I’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.

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


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.


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.


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 but 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.

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!

As already sprayed around on twitter, I have a system installed within my solar domain from a startup called Reposit Power. When I first discussed the install with Natural Solar this was one of the key points in the install; a smart way to use battery power, as well as help reduce my costs.

If you didn’t watch the video, in a nutshell:

Reposit Power provides controller software that adds smarts to the system I have, as well as offering the ability to sell battery power to the grid during peak events (GridCredits).

The SolarEdge inverter with StorEdge Battery interface is quite happy playing with the Powerwall. When the sun is out, it powers the house, directs any leftover to the Powerwall, and exports the rest. Battery is called on when solar is not available. Simples.

Reposit Power takes this ecosystem and adds a layer of predictive analysis, including my usage patterns, type of energy tariffs, and weather patterns, to decide on the best way to manage this power on my behalf.

This is the kind of technology that other companies are selling out of the box, but Reposit are making it applicable to multiple systems. This device-agnostic approach is very important as we move deeper into the IoT (Internet of Things), particularly with connected energy systems.

Reposit Power also provide a sexy, sexy web interface for looking at power usage. Here is a sample from 13th May:

Friday the 13th …

It has a level of granularity slightly better than the SolarEdge web interface, which is really useful to understand house consumption in particular.

My favourite thing about the image above is the Solar generated – almost a perfect curve, gracefully rising from 0720 hours to 3.6kW through midday, and then falling to zero again just before 1700. Beautiful…

Fine… but what does it mean?

At the moment, I’m probably not taking full advantage of the Reposit setup, because I am trying to be the smarts in the system. And while I’m a control freak, there are factors beyond my control.

The guiding philosophy is to use devices when the sun is out, and get the battery to run the house when its not. Life sometimes gets in the way of that, though more often its cloud cover getting in the way of that.

A couple of days in a row of decent cloud cover, or rain, and the battery is going to roll over and go to sleep until the sun comes out again. As we head into winter here in Australia, daylight hours will shorten somewhat.

(I’m still cranking 20+ kWh on a clear day in which is doing alright for a latitude of 33.7S).

If I’m importing power from the grid once the battery gets low, I’m paying a bit over 20c / kWh for it. That means I might spend $3 on power on a day where I have cloud cover, looking at the average consumption.

Winter will require more power consumed on heating, so that cost will go up on a cloudy day. Single rate electricity tariff gives me a level of surety with my consumption, but perhaps to maximise the benefit, we need to shift our thinking and take a bit of a risk.

Reposit Power to the rescue?

In discussions with the guys at Reposit, I’m considering moving to a TOU (Time Of Use) tariff with Diamond Energy. Let’s look at the costs involved in TOU before any discounts apply:

Rate Description Time Period Cost inc GST
Daily Supply Charge 101.20c / day
Peak Rate 1300-2000 business days 32.84c / kWh
Shoulder Rate 0700-1300 business days0700-2200 weekends

0700-2200 public holidays

25.30c / kWh
Off-peak Rate 2200-0700 every day 12.27c / kWh

Compared to the current single-rate of 82.45c / day for supply charge, and the 21.29c / kWh for usage, this could be either terrifying or awesome.

The connection fee increase to go TOU from single-rate is nearly 23%. Over a billing period (quarterly) is a difference of just over $17, or $68.25 in a year. Not huge, but I’m trying to get as close to zero as possible; the related benefits have to stack up.

Peak rates are going to be the killer – 54% higher than single-rate. Ouch.

Shoulder power rates are nearly 19% more expensive than single-rate, which is where quite a bit of our usage probably sits, based on my quick API-based calculations. That is something to put a red line under in considering the switch.

Off-peak power is while off-peak is 42% cheaper than single-rate, so can it help?

Certainly – running the dishwasher overnight is an obvious one, as it has water heating requirements. Water has the highest specific heat of any regular household substance (unless you’re heating Helium or Hydrogen* gases), and therefore needs a lot of power to do it, if only in peaks.

*Author’s note: if you’re thinking about heating Hydrogen gas in your home, just don’t.

What about other devices? Washing machine run before 0700? Perhaps, but ours draws gas-fired hot water so its not a big deal. Hanging washing on a cold winter’s morning doesn’t sound like fun, either.

Oven? Generally not cooking anything between 10PM and 7AM at night. We tend to be asleep or generally less active (and hungry) at those times.

Air conditioner springs to mind as something that needs to operate off-peak as much as possible, particularly in winter where we are warming up the house before getting out of bed. We have a reverse cycle ducted system which sucks a lot of power to cool, so probably a similar amount to heat.

