How many solar panels should you install with a Powerwall 2?

powerwall and solar mix up

Installing more rooftop solar is a better investment than a Powerwall 2, so always rack up as much solar on your roof as you reasonably can first. Unlike this guy.

The Tesla Powerwall 2 is going to be big.  Really big.  I mean that literally and not figuratively.  It’s going to be big as in 13.5 kilowatt-hours of storage big.  From the point of view of most Australian households that is huge.

This large capacity presents households with two main problems:

  1.  It is more than the average Australian household uses at night.
  2. Those that do use that much electricity overnight may not have a rooftop solar system large enough to fully charge it.

So if the average Australian home buys a Powerwall 2 they will use it at less than its full capacity. As Tesla’s warranty is fixed at a maximum of 10 years, this increases the cost of each warranted kilowatt-hour substantially.

The obvious solutions are:

  1. Don’t install a Powerwall 2 unless your household regularly uses 12+ kilowatt-hours of electricity overnight.
  2. Don’t install a Powerwall 2 unless your solar system normally produces enough surplus electricity to fully charge it on a mostly clear day.  Normally this will require at least 5 kilowatts of solar panels.

Charging With Off-Peak Power Is A Suboptimal Solution

A Powerwall 2 can be charged with off-peak power if rooftop solar output isn’t sufficient to do the job.  But this is a second-best solution because, unless you are lucky enough to have a high solar feed-in tariff, charging with off-peak electricity will always be more expensive.  And if you do have a high feed-in tariff then battery storage makes no economic sense for you at all, so get out of here!

Another problem is Tesla offers a 10 year warranty with unlimited cycles and unlimited kilowatt-hours, but only if the Powerwall 2 is charged solely by solar power.  If you charge it with anything else, whether it is off-peak power, a generator, or a balloon rubbed against a cat, your warranty changes to the first of either ten years or 37,800 stored kilowatt-hours.

In practice there is not a large difference between the limited and unlimited warranty conditions, but a lot of people are going to want to keep their warranty unlimited and the only practical way to do that is with a large rooftop solar system.

A Small Solar System Plus A Powerwall 2 Makes No Sense

If you are trying to decide between installing a large rooftop solar system or a Powerwall 2, always go for the large solar power system.  There is a very simple reason why you should.  Despite being the lowest cost battery system available, the Powerwall 2 is still a bad investment compared to solar panels.

For the same money you could purchase a good quality, 7 kilowatt solar system, use just one quarter of the electricity it produces, send the rest into the grid for a measly 6 cent a kilowatt-hour feed-in tariff, then smash the panels to pieces with a sledgehammer after 15 years, and you will still save more money than you can by installing a Powerwall 2.

Under any reasonable circumstances, installing more rooftop solar is going to be a better investment than a Powerwall 2, so always rack up as many solar panels on your roof as you reasonably can first.

If a company ever tries to sell you a Powerwall 2 with a piddly 3 kilowatt solar power system, it means they are either fleecing you, or just very stoopid.  Either way, you’ll want to stay well clear of them.

The Three Best Places To Install A Powerwall 2

If you just want to buy a Powerwall 2 for fun and you don’t care whether or not you get an economic return, then it doesn’t really matter where you stick it, as long as it gives you pleasure.

But if you are in it for the money, and most people interested in battery storage are hoping to save money, then there are only three places in Australia where it has a hope of even coming close to doing that.

  1.  Western Australia and NSW because of the high peak rate their time-of-use tariffs have in the late afternoon and evening.
  2. South Australia because of the high overall cost of electricity.  While it is possible to get a seasonally based time-of-use tariff there, its is not as economically effective for battery storage as the time-of-use tariffs in WA and NSW.

Who Uses Enough Electricity To Benefit From A Powerwall 2?

Most people simply don’t use enough electricity to have a hope of getting a Powerwall 2 within a camel’s spit of breaking even.  But four characteristics that correlate with being able to suck all the juice from a fully charged Powerwall 2 overnight are:

  1. Having a large family:  Mo’ people, mo’ electricity consumption is the way it usually goes.
  2. Being rich:  Rich people tend to have larger houses, larger air conditioners, and often feel less need to economize on electricity use.
  3. Being wasteful:  Note that if this is the only thing enabling you to use a Powerwall 2 at high capacity, your hip pocket would be a lot better off if you just changed your habits.
  4. Not having gas:  People without natural gas or bottled LPG obviously can’t use it for cooking, hot water, or room heating and so generally use more electricity.

I’m not saying you have to be a multi-millionaire family of 14 without gas that likes to run the air conditioning with the front door open to use a Powerwall 2 at a high capacity level.  But it wouldn’t hurt.

cheaper-by-the-dozen-2

Personal Electricity Consumption

To find out if your electricity use is suitable for installing a Powerwall 2, a good place to start is to look at your electricity bills.  If you use an average of less than 13.5 kilowatt-hours of grid electricity a day then you’re not going to use a Powerwall 2 at high capacity.

While electricity bills can tell you how much you consume on average per day, to get an accurate picture of how much grid electricity you use in the late afternoon once solar production drops off and then through the night, you have a few options available to you:

  1.  If you have a smart meter you can request your electricity retailer send you a file that will show your complete electricity consumption broken into half hour periods.
  2. You can install an energy monitoring device that will tell you exactly what you are doing with your electricity consumption.
  3. You can get a notebook and pencil and check your solar inverter and electric meter readings and do a little arithmetic1.

If these options don’t appeal to you, then it is possible to make a wild-assed guess by looking at average household electricity consumption.

Average Electricity Consumption

When it comes to residential gas consumption, Western Australia is gassier2 than NSW, while South Australian residences appear to have the least gas of the three.

