Can A Home Battery On A Time-Of-Use Tariff Pay For Itself Yet?

Home Battery - Time-Of-Use Electricity Tariff

If you have a home battery, a time-of-use tariff can save you money. 

How much depends on…

  • Battery Capability:  This includes usable storage capacity, power output, and flexibility.
  • Location:  Time-of-use tariffs vary greatly from state to state.  To a lesser degree, they can vary within states.
  • Electricity consumption habits and solar electricity production
  • Whether or not you are part of a VPP (Virtual Power Plant) that allows a time-of-use tariff.

Because a battery can provide power during peak periods when grid electricity is expensive, it provides an advantage over a flat tariff.  To show what a Brobdingnagian1 difference time-of-use tariffs can make, I’ll show the advantage it has over a flat tariff for a Sydney household with a high evening electricity consumption that makes it an excellent candidate for getting significant savings from a home battery.

Quick Tariff Overview

The three main tariffs available to households are:

  • Flat tariff:  The same charge per kilowatt-hour of grid electricity no matter when it’s used. 
  • Time-of-use tariff:  The amount charged per kilowatt-hour depends on when it’s consumed.  These can be seasonal or based on the time of day.  Unless you have a reeeeaaallllllyyy big battery, seasonal ones aren’t helpful for battery households.  Requires a smart meter.
  • Demand tariff:  Low per kilowatt-hour charge, but there is an additional demand charge passed on maximum power use during a peak period each month.  Requires a smart meter.

While it may be possible for a solar battery household to be better off with a demand tariff than a time-of-use one, that currently looks unlikely.  The ones I’ve looked at have been surprisingly bad for most battery households and can be even worse than a flat tariff.  

Most Australians can also get a plan that exposes them to wholesale electricity prices.  These can provide considerable savings, but to make the most of them requires a smart battery system able to decide on its own when is a good time to buy or sell electricity2.

In this article, I’ll only compare a flat tariff with a time-of-use tariff.  This is because I want to keep things simple and not confuse anyone.  Especially myself.

Best Locations

The two best locations for getting electricity bill savings through the combination of a time-of-use tariff and a home battery are:

  • New South Wales, and…
  • Western Australia

In both places, peak electricity prices on time-of-use tariffs are high, which maximizes savings from using a battery at these times.

In Western Australia, there are unfairly low solar feed-in tariffs that improve the economics of home batteries.  But because only homes with solar systems of 6.66 kilowatts or smaller can get a feed-in tariff, very few people have a solar power system larger than this, making it difficult to regularly fully charge a battery with solar energy. 

I’m going to consider a Sydney home with a 10 kilowatt solar system.  This size system is large enough to usually fully charge a home battery throughout the day. But in this particular instance, it doesn’t matter because the low cost of off-peak electricity means it’s not a problem to charge the battery from the grid.

Sydney Time-Of-Use Tariff

Time-of-use tariffs are considerably more complex than flat ones.  There are up to three different rates:

  • Peak: Most expensive
  • Off-peak:  Least expensive
  • Shoulder:  An in-between rate. 

The times these different rates apply can vary between retailers, time of year, and time of week. Unfortunately, finding the exact times is difficult as the government’s Energy Made Easy site doesn’t even bother to show them, despite the large amount of money that went into making it.  You may find the times by poking around on electricity retailer sites, but they often do a good job of hiding them, so don’t be surprised if you have to poke hard.

For my example, I’ll use AGL Solar Saver time-of-use tariff for three main reasons:

  1. Unlike some, it charges a peak rate on every weekday of the year.
  2. It has a high solar feed-in tariff of 17 cents for solar systems of 10 kilowatts or less, so it’s a good choice for solar households.
  3. I could find information on it.

Its time periods and charges per kilowatt-hour on weekdays are:

  • Off-peak 10pm-7am:  13.72 cents
  • Shoulder 7am-2pm:  21.78 cents
  • Peak 2pm-8pm:  53 cents
  • Shoulder 8pm-10pm:  21.78 cents

On weekends there is no peak period.  Instead, the Shoulder rate is charged from 7 am-10 pm.

