back to article Tesla reveals Powerwall battery packs for homes, Powerpacks for cities

Billionaire biz baron Elon Musk has revealed Tesla's long-expected battery products and claimed they put an end to humanity's production of carbon dioxide as a by-product of energy generation. “No incremental CO2 is the future we need to have,” Musk said, during the battery packs' launch, advocating that charging his new …

  1. hekla

    Half the world excluded from this

    The maximum temperature of 43C will rule out much of the world between 40N and 40S latitudes. 45C is a regular summer temperature here in Australia.

    1. cmannett85

      Re: Half the world excluded from this

      "Half the world excluded from this"

      No it isn't, it just means you have to have it inside your house.

      1. YetAnotherLocksmith Silver badge

        Re: Half the world excluded from this

        So you can keep the battery cool with your air conditioning. Great idea.

        And you have solar powered air con, right?

      2. Anonymous Coward
        Anonymous Coward

        Re: Half the world excluded from this

        Unless actually air conditioned, many Australian houses can easily exceed 43oC inside, all night.

        1. Leslie Graham

          Re: Half the world excluded from this

          You don't have to air-con the whole house to keep a little box cool. You just need a super-insulated box with a little air-con inside it.

          Basicaly it's like keeping it in the fridge. And seeing as you will be getting unlimited free electricity whats the problem.

          Oh right - there's no problem - just someone who can't stand it that those stupid cuffing hippies have been proved right yet again. Solar is simply a no-brainer for preventing global warming and stupid cuffing hippes lime me have been saying that for nearly 30 years now.


    2. Anonymous Coward
      Anonymous Coward

      "...he proclaimed that all of humanity's energy needs could be met by..."

      ...Rechargeable batteries.

      If he really proclaimed that, then he's a moron.

      Hopefully it's a quote taken out of context.

  2. pro-logic

    I did some back of the envelope calculations.

    USD$3000 -> AUD$3800 (claimed 92% efficiency)

    2kwh inverter -> $625 (claimed 97% efficiency)

    Peak power: $0.35/kwh

    Offpeak power: 0.12/kwh

    7khw (the capacity of the battery) would taking efficiency into account take about 7.8kwh to charge, or about $1.02. Using that same power from the grid during peak would be $2.75.

    So for each cycle you'd save $1.73. To offset the $4,425 purchase price would take 2552 nights. Or pretty much 7 years.

    At least I think those numbers are right.

    These are purely grid-connect time shifting power requirement. Solar generation would change the numbers, but probably depending on your solar farm size. Even assuming you change for "$0" from the solar panels it would still take 1600 nights of about 4.5 years.

    The numbers don't quite stack up in my neck of the woods.

    1. Voland's right hand Silver badge

      The 7 years number is a magic number

      Anything you try doing on energy efficiency of a house (except insulation) the return is seven years.

      Solar ~ 7 years. Heat pump instead of central heating ~ 7 years. Condensing boiler + aux systems necessary to replace at a time) ~ 7 years.

      I have done the math plenty of times and once you account for interest rates, etc you suddenly realize that your old conventional gas boiler is not that inefficient.

      1. John Brown (no body) Silver badge

        Re: The 7 years number is a magic number

        "you suddenly realize that your old conventional gas boiler is not that inefficient."

        Especially when you realise your old boiler ran for nearly 20 years with barely a service and your new combi boiler seems to break down at least every other year and a service is absolutely required every year or it will break down more often.

      2. pottsy189

        Re: The 7 years number is a magic number

        Baxe back boiler here in the UK, last 40 odd years and still going strong , just needs vacuuming every year

    2. YetAnotherLocksmith Silver badge

      I don't get it. You can get 100% cost of the equipment back in just 7 years without having to do anything beyond installing a time clock, & you don't see how it adds up? Really?

      Do you have an ISA or savings account? What does that net you over 7 years? 10%?

      Further, you will be insulated from power spikes, brown outs and cuts almost completely - how many household items will that save? How many times you have to go out because you can't cook at home? For anyone who has even occasional power issues this is brilliant.

      Companies will buy these for removal of business risks, too. (Forget a smelly and dangerous generator, just buy a slightly less dangerous battery pack!)

      I'm going to start saving.

      1. xj25vm

        Unless this is some different type of battery than the normal Lithium based ones - in 7 years it will be completely under utterly dead. Most likely it won't even last long enough to pay for itself. Nobody seems to be tackling that part of the equation. Unless I'm missing something here?

