It’s now been six and a half years (!) since my home battery and solar system was installed. You can read more about my journey in the detailed write-ups I did at the end of Year 1, Year 2, and Year 4. With 2025 having recently come to a close, I wanted to pull together an update on how things have been going.
What started out as a goal to maximise self-sufficiency pivoted in mid-2023 to become all about optimising cost vs. revenue after I joined a wholesale price energy plan through Amber Electric. For the past two and a half years now I have been fine tuning the balance between using each day’s solar generation, importing from the grid when prices are low (including to charge an EV), and exporting any surplus battery into evening peak prices. This has mostly been achieved through a series of automations using the excellent open-source Home Assistant platform (perhaps the subject of a future article if there is enough interest!). A second battery joined the household in early 2025, creating new opportunities to optimise. Alongside changes to household consumption patterns, market price dynamics, and tariff structures, it’s been an interesting year!
So here’s a snapshot of how things have been going. Unless otherwise labelled, data covers the period 1 January 2025 to 31 December 2025.
1. Energy flows in 2025 show how things are very different now compared to the earlier goal of self-sufficiency
Figure 1: Sankey chart of energy flows in 2025
In my Year 1 post I was chuffed to report the system achieved 92% self-sufficiency for the year. As time wore on and home demand increased (including adding an EV in mid-2022) it became clear that the best approach would no longer be about minimising grid consumption at all costs, but rather optimising consumption to work with the grid. This accelerated further in mid-2023 after becoming a wholesale price exposed retail customer. As seen in the Sankey chart, this now means ‘self-sufficiency’ (house load supplied by solar & battery) sits just over 50%, with huge volumes of (very cheap) grid power being used to supply controllable loads and even charge the house battery on days where solar falls short. More on this in the charts below.
2. The difference in prices across the day, even after adding network charges, provides opportunities to create value
Figure 2: Imports & exports across 2025 vs. time-weighed priced
My strategy since joining Amber has been fairly simple – consume as much grid power as possible to meet needs during the cheapest hours of the day, reserve enough battery to power through overnights, and sell any excess battery capacity into the highest priced hours of the day. As seen in the figure above, the results show that a combination of automations and behaviours have pretty well nailed this strategy. My average price in 2025 for all grid imports was 7.3c/kWh compared to an average price for exports of 30.1c/kWh. ‘Imports’ as defined here include any variable based network or market charges (including environmental certificates), whereas exports reflect only the value of the energy sold into the market at the prevailing spot price. It’s also worth noting that my averages are different from the time-weighted average prices (shown on the chart) during the highest and lowest priced periods of the day. This has been achieved by strategically avoiding heavy imports on above average priced days (e.g. cloudy conditions) and only exporting into the evening peak if prices justify it vs. how much surplus capacity is in the battery.
As shown previously in Figure 1, while most battery charging was done using solar where available, a portion of this was supplied by the grid. This has become especially prevalent after installing a second battery where daily solar generation is insufficient during winter and autumn to both meet household demands and give the batteries a good charge. So long as cheap energy during the day remains readily accessible, at this stage I see no need to consider upsizing my solar system, especially when considering the high levels of curtailment that would likely be needed outside of winter months.
3. Over half of last year’s household consumption was controllable to match solar and cheap grid imports
Figure 3: Household usage in 2025 by source
As shown previously in Figure 2, almost no grid imports were required outside of a narrow window of daylight hours. To achieve this, controllable loads were shoved into the middle of the day to match maximum solar availability and cheapest grid pricing. Understanding what portion of load can be controlled this way is an important question for households considering how to size a potential battery purchase – especially with initiatives on the horizon like the proposed free power window. Putting >50% of household usage into the optimal time window means that the battery required for the rest of the day can be a lot smaller than it otherwise would need to be (or more surplus capacity can be freed up for trading on the market). And yes, I acknowledge that having this level of sub-metering in a residential home is not normal! 🤓
4. Wholesale price exposure offers a very cheap way to charge an EV, which has gotten even better since recent changes to network tariffs
Figure 4: Average monthly rate for charging since buying an EV
Before joining Amber in September 2023 I was on a plan with another retailer which offered a ‘super off-peak’ rate for EV charging (which applied between midnight to 4am – pretty old school!). Rates on this plan started at 8c/kWh before increasing later to 10c/kWh. Since joining Amber, EV charging has been shifted to try and align with the lowest priced periods of each day. Since this change, my overall average price for EV charging has been a very cheap 5.5c/kWh. Of note, this works out at 6.3c/kWh between September 2023 and June 2025. At this point in time my distribution network service provider (Energex) updated their tariff structure to offer much lower network fees between 11am and 4pm. Since this, charging costs have more than halved, averaging 2.6c/kWh. This works out to about $1.90 if I was to fully fill my car’s battery from flat, or less than $50 per annum in total charging costs if driving 12,000 kilometres a year (and assuming 16 kWh per 100km efficiency). The combination of wholesale price exposure and this new tariff structure is exactly what I love to see – consumers being rewarded for aligning heavy usage with the right times of the day.
