Victoria’s New Time Varying Solar Feed-In Tariff Is Worth Getting

Victoria Time Varying Solar Feed-In Tariff

As of 1 July 2018 there is a new, optional, feed-in-tariff in Victoria that changes through the day.

A new type of solar feed-in tariff is now available in Victoria.  It’s called a time varying tariff and the amount of money it pays for solar electricity depends on the time of day it’s sent into the grid.  It is worth less during off-peak periods, more during shoulder periods, and the most during peak periods.

Before anyone feels stressed, panics, or starts firing guns into the air, I’ll point out this change is entirely voluntary and it’s not even clear at the moment which electricity retailers will be offering it as an option.  If you are not interested you are free to stick with the single rate tariff that pays the same amount for every kilowatt-hour exported to the grid.  But if you have a choice, I say you should get the time varying tariff.  I’ll explain why in this article.  Eventually.  But first I have to give you a few paragraphs of filler.

Feed-In Tariffs Heading Down

Solar feed-in tariffs are on their way down across Australia thanks to lower wholesale electricity prices, mainly due to increasing renewable generating capacity including rooftop solar.  This is something I wrote about a while back.  Victoria’s minimum single rate feed-in tariff, which is unique in Australia because it takes more into account than just the cost of generating and distributing electricity, dropped from 11.3 cents to 9.9 cents on Sunday.  That’s a fall of 12%.  But the good news is, if you can get the time varying tariff it should average over 10.3 cents per kilowatt-hour and may average higher than the old 11.3 cent tariff.

Time Varying Feed-In Tariff Rates

In order to show you what the time varying rates will be I have stolen this table from Victoria’s Essential Services Commission:

Image: ESC

The off-peak rate isn’t that great at only 7.1 cents, but it only applies before 7am and the amount of solar electricity that will be exported before then won’t be much.  In Melbourne the sun doesn’t even rise until after 7:00am from the start of May till past the middle of August.

The bulk of exported solar electricity will receive the shoulder rate of 10.3 cents, while some will get the impressive peak rate of 29 cents on weekdays after 3:00 pm.  Since this is clearly better than the 9.9 cents of single rate tariff, the time varying tariff is the best choice for Victorian solar households.  A possible exception is if all your solar panels are on a ridiculously steep section of east facing roof.

These are minimum rates and electricity retailers could offer more if they wanted to.  But so far the largest electricity retailers in Victoria have only offered the minimum rate, so I’ll assume that’s what households are being paid for the rest of the article.

An important note about the time periods in the table above is they are in Australian Eastern Standard Time (AEST) and don’t change with daylight savings — just to make things a little more confusing1.

A Graph Of Solar Electricity Output

Here is a graph I stole from the Australian Photovoltaic Institute and then defaced.  It shows the output of Victorian rooftop solar systems on a clear day close to the autumn equinox, which is when day and night are of equal length.  I have coloured in the off-peak period before 7:00 am and the weekday peak period after 3:00 pm and altered the times to AEST:

Solar Electricity Output Graph

As you can see, on this day the off-peak energy produced is puny, while a reasonable amount of peak energy is provided; but because the peak period is only available on weekdays the average won’t be as good.

Melbourne Estimates

I am going to attempt to estimate the average amount of solar energy that will be generated during the different payment periods for a Melbourne household.  I am not going to very precise because I don’t have the detailed information required to do that.  But my estimates should be close enough to see whether or not getting a time varying tariff is a good idea.

I am using Melbourne because that’s where three quarters of Victorians live.   If you are not in Melbourne, the figures I give should still be approximately correct because you can’t get that far from Melbourne and still be in Victoria.  After all, it is the smallest mainland state.  It’s not as if it has South Australia’s 900,000 square kilometers of radical awesomeness.

The average day length from sunup till sundown in Melbourne is 12 hours2.  This because the world is round3 and, unlike Radelaide, Melbourne is not out of this world.

If a home’s solar panels were mounted on a tracker that not only followed the sun but also magically made their output constant through the day, they would produce approximately 13% of their electricity during off-peak periods, 68% during shoulder periods, and 19% during peak periods.  But because the amount of solar electricity produced by normal fixed rooftop panels is much lower early in the morning and late in the afternoon, the portion of electrical energy produced during shoulder periods is considerably higher.

Your Electricity Consumption Will Affect Results

Your electricity consumption habits will affect how much feed-in tariff you receive.  The reason why the feed-in tariff is worth more during peak periods is because people are using more electricity then, so the chances are you will be consuming more solar electricity yourself during these times and exporting less.  If you are on a time-of-use tariff then you will be paying a high amount for electricity during peak periods, so this isn’t a problem.  But most solar households are better off with a standard tariff.

