Tesla Powerwall: Number Crunching Pricing And Payback Times

Back in May, 2015, we crunched the payback figures for the Powerwall, based on an assumed Australian cost and example electricity prices. Now there are local installed costs available, we have broken out the calculator and gone over the figures. The question is, can the Powerwall give a decent payback time?

This post originally appeared on Lifehacker Australia.

Check out our previous numbers, or catch up with the announcement of Powerwall in Australia. Of course, there are other companies offering competing technologies, for various prices.

But for now, this is what the Powerwall will cost. Hot tip, the juicy bits are in bold.


Assumptions

The prices used for this calculation are from the Natural Solar quote system. Due to various factors, such as install issues, prices will vary on a case by case basis.

The calculations are quite simplified and don't account for a lot of financial factors, which can vary from person to person. But it's a starting point.

Electricity prices are based on my own AGL bill and the calculations simplified. Swap your own power usage and costs in and re-run the numbers for a more personalised figure.

Prices used are $0.2377 per kWh, and $0.7596 a day surcharge for peak. Off Peak numbers are $0.0674 a kWh and $0.0517 a day supply charge. Solar feed in tariff is $0.051 per kWh.

We have used an average daily production of 3.9 kWh per 1kW of solar, for a Sydney location, based on figures from Solar Choice.


Powerwall + Solar

Natural Solar quote $16,390 for a 4kW solar system and 7kW Powerwall, installed. A 6kW system bumps the price up $18290. The prices includes any Government rebates.

If ordered before the end of January, 2016, there is a $1000 discount on the prices, which we have not included.

The prices are for single phase installations - three phase saves a little of the price. For our numbers, we used the single phase prices.

As of January 15, the prices are as below (with $1000 discount) for a Powerwall + solar and inverter, installed.

The 4kWp Three Phase $13,990 The 4kWp Single Phase $15,390

The 6kWp Three Phase $15,990 The 6kWp Single Phase $17,290.

The 4kW system will produce 15.6 kWh a day, about which 7.5 kWh is used to charge powerwall. The remainder is fed back to the grid, earning $0.4131 per day.

The Powerwall can offset around 6.5 kWh of power usage, saving $1.54505 a day.

The total saved and earned is $1.95815 a day, or $714.73 a year. Payback is 22.9 years.

The 6kW system saves the same power each day, but earns $0.8109 a day from the feed in tariff. The 6kW system saves $2.35595 a day, or $859.92 a year. Payback is 21.3 years.

4kW Payback: ~ 23 years. 6kW Payback: ~ 21 Years


Powerwall and Existing Solar

For owners with solar already installed, there is also an option to just have the Powerwall installed. Costs vary a bit depending on if a compatible inverter is owned, but given as $9500.

We assume that the current solar system has fully paid for itself (not just been paid for), otherwise it’s remaining cost needs to be factored in.

The Powerwall can offset around 6.5 kWh of power usage, saving $1.54505 a day.

Any potential feed in tariff is not included in the price, as it’s production is not included in the Powerwall cost. It could be giving additional savings however.

By charging the Powerwall (7.5 kWh), instead of getting the feed in tariff, $0.3825 is lost. Total saved is $1.16255 a day, or $424.33 a year.

Payback time is 22.4 years.


Powerwall + Offpeak charging

With no solar, offpeak power could be used to charge the Powerwall.

Assuming the full supply costs, charging the Powerwall costs $0.5572 a day. It can offset $1.54505 a day, giving a total saving of $0.98785 a day, or $360.57 a year.

We assume the same install cost as existing solar - $9500.

Payback is 26.35 years.


Going Off Grid

By ditching the connection completely, we can avoid the $0.7596 a day supply charge, but can’t sell back any excess power.

Each Powerwall needs around a 2kW of solar to be fully charged on an average day. Adding more powerwalls into the system gives greater capacity, but does not increase or decrease payback time.

No specific cost is given, but we have assumed $25,000 - the cost of a two Powerwalls, plus a 4kW to 5kW array, based on a combination of the above numbers.