According to the Australian Bureau of Statistics the average household size is 2.6 people.  If we instead look at households with 4 people and no gas, then the Australian Government Energy Made Easy benchmark site tells me the following about them:

  1. In Sydney they use an average of 20.1 kilowatt-hours a day.  The lowest daily average occurs in summer with 18.2 kilowatt-hours and highest in winter with 24.8 kilowatt-hours.
  2. In Adelaide they use an average of 17.7 kilowatt-hours a day.  The lowest daily average is in autumn with 14.8 kilowatt-hours and the highest in winter with 19.9 kilowatt-hours.
  3. The site doesn’t have up to date information for Perth, but they apparently they use slightly more electricity than in Adelaide.

This means in Sydney a 4 person household with average electricity consumption that draws two-thirds of their total electricity use from the grid in the late afternoon and night will only use 89% of the capacity of a new fully charged Powerwall 2 over a typical night in summer.  In Adelaide in autumn they will on average only use 73%.

But because the capacity of the Powerwall 2 will slowly degrade over time this less of a problem than it seems and we can probably conclude a household’s electricity use will be high enough to make decent use of a Powerwall 2’s capacity provided:

  1. Eelectricity consumption is at least equal to the average of a family of 4 without gas in Adelaide.
  2. The majority of their electricity use occurs at times when rooftop solar production is minimal.  This is often the case for people are mostly out of the house during the day.

A Powerwall 2 Needs Over 13.5 Kilowatt-Hours To Fully Charge

Unfortunately, more energy has to be put into batteries than can be taken out.  The universe is very strict about this.  If you ever find a way around this there is a Nobel prize waiting for you in Stockholm.

The AC version of the Powerwall 2 is the one most likely to be installed in grid connected homes and Tesla gives its round trip efficiency as 89%.  Assuming this is its average efficiency under real world conditions, this means 15.2 kilowatt-hours will be required to fully charge a new Powerwall 2 with 13.5 kilowatt-hours3.  And this means a large solar system will be required.

Has Your Current System Got What It Takes?

The easiest way to check if your current solar power system is producing enough surplus electricity to regularly fully charge a Powerwall 2 is to look at your electricity bills to see how many kilowatt-hours you are sending into the grid and getting a feed-in tariff for.  If it averages less than 15 kilowatt-hours in winter then you are not going to be able to use a Powerwall 2 at its full capacity using solar power, even if your night time electricity consumption is sufficiently high.

Sufficient Sydney Solar System Size

If we assume households only use one-third of the electricity produced by a rooftop solar system, which is possible if people are normally out of the house during the day, then according to PVwatts, a brand new, 5 kilowatt, north facing, rooftop solar system in Sydney will produce enough electricity on average to fully charge a Powerwall 2 for around 4 months a year.  But in May, which is the worst month for Sydney solar generation, it will only charge the Powerwall 2 by 56% on average.

While this is not ideal, it will still allow a Powerwall 2 to be used at a reasonably high capacity of roughly 80% solar electricity when new and perhaps 90% or more over its lifespan due to declining capacity.  So 5 kilowatts of north facing solar panels in Sydney can be sufficient, but more would be preferable.

If the panels face east instead, they will produce about 11% less electricity, while west facing ones will produce about 15% less.

Restrictions On Sydney Solar System Sizes

Unfortunately, many people in Sydney won’t be able to install the 5 kilowatts or more of solar panels they will need to use a Powerwall 2 at high capacity.

In the Ausgrid network area, which contains the eastern suburbs of Sydney, Newcastle, and several other areas, houses with single phase power are limited to installing rooftop solar power with a maximum inverter capacity of under 5 kilowatts.  Fortunately, it is possible to buy 4.999 kilowatt inverters, so households can get very close to having 5 kilowatts.  The maximum solar panel capacity that is allowed is up to 133% the size of the inverter.  This means a house with a 4.999 kilowatt inverter could install up to 6.66 kilowatts of panels4, which should be sufficient to regularly fully charge a Powerwall 2, provided daytime electricity use isn’t too high.

However, people aren’t so fortunate in the Endeavour Energy network area.  This vast domain spreads from Sydney’s western suburbs all the way to the Blue Mountains and millions are caught in its grasp.  Endeavour only permits homes with single phase power to install solar systems where both inverter and panel capacity are less than 5 kilowatts.  This will make it difficult to run a Powerwall 2 off solar electricity at high capacity.

It is possible for people with single phase power in Sydney and surrounding areas to ask their network providers for permission to install larger systems than they normally allow.  If you try that, good luck.

An Adequate Adelaide Array

Adelaide is basically paradise compared to Sydney.  Not only is there more sunshine and better wine5, but people can install up to 10 kilowatts of solar panels regardless of if they have single phase or three phase power.

But while there is considerably more summer sunshine, from June through September a solar energy system in Adelaide will on average perform worse than its twin in Sydney.  If a household only consumes one-third of the solar electricity it generates during the day, then a new, 5 kilowatt, north facing, rooftop solar system in Adelaide will, on average, be able to fully charge a new Powerwall 2 for six months a year.  But in June, the worst month of the year, it will only be able to charge a new Powerwall 2 by 51% on average.

While good performance for half the year is dragged down by not so great winter output, overall a Powerwall 2’s average capacity when only charged by solar paenls should be a little higher than in Sydney.  So again, 5 kilowatts should do as a minimum.  But because South Australians are free to install larger systems, I would suggest having at least 6 kilowatts of panels.  More if they aren’t facing north or people are often at home during the day and using solar generated electricity.

