Year Of The Powerwall

Let’s get straight to it: 50 cents per day.

That is what I paid for electricity over the 350 days of billing I have since the Powerwall was installed, and my electricity provider changed over.

This is important to note, as the two weeks up to change of provider meant I wasn’t getting any export benefits from my solar panels. Mugged!

The saving is over the $2000 mark, but for the sake of round numbers, let’s call it $2000.

OK, so not exactly this good, but pretty good…

To put in perspective what money means to my family: our recent road trip, to central and southern NSW, cost almost exactly that. Essentially, I got my little summer break for free.

Facts And Figures

According to the billing received by Diamond Energy over the 350 day period:

  • Import total was 1349.830kWh (or 3.857kWh / day)
  • Export total was 3807.403kWh (or 10.878kWh / day)

Not quite the 1:3 ratio I was looking for, but that figure is probably no longer simple to calculate, which I’ll explain below.

From the SolarEdge web portal, I have the following factoids:

  • Lifetime energy: 9.1MWh
  • CO2 emissions saved: ~3400kg
  • Equivalent trees planted: 11
  • Light bulbs powered for a day: ~26,200

That is kind of the feelgood stuff, despite the Powerwall not necessarily being “green” as people might imagine.

As with anything, there is a carbon cost associated with production. The early iterations of any battery product are going to be a little bit on the dirty side.

As one example: Lithium ore needs to be shipped from the mine to the refining facility. The refined lithium is then shipped to the cell production facility, which may or may not need shipping to the final place the Powerwall was built.

Tesla are addressing this with “vertical integration” of production, particularly for their cars, but also batteries in general. This means more processes can be done at one site, reducing shipping costs (and therefore carbon c0st) of transporting components.

Other Factors Considered

Keen observers will remember that in October I got more solar panels. That took my total system size to 6.5kW of panels. I just heard a bunch of critics trumpet “AHA!” but keep in mind, I still only have a 5kW inverter.

Therefore the maximum power I can generate is limited to 5kW, though the peak time lasts a bit longer on a sunny day.

It is hard to quantify what effect this has on the system, beyond saying “there is more solar capacity”. As the new panels are oriented WSW they’re not always going to be ruling the roost in terms of efficiency.

Its also a smaller factor than it otherwise would be, having been installed four months out of the year. Granted, they were the sunnier months.

Another consideration is my move to Time Of Use tariffs in the first week of August. This has an effect on two areas of my billing.

If I’m smart enough to “game” the tariffs, and avoid doing anything during peak time, I can save a lot. Unfortunately peak time coincides with oven and air conditioner use, so that’s not always possible.

The billing and the import numbers above will be affected by Reposit Power managing tariff arbitrage. When I import power now, it might be a result of my needs being bigger than the system output, the battery being empty, or because Reposit sees a cloudy day and wants to import some at a cheaper rate.

Putting together the new panels and move to TOU, a better time to revisit this might be October this year. That way, I’d have a true idea of what I can really save with all components working together.

The Vagaries Of Billing

Those out for a bargain will know to shop around with their electricity companies, and see how best to maximise their savings.

Whether that is through generous sign-up rebates, or big discounts for paying on time or via direct debit. It all adds up, and people without solar or batteries can benefit if they do their research.

As I pay such low amounts anyway, discounts don’t add up to much. Pay-on-time discount across the year was $20, and paying by Direct Debit discount was $17.62.

The bigger benefit was referring people on to Diamond Energy, which netted me $105 across the year. Against that, I paid $22 (inc GST) application fee with Diamond, so the benefit was more like $83.

If we add that $83 back onto the billing, it goes from 50 cents per day to 75 cents per day.

I pay about $1 a day to connect to the electricity network, so its still good. There are even a few dollars in GridCredits unaccounted for at this point.

Year Of The Powerwall

When I say “Year Of The Powerwall” I’m not speaking only to the year I’ve had. This year, 2017, marks the landing of Powerwall version 2 in Australia, and overseas.

I’ll level with you: I haven’t really spoken much about PW2 since the launch, because I’m still experiencing some angst.

Year Of The Powerwall
So hot right now…

I thought I’d done OK with my battery, then in the same year, Tesla brings out one TWICE as good.

C’mon Elon… I thought we were mates!

Overall though, this is a good thing. I think we’re about to see the domestic battery market kick off in 2017, with Tesla in front. That is quite amazing, given the prediction was market maturation in 2020. We’re three years ahead!

Talking to a few people getting quotes and installing them, right now there are very few people price-competitive per kWh.

As the manufacturers in Korea and China start their own uplift via vertical integration, prices are going to keep sliding, and competition increase.

This can only be a good thing for the consumer, for the grid, and for energy security and stability moving forward.

And any consumer who is getting a Powerwall 2: I think a zero electricity bill is well within reach.

If you factored in selling power back to the Grid out of the battery, which I think will replace solar feed-in tariffs eventually, you could even turn a small profit.

As always, user experience may vary. Its up to you to make the most out of your investment.

An Addendum

As I wrote earlier in the month, we have had some heat wave conditions here in Sydney, with outside temperatures getting into the high 40s (120oF). That was kind of insane, but it kicked off some GridCredits for me, which is also a good thing.

As we’re moving toward more extreme weather events, having a flexible and robust grid, with user storage available for emergencies, will be important.

First Anniversary of Powerwall

This week I’ll be celebrating the First Anniversary of the Powerwall’s installation at my house. How time flies!

I’ve been on holiday for a few weeks over summer, and what a summer it has been. In two words: bloody hot.

Sydney has been experiencing some of its warmest weather on record, with temperatures hitting up to 45oC (113oF) and not cooling down below 30oC over night. Distinctly uncomfortable.

So you end up with successions of hot days, but worse: hot nights.

At least it wasn’t peak pricing that day, being a weekend… Small mercies.

In addition to the anniversary, I’m also due to receive a bill from Diamond Energy, which will cover November through to January.

Putting in a guess right now: I’m going to say about $1.20 a day, excluding referrals. Similar to Winter, but with a bit of a discount for better export. That would be a bill of around $110 for the 92 day period.

Changing Seasons

Summer has definitely had an affect on the system, in terms of import requirements. As I mused back in December, summer would require more import, despite having more sunshine to work with.

Part of the reason is electricity consumption; on the whole, I am using more energy due to cooling and things like the pool pump.

The air conditioner is variable, depending on ambient temperature, and required comfort level. Short of replacing the thing, I’m stuck with needing the grid during summer.