Likely a real off grid system would need more Powerwalls, but the payback time is the same.

The system can save $3.0901 of electricity costs a day, plus the $0.7596 supply charge, for a saving of $3.8497 a day, or $1405.14 a year.

Payback time is 17.8 years.


Summing Up

For now, most people won’t get a very economically viable result from a Powerwall. Considering the warranty is for 10 years, a payback time higher than this is not ideal.

To get a 10 year payback, electricity prices would need to be $0.40 a kWh - not an overly high figure. Some providers do variable pricing, but the Australian average is closer to 30 cents a kWh, which gives a 14 year or so payback time.

For many people (such as myself), better payback can be had from simply keeping the money in an offset account. In the future, financing plans may improve the proposition.

There are a lot of factors that could affect the payback times, most importantly the cost of electricity. It’s hard to predict what electricity prices will be in the future, but with an increase in solar and battery storage, it is possible they could drop, further increasing the pay back time.

Still, the future of solar and battery storage is a bright one!


Comments

    The payback period needs to be between 5-7 years (or less). Anything more than that and you're kidding yourself. The advancements in battery technology over the last 10 years have been huge, largely driven by electric car development, and portable technology development.

    We will continue to see these increases over the next 5, 10, 15, etc years.
    I was going to consider a solar setup with a battery pack, but the numbers just dont add up yet.

    Solar needs to become a lot more efficient, and battery storage needs to become a lot cheaper before it can be a viable alternative to the grid.

    The power companies know this, and will take advantage of it.

    Lets revisit each year these calculations to see how they improve eh Gizmodo?

      For me the payback period would have to be 5 years max for me too want to consider it.

      I agree. I doubt a lot of people are going to use this same system 15-20 years into the future.

      Also, I did not realise the cost of installing these things are that astronomical... yesh....

      mate of mine bought 20 panels from china and his inverter he lives in a pretty windy place and build several windmills that spin a car alternators that feed a bank of batterys he has no actual grid power with the solar panels and generated from wind

    So, it's a good article and it is very useful for people who are putting solar/batteries into houses they plan to own forever.

    BUT...

    Rather than setting this only against the power, see these systems should be seen as an investment. A $16 - 18k investment. The total house price will easily increase this amount. People will see these systems when buying a house and will pay more.

    A kitchen of $15k will increase the value of the house and has no payback time.

      If i'm not willing to spend $16k+ on a system as it will take 15+ years to pay off, why would i pay extra for a house with it already installed?

        No different to solar panels or a pool or any other non essential feature. Its built into the house price. You couldn't reduce the house price if it was removed. The unimproved value and how many bedrooms you have cover 90% of the purchase price long before luxuries addons do.

        Because it's already installed and will save you time. Time is money and this is why most people who can afford things buy things :)

        by the time its paid off it will be due for new hardware solar panels only good for like 25 years

      That's only an investment if you sell (or can extract the equity, but that is unlikely). If you live there for 20 years, then any potential price increase is not very useful.

      No one is going to pay that extra amount for a house that has $15k worth of solar on it. It's a sliding scale. Panels and the technology around them are only going to get better and CHEAPER.

      As already mentioned, payback period needs to be ~7 years to make it worthwhile

        Not to mention the batteries have a shelf life of 20 years and solar panels only last 30.

      "Rather than setting this only against the power, see these systems should be seen as an investment. A $16 - 18k investment. The total house price will easily increase this amount." Maybe when you install it but how about in six or seven years time when your battery capacity is down to 50% of what it was new? I'd suggest at that time it will become a big liability.

    Completely agree - a 20 year pay back is too long. Tech and cost assumptions would change dramatically over 20 years to safely assume the decisions made today would be positive or negative either way.

    This solution does not seem to make a lot of sense in terms of economics - rather more in getting off grid to reduce the environmental impact of using carbon emitting power sources.

    I guess it comes down to, is protecting the environment worth the cost?

    You seriously think that the cost of electricity might fall? I, on the other hand, predict that in the next 10 years the cost will be quadruple what it is today.

