Solar Hot Water
Using the sun’s energy to heat water will save you energy, lower your hot water bills,
and reduce greenhouse pollution.
Solar hot water systems work effectively in Victoria using mature and established technology. You can now convert almost any existing gas or electric water service to solar.
Using the sun’s energy to heat water can reduce your household hot water bills by more than 60% each year, that’s a saving of around $200 each year for the average family. This could add up to thousands of dollars saved over the lifetime of the system.
Solar hot water systems also help conserve our natural resources and the environment. Converting an existing electric water heater to solar reduces as much
greenhouse pollution as taking one car off the road each year.
Solar water heaters are generally equipped with gas or electric boosters to ensure you are never without hot water. Technology advances in recent years mean systems are now 20% more efficient than their counterparts of 30 years ago and frost problems have now been eliminated.
This fact sheet provides information on the different types of solar hot water systems available, how they work, and the practical considerations of purchasing one for your home.
How does it work?
Solar hot water systems use the sun’s energy to heat water in much the same way as water in a hose left on the lawn gets hot on a sunny day. In a direct heating system, water is heated as it circulates through flat, glazed panels (solar collectors), located on the roof of a house. The heated water is then stored in an insulated storage tank, located either directly above the collectors or on the ground like a conventional hot water system. An auxiliary heater is also included in the system, to
boost water temperature on days when solar energy may be insufficient to meet all your hot water requirements. Boosters may be run on off-peak electricity, gas (natural or LPG) or solid fuel.
Solar collectors typically consist of a blackened metal absorber plate within a glazed and insulated metal box (flat-plate collector). Pipes attached to the absorber plate carry the liquid that is heated by the sun. Collectors should be positioned on a north-facing roof (no more than 45° east or west of north) at an angle between 15° and 50° (standard roof pitch is usually sufficient). Other roof orientations may also be suitable, provided the unit is mounted on a frame to face north.
Victorians have access to 15% more solar energy than Barcelona in sunny Spain and the same amount as North Africa, disproving the myth that Victoria’s climate cannot support solar power.
What systems are available?
Close-coupled thermosiphon (mains pressure)
This is the most common system on the market. It consists of roof-mounted solar collectors, combined with a horizontally-mounted storage tank located immediately above these collectors.
this cycle, commonly referred to as ‘thermosyphon flow’ (see figure 1).
Figure 1: Close-coupled thermosyphon (mains pressure)
Remote thermosyphon system (constant [low] pressure)
This system works on the same principle as the close-coupled thermosyphon system, except that the storage tank is located within the roof space and supplies hot water by constant rather than mains pressure. The base of the tank must be situated at least 300 mm above the collectors (see figure 2).
Figure 2: Remote thermosyphon system (constant [low] pressure)
Forced circulation system (mains pressure pumped)
With a pumped system, the tank is located below the level of the collectors, usually at ground level. Water
pump. Pumps are not expensive to run, costing between one and two cents per hour.
This system can be used when the roof structure isn’t strong enough to support a close-coup
must therefore be pumped from the tank to the collectors and back by a thermostatically controlled
led system. The t
reheaters
is possible to add a preheater to an existing water eater which will maximise the solar gain of the system.
preheater is a storage tank, with solar collector(s) onnected, that feeds water heated by the sun into your onventional water heater when hot water is drawn from
e system (see figures 4 and 5).
system is traditionally boosted by off-peak electricity bu is now also available with a gas booster controlled by a timer which stops the gas burner from operating during sunshine hours (see figure 3).
P It h A c c th
Figure 3: Forced circulation system (mains pressure pumped)
etrofits
ff-pe
re not specifically designed for connection to solar, so is important to ensure that the collectors are of good uality, and that, in the case of pumped systems, the
d is optimised to maximise the solar ontribution.
as water heaters cannot be retrofitted unless there is ufficient water volume in the tank and there is a
ethod to ensure that the gas burner will not ignite due the thermostat during sunshine hours (see figure 6).
put temperatures, it is possible to connect it to a solar reheater. The preheater is a storage tank with solar ollector(s) connected (either close coupled or force
ted by the sun into the uous flow gas boosted hot water system. The ontinuous flow gas boosted system only operates
hen the solar heated water fed into it is below the set mperature, minimising the amount of gas required to he
atmosphere and evaporating in the process (collectors in a heat pump system are often referred to as evaporator plates). The gas then moves along to a coil that is wrapped around the hot water tank where it condenses and gives off the heat it has absorbed to the water in the tank. In some instances the collectors
as Figure
R
Collectors can be connected to existing conventional o ak electric hot water heaters. Conventional tanks a it q pump spee c G s m to
Continuous flow gas-boosted systems
If a continuous flow (tankless) gas water heater is designed to cope with varying (and often quite high) in
p c
circulation) that feeds water hea contin
c w te
heat the water and maximising the contribution from t sun (see figure 7).
Heat pumps
(evaporator plates) are integrated into the same unit as the tank and heat is extracted from the surrounding air, these systems are called “air source” heat pumps. Heat pumps are included as electric boosted solar water heaters they require similar amounts of electricity to operate. Heat pumps are a special type of solar hot water system. Instead of water or a glycol solution passing through the collectors a refrigerant is used. Heat is extracted from the atmosphere using a refrigerant gas and a compressor (in much the same way as heat is extracted from your refrigerator), and used to heat water stored in a tank at ground level. The refrigerant passes through the collectors taking up heat from the
5: Preheater with close-coupled solar system
Figure 7: Instantaneous gas water heater connected to a close
Figure 6: Retrofit (off-peak electric)
What type of tank should I purchase?