Perth’s Possible Plethora Of PV Power Production

Perth households are normally limited to installing rooftop solar with 5 kilowatts of inverter capacity and up to 6.66 kilowatts of solar panels.  The good news is solar power system output is excellent there.  On average a system will produce 9% more electricity than in Adelaide and their worst month is generally significantly better than the worst month in Adelaide or Sydney.

For a household that consumes one-third of the solar electricity produced through the day, a new, north facing, 5 kilowatt system in Perth will on average provide enough electricity to fully charge a new Powerwall 2 for 6 months of the year.  In the worst month, June, it will, on average, only be able to charge a Powerwall 2 by 66%.

While Perth homes are normally limited to 5 kilowatts of inverter capacity, if the panel capacity approaches the maximum of 6.66 kilowatts, many households will be able to fully charge a Powerwall 2 with solar electricity on most days.

When It Comes To Solar Power, Go Big

If you want to install a Tesla Powerwall 2 and get the best economic return possible, or more realistically, the least worst economic return, you will need to a big user of electricity at night and you will need a large solar power system.  While around 5 kilowatts might be just sufficient for some people, definitely go bigger if you can.

If you can’t afford to expand your rooftop solar, then you sure as hell can’t afford a Powerwall 2.  Compared to solar I’m afraid batteries are not a great investment. Yet.

Footnotes

  1. Arithmetic is the branch of mathematics concerned with tormenting school children.  Thank god I survived to adulthood and never had to use it again.  (All calculations in my articles are done by children.)
  2. Thank you to Stuart who pointed out in the comments that gas connections are common in WA.  I originally and stupidly wrote they weren’t, but over two-thirds of Western Australian homes may have gas.
  3. According to Tesla, when fully charged with 13.5 kilowatt-hours the AC version of the Powerwall 2 can provide 13.2 kilowatt-hours of AC power that homes use.
  4. Satan’s favourite size of solar array
  5. and at least 200km more mountain bike singletrack (Finn’s note)
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.

Comments

  1. john nielsen says

    Ah Ronald,
    You have done it again,,, what a fantastic piece of information.
    More power to you.
    john nielsen, Silkwood

  2. thats not big at all.
    let me give you some facts.
    I am an average household with a 24 panel system max out at up to 5KW.
    This produces up to 40KWH of power per day of which I use 12 .
    At night I use another 10KWH not including hot water heating which can be another 10KWH
    yesterday because of the heat i used 27.9KWH of which I provided over half from my solar.
    So how is 13.5KW too much storage ?
    It would mean in the morning i only have a balance of 3.5KW and if there is no sun then I only have 3.5KWh to use. ??

    • One thing that is not addressed here, the fact that there WILL be power blackouts this summer! Vic Energy minister said 1/3 of Victorians WILL be without power . Those with Tesla Powerwall 2 will be able to run their houses. In Country Vic this is vital. We have got an 8 kw system, Powerwall 2, feed back 12 cents.
      We have high use with heated pool and air cons!
      Shouldn’t get a $1600 power bill anymore

      • Ronald Brakels says

        Given how unreliable Australia’s coal power stations have become — especially Victoria’s ancient brown coal ones — the risk of rolling blackouts due to the inability to meet electricity demand is definitely high this summer.

        • I had been procrastinator re solar power, but when I heard the Energy Minister, I rang a solar provider. Then established we would need a Tesla Powerwall. Installed now, but don’t know why the Tesla app and inverter, confines you to 5 kw…we have a pen 8.75 system, 28 panels, and yet it stops at making 4.9 kw! I think we wasted the extra 3 kws

          • We have established it now makes up to 8.1 kws….an inspector found the solar installers hadn’t plugged in 10 panels!

  3. I’m in the Endeavour area and am told that a grid feed-in delimiter which restricts feed-in power to 5kw will qualify a larger installation for grid connection. Is this so?

    • Ronald Brakels says

      As far as I am aware, that is correct. Having an export limited system is one way to get around size restrictions. Unfortunately, it will also normally result in a portion of solar electricity simply going to waste when it instead could have been exported to the grid and reduced fossil fuel emissions.

  4. We use around 60 kWh per day but it’s still not economical when only paying an average peak/off peak rate of 13 cents per kWh. Maybe when it halves in price I’ll look into it.

  5. Every time you write one of these things, you repeat that the distributors won’t allow systems over a certain size. Every time I comment and say I actually worked in the section that approved solar installs and that your information is wrong.

    One of us is wrong.

    Here’s the Endeavour website that explains how to apply for permission to connect a solar system of up to 10 kW to a single phase or 30 kW to a 3 phase residential connection. (again)

    http://www.endeavourenergy.com.au/wps/portal/ee/!ut/p/a1/lZBBC4JAEIV_TcdlRndz9WhiSRRRIuZeYm3XRTIVCqF_3-qlk0Vzmgdv5n0zIOAMopVDbeSz7lrZjFp4l8QNwiRiTnAIkhjDeL3JPJ856RGtobAGnKkQf83nUKxA7PbOaoEhCBC9NFrpR23aSV1rBYWWVFGGSKjLOGFqiaSkY8crxXysNPe43SSmsC8shYXl8zQU0j8ztyBM05X2UXn0uaK_Z7fTgESW_usNol3F7Q!!/dl5/d5/L2dBISEvZ0FBIS9nQSEh/

    • Ronald Brakels says

      Hello Jason. You mustn’t have noticed the article mentions people can ask for permission to install larger systems.

      I didn’t know you used to work in a section that approved solar installs. How did the process work?

      And thank you for providing a link, but could you provide a little more direction? Which of the 59 links on the page it leads to do I have to click to get information on connecting large solar systems?