5. My average bill since joining Amber has been $20 per month, but behind this is a fair degree of volatility
Figure 5: Monthly costs, credits, and net position since joining Amber
Based on the fixed charges I’m stuck with regardless (more on these in the following charts), I need to clear about $55 in export earnings each month plus re-coup any import costs to break even or better. As seen above, that’s been a fairly difficult task, happening just 7 out of 28 months so far, driven almost entirely by whether any price spike volatility occurred. Nonetheless, since September 2023 my bill has averaged just $20 a month. The charts at the end of this article provide more analysis of how this compares to what a BAU scenario would look like (hint: it’s a big saving!).
(A side note that as of the end of 2025 I am actually in around $1,500 of credit since joining Amber, primarily due to government energy rebates and (a couple of) referral bonuses. Given that all consumers received most of these same credits, I have chosen to exclude them from all figures used in my analysis to look only at underlying performance.)
(A second side note – it would be possible to compare my average monthly export earnings to what I may be able to earn with a Virtual Power Plant (VPP) offer from a traditional retailer where they took over discharge of my surplus battery capacity instead of doing it myself with automations. Noting that other aspects of any such plan would need to also be considered (including access to cheap charging energy) this is something I’ll continue to watch over coming months, especially given the pace at which these VPP offers are evolving.)
6. A detailed breakdown of the bill in 2025 sheds further light on the biggest contributors to net cost
Figure 6: Total bill for 2025 broken down by component
When people talk about energy prices, those of us in the industry know that it’s much more complex than just cost of the electrons being generated at the power station. So full credit to Amber for providing all customers with such a detailed and transparent breakdown of the components that make up each month’s bill. This has enabled me to pull together the above pie chart to examine the biggest drivers of my bill (noting this is before applying any credits from exports).
Even I was surprised to see just how small the wholesale energy component is compared to everything else. Overall, variable bill elements made up 38% vs. 53% for fixed elements (excluding the role of GST which applies to both). Of particular interest is that the Amber subscription fee (which is a fixed daily charge) is the largest component of the bill. Whilst relatively high, I see this as the price of admission for being able to take advantage of the benefits offered by access to such cheap imports, as well as the potential earnings from price spikes. Using 2025 as an example, this subscription fee translates to about 4.5c/kWh (inc. GST) based on my total grid imports.
Also surprising was to see the relative size of the hedging fee. This is the fee charged per kWh by Amber to provide capped exposure to all customers against extreme import price volatility across a quarter. As someone who only imports during low priced periods and who uses a battery to cover my load overnight, this does sting a bit. On the other hand, I support the concept in-principle when you think about the ways this retail model could go horribly wrong for consumers, like what happened in Texas during winter 2021.
7. Net trading profits are nearing $1,000 since late 2023, with just over 50% of earnings coming from ‘price spike’ days
Figure 7: Daily import cost (variable charges only) vs. export earnings + cumulative net position
This chart plots export earnings (green bars) and import costs (red bars) for each day since joining Amber in September 2023, with the cumulative net position shown by the dotted line. As noted in Figure 2, ‘import costs’ as defined in this chart include any variable network or market charges (including environmental certificates), whereas exports reflect only the value of energy sold into the market at the prevailing spot price. To the end of 2025, my average daily import cost was $1.17 vs. the average daily export earning of $2.30. If you squint you can see a small uptick in daily export earnings since doubling battery size in March 2025, which resulted in more surplus capacity to trade into the market each day. Gross export earnings totaled $1,958 to the end of 2025, of which $1,021 (52%) came from 47 ‘price spike’ days (average export price >$500/MWh) – these stand out quite starkly on the chart.
8. Factoring in fixed charges changes my net position dramatically, even with earnings from price spikes trying to offset them
Figure 8: As above, but adding fixed charges to the import costs total
As seen in Figure 6, wholesale energy and other variable charges form only a minority of each month’s bill. When adding fixed charges to the calculations of my net position, things quickly swing. These fixed charges have averaged about $1.80 per day vs. average net earnings of $1.13 per day. This has been especially tough since winter 2025, where a distinct lack of volatility and price spike opportunities in the market has seen the cumulative cost line ticking up relentlessly. The challenge of needing to hit a minimum daily earnings target to cover fixed fees is a problem for all amateur energy traders, and one that may possibly get worse in the future as market dynamics and tariff structures evolve.
