Evacuated tube technology was first developed in Australia at the University of Sydney — some 40 years ago.

More recent developments have improved their technical efficiency and they are now rapidly invading the solar hot water market worldwide as Chinese manufacturers have managed to bring down the manufacturing costs to very competitive levels.

So now, at long last, we have a state-of-the-art solar hot water system that is very affordable. They have also stood the test of time, systems installed 40 years ago are still going without maintenance.

Each tube is double walled, with a vacuum between for insulation. The sun’s heat is conducted to the top of each tube and used to warm water pumped up from a ground level tank. The result is a very efficient freeze-proof solar heater without a large tank on the roof.

The glass tubes are open at one end (like a vacuum flask) the glass tube itself being comprised of two layers of glass with a vacuum in between, giving very effective insulation from cool exterior air.

The glass tubes are nothing more than a very effective insulator, enabling the copper heat tube (inside) to reach temperatures of up to 170 degrees. Without the insulation of the glass tube they would not get much hotter than ambient air temperature.

Through this method, the collector is able to gain heat even on quite cold sunny days, and even during light cloudy weather. They are therefore most suitable in cool temperate climes such as ours.

The copper heat tubes are totally sealed, a small amount of volatile liquid inside them assisting with transfer of heat. This makes them vastly more efficient than a solid copper rod.

Hot water supply only goes through the insulated manifold which receives heat via metal-to-metal contact from the collector.

When your HW cylinder gets up to 80°C the pump simply shuts down and the 250ml of water in the manifold turns to steam. This prevents hot water tap temperatures from becoming scalding. When water is draw out of cylinder, the steam condenses back to water and the system reverts to normal operation.

This means it is compatible with all low pressure, and most mains pressure domestic hot water systems.

In closed loop or sealed (dead water) thermal store systems an expansion vessel is often used to prevent pressure buildup as the water expands.

A pressure release valve should also be used as a safety backup.

In areas where freezing is not of concern, open loop systems are often used.

Open-loop systems are also appropriate for cold regions when used in combination with a Delta-T controller that incorporates a freeze protection feature.

Closed loop systems usually incorporate the use of a heat exchanger, either inside or outside the hot water storage tank.

Apricus solar collector are suitable for both open or closed systems, as long as pressure, heat and freezing are controlled.

The Apricus solar collector does not have a built-in tank, in fact the manifold of the 20 tube solar collector only contains about 510ml/1pint of water.

A circulation pump is required to circulate the water through the manifold and back to the solar storage tank.

Generally a Delta-T controller is used to control the pump.

A flow rate of only 2L/min is required for most domestic installations, and therefore a low wattage pump is sufficient.

Larger pumps are only necessary when several solar collectors are connected in series, or when the pump is required to overcome head pressure.

The pressure drop at low flow rates is very minimal, only 700 Pa @ 3.3L/min for 20 tube manifold, and so is not a major consideration when sizing pumps.

Thick glass wool surrounds the Apricus solar collector’s copper header, providing excellent insulation.

The piping to and from the collector are however still susceptible to freezing, and therefore traditional freeze protection should be employed (low temp controller setting, or glycol/water closed loop).

Solar tubes and heat pipes are able to withstand extremely cold conditions without being damaged.

The advantage of solar tubes is that they insulate the inner tube from heat loss.

This means that once heat is absorbed, it is transferred to the water in the manifold, and not lost to the outside environment.

This is the key difference between solar tubes and flat plate solar collectors: the insulative properties.

Combined with the heat transfer efficiency of the heat pipe, the Apricus solar collector can deliver excellent heat output all year round.

The IAM (Incidence Angle Modifier) values of the Apricus are also very different to solar collectors with flat absorbers.

The positive (>1) IAM values mean that the solar collector actually performs best mid morning and mid afternoon, resulting in a more stable heat output throughout the day.

When installing a solar collector on your roof, how it looks is certainly important.

The Apricus solar collector is designed to be low profile, sitting close to the surface of the roof.

The tubes are black and so blend in nicely with most roof colours.

The manifold is available in black, dark brown, or silver powder coated aluminium, and with either rear (R) or end (E) port models.

The rear port manifold allows the plumbing to be hidden behind the solar collector manifold.

In addition by using rear ports, two or more solar collectors may be connected side by side without a gap in between.

