Calculating Solar Panel Savings & what are your power bills like?

• 

  mysterytal on 12/06/2018 - 19:15

  +1

  Is there an easy way to calculate what the actual savings that you make with having solar panels per year.

  No….there is no easy way.

  The LED downlights would only be used when it's dark…when the solar panels are generating nothing so ignore that in your calculation.

  My base usage during the day is 200Wh. That's for the PVR, DVD player, fridge, chargers etc… So…I save about 200Wh times 8 hours (average generating time per day averaged over every day of the year) times 365 days times 20 cents per kWh. approx $116.80 per year.

  Then you've got to add the amount paid to you for exporting. That's usually easy enough that's on your bill.

  • 

    Melb69 on 12/06/2018 - 19:35

    If I were to use the same figure plus say the rebate I received for 2017 $95. It would take me 20years to break even. Not really what they were saying would be the break even period.

    • 

      IVI on 01/12/2018 - 15:46

      I see 2 ways to Save or Earn, resp., depending on your usage,
      during each period:

      1. Use Electricity from your panels to cut your billable usage, &/or

      2. Sell Electricity to to your Supplier (or Highest Bidder, if possible)

      We just paid $68 per 200 W (they say they’re rated “200-299 W”
      UNINSTALLED

      (Of course, we expect lower than 200 W output, per panel,
      due to rain, clouds, etc.)

      The non-linear cost-curves of Electricity tariffs add artificial complexity.

      You could write some calculator-code (that incorporated your Tariff), &
      build a mathematical model of your system, into an Excel spreadsheet,
      to simplify - if you model everything accurately - even check supplier’s
      figures.

      • 

        IVI on 01/12/2018 - 15:48

        Re: My independent panel costs

        They didn’t come with any regulators

• 

  poboy on 12/06/2018 - 20:19

  Yeah, there's no easy way without proper monitoring. But as you know you generate approx 12 kWh in solar a day - you could subtract your export/feed-in kWh shown on your bill.

  E.g bill period is 30 days, so 12 kWh x 30 days = 360 kWh - kWh exported of 120 = 240 kWh of solar utilised. 240 x 20c kWh in normal grid cost savings = $48 in solar utilised per month + 120 x 11c kWh feed in ($13.20). So total solar benefit is $61.20.

  • 

    Melb69 on 12/06/2018 - 20:48

    Ok. Will check my actually feed in per day from the invertor. That 12Kwh was just my average usage not generated power from panels. Obviously, though it will vary as at the moment I would be getting pathetic generation from panels as winter.

    By the way my invertor say the panels have totalled 16,492KWh for the 6 years.

    At the end of the day I suppose I am helping the environment, which was really what it was about and also to reduce some of the power bills. But effectively as we paid 4k it was like paying for power up front.

    Just wanted an idea of whether it was worthwhile given the power bill just came in and it reminded me of the panels.

    • 

      IVI on 02/12/2018 - 00:45

      Three points:

      1. Making PV panels results in Toxic Waste
         (out of view, far away, in developing countries)

      2. Like other renewable energy sources, PV
         panels have Low Energy-Density

      3. The relatively short operational lifespans of
         PV panels means they need to be replaced
         sooner & oftener than, eg:

      • High Energy-Density, Zero-emission Nuclear

      Not only that… Nuclear is about to experience
      a happy Disruptive Pivot:

      . FROM Today’s Costly-to-Build AND Costly to Re-
      . Fuel (~6 weeks of down-time, every ~2-3 years;
      . adding-in Expensive+Wasteful nature of Today’s
      . solid Fuel-Rods, needing Secure-Storage across
      . ~300,000 years)

      . TO: ~2029’s Safe, Cheaper (NO Huge Cooling-
      . Towers; Factory-Made Cores; Less to Build on-
      . site; Quicker to get operational; ~7 year ReFuel-
      . Cycles + each being Quicker (a much-reduced
      . Down-Time, each time); Much Less Waste; &
      . Waste needs ~300 years Secure-Storage)

      Of course, PV panels will need to be replaced &
      Old Panels become Waste, in future. How easy
      will this new?

      PV Panels’ big resource-grab (ie, when not on a
      rooftop) is Agricultural Land… as Food Security
      grows in importance.

      Like Renewables? So, learn “the story-behind-
      their-story” eg, here:

      • YouTube “Conley TEAC8”

      (Two guys have “done the math” comparing
      Renewables to Nuclear (of old & new type),
      & how much Maintenance work Renewables
      would take vs Nuclear.)

      Expect Lots more Injuries + Deaths in the
      Renewables industries, than in Nuclear’s.

      YouTube “MacDiarmid Economy Club”

      (on Liquid-Fuel, Molten Salt Reactor, due
      Next Decade: ~2029?)