      Thanks Lindsay for doing the math.

      Lot's of people will go off grid and get batteries anyway, as this is not just about saving money it's about going green. [The system is after all less than the cost of a small car or a caravan or boat or....]

      People will be leaving the grid so then the cost of electricity will go up to keep profits up and payback will be shorter. Electricity prices doubled since 2007, so it would be good to crunch the numbers based on this.

      Also looking at smart local grids, where I sell my excess power to my neighbour. Looking at electric cars/bikes too and petrol savings, this could easily drop to 10 years or less. Oh and perhaps we will actually try and do something about CO2 emissions as well which will effect fossil fuel subsidies and prices.

      I would say these numbers are just a starting point.

      I said it's possible, not that it will, or won't drop. The influence on new technologies is rapidly changing how we produce and consume power, so it's certainly possible that prices could drop.

      We are using less electricity than ever before thanks to more efficient technologies and also the closure of manufacturing. Energy companies need to pay a lot of money when there are large strains on the grid. There are now fewer strains on the grid. So I wouldn't expect energy usage prices to significantly jump.

      Mind you, energy retailers still want to profit, so they will find a way to get their money.

    So I am on a smart meter in NSW - my peak cost (2-8pm) is 51.1c/kWh and off peak (10pm-6am) is 8.8c/kWh. Assuming I charge the powerwall overnight at 8.8c and use it during peak time at 51.1c, then the savings is $2.75 a day. At an install cost of $9K, that is just under 9 years payback period. And that is ignoring the 4kW solar array on my roof (which - if set to charge the batteries too would reduce the payback period further). But for me, the big savings is the different between the offpeak time-of-use tariff and the peak time-of-use tariff. The environmental benefit of this (I think!) is in reducing usage during peak periods and moving it to off peak - using the base load power (which is there whether people use if or not i think?).

      Yep, that could certainly be a good deal. The important thing will be how your power company will handle off-peak charging - I can see them 'refining' their offers.

        The reality is that they WANT us to use off peak at the moment - that is why it is priced so. Off peak power costs them nearly nothing, whereas they pay huge amounts when usage spikes. But - if suddenly everyone is charging batteries overnight (e.g. in the move to electric cars) then you are right - off peak will start to cost more as the requirement for base load energy increases. But i reckon we have a 10 year window at least before this starts to happen.

      The power companies already have different pricing for Solar Customers – no pay on time or other discounts etc, this could reduce your bill by 10-15%. So I'm sure for battery customers they will remove the off-peak / on-peak pricing eventually. Unless the government regulates that in some way.

      Looking at the figures above, I'm thinking big families with big houses who use lots of energy could knock off a few years from the payback schedule. Because you never want to sell any energy back to the grid. You should use it all, and that's the power of a battery in solar system as most people use the majority of their energy when the sun doesn't shine.

        I have contract pricing with Origin for several large businesses and i have asked the question and they have no problems with solar. They are happy to give the same discounts on a solar sites. We are on time of use metering.

        i cannot say they will stick to this, but at the moment they seem fine with it.

    I think the powerwall concept is about the power stations smoothing out their load, there for not wasting carbon resources to boost peak output when it may or may not be needed.

    But this would require widespread adoption before it could begin to work. The only thing befitting from this is potentially the environment (arguable since manufacturing these things has to be done at a cost to the environment).

    These things (incl solar) are far too expensive to be a viable alternative, for now.

      Powerwall is battery only, no charger nor inverter.

    The thing with the powerwall is its one unit. Where as traditional installations you need more reserve, get more batteries and or cells. Need more continuous power get a bigger inverter. One component dies replace it. With the all in one powerwall it does have size in its favourite but you are kind of locked in to it.

      Powerwall is battery only, no charger or inverter.

        As it's outputting AC, it definitely has an inverter. And as it can store power there is something in there rectifying the mains AC to DC something like a charger. Or from solar something to regulate the charging of the battery like a charger.

    ITT we massively fail at discounting cashflows.

      I don't include anything beyond the basic numbers, as it gets very complex, and specific to individual situations.

