What is an evacuated tube solar hot water system?

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Solar hot water systems use energy from the sun to heat up water that is then stored in a tank. There were more than 800,000 solar hot water heater systems in Australia in 2013i, which we can use to best effect, as Australia has the highest average solar radiation per square metre of any continentii.

In Australia, the first domestic solar hot water heater prototype was created in 1954 by the CSIRO, which then began a solar energy research and development programiii. By the early 1970s the solar industry was well established and it's estimated that 20,000 square metres of collectors were used around the country . Australia had several commercial solar hot water systems by 1974, whereas the US lagged and did not have any commercially-available residential solar hot water packagesiii.

Evacuated tubes: more efficient through the day. Source: Wikimedia Commons, user Ra Boe, https://creativecommons.org/licenses/by-sa/2.5/deed.en

What is an evacuated tube collector system?

An evacuated tube collector system uses a series of glass tubes, each of which houses, in a vacuum, a heat pipe.

The cylindrical nature of evacuated tubes allows them to perform for a large part of the day. Evacuated systems perform better than flat-plate systems in cold climates and give greater protection from frost damagev.

If a tube or tubes are damaged they can be replaced without having to replace the entire unitvi.

A residential solar hot water split system with evacuated tubes.

Heat emitters include:

This differs from the flat plate, or flat panel, system, which is an insulated airtight box with a dark metallic absorbing plate containing water pipesvii. This is most efficient when the sun is perpendicular to the plate surface, but protection is needed against frostv.

As well as the collector, a solar hot water system will have a storage tank made of vitreous enamel, stainless steel or copper. It will need a booster to heat the water - this is usually done with electricity or gas - to ensure your hot water is heated to up to 60 degrees Celsius to stop bacterial growthviii,ix, as well as providing hot water if the solar collectors cannot generate enough heat or if you are using more hot water than they can generatex. If you have a split rather than thermosiphon system, it will need a pump and controller to get the cold water to the collectorix.

iClean Energy Council, Solar water heating, viewed on 29 May 2015,

iiAustralian Renewable Energy Agency, Solar Energy, Australian Government, viewed on 29 May 2015,

iiiAustralian Academy of Technological Sciences and Engineering, Research and Development, Technology in Australia 1788-1988, viewed on 29 May 2015,

ivCSIRO, Solar hot water systems, viewed on 29 May 2015,

vDepartment of Resources, Energy and Tourism, Solar water heater guide for households, Australian Government 2013, viewed 29 May 2015,

viApricus, Flat Plate Comparison: Evacuated Tube vs. Flat Plate, 2012, viewed 29 May 2015,

viiReidy, C., Solar hot water, viewed 29 May 2015,

viiiDepartment of Health, Public health fact sheet: Legionnaires' Disease, Northern Territory Government 2014, viewed 29 May 2015,

ixAustralian, State and Territory Governments, Low Emission Water Heating Technologies, viewed 29 May 2015,

xEnergy Rating, Information for consumers, viewed 29 May 2015,