Choosing a Solar Hot Water System

Why Buy and Install a Solar Hot Water System?

Choosing to install a Solar Hot Water System is one of the best financial decisions you can make when it comes to upgrading your home or business, and reducing your energy use and cost.

As I write this article, world CO2 atmospheric levels top 396ppm, and Australians are looking at another major price rise in the retail cost of electricity in July.

In this article I discuss the different types of solar hot water systems (SHWSs) available, including flat plates, evacuated tubes and heat pumps, and the considerations you need to take into account in choosing the best one for you.

The baking of electric storage hot water systems throughout Australia during 2012 has made needing to know what systems are available, and which will best suit your home, more important than ever.

Every day your home or business keeps using that old electric storage hot water system, is another day that you do not benefit from the lower running costs, improved property value, and lower CO2 emissions, provided by a well designed and installed solar system. Subjects that I'm sure you will agree are becoming more and more important to us all.

Types of Solar Hot Water Systems:

Solar Hot Water Systems come in two main configurations, Close Coupled (tank on roof) or Split Systems (tank on the ground). I will also discuss Heat Pumps which are seen by many as solar based technology.

Configuration Type 1

Close Coupled Systems

These offer lower running costs (excluding boosting) as they do not require any electricity to move the water from the collector to the storage tank, taking advantage of natural "thermosiphoning." The trade-off is a bulker unit with higher system weight on the roof. For example, a 300L storage tank holds 300kg of water + tank and collector weight.

Configuration Type 2:

Split Systems

Split Systems have the collector on the roof and the storage tank located somewhere else- normally on the ground. Split Systems require the use of solar pumps and controllers to monitor temperatures, and move water from the collector (s) to the storage tank. This does involve small amounts of energy being used – normally around 28-60 watts per hour for up to 8+ hours a day.

Collector Type 1:

Flat Plates

The first widely available Solar Hot Water Systems in Australia were designed in Western Australia way back in 1953 by Solarhart, with their flat plate technology. This became the standard design for SHWSs for the next 40 years. Flat plates use a large collector surface to pick up the Sun's heat with water pipes embedded in the collector to transfer heat. The collector surface is protected by a sheet of glass or plastic that generally offers little to no insulation.

Collector Type 2

Evacuated tubes

In the mid-1970s the University of Sydney developed evacuated tube systems but it was to be another 25 years before evacuated tubes became widely available in Australia. This technology provides the highest performance per sq. m. available to the domestic market.

Evacuated tubes take advantage of the natural insulation properties of a vacuum, which allows heat

to enter the glass tube, but then does not allow that heat to escape back into the atmosphere.

The use of a vacuum also gives evacuated tubes natural frost protection, with no need for antifreeze additives like glycol that can also reduce performance by up to 10%, and create ongoing maintenance needs.

Because the evacuated tubes are round, passive tracking of the sun across the sky allows a large collection surface to be perpendicular to the sun and provide greater performance.

Key Advantages

  • Naturally frost protected down to -10 ° C or greater
  • Passive sun tracking for greater performance
  • Low on roof weight
  • Modern stylish design.
  • No Glycol (antifreeze) needed

Collector Type 3:

Heat Pumps

Are Heat Pumps really solar systems?

Well, yes and no … But if you have major shading issues they are a great alternative energy efficient solution.

While heat pumps do not use the direct radiant energy from the sun as both flat plate and evacuated tube systems do, they do derive a large percentage of their energy from the heat on the atmosphere that's created by the sun.

Heat pumps use a compressor to extract heat from the atmosphere and transfer the heat into a water storage tank. It does this very efficiently with a typical system producing about 3kw of rated energy for every 1kw of power used at around 20 ° C.

Key Benefits

  • Does not require direct sunlight. Can even be located in permanent shade.
  • No on-roof installation.
  • More efficient than electric storage systems, even at low temperatures.
  • Can take advantage of waste heat from such things as roof spaces and plant rooms.
  • Are rebated by some government agencies and renewable energy programs.
  • Lower installation costs than on-roof systems.

Reduction in Energy Use

Heating your home's hot water is on average around 30% of the total amount of energy used by domestic homes each year, and with the rising cost of electricity now a major factor in household budgets, moving to solar hot water should be at the top of people's home upgrade options list.

"We think that, by 2020, the cost of electricity will be threefold what it is today …"

Origin Energy Chief Executive- The Australian 14/04/2010

Example of possible return on invest factoring in a 10% pa rise in the cost of energy

Replacing an old electric HWS with a SHWS could reduce your HW energy costs by up to 90%, as well as adding value to your home. A natural gas boosted evacuated tube system offers the lowest running costs but does not come at a higher cost for purchase and installation.

