As the days and nights become warmer, less mechanical heating is required to assist passive solar heating (plus insulation) to maintain a comfortable temperature indoors. Increased solar power exports and decreased grid imports reduced the energy bill to 50c per day.
Learning how to help the passive solar design features keep us warm in Winter is a useful exercise. Sunlight is all we need on clear, cold days. When it's cloudy, we use the heat pump to stop the concrete slab thermal mass cooling too much.
While discussing sustainable home design with others, I realised the word "passive" mu;st be used carefully. Passive solar design is different to Passive House design. It's important to understand the differences and similarities.
While the indoor temperature felt comfortable during hot summer days, I was left with the nagging feeling that wishful thinking was keeping me cool. Passive solar design should minimise the need for mechanical cooling for everything but a run of very hot days. Temperature monitoring data confirmed this is the case for our design.