The pool pump is fairly static in terms of use. A set number of hours per day, and roughly 1kW consumption, makes it easy to calculate.

How you handle your pool pump usage is up to individual circumstance. My pump has a flow rating of approximately 19,000 Litres per hour, and a pool of 31,000L capacity. I have a cover on it all winter, except for monthly maintenance, and no trees or other debris issues around the pool itself.

Therefore, in winter I’ll run it for around 90 minutes per day which should turn the capacity over about once. With appropriate chemical balancing, that keeps it clean.

In summer, I’ll vary it a little. During summer peak – where we use it a lot – the run will be 6 hours, timed for peak sun. At shoulder times I’ll start to move toward 4 hours, as we’re not using it as much.

The idea is to let the filter work as hard as it needs to, while retaining good chemistry and clarity in the pool.

Capacity and Usability

Happy to report that the Powerwall is still reporting its full 6.4kWh capacity, same as Day 1 of the system.

The extreme heat over summer also didn’t trouble the liquid-cooled unit. The Powerwall is rated to 50oC, unlike many of its competitors, so even an Australian summer can’t dent it.

Unless you’re crazy enough to put the thing outside. In the sun.

Businessman Laptop Desert
“Gee, the PC fan is really working overtime today…”

What I did notice was the rest of the system struggling to get to full capacity. With a total of 6.5kW of panels on the house, I didn’t always reach the 5kW capacity of the inverter.

Part of that is the panels getting hotter than their efficiency peak of 250C, and part of it is the inverter starting to feel a bit of heat stroke. Even in the shade, on the south side of my house, it gets bleeping warm.

Back in October I was hitting some sweet numbers, but the ambient temperatures were down in that 25 degree range. Everything performs better when its cool.

Post-Anniversary Focus

As the year has worn on, I’ve slowly weaned myself off frantic chart analysis. Its a bit of a pragmatic move, as constantly worrying about my ROI was a bit stressful.

While it was important to keep an eye on the system, I’m moving into a stage where I need to look at the future path, not just the past performance.

That means I’ll be presenting more ideas-based blog here, and there is plenty to write about.

Tesla Energy released the Powerwall 2, which I’ve avoided talking about due to extreme jealousy and consumer cognitive dissonance.

Accompanying that is solar rooftop, which I’ll talk about in a future post.

World-shaping events like Brexit and the election of Donald Trump are key political events. They have the potential to shape energy policy for years to come.

There are also ideas I’d like to explore in terms of other energy sources. That will lead into producing educational content that I can distribute, through various media.

I’m also aiming to put up more on my YouTube channel, for which I’d appreciate a “Subscribe” if you’re so inclined. Which I’ll try to fit in around the blog itself, work, family, and running a Rugby Club!

It has been a very interesting journey to get here. It wouldn’t be possible without the generosity of time and patience of the following organisations:

Natural Solar


neonblackSolar Edge Logo


Tariff Arbitrage Using Reposit

Wait – what the heck is tariff arbitrage?

The general definition of “arbitrage” is:

… the simultaneous buying and selling of securities, currency, or commodities in different markets or in derivative forms in order to take advantage of differing prices for the same asset.

Clear as mud, hmm? That’s because the definition above relates to financial terms, and those financey guys are wizards of obfuscation.

Pictured: Wizard
Pictured: Yer a Wizard, Gordon!

Enough with the big words though. This is about finance, but not in the way Mr Stock Trading Person above understands it.

The practice of tariff arbitrage for electricity has a much more detailed explanation, but for me it breaks down to this:

Charge my battery when it is cheap, to use when it is not.

“Hang on – you have solar panels! Why do you need the arbithingees?”

I’m glad you asked, random internet person.

Tariff Arbitrage In Practice

Tariff arbitrage needs a set of circumstances to be useful.

Firstly, a battery to store the power. Solar is awesome, but it has issues with needing the sun. That generally means daytime, and not raining.

Secondly, you need the right electricity plan. When I was on single-rate electricity, I’d pay about 23c / kWh around the clock. Now I’m on TOU (Time Of Use), I pay off-peak of around 13c / kWh, and peak of around 33c / kWh.

Third, you need something smart to control all this, like Reposit Power. My Reposit box governs power flows between Solar PV, battery, and grid.

It has a learning engine for my household habits, so it knows when I’ll use power. Additionally, it can look at weather forecasts to see when I’ll have solar energy available.

These are two important things to know, because when I’ll use power and when the sun is shining are going to make a difference for my power bill. Particularly as I pay different rates for power when I use it.

A Graphic Example

Here is a screenshot of the (new) Reposit interface for my battery from this morning. I’ve edited the image to have two labels on it to show the power consumption.

Tariff Arbitrage 28 Oct 2016
29 October 2016 – Battery readout from Reposit web portal

Fairly typical for the household while we’re asleep. The Powerwall slowly draining as it feeds the fridge, any standby devices, and bathroom light for the kids. Only thing that changes is how much is in the battery to start with.

Here is the same screen but with data from the day before.

Tariff Arbitrage 29 Oct 2016
28 October 2016 – Battery readout from the Reposit web portal

Yowzah! It is going UP! And there is a reason for that: tariff arbitrage.

Yesterday, the forecast for Sydney was rain and heavily overcast conditions.

The Reposit software decided, based on the weather and my needs, that it should top up the battery to get me through the day. It uses the off-peak period to do that, and had actually commenced importing at 10PM the previous night.

This is the first time I’ve seen it top the battery right up. As you can see from the rest of the graph, I didn’t get through all this power in peak time. But I was buying it at a much lower cost than I’d otherwise pay.

How Low?

Here are the current rates I’m paying for Diamond Energy on TOU:

Rate Times Cost (c/kWh)
1PM-8PM weekdays
30.53 (0-340kWh per month),
31.49 (balance of kWh)
7am – 1pm,
8pm – 10pm weekdays,
7am – 10pm weekends / public holidays
All other times

Reposit Power aims to lower my costs. This decision to top up the battery is primarily for the peak period of 1-8PM where costs are at a premium. Once you take transmission loss into account (92% round trip efficiency on the Powerwall) I’m still ahead against Peak power cost by a ratio of 2:1.

Everything in between will mostly be taken care of by the trickle of Solar PV I generated during the day, as evidenced by the chart below.

Tariff Arbitrage Solar Gen
Solar Generation 28 Oct – high point noted for reference

This figure of 10.8kWh for the day is a long way from the 40kWh I’ve registered twice so far in October. But every bit counts.