      • You don’t do it, your (accredited) installer does it. Well you could do it, but I’ve never seen the customer do one.

        For systems of 5 kW and above they need to submit a Voltage Rise Calculation in addition to the other paperwork that they submit for smaller than 5 kW systems. If they’ve done the calculation correctly then they’ll be given an approval to go ahead with the install. Other than the submission of the VRC, the process is exactly the same.

        It looks like the link is different for every session as it no longer takes me to the page. The path for Endevour is Home > Residential and business > Connecting to our network > Full list of connection services > Micro embedded generator connection service

        It says quote:

        “Small scale renewable energy micro generation systems, such as home solar power systems, are connected to the network via an inverter. These inverters have to comply with Australian StandardTM 4777 and have a capacity no more than 10 kilowatts for single phase connections or 30 kilowatts for three phase connections.”

        Essential lay out their website much better and give much more information!

        Here’s everything you could need to know for applying in Essential’s area.

        http://essentialenergy.com.au/content/connecting-to-the-network1

        And the link to follow gets you this information:
        http://essentialenergy.com.au/asset/cms/pdf/Reg/CTNIP_FINALv1.pdf

        The significant entry for systems of 5 kW and larger is:

        Voltage Rise Calculations

        All applications for systems with a generating capacity or inverter
        rating of ≥ 5kW urban and >3kW rural must submit the following information (in addition to the requirements above for approval prior to the system being installed). As per Service Installation Rules of NSW 8.6.1.3, details of the voltage rise calculations for each of the three components of the generating system that indicate the system will operate correctly and not cause any adverse effects on the customers installation are required. The three components are the:
        > Service Mains (including any dedicated mains in rural situations)
        > Consumers mains
        > Conductors between the main switchboard and the inverter terminals.

        Blank pages are provided at the end of the application for both the single line diagram and voltage rise calculations. The Connections Portal allows you to upload these items at the end of the application.

        End Quote

        So, just follow the Service Installation Rules (which they should know to get their accreditation) and lay out exactly what’s going on, what you’re going to do and what the final voltages will be. Do that right and it’s a rubber stamp from the boys in Tech Enquires. Stuff it up and they’ll reject it. You just correct your mistakes and resubmit. Couldn’t be easier.

        • Ronald Brakels says

          Thank you very much for all that.

          • No problem.

            If you need any more info, I’d suggest calling 132391 and asking to speak to Tech Enquires. They’re super helpful. My job was to help sparkies lodge their paperwork and let them know how their applications were going or why they had been rejected (99% of the time because they’d just left something out). Tech stuff (like how a VRC is actually done) I put through to the TE guys.

  6. Yes, PW2 is huge. And yes, you’ll need lots of solar panels to charge it, but you’ll also need 100% reliability and true fault-tolerance with your solar system, that is, no single points of failure which can bring the entire solution down. Central string inverters verses microinverters now has a whole new meaning. Enphase’s microinverters with their no-single-point-of-failure, decentralized, fault-tolerant topology are going to be the way to go. For, who is going to want to charge their hulking Powerwalls, EV batteries, et cetera, off of grid power!!!

  7. You have falling into the fallacy that “household” is the same as “house”.

    People living is houses use more electricity than the average of all households, which includes people living in units, which use less electricity and also have on average fewer family members ( or others ) in the household.

  8. john nielsen says

    Hi Ronald,
    It seems the emphasis is on battery storage, and I will take my huge lead gel batteries to the recycling station when on Ebay I can purchase the China Made, PowerFloor, 15 kWh, 20 years warranty, for $1,500 plus freight, meanwhile I will anxiously await news about the next PW. Comparing the specs on PW 1 & 2, as well as prices,,,I bet there will be a lot of PW 1 in Buy & Swap.
    Cheers
    john nielsen

  9. Hmm Strange how you state that Western Australia that home gas is uncommon? Most houses I have been to in Perth have gas. In the rural areas is common to have bottled gas

    • Ronald Brakels says

      Ooops, yes, I have made a mistake. While only about 2% of WA gas use is residential, their total gas use is so high due to mining industry use that 2% covers a huge amount of residential use. Maybe two-thirds or more of the population. I will correct the article. Thanks for pointing this out.

  10. Re > 5kW. I think there may have been a change to the rules :
    This link, dated July 2015, suggests 10kW single phase, 30kW 3 phase
    https://www.endeavourenergy.com.au/wps/wcm/connect/fd2d4f00401ab27b866e8eb80dd2df7b/14.+Micro+Embedded+Generator+Model+Standing+Offer_2014+AER+Approved.pdf?MOD=AJPERES

    This link, dated July 2016, suggests 5kW single phase, 10kW 3 phase
    http://www.endeavourenergy.com.au/wps/wcm/connect/0801a22e-1853-41fa-becb-6909402efee3/Standard+Connection+Service+Model+Standing+Offer+_Final_July+2016_25_08_….pdf?MOD=AJPERES&ContentCache=NONE

    I say “suggest” because that site is not very

  11. Great Stuff but I am waiting for my 10kW Zcell I think it a better value all round.

  12. you talk about all the other states and capitals what about VICTORIA ??? we get sun here to mate

    • Ronald Brakels says

      Hi Ian. I’m afraid that with the lowest grid electricity prices of any state it is not possible for a Powerwall 2 to pay for itself in Victoria. Also, Victorian feed-in tariffs are going to be increased which will make the economics of a Powerwall 2 even worse.

      But if you want to install one anyway, Melbourne is only slightly worse than Sydney as far as rooftop solar output is concerned, so a system would only have to be a few percent larger to compensate.

