By: Solar Commercial  05-Apr-2012
Keywords: Hot Water, Solar Energy, Water Supply


There are more than 16,000 dairy farms in New Zealand. Dairy farms use huge amounts of energy to heat water and back-wash equipment for cleaning. Water heating can account for approximately 40%+ of the energy used in a dairy shed. Solar Commercial water heating systems may be used to supply all or part of these hot water requirements. Average hot water consumption in a dairy shed is between 300L and 900L litres of 85 degree hot water every day.

For dairy farmers there is a huge potential for savings with an effective solar water heating solution from Solar Commercial. Solar water heater systems must be economical for dairy farm use. Solar Commercial hot water systems are highly effective, unique and specifically designed to meet New Zealand requirements. To achieve these savings, Solar Commercial advise that large collectors and extra storage tanks are essential in order to have effective solar water heating and storage. Solar Commercial hot water systems are also modular which means that extra storage tanks and collectors can be installed in order to supply more hot water as needed. A Solar Commercial system can provide a long-term high rate of return.

How the solar heating system works:

The black coating (UV absorber) on the inner cover of the evacuated tubes ensures high solar energy absorption and low heat radiance losses. It converts solar energy into heat energy which is then transferred to the heat pipe by an aluminum fin. The heat is then transferred from the heat pipe to heat cold water in a storage tank. As hot water is drawn off, it is replaced with cold water which comes in from the opposite end of the tank under pressure (up to 28 lbs). The diagram demonstrates how a solar water heater works with an existing hot water system. Water pressure for the whole system and the hot water cylinder can be pumped either from a cold water supply or from a header tank. This system is a low pressure unit so the maximum pressure is 2 Bar or up to 28lb. N.B. Water must always be left in the water tank even when it is not in use. As soon as the tubes are installed the storage tank must be filled with water. If the solar panels are not going to be used they need to be covered and protected from sunlight to prevent burn-out.


There are 2 different models of solar water heater – SC300 (300L water tank and 30 tubes) and SC250 (250L water tank and 24 tubes). These models include all-glass evacuated tubes which contain a heat pipe, a stainless steel water tank, a relief valve and frame. They are designed specifically for dairy farm use. (Thermo Siphon)

  1. The evacuated tubes are extremely efficient. They will continue to absorb solar energy from sunlight even when the weather is cloudy or temperatures are below freezing to as low as -25 degrees.
  2. The evacuated tubes heat quickly and transfer the heat from the absorbed light energy directly into the hot water storage cylinder via the heating pipes.
  3. No water is inside the evacuated tubes. A Solar Commercial solar water heater can still operate even if it has broken tubes.
  4. The stainless steel water tank and tube-seals will withstand a pressure of 0.2MPa or up to 28lb.
  5. Both models can usually be connected to existing hot water cylinders.
  6. The stainless steel inner liners and exterior cylinder have been tested to withstand 1000,000 fatigue tests without distortion.

7. The area between the outer and inner liners of the cylinders is insulated with polyurethane foam.

8. The system is a simple modular structure that is easy to assemble and install Extra units can be connected in series allowing for larger hot water requirements.

9. An optional diffuse flat reflector can also be added to these models for greater performance.

10. A relief valve to protect the whole system is included as part of this system.

11. No pump or controller is required. (Thermo Siphon)

Brief description:

Dairy farmers use a lot of hot water. This can amount to between 500 and 900 litres of hot water (at 85 degrees) per day. Some dairy farms use double this amount and electricity costs can be in excess of $7000+ per annum. There is huge potential for savings with an effective solar water heating solution from Solar Commercial.

Solar Commercial's innovative solar water system is specifically designed for New Zealand dairy farms. The modular system can be enlarged by installing extra storage tanks and collectors. It is a portable and easily installed solar water heating system.

Nationwide there are approximately 16,000 dairy farms, the majority of which are run by sharemilkers. A large proportion of these farms are located in the Waikato region in the North Island of New Zealand. At present there are 5 trial "project" sites on dairy farms in the Waikato region where Solar Commercial solar water heating systems are installed. The purpose of these trial sites is to monitor and demonstrate the effectiveness of the Solar Commercial solar hot water system and controller which have been specifically designed for New Zealand dairy farms. These sites will also demonstrate the energy savings made by using the Solar Commercial system. Once project monitoring is complete, a "lease-to-buy" option will be made available to farmers in order to capitalise on the "dollar" savings made from the power savings achieved using the Solar Commercial system.


Solar Commercial solar water heating units aim to provide the following benefits:

  • To reduce the dependence upon electrical energy in rural regions where power supplies can be unreliable
  • To promote the use of solar heating in order to make financial savings on electricity charges $$$$$
  • To allow for energy and cost savings from the date of installation
  • To provide increased security of supply of hot water
  • To provide easy installation that may not require a building permit application
  • To support the promotion of the NZ dairy industry as clean and green
  • To support the NZ Government's carbon neutral targets in rural areas where there may be limited opportunities in other ways to achieve significant savings
  • To introduce an innovative lease agreement as a payment option.
The information in this article was current at 27 Mar 2012

Keywords: Hot Water, Solar Energy, Water Supply

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Wallace Plumbing Mob: 027 244 0405. Stan Wallace Ph: 06 3749346.


Compare U-pipe with heat-pipe collector

While the two collectors have nearly identical efficiency ratings, the U-Pipe Collectors actually require fewer tubes up on the roof to reach the same peak efficiency levels. Some heat pipes contain chemicals such as antifreeze, which over a period of time can start to lose efficiency, resulting in the need to be replaced.


U-Pipe Collector

Tianpu solar energy group first manufactured a "U" tube design twelve years ago to fit modular solar heating systems. The aim was to produce an all-glass vacuum tube that still works efficiently even if a tube is broken. Test pressure is at 12Kg/cm ², and system working pressure is up to 6Kg/cm. Tianpu has always been a leader in the field of solar energy technology.