Smoothing the Curve

Thinking about the solar figure jumping around a little, it also brings to light the other aspect of battery usage: curve smoothing.

When we have days with scudding* cloud and intermittent sunshine, a solar PV house with no battery is forced to call on the grid multiple times.

* Totally a word. Look it up.

Once the battery gets some juice in it, I’m less reliant on the grid for a sudden change in conditions.

Combine this with the automation of Reposit Power – where I don’t need to think about when the sun is out or not – and I’m onto a winner!

Reposit Power

System Upgrade

If you’ve ever looked at my System Specs page, you’ll see that I’ve got a fair bit of west-facing roof I don’t use. I decided to get an upgrade.

First port of call was Natural Solar, of course.

They looked at the system, and advised placing an extra six panels on the western roof. The same Phono Solar 250W panels would be used, each with a SolarEdge P300 power optimiser.

House Upgrade
Right about… there!

The two existing arrays tie back to the inverter with one string each. The new array would be joined onto the array to the left of picture (western). This made for the simplest install as it didn’t require new wiring to the inverter.

It also provided the benefit of generating from the sun in the afternoon. This is useful in the warmer months where I am more likely to use air conditioning.

Additionally, for those days that have overcast mornings, but sunny afternoons, I’d see the most benefit. Particularly true given the house has a rising ridge line to the east, so doesn’t see much sun early in the day.

With the detail sorted out, we agreed on a date for Splice Electrical to perform the upgrade. James and Nick turned up, and with their usual friendly professionalism, got to it.

While they were here I also got them to disconnect some old PSTN infrastructure that was slowing my NBN connection. Increased speed by 40%! Legends…

A few hours later I was the proud owner of another 1.5kW of panels!

upgrade complete. Now what?

Naturally, with an upgrade of this sort, you’re going to expect some improved results. The system has had a size increase of 30% (1.5 / 5.0 = 0.3). Would I get similar generation increases?

The main factor in all this is still the inverter. The SE5000 in my system is limited to 5kW in any direction. Therefore, expected generation, even with 6.5kW of panels, is limited to 5kW maximum.

I was quietly confident I’d hit this high mark regularly, given I generated 4.9kW or more at points during February and March, and even in May!

However, the panels aren’t in the same orientation as the rest of the system, so what is the effect?

Setting the baseline

According to one source, a solar PV system in Sydney should produce 3.9kWh per kW of installed panels per day. That is under lab conditions.

My initial system setup should (on average) have produced about 19.5kWh of electricity per day. For the lifetime of the system at 5kW, the SolarEdge API reports the following figure:

[wpbusinessintelligence id=”23″ type=”chart” iframe=”n”][/wpbusinessintelligence]

I hasten to point out that the data is a little murky. The SolarEdge API consolidates “generation” from PV and battery, because of the way it monitors flow.

Therefore, that figure only works if we’re assuming the battery is filled and drained every day. This certainly isn’t the case 100% of the time, but its enough to show we’re in the ballpark.

Another part of this is loss due to inefficiency. The Powerwall is about 92% efficient, meaning I have to spend around 1.5kWh of the 19.5kWh figure on the power going into and out of the battery.

The other factor is the timeline; we’re looking at a period from mid-February to early October. This includes the shorter daylight hours.

With all these factors considered, I’d say this is actually looking like a decent marker, even with the accepted error margin (+/- 10%) in the SolarEdge API.

Effect Of Upgrade

An extra 1.5kW of panels should result in a generation figure of 25.35kWh per day, on average, for Sydney.

The first caveat for this figure: it has been spankingly good weather in Sydney for the last week.

The new panels are also a different orientation to the others, which may affect the figure.

It is also a very small sample in terms of days. In the interests of science, I’ll leave this chart here to update daily. You can check in on it any time you like. A rolling 7- and 28-day chart is also on the Statistics page.

*drum roll*

[wpbusinessintelligence id=”24″ type=”chart” iframe=”n”][/wpbusinessintelligence]

Average just shy of 33kWh at time of print. Pretty good weather!

A better analysis might be to look at the curves being produced by the different panel setups. The figures aren’t as important as the shape of the curve.

That was from May, without daylight savings. The curve peaks around midday and is generally uniform. Pretty much what you’d expect. Decent result, too.

Now we throw another 1.5kW of panels on the western side, and add daylight saving to shift the curve to the right by an hour.

A small point: that is my record day so far. And its only October. Tee hee!

More importantly, we see the extension of the curve from the new peak around 1PM (daylight savings, remember), through until the late afternoon. We get a lot closer to sunset for generation as well.

The peak 5kW on this particular day hit at 1128 hours, and it stayed there until 1514 hours. The 5kW system infrequently reached 4.9kW, and then only for short stretches.

With the extra panels, not only is the generation figure much higher, but the long afternoon sun really kicks in.

Looking Ahead

As we move further into the warmer months, I expect the 5kW peak to be longer. Most likely, this will result in much more export until the point the ducted air conditioner is required on a regular basis.

I need to develop a strategy to mitigate that. Perhaps running the air conditioner in “continuous” mode on sunny days will help. This aims to keep the house cool, and the thermostat will lower the overall energy requirement.

I’m still finalising the change in payback time on the new array. Due to the move to TOU pricing, it is getting hard to keep all the facts and figures in order.

For the most part, I’m going to keep rolling calculations based on the single-rate plan offered by Diamond Energy. The rest of it makes my head hurt.

Powerwall Six Months On

Powerwall Six MonthsI’ve had the Powerwall six months now, or in fact a little longer. It would be more accurate to say I’ve had a functioning solar PV with battery system for seven months.

That dates back to when my meter was changed over to a basic bi-directional unit. Importantly, it is the date that billing with Diamond Energy started, with full and accurate detail of import and export.

I have had a  total of three bills, the most recent of which covers 52 days from mid-June to early August. It stops there because I’ve moved from single-rate to TOU tariffs, so Diamond decided to make things easier for calculation purposes.

The other two were covered by my blog post back in July. The full quarterly bill naturally received more attention than the one I hinted at in that post. With 174 days of billing data now in the bank, its time to look at a longer period.

This post will put up the basically points of interest from the three bills and their relevant statistics.

Powerwall Six Months Analysis – Part 1

The first bill covered the period of 17th February through to 23rd March.

