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.
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.
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.
For reference, the figures are in the table below for the three months with suitable data.
* 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.
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!
So here’s a scatter gun approach to energy blogging:
Part 1 of this is a scam warning. A group listed “50% OFF!” specials for LG panels and LGChem batteries here recently. One example:
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.
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.
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…
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.
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.
That is what I paid for electricity over the 350 days of billing I have since the Powerwall was installed, and my electricity provider changed over.
This is important to note, as the two weeks up to change of provider meant I wasn’t getting any export benefits from my solar panels. Mugged!
The saving is over the $2000 mark, but for the sake of round numbers, let’s call it $2000.
To put in perspective what money means to my family: our recent road trip, to central and southern NSW, cost almost exactly that. Essentially, I got my little summer break for free.
Facts And Figures
According to the billing received by Diamond Energy over the 350 day period:
Import total was 1349.830kWh (or 3.857kWh / day)
Export total was 3807.403kWh (or 10.878kWh / day)
Not quite the 1:3 ratio I was looking for, but that figure is probably no longer simple to calculate, which I’ll explain below.
From the SolarEdge web portal, I have the following factoids:
Lifetime energy: 9.1MWh
CO2 emissions saved: ~3400kg
Equivalent trees planted: 11
Light bulbs powered for a day: ~26,200
That is kind of the feelgood stuff, despite the Powerwall not necessarily being “green” as people might imagine.
As with anything, there is a carbon cost associated with production. The early iterations of any battery product are going to be a little bit on the dirty side.
As one example: Lithium ore needs to be shipped from the mine to the refining facility. The refined lithium is then shipped to the cell production facility, which may or may not need shipping to the final place the Powerwall was built.
Tesla are addressing this with “vertical integration” of production, particularly for their cars, but also batteries in general. This means more processes can be done at one site, reducing shipping costs (and therefore carbon c0st) of transporting components.
Other Factors Considered
Keen observers will remember that in October I got more solar panels. That took my total system size to 6.5kW of panels. I just heard a bunch of critics trumpet “AHA!” but keep in mind, I still only have a 5kW inverter.
Therefore the maximum power I can generate is limited to 5kW, though the peak time lasts a bit longer on a sunny day.
It is hard to quantify what effect this has on the system, beyond saying “there is more solar capacity”. As the new panels are oriented WSW they’re not always going to be ruling the roost in terms of efficiency.
Its also a smaller factor than it otherwise would be, having been installed four months out of the year. Granted, they were the sunnier months.
Another consideration is my move to Time Of Use tariffs in the first week of August. This has an effect on two areas of my billing.
If I’m smart enough to “game” the tariffs, and avoid doing anything during peak time, I can save a lot. Unfortunately peak time coincides with oven and air conditioner use, so that’s not always possible.
The billing and the import numbers above will be affected by Reposit Power managing tariff arbitrage. When I import power now, it might be a result of my needs being bigger than the system output, the battery being empty, or because Reposit sees a cloudy day and wants to import some at a cheaper rate.
Putting together the new panels and move to TOU, a better time to revisit this might be October this year. That way, I’d have a true idea of what I can really save with all components working together.
The Vagaries Of Billing
Those out for a bargain will know to shop around with their electricity companies, and see how best to maximise their savings.
Whether that is through generous sign-up rebates, or big discounts for paying on time or via direct debit. It all adds up, and people without solar or batteries can benefit if they do their research.
As I pay such low amounts anyway, discounts don’t add up to much. Pay-on-time discount across the year was $20, and paying by Direct Debit discount was $17.62.
The bigger benefit was referring people on to Diamond Energy, which netted me $105 across the year. Against that, I paid $22 (inc GST) application fee with Diamond, so the benefit was more like $83.
If we add that $83 back onto the billing, it goes from 50 cents per day to 75 cents per day.
I pay about $1 a day to connect to the electricity network, so its still good. There are even a few dollars in GridCredits unaccounted for at this point.
Year Of The Powerwall
When I say “Year Of The Powerwall” I’m not speaking only to the year I’ve had. This year, 2017, marks the landing of Powerwall version 2 in Australia, and overseas.
I’ll level with you: I haven’t really spoken much about PW2 since the launch, because I’m still experiencing some angst.
I thought I’d done OK with my battery, then in the same year, Tesla brings out one TWICE as good.
C’mon Elon… I thought we were mates!
Overall though, this is a good thing. I think we’re about to see the domestic battery market kick off in 2017, with Tesla in front. That is quite amazing, given the prediction was market maturation in 2020. We’re three years ahead!
Talking to a few people getting quotes and installing them, right now there are very few people price-competitive per kWh.
