different power band, (kWhrs produced) that is the difference in temperature between the collectors and the cylinder/pool/heating system, etc. Normal solar systems go from +3C to +7C and switch on and off all day. Surface Power systems do not work like this, they operate a DELTA T of between +10C and +25C bringing much larger amounts of power in any given day; and can stay running ALL DAY. Even at a DELTA T of +15C, it is still cloudy and many times higher than the average of any of the 1st, 2nd or 3rd generation solar vacuum technology’s.

Here is a Surface Power SP501 solar collector, (we only have the one type, size, shape, tube quantity), why have more than 1 type of solar collector ?, you can’t improve on perfection…


Our best advice:

It is our job as manufacturer to provide you with open and accessible information to help you with your research into solar hot water. All systems shown are customer systems. In the year 2011, You should not have to buy a solar system based on theories, probabilities and hocus pocus, it should be based on fact and examples of real outcomes. We don’t TELL you what you “SHOULD” get, we SHOW YOU what you “WILL” get. Any educational questions can be put to our support desk 24/7

And  then;







About pfiddle

Fiddle teacher - mostly Irish trad. Fiddle, mandolin and concertina. Eco-warrior, won E.U. Green Flower Award for Eco Accommodation. Also Irish (Gold) GHA. Green Hospitality Award. Mad keen on self-build - especially straw-bale and cob. 55 with a full head of (slightly) graying hair. No tattoos or piercings. Fond of animals - but legally so. Fond of food - I eat nothing else. Vegetarian by choice, Irish by the grace of birth, Munster by force of (rugby) arms.

2 responses »

  1. Hey there and thank you for your information – I have definitely picked up something new from right here. I did however expertise several technical points using this web site


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