SolarEdge Updates

I’ve been a bit busy to monitor my usage regularly, of late. Feeling out of touch, I made a point of checking my solar generation after recent rainy weeks.

It seemed a little low. Usually I hit 5kW around the middle of the day, but was peaking out at 4.6kW. I was contacted by someone who lives nearby with a corresponding fall in numbers.

The only theory we have to go off is lower angle of the sun. Additionally, because there were two weeks of Autumn where we almost never saw direct sunlight, we didn’t see the slow decline over time.

Its like seeing someone’s kids only occasionally – can’t believe how much they’ve grown! Their parents see it every day.

SolarEdge Updates

Having not checked anything for a while, I headed over to the SolarEdge Monitoring Portal to compare their results to Reposit. Having a second source for comparison is very helpful to sort out any discrepancies.

Well, there certainly have been some changes! And all of them look like winners.

The first noticeable change was the new Monthly profile for Power and Energy.

SolarEdge Updates
April 2017 to date

There was a period where the “self-consumption” figure wasn’t being reported through some conflict with the Reposit interface. That’s back, which is great.

Added to this is the “From Battery” stat which is quite cool. It features both in the Consumption summary figure, and the bar graph. This is only recent, so I look forward to that percentage figure “from batteries” smoothing out with a larger data sample.

If you mouse-over any of those bar graphs it gives you the details, in kWh, for the days that have been completed. Again – very vool.

I also hadn’t given much thought to the year-on-year comparison before I had enough data. Now its very handy to answer questions I and my near-neighbour have about long-term performance.

SolarEdge Updates 2

For reference, the figures are in the table below for the three months with suitable data.

Month MWh 2016 MWh 2017
February 0.728 0.780
March 0.695 0.617
April 0.523 0.588*

* As of April 24.

What I find really interesting is the March figure; despite having an extra 1.5kW of panels this March compared to 2016, the weather meant I didn’t generate quite as much.

Moving forward, I’m sure subsequent years and months will prove to be most interesting. I love me some data!

Live Baby Live!

They’ve also updated the Overview panel to have near-real-time feeds of consumption. I did a quick screen cap of this and stuck it on my YouTube Channel. I like.

All in all, a great round of SolarEdge Updates as we move toward the cooler months.


A List Of Stuff

Realised it has been over a month since my last update. I’ve been kind of busy doing stuff with work, family events, and also putting a Rugby Club through its pre-season setup.

Finding time to sit and think has been a bit hard. At the same time, there is so much happening here in Australia with regards to renewable energy, its difficult to keep up!

Hydro stuff
Thanks to wikipedia

So here’s a scatter gun approach to energy blogging:

Scamwatch Stuff

Part 1 of this is a scam warning. A group listed “50% OFF!” specials for LG panels and LGChem batteries here recently. One example:

LGscam stuff

Now, nobody in their right mind should be writing 7.2kw’s as that’s just bad grammar.

Second issue is they’re using a lower case “w” to represent “Watt” for both panels and battery, which is wrong in every scientific manner.

Third issue is the battery is listed as “kw” instead of “kWh” – always remember that batteries are energy storage. This means they should always be listed with their kWh (kilowatt hour) figure to understand.

Beyond all that, the pricing is just cray-cray, and so is the manner of billing. A friend of mine contacted them and they sent him an invoice for the full $12,990. This is weird as most equipment sales would take a deposit (maybe as little as $1000), instead of the full amount to get started.

As it is, he cold-called LG Australia directly, who were aware of it, but couldn’t say much for legal reasons. He also dug a little deeper on the website with the original promotion to see what he could turn up.

Both leads turned him onto the fact that this wasn’t all that it seemed, so he backed right off. Good move.


As reported both here in Australia and overseas, some interesting tweet action went down between Atlassian’s Mike Cannon-Brookes and Tesla chief Elon Musk.


I don’t need to bore you with the details of the tweets themselves; if you’re here reading my blog, you probably saw it go down.


However, if you’re reading this from overseas, what you need to understand is that the talk about batteries is going ballistic here.

MCB and Musk really kicked things off for South Australia’s call for grid-scale battery proposals. But the process was also well underway in the state of Victoria, seeking to go large on storage as well.

