Having our air conditioner out of service at the start of Summer was an opportunity to demonstrate how a passive solar home in Melbourne doesn't rely on mechanical cooling to keep the occupants comfortable.
Cold, cloudy days in June were a good test of the energy cost for active heating to remain comfortable indoors. The total energy bill to live comfortably in our high-efficiency, all-electric home was a reasonable $2.50 per day.
During May, the colder, cloudier days meant the house changed from passive to active heating mode. The air conditioner was handy to keep the indoor temperature within the target comfort range. Less solar power production and higher electricity consumption left us with a $43 energy bill.
April marks the end of a long run of days of excess solar power exports and passive cooling. Shorter, cloudier days reduce power production. Colder temperatures mean the house has moved to passive heating, with just a touch of active heating using the air conditioner. It's still comfortable indoors but the monthly energy cost is expected to rise from here.
March is a tricky month for a passive solar home. With the Sun lower in the sky, the increasing amount of sunlight hitting the concrete slab is moving the house into passive heating mode. However, the occasional flashback into Summer means the heating isn't required. Covering the pergola with a deciduous vine should eliminate the issue in future.
Passive cooling with nighttime natural air circulation was all that was required to maintain a comfortable temperature indoors. Solar power production remains high with exports ensuring our energy bill was a slight credit.
Our passive solar design home performed well for comfort and cost during a record run of hot weather in Melbourne. Natural air circulation during the cooler nights eliminated the need for air conditioning during the day. Solar power production far exceeded our needs, resulting in a slight credit on the power bill.
Despite increasing temperatures, passive cooling was all that was required to keep indoor temperatures within a comfortable range. The energy bill for December was a credit of $8 due to continuing low household demand and increased solar power production.