The high 29 cent per kilowatt-hour payment for solar electricity during the peak period increases the incentive for households to shift electricity consumption to before 3pm on weekdays.

Visual Aid

I was going to draw you some diagrams to display how much solar output homes produce during different payment periods.  However, I decided against it because I haven’t drawn anything since around the 14th century, which is when people who can draw better than me were invented.  Then it occurred to me that I have children.  And since I have children, I have plenty of toys hidden away where they can’t get to them.  So took my Lego out from where I hide it from my children and made this:

Melbourne house

This is exactly what the average house in Melbourne looks like.  And this…

Queensland house

…is what the average house in Queensland looks like.

North Facing Solar Panels

The daily average number of hours the sun will spend in the sky for the three pay periods is:

  • Off-Peak:  1.5 hours
  • Shoulder:  8.2 hours
  • Peak:  2.3 hours

For north facing panels the sun is only going to be at an average angle of around 11 degrees during the off-peak period.  If Sydney-siders are correct when they say Melbourne has no atmosphere, at that angle only about one eighth as much sunlight energy will hit solar panels  than at noon when the sun is directly overhead.  But assuming Melbourne does have an atmosphere, things are even worse because when the sun is low in the sky its light has to pass through more air; meaning more will be absorbed or reflected before reaching the solar panels, further reducing their output.  The only advantage is the panels will usually be cool early in the morning and so will lose little efficiency due to heat.  In total, only about 3% or less of the solar system’s average output will be produced during the off-peak period.

The shoulder period, which lasts from 7:00 am to 3:00 pm or for the rest of the day on weekends, includes the whole middle of the day which is the most productive time for solar generation.  For a north facing system almost 90% of output will occur during the shoulder period.

While the afternoon peak period lasts longer than the morning off-peak period, it is only available 5 days a week.  Also, higher temperatures in the afternoon will slightly reduce output.  This means that over the course of a year only around 8% of solar electricity is likely to be generated during the peak period.

North facing solar panels

If we ignore household self consumption of solar energy, which is likely to be higher during peak periods, then the average feed-in tariff  for north facing solar comes to around 11.7 cents.  This is better than the 9.9 cents of the minimum single rate tariff..

East Facing Panels

Panels that face east will produce more kilowatt-hours during the off-peak period and less during the peak period.  The exact amount will depend on the tilt of the east facing roof.  While there are steeper ones, most modern roofs are pitched at either 15 or 22.5 degrees.  I’ll use a figure of 20 degrees as that is reasonably close to both.  This gives the following results:

East facing solar panels

This results in an average of approximately 11 cents for the time varying tariff.  That’s considerably more than the 9.9 cents of the single tariff rate.  If a household’s self consumption of solar power is particularly high during the peak period, this can drop down towards 10 cents but will still beat the single tariff.

West Facing Solar Panels

West facing panels cut off-peak production down to nearly nothing while boosting peak production in the afternoon:

West facing solar panels

Over a year and ignoring the effects of self consumption, this should cause the time varying tariff to average around 13.1 cents.

Face West Young Panel

When installing new solar panels, it now makes economic sense to install as many panels as you can can facing west — provided you are confident you can get a time varying tariff.  In the past I would have suggested facing them north to maximize total output, especially in Melbourne where air conditioners are used much less than in other mainland states.

But, if you want the maximum environmental benefit, solar panels facing north is better as it will maximize the total amount of electricity generated and reduce fossil fuel use to a greater extent.  In Melbourne a north facing panel will generate about 12% more than an east facing panel and around 15% than a west facing one.  But you could always face the panels west and then use the extra money saved to pay for more solar capacity.

Solar Panels On West Facing Walls Can Pay

If you have a sunny section of west facing wall, the high peak period rate on a variable tariff means panels installed on that wall can pay for itself.  While panels on a west facing wall will only produce around 48% as many kilowatt-hours as north facing rooftop panels, a large portion of their output will be produced during the peak period.  Unfortunately, installing solar panels on walls isn’t necessarily easy.  But it is something people installing commercial scale solar should consider, especially for new construction, as the western side of the building could be designed to support solar panels.

It Won’t Let Batteries Pay For Themselves — But It Can Help

Time varying tariffs won’t be enough to make batteries pay for themselves.  But it can help by allowing battery systems that have more energy stored than the household will use through the rest of the night to send it into the grid in return for the high 29 cent peak rate.