Several people I’ve talked to in Canberra (our nation’s capital) are saying the phone is off the hook from government offices.

Suddenly people are realising that a smart, integrated grid is a thing we need. The people in power are starting to come around to the fact that coal is going to collapse, and that idiot behaviour about it needs to stop.

Coal stuff
Pictured: idiot behaviour (c)

That is the Australian Federal Treasurer, waving a lump of coal around in our House of Representatives.

Of course, politicians are populists by nature these days, so it remains to be seen whether talk of batteries survives the Next Big Issue they invent.

New Hydro Stuff

And from the book of “Hey! I’m a Populist, too!” comes our own Prime Minister. He’s decided that expanding our big hydro power scheme in The Snowy Mountains* is an awesome idea, and is framing it as “nation-building”

* some of the place naming in Australia is not wildly original…

Lenore Taylor provides a great breakdown in The Guardian on why this is important, in terms of how a leader, thought of as progressive, is still held back by the dinosaurs in his own party. You should read that article. Go ahead – I’ll wait here.

My issue with it is in the execution.

Expanding the Snowy Mountains Scheme in this way is an increase of 2000MW (2GW), which is not insignificant. It’ll cost AUD$2B which is also a pretty fair price.

BUT it will take somewhere between 4-7 years by all estimates. That means it isn’t really going do much more than keep up with demand, if at all.

There is also the danger that the goal posts will have moved entirely during that time. As I posited last year in Agile Energy Projects In The Marketplace: big projects can quickly become unwieldy.

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.

This is true in a market where things are changing rapidly, and particularly true in Australia, where we are shutting down old infrastructure.

The removal of the “baseload” paradigm is going to become more common, and require a smarter, more responsive network to cater for integration of many new technologies.

Hydro Power is as subject to this brave new world as much as wind, solar, or other sources.

I think we’d be better off kickstarting a solar thermal industry.

Solar stuff
Tower of Power. Wikipedia

Powerwall Stuff

This month sees the Powerwall v2 landing on our shores. It promises to be interesting times as we move from the early-adopter stage into mum-n-dad market.

The housing market is already seeing the potential, with Metricon offering Solar + Storage in home builds in the state of Queensland.

Powerwall v2 promises to really shift the landscape, offering twice the capacity of my unit, for roughly the same price. Other manufacturers are going to need to start offering more capacity or other desirable features to keep up.

Along with the big battery moves, 2017 looks like its going to be a very interesting year. Most predicted we wouldn’t hit this stage until 2020, but here we are!

Many jobs, with new types of infrastructure projects, will be required to make this happen. That means opportunities for people to jump on the train as its leaving the station.

Note: I’m always open to proposals in this regard.

Statistics Stuff

Here in Sydney it has been rather damp the last month or so. Tropical cyclones off the northeast coast of Australia have caused a lot of damage there. The storm train they pushed south has kept the cloud in play for many days.

Looking at my statistics, the last 28 days have seen generation below 21kWh / day, compared to a lifetime average of a little over 23kWh / day.

Consumption is also down, which is in part due to tapering off the pool pump now we’re in the cooler months.

Import is sitting around the average, though I haven’t needed the grid too much. The occasional Reposit Power off-peak import has bumped this number up a little, but I’m thankful for saving a few dollars.

Now that its been a year, with statistics, I’m satisfied that things will just tick along without my intervention. I don’t really have time to watch it 24/7 anyway!

I’ve started overriding my obsession with checking the system every 10 minutes.

Its more like hourly, now 😉


Springtime for Positive Billing

As per my tweet earlier in the month, the new bill came in, and it is really  the definition of positive billing.

It is the first bill I’ve received with TOU (Time Of Use) tariffs, which changes the landscape a bit for me.

I already have data from Reposit Power about billing estimates on a daily basis. While they’re pretty sharp, the guys doing the billing are where it counts. I wanted to see how close all the estimates – including my own – would be to the truth.

The net result is a deposit into my bank account (yesterday) of $50.25.

Positive Billing Spring
Billing Summary November 2016

The Breakdown

The fixed costs were as follows, excluding GST, for the 84-day period.

Item Quantity Price Amount
Service connection fee 84 days 98.90 c/day $83.08

Usage over the period at the various TOU rates came to the following (all amounts are excluding GST).