As the manufacturers in Korea and China start their own uplift via vertical integration, prices are going to keep sliding, and competition increase.
This can only be a good thing for the consumer, for the grid, and for energy security and stability moving forward.
And any consumer who is getting a Powerwall 2: I think a zero electricity bill is well within reach.
If you factored in selling power back to the Grid out of the battery, which I think will replace solar feed-in tariffs eventually, you could even turn a small profit.
As always, user experience may vary. Its up to you to make the most out of your investment.
As I wrote earlier in the month, we have had some heat wave conditions here in Sydney, with outside temperatures getting into the high 40s (120oF). That was kind of insane, but it kicked off some GridCredits for me, which is also a good thing.
As we’re moving toward more extreme weather events, having a flexible and robust grid, with user storage available for emergencies, will be important.
As we sit here in a rare Sydney heatwave, I decided to blog. Its all I have the energy for.
Temperatures today are predicted to reach 46oC today. That is 115oF for those of you with funny thermometers. Sydney is supposed to hit a record February day, in fact.
As the temperatures rise, the standard position for most people is to turn on their air conditioner and shut all the windows. And that is great; electricity can often be the most efficient way to cool space.
The problem is the load it puts on the grid, and the possibility of blackouts in many areas, as people ramp up power usage in heatwave conditions.
The kicker: Australia has more than enough generation capacity to cover its needs. This overcapacity is only useful when the market operates correctly though, as this video shows.
* That is a really good article by Lenore Taylor above. Stop and read it. Give her a follow.
The good news is: consumers can help save it.
Combating the Heatwave
Normally you’d expect me to go on a rant here about Reposit Power and how microgrids are going to save the world.
The problem is that we’re continuing to consume high amounts of electricity to keep comfortable. If the heatwave conditions continue due to climate change, consuming even more won’t help – it will just make us hotter!
We’re stuck with fossil fuels for now, even while renewable technologies like solar, wind, and storage ramp up. In Australia at least, they’re going to be the majority of power sources until at 2025. Maybe longer.
As we’ve seen from The Guardian video above, the market can be “gamed” by generators, to help drive prices up. Even if you got a million Reposit Power boxes controlling 10MWh of storage, you’re not going to redress a balance of GIGA watts.
Part of the solution has to be a way to use less power. Therefore, instead of microgrids saving the world, I’m going to talk about something far simpler. Many countries in the world already practice it, but for many and varied reasons, Australia doesn’t.
Its a topic that is not nearly as sexy as GridCredits, but in Australia, its probably more important than ever. Let’s start with a quick diagram:
While that is a gross simplification, the basic truth is there:
Inefficient houses are built a lot here (and at high density)
They need more power to keep themselves cool or warm
This needs more power from (majority) fossil fuels
That makes more profit for electricity companies*
* It should also be noted that it means more (moar) profits for home builders, because the materials for less-efficient houses are correspondingly cheaper.
Its a vicious cycle, and its particularly ridiculous in places like Sydney where land is expensive to buy but houses are cheap to build. And once they’re built, they grow in value (but not efficiency) almost overnight.
I understand this because I bought a house three years ago and watched it increase in price 25% in that time. And it isn’t any more efficient today than it was the day I got it.
Except the pool pump I replaced, but that is another (angry) story.
Consumers Will Consume
Nobody wants to spend any more money than they have to on building their home. I dig that.
I lived in a house with two reverse-cycle split A/C systems for years, and always wish I had ducted.
When I got my new house, it had ducted. And the electricity bills were much bigger. But I didn’t put all of that down to the A/C – it was part of the issue, sure, but I had a bigger house with a few more TVs. Yeah, that must be it.
Now that I have the data on what it costs to run, I’m appalled, and looking for alternatives.
The first part was solar PV and a battery system. That has helped slice my electricity bill into tiny little pieces (blog coming soon on that).
To take it to the next step, I’m going to look at making my house more efficient. As I wrote back in March 2016, there are weak points in my house that need looking at.
Those windows on the west side of the house are next on the list, and I’m getting quotes for double-glazing and glass film technologies as we speak.
Advice For The Home Builder
If you’re building a home at the moment – or even renovating – I’ve got some advice for you, on how you can help with this heatwave situation. This covers both your personal comfort levels, and your contribution to the environment.
Look into designing your house right. Make sure you’ve got decent eaves. Windows that aren’t monstrously oversized. Understand the quality of the wall and ceiling insulation and MAKE SURE it covers the garage; many builders don’t insulate the garage, so its a massive heat collector, and can radiate through internal walls.
DOUBLE-GLAZING. Adds to the initial cost of construction, but will reduce your energy costs by 25-50% depending on aspect.