        1. Anonymous Coward
          Anonymous Coward

          Hmm, maybe you're missing the part of the 10 year guarantee (possibly 20 although details are yet to be know).

      2. pro-logic

        "How many times you have to go out because you can't cook at home?"

        0 in the last decade of living at my current address I doubt I've had more than 12 hours without power. Total. Longest blackout was 2.5 hours.

        I'm not saying the numbers don't make sense for others, in other parts of the world or even Oz they might make a lot of sense.

        The 7 year payback also assumes the battery after 7 years still has 100% of new capacity.

        Musk is smart, but if he's managed to create a lion battery that doesn't lose charge after 2500+ full discharge cycles capacity he's a genius.

        1. Benjol

          Maybe he's using the same tech as SSDs?

        2. Anonymous Coward
          Anonymous Coward

          It's silly to conflate power outage backup power with green energy

          Because outages are sufficiently rare that using a gas powered generator is a non-issue, CO2 wise.

          One can have a 6500 watt generator, and a can of gasoline, for well under $1k. That's about five times the energy (one can) kWh, three times the power, for one-quarter the price.

          If you want one for your solar panel, whatever...

      3. Anonymous Coward
        Anonymous Coward


        "Further, you will be insulated from power spikes, brown outs and cuts almost completely - how many household items will that save?"

        Only if you're 100% off grid. A battery isn't a UPS or a surge protector, and in many (if not most) scenarios decentralised generation has to cut off when the grid power fails - partly for safety reasons, and partly because having unsynchronised local generation when mains power restores can cause interesting problems. You can fix both of these issues, but it'll cost even more, or you could take your chances if your grid operator has lax rules.

        I'm all in favour of people doing their own thing, but on condition that they completely forgo the grid connection, or pay a fairly heft capacity charge for the standby option that they expect to be available. In some parts of the world you might be able to be grid independent and still enjoy a 21C lifestyle, but that will only be feasible for a small percentage of the population.

        1. Missing Semicolon Silver badge

          Re: @YetAnotherLocksmith

          er.. the common or garden UPS has been doing exactly that for years. Mains goes off - UPS alternates independently. Mains goes on - UPS slews the phase of the generated output to match the mains in, then switches over to live input.

          I had an old APC unit which would cold-start without a power input. It would run at 60hz. When the mains was connected, you could hear it hunting around to achieve 50hz, mains phase before switching to live.

        2. JeffyPoooh

          "...still enjoy a 21C lifestyle..."

          23°C isn't bad, as long as there's cold beer.

      4. Omgwtfbbqtime

        Do you have an ISA or savings account?

        10% over 7 years, really?

        My ISA (share not cash) made 25% over the last 12 months.

        Maybe you're doing the wrong calculations...

        1. MonkeyCee

          Re: Do you have an ISA or savings account?

          It's a comparison with a cash ISA.

          Share ISA has no guaranteed return. That's why you get those "your capital is at risk" and "value of investment may go up or down" advice on them.

          But you knew that already.

          In general things giving you 12% ROI with very low risk like these are pretty good investments. Depending on how dickish your local regulations are about generating your own power and requirements to sell and rebuy it from the grid will often determine if say solar PV/micro hydro etc are any good for you.

          I like solar myself, because I get a 10-20 year guarantee (varies on which bit of the installation) that pays itself back (assuming current power usage) at between 5 and 6.5 years. Plus I get an energy rating bump that results in my house increasing in value by the value of the installation.

          It's not going to solve the energy issue, it's certainly not alternate generation, but it is a reduction in cost. Much like improving insulation, or a more efficient boiler. I wouldn't mind getting a micro gas generator, but that's not permitted in my 'hood :)

    3. Benjol

      You have 92% efficiency on an exchange rate?


    4. JP19

      "Or pretty much 7 years."

      You assume a daily full battery cycle - if the battery isn't completely knackered after 7 years it certainly will be down on capacity (especially in warm climates).

      Also the AC/DC conversion happens twice with 3% (if you are lucky) losses. Did you include installation costs?

      On top of that wide adoption will increase the demand for cheap off peak electricity pushing up the price and reducing the savings. If there was money to be made time shifting electricity generation with lithium batteries the generators would be doing it on a huge scale much more economically than little home installations.

    5. Anonymous Coward
      Anonymous Coward

      Don't forget the time value of money

      Once you take the time value of the investment into account, this goes from not quite stacking up to being an insane investment.