Item Qty (kWh) Price (c/kWh) Amount
Peak – Rate 1* 24.962 30.5300 $ 7.62
Peak – Balance 0.000 31.4900 $ 0.00
Shoulder Rate 76.635 24.9700 $19.14
Off Peak 74.584 13.8400 $10.32

* This covers the first 340kWh / month

I imported only 176.181kWh over an 84-day period. That works out to just under 2.1kWh per day during that time. Only 0.3kWh in peak tariff period!

There were a couple of rainy days in a row that I recall. One of those coincided with hosting a family event, using the oven, and dishwasher a couple of times. As it was the weekend, shoulder rate tariff applied.

Factors in my favour are summarised in the table below.

Item Qty Price Amount
Net feed-in tariff -1099.299 kWh 8 c/kWh -$87.94
GridCredits -5.04 kWh 100 c/kWh -$ 5.04
Renewable Reward 84 days -8.710 c/day -$ 7.32
Direct Debit Discount 3.0 % -$ 3.60
Pay on Time Discount* 7.0 % -$ 6.75
Diamond Referral  2 -$35.00 -$70.00

* This amount is calculated against the previous bill

The export figure is massive at nearly 13.1 kWh per day! Its worth noting that the new panels I got in October covered about 25 of the 84 days in this billing cycle.

The first lot of GridCredits were applied to this bill, and that $5.04 is handy for knocking the top off that peak tariff.

Once you throw everything into a pile, and calculate GST, you get the balance of -$50.25. Diamond will credit your account for any amount of $50 or more owed. For the first time ever I have positive billing for electricity in my favour!

About those referrals…

Yes, Diamond have a pretty generous referral scheme. Both the existing customer and new customer get a $35 credit which is pretty sweet. Long may it continue!

Having just one of those per quarter could help the electricity bill head drastically toward zero. The question is, how many friends and family can you tap into on a regular basis? 🙂

Let’s remove that $70 amount from the equation to look at the regular money.

Just The Facts, Ma’am

You know the deal...
You know the deal…

We now have an electricity bill of $19.75, or 23.5 cents per day, which is even lower than my first full bill in July.

When you export enough energy to cover your service connection fee, you’re doing pretty well.

When you self-consume most of the rest, and only bring in a very small amount of peak power, that is obviously much better.

The Powerwall is essential to this plan, because it avoids peak tariffs using Reposit Power for tariff arbitrage.

That said, summer reality is starting to hit. As I write this, the outside temperature is creeping up toward 37oC (99oF). The air conditioner is running. Cloud cover is building as we head into the afternoon, and peak power tariff kicks in.

I’m taking this opportunity to experiment with the ducted air conditioner. I need to determine how to minimise cost without unduly affecting comfort levels.

Billing cycles will now fall roughly into quarters ending in October, January, May, and August. I need to think about maximising the two “good” periods, and mitigating the damage during peak summer and winter.

Of course, climate change might make the summer period even worse. That is something scientists already say is being felt, and will only increase.

The cosmic ballet goes on...
The cosmic ballet goes on…

Positive Billing Into The Future

How will things look this summer? There will be more sunshine than in winter, but more electricity consumption as well.

The data I have for the year ending January 2016 (when the system was installed) suggests summer usage is a couple of percent higher than winter.

Will this be offset by any exports I do? How does the temperature affect this calculation in terms of air conditioner use? Pool pump running? More events in warmer weather?

These are questions I can’t yet answer.

For now, I have 258 days of finalised bills, with a net electricity cost of $113.28 with referrals. That’s 43.9 cents per day for electricity, so I’m pretty stoked.

Even without the referrals, the figure is 71 cents per day, which is lower than my connection fee, and works out to $260 a year for electricity.

Even extrapolating the summer quarter as $1.30 per day (higher than winter), it works out to around $310 per year.

That still puts me in the box seat for a payback under 10 years, so its all systems go for now.

Relentless Self-Promotion Bit

Hey did you catch my recent video? I did a bit of off-road driving a couple of weekends ago. I’d love some more subscribers to my YouTube channel, so I can make more videos of things relating to solar panels and my own interests.


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:

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*

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.

South Australian Storms

I’ll keep this pretty short, because the South Australian Storms are consuming a lot of media attention at the moment. This article is a bit of a linkstorm, because people have said most of this more eloquently than I could.

