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Vacuum or Flat plate

This was a very dificult question to get answers on for a very long time, but in the end I have an answer that I am happy with.

The issue appears to be that flat plates are easier to make and therefore can be made DIY style, vacuum units are mainly made in China and shipped half way around the world and then badged to suit.

The issues as I see both types:-

Vacuum units.

 

Advantages Disadvantages
Lower thermal mass, and so start heating the water quicker and in lower solar radiation levels Lower collector area compared to the area taken up by the unit
Start to heat the water earlier each day More complex to maintain
Damage to one vacuum tube does not stop the whole unit from working More expensive to purchase
  More damage to the planet because of the transport around the world

Flat panel.

 

Produce more heat energy for the same roof area Slower to react in the morning           
Lower cost  
Can be make by most people IE DIY  

 

For some detailed real world results please see http://solarishot.com/   http://cwc-das.com/wcsd//tabs.php?loggerids[]=485E700680A6C389 this site shows a setup of flat panels and vacuum systems on the same roof and each day the vacuum panel starts to produce energy earlier in the day (by a few minutes) but the flat panel normally produces more energy per day.

Also because the only point here is cost per kWh the flat panel wins.

One thing that I was originally told about vacuum systems was that they were more efficent in low energy days but 15% to 20% more on a low energy day is not much extra energy IE flat panel 1kWh per day and a vacuum 1.2kWh per day, so that does not make too much of an improvement for the extra money.

Most DIY panels are approx 15% less effective than commercial panels but at something like 1/5th to 1/6th of the cost.

Anyway because of the things I found out I chose to build my own.