If we had off-peak power, we could time our heating and cooling to maximise use of off-peak power, though that is less useful in summer when the heat is coming in the afternoon i.e. during peak.

However, if we’re talking about the ability to effectively use off-peak power, we need to consider the most useful device on the premises.

If Sydney is going through a cloudy period, and I’m not able to generate enough solar power to both run the house and fill the Powerwall, why not use off-peak power to do it?

Even though its one of the stated benefits of the Powerwall (time-shifting solar and off-peak power) I wasn’t really considering how to do it until Reposit Power came along.

The Reposit Power box is capable of analysing my usage patterns, and understanding that I get up around 0700 every day, flick on a few devices (not simultaneously if I can help it) and make breakfast. Over time it gains an understanding of how much electricity I require for breakfast.

So, if I moved to off-peak power, Reposit could pull that off-peak power in, and reduce my breakfast costs by 42% on days where I don’t have the battery to boil the kettle, compared to what I have today.

What if its a wet week? At the moment I’d trickle a bit of solar into the house, maybe the battery, but my import costs would climb at a set rate of 21.29c / kWh.

If I move to off-peak, Reposit could pull in 6kWh at 42% lower cost, and deploy that power at peak time to avoid the higher rate. I’d take a bit of a hit on the shoulder time, but would be better off overall if the figures work out.

My next step is to look into the exact numbers, and discuss some points of interest with the guys at Reposit Power. Scientifically speaking, I’d like to just let this single-rate billing period finish, then switch over to TOU for the next quarter and look at the results.

Yes, it would be an Autumn compared to Winter comparison, but in theory Winter should be even better for this strategy.

Whether I stop being lazy and look at the figures might be irrelevant in light of another factor introduced by Reposit Power…

GridCredits FTW!

At the moment, I get 8c / kWh for exporting power off my solar generation. Not crash hot, but not bad either compared to some in the Australian market.

One of the reasons for the low rate compared to what I pay for electricity is that solar generation is not a guaranteed resource. It peaks and troughs with available sunlight, and of course doesn’t run at night.

If you go back to the table on power pricing with Diamond Energy, you’ll see “peak” runs from 1300-2000 hours business days. This is generally when most power is required, so companies can sell power for a higher rate as they crank up the hamster wheels.

Even though my solar may be exporting during peak times, the environment today is such that the pricing is not adaptive. Firstly the technology doesn’t really exist at a network level, and secondly the power companies are keen to maximise their projected profit.

This is where GridCredits step in, and home storage steps up.

Anything I have stored in the Powerwall is guaranteed power. Besides a minor amount of efficiency lost in transmission, if I have a full Powerwall, I have about 6kWh available that could go into the grid to help smooth a demand surge peak.

Of course, given this is now a guaranteed source of power, and isn’t subject to interruption from the sun disappearing, I’m going to want decent compensation for it. That compensation works out to a figure state as “up to $1 / kWh”. Yep, a whole, tasty dollar.

And if its a bright day, I can keep pushing power into the battery from the solar panels, or exporting at 8c /kWh. Bonus!

Financially, that is a major windfall for the Pfitzner household, as the first exported kWh will pay for my supply fee that day, and any subsequent kWh exported will cover other days.

With around 77 peak events per year in Australia, with the right conditions I could get that power bill well below zero, and even pick up some beer money.

Beyond my selfish personal gain, systems like Reposit Power are a game changer for the electricity network. Long range power distribution seems a little odd when we’re capable of generating it on our rooftop.

The Rise of the Microgrid

There are a few projects around Australia at the moment that are looking at microgrids, or discrete systems that don’t require the main power grid as we know it.

Think about it like peer-to-peer power sharing. Its basically the bit torrent of electricity.

The concept of a nation- or state-wide grid will probably fade over time. Connected energy systems at the current scale are only 50 or 60 years old, and the concept of connected electricity grids just over a century to date.

I see the grid as something like the automobile, powered flight, or telecommunications. They are all recent innovations in human history, and as such are subject to more rapid change in their short life cycle.

People are naturally resistant to change, and only like a change that introduces convenience, financial benefit, or exceptionally pleasing aesthetics.

Renew Economy ran an article relating to the thought process of microgrids in Western Australia. Asset Manager for Western Power, Seàn McGoldrick, gave a talk on the peculiar set of circumstances in the west. As mentioned in the article from Giles Parkinson and Sophie Vorrath:

… when you have a service area equal in size to the entire United Kingdom, but with just one million customers (as opposed to 73 million), it’s a big challenge – economically and logistically.