You can pretty much sum up the situation with this tweet:

The state of South Australia here has been hit by what is being described as a 50 year storm. The damage you see in the picture above has contributed to the entire state losing power.

As this article explains, tornadoes brought down critical infrastructure, and the network was brought down as a safety measure. Note that tornadoes aren’t a very common occurrence in Australia.

South Australia is connected to the state of Victoria for power sharing, as part of the South East grid. If the interconnector stayed up, and started demanding power from Victoria, it had knock-on implications for the whole grid.

The Good

Despite the magnitude of the disaster, there are some silver linings to the South Australian storms.

It puts battery storage at the forefront of maintaining a decentralised power supply. One household had their Powerwall running the house until power came back, thanks to Natural Solar.

Reposit Power also had a customer request for power, in preparation for the storm. Why not use the grid import facility of Reposit to grab power before the storm hits? That way, even threats to infrastructure won’t hurt the average household.

While most people can see themselves getting a battery in blackout hotspots, most would never have considered the magnitude of such an event.

Though, in fairness, I suppose most people haven’t seen a storm this big.

The Bad

Of course, it didn’t take some peanuts long to have a crack at the high percentage of renewable energy in South Australia. The state closed its last coal-fired power station a few weeks ago. It has been a nonstop bunfight since.

Renew Economy covered the primary points of attack relating to the South Australian storms. The coal lobby is really bricking it over renewables, and that’s no shock as more coal power stations are going to close.

It is surprising that someone would try to pin this on renewable energy. Particularly as the energy mix played zero part in the problem.

Another good read was from Ketan Joshi, who ran through the speed of truth versus the speed of emotion. Misinformation gets a Tesla Model S, it would appear, while Science gets a bicycle…

The banner image for both articles was this unmitigated rubbish:

The Ugly

It really boils my piss to see this kind of thing go down. You’d think no-one in recorded history had ever had a blackout before. Or that, in some wild universe, humanity has never seen a storm of this scale until solar panels were invented.

Correlation does not imply causation. Maybe some of these idiots should learn something about that.

We’ve got a state suffering the effects of one of the biggest storms in living memory, and people are playing politics, as South Australian Premier Jay Weatherill states so well.

Stay safe, South Australians. Hope you’re back on your feet soon.

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.

Energy Networks Conference

While I was in Melbourne last month, the guys at Reposit Power contacted me to see if I was interested in attending Energy Networks 2016.

Energy Networks 2016

This is a conference for Energy Networks Australia, whose members make up the industry responsible for building and maintaining the poles, wires, pipes, substations, and other media for distribution of electricity and gas services.

“Oh you mean those guys who send me the damn bills every month?!!”

Well, no. That is your retailer and its important to understand the difference. The AER (Australian Energy Regulator) website describes the distribution networks clearly:

Electricity and natural gas distributors own and maintain the distribution networks, including electricity powerlines and power poles, and natural gas pipelines that carry electricity and natural gas to houses and businesses.

Your retailer is the company with the relationship to you. The Distributor – usually referred to as the Network – is the company building and maintaining the hardware.

My electricity retailer is Diamond Energy. I have an agreement with them whereby I pay for electricity usage in my house, including an agreed price per kWh and daily connection, as well as my feed in tariff (FiT) for exporting solar power. If I have any questions over my billing or service, I go to Diamond.

Diamond Energy sell their product to me via a network owned and maintained by Endeavour Energy (the Network or Distributor), who are responsible to ensure the network is up and running. If there is an outage, Diamond talk to Endeavour about resolution, and feed information to me.

The Network is focused on a working system, and the Retailer is focused on a happy customer. Classic, two-layered B2B (Business To Business) situation, operating in parallel with a B2C (Business To Customer) relationship.

On to Energy Networks 2016

I decided it would be pretty cool to take a few days off work, and go see how the big end of town do things. Trains, planes, and automobiles later, I was in Adelaide.

OK,  its DISCLAIMER time: Yes, I was there as a guest of Reposit. No, I was not under any instructions to say certain things or do certain things. You can believe what you wish in that regard, and you probably will!

All I know is I’ve seen the technology at work, and it is good.

