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My first solar- and PW2-powered electricity bill

Discussion in 'Australia' started by Vostok, Aug 25, 2019.

  1. Vostok

    Vostok Member

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    After having my solar/PW2 system commissioned in late May, I have just received my first electricity bill. Ten days of the quarter were non-solar when our inverter failed a month after installation (apparently a rare but known fault occurred). It was replaced swiftly under warranty!

    While running the risk of appearing to be bragging etc (sorry, I am just so excited by what solar and PW2 have done!), some noteworthy outcomes:

    • We have gone from power hogs (daily usage above that of a 5-person household) to being less than a 1-person household
    • Grid consumption down 82% compared to same time last year
    • Our solar export was about half of our total grid consumption (and this was through winter!) and with 10 days of solar being out of action :)
    • There was a delay in moving us from the general tariff to the time-of-use tariff. Our average daily cost reduced by about 75% going from the general tariff to the ToU tariff, due to our ability to shift the vast majority of our grid demand to offpeak times with the PW2. Only 5% of our grid demand has been at peak rates.
    It’s all been simply wonderful and liberating!!!
     
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  2. Blue heaven

    Blue heaven Fair Dinkum Tesla

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    Good work @Vostok, brag away as much as possible, solar and battery or just solar alone, the best promotion is someone actually doing it and possessing lower power bills that can't be disputed by some moronic naysayer disparaging renewables.
     
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  3. TASKA9

    TASKA9 Member

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    what size is the solar?
     
  4. Vostok

    Vostok Member

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    5.8 kW.
     
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  5. technerdx6000

    technerdx6000 Member

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    Wow! I think you are consuming less as a household too now, due to being able to monitor your usage with the app?

    I have 8kW of solar (in QLD) and in winter, it really struggles to keep up! Often the battery doesn't fully charge.
     
  6. DBPhil

    DBPhil Member

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    Also had solar and PW2 installed 1 August. Very impressed so far. Only used 80kwh this month and sent 190kwh back to the grid. With any luck our bill will just be the standing daily charge.

    Payback is much better when factoring the use of an EV (even of considering EV using just grid).
     
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  7. Vostok

    Vostok Member

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    On a sunny day, our battery is usually full by 11am. Our roof plane is almost optimal though for solar panels in slope and orientation. We are consuming less power in total because we also replaced every window in the house with double glazing which means we don’t need the A/C on nearly as much. That’s made a big difference.

    The Tesla App is great for monitoring use, but its greatest benefit to us has been to help identify & shift demand to maximise self-consumption and shift grid use as much as possible to offpeak times. For example, I reprogrammed the charge timers for my LEAF to charge during the day on days when it is usually at home, and never at peak times. The dishwasher uses a lot more power than I thought, so we run it during the day instead. Stuff like that.
     
  8. JayTee

    JayTee Member

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    I put in a 8kw Solar sytem 12 months ago and we havent had a power bill so far. Payback should be about 3 to 4 years.

    Running the numbers though, a powerwall has about a 15 year payback, thats not great on something that has a 10 year warranty. I think they need to be about $8k or less before being financially viable beyond just getting one for the hell of it.

    Personally, ill pass and add another 8kw system, will work out much better financially even if I feed it all into the grid and collect the FIT. If you have 3 phase power and a big roof, go big with the solar imo.
     
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  9. Vostok

    Vostok Member

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    Payback time depends a lot on usage patterns & consumption. Now that the 5-minute data can be downloaded from the Tesla App (although you need to download each day individually o_O) it will be fairly easy to spreadsheet it and do the “what ifs” on real generation and usage data, and work out exactly how much higher the power bill would have been without the battery.

    It will be cool to also accurately test different grid rateplans and work out which one is best. For example, is a 20c FIT but eye-watering peak rate of 60c better or worse than 11c FIT and 45c peak? With a year of 5-minute data, I will be able to work out exactly that.

    I estimated with a clunky model before I had the system installed that adding PW2 would add only 2 years to the system payback time (6 years solar only to 8 years with PW2). With a year of data, I’ll be able to calculate the real answer!
     
  10. paulp

    paulp Active Member

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    Quite small.
    Surprised if that would fill a power wall in winter
     
  11. paulp

    paulp Active Member

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    Agree it depends on your circumstances, but never heard anyone claim batteries have a 2 year payback. A well sized system should see a solar payback of 2-3 years and a battery payback of 7-8 years, depending on efficiencies and costs. If you have too much battery for the solar to fill the battery payback is extended.
    If your solar only is taking 6 years to pay back something is very wrong with either the orientation, they system size, or the rates being used. Mine is super efficient, and paid back somewhere between month 22 and 23.
     