        But then you are equating a dollar 'saved' in 20 years time to a dollar spent today. In reality, that future dollar is going to be worth more like 61c in today's currency, so the 'payback period' is actually far worse than the article implies - closer to 35 years.

        And that's just using inflation. In reality, spending $15k on a magic house battery means that you either borrow it, don't save it or don't invest it. So the true discount rate is going to be higher.

        Using real numbers, that 4kw single phase system doesn't 'pay for itself' ever unless you start making some leaps about future energy price growth and assuming Elon's dark sorcery gives it an infinite, maintenance free lifespan.

        Last edited 18/01/16 5:23 pm

          For my calculations I assume that the payback rate stays the same, so all the numbers used are in today's dollars.

          I am not sure I follow your example though. If I understand correctly, you are saying that the payback rate will reduce over time - so electricity costs (and thus potential savings by the system) will decrease over time (in today's dollars), and give a longer true payback.

          What causes that, or is there some other factor I am missing?

            If inflation is 2.5% then $1 today will be worth 61c in 20 years. This is what discounting tells us. jjcf is making the point that, accounting for inflation alone, the actual discounted pay back time is 32 years (by my calculations anyway) for a single phase 4kw system.

            And inflation is just 2.5% while a realistic discount rate would be at least 5% - and likely more. But even if you make the discount rate 5% then the discounted payback period is infinite (Excel errors for me at 14,500 years and the NPV at that point is still -$1,095 and hasn't changed in some 14,250 years).

              And applying 2.5% inflation, the $1 electricity bill in 20 years costs 61c in today's dollars. So $1 of savings today will be $1.59 of savings in 20 years.

              The payback rate stays the same, unless you assume that electricity prices (in today's money) rise or fall over time.

              I assume that electricity prices stay the same in today's dollars. That is unlikely, but without hard data on a decrease (such as your example), or an increase, I think using no change is the best bet as a starting point for further calculations.

      Hate to make this look any worse, but adding $16K to your mortgage adds $700+ per year to your interest payments making this a net $0 income, with a depreciation well over $1000 per year as it's a finite product. Even if electricity prices are likely to rise in the future, so are interest rates, even though neither are guaranteed.

      That said, wasting $1K per year on this product would still put you well ahead of what people waste to look cool each year, so this might be a more appealing thing to throw a bit of money at for some people than a cool car or clothes.

    I can see one critical flaw here and that is the service life of the solar panels. Generally its 15 years and then their output efficiency begins to decline. Replacing the panels then becomes costly as not only do you have to purchase and install new ones, but also dispose of the old ones correctly.

      25 years if 80% new capabilities is often used. But yep, that will increase the payback time, depending on exact numbers.

    Doesn't lithium batteries have a limited lifespan and certainly not in the twenties?

      The batteries are rated at 5000 cycles, which is typically to 80% of new capacity.

      But there is no specific data on that (and there are a lot of factors, such as exactly what they count as a cycle, load levels etc), so I have not included it in the calculations.

      But 14 - 15 years to 80% new capacity means that there should be significant lifespan left in the batteries up to 20+ years.

      But very likely the loss of capacity over time will increase the payback times.

        Tesla are offering what they say, is a battery that now makes home storage practical - but it's not cheap enough, nor is it good enough.

        Some revised specifications are now available from Tesla's website, under Operator's Manual and Warranty.

        1) Capacity of the 7kWh unit is 6.4kWh. (That is the amount that may be stored and extracted.)

        2) Cycle efficiency is 92.5%. (Meaning that to get 6.4kWh out, input must be 6.9kWh.)

        3) Power output is 3.3kW continuous.

        4) Warranty is 10 years. Capacity 'retention' is 'at least 60%', leaving ~3.9kwhr to be extracted. The rate of decline is not stated, but it is certain that the full 6.4kWh will not be available for the period of 10 years. Cycle efficiency will decline, too. That can be very bad, if loss of (initial) capacity, is compensated by increased depth-of-discharge. Since cycle efficency is not guaranteed, that is a real possibilty.