While wandering around the displays, I saw a lot of people who are high up in the industry domestically, such as CEOs and COOs and other positions with abbreviations starting in “C”.

There were also overseas players like Enphase CEO Paul Nahi, who was in town to get a look at the scene, and back up their announcements about working in Australia.

Our nation is gunning for a leading role in battery implementation, to go with its solar PV penetration rate. If only our governments would see this and pull their finger out …

Of course, a few ruffians were about the joint like Giles Parkinson and Finn Peacock, to report on proceedings and relay the vibe.

It was slightly unusual that Reposit were bringing a customer to see the Networks, without a Retailer necessarily being in the way. The reasons why are down to what Reposit is offering to all layers of the market.

I discussed the ins and outs of Reposit in a previous post, mainly from my own point of view, alluding to the advantages an on-grid battery can offer everybody in terms of an available power resource.

An Important Step

Things just got real in light of an announcement made last week by SA Power Networks (SAPN), the Network Distributor for South Australia.

They will be engaging 100 households in a Residential Battery Storage Trial in the Salisbury area, in the northern suburbs of Adelaide.

This is huge for customers, as they will benefit from installation of a subsidised system with either a Tesla Powerwall or Samsung ESS battery. Lower bills are practically guaranteed.

It gives the Network an unparalleled look at how battery technology can smooth peaks and troughs, and give them on-call resources in addition to existing generation. It may also help reduce network implementation and maintenance costs.

The smarts at the centre of systems installed? Reposit.

Bringing The Tech

Energy Networks

That’s Dean Spaccavento, one of the founders of Reposit, being interviewed at the stand on Thursday. Good hustle!

In that shot, you can see a Macbook, which is running a live demonstration of the Reposit Marketplace application. This allowed networks to understand the capabilities Reposit from the back end, including the virtual power station concept.

The consumer end was demonstrated with a new iOS app, and as this involved dispatching power from my Powerwall, I made a couple of dollarydoos over the course of two days, which was a nice little bonus.

Together, the applications aptly demonstrated solving the problem for the network, and bringing the user into the circle of trust.

Along with a detailed rundown on how the Reposit Box makes decisions on behalf of the consumer, it provided a really good look at not only how the products work in theory, but how they were going to be applied for the SAPN trial. It is a very tasty thing to get a feel for it, while knowing a real-world scenario available for analysis over the coming months.

In addition to the Reposit team talking about technical aspects of the system, I personally fielded questions about where I sat as a consumer.

Understanding The Customer

For networks, the experience of battery users to date has tended toward those who want to get off the grid altogether, for two primary reasons:

The lifestyle consumer wishes to live in a location the grid can’t service today, typically in a rural area where land is cheaper. The capital cost of extending poles and wires can be prohibitive, so a battery system is often a better option, financially. At the same time, these people seek to build an efficient house, investing up front to ensure ongoing costs are minimal.

The combative consumer no longer wishes to pay for what they see as extortion from either the network, retailer, regulator, or government. Sometimes a combination of two or more. They tend to be older, cashed up, and technically minded. They’re ready to leave the grid at the drop of a hat, regardless of where they’re located.

In both cases, it is a very small percentage of households who can afford to take the option of off-grid living. Most of us don’t have money for enough batteries and solar panels to get us through a week of wet weather, and can’t even fathom being away from the safety of the grid.

Energy NetworksNow, with the advent of smaller lithium storage tech, the networks and retailers are going to need to deal with a third type of consumer: the grid-connected battery user.

How to address this?

I suppose, after talking to a few people from the industry, some of whom alluded to specific service issues they were having in their backyard, the message I want to broadcast as a user is: don’t panic!

We Don’t Have Horns

A lot of us like having electricity that is reliable, safe, and affordable. While some might complain about their electricity bill, the fact is electricity still isn’t the biggest cost factor in a lot of households.

We’re not all about to up and leave the grid because Elon Musk mentioned it was a possibility. In a lot of cases, it still isn’t financially practical.

I spent a fair bit of money and solar + storage, and still have days where I run out of battery, or don’t fill it up. So I need the grid, because I don’t want to leave my family stranded. I also need fresh water connection and gas to cook with. This is all part of modern living.

