Although I should wait until I have a full year’s worth of usage data (or possibly wait for multiple year’s worth) I realised that I could make a comparison of the last four months against the same four months last year. Why four months? Because that is a period of time since my solar was fully set up and that aligns with the two monthly cycle for the gas bills.
Let’s start with some numbers from 2023:
Gas:
| Period | Daily charge | Usage | Usage cost | Total cost |
|---|
| March and April | $58.65 | 5971.65MJ | $165.94 | $224.59 |
| May and June | $56.72 | 18902.29MJ | $456.71 | $513.43 |
| Total: | $115.37 | 24873.94MJ | $622.65 | $738.02 |
Electricity:
| Period | Daily Charge | Peak Usage | Peak Cost | Ctrl Load Usage | Ctrl Load Cost | Total Cost |
|---|
| March | $33.00 | 227.982kWh | $52.51 | 155.894kWh | $25.17 | $110.68 |
| April | $30.92 | 259.150kWh | $53.72 | 187.934kWh | $27.32 | $111.96 |
| May | $31.68 | 310.073kWh | $58.32 | 193.811kWh | $25.58 | $115.58 |
| June | $30.66 | 355.005kWh | $66.78 | 206.605kWh | $27.27 | $124.71 |
| Total: | $126.26 | 1152.21kWh | $231.33 | 744.24kWh | $105.34 | $462.93 |
This means that for this four month period in 2023 my total energy cost was $1200.95. (it is a coincidence that this is almost a round number…)
So how about 2024:
Gas:
Electricity:
| Period | Daily Charge | Peak Usage | Peak Cost | Solar Usage | Solar Cost | Total Cost |
|---|
| March | $33.18 | 140.549kWh | $31.85 | -471.211kWh | -$25.45 | $39.57 |
| April | $32.11 | 164.270kWh | $37.22 | -241.687kWh | -$13.05 | $56.28 |
| May | $33.18 | 247.318kWh | $56.04 | -206.565kWh | -$11.15 | $78.07 |
| June | $32.11 | 264.730kWh | $59.99 | -132.671kWh | -$7.16 | $84.94 |
| Total: | $130.58 | 816.867kWh | $185.10 | -1052.134kWh | -$56.81 | $258.86 |
So the total amount I was charged for these four months in 2024 was $258.86. This is a lot less than the same period in 2023, around 80% less which is quite nice.
However this is only one perspective of my usage, the amount of energy fed in or out as seen by the smart meter. How much energy am I consuming? For that I can go to the monitoring for my solar panels:
| | Electricity bill | Enphase monitoring |
|---|
| Period | Imported | Exported | Imported | Exported | Produced | Consumed | Consumed (+10%) | |
|---|
| March | 140.5kWh | -471.2kWh | 129.2kWh | 507.6kWh | 704.0kWh | 325.6kWh | 358.1kWh |
| April | 164.3kWh | -241.7kWh | 148.3kWh | 235.1kWh | 382.8kWh | 296.0kWh | 325.6kWh |
| May | 247.3kWh | -206.6kWh | 229.3kWh | 199.7kWh | 386.9kWh | 416.5kWh | 458.2kWh |
| June | 264.7kWh | -132.7kWh | 244.9kWh | 125.2kWh | 261.9kWh | 381.6kWh | 419.8kWh |
| Total: | 816.9kWh | -1052.1kWh | 751.7kWh | 1067.6kWh | 1735.6kWh | 1419.7kWh | 1561.6kWh |
The first thing that I noticed was that the Enphase Envoy is consistently measuring values that are about 10% lower than what my smart meter is measuring. For the purposes of this comparison I have adjusted the Enphase consumption value up by 10%.
This has given a result I did not quite expect.
- When I had gas heating and resistive hot water in 2023, my electricity consumption for these four months was 1896kWh.
- Then in 2024 with heat pumps for heating/cooling rooms and heating hot water, the electricity consumption for the four months was 1561kWh.
So even without taking into account the gas usage, I am now using 335kWh less electricity? This is a good overall result.
I also need to ask, what would I have paid if had only changed the heating and hot water? The daily charge would have remained and if I assume the same 22.6c/kWh rate my overall bill would have been $483.50. This is only slightly lower than what I had paid for electricity in 2023, so not having a $738 for gas really stands out, and based on how the gas rates were increasing, that would have been nearer $1000 in 2024.
I think I could make the following conclusions:
- Switching away from gas is worth it and gives the biggest difference of not having that $738 bill, even if you only take into account the financial aspect
- Adding solar panels gives a decent financial benefit, in this case reducing the cost by half from $483 to $258.
- Moving to heat pump for hot water gave a smaller, my previous estimates were that it halved the electricity needed, so from $100 to $50 for the four months
I did mention that gas prices were already going up, and my electricity rate increased at the start of August from 22.6c/kWh to 27.7c/kWh. This is combined with my feed-in rate already dropping from 5.4c/kWh to 5.0c/kWh at the start of July. I need to think about more/better ways to self-consume my solar generation, and if this trend continues I might consider batteries sooner than later…