  13. West facing panels, while producing less electricity than north facing panels, produce more at the peak usage time and so if charging a battery is not an issue, west facing panels can have some advantages in producing electricity for longer in the late afternoon and evening at peak time when air con ios most likely to be run by those away from home during the day..
    East facing panels on the other hand are most effective during a shoulder period and so not as economically powerful, as well as being less efficient than north facing panels.

    Thanks for this analysis taking into account specific areas and TOD pricing regimes.

  14. Jack Wallace says

    How many solar panels should you install with a Powerwall 222?
    None.
    Stick to ‘proper’ lead-acid batteries:- much cheaper, much less likely to ko your entire system, and much easier to fix when necessary.
    Remember:- Murphy was an optimist,

    • Ronald Brakels says

      Well, the Powerwall 2 is warranted for 37,800 kilowatt-hours of storage. If the average cycle is 12 kilowatt-hours that’s 3,150 cycles. To get lead-acid batteries to provide 12 kilowatt-hours for 3,150 cycles would require roughly 27 kilowatt-hours worth, as even with durable lead-acids it would only be possible to do a depth of discharge of around 45% and hope to get that many cycles out of them. That means they’ll have a lot of extra charge that can be drawn on if needed, which is great for off-grid applications, but not so important for on-grid storage. So depending what batteries were bought 27 kilowatt-hours would cost roughly $6,500. But at that price there is only going to be a one year warranty, while with the Powerwall 2 example I gave the warranty will last 8.6 years. The lead-acids won’t take up a huge amount of space, but it is a lot more than the Powerwall 2. They may need racking, and they will need cabling, some sort of enclosure, a charge controller, multimode inverter, etc. They will need some maintenance and the replacement of batteries that fail. Then there’s the big cost – installation. This is invariably going to be more involved and costly than installing the AC version of the Powerwall 2.

      So I don’t believe the typical household wanting to install on-grid storage would be better off economically with lead-acid batteries. If it was possible for them to be better off, then where are the companies saying, “We’ll install a lead-acid system that can do everything the Powerwall 2 can with the same warranty, but a lower price.”

      If I have missed companies that are doing this, please point them out to me and I’ll write an article about them.

      • Paul Wilson says

        Thanks for this.
        The company installing my solar system basically ignored my suggestion of using lead acid batteries, but I’m much happier to read genuine reasons why I was making a dumb suggestion.

  15. Hello there, and thanks for some very helpful info.

    We are building a home situated too far from the electric grid to connect and are thus studying solar/battery/generator options.

    Our average consumption where we live now (on grid) is around 6-8KWh/day (yes…everyone says that’s quite low!)

    If that rate of consumption continues, then during the cloudy, dark (2.5 hrs of useable insolation) autumn and early winter around here (eastern Canada at 45N latitude), when we’d want to have several days of backup power before having to resort to a propane generator, a couple of Powerwalls providing roughly 28KWh seems ideal to provide 4 or 5 days of power.

    Any thoughts or suggestions that could guide us would be wonderful.

    Many thanks,
    Richard Hoenich

    • Ronald Brakels says

      Two Powerwall 2s will give you redundancy, which is handy in case one fails, and they could provide a considerable amount of power, allowing you run many appliances at once, although with your currently low electricity usage it doesn’t sound like you would need a great deal of power.

      If you were in Australia I would suggest considering getting just one Powerwall 2 and using the money saved to install a larger PV array, as that may be more cost effective. But my understanding is you have to pay considerably more for solar in Canada, so I don’t know if greatly over sizing your PV array will make sense for you.

  16. Ronald, that was great info. I am surprised that as you were born in Toowoomba, you did not provide any analysis for Queensland. I hope it has nothing to do with mutant attack goats. 🙂
    Being a Brisbanite, it would be wonderful if your above analysis includes Queensland or SEQ.

    • Ronald Brakels says

      Hi Wilson. I left out Brisbane because the economics of the Powerwall 2 aren’t quite as good there, but electricity prices there aren’t that far behind Adelaide these days and it might not be too long before they’re about the same. The total output of rooftop solar in Brisbane will only be slightly more than in Adelaide but will be more consistent through the year as winters are not so cloudy. Because you can get a 5 kilowatt inverter and up to 6.66 kilowatts of panels without special permission in Queensland I’d suggest a 5 kilowatt inverter and about 6.5 kilowatts of panels.

      If you want to go larger and can’t get permission, the cost of getting a system that is export limited to 5 kilowatts and gets around the inverter size restriction has been falling.

  17. Hello Guys, last month I installed additional 5 KW panels in preparation of Tesla/ Solar battery. My initial system was 6.3 KW. What I have noticed that the solar production has increased…nearly doubled but the consumption has nearly doubled as well. We haven’t really changed how we use the power in our household. I have spoken to my installer and I cannot get a clear answer. One thing is for sure is that I won’t consider solar battery at this stage.
    Any help will be appreciated.

    • Ronald Brakels says

      It could be the result of the heatwave, but if you are certain that’s not it then there is a mystery. A friend of mine was caught out by a leaking hot water system that pushed her electricity bills through the roof for months before she cottoned on. It is also possible that you have some other appliance, such as an old refrigerator, that is about to give up the ghost and is operating inefficiently. One option is to switch off various loads to see if you can identify what is using large amounts of electricity.

      Sorry I can’t be more helpful.

  18. There are a couple of issues you didn’t recognise with a PW2. Firstly, the capacity of the battery is 13.5 kW but the usable storage figure is lower than this.