Item Days Cost Import Export
Total 35 $23.89* 121 322
Average / day $0.68 3.46 9.2

* This amount removes the $20 establishment fee with Diamond ($22 inc GST)

With a connection fee of just over $0.82 / day, and an export tariff of 8 cents/kWh, I was almost covering the connection.

Of course, import was going to hit a bit harder in summer time. The last week of February was a record-setter in Sydney.

The temperature was minimum 26oC / 79oF for nearly the whole week. Frequently the temperature was over 35oC (95oF) in the late afternoon, hitting those big, west-facing windows. I can only sweat so much!

That kind of heat requires air conditioning, which you can see in the red spikes below.

SolarEdge Portal

It probably wasn’t even the amount I imported, more a case of when it was imported.

This is a small precursor to what you can expect from an Australian summer in this part of Sydney region. No ocean breezes this far inland.

During this period I clocked some fairly hefty production figures, topping out at around 34kWh, with several days in excess of 30.

The heat of a Sydney summer makes me a little cautious in regard to power usage. In addition to the extended hours for the pool, the heat will require air conditioning. That means import.

January tends to be the wettest month in Sydney, and storm season. Luckily, for those cloudy days and weeks I’ve got Reposit Power to do the thinking for me.


The start date was 24th March, running through until 17th of June, 2016. This was the big quarterly bill which grabbed the media attention here in Australia, with a few overseas articles published as well.

I won’t go into too much detail as you can read about it here. The key data to consider

Item Days Cost Import Export
Total 86 $50.39 244 736
Average / day $0.59 2.84 8.6
Previous bill $0.68 3.46 9.2
Difference -$0.09 -0.62 -0.6

As you can see, the daily figures show slight decreases across the board.

At my import tariff, this equates to 13.2 cents / day decrease in costs as I’m importing less.

The export is 4.8 cents / day cost increase as I’m exporting less.

This comes out to 8.4 cents per day. The actual decrease of 9 cents per day is due in part to rounding.

Additionally, Diamond single-rate tariffs step up by a small amount once you use more than a certain number of kWh per month.

The weather during this period was pretty good. We had long weeks of sunshine, with few rainy days. The temperatures were very mild, meaning we didn’t need air conditioning or heating.


The latest bill runs from 18th June through to 9th August, or a total of 52 days over winter.

In terms of “winter”, I should mention it never snows here. The closest snow I think fell about an hour’s drive away, in the Blue Mountains. It isn’t frosbite territory, and with the climate warming, isn’t ever likely to be. Short of another ice age, I guess.

We do get frosts, sometimes on consecutive days, and the lack of double-glazing, with basic wall and ceiling insulation batts, does mean the house gets cold. We also have a lot of tiled floor.

This bill gives a valuable insight into the changes that occur, in a period with less sun and more heating.

Item Days Cost Import Export
Total 53 $67.25 288 335
Average / day $1.27 5.43 6.3
Previous bill $0.59 2.84 8.6
Difference +$0.68 +2.59 -2.3

A little over double for daily cost, and the reasons why are fairly obvious.

Import rose by 91%, and export fell by nearly 27%. So it cost me an extra 50 cents per day for import and I missed out on around 18 cents for export. In the ballpark at 68 cents.

There were only a couple of days where we ran the heating longer than an hour or so. With the big motor on this ducted system, that was more than enough to start hitting the import hard.

Next winter, with TOU now in place, we’ll be a bit smarter. I’m talking to Reposit about the best ways to utilise off-peak power, and how their software handles it.

Note: the reason behind the short interval for this bill is replacement of my meter. The GridCredits scheme is reliant on a sophisticated unit, which I’ll put up video of when I get the time.


Putting all the information into a table gives a nice summary of the solar with Powerwall six months down the track.

Item Days Cost Import Export
Part 1 35 $23.89 121 322
Part 2 86 $50.39 244 736
Part 3 53 $67.25 288 335
TOTAL 174 $141.53 653 1393
Daily avg $0.81 3.75 8.01

Not bad, though of course I have yet to experience a full summer with this system.

Summer will mean more power imports as we use the air conditioning. It also means longer daylight hours. Greater export will offset higher import, to a degree.

Compared to winter, where heating and shorter daylight hours have clearly had an effect, summer should be slightly better. I’m still at the mercy of those 40oC+ days, but at least I can pay them back a bit.

Of course, as panel temperatures rise above 25oC, efficiency will drop. More light = more heat in summer, so I might not see many days above 35kWh with the existing system.


Autumn and Spring are looking like the “Kill Bill” (*snigger*) periods for the year. The milder weather and lower heating/cooling requirements are really where its at.

Powerwall Six Months
Not bad for 6th September…

Winter is going to be an issue ongoing, with lower daylight hours, and heating requirements. Summer will still need a lot of electricity imported, but can be offset with big exports.

The real challenge, moving forward, is to maximise self-consumption, and minimise waste. As always.

If I can keep the costs below $1 / day for my electricity, even with recent increases in tariffs, then I’m well on track to save $1900 in the first year. Maybe more after that!

Opportunity Cost Calculations

One of the outcomes of my recent bill were the articles written. Lindsay Handmer over at Gizmodo wrote an interesting piece about opportunity cost.

Opportunity Cost
A blast from the past! Aussie $50 note from 1973-1995

For those playing at home, “opportunity cost” is an economic term, defined as follows:

…the loss of other alternatives when one alternative is chosen.

In particular, looking at my statement about leaving the money in the mortgage offset account, versus buying the system.

I had confidently stated my preference for the financial outcomes of the system early on. As it was likely to save me (at least) double the value of my offset in terms of electricity savings, it looked like an easy choice.

Honestly, opportunity cost was not something I gave much thought to. I decided to invest the money in acquiring a hybrid solar system. I wanted to save on electricity bills, and the money looked well-spent.

What some may not know is Lindsay and I had a fairly long email discussion about the direction of the article. We checked facts and figures,and compared notes in terms of thought process.

The ultimate conclusion is the one that most basic analyses have come to; the Powerwall is not yet considered financially sound in terms of payback, against its warranted 10 years.

Estimates for payback vary widely on how you analyse it, and individual circumstances. I had calculated mine at around 8-10 years, and that looked good after the first bill produced savings of ~ $450 compared to same quarter last year (or about $1800 per annum).

A small diversion

One question I’ve been asked via various forums is “how much did the Powerwall contribute to those savings?”