Sydney Flat Tariff

I will compare the time-of-use tariff to the flat tariff version of the same plan.  This charges 26.36 cents per kilowatt-hour and has an identical 17 cent solar feed-in tariff. 

A Good Day For Home Batteries

For my example, I will use a household with electricity consumption patterns that are well suited for maximizing the return from a solar battery.  Here’s an example of weekday electricity consumption and production graph from the home’s Solar Analytics consumption monitoring system before a battery is added:

Weekday electricity consumption and solar energy generation graph

On this particular winter day, everyone left the house early and used very little electricity between getting up and heading out.  (The house must be infested by those weird people who don’t eat breakfast.)  Although there were lots of clouds that day, especially in the morning, the solar system still produced more energy in total than the household consumed.   When people returned home in the evening, they turned on the air conditioning to warm the place up, turned on the oven, and who knows what else.  This caused electricity consumption to soar during the peak period. 

By downloading the smart meter readings I was able to make a graph of the grid electricity consumption for each half-hour::

Grid electricity consumption graph - half-hour

As you can see, thanks to low consumption early in the morning and solar energy production throughout the day, they used very little grid electricity until evening. 

To work out how much they’d have to pay with a time-of-use tariff, we’ll need to break down their consumption into Peak, Shoulder, and Off-peak periods:

Grid electricity consumed and cost - time of use tariff household

While the heaviest electricity consumption occurred in the evening, peak electricity consumption was only 37% of total grid electricity use.  However, it was 63% of the total cost, which came to $7.17 for the day.

If we compare the cost of grid electricity for the time-of-use tariff and the flat tariff, then — ignoring supply charges — we get this:

Time of use vs. flat tariff

The time of use tariff costs $1.07 more than the flat tariff.  Because electricity consumption was high during the peak period, it’s no surprise the time-of-use tariff was more expensive. 

Installing a home battery will change this.

Note: if the electricity bill was lower with a flat tariff than a time-of-use tariff before you installed the battery, then you should compare the savings from having a battery to what the household would pay without one on a flat tariff and not to what they would pay without a battery on a time-of-use tariff. I’m sure you won’t make this common mistake now you’ve read about it in a paragraph buried in the middle of a long article that utterly fails to reinforce your memory by referring back to it again.

Average Consumption Assumption

While I took the electricity consumption given above from just one day, I’m going to assume the household electricity consumption during the evening peak and shoulder periods on that day is the average for those times through the year.  This means the home consumes more than twice as much electricity in the evening as the Sydney average. 

Adding A Solar Battery

To work out what adding a solar battery does, I’ll have to decide how big it will be.  I’ve decided on one with…

  • 13 kilowatt-hours usable energy storage  

This is very similar to a Tesla Powerwall 2.  According to its warranty, when new, it has a usable capacity of 13.2 kilowatt-hours. 

Tesla Powerwall battery installation


For now, I’ll assume it’s a magical battery that is 100% efficient and can supply exactly as much power as is required. 

Home Battery + Flat Tariff

Assuming the battery was fully charged with solar energy, it would enable the home to avoid paying for 13 kilowatt-hours of electricity in the evening.   But, because energy going into the battery for use at night can’t be exported to the grid, the home would also lose 13 kilowatt-hours worth of solar feed-in tariff.  This lets us calculate the savings from having a home battery with a flat tariff as follows:

  • Savings from reduced grid electricity consumption = 26.36 cents multiplied by 13 = $3.43
  • Loss of feed-in tariff = 17 cents multiplied by 13 = $2.21
  • Total savings on flat tariff = $3.43 minus $2.21 = $1.22

With a flat tariff, the battery saves $1.22.  If this is the average daily amount saved, it would come to $445 a year or $4,450 over 10 years, which is the maximum length of most home battery warranties. 

Because an installed battery with 13 kilowatt-hours of usable storage is likely to cost over $15,000 installed, it’s clearly difficult to make one pay with a flat tariff, even if the battery is magical and — completely unrealistically — fully charged with solar energy each day and fully discharged each night. 