Who Will Offer Time Varying Tariffs?

It’s still not clear just who will be offering time varying tariffs.  I rang the three largest electricity retailers in Australia and received the following information:

  • Origin Energy told me that while it’s not confirmed, they are unlikely to offer a time varying tariff.
  • AGL said they are likely to put together a time varying tariff plan and offer it sometime in the next few days.
  • The person I spoke to at Energy Australia said they currently did not have any information that they would offer a time varying tariff but it was a possibility.

These Are Times Of Change

While time varying tariffs give a good incentive at the moment to install west facing solar panels, as more is installed it will result in feed-in tariffs changing again.  A likely result is the peak time will start later in the day.  So while it is a good idea to take advantage of the new feed-in tariff, it’s not a good idea to rely on it always remaining the same.


  1. Or possibly less confusing.  I’m so confused I can’t tell which.
  2. This isn’t exactly correct since the atmosphere refracts light, which makes the day about 4 minutes longer.  If this worries you, please feel free to provide your own, much better, calculation in the comments.  I promise it won’t accidentally get eaten by my dog.
  3. An idea first proposed by Christopher Columbus.  Mind you, he proposed it when he traveled back in time 2,000 years to visit Pythagoras — shortly before attempting to steal all of his gold, silver, and syphilis.
About Ronald Brakels

Ronald was born more years ago than he can remember. He first became interested in environmental matters when he was four years old after the environment tried to kill him by smashing fist sized hailstones through the roof of his parents’ Toowoomba home. Swearing revenge, he began his lifelong quest to reduce the harm the environment could cause. By the time he was eight, he was already focused on using the power of the sun to stop fossil fuel emissions destabilizing the climate. But it took him about another ten years to focus on it in a way that wasn’t really stupid


  1. Hi Ronald,

    I’m with Tango Energy (formerly Pacific Hydro) and live in East Gippsland.

    Recently received a letter from them saying the following:

    Important information about your Solar Feed In Tariff

    Effective 1st July 2018, the Victorian Government’s mandated minimum Single Feed In Tariff will reduce to 9.9c/kWh. The minimum Feed In Tariff sets the minimum rate that retailers must purchase excess generated power from eligible residential and business installations, such as a solar photovoltaic system.

    The good news is Tango Energy will continue to pay your current Single Feed In Tariff of 11.3c/kWh at a rate higher than the mandated minimum.

    I will be calling them to ask about the time varying tariff.

    cheers Peter

  2. I called up Simply Energy, and the person I spoke to was totally clueless about a time-of-day variable FIT. Gauging by that, they don’t seem to have any plans any time soon to offer one.

    • Origin Energy to sent a nice polite letter advising FIT reduction to 9.9.cents from 1/7/18. No mention at all of variable Tariff. Also Ronald perhaps you could enlighten as to how the existing smart meters ( in Victoria) might record the variable FiT. The Victorian Essential Services Commission also acknowledge d concerns by industry groups about battery storage of low FIT generated power being exported to the grid during high FIT periods. Some retailers are calling it cheating already, and in Qld the practice is likely to be disallowed.

      • I don’t see a problem with existing smart meters, as they report data in 30 minute intervals. That is sufficient for the time-of-day FIT.
        As for owners of battery systems using the power stored in their batteries to export to the grid during the peak period, I don’t think that can be regarded as cheating. Firstly, depending on the round-trip efficiency of their battery systems, the real benefit of getting the higher FIT is not as good. Secondly, even at 29c/kWh, they are still probably losing money (i.e. they are getting less that the warranted cost per kWh of power delivered by their battery system). They are however doing the grid a favour by providing power at peak periods when wholesale prices can go through the roof. I haven’t done the numbers, but I suspect that they will be getting less than the wholesale rate (that needs checking). If that is the case, then they are actually doing everyone a favour, at their own expense, as they are actually losing money doing it (although their overall losses may be lower than if they didn’t do it).

        • The Victoria. Essential Services Commission has history here. The first 12 months of variable FIT is voluntary, as attested by the Retailers silence. 12 months hence they will be lobbying for further reductions. If you are planning on Solar the main incentive should be utilising what you generate….which is inherently environment friendly. There are a stack of Solar farms planned up here in NW Victoria and over the river in NSW. Electricity Retailers will dump home Solar as soon as they are allowed.

  3. Thanks Ron
    My recent searches of retailers in VIC offering time varying solar feed-in tariffs has so far come up empty. I hope someone can correct me! Being not compulsory I wonder if very few (or no) elec retailers will end up offering it.

