Solar Water Heating Collector Tubes

Solar water heating collector tubes are said to be the most efficient method of heating water or providing heat for under floor heaters. The other method is the flat plate. Some people use electric mono-crystalline solar photovoltaic cells but these are not as energy efficient for delivering hot water to your home.

The question is should you use evacuated or the conventional collectors for your solar heating system. Evacuated collecters are very well designed. You have a series of tubes in a panel. Each can be individually replaced should it become faulty or get damaged.

What you have is two tubes, an inner and an outer one. The inner carries the water and the outer one creates a vacuum. This vacuum makes the system very efficient. The solar water heating glass tubes heat losses are kept to a bare minimum, less that 2%. It also means that these units can work in very low temperatures even down to as low as -40 deg F.

The liquid is pumped round the system, and the heated liquid transfers its heat to the water held in a hot water heater storage tank.

All very good, so why do people still use flat plate absorber panels for a solar hot water system? There are two main reasons. One is that the evacuated collector tube systems are larger and heavier than the flat plate collectors, this means you need at least two people to install it. Where as the flat thermal systems can be carried and positioned by one man.

The other reason is that because they are more sophisticated and have a lot more parts to them, they are more prone to damage. Remember you are dealing with glass with a vacuum between the two tubes. In the past, these panels have been susceptible to damage due to the thermal expansion of the different materials. The glass is connected to a copper pipe with a waterproof seal. Because glass and copper expand at different rates, this seal often became damaged. I understand that modern production techniques have by and large overcome this problem but when you compare them to flat plate systems there is still a lot more to go wrong.

In fact, the flat plate solar hot water system is extremely simple and have very little that can go wrong. The main things you have to look out for are joints leaking and ensuring your system is designed that it can never freeze up should the temperature plummet below freezing point.

There are plenty of suppliers who are offering solar tubes kits for easy installation and it might worth experimenting with it to see if it is right for you.  However I have seen reports and some independent organizations are saying that the efficiency of the evacuated type compared to the flat type, when measured over a year is not that much, perhaps 5% better. They are also suggesting that because there is less maintenance and fewer things to go wrong with flat plate, flat plate is a better option.

Solar water heating collector tubes are more efficient but you have to decide if the advantages are great enough to warrant the higher cost over flat plate.


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