    Also, there are systems like Reposit coming out that allow you to sell your stored electricity into the grid when the spot price is high. If you feed in off your panels you just get the mandated FIT. Instead, store into the battery first until it’s full, then sell excess PV at the mandated FiT. Then when the spot price is high, sell your stored energy off the battery. You can set the system to hold enough electricty in the battery for overnight use. The system will learn your usage patterns, look at the weather etc and predict your usage accordingly.

  19. All this blah blah blah and no one including the author answered the question of the tile to this article:

    How many panels does it take to charge a powerwall2 ?!?!?!?!?

    5? 10? Does anyone have an integer ???

    • Ronald Brakels says

      Howdy. Average panel size used to be around 250 watts. That would make a 5 kilowatt array 20 panels and the maximum amount of panels that could be installed with a 5 kilowatt inverter would be 26 for an array total of 6.5 kilowatts. But now higher wattage panels are becoming more common. The standard sized panel with the highest wattage available is SunPower’s 360 watt X22. It would only take 18 of them to make an array of just under 6.5 kilowatts. They’re a great panel, but carry a premium because of their high efficiency and reliability.

    • That would depend on your location, panel orientation and if you potentially have any shading issues plus taking into account any efficiency losses. If the powerwall is 13.5 KWh then your solar system will need to generate a bit more than that over the day to charge it from flat.

    • The article says you need at least 5kW of panels on your roof. How many panels that is depends on the rated capacity of your panels, the configuration of inverter(s) and roof orientation. I thought it was pretty clear.

  20. Great informative article. This is why I like Enphase’s approach to battery storage, just like their approach to solar PV — modularity. Buy just enough battery storage for the electricity your solar PV system produces in excess. A single Powerwall is overkill for most people, plus it still has that single point-of-failure that a group of modular AC Batteries won’t have. Hoping that the IQ Battery being released Q2-Q3 2017 will have a better charge rate.

  21. Hi ronald,

    I live in indonesia where we got so much sun shine like 7 hours a day. We need 20 kwh perday for our house. Our house size is only 200 square meters. Mybhouse roof size is about 174 square meter.

    Is this solar city and pw 2 can be a good deal. I plan to sell it in jkarata indonesia and some other city.

  22. Ronald

    Could you discuss how feasible it would be to charge your Tesla (or other electric car) with a large household solar array and a single Powerwall 2? The Tesla Model S battery (85kWh version) is huge compared to the Powerwall 2’s 13.5 kWh of capacity. The new Model 3 will be less no doubt …..but still it seems that it won’t be practical to charge from a home solar setup. Rather, you’d have to use the mains power.

    So is it completely out of the question to be able to charge an electric car from a home solar array (without buying multiple batteries and having a huge number of panels) ?

    • Ronald Brakels says

      Hi Tony.

      Australian passenger cars are only driven an average of around 42 kilometers a day. According to the US EPA the Tesla S gets 5 kilometers to the kilowatt-hour so that will only consume around 8 kilowatt-hours a day. With charging losses and real life driving conditions I’d round that up to 10 kilowatt-hours a day. A Powerwall 2 has 13.5 kilowatt-hours capacity when new and that is more than sufficient to fully charge a Tesla S driven an average number of kilometers a day.

      But economically and environmentally it makes no sense to charge an electric car using home battery storage, unless there is no other choice. Economically it is bad because it puts wear and tear on the Powerwall 2 battery cells. Environmentally it is bad because energy is always lost when storing it. If your electric car isn’t parked at home during the day then it would make economic and environmental sense to charge it with off-peak electricity late at night or very early in the morning.

      But if it is parked at home during the day, then unless your solar system is very small, rooftop solar will normally be sufficient. Most homes with 5 kilowatt or larger solar systems export an average of over 10 kilowatt-hours a day.

      I will write an article on charging electric cars in the not too distant future. If anyone wants to lend me their Tesla S for a few weeks so I can get the hands on experience required for a really in depth article, it would be much appreciated.

      • Plus heres the kicker – with AGL at the moment (and no doubt other power companies have similar deals) you can charge your car no matter how much energy you use for a dollar a day. Unless you can get direct solar where the EV is parked, then the alternative – using an inefficient battery to charge an inefficient battery doesn’t make much sense – although you could use a direct DC charger with a different battery technology – its not economic and all batteries are inefficient but it could be “less” inefficient. Most EVs have a direct DC charging option built into the plug – usually used in fast chargers.

  23. a.thomas says

    Alternatively buy a Prius. The EPA says it emits an average of 190g/mile
    ( 118g/km) including upstream gasoline ghg.
    ( If charged in California, where there are renewables, the figure is 140g/mile or 88g/km).

    Taking the higher figure, 5km totals 590g.
    1kWh of home solar could offest 1kWh of coal generation, saving around 900g,
    while also eliminating the tons of embodied GHG in the Model S’ battery.

  24. I got my Powerwall 2 installed yesterday. I got a 3.2KW solar panel system(German. ) Yesterday after they completed the Powerwall 2 installation at 11 AM, battery was charged 81%. Today it charged fully (100%) while providing electricity to my ongoing usage I checked my Grid usage today and it was only IKW though not sure how it happened. Very satisfied with the product.

    • Hi, I am looking at some specs from a builder who has said they would install a Tesla powerwall 2, 5Kw solar system , and a single solar panel? We live in Melbourne Victoria…. does this seems reasonable to anyone?

      • Ronald Brakels says

        Hello Debbie.

        I am afraid I don’t understand what you have been offered. A 5 kW solar system is usually around 18 solar panels these days, so I don’t know what they mean by single solar panel. Perhaps they mean a single solar inverter for the system?

        I will let you know that at the moment batteries won’t pay for themselves, especially in Victoria which is the state with lowest electricity prices and one with above average solar feed-in tariffs.

