Solar Hot Water Calculator

Solar Hot Water Heater Split
hot water shower

  • What does hot water cost you now?
  • What savings can be made with solar hot water?
  • What types of solar hot water are available?
  • How much hot water, power and money can be saved with efficiency?
  • What savings can be made with an efficient shower head and tap aeration?
  • Calculate your answers here.

Solar Hot Water Savings Ideas

Replace a shower head for a water efficient one and Save 55% in water and associated heating costs.
Install tap aerators and Save 75% in water and associated heating costs.

Solar Hot Water Calculator

Calculate your yearly hot water consumption and hot water costs.
See what a different efficient shower heads and aerators can make.
Evaluate if solar hot water capital costs compare with 20+ years of hot water savings.
Fill in the values in the top 3 tables.
Press Get Results button.
See you hot water annual costs
and possible water efficiency savings.

Water Use

Consumption Guide: Open tap 20 l/min, 3 star shower head 9 l/min, aerator tap 5-7 l/min.
Time the filling of a known sized container for more accuracy.
Consider trying to keep showers to 4 minutes each.

Description Time in minutes per day
e.g. 10
Proportion Hot Water
(0-1) e.g. 0.5
Normal use in
Efficient use
in litres/minute
Shower 20 litres per minute 9 litres per minute
Hand washing /
dish rinsing etc.
20 litres per minute 5 litres per minute

Water Use continued

Consider only using the dishwasher when full. Compare water use of a shower versus a bath.

Description Quantity per day Proportion Hot Water (0-1) Total Litres

Power Costs and Solar Power Available

Power Cost in Dollars per kWh example 0.18

Your local average daily Solar Radiation

World Map Solar Radiation (kWh/m2/day)

World Map Solar Radiation small

Press button after completing or adjusting fields in the top tables.

Local links: Homepage , Energy Efficiency , Solar Section , Energy Calculators , Efficiency eBook

Water and Energy Use Results

The power and cost calculations is based on a conventional electric storage water heater. Water efficient shower heads cost about $40, tap aerators cost about $10. See how much savings can be made by their use in the short and long term. The return on investment should be good in most cases.
Solar hot water can save even more. The capital cost must be compared to the potential savings. Do you still use enough hot water to make a case for its installation?
Calculate all possible energy efficient activities and see which ones are easiest to implement and get the best return on investment.

Parameter Normal Values Water Efficient Values Water Efficient Savings
Total Hot Water Use for day in litres.
This is useful for calculating hot water storage size needed.
Total Hot Water Use for year in litres litres
Hot water power consumption per year estimate (kWh) not including reheating kWh
Electricity hot water costs per year ($) $$
Electricity hot water costs per 20 years ($) $$
Potential local Solar Hot Water savings over 20 year (kWh)
Also Potential CO2 reduction in kilograms for coal electric power
Potential local Solar Hot Water savings over 20 year ($) $$$$

Does the Solar Hot Water Calculator show you efficiency savings?

Solar Hot Water Configurations

Solar Hot Water Type Advantages Disadvantages
Solar Collector pre heating
($1000-$1500 AUD)
Can be used with existing hot water tanks.
Only requires a plumber.
Is not useful for reheating hot water.
Solar hot water with rooftop tank
($3000-$4000 AUD)
Single Unit on roof.
Booster heater is built in.
Roof must be able to support weight when full of water.
Solar hot water split system
($4000-$6000 AUD)
Solar collector on roof, water tank on ground.
Solar collector is modular and can be extended.
A small pump (~50 watts) is needed for water circulation.
Power point is needed near tank for controller and pump.
Solar retrofit hot water split system
($2500-$3500 AUD)
Solar collector on roof, reuse existing water tank on ground.
Cheaper than complete solar split system.
A small pump (~50 watts) is needed for water circulation.
Power point is needed near tank for controller and pump.

Solar Hot Water Considerations

  • A larger water tank can take compensate for a cloudy day causing lower solar water heating.
  • Size the solar collector for your hot water consumption and average daily solar radiation.
  • Special considerations are needed in frost or snow areas.
  • Instantaneous gas heating can be used after the hot water tank to make up any shortfall in water temperature.
  • Become familar with any government rebates available. E.g. $1600 is available in Australia.
  • Renewable Energy Credits (RECs) can be sold after installation of solar hot water in some countries (~$1000-$2000).

Solar Alternatives to consider

  • If solar hot water is not economically feasable then consider gas water heating. This has about 1/3 the environmental impact compared to electricity from Coal sourced electricity.
  • Using gas for cogeneration producing electricity first then heat. The proportions are 1 kW of electricity for every 3 kW of gas heating.
  • Electric hot water using heat pump technology is much more efficient than an electric element heating. This is like reverse cycle heating.
  • Consider off peak electricity tariffs for any electric hot water use.
  • Solar skylights, solar lights, solar pool heating and Solar Power

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