The profitability of Western Power is almost nonexistent, but it is an essential service, subsidised by the West Australian State Government to the tune of half a billion dollars per annum.

What if that money could be shifted to communities, to reduce the long-term costs of network maintenance? Provide customers with reliable power, while not having to manage the poles and wires across the wide brown land?

McGoldrick presented four general approaches, and bucked for option 3 below (Modular Network).

Credit: Renew Economy, Seàn McGoldrick


If you take some of the maintenance budget out of the equation, Governments could save money, or put it into development of newer, more efficient technologies.

You create a snowball effect, that can allow low-carbon generation, electric vehicles, and storage technologies to leverage off each other.

I remember having a PC back in the day and moving to Windows. This change forced the need for better components. As CPUs got better, memory had to advance, along with graphics cards, and the motherboard technologies that tied it all together. Something similar can happen with renewables.

There are still issues around reliability for microgrids, but a combination of efficiency measures, storage, and generation diversity (e.g. wind and solar PV together, along with solar thermal) can contribute to advances across the board.

Further, it can remove the issues of the grid going down at some distant location, leaving consumers stranded.

With smarter devices, smarter management, and more efficient housing, domestic microgrid implementations can lead the way. Once the base is established, and more research money flows in, light industry can also benefit as the technology advances in leaps and bounds.

From there, we won’t just be talking about decentralising our power needs, we can start talking about decentralising our population.

If only the government would hurry up and get us a first-world internet. In an election year, anything could happen…

My solar system has now generated over a MWh (Megawatt Hour) since it was installed in late March with the Powerwall. Essentially that means my panels have generated…

wait for it…

zoom in to close up …

dr evil


One Million Watts!

Yep, that’s lame, but I’ve been waiting to kick that off for weeks now. And some would say that picture has a striking resemblance to me.

On average that makes it a bit over 25kWh per day solar power generated, which is quite good considering we had a few cloudy days. Record day so far is about 33kWh generated, which might get broken around the summer solstice next year when the days are a bit longer.

March in Australia generally resembles February, but at this stage it is even warmer than usual in Sydney. You can read a really good summary at The Conversation about why its happening this year in particular.

I’m also following 9th Dan Chart-Master, Ketan Joshi on twitter, to see what statistical wizardry he’ll come up with next in terms of climate science and weather patterns.

This record period above 26oC (79oF) has certainly provided some amazing solar power statistics for the first week in June.

Fairly healthy rates for import and export, and its just a shame I’m yet to take advantage of feed-in tariff. I’m still awaiting changeover to Diamond Energy so I can take full advantage of Reposit Power with the Powerwall later this month. SO excited. GridCredits!!!

If I was on my current provider’s plan (which I’m not because I’d have to sign a new agreement), I’d have imported about $1.70 worth of power after all discounts, and made about $4.40 in feed-in tariff. Throw in 7 days of connection charges of $4.94 after discounts, and I’m $2.24 in the red, theoretically.

However, I’ve consumed 110.17kWh of my own making, or nearly 16kWh per day. That is actually pretty low against the household average over the year (~20) and if I didn’t have solar panels, that 110.17kWh + connection fees would be somewhere in the order of $31.70.

So really, when you think about it, I’m almost $30 to the good!

Right at the start of you can see a little red block. This was an anomaly where the battery management firmware was confused by 29th February (Leap Day). Yeah, as a developer I can tell you it happens, occasionally. I’m assured its fixed, and because we’re on daylight savings time right now it started at 1AM on the 29th Feb and went through until 1AM on 1st March. Cool.

There is a big spike on 3rd March which was air conditioning going on for a very warm afternoon. On the morning of 7th March the battery finally went to sleep after the previous evening’s efforts cooking dinner and dessert.

Why burn stored energy doing all that baking in the evening? Firstly, it was a work day, but mostly, let’s just say that you can’t put obsessive battery monitoring ahead of my wife’s roast chicken, followed up by chocolate cake. You just don’t.

Our electric oven is running a bit out of kilter at the moment, judging by the noise coming out of the fan assembly. I’m getting that rectified next week, which should decrease duration of usage, by providing a more efficient cooking cycle. Moar cakez!

I recently added a new network attached storage (NAS) for backup duties, after the old one finally threw a shoe – i.e. one of its RAID partitions. The new one has power recovery so can handle being on a timer, along with the TV and games console running from that outlet. Only a few watts saved, but every bit counts when you’re trying to get the battery through the night as often as possible, under varying circumstances.