  25. My electricity consumption is about 3 kilowatts a day, I have back to the grid solar and get the 66 cent rebate, it runs out in 7 years which as I have a property and a lot of space I can install wind and bigger solar systems, I read your statistics but when I built my property I paid over $40 thousand just to be connected to “the grid” to subsequentially be charged a connection fee of $120 a quarter so your statistics are completely incorrect, if per say I used Tesla’s technology and my daily electricity as I have wood fired heating and it’s connected to my hot water system in winter and solar in summer, I fail to see how your statistics have any logic? I’m subsidising the grid and I’m subsidising clowns making themselves money because people are dumb.. give me back my $40 grand and I’ll go offline.. the realisation for powerprocers is .. their upthecrapper when peoplework it out.. cheaper to produce it yourself like having rainwater tanks..

  26. Great article as always R. One aspect of the PW2 you also need to consider is that (with the addition of a gateway) it can provide backup power. Thus the value to me wasn’t so much in it catering for nightly power consumption, but rather knowing it can kick in if I lose grid power – a problem all too common in rural Southern NSW. The problem with losing the grid feed is exacerbated as a result of also not having town water in these areas, thus having a reliance upon pumps for wet areas in the house, and stock irrigation etc. Finally, rural areas also experience ‘brown outs’ where voltage fluctuations can play havoc with not only lights, but also household appliances, technology etc. Again, the PW2 kicks in nicely to mitigate such events.

    Keep up the good work!

    — Fizz
    6.2kW & PW2

  27. Allan Burrow says

    Hi Ron,
    terrific website you have here. A bit of a problem I have is thatI’m not at all tech minded!
    I live near Penrith, NSW. I got in with the solar panels when we were able to get a 60c rebate. “They” saw the error of their ways and have now discontinued the 60c rebate and I now get a feed in tariff of 9c/Kw. The system I originally had installed was 2kw on a north facing roof with no trees to get in the way. I have 3 phase power (because of reverse cycle air-con but I have no idea whether the solar system I currently have has been connected to the 3 phase or not). My provider is Origin.
    My consumption during the last quarter was 25kw per day. Presently my daily consumption is about 30kw. Due to the usage and the costs involved I have been looking to do something about this but for this old bloke it is all too confusing, so I hope you will be able to throw some light on the subject and thank you for getting thus far! I get the impression that you are not an advocate of batteries?
    Question: Your opinion regarding what system I should have installed to reduce my bills to practically zero without coming off the grid entirely?
    Many thanks for your advice.
    Regards,
    Allan

    • Ronald Brakels says

      Hello Allan

      Penrith has Endeavour Energy as their Distributed Network Service Provider so with three phase power you can install up to 30 kilowatts of inverter capacity with up to 40 kilowatts of solar panels. So you aren’t going to need to worry about not being allowed to install enough.

      If you are using around 27 kilowatt-hours of electricity a day then a 5 kilowatt inverter with around 6.5 kilowatts of north facing panels should almost equal this in Penrith. This won’t be enough to reduce your electricity bills to zero, but it should cut them by over one-third. To get your electricity bills down to zero will require a much larger system and most people don’t have room on their roof for more than 10 kilowatts of panels, so it would be difficult. My advice it just to install as large a system as you reasonably can.

      If you are going to install as large a system as you can then it is likely to make sense to remove your old one to make room. This will mean you won’t have to worry about maintaining two systems.

      You are right that I don’t approve of batteries because at the moment they don’t pay for themselves and are an environmental negative. But if people understand the drawbacks and want to get them anyway, that’s fine with me. In a couple of years they might save money.

  28. Allan BUrrow says

    Ron,

    many thanks for your reply. I will take on board your comments.

    Depending on the costs involved and taking into account that me and the boss are in our early eighties I’m starting to wonder about whether we’ll get our money back before we fall of this mortal coil or should I just continue coughing up to these thieving electricity companies and increasing tariffs.

    I am also wondering whether buying the biggest output panels I can get would be beneficial. I have seen 500 watt panels but have no idea of their size or weight and whether I can save any roof space by doing that. It appears that 250/300 watt panels are about 5’6″ x 3’3″ in old money so I’ll have to see if I can find out more.

    Once again, thanks for your advice and you have a good website. I will be referring anyone I know who is going down this track to have a look at it. Pity you’re not in NSW if an d when I do this!

    Cheers

    Allan

    • Ronald Brakels says

      Hello again

      If payback time is important then don’t go for the largest system you can. A 5 kilowatt inverter with around 6.5 kilowatts of panels can pay itself off in 5 years if people are usually at home during the day. If you want a faster payback period you can get a smaller system. This will make it easier to leave your current one in place.

      Generally you should avoid the larger solar panels that are around 500 watts. These are made for solar farms and operate at higher voltages than normal residential panels and so I don’t recommend them for homes. The largest residential panels are 360 watts and that’s a premium panel that costs considerably more than average. Most residential panels are around 300 watts or less.

  29. Allan Burrow says

    Thanks for your advice Ron.

    I think I will aim as a minimum the 6.5 Kw system you advised but I will also have a look and see what an 8 Kw system would cost and maybe covering the whole roof as well. I don’t think I will go for a “battery ready” system for the reasons you have mentioned.

    Thanks again Ron for your time and advice, much appreciated. The “advice” I have received to date on this subject has been tendered by salesmen who have great difficulty with speaking English!!

    Cheers,

    Allan

  30. Hi Ronald,

    With batteries the way of the future, would I be better off installing a larger than presently required system that has some amount of spillage after the maximum 5 Kw amount had been exported to the grid ? or would I be better off installing only what I would use now plus the maximum 5 Kw grid export and installing the required additional panels at the same time that I purchase the battery in the future?