      YouTube “Pedersen TEDxCopenhagen”

      (Compares Old & New Nuclear Reactors)

• 

  DarrylD on 12/06/2018 - 20:48

  +2

  I've been working in the solar PV and renewables industries for 8 years and your query is very common, particularly prior to the advanced monitoring and smart home technology now available.
  Here is a simple way to see what savings your system has achieved. Your inverter will have a "Total kWh" somewhere in the menu. Write it down.
  Your electricity 'net' meter which was installed when you got the solar PV system shows power Imported from the grid and unused solar power production Exported to the grid, both in kWh. Write them down.
  You can see your household's consumption of the solar production by deducting the kWh Exported from the Total kWh figure shown on the inverter. Give this home consumption a value of 22 cents a kWh which would be conservatively the average cost per kWh since 2012. If you have all your bills back to 2012, you can be much more precise.
  You then have to factor in the amount you received for exported power. I'm in Sydney but I used to sell into Melbourne and you would have been on the Transitional FiT of 25 cents per kWh up to 31/12/16. You would have then dropped to around 6 cents before climbing to 12.5 cents since last year with Energy Australia. If you don't have all your bills, divide the Export figure by 6 (years) then muliply it out at 4 years at 25c, 1.5 years at 6c and 0.5 years at 12.5c.
  Good luck with the maths but, if you do it right, you should be really close to seeing the value you've received from you system to date.

  • 

    Melb69 on 12/06/2018 - 20:54

    Your electricity 'net' meter which was installed when you got the solar PV system shows power Imported from the grid and unused solar power production Exported to the grid, both in kWh. Write them down.

    How do I find that unused power exported figure to grid? Is that on the new meter?

    Your calcs are more helpful. Don't have all my bills, but can try and extrapolate from what you are saying with the multiples over time.

    • 

      DarrylD on 12/06/2018 - 21:38

      The electronic meter in the meterbox will have readings that, depending on the type of meter, either change every few seconds or you have to push a button to make them change. AS the numbers scroll through, you should see a 'Register' number to the side of the kWh figures. Those register numbers can vary depending on who your distributor is (Ausnet, Powercor, etc). However, it is typical for the Import to be the higher figure, especially with a small system such as yours.
      You can also record the figures over 24 hours and you'll see that the Export number increases during sunlight hours whereas the Import will increase overnight.
      I can't be any more hlpful than that without walking you through all this over the phone :-)

      • 

        Melb69 on 13/06/2018 - 06:09

        Thanks. Appreciate your detailed reply. Im sure I can work it out. Sounds like its 1 of 2 figures on the meter.

      • 

        Melb69 on 13/06/2018 - 09:38

        Ok. So have 24,742.3KWh as import and 7,654.2KWh as export. 16392KW from inverter less 7,654.2 =8,837.8KWh x.22 cents per Kwh. = $1944.32. With the breakdown of the exported power. I get a total of $1470.24. So that works out as a total of $3414.56 saved over those 6 years. Approx. Which would take it to around the 6.5 to 7 year mark for return period.

  • 

    IVI on 02/12/2018 - 00:57

    +1

    This can be done Once, eg, in an Excel spreadsheet “model” &
    used to calculate updated savings, as any of the inputs change.

• 

  mskeggs on 12/06/2018 - 21:08

  +1

  Your system will generate approx 8.8kWh per day. (Rule of thumb 4 times installed capacity averaged over the year).
  You know you use 6 of them, if your power bill is 25c/kWh that is $547.50p.a. you saved.
  The remaining 2.8kWh gets you $127.75p.a from feed in.
  So a total of $675.25p.a.
  At that rate it would take 5.9years to pay off.
  So you are very close to paid off, then you will enjoy $675 per year of savings.

  • 

    Melb69 on 12/06/2018 - 21:21

    Thanks, mskeggs. That's more like it. That is what the panel suppliers said would be the pay off time around 7years. Sounds like I am ahead of schedule.

    By the way, what are peoples annual total bill costs like. I know some families are paying well over $2k per year. Mostly due to using those clothes dryers. We have one but never use it. Upgraded our fridge to a more efficient one as well, so that should make a difference over the long run.

    The AC head units are the worse for power consumption during summer. But you do need it in Aus.

    • 

      Elppa8 on 13/06/2018 - 01:10

      +1

      Not quite, your system generated 16,492kWh for the 6 years which is an average of around 7.5kWh/day which is about the same to what mine generates over a similar period in NSW.

      So about 6.5 years, still ahead of schedule though.

      • 

        Melb69 on 13/06/2018 - 06:11

        Great.

      • 

        mskeggs on 13/06/2018 - 08:13

        Oops. Based it off the inverter, not the panels.

      • 

        Elppa8 on 13/06/2018 - 12:13

        +1

        @Dedbny:

        I had rethink overnight and I think you you maybe very close to even.

        Assuming you had the panels in for the 4 years when the feed in was 25 cents you would be saving 25c for the full 7.5kWh regardless of using or feed in which is $2737. For the next 2 years if were using 6kWh at 25c, that's $1095 for a subtotal of $3832. Add another $90 odd for the feed in over the last two years would put you close at around $3922.

        So you can crack one open in about 7 weeks to celebrate.

• 

  Melb69 on 13/06/2018 - 09:41

  Thanks all. Used DarryID method as well and it seems to fall in line with what others are saying. Good to know I am on track to making a positive return on investment soon.