Powerwall Zen

As I’ve learned a bit more about the Powerwall, I’ve also tweaked some of the larger hardware pieces to exist in harmony with each other and the solar system in general.

Powerwall Zen

For example, the pool pump needs to be running for a certain number of hours per day to ensure cleanliness, and takes about 0.8kWh at standard operation. I’ve worked out the pump capacity (Qmax) and rate of flow correctly, to ensure I use only the minimum hours per day. I also figured out that running it later in the day allows the battery to top up earlier as the panels start cranking up the flow mid-morning.

In partnership with this, the timer on both our washing machine and dishwasher are set for the early afternoon, when the sun is at its highest. I leave a gap in the pool timer of 2 hours in the middle of the day so both these devices can run without issue, even when the sun isn’t so bright.

As always, a solidly overcast day can throw some of these plans out of whack, and that’s why a grid connection is a must. Beyond keeping the warranty of the Powerwall at 10 years (off-grid is only 4), in suburbia there is simply no reason to disconnect, with the grid as your fallback.

And I’m only a couple of weeks away from generating GridCredits, getting the battery topped up before the 2PM peak boundary makes sense both financially, and from the data it will provide to advance our knowledge of micro-grids in a modern urban environment.

Now, if you’ll excuse me, I smell cinnamon cupcakes baking…

In my last post I alluded to having some thoughts on whether my house was making the most of solar power, particularly in regard to how I was using it. Knowledge is power, and the knowledge I’ve gained in the past few of weeks of my solar power usage has been very interesting.

Understanding which appliances burn the most power, what the usage patterns are, and the effect of weather, are all critical to getting the most out of the investment. This ensures that I can achieve the ROI I want, and that I’m a responsible user of any fossil fuel energy I’m required to draw from the grid.

Though the weather today was pretty good.

In all my analyses, the ducted air conditioner keeps cropping up as the villain (and at some point I’ll reconcile myself to that).

Its a difficult issue to address, as ripping it out of the roof space and replacing it with something else would just cost a load of money, and may not practically address the issue of solar power for cooling on a bang-for-buck basis. I need to ensure I’ve investigated other ways to either offset its use, or reduce my reliance on it.

Air conditioning comes down to a simple premise: comfort. You use it because you have too much outdoors in your indoors, so to speak.

That’s not a bad thing in the world of modern convenience, where our cars, offices, and houses are all air conditioned. However, have you ever thought that air conditioning is just treating a symptom of the main problem, and not the root cause?

The root cause – intrusive heat in this case – is going unaddressed. Even if you have a really efficient unit with all the bells and whistles, you may be able to do even better through other, more practical means.

Beyond “don’t leave the door open!”, there are many factors affecting your use of air conditioning or heating, often reflected in the design and quality of your building. Do you have adequate insulation of suitable quality? When was the last time you had it checked? Gaps around the doors? What about covering the windows?

Windows are a general weak point for heat transfer into or out of a building, particularly in large parts of Australia, where we don’t suffer the kind of harsh winters that require central heating or double glazing.

As a design point, a lot of modern houses here open up windows far more, which often results in more energy usage. One design element I need to deal with in my house are the large, west-facing windows.

About 8 square metres of glass, pictured at 1PM Sydney time today, before the sun hit

Both windows are in the same room at the front of the house, are 1800mm (6 feet) high, with the one on the left nearly square and the other about 2700mm (9 feet) wide, getting hit by sun all afternoon. The internal venetian blinds, while slowing the direct heat down a little, aren’t stopping it from advancing into the room in the first place.

Simple science: the sun hits the glass, which heats up, subsequently transferring its heat to the cooler air inside that is right up against the glass. That air rises (because heat) and more cool air is drawn against the glass. Rinse and repeat for 4-5 hours on a hot Aussie summer day!

Some people also look at tinting their windows or installing double-glazing to assist with this, but I remain unconvinced about either option in terms of value-for-money in most parts of Australia.

Tinting provides an extremely thin buffer, so it is only going to slow things to a certain degree – better than nothing of course, and relatively cheap compared to other methods. The downside is that in winter its going to perform the same function, stopping heat from entering the house via those windows. As a side note, the privacy aspect of tinting is lost when the lights inside are brighter than the lights outside i.e. at night when you are using that space.