Well, I could go full sarcasmo and say “100% because If I didn’t like Powerwall I never would have bought the system!” Obviously, that is no help to the realists 😉

Without digging into the nitty-gritty, I’ve looked at the figures and come out in this ballpark:

  • 50-55% Solar PV array in combination with time shift of usage
  • 25-30% Powerwall ability to store and deliver power in evenings
  • 15-20% reduction of usage – knowledge gained by SolarEdge and Reposit
  • 5-10% change of retailer – I didn’t really import much.

Make of that what you will. No doubt for winter, that will change a little as heating becomes a priority.

Moving forward, there will be other factors like my move to Time Of Use power and power arbitrage. Also there are battery-related initiatives like GridCredits that will help keep costs low.

Opportunity Cost

I got to thinking about my financials, since Lindsay’s article. During a subsequent proof read for another article I’ve written (to be published in the near future), I decided to go back and review “opportunity cost” as a thing.

I wondered if I’d made the right decision.

The article on gizmodo was right: while I was going to save on electricity bills, that money would no longer be helping slaughter my loan. By sticking it to the power company, I’d lost the chance to stick it to the bank!

What a conundrum…

I should mention that in the weeks before the install, I’d moved my mortgage to a product without an offset. I still could have dumped the lump sum it the mortgage directly, and let it ride.

But would I? Really?

Even in Aussie dollars, $16k is non-trivial amount of money to the average family. Maybe it was time to have a family holiday? Pay off some other debts? Do some enhancements around the house? Buy a GoT-themed jumping castle? Wait. What?

The point is, while its all well and good to say “stick it in the offset”, there are no guarantees that it would stay there. The problem with ready cash is that there are always things for which it could otherwise be used. Life happens.

Doing The Numbers…

For the sake of this discussion, let’s say the money went into the mortgage, for the Powerwall’s warranty period of 10 years.

Assume the interest rate stays at 4% (unlikely), and we keep any benefits in the mortgage. Under the principal investment of $15,990 the interest saved is $639.60 over the first year. Second year is principal $16,629.60 (adding the savings), which saves $665.18 and so on.

Now, based on rolling the principal + interest over every year, after 10 years we arrive at … carry the three … square the hypotenuse … divide by the tangential inverse of pi …

A total interest saved figure of $7,679.11 from my investment of $15,990.

Not bad!

I’ve continued to pay electricity bills during that time, of course.

Starting with my base usage costs of $1920 from the 12 months leading up to Powerwall, let’s be extremely generous to the retailers, and flag an upward move of 0.5% per year, on average.

That means in the first year the new usage costs are $1,929.60. Second year $1,939.25 – and so on.

Over 10 years, that little hike makes for a total electricity bill of $19,736…

I feel your rage, angry penguin... (c) Business Insider (click for page)
I feel your rage, angry penguin… (c) Business Insider

Therefore, despite saving money in my offset, I’m still down by a figure of just over $12k. If the price rise was just 2% per year on average, its more like $21,443.93 paid to the electricity retailer (loss of nearly $14k).

Just for reference, 2% increase on usage costs, for the average of 25 cents per kilowatt hour in these parts, is half a cent.

If the increase was 4% (1 cent per kWh), I’m paying out nearly $24k in electricity. That’s enough to cancel out the interest savings AND put me in the hole for the value of my system!

Now For Something Completely Different

Man. Who knew an increase of 1 cent could hurt that much?

Let’s take another tack, and look at using the money I save on electricity against the mortgage.

Again, we need to make some assumptions:

  • mortgage interest rate will be 4% ongoing
  • $450 saving on the first quarterly bill extrapolates to $1800 per annum
  • degradation in Powerwall is cancelled out by increases in electricity price
  • money saved on bills will be put back into the mortgage*

* Again, it probably won’t, but given the opportunity cost matrix assumes that all monies stay dedicated to the mortgage, I say game on!

Starting at Year Zero with a capital position of negative $15,990 we can compound all our numbers moving forward. Remember, we’re adding $1800 into the pot every year from bill savings, as compared to my old provider.

Therefore in the first year, we subtract $639.60 in lost interest from the starting capital position, but add $1800 per year in bill savings. That rolls over to the new amount for calculating the offset in the next year.

Year Lost offset Bill Savings Capital Position
0 n/a n/a -$15,990.00
1 -$639.60 $1800 -$14,829.60
2 -$593.18 $1800 -$13,622.78
3 -$544.91 $1800 -$12,367.70
4 -$494.71 $1800 -$11,062.40
5 -$442.50 $1800 -$9,704.90
6 -$388.20 $1800 -$8,293.10
7 -$331.72 $1800 -$6,824.82
8 -$272.99 $1800 -$5,297.81
9 -$211.91 $1800 -$3,709.72
10 -$148.39 $1800 -$2,058.11
11 -$82.32 $1800 -$340.44
12 -$13.62 $1800 $1,445.94

This indicates that some time very early in the twelfth year is when I hit payback, under the opportunity cost calculation. That would be the system paying itself off in full, and accounting for the mortgage offset.

Does It Really Matter?

Really, these numbers are just an exercise in maths. And a bit of fun.

It would be highly unlikely in either scenario, that spare money would sit in the mortgage that long. There are things to do, and locking up a bunch of money for a few percent interest until I’m in my 50s? Sounds like wasted beer money, or holiday money, or holiday beer money.

Beyond the first year will I really save $1800? Will the addition of Reposit Power improve things further? What happens when the interest rate on my mortgage shifts?

Trying to cater for all these factors could drive a bloke crazy.

Looking at the opportunity cost is an interesting exercise, but it won’t keep me up at night. I’m hardly tying myself in knots with post-purchase cognitive dissonance either. I have a power bill that makes me smile.

There are also intangible benefits I’ve had on a personal level.

My rough biscuit has been on TV a few times, and across other media, which was a bit of fun.

I have created a little corner of the internet to blather my thoughts into the ether, and I’m flattered that people read it!

One of the best parts has been meeting with switched-on people, who want to make a real and positive change. They have a lot to teach, and I am in awe of the chance to learn from them.

You can’t put a price on that.

Agile Energy Projects in the Marketplace

It has been a hectic couple of weeks, after the release of my first quarterly power bill. I’ve been on radio, TV, in print, and sprayed around the internet. Its a bit like the install day back in January, but obviously with a dollar figure attached.

Despite that, there is still a lot of people ready to step up and put the boot into Powerwall, and lithium storage in general. I will never fathom why these parties are against progress, so I don’t read into it too much.


During that time the world rolled on, and it appears renewable energy, particularly solar hybrid, has been going from strength to strength. One tweet in particular caught my eye, from Noah Smith.

