Based on our experience in 2023, all-electric, efficient homes offer an exciting future for residential living in Australia. Clever house design maintains a comfortable indoor temperature without the need for excessive mechanical heating or cooling. Using electricity from rooftop solar panels cut our energy bill to $410 pa or a little more than $1 per day.
What is our home?
Our home is new-build which was conceived when we decided to move out of our family home. It’s a single storey, 2 bedroom, 2 bathroom house, located in the eastern suburbs of Melbourne.
What is an all-electric home?
Rewiring Australia defines all-electric as a home using only electrical devices, including the car.
There is no provision for a methane gas connection. In our case, the property’s gas connection was abolished before construction started.
Our household appliances are efficient, electrical devices. If required, two reverse cycle air conditioners provide additional heating or cooling in the living area and main bedroom. Hot water comes from a heat pump hot water service. Other devices include an induction cooktop, oven and ceiling fans.
An MG ZS electric vehicle (EV) sits in the carport, ready to provide transport when walking or public transport won’t do.
On the roof, an 8kW solar panel array generates electricity for the home during daylight hours. A 9.8kWh battery powers appliances overnight. After recharging the battery, any excess solar power is exported and shared with the local grid.
What is an efficient home?
I think of efficiency as how well the house uses energy to maintain a comfortable indoor temperature. The more efficient a home, the less energy needed to operate mechanical heating and cooling devices. Any home can be made comfortable if the resident is willing to pay for enough energy (gas or electricity) to maintain a comfortable indoor temperature. However, I’d say that is an inefficient home with a large energy bill.
During winter, any sunlight streams through the north-facing windows, warming the indoor thermal mass. Excellent insulation reduces heat lost through the building envelope. On a cold, clear winter’s day, it’s possible sunlight alone heats the interior, eliminating the need for mechanical heating.
In summer, an eave shades the windows, stopping sunlight from warming the concrete slab. Now the insulation reduces internal heat gain so the slab keeps indoors comfortable. If the temperature does rise, turning on the air conditioner is not the first option. Ceiling fans are often enough to supply a cooling breeze. Also, Melbourne’s changeable weather helps. When a cool change arrives after a hot day, opening all the windows for natural air circulation flushes warm air out of the house. Next morning, closing the windows traps cool air indoors.
Combining all-electric with an efficient house design is an effective combination
The energy required to heat or cool the standard home in Victoria is by far the largest contributor to total domestic appliance energy consumption. Sustainability Victoria estimates 47% of the household energy budget goes into heating and cooling.
Cutting energy consumption by switching to a reverse cycle air conditioner for heating and cooling is a good start for a home using ducted methane gas heating. Modern air conditioners use heat pump technology to achieve a coefficient of performance (COP) between 3 and 5. That means the device only needs 1kW of electricity to deliver up to 5kW of heating or cooling into a room. To put that into context, a methane gas heating system has a 0.9 COP (buying 1MJ of gas delivers 0.9MJ of heating).
Combining reverse cycle air conditioning with a 7+ Star efficient home design takes energy savings to the next level. The home needs less mechanical heating and cooling to remain comfortable indoors.
So, the message is clear. Almost half the appliance energy cost in the average Victorian home is due to heating and cooling. Efficient house design plus reverse cycle air conditioning equals minimum energy cost.
What is the energy cost for our all-electric, efficient home?
Although we used a daily average of 13kWh of energy (electricity only) to power our home, the 2023 total bill was just $410.
According to our electricity retailer, Powershop, this daily consumption is similar to other 2-person households in our neighbourhood. So, the number of kWh isn’t a surprise. Although, it’s worth pointing out that many of those households would also be using, and paying for, methane gas ducted heating. Our 13kWh includes heating and cooling.
Importing that amount of electricity from the grid would cost roughly $2,300 pa or $6 per day. More to the point, just paying the $1.40 per day grid connection fee should cost us $511, even if our electricity consumption was zero!
Now the benefit of rooftop solar and a battery becomes clear. In summer, the panels produce more electricity than household demand, meaning we earn a credit for grid export. Although the feed-in tariff has shrunk considerably, exporting around 4 MW of excess electricity does add up to a reasonable sum. The situation is reversed in winter with lower production leading to grid importing, most often at the end of a cloudy day. However, on average, grid imports are just 2.6kWh per day of GreenPower, dramatically reducing the energy bill.
Major items in the energy bill
Living in an all-electric and efficient home means we get the benefit of a substantial reduction in energy needed for heating and cooling (47% of average energy bill).
As per the Sustainability Victoria data, the air conditioner is used mostly in winter. However, passive solar design means the indoor temperature doesn’t vary significantly so the heat pump doesn’t have to work too hard to maintain comfortable conditions. If the indoor temperature rises in summer, a combination of ceiling fans and overnight natural ventilation is usually enough. The air conditioner might get a run after a series of hot days with high overnight minimum temperatures.
At 17%, hot water is the next major contributor to the average household energy bill. It would be an unusual event for our hot water system to need grid electricity for two reasons. Firstly, it is set to reheat the storage tank contents during the middle of day, using solar power. Secondly, the heat pump technology ensures reheating requires minimal amounts of electricity. Making enough hot water for the two of us to use in 24 hours takes only 1.5 to 2kWh.
What about the electricity used for charging our MG ZS EV? That’s included in the 13.3kWh daily average.
In 2023, we drove approximately 8,000km in Melbourne and regional Victoria. Most of the recharging was done at home, contributing a total of about 1,100kWh to household consumption. That’s consistent with the average EV consumption of 15kWh/100km.
Whenever possible, I charge the EV using excess solar power. That “costs” 5.2c/kWh because otherwise it would be exported to the grid. If there was insufficient solar power or I wanted to charge more quickly, I’d use my fast charger between midnight and 4am. Powershop has a special low rate for EV owners between those hours.
As a result, I “spent” $76 out of the $410 annual energy bill on electricity for the EV.
Going the same distance in a petrol car in 2023 cost roughly $1100, with an average fuel cost of $1.90 per litre.
Savings add up
Using an EV instead of a petrol car and using solar power instead of grid electricity saved us almost $3,000 in 2023.
Rewiring Australia estimates the average household can save $3,450 per year over 10 years by changing to an all-electric home. The greenhouse gas emission reduction is also impressive (assuming any grid electricity imports come from renewable energy sources).
Based on our experience, these numbers are realistic.
What about indoor comfort?
Of course, cutting costs is important, but this shouldn’t be at the expense of indoor comfort.
We haven’t sacrificed comfort in our all-electric, efficient home.
This chart shows major fluctuations in outdoor temperature during the year. Note the indoor temperature stays within a comfortable range due to the passive solar design supported by reverse cycle air conditioning when required.
I recommend anyone replacing a household appliance (eg hot water system) or renovating their home consider going all-electric. Somebody contemplating a new build should investigate designing an all-electric, efficient home.
The ongoing savings in energy bills are significant but will vary according to individual circumstances.
Energy bill savings from going all-electric are unlikely to reduce comfort or convenience.