Savings for an average family of four in Australia is estimated to be over $ 700 pa, and saves about four tonnes of CO2 if replacing an electric boosted hot water running on main tariff power. That can equate to well over a 15% return on your investment (ROI).

Replacing an old electric HWS with a solar hot water system could …

  • Reduce your hot water energy consumption by up to 90%
  • Add value to your home.
  • Reduced energy bills.
  • Rebates still available (See Solar Hot Water Rebates).
  • Lower you greenhouse gas emissions.
  • Can offer a far greater ROI over other investment options.

The Ideal Roof Orientation:

Solar orientation is one of the largest factors effecting solar hot water performance. In the southern hemisphere, a SHWS's ideal orientation is due North, with the reverse being true in the northern hemisphere. The further a system is from due north, the less energy it will be able to harness.

Not all technologies handle having their orientation off true north as well as others. Evacuated tubes with their cylindrical tube design allow for greater performance over flat plates, as the degree of orientation from true north increases right up to 90 ° C with minimal performance loss.

Roof Pitch:

The pitch of your roof does affect the performance of a solar hot water system, and should be taken into account when designing any system. In Australia, typical domestic roof pitch is between 22.5 ° and 25 °, but many homes have a higher or lower roof pitch. Generally the higher the roof's pitch, the better winter performance will be, and is recommended over lower pitches that increase summer performance.

To find the optimum pitch for your SHWS, take the latitude of the home location, then add between 10 ° -20 °. To comply with AS / NZS 3500.4: 2003, a collector's incline angle of deviation is not to be greater than ± 20 ° from the latitude of the installation location. Eg: Canberra lies at a latitude of 35 °, so the optimum winter angle would be 55 °

For roofs that have pitches lower than 20 °, you should have the system placed on a frame to raise the pitch to the optimum angle. The additional cost of the frame will more than be made up for the increased performance of the system.

Shading Considerations:

The shading of a solar hot water system has the single largest effect on the performance of the system through the year. You should always try to have the unit installed in a location where there is minimal or no shading.

Trees are one of the two main causes of shading and typically have a great effect during winter when the sun is lower to the horizon. Trees are generally only a major issue in winter, and deciduous trees are better than native Australian trees that do not drop their leaves during winter. Trees in most cases can be cropped or removed to give better solar access, but this does depend on factors such as property ownership etc.

Buildings of two stories or more in height that are adjacant to the solar hot water system can have a dramatic and permanent impact on performance, and should be taken into account before proceeding with any installation. If shading is an issue and another location for the installation can not be found, then Heat Pump technology should be considered as it does not rely on direct heat from the sun.

Owners of homes that lie in valleys where there is the likelihood of significant shading during winter months in particular, should consider carefully before choosing to install an on-roof solar hot water system. This type of situation is another good candidate for Heat Pump technology.

Frost and Freezing:

In areas where frost and snow are factors during winter, not all solar hot water systems are the same. If you live in a frost-prone area, careful consideration should be given as to which technology to employ.

Evacuated tubes have by design passive frost protection, and typically handle temperatures down to -10 ° C – 15 ° C with no loss in performance, or additional need for frost protection. Quality evacuated tubes do not have any water passing through the glass tubes themselves, and are protected by the vacuum area of ​​the tube, which does not allow heat to escape back into the atmosphere. Most evacuated tube systems do have some form of frost protection built in for the piping that pumps small amounts of water from the storage tank to the collector drops during periods of below zero temperatures

Flat plates typically had no insulation between the glass and collector surface, and as such have required some form of active frost protection. Older flat plate systems used heating elements in the collector, that heated the water when temperatures dropped below 0 ° c. Heating elements use significant amounts of energy, and negate much of the solar benefit. Most flat plate systems use Glycol as antifreeze to avoid freezing the collector (s), and this does come at a performance loss of up to 10%. Glycol also requires maintenance during its life at additional cost to home owner, and lack of maintenance may in many cases void warranties.

Over the past couple of years hybrid systems using combinations of flat plate and heat pipe technology have started to enter the market, and offer far better performance over glycol flat plate systems.

Backup Booster options:

All solar hot water systems require some form of backup booster. This is because there are times throughout the year when even the very best solar hot water system is not able to supply water at the desired temperature. Backup boosters come in two main forms, Electric Element or Gas.