      The calculator at sums it up better than I can:

      With a discount rate of 4.00% and a span of 10 years, your projected cash flows are worth $606.73 today, which is less than the initial $4,425.00 paid in order to begin. The resulting NPV of the above project is -$3,818.27, which means you will not receive the required return at the end of the project--pursuing the above project may not be an optimal decision.

      In reality this doesn't pay for itself after seven years, it never even comes close to break even for a grid connected system.

  3. Paul J Turner

    So it's a 20 year project...

    If making a battery pack is as complicated as building a car or truck. I wouldn't think so.

    On the other hand, how many other manufacturers will join in to make an open spec' product?

  4. James 51

    I've heard it might be possible to rent rather than buy. Depends on how much it is of course but might end up cheaper than having to dispose of an old one safely and buy a new one every few years.

  5. Duncan Macdonald


    These Lithium batteries are sufficiently large that they should not be kept inside the house - if a battery fails and goes into thermal runaway then goodbye house. The Heathrow 787 showed what a much smaller Lithium battery can do. For safety these batteries should be kept in an external brick or concrete structure far enough away from other buildings for safety.

    1. Dave 126 Silver badge

      Re: Fires

      A conventional boiler can kill you with Carbon Monoxide. You could keep it in a brick out-house, but making it safe is an engineering solution that has been solved. So now we have them inside our houses.

      Making sure that a Tesla Powerwall doesn't kill you with fire is also has an engineering solution. Unlike the Li-Ion batteries used in aircraft, any cooling system or fire-protection system can be made without having to worry about its weight too much. Details at the moment are scant - a liquid cooling system is mentioned - but the design is due to be open-sourced.

      There hasn't been a Tesla car battery fire since 2013 - though I don't have the figures required to put that into context.

      1. Paul Shirley

        Re: Fires

        Making boilers safe is a *maintenance issue* and it's far from solved, we still have deaths and CO monitors.

        Given the tiny number of Tesla's, 2 years since the last fire proves very little. We want considerably lower rates for devices meant to ship millions and able to destroy houses.

        1. sabroni Silver badge

          Re: We want considerably lower rates for devices meant to ship millions and able to destroy houses.

          We do indeed. And to get to that point we have to start somewhere.

  6. Paul Shirley

    Think I'll wait...

    ... For those cheap aluminium batteries we were talking about a couple of weeks ago. Unless Musk has cracked lithium cell degradation rates that 10yr guarantee seems hard to take seriously for a device expected to be continuously cycled.

    Not having an explosive that large in my house either!

    1. Raumkraut

      Re: Think I'll wait...

      Think I'll wait...For those cheap aluminium batteries we were talking about a couple of weeks ago.

      I'm still waiting for those cheap batteries we were talking about last year. And the year before, and the one before that, and the one before that, and... pretty much every year this century.

      So I wouldn't hold your breath.

    2. Anonymous Coward
      Anonymous Coward

      Re: Think I'll wait...

      " that 10yr guarantee seems hard to take seriously"

      There's a tendency to judge industrial applications of li-ion by our experience of consumer devices, but that is a bit like trying to extrapolate the performance of an articulated lorry from the performance of a small family car.

      The economics are certainly challenging, but the lifetime and guarantee is actually easily sorted - my employers have looked at this very seriously from a grid scale perspective. Firstly the maker needs to make the battery to the required standards, second they specify materials and design conservatively, and third they use control gear to very carefully control the charging and discharging regime to make sure that the battery is optimally managed for service life.

      So to get that sort of service life you'd have limits on both charging current and discharge rates, you'd need to manage the cycling between too much and too little, and you'd need to adjust the management according to the temperature. Even with those extended warranties, the problem is that the value of a storage is fairly low, and the financial case only works in isolated high value situations and at small volumes. You can (for example) bid into the network operators ancillary services market, but the relatively low energy density makes batteries less competitive than a lot of other options, and where batteries win out is only really on their speed of response, rather than their ability to support extended outages (cf a diesel generator with enough fuel for five days running, say). If you think about a data centre, for example, you might well have a battery UPS, but that's only there to cover the few minutes until the big Caterpillars out the back have rumbled into life. Cheaper unit prices for batteries don't look likely to change that any time soon.

  7. wiggers

    I think I'd rather be connected to a nuclear power station than buy one of these and a shed load of solar panels.

    1. Mike Wilson

      Surplus power

      I'd rather be on a nuclear powered grid. If every home has its own battery and the household uses, for example, an average of 80% of the capacity each day, there's a lot of unused energy. Kind of like having millions of litres of fuel sitting in peoples' car tanks. Battery only makes sense to me where there's no grid.