  Still waiting on some idea on ppls power bills by comparison. Suppose the more panels you have if solar panels installed it could be $0.

  Be interested to know what ppl are paying then for those who don't have panels.

  • 

    mskeggs on 13/06/2018 - 10:57

    You can only cost effectively offset your daytime power use. The feed in tariffs take 10 years to pay off a system if there is no on-site power use to off-set, and they won't offset night time usage against daytime production (which is why some people are looking at batteries to store solar free power for night time use - but the economics aren't there yet).

    The biggest users of power are things that heat or cool, so if you can make them run during the day when you are getting power for free, that would be good. Examples are running the dishwasher after breakfast instead of after dinner, or cooling the house down with AC on a timer before you get home at dusk, rather than after.

    Laptop computers use negligible power, so consider switching to those instead of desktops next time you upgrade. If you have an old beer fridge, consider whether you need it at all, and whether a new model might pay for itself in power savings in a year (A 1980s fridge might easily use 70c or more power per day, while a new one less than half that).

    • 

      Melb69 on 13/06/2018 - 11:06

      That's why if batteries come down to a nominal amount it could be a game changer. At the moment they are too expensive and to be honest I don't think there has been enough development in the battery technology yet as well to make them last a long time.

      Ironically I heard on the news last week that in Victoria where the take up of solar is good there may be potential power outages as the old power supply infrastructure cant take the extra feed in all at once. So it could get to a situation where the system gets overloaded and like a fuse set up the network shuts down to protect it. They may need to limit the update of solar panels. Which they don't want to do, but there may be controls required for feed in.

      • 

        mskeggs on 13/06/2018 - 11:55

        potential power outages as the old power supply infrastructure cant take the extra feed in all at once

        If you look at who is claiming this, it is the representatives of the companies that make their profits by expanding network capacity. What they are claiming may happen one day, but I don't believe it has happened anywhere in Australia, and I am cautious about investing more in transmission, as it is largely what has driven such huge cost increases in the last decade.

        That's why if batteries come down to a nominal amount it could be a game changer.
        Yes. They are breakeven over 10 years with 35c/kWh in SA if you have solar to feed them. If they halve in price they will have similar pay backs to solar panels everywhere in Oz.

        The other thing, though, is there are already things possible to improve network efficiency and lower power costs, but they aren't happening as vested interests protect their past investments. For example, virtual net-metering allows one household to supply power to another (imagine me with a big roof full of panels could allocate some of my power fed to the grid to my sister down the street who lives in an apartment). This would reduce the amount of power that needs long distance transmission, and provide solar options to people that don't have them - but it would be financially ruinous for the power companies if less power is bought from them.

      • 

        Euphemistic on 13/06/2018 - 15:44

        @mskeggs: >The other thing, though, is there are already things possible to improve network efficiency and lower power costs, but they aren't happening as vested interests protect their past investments. For example, virtual net-metering allows one household to supply power to another (imagine me with a big roof full of panels could allocate some of my power fed to the grid to my sister down the street who lives in an apartment). This would reduce the amount of power that needs long distance transmission, and provide solar options to people that don't have them - but it would be financially ruinous for the power companies if less power is bought from them.

        Solar panels don’t ship their excess power back to the power station who then redistributes it. It just goes to the nearest consumer. It is already reducing the need for long distance transmission by its very nature of being local.

        Solar power and battery storage is going to disrupt the old power station models and shift the peak energy patterns. Power stations won’t need to generate as much during the day as they used to because more will be coming from the sun. Then off peak power rates are going to change when we get more and more electric vehicles wanting to charge overnight because they’ve been out and about during the day. Off peak hot water will not be as cost effective because the power stations wont have as much excess power when most of us are asleep.

      • 

        mskeggs on 13/06/2018 - 16:05

        @Euphemistic:

        Solar panels don’t ship their excess power back to the power station who then redistributes it.

        Obviously, but if I have an incentive to install more panels than I need to produce power that can be used by a neighbour, the total transmitted from central generation declines. At the moment, there is no incentive for me to install more panels than needed to off-set my peak daytime usage.

        If virtual net-metering was possible, premises with cheap and good solar availability could install more and neighbours with poor solar could use up the excess locally generated.

        In QLD they have already switched controlled load (off peak) to midday as they had more excess power then than at night. The battery cars likely will do the opposite, and charge on sunny weekends or other times when plugged in during daylight. Figures recently showed most cars would only need to be charged once or twice a week, as most vehicles drive so few kilometres usually. Which means they might be routinely used as night time batteries, setting it by an app to use up to 50% of the battery capacity to power your house at night, for example, except the week before your driving holiday when you tell it to charge up to 100%.

        The best system would be one with modest grids and plenty of distributed local generation and storage, so it could be both resilient and also economical by not needing to be over-engineered for infrequent peaks.

• 

  Euphemistic on 13/06/2018 - 15:33

  The easy way to do it is what you have already done. Compare your usage and bill costs before and after.

  The hard way is to get all technical and work out exactly how much you generate, how much you use, how much you export, etc then apply a cost to all those factors.