End ports may be preferred for large scale applications for ease of connection in series, and reduction of pressure drop through the piping.

Corrosion is always a consideration for any system that involves water and high temperatures.

In warm environments, heavily chlorinated water can become a strong corrosive agent.

In order to provide maximum corrosion resistance, the Apricus solar collector uses high purity (99.93%) copper piping and silver braze for the header.

Copper provides excellent corrosion resistance and is commonly used in household plumbing.

If corrosive liquids are to be used in the system, then a closed loop is highly recommended, thus allowing a non-corrosive liquids to be used in the solar collector loop.

If installed in open flow with a dead water thermal store style tank, corrosion and scale are almost eliminated as the system accepts almost no fresh water supply.

The high cost of solar tube style collectors, and in fact all solar collectors, has been a major obstacle to their popularity and wide scale use.

The Apricus solar collector is a high quality system that provides excellent heat output and reliable operation.

As a result of clever product design and low manufacturing costs, Apricus solar collectors are now very affordable, providing fast payback times.*
Please contact you local distributor for retail pricing in your area.

Depends on factors such as total system cost, energy costs and solar insolation levels.

Apricus solar collectors are ideal for large scale solar water heating applictions, able to be used in hotels, airports, apartment buildings or anywhere where hot water or heating is required.

The economics of large scale applications are generally more favorable than domestic, as instead of having a pump and tank for every one or two solar collectors, a single tank and pump can be used for 50 solar collectors.

Apricus solar collectors can accept mains pressure, are corrosion resistant and can be installed in series and/or parallel, thus are suited to a wide range of large and small scale applications.

The cost involved in repairing a household appliance is increasing all the time, not due so much to spare part costs, but rather the labour cost involved in having a technician visit.

With this in mind the Apricus solar collector is designed to be maintenance free, but if for some reason a solar tube should ever be damaged, it can be replaced quickly and easily by any person possessing basic trade skills.

The heat is normally absorbed by water, or a freeze resistant water mix, which can then be used to supplement hot water heating, space heating and even space cooling via use of an absorption chiller or dessicant cooler technology.

Below are the key features of the Apricus Solar Collector design.

1. Internationally certified product
2. Reliable, efficient, twin-glass evacuated tubes
3. Copper heat pipes for rapid heat transfer
4. Easy plug-in installation
5. Maintenance Free
6. Suitable for mains pressure water (up to 8 bar/116psi)
7. Corrosion resistant silver brazed copper header
8. All stainless steel frame (439 grade SS)
9. Black or Silver aluminium casing
10. Stable solar conversion throughout the day (tubes passively track the sun)
11. The perfect solar collector for domestic solar water heater systems
12. Ideal for commercial solar water heating applications
13. Comprehensive 10 year limited warranty

The operation of the solar collector is very simple.

1. Solar Absorption: Solar radiation is absorbed by the evacuated tubes and converted into heat.
2. Solar Heat Transfer: Heat pipes conduct the heat from within the solar tube up to the header.
3. Solar Energy Storage: Water is ciruclated through the header, via intermittent pump cycling. Each time the water circulates through the header the temperatures is raised by 5-10oC / 9-18oF. Throughout the day, the water in the storage tank is gradually heated.

Evacuated tubes have already been used for years in Germany, Canada, China and the UK. There are several types of evacuated tubes in use in the solar industry.

Apricus collectors use the most common “twin-glass tube”. This type of tube is chosen for its reliability, performance and low manufacturing cost.

Each evacuated tube consists of two glass tubes made from extremely strong borosilicate glass.

The outer tube is transparent allowing light rays to pass through with minimal reflection. The inner tube is coated with a special selective coating (Al-N/Al) which features excellent solar radiation absorption and minimal reflection properties.

The top of the two tubes are fused together and the air contained in the space between the two layers of glass is pumped out while exposing the tube to high temperatures. This “evacuation” of the gasses forms a vacuum, which is an important factor in the performance of the evacuated tubes.

Why a vacuum?

As you would know if you have used a glass lined thermos flask, a vacuum is an excellent insulator.

This is important because once the evacuated tube absorbs the radiation from the sun and converts it to heat, we don’t want to lose it!

The vacuum helps to achieve this. The insulation properties are so good that while the inside of the tube may be 15°C, the outer tube is cold to touch.