The Telegraph article linked by that tweet, written by Ambrose Evans-Pritchard, is an interesting discussion on battery storage as it affects the landscape. It is also a bit of a dig at the Hinkley Point nuclear project in England.

I wrote something previously on Nuclear Power, so without a re-hash I will reiterate: I AM NOT ANTI-NUCLEAR. However, I did point out there are significant financial hurdles to overcome in Australia. Leaving aside the social issues, that is.

Three paragraphs in the article from Evans-Pritchard got me thinking.

Perhaps the Hinkley project still made sense in 2013 before the collapse in global energy prices and before the latest leap forward in renewable technology. It is madness today.

The latest report by the National Audit Office shows that the estimated subsidy for these two reactors has already jumped from £6bn to near £30bn. Hinkley Point locks Britain into a strike price of £92.50 per megawatt hour – adjusted for inflation, already £97 – and that is guaranteed for 35 years.

That is double the current market price of electricity. The NAO’s figures show that solar will be nearer £60 per megawatt hour by 2025. Dong Energy has already agreed to an offshore wind contract in Holland at less than £75.

Those are some pretty compelling numbers, but the reasons why it got me thinking relate to my own work life.

A Short History Of Dwarves

I’ve been an IT guy for a living nearly 20 years now, working mainly in databases where I can help it. I’ve seen almost every tech acronym or buzzword put into practice, sometimes very poorly. Or for the sake of change.

One of the better periods was back in the day, when the technical stuff was held apart. I like the imagery that Neal Stephenson uses in Cryptonomicon – IT guys were like the Dwarves in Tolkein; working away in the dark, hammering out things of beauty like Rings of Power.

The company (Elves) would frolic up to the entrance of the forge, beseeching the Dwarves for a solution. The Dwarves would give a range of timelines and costs, and the Elves would pick one. We’d go into the forge, create what they wanted, and the land was content.

With advances in technology, and the hunger for globalisation, things needed to move faster. Thus, “Agile” was born as the new way to do things.

Dilbert official site "Agile" search - click for more...

Generally speaking, the move to Agile is positive from my point of view. It seeks to guide the Good Ship Project through the icebergs as each one appears, not assert a course from Day 1 and expect no issues with implementation at all.

As long as Agile is implemented the right way, it can do good things.

There is a caveat though, and the seed of this started with smart devices in my opinion. If we’re ever having a beer, talking shop, I’d pinpoint smart devices as disruptive in more than just a good way.

Now non-technical people see an awesome app for $1.99 and wonder why projects still cost millions. As a result, they demand more.

Agile has collided with this belief that speed of delivery, and convenience, is cheap. Non-technical people don’t necessarily understand the systems. They’re trying to tell the developer how to do their job down to the finest detail. That isn’t actually helpful.

Dear Managers: right now, there IT guys reading this, and nodding their heads. Maybe muttering. Likely, swear words and dark thoughts are being countenanced.

Agile Energy Projects

One thing that holds true of IT projects, energy infrastructure, and pretty much anything down to a backyard deck, is the Quality Triangle.

Time vs Cost vs Scope as it affects Quality

If you are going to implement or change the project in terms of finances, timeline, or scope/size, then you have to accept it will affect the quality of the outcome. Aiming for all three is purely theoretical, in my opinion.

As with the recent Census Fail incident in Australia, sometimes it doesn’t matter how many resources you throw at a project, or how long it runs. The excreta hits the rotary ventilator, and its time to put out fires.

Hinkley Point C is subject to some base requirements, but the main one is the generation of 3200 MWe from a nuclear reactor. Not the biggest in the world but still a mighty undertaking.

Once you’ve decided it will generate that much, you’ve set your course. A prescribed amount of effort, human resources, and other elements must go into it. Critically, the reactors will be of a certain size and type, and you’ll pay the capital cost of that regardless.

If you encounter cost overruns or other issues, generally speaking you just have to suck it up, as per the article:

… the estimated subsidy for these two reactors has already jumped from £6bn to near £30bn. Hinkley Point locks Britain into a strike price of £92.50 per megawatt hour – adjusted for inflation, already £97 – and that is guaranteed for 35 years.

In Australian terms, that is $160 / MWh, which is frankly ridiculous.

All of this points to the fault lines emerging in “baseload” power argument. Not only is “base” power a myth, but the agility of these big power generation units is practically nonexistent from conception through to decommission.

As Hinkley Point C, and Finland’s Olkiluoto construction debacles show, centralised nuclear power might be green, but it isn’t necessarily going to stand the test of time, economically.

Smart Advantage of Renewables

Technologies I have seen work, or worked with directly (like Reposit Power) show us that agility is the biggest factor in any tech marketplace today.

And let’s not kid ourselves: energy delivery is now a technology field. This is particularly true of renewable energy, which eschews the old school sledgehammer approach to power generation, in favour of smarts.

Smart use of power, smart direction of power, are going to be the big players moving forward. It starts with domestic applications, such as Tesla Powerwall, and smart management to deliver benefits for the home owner.

Beyond serving one household, it has the potential (and in some ways, the obligation), to serve the wider community.

This is achieved by using the battery as a trading platform. Benefits abound for the network willing to engage with customers, as I discussed in May. Reduced overall costs and waste benefit everyone in the longer term.

This move toward smarter storage also helps address the business sector. The power needs there are large, and despite being mainly during the day, will not going to tolerate the intermittent fluctuations of solar PV and wind.

Storage using batteries is one leg of the argument, across a various range of chemical makeups. Energy storage like pumped hydro can also assist deliver stable power on a larger scale. The big one for Australia should probably be molten salt reactors, particularly for South Australia, which has suffered issues recently.

Certain industries have scope for change today. Heavy transport, and transport in general, is already under the microscope in nations like Sweden, where they seek further reduction in carbon emissions.

Electric Vehicles take carbon off our roads and out of the manufacturing process through a simpler template of construction. If you don’t believe that, think about the amount of metal required to build a drive train for a petrol engine, versus an EV’s battery & motors setup.

How do we address the remaining heavy industry players, and areas outside domestic power supply that aren’t easily converted to renewable technologies?

Scale Advantage of Renewables

Critics of renewable energy sources often derisively quote land area required for building large-scale generation. Regardless of whether its wind, solar PV, pumped hydro, molten salt, or another method, a “farm” for renewable power will take space, that is true.