What we want, as consumers, is to be treated fairly when it comes to giving you access to resources that we paid for. After all, it is what you expect in return for your resourcing of the grid.

Mistakes were made when it came to some of the early gross tariffs. Uptake of systems with a FiT of 40 cents / kWh or higher were higher than expected, probably due to poor planning.

That doesn’t mean the users contributing their exports outside those schemes should be given a rate approaching 50% of off-peak, either. It wasn’t our fault the government got a bit trigger-happy and / or gun shy about solar systems back in the 2000s.

Potential Solution

I don’t really have a problem with solar export being paid at rate smaller than the single-rate import tariff. And I realise a lynch mob will be after me for saying that.

It comes down to simple economics: as you can’t guarantee supply of solar from rooftop panels, you can’t expect to charge the same as a guaranteed supply from the grid. That said, 5c / kWh is bloody ordinary.

It might not matter for much longer, because batteries change this dynamic – I absolutely can guarantee the delivery of power from my battery.

It is stored, often idle, and usually ready to go during the day by 1PM, with about 6kWh to deliver outbound. Get hold of another 100-200 users with varying battery types, and that might be a Megawatt or more, to help you fill a hole.

Particularly with Reposit managing my usage, I’m confident that most days I’ll be available for you, provided I’m going to get fair recompense for use of my resources. After all, if you come to me, chances are its cheaper than going somewhere else.

I can see a point in the future where solar feed-in-tariffs are no longer used, because it will so be advantageous to own a battery and keep a steady stream of electrons moving through it, rather than from the panels. Retailers will run to this solution, and networks will benefit.

Its just a question of how the reward will be calculated.

Getting To Know You

The first step for any Network stepping into this brave new world might be a tighter relationship with Retailers, and disseminating information you have on where the industry is headed with batteries. In turn, they can share with you their experiences, and what they’re seeing out in customer land.

Together, you can get schemes like GridCredits moving, with early intervention to prevent another financial blowout like Gross Tariffs. Can’t leave these things to the government, based on experience so far.

Will you look to have a flat rate like Diamond Energy’s GridCredits 100 scheme? Can you leverage your existing market spot rate calculations to flow through to users or chip a little bit of profit off that? Those are big money questions that this IT guy doesn’t have answers to. Its a work-on for you and the rest of the industry.

It might even be that you need to provide information on the practical costs of peak demand to the consumer base, in order to give users a view that goes beyond a perception of simple greed.

Of course, there are some people you’ll never convince otherwise 🙂

You’re still unlikely to see mass defections from the grid, but as the price of batteries drops, certainly more people are going to investigate the outlay to do so.

Increase in batteries and PV is going to see a decrease in grid usage against projected growth, which is already softening on a per-capita basis. This might affect profitability, particularly where a network needs to be extended to reach a growing population.
Power Consumption Per Capita in Australia Credit: Trading Economics (click image for link)

One of the facets of SAPN’s trial is to look at mitigating network capital costs by using the network resource that is user batteries. I’d be paying close attention to that, particularly where you are responsible for remote networks that require backup diesel generators etc.

How To Engage Consumers?

This is the multi-billion dollar question. As you may have surmised, I’m quite engaged.

Since this whole Powerwall thing landed in my lap, I’ve made it almost my second job to know everything I can know about how to most efficiently use the resources I have.

In this, I’ve been helped by companies like Natural Solar and Reposit Power, and I consider myself reasonably well-informed as a result of their input.

I follow sites like Renew Economy and filter their comments section to see where users are. Once you chop out the mad hatters, its very interesting to see where other consumers sit.

The rest of your customer base are probably going to tail away from that in terms of knowledge, right down to those who don’t understand the difference between Network and Retailer. They need help.

There is a wealth of data there, in terms of human feedback, that you – and the Retailers – need a relationship with. It will serve you well in the long term.

I shall sign off by imagining myself back in a trendy bar in an Adelaide laneway, hoping everyone looks forward to this bright new battery future as much as I do.


P.S. In terms of awesomeness: besides Reposit, the guys from Redstack have to rate right up there. Their UAV with 3D-printed parts was totally rad. WANT.

Reposit Power and the Microgrid

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:

Reposit Power
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 days

0700-2200 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.

Yeah, baby…

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.

As I touched on in my post about Nuclear Power, 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…