Everything you need to know about solar hot water

Everything you need to know about solar hot water



The greenhouse effect is the single most pressing ecological problem facing our planet. One of the most effective responses, and something most of us can do, is to install a solar hot water system in the home.

By Tracey Hordern

On a per capita basis, this sunny country of ours is the world’s worst contributor to greenhouse gas emissions. One of the most efficient ways to reduce our toxic output is to harness the sun’s abundant power and minimise the fossil fuel-generated energy that we use in our homes. For most Australian households, after transport the single largest impact on greenhouse gas emissions is electrically generated hot water. This energy consumption accounts for about a quarter of an average household’s total energy use and unnecessarily produces almost eight tonnes of greenhouse gas emissions each year.

On his recent trip to Australia in September 2007, Al Gore spoke of the emergency we are facing in terms of the effects of climate change, stressing the speed at which the greenhouse effect is now occurring and the importance of each person not to just talk about it, but to take action to reduce their own carbon emissions. Gore suggested that if individuals changed their day-to-day living habits to reduce their personal carbon outputs, climate change could be neutralised, but it could take up to 50 years before half the carbon dioxide now in the atmosphere returns to the earth. Gore summarised that all of us can and should contribute to a solution, that every person can do something — and that something can start in our homes.

In reality, we should be seeing solar panels on every house in Australia. A solar hot water system is the perfect alternative for hot water; it’s a clean, green energy source. Nothing is more Australian than sunshine, so it’s no surprise our climate is ideally suited to solar power and that our hot water should be heated from harnessed solar energy. Using solar energy to heat water can also substantially reduce energy bills, even in cooler climates and regions that previously were not deemed possible for solar systems.

Unlike carbon-neutralising options like planting trees — which is definitely part of the solution — tree planting will by no means deliver the urgently needed immediate result, taking around 40 years on average to sequester carbon. Installing a solar hot water system, on the other hand, will have a virtually immediate and positive environmental effect as well as provide the household with a significant financial saving.

What is the greenhouse effect?

Greenhouse gases are a natural part of the earth’s atmosphere. They trap the sun’s warmth and maintain the earth’s surface temperature at a level necessary to support life. However, the problem we now face is that human actions, in particular burning fossil fuels such as coal, oil and natural gas to produce energy as well as the exponential rate of land clearing, are increasing the concentrations of these gases that trap more heat and change the climate. This is what we refer to as the greenhouse effect.

We know that our activities have added extra carbon to the atmosphere, but what we are starting to realise is that it only takes a small change to upset the equilibrium. Our excessive reliance on burning fossil fuels has put the carbon cycle out of balance and this cause and effect is expected to result in continuing increases in atmospheric carbon dioxide concentrations. The projected global warming of just a few degrees in the 21st century is likely to result in more heat waves and droughts in some regions of the world and more intense rainfall and resultant flooding in other areas.

Unfairly, the worst projected consequences will be felt most by developing countries that have fewer resources and less capacity to respond to the effects of climate change. As a direct result of thermal expansion and melting glaciers, our sea levels will rise and consequently some low-lying coastal areas and islands will be more prone to flooding and storm damage. Devastating flooding impacts, such as those we witnessed from the Indian Ocean Tsunami on Boxing Day in 2004, will be far more commonplace. Many plants and animals are unlikely to be able to migrate or adapt quickly enough to survive in a warmer world. Habitat clearing also means many animals will not be able to adapt to increasing temperatures by moving to other locations. The bottom line is we are heading towards catastrophic change if we don’t alter our way of life. About the only good news is that awareness and the call to action is finally penetrating the general population.

Solar hot water basics

Solar hot water systems generally consist of a collector that heats the water, a tank that stores the heated water and a booster system that is used in times of limited sunlight (for example on a cloudy or rainy day). A few years ago solar water heaters were quite simple affairs, consisting of pipes running through a black-lined, glass-covered box. The sun would heat the black lining that heats water running through the pipes — these are known as flat plate collectors. They were great for areas with high levels of solar radiation, but were not so efficient in winter or cooler climatic zones, requiring regular maintenance and chemical treatments to stop the water freezing in the pipes. Today the options are greatly expanded, providing solutions for almost all locations and circumstances.

The solar hot water options

There are many companies out there offering a variety of solutions, from well-known names such as Dux, Rinnai, Rheem and Edwards to solar-specialised providers such as Solar Lord, Ecosmart and Endless Solar to name a few. All of these companies provide excellent technology and comply with specifications, but it’s best to research what your specific needs are to get the best solution for your home. Here’s a general breakdown of the systems available.

Size does matter

Each person on average uses around 50 litres of hot water every day. But that’s on average; if you have a spa or enjoy deep baths or long showers, have a dishwasher or wash your clothes in hot or even warm water, that figure can be much higher. Based on this average consumption of 50 litres of hot water, for solar heaters an average four-person household needs about two flat panels, or four square metres of solar collector area and up to a 360L tank. This is a prudent estimate that will allow for cloudy days or times of greater demand, such as when you have visitors. Alternately, the next-generation ‘evacuated tube’ solar hot water systems require less collector area and a smaller storage tank. For a household of four people, a single collector consisting of 22 tubes combined with a 250L tank would be sufficient.

Solar Thermosiphon (or Closed / Coupled) Systems

With a thermosiphon (sometimes called a closed or coupled system), both the storage tank and the solar collector panels are mounted on the roof. As the complete system can weigh several hundred kilograms when filled with water, you need to make sure your roof can support such a weight, and reinforce the roof if necessary. The advantage of this system is the ability to free up space around the base of the house — ideal for courtyard homes or small blocks. In the installation, the solar tank is mounted above the collectors on the roof and the water heated in the panels rises by the natural thermosiphon principle through the collectors into the tank, and is then recirculated through the panels until the water reaches the required temperature.