Double (or triple) glazing is the architectural method of choice for sound proofing and insulation of glass. While its overall effectiveness year-round as an insulator cannot be questioned, the expense often makes the average home owner hesitate. Double-glazing in summer is best used where you can keep the internal temperature cool, and therefore stabilise the buffer between glass panes at a temperature somewhere between the outside and the inside. Generally speaking, if you’re not keeping the room cool through e.g. air con, the buffer will heat up, and start transferring that heat into the room.

In my opinion, and that of several electricity companies, the best way to stop this kind of heat transfer is to stop the heat hitting the glass in the first place. In essence, you create an external buffer zone where the sun’s heat and UV rays can’t get to the glass in the first place.

There are several options available, from adjustable fabric awnings, metal shutters, louvres, window shades or fixed awnings.

Rather than run out and spend a pile of money on anything custom-made for those windows, I decided to experiment first on our north-facing garage window. In the garage I have a network cabinet* in which I have my network backbone with appropriate patch panel for all the points around the house. I don’t want that equipment to overheat, and shielding that window should help prevent that.

* on reflection, probably a mistake to put it there, but it wasn’t going anywhere inside the house, according to my wife. Its called “compromise” I think…

Window coverings

I went to Bunnings Warehouse and, for the princely sum of $297, bought a fabric awning (1800mm wide, 2100mm drop) to cover the garage window from the worst of the heat. That’s it on the right, and I put it up myself in about an hour.

The awning can quickly be retracted in case a storm blows up, or in winter when I want the sun to warm up that side of the house. Sydney winters may not be harsh with snow and such, but we tend to have low tolerance for cold as a result ?

I’m going to keep an eye on this for the next couple of weeks, as we move into cooler months, and see how it performs as the sun moves back north and puts more sun on this window.

Some (including my wife) may say that these kinds of awnings are a bit daggy, and yes you can buy them in stripy patterns if you want to be reminded of your grandparents’ post-war bungalow. However, if they do the job then I think for next summer I’ll be pushing to cover the rest of the problem glass on the north and west sides of the house.

It will be a battle royale between her Better Homes and Gardens and my New Scientist approach to this whole thing.

In the meantime, the best we can do is shut the problem room off during the heat of the day and let it become the buffer zone. My issue with that longer term is the electronic equipment in that room is under strain during that time from heat. And its the rumpus room for the kids, so now I have them in the main room watching my TV!

Garage door

The double garage door also faces west, and therefore gets a lot of heat in the afternoon. That was an issue from the day we moved in (late 2013), so after a bit of research I bought a roll of Green Insulation Reflecta-GDI which looks a bit like this once fitted.

Garage Door Insulation
Reflecta Garage Door Insulation
It definitely works – I can’t touch the bare metal of the door for more than a few seconds on a hot day like today (35oC / 95oF in the sun), while the insulation is merely warm , slowing the heat transfer into the space.

Measure your door panels before you order and, once fitted, you may need to recalibrate the garage door lifter to account for any weight change (it isn’t much but some units are sensitive). No adhesive required as it designed to fit most modern panel garage doors in Australia by sliding into the space at the correct width. That is actually a shot of it overhead – no issues whatsoever with staying in place in over two years.

While we’re on the topic of garage heat, DON’T close your garage door immediately in summer after you park the car in there. The heat you trap will radiate into the house through plasterboard before it will escape through brick or wall insulation. Leave the door up and get some air flowing through the place for at least half an hour.

Not so bad to trap that car heat in winter, but make sure the engine is off!

Solar Power Design – more than panels

If you’re in the process of building or renovating, you may have already made a lot of decisions around how you wants things to look. Some of those things may focus on solar power, while many more are about the right fittings, colours, and facade for your home.

Those with solar power aspirations will already know how important aspect is, though after discovering what I have about my own house, I believe it should be more than how many panels your roof can hold.

If you haven’t adequately considered the thermal efficiency of your home, you may not be capitalising on your investment properly.

Even if you’re not considering solar power for your house at this point, you might think about getting the place pre-wired while the build is occurring, as Jennian Homes in New Zealand is doing with all new builds.

Consider the design factors around your insulation (wall and ceiling) as well as windows and cooling or heating options. Sometimes these things can be lost when you’re focus is on the right marble bench top, or the right tapware.

The builder may promise the latest, you-beaut ducted AC, but it may end up costing you more over the longer term. Look instead at smaller, more efficient air conditioners (like split systems) to cool or heat the space you need. In either case, make sure you understand the energy requirements of these add-on extras and how they will affect your power usage.

A few little decisions now can save you hundreds or thousands in the future, particularly as prices rise (and they will) and governments feel pressure to adopt renewables standards across the world.