    • Why would they… Whilst it’s voluntary…and has been reduced to 9.9 cents per KWH…. retailers will price gouge as long as they can.

  4. Out of interest, I pulled the data for 21 March this year from my inverter and calculated what the feed in was on the old 11.3c/kWh, on a flat rate of 9.9c/kWh and on the variable FIT.
    I have a 6.48kW system (5kW inverter) with the panels on East- and West-facing sections of the roof (I have no choice, that’s just the way my roof is).
    My feed in for that day was 15.73kWh shoulder, 6.739kWh peak.

    The amounts work out to:
    @11.3c/kWh: $2.54
    @9.9c/kWh: $2.22
    @variable: $3.57

    That immediately shows why retailers are so coy about offering a time-of-day FIT, as they would have to cough quite a lot more. – On the Austumn equinox a retailer would have to cough about $1 more. On a sunny summer’s day the difference would be north of $2.50. That means a customer could expect to collect another $50 or $60 (or more) in December.

    I think it will make a lot of sense for Victorian solar owners to move to retailers offering time of day variable FIT tariffs, as stand to benefit quite significantly.

    For those who may be interested, I have written a python script to pull data via the RESTful API from the Fronius Datamanager. The Fronius Datamanager stores data in 5 minute intervals. There is a goldmine of data on your Fronius inverter!

    • Hi Geoff, I’d be interested in your script, I’m assuming it will work on a Mac .
      [email protected]

      • I’ll email the script later. It should work on a Mac – it just requires Python 3.x (where x is probably about 5 or greater) and the requests library. I have just been developing on a Debian VM.
        One note: the script does require a Fronius smart meter.

    • Do you know what the peak rates you are going to be charged are.they can be as high as 45c and vary ,which you need to put in the o the equasion for variable time of day.Suppliers have all the data they need to make sure they get the benifit of cheap power whil slugging you a higher rate at peak times

  5. paul coombes says

    Thank you – book in today. It looks good and very handy – regards Paul Coombes

  6. I’m in the middle of changing from Energy Australia to Tango Energy. The distributor is Ausnet.

    After being on the phone to Energy Australia in an attempt to get a better deal for almost an hour, (most of it waiting for them to actually answer) I eventually got somebody who just offered me a bigger % ‘discount’. I asked what their rates per kWh are and they had no clue. I was passed onto the ‘retention specialist’ who also could offer nothing but a slight increase in % off but did know the rates/kWh.

    I decided to go with Tango today and was told they can only offer peak and off peak (peak being 7am to 11pm weekdays only, rest is off-peak) as that is all Ausnet pass on to them. And since I have solar panels (4kW) there is no other info available from them (Ausnet) Tangos fact sheet is TAN70754MR for details. (Google it)

    Tango are holding the 11.3c feedin for now.

    It’s high time that the Govt stepped into this whole mess and made it compulsory to state the actual rates they charge for a plan, when they advertise. And not in tiny number sin the fine print you can’e even read on the TV set.

  7. Thanks for the article, Ronald.

    My advice is to take advantage of the variable FiTs if they suit you, but I wouldn’t be designing a new system around the new FiT. The last one only lasted 12 months. They are so variable that to make design decisions around them is fraught with loses if (when) things change.

  8. Alistair says

    I’ve been looking for a time-dependent tariff for months and found nothing. But AGL Solar Savers seems to be offering a time-independent rate of 20c but with higher daily supply charge and per kWh rate than my current supplier. As usual, not a simple calculation.

  9. Hey Ronald we don’t have time of day tariffs down here in Tassie either but then we only get 3 minutes 25 seconds of sun in winter per day which helps keep the Mainlanders out. Must admit to admiration for your Lego skills – was wondering whether those houses were constructed in Finn Peacock’s time or outside working hours ? Maybe you should consider adding something into your “About Ronald Brakels” ?

    • Ronald Brakels says

      Finn hired me because of my Lego building skills. I owe my master Lego ability to my father who gave me my first real present when I was three. A stack of bricks.

  10. Doug Mason says

    Thank you for another interesting article, Ronald.

    I was keen to evaluate time-dependent FiTs as they might apply to my own domestic circumstance*, so made some calculations from my daily production and consumption data over a full year, modelled hourly.

    Using your proposed VIC time-dependent FiTs, the additional benefit (as compared with your standard VIC FiT) for my original 4kW PV, current 7kW, and arbitrary 10kW are:

    4kW: $16 p.a.
    7kW: $51 p.a.
    10kW: $90 p.a.