One of the key benefits of a thermosiphon system is that technically it is very efficient, economical to install and requires little maintenance. There is no need for recirculating pumps and pipe runs, which reduce heat losses and improve running efficiencies. No electricity is required to operate the pumps to recirculate the water through the panels — this also allows for this solar system to work in remote areas where electricity is not available.

Solar Pumped or Split Systems

Either because you don’t like the appearance, or because your roof can’t support the weight, you may not want to have the storage tank on the roof. With a pumped solar system, the tank is at ground level while only the collector panels are mounted on the roof. As the thermosiphon effect can’t circulate the water from tank to collector in this case, the system needs an electric pump. The main benefit of this system is that the tank is installed remotely from the panels in the most convenient and aesthetically pleasing location — usually on the side or behind the house. A small pump circulates the water from the tank through the panels to collect the heat energy from the sun. This pump is automatically regulated by a controller that monitors the temperature in both the tank and collector panels and optimises solar gain. Another advantage of pumped systems is they don’t require a heat-exchange fluid for frost-protection. If the temperature in the collector panel is close to freezing point, a sensor switches on the pump, which then circulates warmer water through the panels.


Boosting is required for overcast or rainy days when the sun isn’t quite enough. Boosting can be by electricity, gas, or a combination of both. The size of the booster depends on many factors including the number of bathrooms, your location and hot water usage patterns. Again, it depends on individual requirements but here’s a rundown on the boosting options for solar hot water.

Electric boosting

Electricity is recommended where connection to either Natural Gas or LPG is not possible. Aside from easy access, one of the other benefits includes access to electricity, often during cheaper off-peak periods.

Gas boosting

Gas is the most economical and environmentally friendly way to boost the water temperature if required. This system can operate only when the hot tap is turned on and even then, only if the water in the tank is not already hot enough. Continuous flow booster ensures an endless flow of hot water regardless of whether the sun is shining or not.

Combined gas and electric boosting

EcoSmart™ produces gas or electrically boosted solar hot water systems, employing the patented HotLogic™ processor technology, which constantly searches for and switches to the most cost-effective energy source available. This technology constantly utilises the ‘cheapest’ available energy source, whether it be solar, gas or electric energy.

Frost protection for solar systems

For these solar hot water systems, it is important you install frost tolerant collector panels or solar frost technology kits to protect your system from freezing. If you live in a cool region or a frost-prone area, this will provide you with the opportunity to enjoy solar hot water benefits in almost any area of Australia.

Evacuated tubes

Planet Ark is an Australian initiative that uses mainstream media to drive positive behaviour change among consumers — aimed at reducing their environmental impact. Endless Solar is the only solar hot water system to be endorsed by Planet Ark and they are at the forefront of development in manufacturing technology that has produced a new generation of a solar hot water heater called an evacuated tube system. The new breed of solar heaters using evacuated tube technology was invented in Australia over 30 years ago at the University of Sydney.

Evacuated tubes work much like a thermos flask, with a vacuum layer between two layers of absorbing glass trapping about 97 per cent of the energy from the sun. This energy is then transferred to water via a special heat pipe located inside each tube. A small amount of distilled water inside each pipe is turned into gas by the sun’s energy. The gas rises to the tips of the pipes, which are inserted into a heat transfer device, through which cold water is then pumped. The water absorbs the heat and is stored in a water storage tank located on the ground.

The result is an incredibly efficient system that harnesses the heat of the sun, even in extremely cold regions. Evacuated tube systems don’t require full sun and can work on cloudy or even rainy days. To get the best result, collectors should be positioned facing north. Flat plate collectors are effective up to 20 degrees either side of north, while evacuated tubes are effective up to 90 degrees either side of north.

Unless you live in the tropics you will probably benefit from an evacuated tube system, otherwise you will need to treat your flat plate system with chemicals (usually glycol) to prevent damage to the system from freezing. Treating a flat plate with chemicals is expensive and reduces efficiency by around 10 per cent — this is required at a frequency of every three years or so. Evacuated tubes are up to 40 per cent more efficient than traditional flat plate collectors, and can be even more efficient in colder climates.

Widely used throughout the world, evacuated tubes are a proven technology, particularly in European countries where extremely cold weather is a problem for flat plate collectors. Even though it was invented here, evacuated tube technology is relatively new to Australia. Evacuated tubes are maintenance free and self-cleaning. Flat plates, on the other hand, can attract a layer of atmospheric grime that must be cleaned regularly to maintain efficiency. Solar collectors can be fitted to existing solar hot water systems; this is called ‘retro-fitting’ but it is not recommended if the existing tank is over five years old.

With current technological developments, evacuated tube systems can be produced quite cost effectively and are now similar in price to comparable old-style solar systems. Evacuated tubes have a sleek, stylish profile that is becoming very popular with architects who use the aesthetic properties and versatility as features in their house designs.

There are several evacuated tube suppliers in Australia, though Endless Solar is endorsed by Planet Ark and is an Australian-designed system built specifically for Australia’s harsh and varied conditions. Endless Solar has licensed its unique design to Hills Industries for distribution throughout Australia and New Zealand. Hills is the inventor of the iconic Hills Hoist — the original solar-powered clothes dryer!

Solar rebates

As Australian households are responsible for more than half of all energy-related emissions, the Australian federal government and the individual state governments are helping Australian households install greenhouse-friendly hot water technologies. Information about the Solar Hot Water Rebate Program can be obtained from www.greenhouse.gov.au/rebates.