Gas-boosted solar hot water systems come in a few different configurations, which one you choose will depend on your situation. Condensing natural gas boosters are the most efficient systems, as they only heat water coming from storage if the water temperature is below a set level. Gas storage systems have a burner in the base of the tank, that will use more energy than condensing gas systems, but can be a less cost option initially. In areas were natural gas is not available, bottled LPG can be used for both storage and instant gas systems, but does have higher running costs.

Electric-boosted systems typically use a heating element to heat any water that's not able to reach ideal operating temperatures. Most elements draw around 3.6kw per hour, and do require control on the times of day the booster may come on, so as not to "compete" with the solar collector.

It is recommended that the electric booster will be connected to Off-Peak power that only allows for boosting during the night. If off-peak is not available then a timer can be used. Many energy utilities offer various Off-peak plans, be sure not to select a plan that allows for boosting during daylight hours.


All SHWSs in Australia must be installed by a licensed plumber / gas fitter, and comply with all state and territory codes and standards. Not all numbers are the same, and one should always choose a plumber / installer that has experience with the technology you choose, as each technology has its own particular requirements.

Tempered solar hot water

All new hot water systems in Australia are required by law to be "tempered" to a maximum of 50 ° C to all bathrooms in the home; This is done by using a tempering valve that mixes cold water into the hot water line, to achieve the desired temperature. This is a safety feature designed to protect children and adults from accidental scaling. A high quality solar system can have hot water temperatures as high as 90 ° C during summer. Laundries and kitchens can be untampered but is not recommended and comes at additional cost.

Solar rated Insulation

Installations in cold or frost prone areas should always use quality solar rated pipe insulation (lagging), not only for any pipework exposed to the atmosphere, but also on any pipework inside walls and roof cavities.

Roof system weight

When installing a "close coupled" solar hot water system in / on your roof, it's advisable to check if the roof structure can handle the substantial extra weight of these systems. The weight can be in excess of 500kg +. If weight is a problem then a "Split System" should be used, giving a much lower on-roof weight.

Solar Hot Water Rebates:

Solar Hot Water Rebates have been widely available from Local, State, Territory and Federal Governments, as a way of encouraging the uptake of solar that typically has higher purchase and installation costs. Rebates are generally only available for complete systems that have been tested by accredited testing laboratories.

Over the past few years we saw the peak on rebates for SHWSs reached, with combinations of rebates from various governments sometimes being available. Recently we have seen a reduction in available rebates, as well as a reduction in rebate values, as new building codes, the banning of older technologies like electric storage hot water systems etc is implemented. In many cases one or more rebates may be available and your retailer should be able to provide you with the full details of all rebates for solar hot water in your area.

In Australia the Federal Government has set up a testing and approval program for systems classed as solar hot water or heat pumps, and applications Renewable Energy Certificates (STC's) based on the tested efficiency of each system. STC's can only be created once a system has been installed. STCs can then be sold on the REC-registry market in return for a dollar amount. The value of each STC is based on market forces, and variies over time.

Example of STC's on cost of system

System cost $ 4000.00

No of STC's 30

Value per STC $ 34.00

Total STC value $ 1020.00

System cost after STC's $ 2980.00

The rising cost of energy is increasingly putting pressure on households. With or without rebates, installing a solar hot water system on your home is fast becoming one of the greatest changes you can make to reduce your electricity and gas costs, offering a great return on your investment.

The Economics of Solar Hot Water:

The savings made by installing a solar hot water system, and the Return on Investment (ROI) achieved, varies from family to family, place to place, and system to system. But to give a simple example, if a system cost $ 4000 all-up to purchase and install, and saves your family $ 700 in the first year,

• That's a tax-free Return (ROI) of 17.5%

• If your marginal tax rate is 40%, you've got to get a 29% pre-tax ROI somewhere to match your solar hot water investment. There are not many of those around.

• That's just your ROI in Year One. Every year electricity goes up, so does your ROI.

In Conclusion:

Thank you for taking the time to read this article on choosing a solar hot water system. I hope you found it informative. I have been involved in the design, sales and installation of solar hot water systems for over 8 years.

With the need to address global warming, the introduction of carbon taxes, and pressure on our aging utility infrastructure, installing a solar hot water system is not a only a great investment for your home or business, but also for the wider community.

I hope you find the information provided in this article of value, and that you'll soon join the millions of people around the world enjoying all the benefits of solar.

Kind regards

David Payne

June 2012

roof contractors