Get the Air Conditioner you NEED. Don’t just get the biggest one or look at the cheapest price. With the weather warming in Australia, you need to be sure that your A/C is smart. Make sure it is an inverter, and don’t worry about the slightly higher initial cost. It will pay for itself in efficiency measures, while electricity prices continue to rise.
If you find its not enough, then installing a small split system in a particularly bad area of the house can be done later. If you buy the big unit, you’re stuck with it for good.
Also, don’t be that guy who sets it to 21C appropriate. Your house should never really need to go below about 25C to stay comfortable if the thermostat is set up correctly, in the right location. This will save you thousands in electricity costs over the lifetime of the system.
Use ceiling fans and portable fans tactically, to keep air moving around your house. This is also part of using the 25C rule. If the air is moving, it often feels cooler, and the cost to run one is minimal.
The last measure you can do is speak to your local member about raising building efficiency standards in Australia.
At least it wasn’t peak pricing that day, being a weekend… Small mercies.
In addition to the anniversary, I’m also due to receive a bill from Diamond Energy, which will cover November through to January.
Putting in a guess right now: I’m going to say about $1.20 a day, excluding referrals. Similar to Winter, but with a bit of a discount for better export. That would be a bill of around $110 for the 92 day period.
Summer has definitely had an affect on the system, in terms of import requirements. As I mused back in December, summer would require more import, despite having more sunshine to work with.
Part of the reason is electricity consumption; on the whole, I am using more energy due to cooling and things like the pool pump.
The air conditioner is variable, depending on ambient temperature, and required comfort level. Short of replacing the thing, I’m stuck with needing the grid during summer.
How you handle your pool pump usage is up to individual circumstance. My pump has a flow rating of approximately 19,000 Litres per hour, and a pool of 31,000L capacity. I have a cover on it all winter, except for monthly maintenance, and no trees or other debris issues around the pool itself.
Therefore, in winter I’ll run it for around 90 minutes per day which should turn the capacity over about once. With appropriate chemical balancing, that keeps it clean.
In summer, I’ll vary it a little. During summer peak – where we use it a lot – the run will be 6 hours, timed for peak sun. At shoulder times I’ll start to move toward 4 hours, as we’re not using it as much.
The idea is to let the filter work as hard as it needs to, while retaining good chemistry and clarity in the pool.
Capacity and Usability
Happy to report that the Powerwall is still reporting its full 6.4kWh capacity, same as Day 1 of the system.
The extreme heat over summer also didn’t trouble the liquid-cooled unit. The Powerwall is rated to 50oC, unlike many of its competitors, so even an Australian summer can’t dent it.
Unless you’re crazy enough to put the thing outside. In the sun.
What I did notice was the rest of the system struggling to get to full capacity. With a total of 6.5kW of panels on the house, I didn’t always reach the 5kW capacity of the inverter.
Part of that is the panels getting hotter than their efficiency peak of 250C, and part of it is the inverter starting to feel a bit of heat stroke. Even in the shade, on the south side of my house, it gets bleeping warm.
Back in October I was hitting some sweet numbers, but the ambient temperatures were down in that 25 degree range. Everything performs better when its cool.
As the year has worn on, I’ve slowly weaned myself off frantic chart analysis. Its a bit of a pragmatic move, as constantly worrying about my ROI was a bit stressful.
While it was important to keep an eye on the system, I’m moving into a stage where I need to look at the future path, not just the past performance.
That means I’ll be presenting more ideas-based blog here, and there is plenty to write about.
Tesla Energy released the Powerwall 2, which I’ve avoided talking about due to extreme jealousy and consumer cognitive dissonance.
Accompanying that is solar rooftop, which I’ll talk about in a future post.
World-shaping events like Brexit and the election of Donald Trump are key political events. They have the potential to shape energy policy for years to come.
There are also ideas I’d like to explore in terms of other energy sources. That will lead into producing educational content that I can distribute, through various media.
I’m also aiming to put up more on my YouTube channel, for which I’d appreciate a “Subscribe” if you’re so inclined. Which I’ll try to fit in around the blog itself, work, family, and running a Rugby Club!
It has been a very interesting journey to get here. It wouldn’t be possible without the generosity of time and patience of the following organisations:
As scientific bodies continue to explore and model the effects of climate change, the technologists, disruptors, and entrepreneurs are seeking ways to combat it. The use of renewable power in the form of wind and solar is one of the key areas.
However, a valid criticism of renewable energy is stability: if the sun doesn’t shine, and the wind doesn’t blow, solar and wind are in under-supply. If the sun DOES shine brightly and the wind picks up, the renewable energy grid produces oversupply.