        Your expections of battery life appear to be based upon general standards, such as 80% end-of life, and defined depth of discharge, etc. But, Maverik 'game-changing' battery companies, have other ideas, too.

        Now that more details are known, payback will be even longer.

          Some more warranty details, as of 22-Jan-16.
          https://www.teslamotors.com/sites/default/files/pdfs/powerwall/Powerwall_Warranty_Australia_en.pdf

          From the warranty;
          >85% at the earliest occurrence of 2 years or 4MWh accumulated discharge.
          >72 % at the earliest occurrence of 5 years or 9MWh accumulated discharge.
          >60% at the earliest occurence of 10 years or 18MWh accumulated discharge
          Measured at 2kW output, ambient 25C.

          My comments.
          At 6.4kWhr/day, 4MWh arrives after 625 days, but the warranty does not guarantee more than
          85% retention, so capacity could be as low as 5.44kWh.
          72% retention means that after 5 years, capacity could be as low as 4.61kWh.
          60% retention means that after 10 years, capacity could be as low as 3.84kWh.

          Assuming the intial capacity is retained, the accumulated total discharge is approximately 2.3MWh/year, so 23MWh over 10 years, and 46MWh over 20 years. But, the battery is all but expended after a total of 18MWh is obtained.

    Would love to see the comparison to AGL's $0 down plan. Popular in the states. http://aglsolar.com.au/zero-dollar-solar/

    This entire argument is flawed. It's all horse-shit.

    There isn't an expected payback period on ovens, or hot water heaters, or other household appliances that are commonplace now.

    Getting a battery bank, be it a Tesla Powerwall or something else, is adding functionality and independence to your home. Household battery systems will become absolutely standard and expected.

    In the not too distant future, all real estate listings will have the home's kWh storage potential, just as they currently have bedrooms, bathrooms, car-spaces, and gas/electric cooking.

    If you want to try and apply some kind of potential payback metric to it, you're fundamentally misunderstanding the product's purpose in the first place.

      I have experienced about 5 blackouts in my life, none of which lasted for any significant length of time. The longest was a scheduled outage while I was not there.

      My laptop is good for 15 hours+, my phone double that and I have a power bank which can run my modem for days (or recharge the other devices). I have stored hot water, so I am good for at least a day of showers.

      My biggest issue is that I have to watch Netflix in bed on the laptop, instead of on the TV. And light the gas stove with a match, or eat leftovers.

      What's the functionality worth the cost of having a Powerwall?

      I understand that for some people, being independent of the grid is very useful and important. But for most of Australia, interruptions are minor and I don't see much point of grid independence.

        I can't tell if you're deliberately missing the point.

        The idea that we've been boxed in to for many years/decades now, which is only thinking in what something does for us in purely economic terms, is a complete mirage.

        Battery systems, and power generation arrays, are going to become so ubiquitous that any household that doesn't have one will be seen as an outdated relic in need of immediate upgrade were it to be on the property market.

        I grew up in an old, old home. We had a slow combustion stove where the cooking and heated water was from the continuous fire you had to keep fed with firewood. We had a copper and a mangler to do the washing. I don't know what the payback period on a washing machine or stove is, but I can tell you that if you were to try and get people to go back to using a copper and a mangler, you'd have a tough series of discussions in front of you.

        (Fun non-sequitur- during one of NSW's longest ever blackouts in the early 80s, our house was one of the only ones to actually have hot water and a way to reliably cook something hot. Maybe we've all missed a trick moving on to the electric versions of these appliance?)

        There's a whole new language we're all going to become familiar with, and it will be all around kilowatts and kilowatt hours.

        I would really, really hope that a tech site like would have that ground figured out by now.

          Your stove and washer examples both offer big gains of functionality.

          If I install a Powerwall, the functionality of my electrical system is almost unchanged. The main consideration to me are the financial gains, or lack thereof.

          A better example would be upgrading from a standard hot water system, to a heat pump or solar system. The functionality remains pretty much the same, but there can be significant financial gains.