The Powerwall copped a hammering this week, with another really hot day in Sydney showing up to get everyone’s air conditioner roaring, and the good news is I can see how much.

The SolarEdge inverter I have (SE5000 model for those playing at home) feeds back data to their HQ, which I can access through a web portal. At the moment I’m just taking screenshots to log interesting events, and provide feedback to everyone in the chain.

As you can see, its great from a consumer perspective to understand your power usage at-a-glance, as well as the Powerwall and panels data. So I know this week how much I’ve exported, used on my own needs, and what I had to take from the grid.


You can see that 25th Feb was the hot Thursday, with temperatures reaching 41oC in the shade. The ability of our family to tolerate that kind of heat is not pronounced, so the air conditioner goes on.

The big red spikes above the “4k” line represent our ducted air conditioner going on. Yep, its a hungry beast. Generally speaking, it seems to kick off around 5kW to run as an absolute minimum, and generally goes around 6kW, depending on the ambient (room) temperature versus the thermostat.

One thing I didn’t fully understand when I got my system installed was the power parameters. I have a 5kW inverter, that means the system can move 5kW from the panels and Powerwall as a maximum.

So, for example, if the panels are blazing and the Powerwall  is full, but I need to run the ducted air, it is going to pull a maximum of 5kW from my panels and battery combined, and then go to the grid for the rest.

Yeah, bummer, right? Unfortunately, the house came with this A/C so there isn’t much I can do about it at this point, beyond mitigating my use of it and setting my house up a little better. More on that point in a later post, when I get more time to think about it.

So, back to reviewing the data, and let’s continue by just looking at the solar generation side of things – and to make it interesting, let’s drill down on the days leading up to the full moon (yes, the portal has a drag-zoom setup – its pretty cool).

So we have some nice, parabolic curves representing power generation during the day. The peak is generally around 2PM each day (keep in mind we’re in DST here) and quite often hits in around the 4kW mark. However, I’ve seen individual readouts above this. I guess the graphing software tries to smooth curves as often as possible.

This isn’t the best bit though – notice the little squiggles happening around midnight on each day? I’m told by the installer that customers have reported moonlight triggering the panels, and I guess, being photo-voltaic in nature they respond to any light bright enough. Yep, that’s right:


Here is a zoomed-in version from the night of the 24th Feb through to about dawn on the 25th, showing the fluctuations. Not much graph smoothing here!

I’m kind of geeking out over this, in case you hadn’t guessed. Sure it isn’t a lot of actual power (up to 70 watts), but you must admit, that is pretty cool.

But going back to the top chart for a minute, you can see from the 25th onward a lot of red readout in the low-levels, meaning the Powerwall has ceased covering “Self Consumption”. The day after was cloudy, so little opportunity to replenish the levels.

After some awesome sunlight today with a nice cool breeze (no air con!), the Powerwall is sitting around 70% to get me through tonight and beyond.

It helps that we were out today, not using much power, and having an awesome lunch at Barbuto Restaurant in Narrabeen, followed by a stint on the beach in the afternoon. Great day!

My name is John, and I had the privilege of the first Tesla Powerwall installation in Australia (maybe the world, they say). It has been a short, but very interesting journey so far, and as it continues I hope to share useful information, a bit of humour, and a hopefully less swearing than I provide in person*.

It would be remiss of me if I didn’t mention Natural Solar at this point. Chris Williams, Oliver Coleman, and the whole crew have been really helpful in putting my system together, and I’m seeing results already.

Tesla Powerwall

I’ve got all these grand ideas about what I want to do here, but I typed most of this up on a Thursday night, having come home from at work with little in the way of motivation after a 41oC day here in Sydney (106oF for any Americans reading).

You’ll have to forgive the absence of anything like style on this site. I am one of the least creative people you’ll meet in terms of design and UX in general. My job as a database guy is more about structure and numbers, and its a different kind of beauty…

The good news is, I know people who are fully conversant with the interwebs, and have great advice, which they will no doubt give, so this will improve over time.

I just thought it was time to get it started, and the best place to start is at the beginning.

Why did I install Tesla Powerwall?

There were many battery options out there already, but this one happened to fit my needs best, and I’ll definitely cover that in more detail in a future post.

The installation itself has been covered in a fair few outlets in the mainstream like The Australian/AFRNews CorpSydney Morning Herald. All of them seemed to have their own angle on Tesla Powerwall, and what its going to do for the planet, or their otherwise empty column inches that week. At least, those they’re not stealing from Huffpost or some random entertainment website…

Further coverage in tech sites like Gizmodo and Mashable got a few tongues wagging, as well as some extremely weird translations resulting in me being “aristocrat of a nerds” (seriously, read it).