This situation is prominent in the California “Duck Curve”. The belly of the duck is over-generation from solar, while the head of the duck is the consumption ramp for night-time domestic use.
As domestic and commercial solar uptake increases across the world, there is a genuine risk to existing grids. Trying to address this issue alongside a mix of traditional power generation is difficult. Large, traditional generators cannot uplift generation, or halt it, at short notice.
I believe the natural solution is widespread adoption of storage technology.
Domestic storage will mature rapidly over the next 5 years, as household battery options become cheaper, due to vertical integration of the production process. This will be particularly true in established Western housing markets, particularly those dwellings with rooftop solar options.
It also enables the concept of virtual power plants for retailers to access power stored in domestic appliances. In the future, consumers will engage in peer-to-peer trading via blockchain and other smart technologies. The net result is to lower the need for a traditional “grid” and the associated maintenance for poles and wires.
Industrial storage will see positive disruption to hi-tech engineering solutions, using renewable generation. Efficiency has a large role to play here, as innovation across multiple sectors leads to better production engineering.
The volatility of frequency required for running many heavy industries can be offset with larger scale storage. These battery systems act like a buffer, or regulator, in order to provide assurance of stability. Large storage can also be deployed by energy networks in order to back up local power infrastructure.
Transport storage is a key area for addressing carbon emissions. While cars are the major playground for this technology right now, the move to heavy transport, agriculture, and public transport offers a range of other benefits.
I call it “Transport storage” because it offers more than just a way to move people or goods from one place to another. There is the opportunity to place domestic, industrial, and transport storage in synch, to produce a more efficient outcome for renewable energy.
Consider the California Duck Curve I mentioned before. This is the result of “too much of a good thing” when we have an over-abundance of solar PV! What if there was a way to mitigate this?
The average shopping mall in most countries has a roof space in the hundreds of square metres. They also contain hundreds, if not thousands, of car spaces.
If we add solar panels on that roof space, and storage in the basement, we can effectively create a curve smoothing apparatus by plugging in a suitable number of EVs during daylight hours. A similar system could be used by places of work for the benefit of employees.
Such a system would draw not only from the local (mall rooftop) power, but also spill excess renewable energy into recharging the transport network in other places. This might take the form of powering connected public transport – like electric buses or trains – on site, or via the grid.
All the while, this large-scale storage and renewable generation helps flatten the belly of the duck during the day. When people return to their homes at night, they can cut the head off the duck using their domestic storage.
Storage, along with the associated smart management technologies, provides the cornerstone for a renewable energy future. The combination of increased efficiency, and reduction of fossil fuel burning, is undeniable.
Of course, its not all gravy, with this last week in December producing two extremely hot days above 36oC (~97oF), followed by two days of rain. The former item consumed a lot of air conditioning, while the latter didn’t generate a lot of PV energy.
I’d love to have a Powerwall 2 to ride all that out! But I make do with having a grid connection.
The new panels were $1320 including GST. That takes the total system cost to about $18k at this stage, now including 6.5kW of PV, inverter, Powerwall, and Reposit.
That is an increase of roughly 8% over the original cost.
Generation capacity has increased by 1.5kW / 5kW = 30%.
That figure is a bit fuzzy because the existing panels don’t face the same direction as the recent additions. Also, the inverter I have is limited to 5kW of throughput. So chances are I won’t use all of that capacity across the year. Let’s call it 20% as a “real” figure.
Regardless, the main point is looking at the cost increase over the capacity increase. Extra funding of 8% has allowed my system to gear up by a potential 20-30% in terms of generation.
This shows what anyone experienced with solar will tell you: panels are cheap. Get as many as you can, with the biggest inverter possible.
As I mentioned in my last blog post, I now have data on finalised billing to cover about 70% of the year.
It shows my electricity cost – including daily connection fees – at roughly 71 cents per day.
Summer is yet to be added to this data set. Like winter, the primary environmental control (my ducted air conditioner) will get usage. I also have a pool pump that runs more in summer than winter.
Looking at historical bills, I tend to use about 3% more in Summer than Winter. Whether that still holds true depends on a lot of factors, particularly seasonal variance. Maybe we had a warm winter last year? I can’t remember.
This may not be significant in the face of increased solar generation:
Self-consumption can increase with longer daylight hours
Export can increase with higher generation capacity
Taking a Stab At It
Alright, so putting my analytical neck on a chopping block, here is what I think will happen.
Disclaimer: I am cheating a little in that I have data from Reposit Power to guide me on the days I know about since the last bill. To balance that out, not all my billing days were time-of-use (was on single-rate until August), so I’m flying blind in other ways.