    For small to medium PV systems, the benefit is small compared with the major savings from self-consumption. Your point about the benefit of west-facing panels is well-taken, but inapplicable for many circumstances. As Scott says above, potential variation in FiTs makes this type of financial calculation unreliable into the future.

    *: Conditions
    Location: Greenhill, SA
    Total consumption = 5420 kWh p.a.
    PV orientation = 035°
    PV tilt = 18°
    Hourly modelling based on Chris Cooper, 7 May 2015 (
    Modelling verification: Modelled hourly results for grid usage are +1.5% compared with summed daily data over the year.

    • A 10kW system, with 5420kWh/year consumption, would export something in the vicinity of 10,000kWh over the course of the year. If this was all in the shoulder period you’d be $400 ahead over the course of the year, so you’ve either made a mistake or you’re expecting a lot of generation before 7am.

      • Doug Mason says

        “A 10kW system, with 5420kWh/year consumption, would export something in the vicinity of 10,000kWh over the course of the year.”
        Yes, 11963 kWh by the model based on daily measured production, export, consumption and import (see conditions in my original post).

        “If this was all in the shoulder period you’d be $400 ahead over the course of the year,…”
        The time periods and modelled export kWh and FiT values are:
        Shoulder (7am-3pm): 11364 kWh, $1136 (at 10c/kWh)
        Peak (3-8pm): 599 kWh, $174 (at 29c/kWh)
        The total FiT benefit ($1310) would be $90 more than for a fixed FiT ($1184), as given in my original post.

        I hope this clarifies my results.

        • Doug Mason says

          Sorry, further clarification required!

          For 10 kW PV, annual FiT comparison is:

          Standard FiT = $1184 (11963 kWh export at 9.9c/kWh)
          Time FiT = $1274 (being weekend days at standard FiT =$337 + balance of days at time FiT = $937.00)
          Hence time FiT is $90 better off over the year.

  11. Just_Chris says

    This is a great article, I particularly like the picture of a house in Queensland. As an immigrant scientist with an autistic wife who strongly believes in preventative medicine I always feel as if Queensland, One Nation heartland, gets off too lightly – if nothing else, there should be more village idiot jokes at their expense.

    I am pretty excited about what is happening in Victoria at the moment wrt to energy billing. We are gradually transitioning to a point where the cost of electricity begins to reflect the actual cost of generation. In my opinion this is critical if we are ever going to reduce the cost of electricity.

    I think what would be interesting would be to start to think more deeply about how solar, battery storage, electric vehicles, variable rate tariffs and life style choices can start to have an impact on how much you pay for your electricity. There is so much diversity in what tariff’s you can get in Vic now I really feel as if you can’t make statements like “larger solar systems don’t stack up financially” or “batteries won’t pay for themselves”. I’m on a new tariff this year by Momentum with a demand charge. This works really well for me as I do 20,000 electric km per year in our leaf which roughly doubles my energy usage. I don’t have solar or a battery storage system but even without those I can shift around 70-80% of my load. I would imagine someone with a battery/solar system in addition to the electric car could make some serious differences to their energy usage pattern and really start to take advantage of some of these new tariffs and FIT. My daily charge is $0.89 and energy usage is $0.155 (including GST), clearly there is a network charge to consider but if that was taken care of by the battery and I was able to essentially run off stored energy in the peak period to maximise any solar export opportunity it’d be a pretty different economic story to a flat rate FIT and electricity rate. I’m not saying there are any economic no brainers but there is certainly an emerging opportunity to think out of the box.

  12. Chris. Those rates are excellent but in my experience, once you add solar panels you wont get such good rates. I’m in an Ausnet area and they dont do variable time meter reading to pass on to the retailers yet.

  13. It looks like Simply Energy are remaining clueless and/or stumm. In my latest bill, my FIT has remained at 11.3 c/kWh for the entire billing period, which extends halfway into July. When I called their call centre in late June, the agent had no clue.

    I get the feeling that most retailers are trying to divert attention away from the time of day FIT, as they really don’t want to pay it.

    What I suspect they will want to take advantage of is that most owners of rooftop solar systems do not have enough data and don’t know how to calculate what the benefit of the time of day FIT would be. By staying at 11.3c/kWh they may hope to keep risk-averse customers on a lower payout. Anyone who has access to generation and usage data will immediately know how much better off they would be on the time of day FIT.