Ultimately, there is a financial argument that underpins why I got a Tesla Powerwall (or any solar hybrid system) installed. Despite being accused of a “profligate Western middle class lifestyle” I’m by no means rich (and no steve f – if that is your real name – the pool isn’t heated). I earn above the national average, and am fortunate enough to have a smart, talented, hard-working fox of a wife who earns something similar.

Ultimately, I make no apologies for trying to enjoy my life while offsetting that with investment in renewable energy, but some people can’t be pleased.


Renewable energy investment makes up the second leg of the argument. There is a growing need for research and development into solar, wind, and other forms of power. We can’t keep burning things to make lights come on when we have, as Elon Musk said, a giant, free source of energy right up in the sky. All we need is the will to change.

The good news from my perspective, now that I’m following sites like Renew Economy and One Step Off The Grid, it is clear that this movement away from coal and oil is only accelerating, if we can get our politicians to listen for long enough.

The third part of my desire for this is sheer nerdliness. I’ve been watching Tesla for a while now, and what they’re doing is impressive under the leadership of Elon Musk. You can read about Elon Musk in a long and humorous fan perspective at Wait But Why if you don’t know much about him already.

In summary: Built Paypal, started Tesla Motors with the world’s sexiest electric car, and has this thing called SpaceX who launched and then landed a freaking rocket so they could re-use it later.

In any case, Tesla and SpaceX are working to improve our situation on this planet, and try to get us to other planets. If you haven’t watched the Tesla Powerwall launch, I recommend it.

For me, its about looking at the system and how I can learn more about it. Maybe there is a job in renewables that I can take my tech skills to? I don’t yet know all of what the future will hold.

What I do know is that I’m down with lower household running costs, a smaller carbon footprint, and analysing the data available to me from the system.

A few people – friends, friends of friends, complete strangers – have asked me what the best solar system to buy is. “How many solar panels?” or “Should I get a battery?” and “What is that thing growing out of your head?”.

To them I say:


Everybody’s house is a little different. Everybody’s use case is a bit different. Solar isn’t just a cookie cutter approach; at least, not yet.

What I can say is that there are a few steps I’d recommend to anyone thinking about installing solar panels and/or a battery.

(Oh wait: I forgot the paragraph wailing about how slack I’ve been on the blog. That was it – well except to say I got a new job in November 2017 working in energy which is pretty rad, but keeps me way busy).


People want solar for different reasons, and from my experience of the last two years, it breaks down into a few things.

Driving down electricity bills is usually numero uno, and there is nothing wrong with that. Investing thousands into something functional like a solar PV system, you’d want to see some payback and/or stick it to “The Man” if you’re angry about whatever it is “The Man” has done.

Green feelgood is another factor. Reducing your grid needs helps save operating costs on your house, as well as your carbon footprint. You also get to understand your ability to contribute to the energy ecosystem via renewable energy.

Curiosity is a relatively new thing, particularly for modern systems with API-driven inverters. Some people (me) like to watch what is happening on their solar system at various intervals, e.g.

After that, its a question of “Do you really *need* solar?”


First place is your electricity bill.

Look at the amount you consume on a daily basis across the year. Figure out whether there are major differences between summer, autumn, spring, and winter, and I’ll bet you start to see where the pain points are in terms of running certain devices in summer (AC) or winter (heating).

As I’ve said before: most of us get our bill, have a bit of a rage about it, and then pay it and move on. You need to take the time to analyse who you are, and what you use. It will be very helpful.

Have you spoken to your electricity provider about getting the best deal? Sometimes we pay too much via “lazy tax” where we can’t be bothered even making a phone call.

Have you told your electricity provider that you’re speaking to other electricity providers about the best deal? That can be quite the motivator.

Does your electricity provider offer “green” power options? That might elevate your bill slightly, but give you part of that feelgood factor you’re after.


Next, I’m going to ask whether you’re doing everything you can to reduce your electricity consumption.

Energy Efficiency is a very much overlooked part of housing, particularly in warmer places like Australia. Building standards here aren’t so great compared to other parts of the world, and we compensate using air conditioners.

I have to say I’m guilty here of jumping into solar + storage before really checking why my bills were so high. The good news is, I’m addressing these issues now by getting awnings on my west-facing windows as well as installing downlight covers in the ceiling to reduce insulation gaps.