As I’m writing this, I have realised just how many moving parts there are! This is going to be tricky, so let’s start with actual data.
Looking at the Statistics page of the site, fed by SolarEdge API, I can see my lifetime system statistics. All of which is very interesting to look at, but only two matter; import versus export.
These two factors are Summer in a nutshell. Increased import, possible reduced export. The daily average covers each day in the last week (up to 16th December, inclusive).
If we add the 3% increase I am predicting for summer from my historical billing, it doesn’t change the import much. The lifetime import has only been around 3kWh per day, so 5.47kWh per day represents an increase of 2.5kWh.
With peak tariff, this could be as high as 90 cents per day! Shoulder rate and offpeak rate make it 69 cents and 35 cents respectively.
I also need to factor in that Reposit Power imported a few offpeak kWh on Friday morning, so will call the extra import 2kWh per day. I’ll use the peak tariff rate to established increased costs of 75 cents per day.
On the flipside, I don’t think the 9kWh export figure is accurate due to the amount of cloud we had over the two days. The lifetime average is about 11kWh. To this, we add the 20% of our extra generation capacity to arrive at 13kWh per day.
“Wait a second!”, I hear you cry, “you’ve already had those extra panels on for a couple of months!”
Yes, I agree. However, we’re now hitting peak summer, so given my 20% figure was a fuzzy projection, based on 30% increase in capacity being the limit, I think it still works.
Again, looking at the statistics, you can see the 28-day retrospective is 13.92kWh. So I’m sticking with about 13kWh per day, keeping in mind I’ll be self-consuming a bit more than usual with the pool pump running.
An extra 2kWh per day exported is 16 cents in reduced costs.
Combine the two of those, and we had 75 – 16 = 59 cents per day.
This is extra, over the historical average of 71 cents per day. This brings us up to $1.30 per day for the summer bill.
Remember, I proposed a 3% increase of Summer over Winter, based on historical billing. The “Winter” bill I received back in September was $1.27 per day.
If you add 3% to that, you come out at $1.31 per day, so I’ll be keen to see if I get that close to my estimate of $1.30.
But What About Payback Time?
Very good question. I’ve just added $1320 capital cost to the system, and spent the last couple of hundred words speaking about Summer only.
Using the summer figure I calculated above, and wrapping that up into the billing I’ve received, puts the annual cost of electricity at my house around $310 as I’ve stated previously.
That is a saving of roughly $2k per annum over my old billing from last year. With the system cost now at $18k, that is a 9 year payback on simple calculations.
However, Autumn and Spring are the counterpoint to the Summer and Winter electricity burn for cooling/heating. Those times of year need to be exploited.
If my exports climb by 20% for both those seasonal bills, then the gains per year could be quite gratifying.
The two bills I have for these periods work out to 59 cents per day (March-June using single-rate tariff), and 24 cents per day (August-October on time-of-use).
The other key factor was full operation of Reposit Power with TOU tariffs, with is another massive advantage along with GridCredits. I can import very cheap power for anticipated poor days of PV generation.
Along with the extra generation capacity of my new panels, this shunted the power per day figure down by nearly 60% for Spring over Autumn.
If this holds for next year, and the Autumn power bill goes down to under 25 cents per day, it will mean for half the year I’m paying $44 for electricity. For the other half (Summer and Winter) I might be paying about $240.
An annual power bill of $282 sounds a lot better than the $2300 I was paying a year ago. And shifts simple payback under 9 years, by a few months.
The addition of these panels doesn’t look like a big deal on the face of it, but I’ve been fairly conservative in a lot of estimates.
I haven’t taken into account any GridCredits I receive, or the Diamond Energy Customer Referral fees I might get. So perhaps under 8 years is possible once the whole-of-environment changes are considered.
I’d like to thank everyone who has popped in for a look at the blog this year. Thanks for the connections on Twitter as well!
It has been quite an interesting 11 months since I got the Powerwall installed, and I’ve certainly learned a lot.
I have made an effort the last few years to put up Christmas lights, and copped sunburn, cuts and scrapes doing it. But its definitely worth it for the look on the faces of the local children.
I would like to wish you and your families a safe and happy holiday season, wherever you are.
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.
The fixed costs were as follows, excluding GST, for the 84-day period.
Service connection fee
Usage over the period at the various TOU rates came to the following (all amounts are excluding GST).
Peak – Rate 1*
Peak – Balance
* 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.
Net feed-in tariff
Direct Debit Discount
Pay on Time Discount*
* 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
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.
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.
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.
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.
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.
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.
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.
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!
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.
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!
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.
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.
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.
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.