      1. phuzz Silver badge

        Re: Surplus power

        One of the problems with nuclear power is that it can't spin up quickly to meet demand, it's better at providing a steady, constant level of power.

        Using a battery in the home to level out peaks in demand allows the load on the grid to stay constant (eg trickle charge all day, and then when you get home and put the kettle on, use the battery to provide energy and keep the draw from the grid at the same level).

        Also of course this is useful for renewable sources, most of which produce power at certain times (eg during the day for solar, or when it's windy for turbines) which may not line up with when people want to use that energy. Again, a battery in the home helps balance the supply/demand.

        There's a related advantage, which is that if you have your own PV panels on the roof, you can store the energy locally which avoids most of the transmission losses that you'd incur selling it back to the grid.

        1. Anonymous Coward
          Anonymous Coward

          Re: Surplus power

          "One of the problems with nuclear power is that it can't spin up quickly to meet demand, it's better at providing a steady, constant level of power."

          If DECC and the eco-brigade get their way, then they will be adding many TWh of transport and heating demand to electricity demand, and because even a fossil grid can't support the instantaneous demand that implies, the grid will need to move from despatching generation to meet demand, to despatching demand to meet generation. This is absolutely inevitable if DECC's decarbonisation agenda is to be delivered. And in this low carbon nirvana, renewables will never be able to supply the additional circa 500 TWh/a of electrical energy (cf 360 TWh/a UK electricity demand at present).

          Put simply, car charging would be remotely controlled overnight by a third party, as would heating, and we'll then be in a land where the network operator manages the demand profile. If you they do that, we will be able to easily get very close to a flat demand curve (albeit with seasonal variation on the heating load), and the logical solution is nuclear power, and to stuff the hippies' unreliable, subsidy dependent eco-toys.

          You do then have household storage (the car battery and heat storage through a thermal store of thermal inertia effects, rather than battery storage for household use), but you'd not get the volume of additional energy from renewables. And running a grid with nice big nuke plants is a lot easier than managing a grid with poorly controlled and huge daily and seasonal swings in manky, asynchronous inputs. I would expect sometime in the next few years we'll see a major grid failure due the problems of balancing and synchronising the grid with all the crappy subsidy farms that have sprung up in response to DECC's misguided policies - this is probably a greater threat than winter blackouts due to lack of gross capacity.

        2. JP19

          Re: Surplus power

          "One of the problems with nuclear power is that it can't spin up quickly"

          The cost of nuclear fuel is relatively so trivial there no point spinning them down to save it - not much of a problem.

          1. Fonant

            Re: Surplus power

            It can get expensive dumping excess electical power, especially when all the pumped-storage power stations have their top reservoirs full. The power being generated has to go somewhere, and dumping Gigawatts from a power station isn't easy. If you don't match it with load, the grid voltage and frequency go up beyond allowable limits and grid-connected equipment starts getting too fast and too hot! Keeing the grid's frequency between 49.8 and 50.2 Hz is a very fine balancing act.

            Nuclear is great for base loads, but rubbish for daily load fluctuations, and so can't usefully be used for more than base load, perhaps 50% of peak demand maximum. Gas power stations can be turned up and down to balance generation with demand much more easily, and pumped-storage and hydro has very fast reaction times ideal for sudden surges like kettle-on time at the advert break in a popular soap on TV.

        3. iranu

          Re: Surplus power

          The French manage with their nuclear stations because they are designed to do just that.

      2. Hairy Spod

        Re: Surplus power

        actually link these to an economy 7 electricity tariff topping up overnight when a fair amount of generation capacity is currently wasted and these might actually make a lot more sense.

        More controlable than a storage heater and you can use it to power your tv or washing machine later in the day rather than just heat your house.

        1. Anonymous Coward
          Anonymous Coward

          Re: Surplus power@ Hairy Spod

          "actually link these to an economy 7 electricity tariff topping up overnight when a fair amount of generation capacity is currently wasted and these might actually make a lot more sense."

          Problem is, if you increase overnight utilisation, then the generously low off peak prices disappear. This will happen as cars and heating shift to electrical power, but it has some very regressive implications for existing E7 heat customers. For early adopters (eg those swanning around in £85k's worth of Tesla Model S) this is hunky dory, but as the demand and daily price curves flatten you'll start to see relatively low income households paying higher heating prices to give rich EV drivers cheaper transport, as an inevitable but unintended outcome of a largely left wing set of "climate change" policies.

