Credit: Julie Knoblock
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Who doesn't love a hot shower? But these days, showers can be such a guilty pleasure. Besides all the water gurgling down the drain, the energy used to heat the stream is contributing to climate change.
But don't despair! It's quite a simple matter to change the most energy intensive appliance in the house into one that is almost climate neutral.
By installing a solar hot water system, for just a few thousand dollars you can cut your household emissions by the equivalent of three to four tonnes of carbon dioxide a year, which is equivalent to taking one small car off the road. It sure beats spending $40,000 on a hybrid car!
Hot water is the biggest user of energy in the home, on average 40 per cent of your bill. Installing a solar hot water system can reduce your hot water bills by up to 90 per cent so your reward for saving the planet is about $300 a year.
This means in five to ten years your investment will be paid off and your hot water will be essentially free.
Elements of a solar hot water system
The bare basics of a solar hot water system consist of:
- a hot water tank to store the water
- solar collectors to warm it up
- a booster system in case of a cloudy day
Close-coupled system
The most common set-up, called a close-coupled system, uses solar collectors and a tank located on the roof.
As the water doesn't need to travel far, the fact that hot water rises (in the same way hot air does) provides the circulation from panel to tank so you don't need a pump.
The main advantage of these systems: they are low cost. The downside: the tank is located on the roof, which is not particularly attractive.
The roof also needs to be strong enough to support the tank's weight. If the roof needs reinforcing you might want to consider a different configuration: a split system.
Split systems
These also have solar collectors on the roof, but the tank is located on the ground and a small pump is required to circulate the water.
While they usually cost a little more than a close-coupled system, they won't ruin the look of your roof.
From an efficiency and maintenance point of view there is little difference between close-coupled or split systems.
Tanks
When it comes to tanks, there are two main considerations: materials and capacity.
Material range from stainless steel and vitreous enamel (also called mild steel) to UV stabilised polyethylene.
Stainless steel tanks have a reputation for being tougher than vitreous enamel, which corrodes if you don't replace a sacrificial anode every five or so years.
However, "If the tanks are properly maintained and the water quality is good, the difference between stainless and vitreous enamel is minimal" says Ken Guthrie, Sustainability Victoria's manager of renewable and distributed energy.
Less common is stabilised polyethylene, which according to Solco, the supplier, is so tough that it comes with a lifetime guarantee.
Solar Collectors
Solar collectors come in two varieties: the traditional flat plate and the newer cylindrical evacuated tubes. Each work slightly differently.
Flat plate collectors consist of a network of pipes in a glass-covered box with a black absorber plate on the bottom. The sun heats the absorber plate, which in turn heats water in the pipes.
Evacuated tubes are more sophisticated and work a bit like a thermos flask: the tubes consist of two layers of glass with a vacuum in between, which prevents heat from escaping and increases the efficiency of the system.
Also, the cylindrical shape means that there's always one part of the tube perpendicular to the sun, allowing it to absorb more radiation.
If space on your roof is limited, the more-efficient tubes take up less space. Not only are evacuated tubes more efficient than flat plates, but the vacuum also prevents frost from freezing the water in the pipes.
Evacuated tubes generally perform better than flat plate collectors in cold weather, while flat plates can work better in warmer weather. However, the energy saved depends on climate and the system installed, not just the efficiency of the collectors.
Evacuated tubes are more expensive than your bottom-of-the-range flat plate close coupled system, although they become more competitive when compared with a quality mid range split system.
It's worth bearing in mind that evacuated tubes cost around $30 to replace (per tube), while if a portion of a flat plate breaks, the whole thing needs replacing - which can cost around $500.
All solar hot water systems need an electric or gas backup or booster system for cloudy days. Instant gas is cheaper to run than electricity, but costs more upfront. If you're still not convinced, remember gas produces far less greenhouse gas emissions. Even if you don't have gas plumbed in, bottled LPG is still better on the environment than electric.
What you need to know before buying a system
Most people require around 50 litres of hot water a day. So a family of four is likely to need at least a 200-litre tank. More if there are teenagers in the home.
Solar hot water can be installed in most Australian houses - even damp cold Tasmania gets enough sunlight. You might even be able to convert your existing system.
To get the most out of your system, solar collectors should be positioned on a north-facing unshaded roof (in the southern hemisphere), sloping at least 15 degrees.
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.
For other orientations or incorrect roof slope, collectors can be mounted on a stand.
If the roof is heavily shaded it may not be suitable for a solar hot water system - in this case, the most environmental runner-up is instant gas.
Cold nights
Unless you live in the tropics you will need frost protection.
Evacuated tubes come with inbuilt frost protection while if you get flat plate collectors it's an extra add on.
The most common type of frost protection for flat plate collectors uses heat exchange from an antifreeze fluid such as glycol. The level of these fluids needs to be checked regularly in order to maintain performance.
An earlier frost protection technique was valves; these have largely fallen from use because of reliability problems, while a third system, forced circulation, is considered to be inefficient. Water quality also affects the longevity of the tank so if your water quality is poor choose a tank that resists corrosion.
Longevity
As long as you choose the right system, and it's properly installed, solar hot water systems need little maintenance and according to Con Jamos from Eco Smart Hot Water "are likely to last as long as 20 years".
To ensure your system works well choose a plumber who has been specially trained in solar hot water installations, for example a Green Plumber.
Maintain efficiency by cleaning dust and debris off solar collectors every six months. Evacuated tubes are less likely to need cleaning because of their round shape.
Convert your existing system
If your hot water tank is relatively new and in good repair you might be able to convert your existing system to solar.
Electric tanks less than five years old are the best candidates for a retrofit kit, costing about half the price of a new system. Gas tanks less than three years old also can be converted to solar using a preheater.
However, government rebates designed to encourage purchase of solar hot water systems are not always available for conversions.
How much will it cost?
Solar hot water costs a bit more upfront than conventional systems, with prices ranging $2,700 to $5,000. Installation costs up to $700 extra. A conventional hot water service can cost less than half that.
There are, however, substantial discounts in the form of renewable energy certificates (RECs) and rebates.
RECs up to $500 are available as a discount at the point of sale depending on the type of system. The West Australian, South Australian and Victoria governments also offer rebates up to $1,500, which about evens out the cost.
And don't forget that after five to ten years the savings you make on your bills will have paid for your system.
If the upfront cost still seems daunting look for an interest-free payment plan offered by some companies.
Another option is to install a gas system now and add the solar collectors later when you have the money. Just make sure that your new gas system will be compatible with a retrofit.
Soon enough you'll be steaming up the bathroom free of charge, courtesy of the winter sunshine.