Solar Sunwerx 6 Florence Street BURWOOD VIC 3125
Nyngan Solar farm, Australia. Credit: Solar Sunwerx

Renewable energy projects are much simpler to implement from an engineering point of view, compared to a nuclear reactor. They are also more flexible.

A nuclear plant, once scoped, has very little opportunity for changing the Quality Triangle. It also isn’t going to get much more efficient if you delay implementation, because the technology is largely static.

Manufacturing issue with your solar PV arrays? Let’s just get less panels for now. They’ll be cheaper later on, or more efficient, anyway.

Dispute over one of your wind turbines? Fine: proceed with the rest of the farm until the outcome is known.

These are two examples (there are more) where the scalability of renewable energy creates a huge advantage. The unit size of a wind turbine, or a solar array, is in no way limiting for people who know how to implement them.

Concentrating Solar Power for an MSR (Molten Salt Reactor)

Pumped hydro and molten salt reactors are similar to traditional power stations, in that their capacity is roughly determined at time of construction. The key difference is they are primarily storage, over and above being generation.

They don’t need to be on all the time, only engaged when other resources are running low, or as demand spikes. This is another advantage over “baseload” coal or nuclear, which cannot uplift to address demand spiking.

Only gas-fired stations have this ability at the moment. The surging price for gas, as well as its status as a fossil fuel, renders it a short-term option at best.

The Paradigm Shift

You cannot simply build a traditional network and throw more and more renewables at it until you reach a very high number.

Coal in Australia has been built to over-capacity, resulting in wasted capital expenditure, and poorly managed outcomes. Witness the issues South Australia has at the moment, because of short-term thinking around renewable energy integration.

We need “smart” implementation of renewable energy projects. Flexibility must remain a core tenet of implementing this intelligence.

As Evans-Pritchard covers in his article, there are many storage options in development across the world right now. We’re in a period of real transition where more options will blow the marketplace right open.

This requires the right thinking, to engage renewable sources on a far larger scale, holding hands with storage options of all kinds. Markets will shift rapidly. Consumer needs, particularly in the developing world, will have no need, and no money, for sledgehammer tactics like “baseload” power.

Projects designed for even 30-year life cycles will find themselves at risk of rejection. It will be simply uneconomical to support such inflexible systems.

With the right people at the wheel, concerns over our energy needs, and the perceived shortcomings of renewable energy, needn’t be a concern.

Billing Awesomeness Powerwall Style

As I’ve been hinting for a while, the first bill has landed – Billing Awesomeness Powerwall Style! The guys at Natural Solar and I have been jumping out of our skins to get this moving, but all good things in time.

Natural Solar

I’d better come clean – technically this isn’t the “first” bill. I actually got one over a month ago, which only covered 35 days due to various scheduling issues with the meter changeover and reading.

And don’t get me wrong: that 35 days was a very small amount, particularly as my last summer bill was $660 (!!!), but I felt it best to wait and see.

Now that we have a quarterly amount, which also lines up roughly with the same billing period last year, I (and everyone watching) can compare apples more easily to apples.

Let’s go to the numbers, courtesy of my poor quality photography. Here is the bill from the “Autumn” quarter last year:


Of course, I’m a fine and upstanding citizen (stop giggling), so I paid on time to get the appropriate discount under my plan.

And here is the bill from “Autumn” quarter this year – this amount also includes the pay-on-time and direct debit discounts:

Billing Awesomeness Powerwall Style

Ninety per-freaking-cent reduction!

Not too shabby, but as always, it isn’t the whole story.

The 2015 bill overlaps the 2016 period by a few days at each end, so this is only a fair comparison if we look at the number of days on each bill. Hey let’s do that to FOUR decimal places!

Year Days Cost $ / Day
2015 99 $490.38 $4.9533
2016 86 $50.39 $0.5859

So… yeah… that’s 59 cents per day for electricity. And if you recall my ROI/payback article from April, you’ll know that under Diamond Energy single rate plan I pay a tick over 82 cents per day for connection, so I’ve even reduced the connection fee by a fair whack.

That makes it pretty clear that I was smashing out the solar power with extreme prejudice from my 5kW array. The final number was a tick over 3 kWh exported for every 1 imported. Always going to look good when you’re getting 8 cents for export, from the legends at Diamond Energy.

I will throw in here: that bill doesn’t contain a single GridCredit sale, either. Nor does it contain any off-peak (TOU) power. That is pure, single-rate, import versus export.

And I think I could do better, but we’ll get to why that is later.

Billing Awesomeness Powerwall Style – Factors

I suppose it was a pretty mild weather period, but then in Sydney for the Autumn period that’s not unexpected.

Looking at the energy consumed per day is also helpful:

Year Days kWh consumed kWh / Day
2015 99 1777 17.9495
2016 86 1180 13.7209

Note that because I don’t see how much I consume on the bill, I’m having to use the data generated by the SolarEdge API. In my experience so far it is fairly accurate, though it has a small degree of variance due to updating on the quarter-hour, as I understand it.

A good reduction in usage, due in part to having a couple of new devices we needed to replace, like the oven. The old one was listing badly to port, in naval terms.

That reduction is also about learning my consumption patterns via the SolarEdge and Reposit Power portals, and coming up with the best way to eliminate waste.

I’m also paying a bit less for my power overall since changing providers, but as I’m only importing around 3kWh per day, that is of negligible effect on terms of cents per day. The connection fee is only a tiny percentage different.

Critics will be quick to jump in at this point, with smugness, clamouring that its NOT just the Powerwall.

While that is a fair point, at the same time, they should not be dismissive of the lessons the system has taught me.

To digress into simile for a moment: I went to University, and it cost me a lot of money, but it didn’t get me a job; it gave me a mindset, problem solving skills, and the experience of those who were my educators.

Likewise, I have not just purchased a battery, but an entire solar PV system with smarts. With it, I have been given the opportunity to generate, store, and export that energy. I can access new energy trading markets such as GridCredits.

Most importantly, I have a new way of thinking, evidence to track my progress, and help from a range of people across the industries involved.

The battery, by itself, doesn’t deliver miracles, not was it ever intended to. I’ve made it very clear from early on that there were tangible benefits to the Powerwall.

The power shifting aspect of the battery is extremely important to reducing my import requirements. I don’t get Gross Tariffs, so moving what I can to the daytime is great.

BUT we don’t get to spend our whole day at home (the kids would drive me up the wall), so there needs to be other ways to reduce or offset that cost. That’s where the Powerwall takes over.