    Cheers,
    Tony.

    • Ronald Brakels says

      Hi Tony

      If you have the room on your roof I’d say your should pretty much always get as close to the maximum panel capacity of 133% of your inverter capacity. So If you have a 5 kilowatt inverter I’d suggest having as close to 6.66 kilowatts of panels as is practical. The amount of output that is lost doing this is not significant. I go into this here:

      https://www.solarquotes.com.au/blog/oversizing-solar-arrays/

      It is always going to be cheaper to install a larger system from the beginning than to add extra panels later and you’ll benefit from the extra electricity immediately.

      • Tony Chiverall says

        Thanks Ron,

        Apart from wasting generated solar energy and a having a slightly reduced ROI, are there any other negatives to having a larger system than is immediately required? i.e. damage to hard ware or the alike?

        I’m trying to decide on whether to install a 7.8 or an 8.5 kW Enphase IQ7 plus system using REC 355 kW panels. If the only negatives are the ones I have already identified than I will go the larger system in preparation for the possible addition of a battery system in the years to come.

        Regards,
        Tony

        • Ronald Brakels says

          Hi Tony

          I can’t think of any drawbacks. With Enphase IQ7+ microinverters and 355 watt panels you will panels will be at only 122% of the inverter’s capacity. Inverters can usually handle at least 150% of panel capacity — often considerably more. Their datasheets says they are commonly paired with 440 watt panels would would be 152% of the inverter capacity. So I don’t see any reason not to get the larger system.

          REC panes recently increased their product warranty to 20 years:

          https://www.solarquotes.com.au/blog/rec-solar-panel-warranty-mb0897/

          And while Enphase microinverters only have a 10 year warranty in Australia they have a 25 year warranty in the US which I consider a good sign. (But note they aren’t exactly the same product because of different electrical standards between the two countries.)

  31. Peter Ross says

    Will Enphase allow the IQ7 to be used off grid?

    • Ronald Brakels says

      Enphase’s IQ7 microinverters aren’t made to provide power during a blackout and will shutdown if the grid goes down the same as a typical solar inverter. But Enphase says their IQ8 microinverters will be able to supply power to a home when the grid goes down and they may be available this year according to Enphase.

  32. Ausgrid in Sydney, at least in my area (Sutherland Shire) allow 10kw systems (not 5kw as stated in the article).

  33. RON, Thank you for some very pertinent information. We live in Canberra. We are building a new house and the builder has offered a”deal” amounting to a 6KW solar array and Tesla Powerwall 2. The house will have a 20KW reverse cycle system and has a good NNW orientation. We are retired and will spend a lot of time in the house. We are trying to decide whether to increase the cost of the house by installing an 8m meter by 5 meter electric undertile heating system in the family/meals/kitchen area. The idea is that we would use the solar energy stored in the battery each day to get the undertile heating system warmed up in the early morning; we understand it can be quite power hungry. Anything left over will go towards the reverse cycle system as we will need a deal of heating in winter. However, although we have cold mornings in winter we do get good sunshine most of the time.Will this work?

    • Ronald Brakels says

      If you want to get a battery system for non-economic reasons that’s fine, but when it comes to economic return it will never pay for itself in Canberra at current prices even with the ACT’s battery subsidy thanks to the low price of electricity in Canberra. You’d be much better off spending the money getting as a large a solar system as you can reasonable fit on the roof. As you are getting a large air conditioner that should mean you have 3 phase power which means you shouldn’t have a problem getting a solar system much larger than 6 kilowatts.

      The 20 kilowatt figure for your air conditioner would refer to its cooling power. At full power it might draw 5 kilowatts, which is still a considerable amount.

      Under the floor heating is extremely wasteful of energy if it’s not properly designed. In Europe they put massive blocks of insulation under the floor when installing it. Without that sort of insulation in Canberra the water content in the soil will wick the heat away. If you use lower cost electric resistance heating for the floor will will use around 4 times as much energy as if you use a much more expensive heat pump floor heating system.

      Using an air conditioner as a heater is more energy efficient than electrical resistance heating that space heaters use. Provided your home has reasonable insulation you can get it nice and warm during the day using solar power and it will remain tolerable until the next day. Good insulation is a cost effective way to keep your house warm using solar power.

      Unless there is a special reason to have solar installed by the builder you can be better off waiting until the house is built and then seeing what’s available. That way you keep your options open.

  34. Why are Australian systems limited to just 5 kW inverter systems or 6.66 kW solar panel maximum?

    We have a 16.38 kW solar system in Florida USA.
    We also have two of the Powerwall 2 battery packs for a total of 27 kWh of storage.

    Frankly, for having a 3,000 sq ft house with two AC units and one electric vehicle, I feel all of that is sized just about right for our household of 6 people (4 kids).

  35. We have a Powerwall 2, 8.91 kw system, 28 solar panels. We are making up to 65 kWh per day as in full summer. We are in Victoria, Australia. We do have a 5 kw limit of export to the grid, and a 5 kw charge and discharge to the Powerwall. 5 kw back to the grid seems pretty standard in Australia, although there are some people, some areas, where their feedbacks are even less. Sometimes they are cut to 0, all depends on the capacity of the grid. Some areas are now encouraging people to use more power in the middle of the day to prevent overload of feedback to the grid.,In one state they going to offer off peak prices to peak times, so appliances, like hot water services, are programmed to come on midday, not midnight.

Speak Your Mind

*

GET THE SOLARQUOTES WEEKLY NEWSLETTER
%d bloggers like this: