My House

1. Using renewable energy and making modifications at home to reduce consumption and costs

The house was built by owner-builders in 2011. I purchased it in May 2015. It already had some good environmental features such as:

• Energy efficiency rating was 5.5
• Ceiling and wall insulation R3.5 and R2.0 respectively
• The living area and study windows face north (less 10 degrees east) and are protected from the sun in summer by large eaves 
• The north-facing part of the house is not shaded
• Westerly facing bedroom windows are partly shaded by deciduous trees
• High and low lounge windows provide cross ventilation cooling on summer evenings
• Air conditioning and heating is achieved with a Daikin split system.

Tesla Powerwall 1; Solar panels and hot water; Double-glazed windows

Energy efficiency modifications and a plug-in hybrid electric vehicle (PHEV) were added in this order:

• July 2015: purchased a plug-in hybrid car (Audi A3 e-tron)
• Nov 2015: installed and switched on a 4.5kW solar system
• May 2016: disconnected gas hot water, the only gas appliance, and put in solar hot water
• Sept 2016: installed and switched on a Tesla Powerwall1 (6.4kWh) and Reposit battery management system (There is ~24% subsidy on batteries from ACTGov). I signed up to be part of Canberra's Virtual Power Plant.
• Dec 2016: installed double glazed windows to living area
• Mar 2017: installed double glazed and sealed doors to living area

1.1 Graph of Average Daily Energy Use from Grid over Time 

This graph shows the average daily energy use of both gas and electricity since the house was purchased in May 2015. 

Notes for graph:

• The energy readings are such that Summer includes November, December and January; Autumn is February, March and April; Winter is May, June and July; and Spring is August, September and October
• The early gas records have been converted from mega joules to kilowatt hours and averages added to those of electricity
• If the house was unoccupied for a significant amount of time, the number days energy was used was reduced accordingly to create the average.

The decline in energy use shown in the graph fits with the addition of renewable energy appliances as listed above. In Winter 2016, despite the fact that solar panels and hot water were fitted by then, there is an increase in use compared to Winter 2015 due to the addition of the electric car and that the electric boosters for solar hot water were unknowingly and unnecessarily on twice a day! A panel heater plus the split system were used in 2015 and 16 but only the more efficient split system in 2017.

The reductions in energy use in 2017 are due to the addition of battery storage and double-glazed and sealed windows and doors. With the battery management system (Reposit Power), it was possible to see when energy use was unnecessary and how to better stagger appliance use so that grid energy was seldom required. The car was charged mostly in the mornings and used both solar panels and battery on sunny days, not the grid.

1.2 Graph of Energy Costs over Time

This graph shows my house costs (A$) of both energy supply plus fixed service fees less the solar feed in tariff for surplus energy from the solar panels over time. Figures include those for both gas and electricity from May 2015 when I moved into the house. The gas was switched off in early May 2016 (the beginning of the Winter 2016 quarter) and from then on the house was all electric.

Notes for graph:

• The energy readings are such that Summer includes November, December and January; Autumn is February, March and April; Winter is May, June and July; and Spring is August, September and October.
• The values of gas service fees and supply were added to those of electricity from May 2015 to May 2016.
• If there was a significant period away from the house for a quarter then the appropriate values were converted to those for 91 days.
• The graph is best read together with the chronological list above which shows the gradual addition of renewables and double-glazing.
• The figures do not include discounts, rebates and concessions.

The graph shows a gradual drop in energy costs for each season as the house went all electric, added renewables and double-glazing. This was achieved while charging the plug-in hybrid car and a cordless battery-powered mower, which are mostly charged in daytime from solar panels and battery. This means there are also savings in car and lawn mower running costs.

Switching off the gas added big savings because it was just instant gas hot water for one person, so the service fee was, on average, 80% of the bill. This also helps explain the discrepancy from the top graph (1.1), which shows an increase in daily energy use in Winter 2016 from Winter 2015, whereas the costs for Winter 2016 are less than 2015 in this graph due to addition of solar panels with a feed in tariff and the exclusion of the gas service fee. The other reasons for the increase in daily energy use for Winter 2016 over 2015, despite the addition of solar panels and solar hot water, are explained in the above section.

Another devise added was the Reposit battery management system which, among other features, has the ability to take energy from my battery and send it to the grid at times of peak demand. For example, this happened on two heatwave days in February 2017. Since then there have been a few grid credit events happening in each season. At such times, the battery owner is paid a premium price (Australian 100c/kWh) for the power to the grid which is much greater than the cost of power from the grid. This is part of Canberra's Virtual Power Plant and is also described by another owner here.

In summary, the drop in costs from Winter 2015 to 2016 is due to switching off gas and adding solar panels. The further drop in costs from Spring 2015 to 2016 is the addition of the home battery with energy management system. The overall fall in costs from 2016 to 2017 is mostly due to the addition of solar hot water, the home battery and double-glazing.