The ROI blogs I’ve written state quite clearly that any household could save money by making simple changes. Smarter devices. Better practices. Maybe a new billing provider. It didn’t matter whether they had even had solar PV, much less a battery.

A household with Solar PV on Net Tariffs has probably learned some of these lessons already. For them, the cost of a battery is a marginal prospect today but is certainly on the radar.

A household with Solar PV and Gross Tariffs in NSW is probably looking for “what next” as they lose those benefits at the end of the year. Perhaps they haven’t had to think about these factors, but they probably will (and I know some who are), once they start actually importing power at a cost ratio which reverses Gross Tariff costs.

I just look at the FACTS: I’m saving about 90% on my power bills. I’m making my household greener than it was, through waste reduction and buying green power. I’ve been asked to relate my experiences at conferences, schools, and work places.

People are interested in this technology, and want to see it in action before they commit. Hopefully this kind of real-world data, even if its only one site, will help.

As a side note, based on this one bill, the return is in the order of 10%. Extrapolating that, factoring degradation versus increase in power costs, the 10 year window on my warranty is looking pretty safe.

And I’m not done.

The next arrow out of the quiver is my upcoming move to time-of-use
billing. That way, I can start really getting the most out of the Reposit Power software to drive those costs down even further.

Energy Networks
This lighting really makes me look good…

Billing Awesomeness Powerwall Style, away!

Test Driving the Model S

Today I had a crack at driving the Model S. This was a favour teed up for me by the good people at Reposit Power. They used it as a bit of a thank you for my help at that conference back in May.

I’ll level with you: there is no way I could afford even a base Model S.

In Australia the absolute base standard model is over $110K. That includes all discounts and incentives – of which, thanks to our backwards government, there are few.

I drive a Nissan X-Trail (the last of the “boxy” X-Trails from 2012). The wife has a Yaris. So we’re not “rich car” people. Even the base Model S is about 3 times the cost of the most expensive car I’ve ever owned.

However, in good news, today’s test drive was not in the base Model S.

I was in a dual-motor Model S 90.


I have been thinking about owning an EV for a long time now, and about how it would feel, and how it would respond.


I was unprepared for the sheer awesomeness of this event. The lightness of the steering, the road responsiveness, and that is without me even thinking about the tech that underpins the whole thing. Sure, I’m not a luxury car drive ordinarily, but MAN!

We spent a bit of time driving around Sydney’s lower north shore, getting a feel for the capabilities and luxury of the beast. And the silence, which I found a little unnerving at first, but quickly learned to laugh at… somewhat deliriously.

What I hadn’t appreciated previously, when freaking out about the Model S, was the simplistic elegance of the design. Besides the main screen with all its configuration (handled wonderfully by Adele from Tesla, guiding us on our magical space journey), everything is really thoughtfully laid out and simple to operate.

You just get in, and drive, and nothing about it is an issue, even for a first-timer. Well, except the left-side indicator stem… European layout… Hmph. I’m just used to Japanese cars so no biggie.

We experimented a little with the different modes, and it was really amazing how quickly the car shifted to Sports and Performance modes. You could feel the suspension and steering sharpen up as soon as Adele switched it over, even at 60 km/h.

We also drove past an Audi R8, and we all had a good laugh at the difference in price versus performance.

The Autopilot was really cool at notifying cars and other objects that were within the car’s sphere of influence. It was really noticeable how different the layout was to other cars I’ve driven, particularly the space down the middle of the vehicle, and smart use of every area.

And then, there is that acceleration… I’ll let this short video (and my daughter) do the talking…

We also had a poke around the showroom, looking at the cars and bare chassis, as well as the Roadster they had on display.

IMG_20160723_123954 - Copy IMG_20160723_124043 - Copy

I am also proud to say that I have now added a second Tesla to my fleet.

The Winter Of Our Discontent

Now is the winter of our discontent
Made glorious summer by this sun of York;
And all the clouds that lour’d upon our house
In the deep bosom of the ocean buried.

– Gloucester, Richard III (William Shakespeare)

OK so perhaps I’m using that a bit out of context; where Glouceser is speaking on a time of unhappiness past, I’m in the middle of winter, and I’m fairly discontent!

Mainly because it is one of the coldest winters in Sydney for about 20 years so far, with some record days in terms of low temperatures. I’m not even going to type that much because a warm bed is calling me.

Frost isn’t unusual for Sydney, of course, particularly in the western suburbs. But it has hit a little earlier than I remember, and daytime temperatures are staying in the mid-teens, or around 60oF.

This is Australia for goodness’ sake! We don’t DO cold.

That attitude is reflected in our lack of double glazing for standard housing. If I had the money, I’d give it some serious thought.

What it has meant for the UTP household is an increase in imported power as we run that (cursed) ducted air conditioner for heat.

Here are some of the dials, edited to exclude GridCredits/Battery, from Reposit Grid Portal, Wednesday 29 June.

winter discontent

This is the general pattern on a bright winter’s day – we get up and consume a whack of energy in the morning, with the ducted heating adding to the breakfast needs. The green spikes on the top right are around 5kW consumption, mostly import.

The Powerwall is typically exhausted by morning in this weather, due to evening heating requirements. This is utterly necessary to prevent widespread misery, wailing, and gnashing of teeth.

I’m not even complaining about the heater usage because brass monkeys are getting distinctly uncomfortable. Its that cold.


Get the ice scraper, Edgar… and the thermals…

You can see from the Reposit data screenshot that the solar generation is still kicking a fair amount of butt on the bright days, with the light hitting the panels from around 0730 hours through to around 1630 hours here. It’ll get up to around 3.8kW in the middle of the day.

That is a fairly good amount of power considering we’re in the shorter daylight period of the year. A week earlier, right around the equinox, I did 21.5kWh which is pretty schmick. Either side of that, it was closer to 12.5kWh as intermittent cloud interrupted my flow.

I’m even exporting a few kWh because the battery is still filling up before midday. On cloudy days, I’ll turn the pool equipment off to save about 1.5kWh of electricity as well. So while its not all gravy, its still cheaper than having no solar/Powerwall at all!

Its just addressing those morning and evening heater requirements that is the issue, and even with the thermostat set to 19oC, there is a fair bit of juice needed to kick the old girl off.

I’m getting a meter changeover done so that I can move to time-of-use. This will take full advantage of Reposit’s ability to charge the battery off-peak and deploy that power when I need to head off peak running.

Speaking of which – first bill due in the next week, so expect excitement!