  14. John Sadler says

    We were about to take the plunge and purchase a 6kW PV system, but everything has now been put on hold since hearing from our installer that the pre-approval application submitted to the local power supplier (Powercor) has come back requiring our system to be set to export no more than 2kWh of energy at any time throughout the day. This is apparently due to the number of houses in the area which already have solar.

    Our installer has suggested ‘the impact to your system will be tiny at best’ and I guess this was based on an understanding or expectation that a large proportion of energy produced during daylight hours would be used in the house and there wouldn’t be too much being exported to the grid anyway.

    Regardless, I feel that the imposition of such a restriction is unreasonable and certainly acts as a deterrent to people wishing to go down the path of installing PV systems (this obviously benefits the power supplier as the fewer household on solar, the more electricity they sell).

    Not sure where to go from here – either install a smaller PV system or not one at all. Would appreciate any advice you may offer. Our Average Daily kWh Usage during summer is 20.5 and during winter 18.5.

    Look forward to your response, not only in respect to where we should go from here, but also regarding the appropriateness or otherwise of power supplier setting restrictions on excess electricity being exported to the grid.

    • Ronald Brakels says

      Hi John

      Being restricted to exporting no more than 2 kilowatts of solar power will affect the economic return from a 6 kilowatt solar system, but not by as much as most people expect. In your situation it might reduce savings by under $100 a year.

      If your self consumption of solar electricity averaged half a kilowatt and your solar inverter always magically provided its maximum output of 5 kilowatts then you’d lose half your potential feed-in tariff from being export limited to only 2 kilowatts as on average you’d be consuming or exporting half the power. But because the sun spends most of its time at less than an optimal angle the system will spend a lot of its time producing less than 2.5 kilowatts and so you’d probably only lose about one quarter of your potential feed-in tariff. If you are in Melbourne, which is a really cloudy place, you might only lose one eighth. So all up you will probably have your total amount of feed-in tariff reduced by less than 20%. At today’s feed-in tariff of 9.9 cents that is likely to come to reduce your savings by less than $100 a year. The exact amount will depend on if there are usually people at home using electricity during the day.

      Unfortunately, the need to export limit a system can increase its cost. So while the amount of feed-in tariff lost may not be that bad you still may not find it economically worthwhile to get a 6 kilowatt system. In this case the lowest cost option would be to install a small 2 kilowatt inverter with close to the maximum allowed panel capacity of 2.66 kilowatts as possible. Because a smaller system will result in higher self consumption of solar electricity the payback time can be very rapid although the total reduction in your electricity bills will be considerably smaller than with a larger system.

      • Doug Mason says

        What Ronald said.

        A quick modelling exercise for a 6 kW system with inverter limiting export to 2.5 kW (with assumptions below) gives these results (all per annum):

        Lost export = 1272 kWh = 23% of potential export
        Lost export = $126 (1272 kWh at 9.9c/kWh)
        Total consumption = 7046kWh = 19.3 kWh/day
        Total production = 8117 kWh from PV = 6 kW

        With 6 kW of PV, you have the option of increasing your self-consumption, and you could also fill a battery if you wish.

        • John Sadler says

          Hi Doug

          I’m a real novice when it comes to looking at the fine detail of how to calculate solar energy production, self consumption and grid exporting etc,, but was very interested in your blog in which you provided a modelling exercise in respect to my circumstances where the power supplier has indicated it will set a grid export limit of 2kWh if I go ahead with installing a 6kW system.

          Just about wore a calculator out trying to make all the figures make sense, and the only one that worked for me was the Total Consumption of 7046kWh (19.3kWh x 365 days). Just wondering if you wouldn’t mind providing some further detail regarding the modelling. For example, how did you work out the Potential Export and then applied 23% to arrive at Lost Export of 1272kWh ? Also, what formula did you use for working out Total Production (ie, 8117kWh = 6kW) ?

          You sound as though you know the ins and outs of solar pretty well, so I will also ask you for your thoughts on how I should proceed. Should I regard the $ value of the Lost Export ($126 per year) as a reason not to proceed with a 6kW system or should I just suck it up and go with it, particularly as we hope to add batteries when they become more affordable (hopefully in the near future). Didn’t particularly want to install a smaller capacity system and then bitch about it being too small when we come to add batteries. Another option is to not install PV at all, but I suspect this is not a sensible one as the cost of purchasing electricity will continue to increase year by year and probably at an even greater rate than at present due to the increasing popularity of solar.

          I would welcome any thoughts from yourself or any one else who might have a view.

    • Alistair Campbell says

      I think this is just outrageous. It’s not just about the lost income, which will vary depending on the setup of your array, North vs West etc, and your pattern of use during daylight hours.

      With my 5.5kw system, divided almost equally between North and West facing, we use 15-18 kWh spread across the day, so normally instantaneously below 1kw usage. According to the output from our Fronius smart meter on a good sunny day from December to May the power exported to the grid exceeds 2kW from about 11 am to 5.30 pm. So imagine the frustration of looking at your smart meter output. Between 11 and 6 it should be showing you a bell shaped curve of instantaneously exported power rising then falling around a peak of 4.5 -5kW. Instead of which its a flat line at 2kw from 11-5.

      I guess the reason they want to restrict the output is to help them control grid voltage. I’m also on Powercor, about an hour west of Melbourne and can tell you the job they currently do to regulate grid voltage is already poor. The PV systems installers don’t tell you about this, but the PV system stops exporting power when the inverter senses that grid voltage hits an upper limit. During the summer there are days when my Fronius stops exporting 30 to 40 times a day because Powercor are unwilling or unable to do their job properly.

      • I only have a limited understanding of the advanced grid management capabilities that are available in conjunction with solar PV systems, however the behaviour displayed by Powecor just seems to reflect an unwillingness to invest in the technology necessary to maintain a stable grid.
        In all honesty, the likes of Powercor are ripping us off blind with their charges, so I think we have a right to expect them to invest in the kind of advanced grid management technology that is in use on countries like Germany.
        It also appears that battery systems can contribute to improving grid stability. This raises the question as to whether it might be advantageous to encourage more owners of rooftop solar systems to install batteries.
        I think we are once again seeing a case of distributors and generators dragging their heels and trying to milk every cent out of their assets rather than making investments necessary for the future.

      • I had same issue of disconnect multiple times during the day. I have a 4kw system and it set to disconnect at 253v.
        I could watch the voltage rise rapidly on the inverter when the sun came out a few seconds later it disconnects. Since my inveter is in the garage i could hear it disconnect. Many people would be totally unaware of this with usual external installs.

        There are many solar systems in my street i called Ausnet who came around of course on a non sunny time and sait voltage is in spec.

        After contact with my solar supplier they eventually adjusted it remotely to 258v. Had no problems since.

  15. The Australian standard for the grid supply is 230V -6% +10%. That means, your grid supply should never exceed 253V. If it does, the grid is “in the wrong”. Not that I think the likes of Powercor care.

    • Nobody cares, i just got the runaround except for a cursory check of the voltage which can be done on the smart meter for those who don’t have solar.

  16. John Sadler says

    This is in response to Doug’s Blog on 22 July 2018

    Hi Doug

    I’m a real novice when it comes to looking at the fine detail of how to calculate solar energy production, self consumption and grid exporting etc,, but was very interested in your blog in which you provided some modelling in respect to my circumstances where the power supplier has indicated it will set a grid export limit of 2kWh if I go ahead with installing a 6kW system.

    Just about wore a calculator out trying to make all the figures make sense, and the only one that worked for me was the Total Consumption of 7046kWh (19.3kWh x 365 days). Just wondering if you wouldn’t mind providing some further detail regarding the modelling. For example, how did you work out the Potential Export and then applied 23% to arrive at Lost Export of 1272kWh ? Also, what formula did you use for working out Total Production (ie, 8117kWh = 6kW) ?

    You sound as though you know the ins and outs of solar pretty well, so I will also ask you for your thoughts on how I should proceed. Should I regard the $ value of the Lost Export ($126 per year) as a reason not to proceed with a 6kW system or should I just suck it up and go with it, particularly as we hope to add batteries when they become more affordable (hopefully in the near future). Didn’t particularly want to install a smaller capacity system and then bitch about it being too small when we come to add batteries. Another option is to not install PV at all, but I suspect this is not a sensible one as the cost of purchasing electricity will continue to increase year by year and probably at an even greater rate than at present due to the increasing popularity of solar.

    I would welcome any thoughts from yourself or any one else who might have a view.

    • Doug Mason says

      Hi John,

      Your original post has been re-posted. Strange. Yesterday I made a lengthy reply to your post, but it seems to have disappeared – perhaps the blog software objected to some lengthy links. In any case, I will try to recreate my reply without those links.

      I am not a professional in the PV industry – just an interested observer and user of PV in my domestic environment. Like a lot of people, I accumulated my production and consumption data, and put it into a spreadsheet for better evaluation. I also extended the spreadsheet to calculate results for systems with different PV size, with or without battery of different size, and varied total consumption. I based my modelling on the algorithms of Chris Cooper (see link in my original post to the Reneweconomy web site), and extended it to account for hourly production and consumption.