Storage tanks for solar hot water systems are generally made from either stainless steel, copper (low pressure systems only) or mild steel with a coating of vitreous enamel (mains pressure).
Vitreous enamel lined tanks have a ‘sacrificial anode’ which is designed to reduce corrosion of the tank. These anodes require periodic checking and replacement every 5–7 years on average. The life expectancies of storage tanks are often
How much does it cost?
Solar water systems vary in price depending on model, tank size and number of panels. It is often possible to
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Is it a good investment?
d reduction of
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system performance
ove the hot
is period will be shortened if tariffs reflected by the length of the warranty period
Check this with the manufacturer or supplier. In terms of the environment an
greenhouse gas pollution, solar hot water is an excellent investment and should be considered. However, to determine whether or not solar hot water a good fina
Frost protection
It is sensible in Victoria to consi
to be considered: > geographic location > hot water usage protection for your solar hot water system. Passive
forms of protection include using an indirect heating system (using some form of heat exchanger) o
frost protection valves. The valves are a che > less reliable option than using a heat exchanger.
Indirect systems use a heat exchanger and are recommended for areas that are susceptible to
> type and cost of system > type of auxiliary heating used.
For an additional investment of around $2000 ab price of a conventional hot water system, a solar water system in Melbourne will pay for itself in approximately four to ten years at today’s gas and electricity tariffs. Th
W
freeze (such as glycol) an The heat that is abso
freeze is transferred by the heat exchanger into the water in the storage tank. The anti-freeze treated wa is kept totally separate from the water used for dome purposes.
Active systems use pumps to circulate water through the collectors when the temperature drops below a
rise.
certain point. In areas where the power supply is unreliable, this could be a risky option as the pump will not operate if the electricity supply is off.
What size system will I need?
The following table can be used as a guide to sizing a solar hot water system, however consult your supplier for Number of persons served Capacity (litres) Collector area (m2) 1–2 160–200 2
3–4 300–370 4 Figure 8: Annual running costs of different hot water systems (Off
peak electric tariff of 8.15c/kWh, Natural gas tariff of 0.936c/MJ and LPG tariff of 61c/litre used)
Bear in mind that solar systems have longer life expectancies than most conventional systems, which further improves their cost effectiveness.
A shorter payback period can be expected in areas with higher levels of solar radiation (e.g. north of the Great Dividing Range) or more expensive fuel sources (e.g. LPG). For a comparison of the running costs of different hot water systems see the Annual Running Costs chart (figure 8).
Hot water and the environment
Solar hot water systems are friendly to the environment. The graph below compares the amounts of greenhouse pollution (CO2 equivalent) released by different fuel
combinations when each supplies the same amount of hot water.
Important considerations
To get the most out of your solar hot water system, make sure:
> you carefully read the warranty details (check that it includes frost protection)
> your roof’s structural strength is assessed (by the installer) to ensure that it can support the weight of the system
> solar collectors will not be shaded by trees or nearby buildings
> the storage tank and solar collectors are as close together as possible to reduce the length of the connecting pipes (in constant pressure and pumped systems)
> all pipes are well insulated
> some form of frost protection is included > all plumbing must be carried out by a licensed
plumber. The plumber will issue a certificate of compliance
> all electrical work for the installation of electrical heating elements and electric pumps must be carried out by a registered electrical contactor. The Contractor will issue a certificate of electrical safety > if your water quality is poor, then you need to be
aware that the system’s warranty may be affected.
Tips for better performance
The most effective way to obtain maximum
performance from your solar hot water system is to make efficient use of hot water in your home. Take note of the following points.
> when possible, do jobs requiring hot water early in the day. This allows the water remaining in the tank to be reheated by the sun and reduces the auxiliary heating period.
> the recommended setting for the booster thermostat is 60°C. Remember, the lower the thermostat setting, the lower the energy used to supplement solar heating.
> install your system as close as possible to the kitchen, bathroom and laundry, which are the main hot water draw-off points around the home. If this is not possible, install it close to the kitchen.
> conserve hot water by using it efficiently.
> fit a low flow showerhead. Showering makes up over 30% of hot water usage in the home. This can be dramatically reduced by fitting a low flow
showerhead, or a flow restrictor to an existing showerhead.
> make sure you follow the manufacturer’s
recommendations for maintenance of your solar hot water system.
Solar Hot Water Rebate program
The State Government of Victoria is offering rebates of up to $1500 for solar hot water systems that replace conventional gas, wood, briquette or oil fuelled water heaters and result in reduced greenhouse pollution. The rebate generally takes the form of a point-of-sale discount. However, some manufacturers pass on the rebate after being reimbursed by Sustainability Victoria. NOTE: Solar water heater installations in new homes or buildings or that replace an electric water heater are ineligible for the rebate. A financial incentive through the Commonwealth Government’s Renewable Energy Certificates (RECs) is available. Your manufacturer can advise on RECs eligibility.
For more information on the rebate program please visit our website at www.sustainability.vic.gov.au
This has a list of accredited solar hot water systems, their recommended retail prices and the savings that they will achieve in northern Victoria as tested to Australian Standard 4234. In southern Victoria the savings will be marginally reduced.
Further information
Visit Sustainability Victoria’s website for more information and advice on:
> Reducing your energy bills > Energy efficient house design > Hot water systems and usage > Renewable energy options
Sustainability Victoria
E-mail [email protected] Web site www.sustainability.vic.gov.au
The information in this document is derived from various sources and is understood to be correct at the time of publication. However, the information may not be error free and may not be appropriate for a particular purpose. Sustainability Victoria accepts no liability whatsoever to any person for any injury, loss or damage that may arise in connection with any use or reliance on the information.
