Do You Still Need Energy-Efficient Hot Water If You Have Solar & a Battery?
Installing solar panels and a home battery can dramatically reduce the electricity you buy from the grid. But there's one important question:
Does your solar system actually generate enough electricity to run your home, heat your water and recharge your battery?
Your hot water system can be one of the largest energy users in your home. Use our calculator to see how your solar generation, battery capacity, household consumption, air-conditioning and hot water demand work together.
All these appliances compete for the electricity generated by your solar panels
A 13.5 kWh Battery Doesn't Give You an Extra 13.5 kWh Every Day
A battery is an energy storage device. Before your battery can supply your home overnight, there needs to be enough surplus solar electricity during the day to charge it.
Even if the homeowner owns a 13.5 kWh battery, there may only be 8 kWh available to put into it. The battery stores electricity — it doesn't generate it.
Can Your Solar System Power Your House, Battery AND Hot Water?
Adjust the settings below to estimate where your household electricity is going.
Disclaimer: This calculator provides an indicative estimate only. Actual electricity generation and consumption varies according to weather, season, solar orientation, shading, appliance efficiency, usage patterns and equipment. Your electricity bill and smart-meter data provide the best indication of your actual consumption.
The 115% and 70% scenarios are illustrative modelling assumptions, not official generation guarantees. Try the Lower Generation Day to see how it changes things.
Battery capacity: 13.5 kWh · Estimated usable capacity: 12.2 kWh (90% usable factor)
You can usually find your average daily usage on your electricity bill. Using your actual consumption will make the calculator considerably more accurate.
Estimated additional air-con consumption: 0.0 kWh/day
Energy Flow Breakdown
Your solar generation and household electricity consumption are relatively close.
Reducing hot-water electricity consumption could leave considerably more solar available for your battery and evening electricity use.
What If You Reduced the Electricity Used for Hot Water?
Heat-pump performance varies by product, climate, installation and usage. This is an indicative comparison based on heat pumps requiring substantially less electricity than conventional electric resistance water heating.
Think of Your Solar System as Your Household's Energy Budget
The electricity produced by your rooftop solar system needs to cover many different demands. Every appliance is competing for a share of the same energy budget.
Home Appliances
Fridges, cooking, lighting, washing, dryers, computers and everyday appliances.
Air Conditioning
Queensland summers can significantly increase household electricity consumption.
Pool
Pool pumps and heating can consume additional daytime solar.
Electric Vehicle
Charging an EV adds another major electricity load.
Hot Water
Water heating can represent a significant portion of household energy consumption.
Battery
Only the solar electricity left over after daytime consumption can recharge the battery.
Isn't Heating My Water With Solar Panels Basically Free?
It can be extremely economical to use excess rooftop solar PV to run an electric hot-water system during daylight hours. But the important word is: excess.
If the house has plenty of unused solar production during the middle of the day, using that electricity for hot water may make excellent sense.
But if solar electricity is already being used by air-conditioning, appliances, pool equipment, a home office, EV charging or battery charging, there may not be as much spare electricity as expected.
A high-energy conventional electric hot-water system can consume electricity that could otherwise have charged the battery for use later. This is why homeowners need to look at the whole-house energy equation, not simply whether they own solar panels.
Solar PV and Solar Hot Water Do Different Jobs
Solar PV
Solar PV converts sunlight into electricity. That electricity then has to be shared between all electrical loads in the home.
Solar Hot Water
Solar hot water captures solar energy specifically for heating water. That can leave more electricity generated by the PV panels available for other household loads or battery charging. An electrical or gas booster may still be required.
Where Does a Heat Pump Fit In?
A heat pump still uses electricity. However, rather than creating all its heat through electrical resistance, it extracts heat from the surrounding air and transfers that heat into the water. That means substantially less electrical energy can be required to produce the same hot water.
Conventional Electric
Heat Pump
For a solar-powered household, this can mean more of the solar system's electricity remains available for battery charging, air-conditioning, appliances, EV charging or export.
When Might Conventional Electric Hot Water Still Make Sense?
- ✓The existing system is relatively new
- ✓The household has substantial excess daytime solar
- ✓The hot-water system is programmed to operate during excess-solar periods
- ✓Household hot-water demand is low
- ✓Replacement cost outweighs likely energy savings
- ✓There are installation constraints
There isn't one hot-water system that is best for every Queensland home.
When Should You Consider Heat Pump or Solar Hot Water?
Consider investigating an efficient system if:
- →Your battery regularly fails to reach a full charge
- →You import significant electricity overnight
- →Your existing electric hot-water system uses a large amount of electricity
- →Your household has high hot-water demand
- →You frequently run air-conditioning
- →You have a pool
- →You're planning to charge an EV
- →Your existing hot-water system is approaching replacement age
- →You want to maximise the amount of household demand met from your own solar generation
Check Your Data Before Replacing Anything
Before replacing a working hot-water system solely to reduce electricity consumption, look at the data. If available, check:
- 1Your average daily electricity consumption
- 2Your solar system's daily generation
- 3How much electricity you're exporting
- 4How full your battery normally gets
- 5When your household imports electricity from the grid
- 6When your hot-water system operates
- 7Your seasonal consumption
If you have smart-meter, solar inverter or battery monitoring data, this can provide a much more accurate picture than relying on an annual electricity bill alone.
Not Sure Which Hot Water System Makes Sense for Your Home?
The right answer depends on more than whether you have solar panels. Todd's can help you compare your existing hot-water system, household size, hot-water demand, solar PV, battery capacity, available roof space, electricity consumption and installation requirements.
Then we'll recommend whether it makes more sense to keep your current system, replace it with efficient electric hot water, install a heat pump, or install solar hot water.
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The Question Isn't Simply "Do I Have Solar?"
"After running my home and heating my water, how much solar electricity is actually left?"
A battery can help you use your solar electricity later. But it can't store electricity your solar system never produced. Understanding your household's complete energy picture can help you decide whether conventional electric, heat pump or solar hot water makes the most sense for your home.
Compare My Hot Water OptionsFrequently Asked Questions
If I have solar panels and a battery, do I need a heat pump?
It depends on solar generation, household demand, hot-water usage, battery capacity and when electricity is consumed. If your solar system produces more than enough electricity to run your home, heat your water and charge your battery, a heat pump may be less critical. If demand exceeds generation, a heat pump can significantly reduce the electricity your hot water draws.
Isn't electric hot water free if I run it from solar?
Excess solar may make the operating cost very low, but solar electricity has other potential uses including battery charging, appliances and export. If demand exceeds generation, grid electricity may still be required.
Can my solar panels charge my battery and heat my water at the same time?
Yes, if sufficient solar power is being generated at that time. When demand exceeds solar output, the difference must come from the battery or grid.
Does a larger battery solve the problem?
Not necessarily. A larger battery stores more electricity, but the solar system still needs to generate enough surplus electricity to charge it.
Does solar hot water still make sense if I already have solar PV?
Potentially. Solar hot water captures solar energy specifically for heating water, which can reduce the electrical load placed on the PV system.
Does a heat pump work well with solar panels?
Heat pumps can be particularly useful with solar PV because their lower electrical consumption can be scheduled during daytime solar-production periods where appropriate.
Should I replace a working electric hot-water system?
Not necessarily. Compare the likely savings against replacement cost, system age, solar export, household demand and how much grid electricity you're currently buying.