          Rlnce, at least include some examples or predictions of how battery banks will add additional functionality to homes in the future, rather than just ridiculing the article like a crazy homeless guy ranting on a street corner!

    We have solar power at home. Survivalist chic, completely off grid (no mains power running to the house at all)... all started with gas lights and a gas fridge then a small solar system for lights and a small television, upgraded the system with the extension, upgraded again when more kids came. Now with an inverter we can run any 240v appliance including a fridge, thermomix, PS4 and other high power devices, no problem.

    Yes, very rarely the batteries run out... but then again, when the grid cuts out, we are the only ones left with lights on! Is it worth it for being off-grid and 100% self reliant? Of course it is! Why are you still even debating this :D

    My question was always: what's the lifespan on the Powerwall battery?

    10 year warranty, fine. But what's the degradation on the cells? How long does the actual unit stay at ~100% efficiency? I always imagined this would dwindle over time, which is something that doesn't seem to come up in conversations

    Decreased consumption is precisely why prices will rise, as sales fall the only way for utilities to protect their revenue is to raise prices, this progressively makes self generation or even going off grid more desirable which makes demand fall faster. This is the utility death spiral and examples of it are occurring all around the world.

    Too expensive atm...Elon M said 3500 US so how it then gets to 9500 AU is laughable and sadly means I won't be partaking of this anytime soon. If EM wants to change the world he has to expect the world to pay a whole lot cheaper than nearly 10k for everyone to have a Powerwall.

      $3000 US for the 7kW system in discussion here. But that is the pre-tax, wholesale price.

      So at today's exchange rate, that's $4,338.

      Plus GST, is $4772.

      Which is about half of what it costs in Australia right now.

      So what is that included in the other ~$4728?

      Transport / storage costs, an inverter, wiring etc, the actual installation costs, plus some actual profit for the company doing it all.

      Prices will drop, but what we are seeing right now is pretty reasonable.

    I looked at this a different way - cashflow. Tell me if my logic is sound? I spend $2500 on power a year. If I can offset 100% of this in 10 years that is a 25k saving. What I see solar + battery helping is moving the existing workloads around to try and offset as much as possible. If I can offset $1700 of my existing usage using a combination of both it might be possible to payback in <10 years. The Feed-In tariff is great but running all my appliances during the day at 0 cost is greater.

      I don't know your power rates, but at my rates, you would need 4.5 Powerwalls to offset your usage each day.

      With solar, it's probably about a $50,000+ cost to install. So the same ~20 year payback.

      Higher consumption does not really decrease payback time, because more units are required.

      It also get's more complex if you want to include the 'cost' of not investing that $50,000 instead.

        Thanks for your reply. Yes the full cost will be a bit as you stated but what about part of the cost - would it be possible for you to offset A single powerwall + solar system or $1700 a year by moving things around? I have an electric car hence the higher power usage (7kw a day).

    Powerwall is a battery only. It is an add-on to a normal solar system of panels and inverter.

    Nobody if they negotiate their tariffs with their energy supply company should be paying more than 28c/kwhr peak (0700-2300) and 18c/kwhr off-peak (2300-0700) for usage and supply charges (poles and wires) should be around $1.25/day inc GST depending on where you live. I already have a solar system installed at my home in Victoria and my average quarterly bill was approx $750 ($2500/yr) family of 5 in a 4 bedroom house. My system cost me $6000 and the payback will be less <5 years taking into account an estimated saving of $1250 a year and people forget the ever increasing prices in power from when you have first installed your system. The systems quoted above are entire systems so you achieve the same savings that I have but also the added savings from being able to store the extra you don't use to remove your home usage during peak times up till 2300hrs where depending on your export tariff with your supplier 5c/kwhr for people putting in systems now or maybe a little better if you can negotiate it with your Energy supplier as I have heard some people have. So instead of getting 5c/kwhr you are now making 28c/kwhr because your not paying to import it!
    Then when your usage is low if the Tesla battery is low it will recharge after 2300hrs at your off peak Tariff.
    But every ones situation is different as in the climate they live and the size of their family and this all affects the payback on the system you install but I believe they are a great investment in our environment and the paybacks are not as long as the estimates given above.