Solar Panel

Perhaps it is something as simple as setting your thermostat too hot/cold, and trading money for a tiny bit of discomfort. In modern HVAC (Heating, Ventilation, Air Conditioning), each degree you set your AC up or down from 25oC can cost 10% more energy. Not cool. Or hot. Whatever.

Check all the gaps around your doors and windows. Deploy window coverings against the sun, or heavy curtains against the cold, wherever possible. Turn off the beer fridge if you’re not really using it. When you replace a device, look at the energy efficiency rating system (it can save you hundreds).

The possibilities are not endless, but they’re available, and significant.

The goal is to consume the minimum amount possible without making yourself too uncomfortable. And maybe a little discomfort isn’t such a bad thing ?

Alright, so let’s say you’ve covered the energy efficiency thing, and have a fair handle on your bills. That’s half the battle. Let’s talk about solar.


Not every roof can handle a solar PV setup. I’ve lived in a house that could not, due to a lack of appropriate space.

Start by looking at your roof space on Google Maps, and see if you have north- or west-facing roof space that might host a decent array of panels, if you’re in in the Southern Hemisphere.  For those north of the equator, its south- or west-facing, obviously.

In some cases you might even want to have east-facing panels as well, due to your usage patterns. Morning people; they exist.

The more complex your roof layout, the more it is likely to cost for installation. Two storey installs can cost more in some cases. Single storey might get tricky if you’ve got multiple roof lines with minimal contiguous area.

Roofing material may also determine how difficult the install becomes, as different fixings and sealing methods are required.

If in any doubt, talk to a local installer. That’s where Google Reviews and recommendations can come in handy – find the right team and you’ll reap the benefits.


The trouble with me recommending anything is that the internet will immediately have an opinion on it. You will read reviews that are negative about perfectly good solar PV equipment, maybe because an individual had a bad experience.

There are thousands of combinations of solar panels, inverters, and (if you require it) storage systems from which to choose. You’ve also got different metering options, which can affect how you get billed, and how you might leverage peak/offpeak power rates.

“How many panels do I get?” is a pertinent question, and my response is always that panels are cheap, so get as many as you can afford.

Remembering that in most new setups, you’re in a “net” situation i.e. the panels feed your house first, then sell any leftover energy back to the grid at a modest rate.

Trying to self-consume every last kWh you produce is a waste of time for a grid-connected system, in my opinion. You’ll end up with a smallish system that meets your needs generally, but you’ll miss a lot of the cost offset you get from feed in tariffs, and payback time will be no different, or longer.

Panels are cheap. Get as many as you can afford.

At the same time, get an inverter that will handle that load. Having 6kW of panels isn’t going to mean much if your inverter is designed for half that. I’ve got 6.5kW of panels and my inverter maxes out at 5kW, which is generally OK, but I’d like a bit more ?

In Australia, I’d recommend a minimum of 5kW of panels. A system of that type will cost you around $6000-$7000 in Australia (installed). In the USA, Trumplandian authorities will ensure it continues to be about double that.


Adding storage can double (or more) the cost of a system pretty quickly.

At this point (February 2018) it will extend the payback time accordingly because lithium batteries are still coming out of the early adopter phase. It becomes a question of capital investment versus operating cost.

If you get only the solar panels, you can get payback in under 6 years.

This makes the assumption that you’re operating the system with a decent amount of thought. Move heavy loads to the middle of the day when the sun is shining and the panels are blazing. Make the most of your feed-in-tariffs, where available. Be aware of your efficiency issues, and address them.

If you do all this right, you could get payback down below 5 years, BUT you’ll still be paying an electricity bill, even if its smaller now.

Today, the battery option will take your payback up past 6 years again, and maybe as high as 8 depending on the specifics.

There is a benefit, though: your operating costs for electricity will be closer to zero than if you have solar alone. Heck, maybe you might even turn a small profit!

There are additional benefits to your battery install as well, if you have smart technology like Reposit Power attached to the system. Selling power for $1 / kWh a few times a year might not sound like much, but when your total bill is close to zero, its heading toward profit.

It can help you save money on electricity via arbitrage if you have the right metering setup. Reposit maintain a list of good installers to use in Australia, who will ensure you get the best result.


Well, I can’t really answer that, unequivocally. A lot depends on individual circumstances.

I’m saving about $2000 per year over the first two years, having made small changes to how I run my house. I continue to make these changes as I explore ways to reduce my usage.

If you’re just going to whack the system in for something cool to look at, but not change any of your habits, expect your savings to match your behaviour.