Battery + Time-Of-Use Tariff

Determining savings with a time-of-use tariff is more complex.  The household used 8.59 kilowatt-hours during the peak period, so the solar battery will be able to cover all that as well as 4.41 kilowatt-hours of consumption during the shoulder period:

  • Savings from reduced Peak consumption = 53 cents multiplied by 8.59 = $4.55
  • Savings from reduced Shoulder consumption = 21.78 cents multiplied by 4.41 = $0.96
  • Loss of feed-in tariff = 17 cents multiplied by 13 = $2.21 
  • Total savings on time-of-use tariff = $4.44 + $0.96 – $2.21 = $3.30  

The total savings of $3.30 are more than two and a half times as much as on the flat tariff.  If this were the average saved each day, it would come to $1,205 over a year.  But this is impossible because the peak tariff is only available on weekdays.  On weekends the battery would only save $2.83 per day.  Over a week, the average savings per day would come to $3.16, and over a year, they’d total $1,155.  That’s still much better than the flat tariff, but it’s possible to do even better by charging the magic home battery with off-peak electricity. 

Off-Peak Battery Charging Improves Savings

Because the solar feed-in tariff is 17 cents and off-peak electricity is only 13.72 cents, rather than charging the battery with solar energy, it makes more sense to export all the solar energy produced and charge the home battery with off-peak electricity.  This would increase the average daily savings from $3.16 to $3.59.  Over a year, that would come to $1,310, and over a decade it would be $13,100. 

Normally the off-peak rate is higher than the solar feed-in tariff, so this situation is unusual.  If the solar feed-in tariff were to fall by 2.3 cents and/or the off-peak rate increase by that much it would no longer be cheaper to charge the battery with off-peak electricity.

No Such Thing As A Magic Battery

So far I’ve assumed the solar battery is magical with 100% efficiency and can always supply exactly as much power as needed. However, in real life, batteries have several drawbacks that include:

  • Efficiency losses
  • Inability to perfectly match power output to power consumption.
  • Inflexibility
  • Battery capacity deterioration.
  • Unable to always be fully charged with solar energy.

Efficiency Losses:  In real life, a Tesla Powerwall 2 has a round trip efficiency of around 88%.  This means 1.14 kilowatt-hours of electricity have to go in to get 1 kilowatt-hour out. 

Inadequate Power Output:  Batteries also have difficulty eliminating grid electricity use when supplying power.  It is common for batteries not to start supplying electricity until around 100 watts or more is being drawn from the grid.  Over a 6 hour peak period, this could easily come to 0.6 kilowatt-hours of peak electricity coming from the grid rather than the battery.  

Home batteries are also limited in how much power they can supply.  Some, like the Powerwall 2, can supply 5 kilowatts of continuous power while a considerable number supply less.  If the household’s power draw exceeds what the battery can supply, the excess will come from the grid. 

Inflexibility:  It’s possible for a solar battery system to be plain dumb and run flat, providing power to the home before the peak period starts.

Battery Capacity Deterioration:  The capacity of most batteries deteriorates with time and use.  For lithium batteries, this may be a few percentage points per year.

Inadequate Solar Energy:  Because of clouds and/or high electricity consumption during the day, it’s often impossible to fully charge a home battery with solar energy throughout the day.  While not a problem with a time-of-use tariff in this example, this is an important consideration for most battery installations. 

Real Life Battery & Time-Of-Use Tariff

If we assume our battery with 13 kilowatt-hours of usable storage has the following real-life drawbacks…

  • An 88% round trip efficiency
  • An average of 0.7 kilowatt-hours are drawn from the grid during peak periods

…then when used with a time-of-use tariff, the average daily savings drop from $3.16 to $2.57.  Over a year, this comes to $938. 

If we also assume the battery capacity declines at a constant rate to 80% of its original 13 kilowatt-hour capacity over 10 years, then the total savings over a decade would come to $8,440. 

Real Life Battery & Flat Tariff

Installing a home battery with an 88% round trip efficiency on a flat tariff, savings would fall from $1.22 a day to 92 cents a day.  This would come to $336 over a year.

If the battery capacity declines at a steady rate to 80% after 10 years, then the savings over a decade would come to $3,020. 

But, because there isn’t an option to charge the battery with off-peak electricity on a flat tariff, we should allow for periods when the battery cannot be fully charged with solar energy.  If we assume it’s used at an average of 80% of its full capacity, then the average savings per day would be 74 cents per day or $269 per year.  Including battery deterioration, total savings would come to $2,686 over 10 years. 

Time-Of-Use Tariff Is The Clear Winner

I’ve shown the savings over one year of for the flat and time-of-use tariffs on the following graph:

Annual savings - time of use vs. flat tariff with a battery

I included the savings with a flat tariff if the battery is used at 100% capacity because I felt sorry for it, but it’s not a situation likely to occur in reality.  Not unless a home has a 30 kilowatt solar power system and low daytime electricity consumption. 

Using the more realistic 80% capacity factor gives savings of $269 over a year.  The savings from the time-of-use tariff are three and a half times higher and come out around $670 ahead.  This makes it clearly superior for anyone with a solar battery that can offset at least some of their peak electricity consumption. 

The home in my example consumes more than twice as much electricity in the evening as is the average in Sydney, so this is not a result most households will have.  However, there are plenty of homes in Sydney that use this much or more.  If you live in one of them, you may be getting close to solar batteries paying for themselves solely through savings on electricity bills.  If you place a high value on having clean, quiet, backup power, then — for you — they may already be worthwhile.  

But when deciding whether or not to get a home battery, leave some leeway for both electricity prices and solar feed-in tariffs to change.  As both smart meters and solar battery storage become more common, the difference between peak and off-peak electricity rates should decrease.  But we’ll have to wait and see what actually happens.


  1. Brobdingnagian is a word that means “very big”.  Currently only used by strange people who enjoy writing explanatory footnotes.
  2. This means it would have to be smart enough to act as though it was part of a VPP without being a member of one.
About Ronald Brakels

Many years ago now, Ronald Brakels was born in Toowoomba. He first rose to international prominence when his township took up a collection to send him to Japan, which was the furthest they could manage with the money they raised. He became passionately interested in environmental matters upon his return to Australia when the local Mayor met him at the airport and explained it was far too dangerous for him to return to Toowoomba on account of climate change and mutant attack goats. Ronald then moved to a property in the Adelaide Hills where he now lives with his horse, Tonto 23.


  1. “Because an installed battery with 13 kilowatt-hours of usable storage is likely to cost over $15,000 installed”

    Hey Ron – just for reference, in Victoria the installed Powerwall cost is about half that price @ $11784 – $4174 vic solar battery rebate = $7610

    • Ronald Brakels says

      Getting a battery subsidy certainly helps. While eligibility for the Victorian battery rebate is limited — which has caused battery sales outside of eligible areas to crash — it can definitely be enough to convince people a battery’s worthwhile. Unfortunately, the Powerwall 2 has increased in price and the hardware cost is now $12,750 with the cost of installation on top of that. DC coupled batteries can cost less, but generally require the installation of a hybrid inverter.

      • Tim Efthymiou says

        Hi Guys, there is other options than the overpriced powerwall. I have been using a powerwall and two lg chem resu batteries for solar storage. I can confirm hands down that the lgs are much smaller, work better (no fan noise or standby issues) and are almost half the price of the powerwalls. This is a long term review, I have owned the lg batteries since 2017 and the powerwall 1 since 2016. p.s. the standby issue I have with the powerwall is that sometimes it goes to standby mode, which means it will not charge or discharge until I flip a rocker switch on the invertor back and forth to fire it up again. I’m lucky that I’m retired and can keep an eye on these things otherwise, if I was busy and not see the standby mode, then, it’s like not having a battery at all. The lgs have been faultless since installation.

      • Ronald,
        Nice article.
        On the subject of Smart V Dumb batteries and potential for making your ” personal VPP” work (your footnote #2).

        My question, what is the average IQ of the BSS out there, can one program them when to charge and when to dump? how would a consumer looking to by a new system (like me) assess if it is going to be smart enough to take full advantage of potential TOU tariffs?

        Or if i am smart enough, how programable are they?
        for example , could i tell it to hold charge all night and discharge in the early hours of the morning? (thereby maximising the time i have off grid backup in case of outage)

        • David Bruce-Steer says

          I am a member (based in Sydney) of the VPP Evergen for the past couple months.
          They have total control over when I discharge and charge the battery. I trust them since they save me money – so far.
          Since they know the weather and the the feed-in tariff in advance they claim to use AI to then work out when to charge and discharge.
          It also helps if you are with Amber who vary the feed-in tariff and your kwhr charge every half hour.

  2. So this would be even more cost effective in ACT where the feed=in tariff is only $0.07 per kWh. Correct?

    • Ronald Brakels says

      I’m afraid that because time-of-use rates in Canberra are more around 16 cents for off-peak and 34 cents for peak, the potential for savings is less and the lower feed-in tariff won’t make up for that.

  3. Hi Ronald,

    AGL have just moved me onto ToU without any consultation.
    I’m in NSW but my costs are completely different to the ones they gave you.

    Peak: 0.39523

    Shoulder: 0.38423

    Off Peak: 0.20856

    Confusing isn’t it.

  4. Dominic Wild says

    In WA one would expect Synergy, our supplier, to be the one installing batteries, after all, until 3PM our feed in tariff is only 3c/kWh, but they sell it to us at 26c/kWh and they proudly advertised only two achievements so far.

    Batteries will become more interesting once we jumped the hurdles of hybrid to plug-in hybrid and then to cheaper plug-in hybrids, which can also become the home supply. At the moment one hybrid also comes as a plug-in hybrid at an extra cost of $6,000 or at 25c/kWh we are talking 24,000kWh or 24MWh!

    And that is not even a home-supply model

  5. Some comments:-

    Since January 2020, AGL put me on a Seasonal ToU tariff. That is, there is no shoulder period because Endeavour Energy (Sydney/Blue Mts) has rendered the old ToU tariff obsolete (Peak/Shoulder/Off Peak).

    Now, there are two peak periods – High and Lo (Summer/Winter) and Off peak is year round.
    High Peak starts from 1st Nov and ends 31st March
    Lo Peak starts from 1st April and ends 31st Oct
    Both Peak periods start at 4pm and ends 8pm M-F

    Off peak applies all other times, so, off peak is now 8pm to 4pm next day (16 hours of off peak per day!). Off peak all weekends (24hrs) and public holidays (24hrs).

    I’m now with Momentum. They put me on SToU. (Hi/Lo peak periods/1 off peak period). Calendar dates are same but times are different to AGL,
    Peak times – 7am to 11pm M-F
    Off Peak times – 11pm – 7am M-F and all weekend

    Peak is 21c/kWh
    Off peak is 11.94c/kWh.
    Solar FiT is 7c/kWh
    Supply charge is 102.28c/day

    I have no controlled loads. Now, I can’t beat the 11.94c/kWh for off peak rates (no, it’s not controlled load tariff either) and I’ve taken significant advantage of it (charging the Powerwall up in winter for next day when solar is low), it’s even better than what Amber/Powerclub can offer with their “wholesale” price.

    I also have a heatbank which I charge from offpeak for that nice radiated warmth that air conditioners don’t seem to have.

    However, in 2 weeks, I will shift back to AGL because they offer 17c/kWh Solar FiT. By then, I will not be importing much grid electricity for the next 9 months and heating will decrease as the days get warmer. With summer air con cooling, both solar and battery can easily supply with almost zero imports.

    It’s only those 3 months in Winter when 90% of my yearly imports from the grid occur. But that’s OK, it’s still cheaper than buying a bigger solar system to cover winter. I already have 11.3kW of solar.

    On a side note, I do notice I always draw about 0.7 – 1kWh per day from grid with the battery. It’s mostly when solar is down for the night.

    However, there is a new feature on the PW2 webpage, you can click to take the PW2 “Off Grid”, It will disconnect your house from the grid via software control. I tried it for 1 day. Result = Absolute Zero grid draw for 24 hours. But I found this will probably only save me about 365kWh and would have to be mindful not to forgot to put back on grid.

    But the number says this…. saving this grid draw will mean significant exports having to be avoided to neurtalise the costs. The greater the gap between FiT and Import, the bigger the export will be required.

    Eg., FiT at 7c, Imports at 21c, means I would have to export 1095kWh to offset 365kWh. One could do a fair bit with 1095kWh!

    However, Power factor and response times from the PW2 when connected to the grid alters its efficiency and results in grid draw. Running a battery “off grid” means that loads with PF less than 1 will make the battery draw more current to meet reactive and real power requirements. The PW2 specs says its PF is -/+ 1.0, meaning it’s unity (does that mean it doesn’t handle loads with less than 1 PF? very odd though). Most solar inverters have PF of -/+ 0.8.

  6. Chris Thaler says

    Origin appear to turn the off peak on and off during the 10.00 p.m. til’ 7.00 a.m. period at my home. i see this by the consumption ramping up at 10.00 p.m. for about an hour or two and then shutting down until around 3.00/4.00 a.m. for another hour. No other activities are occurring on a regular basis to indicate alternative usages.

    • Retailers don’t control when off peak comes on. This is actually called controlled loads which are governed by by the distributors. Generally there are two types CL1 and CL2. Usually CL1 is on for about 7-9 hours (between 10pm to 7am). CL2 is on for up to 17 hours (but not necessarily on for the full 17 hours). This is irrrespective of the load itself is on or off. Eg. hot water systems may only need to run for a couple of hours (not the full 9 hours). But these CL systems are becoming obsolete when they should be soaking up excess generation during the day. This will only serve to kill off more base load generators running at night.

      Off peak tariffs is just a time window for billing purposes as there is no special equipment required to put the whole house on off peak rates. Controlled loads are hardwired (usually a hot water system, or pump or in some cases heatbanks) One can not simply plug any device on a controlled load circuit.

      Controlled load circuits are facilitated by a Decabit/Zellweger ripple control device (usually a small box with a visible switch that is out of reach for consumers). This technology is over 50 years old. It injects a 1050 Hz signal into the grid for a short burst of time (sometimes it’s audible through certain devices given the frequency range is at the very low end of the audible spectrum. (it’s like a buzzing sound).

  7. When calculating savings of adding a battery to a solar PV system, the comparison needs to be between the lowest cost tariff plan for each scenario, i.e. the lowest cost plan for solar PV alone vs lowest cost plan for solar + battery. Rarely is the same tariff plan the optimal option for both scenarios. Quoting “savings” as the difference in cost between two non-optimal plans is a bit misleading.

    As to TOU periods, every TOU plan I view on Energy Made Easy website shows all the time of day, day of week and month of year details for the TOU periods. Months of year are in a drop down menu and time of day is shown with a confusing pie chart layout, when it really should be an analogue clock layout.

    As to demand plans, I modelled the effect of a battery if I was on Demand TOU plan. 11kW PV + 13.8kWh of battery.

    Initial instinct might suggest adding a battery to a demand plan would really be able to drive down your bills a lot compared with regular TOU plan because of the ability of the battery to reduce peak consumption during the applicable period, while all the rest of imports are at much lower tariffs than regular TOU plans. Which it what the battery does a lot of the time.

    Unfortunately however, as we know with demand plans it only takes one bad 30-minutes in a month to drive the cost up, and it turns out that at least once per month the battery doesn’t have enough juice to cover the peak consumption period so effectively and so the savings really don’t emerge, or are relatively minor.

    Part of the issue is the current crop of batteries are pretty dumb with little in the way of programmable smarts to be able to decide when/if a pre charge from the grid is warranted.

  8. VickI Fenton says

    This is absolutely achievable. In fact I feel like you have just described our Tesla PW2 installation journey in Sydney. We are on the same TOU tariffs. We are topping up from the grid at night on low sun day. And we simply reducing our reserve by 10 in the morning to get through the breakfast spike (we are not too weird) . Our house putters along on 0.4 most of the day so even with a small 4.9kW old BP Solar ( old SMA) we have plenty of power to recharge the PW2. Our goal is to minimize $ by avoiding the grid… and our average daily use is still 8-10kWhrs (40 before Solar) BUT our average daily $ has dropped dramatically from $10 to $3 post PW2 installed Apr, 2021. Bring on Summer . Even less top ups.

  9. Cameron Church says

    This is great! I’m on TOU and trying to calculate ROI is challenging to say the least.

    Is this coming in the Advanced Calculator? 😬

  10. David Bruce-Steer says

    Thank you Ronald

    However, these days we have VPP (Virtual Power Plant) companies which further complicate the analysis.

    I have a PW2 and my energy supplier is Amber and I use Evergen as my VPP.

    Now Amber as know charge you a variable rate which changes every 30 minutes they also change the FIT (Feed in Tariff) every 30 minutes.

    This is where Evergen come in. They take control over when you discharge your battery back into the grid. They know in advance when the peak charge and what the FIT will be.
    They claim and I have proved over the last couple of months that they can reduce your power bill.
    They do this by discharging my battery when the FIT is high. My last bill (May) the average FIT was 34.6c the month before 37.9c

    To use Evergen appears to be free of charge. I did ask how they make money and was told that Industry supports them.

    I would be interested in your comments. Would you know who sets the policy around FIT?

    • Ronald Brakels says

      That is very interesting. If Evergen software is letting people gain most of the benefits of being in a VPP without the disadvantages, it’s definitely worth me looking into it.

      Update: No, wait, they are a VPP.

      Solar feed-in tariffs are mostly based on the wholesale price of electricity during the day and can be up to electricity retailers or there can be a minimum are set by the state. In Victoria there is a minimum solar feed-in tariff set by the Essential Services Commission. It explicitly includes some benefits of solar that aren’t the wholesale price, but it’s mostly wholesale price.

    • David Bruce-Steer says

      A couple of possible downsides with Evergen
      1 They run the PW2 down to zero capacity – as indicated on my phone – but when asked they say that the PW2 has a safety margin built in.
      2 They appear to be cycling the battery much more than I or the sun would. I guess this might reduce the life of the battery.

      I note with Amber that one afternoon I had zero feed in tariff!

      Incidentally I live in Sydney.

  11. Ian Thompson says

    These people apparently saved “a whopping $ 8,463” (not my quote) on their Tesla PW battery system over 4 years:

    Seem to have forgotten they probably paid nearly twice this for the battery alone (if we include installation) – so not much left to pay for the panels?

    Unless, of course, they got some damn good subsidies.

    A case of ‘blended payback”?

    • Ronald Brakels says

      If they saved $8,463 dollars with just their Powerwall 1 and each stored kilowatt-hour saved them 20 cents after accounted for efficiency losses and forgone solar feed-in tariff, then they have gotten 40,000 kilowatt-hours of stored energy out of it in four years. That’s around 30 kilowatt-hours a day. Not bloody likely for a 6.4 kilowatt-hour battery.

      • Hi,
        I have 4 of Zenaji 1.9Kw batteries, & basically offset my peak power demand 5pm to 8pm. I calculated the savings at a similar amount to your calcs.
        I use Enova energy: A Community owned retailer that now sells to most of NSW, & southern Qld. My rate is 33c peak (17:00>20:00 weekdays), 26c shoulder (7:00>17:00 & 20:00>22:00 weekdays) & 18c off peak all other times. Even without having batteries, this saves abt $80 qtr over flat rate, but one needs to control usage in peak times! My house is 100% electric, with hot water timed off solar 10:00>14:00.
        With my 15Kw panels, I still manage to export abt 50Kw on a sunny day.

        My battery system cost abt $12K. Zenaji batteries have over 20K cycles, so much better than Li Ion. Still take a LOOONG time to recoup the cost!
        (I am an early adopter)

    • Yeah, I can’t see how it was possible with a 6.4kWh PW1 and 5kW solar system. I have a PW2 with11kW solar and I can’t get those savings. No way.

      What it does not say, is how much did they change their habits to reduce their consumption pre and post battery. Was there a change in consumption levels that also reduced their bills?

      That article is flawed, it’s not forthcoming with truths how the savings are made.

      But worse still, why couldn’t they wait for the PW2 to come out, it wasn’t long before it did come.

  12. Dr David Reiter says

    Hoe about an analysis of Demand Consumption Plans with a battery? Alinta wants to force us onto one from any Any Time Use contract because they claim Energex says our consumption has changed. It hasn’t. And our LG system is a year old, so hardly a sudden change – unless it takes Energex a year to determine consumption. Alinta also charges slightly more for Controlled Load 2 than Any Time, which is strange given that Controlled Load 2 is supposed to give energy companies more predictability about usage.

    • Rob Hodges says

      Hi David,
      As of 1st July 2021, Energex is putting everyone with a smart meter onto the demand tariff and there is no option to stay on a flat tariff. You can still nominate to go onto a Time of Use tariff though.
      The only people with a smart meter that will continue to get charged a flat tariff are those whose retailer decides to act as a buffer and get charged according to the demand or time of use tariff but still charge their customers according to the existing flat tariff.
      Google “Energex 2021-22 Pricing Proposal” and “Energex Tariff Structure Statement 2020-2025” if you want to know detailed information about this change.

      **The above is my personal opinion and is not related to my employment.

      • Dr David Reiter says

        Hi Rob
        We played hardball with Alinta over this, given that we had info from other retailers who offered a flat rate, and I think they have backed off the change – for now. Applying a Demand Tariff would be a disadvantage to solar customers as far as I understand it because the rate would be determined at night, cancelling out any benefit of lower tariffs during the day when we would be exporting to the grid. We will see what we will see.

  13. Johan Rosman says

    You make regretfully the wrong assumptions about WA being a good place for a battery. Western Power has a monopoly here and just having bought a Tesla, I see myself now confronted with very hostile anti-solar rules as we have them in WA.
    1. The battery can not be charged at 5 kWh as usual, but needs to be clamped at 3kWh, so in full sun the battery gets drip-fed and using the battery is limited to 3 kWh at any time.
    2. Even worse: Western Power has Tesla block the discharge os the battery completely between 10 am and 3 pm. This is theft. It is my electricity in my home, and on a rainy day, i want to be able to use the electricity in the battery to power appliances. Instead the battery is locked every day between 10 am and 3 pm.
    All this to keep us on coals and addicted to gas.

    I wish there was an article on the Forum discussing this and ask the motivation of Western Power.

  14. Our Tesla battery seems to be working well during winter. We have a lot of shade at this time of year so solar only meets about half of our electricity needs. With the Tesla set to “cost saving” it has learnt our energy habits and usually charges off-peak at night. It then supplies most morning energy and recharges by solar during the afternoon when the panels are not shaded.
    This means we use almost no peak-tariff electricity during winter evenings (peak is 5pm to 9pm here – which I suppose reflects the demise of manufacturing industry in Sydney).
    To my point… I was wondering if the peak grid electricity is now the worst for greenhouse gas emissions since I assume this is mainly from coal-fired power stations once the sun sets?

  15. Walter van Praag says

    Can I add a battery to my battery ready inverter (5kw) and have it only charge from solar and only be used during peak hour rates??? That would be ideal…

    • Ronald Brakels says

      That definitely can be done, but what is possible will depend on the inverter and the battery.

  16. I wonder if anyone has done that, or do most battery setups just use battery first???

    • Ronald Brakels says

      It is common for modern battery systems and hybrid inverters to come with that ability. For example, with a Tesla Powerwall 2 you can enter how much you pay for electricity in different periods and it will try to maximize your savings based on that.

      • Michael Paine says

        Yes – as I indicated above my PW2 is, in effect, set to avoid grid usage during peak hours (“cost saving”). So far in 2021 we have used a net of 3828kWh from the grid (we have a pool heater!) of which only 12.3kWh was consumed during peak hours. Note that peak hours apply during summer (2pm to 8pm) & winter (5pm to 9pm) in Sydney, not during autumn.
        The numbers this August are net 333kWh from the grid with net zero during peak hours.
        The PW2 has been charging from the grid during off-peak times in winter – topping up the solar stored during the day.
        While I find this impressive it still only amounts to savings of several hundred dollars per year so I doubt if the economics stack up at present. I must admit I was expecting electricity prices to soar when we installed the system but, pleasingly, renewables have changed that prediction 🙂

  17. Michael Paine says

    An interesting postscript – there is a storm warning for Sydney at 4:30pm and I just noticed that the PW2 is charging itself from the grid in case there is a blackout tonight. This is an optional setting in the PW app.
    Of course if that occurs I will need to turn off/not use high-consumption devices but the fridge and lights should be OK for many hours, if not days.

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