    The other thing to remember is that solar systems on their own were the big thing, how much were they? Much dearer than they are now and now more superior in quality also.

    Teslawall payback: The whole discussion for a sensible payback time is a good one but must include not only kWh prize figures. It is very important to actually make a real calculation rather just based on kWh prizes and must include real lifetime cycle cost inclusions. Then the picture become a lot better for solar energy providers in comparison to coal or nuclear.

    When we started with solar energy in the mid seventies in Switzerland the whole economic industry was having mild smiles on their faces and regarded us solar startups as kind of "play in the sandpit" physicists who are dreaming.

    Well, we all know now that photo-voltaic silicium cells have droped down so dramatically that today solar installations in Western Australia for a 5kWh system cost about $4000 installed. And prizes are falling further.

    The real discussion should be that the actual kWh prize from the facility providers are far to low and in fact if one really takes into account the real environment cost from coal power stations or nuclear power stations [where burnout radioactive cells will be stored for hundreds of years and left as problematic inheritance for future generations] that the actual kWh prize would be even higher.

    Therefore, actual comparison costs discussions are really not apple with apple comparison discussions and do not show the real picture.

    Germany for example has decided with a political decision that the investment for sustainable energy pathways are no longer an illusion, rather they have to be a complementary solution in the whole energy provision discussion. Further sustainable energy facilities provide jobs.

    The real discussion should be how long do we want to continue as a society to accept that fossil fuels are no longer really the right tool for our energy problem worldwide. We require to find new models that provide real solutions where the whole environment is included in a holistic thinking process.

    If anybody takes the time to explore the universe one will realize that there is no other EARTH parked next to our EARTH and we cannot just jump ship. If we take time to study the complex relationships that the whole planet is trying to keep a fine balance between nature and the influence that human beings have on this extreme fine natural balance than one would very quickly realize that our behavior is essentially the key to the solution for our energy problems. One solution is to think in what state do I leave this planet for future generations, rather than thinking how can I profit optimize the payback time of a solar system.

    Most of you, including the articles author are missing the point. Someone looking to have a battery backup such as a Tesla Powerwall, wants it for when the power goes out, not to get some sort of return on investment. A generator is several grand by itself and doesnt save you money on your electricty bill, its there for when the power goes out, that is the market that the Powerwall really applies to, especially to people with wind/solar generating on their property.

    Also every one of you is wrong, solar panels do increase property values.

      Solar panels are like swimming pools, a liability if not fault free. In Sydney solar panels are supposed to be flush with the roof (parallel is not the same as flush) and very few are. Many homes are sold without title to the solar panel system. Most systems do not support the emerging 48V bus standard. Unless you are mining crypto currency directly there is very little benefit any more, you sell at 5c and buy at 26c, why would you ever sell ? This is where the battery comes in, there is no real ROI in storing off peak as the capacity costs too much. 26 years, really, the opportunity costs and capital costs are too high. I would use one in an apartment (if allowed) for redundancy and power conditioning. A mitigant for brownouts, surges, and blackouts. The UPS value alone from a 7KWh unit in a single bedroom flat is considerable. As an IT professional I would aggressively depreciate the unit over a lot less than 26 years. Recognise too that these things "create their own demand" as utility companies world wide use reduced demand to justify retail price increases.

    "The 4kW system will produce 15.6 kWh a day, about which 7.5 kWh is used to charge powerwall. The remainder is fed back to the grid, earning $0.4131 per day.

    What about actually using the power during the day, rather than just feeding it back into the grid? Surely if you can use the power it's worth more.

    Also, what about interest on capital?

    So disheartening that the majority of comments above centre around the economic viability of these systems whilst completely ignoring the positive environmental implications. I earn less than $60K per annum and for me the equation is simple, if I can afford to pay for 15-20 years worth of Power usage UP FRONT and completely eliminate my dependence on Coal Fired Electricity, IT'S WORTH IT!

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