July 2025

July was decidely wintery (median temperature 11 °C). Outside temperatures ranged from 1.5 to 20 °C, while inside we were a comfortable 18 to 22 °C. The HRV was in the heating season and the split system was set to heat to 20 °C. Now that we have solar house batteries we no longer need to schedule the split system to run during solar generation as we have done prevously. We have made a decision to keep the house above the WHO recommended 18 °C rather than the passive house standard of 20 °C.

Temperature from inside and outside the house as the percentage of hours in 0.5 °C bins. I've scaled the temperature in hope that I will be able to use the temperature range for all months.

Methods: I have taken the 5 minutely data from the wirelessTag sensors and calculated the median temperature for each hour and determined the proportion of hours falling inside of the 20 - 25 °C target temperature (using the R functions 'aggregate' and 'hist'). Inside includes data from the wirelessTag sensors spread across nearly every room of the house. Outside is the data from the wirelessTag sensors outside near the cubby house. The water wall data are not included.

Energy production and consumption: 1. total daily consumption and solar production, 2. daily net energy production (energy produced - consumed), 3. energy independence (1 - (imported / consumed energy)), and 4. solar offset (energy produced / consumed).

Some notes about the energy plots... Currently the batteries are configured to minimise our electrical cost, which means ensuring that we don't import electricity during the peak demand period. That means that we still import and export electricity to/from the grid, even on days when we generate as much as we need. It is also possible to have negative independence when we import more than we consume due to charging batteries and averaging across days. So far the real world efficiency of the batteries has been ~ 80%.

Popular posts from this blog

Five year retrospective

Image
Every so often I find myself chatting with someone about the performance of the house and I am caught out with not actually having looked at the numbers except on a month-by-month basis. So here is a bit of a look at 5 years of data. March 2020 - February 2025. Hard to believe that we have been living here for over 5 years, but we have been (actually longer than that, but the data are consistent back to mid-February 2020). For the record, I am using data spanning the 1st of March 2020 through 28th of February 2025. A few things of note. In winter months, we aim for a house temperature at or above 18 °C inline with the WHO recommendations and a general happiness with sleeping / waking up to a house that is ~ 18 °C. Using the hourly averages, the outside temperature ranged from 0.2 to 42.4 °C with a median temperature of 17.1 °C. The inside temperature ranged from 17.6 to 26.6 °C with a median temperature of 22.2 °C. Over the past 5 years, we have been in the passivhaus temperature t...
Read more

Batteries

Image
We did it. It is not clear that the batteries will save us money, although with the way electrical prices are going, they might, and it isn't clear that they won't save us money either. At some point, we wanted to be part of the solution, so the likely breakeven-ish economics were good enough. Call it an investment in the future stability and sustainability of the Australian electricity grid. In terms of economics. Relative to my last statement on the topic, back in 2021 , four years is a long time. Batteries have gotten better, the cost of electricity is up (and demand pricing has arrived), solar feed-in tariffs are down, and NSW has a battery rebate at the moment. The cost of electricity has become increasingly complicated, making modeling costs/savings more tedious as the costs vary by time of day with times of day changing seasonally. Which also means there are more ways that electricity costs will likely change in the future. Minimally, with the battery system, we shou...
Read more

Water wall...

... Currently a work in progress... Thermal Mass A material’s capacity to absorb, store and release heat. Thermal mass is typically used to moderate temperature extremes by releasing heat when the home is cool and absorbing heat when the home is warm. Specific heat capacity A material's capacity to store heat (measured per unit mass). Some materials are better at storing heat than others. Water can store 4× as much heat per kilogram as concrete. Density Mass per unit volume (mass / volume). Denser materials have more mass per volume so they can make up in density what they lack in specific heat capacity. Concrete has twice as much mass per m3 as water. Thermal conductivity The ease with which heat travels through a material. Ideally, thermal conductivity should be moderate so that the absorption and release of heat synchronises with the building's heating and cooling cycle. Both water and concrete are highly effective! In comparison, steel and water hold a similar a...
Read more