This means that evacuated tube water heaters can perform well even in cold weather when flat plate collectors perform poorly due to heat loss.

In order to maintain the vacuum between the two glass layers, a barium getter is used (the same as in television tubes). During manufacture of the evacuated tube this getter is exposed to high temperatures which causes the bottom of the evacuated tube to be coated with a pure layer of barium.

This barium layer actively absorbs any CO, CO2, N2, O2, H2O and H2 out-gassed from the evacuated tube during storage and operation, thus helping to maintaining the vacuum.

The barium layer also provides a clear visual indicator of the vacuum status. The silver coloured barium layer will turn white if the vacuum is ever lost. This makes it easy to determine whether or not a tube is in good condition. See picture below.

The Getter is located at the bottom of the evacuated tube. Left Tube = Vacuum Present. Right Tube = Faulty

Evacuated tubes are aligned in parallel, the angle of mounting depends upon the latitude of your location. In a North South orientation the tubes can passively track heat from the sun all day. In an East West orientation they can track the sun all year round.

The efficiency of a evacuated water heater is dependent upon a number of factors, one important one being the level of evacuated radiation (insolation) in your region.

Solar hot water systems are in widespread use in much less favourable climatic conditions — such as Northern Europe and Alaska.

The development of the evacuated tube solar technology has enabled solar hot water to become even far more financially attractive in cooler climates such as ours.

All you require is an unshaded roof facing roughly north (any aspect between north west and north east will give good results). Even an Easterly facing roof can work without too much loss of efficiency.

The solar collector should be mostly unshaded by large trees and buildings, especially between the hours of 9 am to 3 pm.

If your roof aspect is very limited, there are always solutions. An offset frame can be installed, or in some cases, it is possible to face part of the system in one direction, part in another.

(Some houses do get too much shade for adequate solar gain. If your house has limited solar access for some reason, then consider installing a hot water system driven by a heat pump technology. These are extremely efficient and will reduce your hot water bills by a similar amount.)

You also need to consider any likely changes to any of these factors in future years (growing families, possible sale of house, children leaving home etc).

Household hot water consumption can vary from 70 litres per day to several hundred, depending on usage patterns.

If you under-invest, you are likely to need excessive electric/gas boosting which will end up costing you more than your saving in capital cost.

If you over-invest, you may produce more solar heat than you can use up and will also increase your payback period.

The difference in price between a 20-tube system and a 30-tube system is approximately $300, so if there is doubt and you can afford it, it is generally better to opt for the larger system.

In Tasmanian conditions for a typical household (3 people or more) it is generally recommended to install a 30-tube system.

Remember that solar hot water cylinders are normally designed to store water for use over 2 days, rather than one, thus allowing you hot water even if the following day is cloudy.

For Tasmanian conditions, we recommend a minimum cylinder size of 250 litres if you install a smaller (20-tube) solar system and 315 litres if you install a 30 or 40-tube system.

If you fit a smaller cylinder, you may have hotter water, but less of it, and you will lose some system efficiency.

If retrofitting to an existing smaller cylinder (say 170 litres) you can expect some loss of efficiency. However, this is not advisable if you install a larger solar system because you will waste much of your solar gain.

A larger cylinder will enable you to store more heat during periods of inclement weather and will enable you to maxi mise the efficiency and solar gain from your system.

But the technology works well in cooler climates too, and you will get significant heat even on cooler days that have light cloud cover, so expect solar gain throughout the year.

While evacuated tube technology works efficiently even on very cold sunny days, keep in mind that the solar intensity is 5 times less in Winter than in Summer.

For this reason, it is best to optimise your system for Winter conditions by tilting the solar tubes to a slope of 45 degrees. By doing this you will get maximum efficiency in Winter whilst avoiding excessive heat wastage in Summer.

Low cost stainless steel frames are available if your roof is not steep enough.

(In Summer, you can expect to get 25kWh of heat per day from a 30tube array, whereas in July you can expect 5kWh per day on average. Even in the winter, it is possible to preheat the water to 40C or more if the sun comes out. The booster will then take it up to your desired temperature.)

The Apricus system will boost the cylinder temperature to 80°C, so a fully charged hot water cylinder will give you ample heat capacity for a typical home.