9. The real benchmark of how things are going is comparing what a BAU scenario would look like – this shows that installing solar & battery (plus expanding the battery) has delivered a lot of value so far, with plenty more to come hopefully
Figure 9: Forecast of cumulative BAU costs vs. actual costs since installing solar + battery
Since installing the solar + battery system I’ve been keeping track each month of the savings it has delivered. To do this, I look at the actual billed cost each month compared to what costs would have been without solar and battery (i.e. BAU). This is done by applying the relevant financial year’s basic tariff + fixed fees from a traditional retailer to each month’s grid imports (but excluding any gird imports used to charge the battery). As noted previously, any credits earned from government rebates or referral bonuses are ignored for this calculation.
Since August 2019 and to the end of 2025, total savings now stand at almost $12,000 vs. BAU. Savings accelerated when an EV joined the household (and consumption went up) and have also increased since joining Amber (with actual costs being notably lower each month than they were under a more traditional retail plan, even with solar & battery). My original investment was $18,000 ($10,000 of which was via a 10-year, interest free loan), so breakeven is approaching. The second battery that was added in March 2025 will complicate this payback calculation going forward though.
10. Monthly savings (vs. BAU) since joining Amber have been more volatile but higher, averaging around $250 per month compared to BAU over the past year
Figure 10: Monthly savings based on actual costs compared to a BAU scenario
Using the same data as Figure 9 also shows how monthly ‘savings’ have evolved since solar and battery were first installed. There are several distinct phases visible on this plot. Under a traditional retail plan and before the EV arrived, savings followed a seasonal pattern (linked to solar generation). This is because there was surplus solar and it was being exported for a profit at the time (10c/kWh at the beginning – how long ago that seems now!). After an EV joined the household the majority of this surplus solar was eaten up charging it, but savings vs. BAU also increased as overall monthly consumption was higher. After joining Amber, average savings became a lot more erratic (driven largely by the presence or absence of price spikes to sell into each month) but have been higher overall. And finally, whilst it is still early days, the addition of a second battery does seem to be paying off, with monthly savings taking another step change up thanks to the ability to supply more energy for overnight in tough conditions (e.g. high air conditioning usage), as well as more surplus capacity to sell into the grid. Whilst I would caution assuming my experience translates for others, this does help show that the value to my household of a 6 kW solar system + 27 kWh of battery storage is currently worth around $250 of savings per month if usage is optimised and surplus battery capacity is traded into the spot market.
I acknowledge these figures blend the benefits of solar + battery, rather than looking at the benefits of battery alone. My view however is that this is an increasingly irrelevant comparison for someone considering an investment today. Firstly, because battery prices have dropped so much thanks to the federal rebate, and secondly, because the value proposition for solar alone is now so poor (with daytime feed in tariffs at or near zero). While exciting for consumers, this changing paradigm is likely to present new challenges though as market dynamics and prices are impacted by a huge influx of behind the meter and grid storage. It’s certainty going to be an interesting few years ahead!
This article was originally posted on LinkedIn, and has been reproduced here with permission.
About our Guest Author
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Andrew Wilson is the Head of Renewables & Firming at CS Energy. He and his team are responsible for the transformation of CS Energy’s portfolio through the development, transaction, and delivery of new renewable and firming assets.
You can find Andrew on LinkedIn here. |
Seriously guys – are you suggesting that all electricity consumers should engage in this process in order to get their electricity bills under control.?
Why not just go off-grid and be done with it? (And do it at one’s own expense?)
And why not reflect on the incredibly generous taxpayer cash splash that drives this behaviour.
Then there are all those consumers whose residential circumstance preclude using panels and batteries but are being obliged to help fund them anyway.
And if this circumstance is not fair and just as it stands, pray tell what taxpayer subsidies will flow when all existing batteries and panels (and wind turbines) reach end-of-life status?
Let’s be honest – most people just want reliable and cheap electricity whenever they need it!
And an electricity grid based on nuclear power is the only honest way to deliver that!
A really insightful analysis.
A few things which would have been great to see in addition:
1. Energy inflow breakdowns to battery, load and grid export on Sankey diagram.
2. 12% energy lost from battery?! Much higher than I would have thought (and what is generally touted by industry). Is this the efficiency reality, or are there other factors contributing to “battery losses”?
3. Hot water being the largest energy consumer is surprising too. Resistive system? Not much distance travelled in EV? AC used infrequently or otherwise efficient building envelope (or moderate climate)? Some discussion on this would be illuminating.
4. Any import earnings (i.e. getting paid to consume)? Or are the negative wholesale price instances needed to overcome the various variable network/market charges just not there yet?
5. In Fig 9, another useful comparison would be to add the upfront capital expenditure to the solar + battery curve in a new data series and adjust all $ numbers for inflation. Could include another series with un-subsidised capital cost as well (if known). These additional series would show the overall payback period (eventually) and should include the costs of the EV & charger (if counting the fuel savings in the BAU data), the 2nd battery, and any other infrastructure, efficiency or fuel switching changes that have been made. It feels like the true payback period might be a while off yet, but that’s not accounting for any non-monetary value gained from the whole exercise.