      Some comments on your queries about my modelling:

      – The total exported kWh = Production – self-consumption.
      – The lost export (per hour) = Total export (per hr) – Export limit (per hr). I can then calculate the total lost export by summing over all hours.
      – For total production, I used PVWatts (see further comment below) to determine the total production for PV=6kW at Melbourne/Tullamarine (nearest location to you), and used that in my model. This meant I had to lower my PV=5.7kW, because in the Adelaide area I produce a bit more than Vic.
      – I re-calculated the lost export, with export limit = 2 kW (because I erroneously used 2.5kW in my original response, sorry, my error), and calculate an export loss of 33% (1810 out of 5531 kWh) = $179. The FiT return to you is still a healthy $369 ($548 original total FiT – $179).

      Some other responses:
      – My personal suggestion is you should still consider PV=6kW. Even if export-limited, this will still provide a very healthy return-on-investment (~$1150 p.a. = ~$800 electricity not bought from grid + ~$350 from the limited FiT).
      – I suggest you read as much as possible about Tier 1 PVs, and inverters versus micro-inverters (there is lots of good stuff on this site about those matters).
      – I suggest you use PVWatts (Google it) to calculate PV production for different PV sizes and orientations for your specific location. It’s a really great tool.
      – I suggest you use some on-line PV + battery calculators for your particular situation (see a good one at Solar Choice site, another excellent Australian site).

      Good luck,


  17. Alistair Campbell says
  18. John Sadler says

    Thanks a lot Doug. Really appreciate your feedback, although it has highlighted just how little I know about the technical side of solar. However, I do find it all very intriguing so I will keep at it. Thanks again.


  19. Hi John – fully endorse Doug’s recommendation to use PVWatts, and then to download hourly results to a spreadsheet where you can graph what’s happening through typical days.

    Apart from the great advice above, consider diversifying panel orientation to reduce and spread peak generation profile. You’ll get less overall generation but also less potential power clipping around noon. Creating a westerly bias yields more generation during peak FiT (3pm – 8pm) and peak grid events (exploited via Reposit) and into the future, deX or blockchain trading platforms.

    We also live in an Outer Melbourne Powercor area with high PV penetration. I hope to install an east-west system around 5kW with 4kW 3ø smart inverter, ideally by equinox this year!

    Once I get round to it I’ll be seeking to confirm via PVWatts spreadsheet viability of installing around 3kW west and 2kW east, using current proposed VIC variable FiT as a simple long-term assumption.

    As rightly noted, the current VIC variable FiT may well get mangled but as rooftop solar penetration deepens and summers get hotter there should always be more value in better alignment of export with weekday grid stress periods. Over the lifetime of your new solar system market forces will spawn adequate export incentives (via FiTs and/or energy trading platforms/VPPs) during weekday grid stress.

    I’m hoping someone is planning to launch an inverter with IFTTT logic that would maximise self-consumption of compatible compliances. Does anyone know if that’s in the pipeline (other than via Reposit’s bolt-on box)?

    • Depending on your inverter, you can also download the data directly out of the inverter – as I pointed out earlier in the thread, if you have a Fronius inverter you can use the RESTful API and get data down to a 5 minute resolution.
      I am also in an outer Melbourne suburb served by Powercor. I installed a 6.48kW system with a 5kW inverter nearly a year ago with panels facing East and West (2.4kW East-facing and the rest West-facing). That was a necessity, due to lack of North-facing roof area, but has benefits in terms of generation earlier in the morning and later in the afternoon, which fits our usage profile. The lack of North-facing panels does seem to be a drawback in Winter. Also, try to get as close to a 5kW inverter as you can – even with my 6.48kW worth of panels, in mid-Winter I am barely getting 3kW in the middle of the day – we are back to just over 4kW around noon at the moment.
      What is also worth pointing out is the value of installing a smart meter at your feed-in point so that you can measure power flow to and from the grid, as your inverter itself only measures generation. I can again only speak for what a Fronius system looks like here – the meter connects back to the Data Manager on the inverter via Modbus, so you just need to query the inverter for data.

  20. Have you seen that Energy Australia is offering the TOU FiT now?

  21. Geoff James says

    I have recently installed solar panels with Energy Australia and they are now offering variable time rates 29c peak, 10.3c shoulder and 7.1 off peak.

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