  12. JayTee

    JayTee Member

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    Single phase power that most homes in Sydney are on are limited to 5kw Solar systems. Though normally they oversize by 33% with panels and go with 6.5kw panels with the 5kw invertor. (Assuming 6.5kw of panels fit on the roof)
     
    • Informative x 1
  13. Blue heaven

    Blue heaven Fair Dinkum Tesla

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    Before installing a Powerwall 2 I concluded the payback would be 10+ years, we installed regardless for a number of reasons, 1.we have power during a grid failure, 2. we wanted to be fully solar powered rather than daytime solar, night time fossil fuel, 3. Many people across WA spend far more than $13,000 on swimming pools, holidays and weddings (and divorces) that are money pits not investments.
    It didn't take long after installation to work out that due to the app helping tidy up our power usage the payback would be less than 10 years, to do this you also have to disconnect the gas and go full electric, have a steady power usage across each week and self consume as much daytime solar as possible.
    Besides buying a Tesla car it's the best thing we ever did, having electricity during a grid failure is priceless while the neighbours stumble around in the dark trying not to fall into their swimming pool.
     
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  14. Vostok

    Vostok Member

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    Well prepared to be surprised, because if it’s a sunny day, it does, frequently.

    Looking at the Tesla App, sunny days in June were generating 27 kWh (averaged 14.5 kWh/day over the month), and sunny days in July were generating 29 kWh (average 22 kWh/day). More than enough to fill a 14 kWh battery when household consumption up to that time is not much (i.e. most of the solar generation in the morning is filling the battery).
     
  15. Vostok

    Vostok Member

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    2 year incremental payback (on top of solar 6 years), hence an 8 year payback for the whole system. Quite different. But I’ll be able to talk to the facts of what it actually achieved after a full year of data collection, so that’ll be fun.

    You make a few false assumptions. My system is almost optimally oriented and sized. But it was just about the most expensive system that could be installed. Why? Because I have extremely limited roofspace.

    So to have sufficient solar generation capability to come close to powering the entire house, not only did I need to reduce my daily average consumption (hence the double glazing), I needed to install the most expensive high efficiency residential panels available - 365W. If I had more roofspace and could have installed double the number of panels that cost 25% as much each, then yeah, it would have a much quicker payback time.
     
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  16. smithy

    smithy Member

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    On average it hasn't fully charged the powerwall in June. Sorry, not putting a dampener on your installation, but with 5.8kW of solar and a PW2, you'll never get through winter with it charged each day, and you'll definitely be importing power.

    I'm also in Sydney and have 10kW of solar, plus have had a PW2 for over 3 years (one of the first installed). You need to be exporting 7-8kWh per day, every day on average just to pay for your grid connection charge. For every kWh imported, you need to export 2kWh to cover the cost of importing. With my system I export sufficient power over 8 months of the year to fully cover the cost of grid connection and import for the entire year, so my annual power bills are zero. I also charge my S with excess solar for around 7 months of the year when it is generating enough.

    I'm with you on system quality...likewise mine is Sunpower X22-360W panels and I'm on 3-phase, so an expensive system with longer payback. I don't really care though, as my annual power bills will be a big zero for many many years to come.
     
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  17. JayTee

    JayTee Member

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    I was doing pretty well for the first few months of solar but then bought the S which has blown out our imports and self consumption. This was from November last year. Imported less than 6kw per day.
    20190827_211521.jpg

    Now I have the S I have to charge it at night which uses about 20 to 30kw to get through my daily commute. Im thinking going to 15kw Solar would be good but it seems like most retailers cap the FIT to maximum of 10kw systems?
     
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  18. Blue heaven

    Blue heaven Fair Dinkum Tesla

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    If you're driving 100-150kms a day that's good value from the car, squeezing a bit more solar into the car would bring the costs down even more.
     
  19. Vostok

    Vostok Member

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    Well, yes, I know that. I was responding to “surprise” that a 5.8kW system would fill a PW2 in winter. It does, on sunny days, or even mostly sunny days, but obviously on average it didn’t. However the 10 days in June when the system was out of action due to a dud inverter (and which I excluded from the average calculation), it was mostly sunny so we missed out on quite a bit which would have lifted the average. There were 10 days in June where solar generation exceeded 15 kWh.

    On the flip side, this Sydney winter has been exceptionally dry and so we’ve barely had more than 2 overcast days in a row. Next year might be different.
     
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  20. paulp

    paulp Active Member

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    The odd thing with solar, and I’ve been logging monthly use for a couple of years, the total created by my system so far this year is near identical to same time last year, however the month by month comparisons are considerably different. So its looking like year on year doesnt change even though month on month does. This winter is a lot wetter in Adelaide. I’ve had to lower the pool 3 times compared to none last year.
     

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