        2. Missing Semicolon Silver badge
          Thumb Up

          Re: Surplus power... economy 7

          Somebody's already done this.

          That PhotonicInduction. He's a card.

  8. DrXym

    4,192 KWh

    That works out to be 11.48KWh per day. I reckon people would be motivated to cut that down to 8KWh if they were paying for the difference from the mains - turning off lights, not leaving appliances in standby etc.

    Bigger issue is how much charge do you get from installing solar panels, particularly during winter time. It's not much use to have a battery bolted to the wall if the panels only manage to partially charge it.

    Anyway, this has the potential to be a massive disrupter in places where solar *is* viable. Lots of US states get plenty of sunshine. Some states like Florida get so much it beggars belief that solar isn't the primary source of power.

    1. auburnman

      Re: 4,192 KWh

      The problem then becomes keeping the battery sufficiently cool in a hot environment. Anyone smarter than me done the sums for the additional energy draw on your AC in a hot climate? It's bound to put out it's own heat with constant charging & discharging, and with the battery size it can't be an insignificant amount.

      1. Brenda McViking

        Re: 4,192 KWh

        well batteries are coming close to 100% efficient (we'll call it 99% for the sake of argument) in terms of losses for charging and discharging, so really it is a very low amount. You lose more in the power electronics (inverter/rectifier etc) connecting it to whatever it's connected to (grid/solar panel) which are around 97% efficient.

        Couple the cooling to a heat pump, which transfers 4 units of heat for every 1 of electricity (i.e. sometimes marketed at 400% efficient, but doesn't break the laws of physics as you're transferring heat energy from one place to another) and you actually have a very small power demand to keep the thing cool. maybe 4% of peak charge/discharge capacity, which might be a few kW, so we're talking about the same energy (10W heatpump for 40W heat removal) to light an energy saving lightbulb to remove said heat per 1kW power input/output.

        And you'd accept a lot more than that anyway, as proper heat management prolongs the life of lithium chemistry batteries. The reason your phone battery lasts 3 years is because it follows you around through the heat and cold. Keep it in a temperature controlled room and you'd get 10 years out of it.

        So in short, the extra heat generated by a battery charging a discharging, even and big one, is probably about as significant as the heat you get from a desktop PC.

        1. Anonymous Coward
          Anonymous Coward

          Re: 4,192 KWh

          "well batteries are coming close to 100% efficient (we'll call it 99% for the sake of argument)"

          A lot better than they were, but probably more like 90% at best in the real world. Personally I don't see that gap closing any time soon. If 99% efficient energy storage were possible, I think 3.6 billion years of evolution would have sorted it out already.

    2. phuzz Silver badge

      Re: 4,192 KWh

      "KWh per day"

      You're dividing (power x time) by time, so at this point you might as well just give your answer in kW. Oh, and the 'kilo-' prefix is marked with a lower case k.

      SI units FTW!

      1. DrXym

        Re: 4,192 KWh

        "You're dividing (power x time) by time, so at this point you might as well just give your answer in kW. Oh, and the 'kilo-' prefix is marked with a lower case k."

        No, I'm just taking the figure 4192 which I assume to be annual consumption and dividing by 365 for the daily consumption. Both are still measured in kWh.

    3. Fatman

      Re: 4,192 KWh

      Some states like Florida get so much it beggars belief that solar isn't the primary source of power.

      There is a simple answer: A Bought and Paid For State Legislature

      SHIT, we are still paying for a nuke plant that will NEVER be built.

    4. Anonymous Coward
      Anonymous Coward

      Re: 4,192 KWh

      The thing only stores 10-kWh worth of power. Use your local power rate per kWh ($0.05-$0.25?) and multiply by 10 of them. $0.50 - $2.50? About the price of cup of coffee.

      It's kinda difficult to imagine it making much difference in people's lives. Other than wishing that they had their $3,500 back.

  9. StaudN

    "the horrors of an electric stove"

    Not tried an induction hob I see - try it, you'll like it... green eggs and ham!

    1. sabroni Silver badge

      Re: Not tried an induction hob

      Bah. Burn gas underneath your saucepan. Works with all kinds of pots, including woks, ferrous or not, and you can see the flame to adjust it.

      Never understood the logic of burning gas in a power station and turning the heat to electricity only to then turn it back into heat on a stove.

      1. Mike Wilson

        Re: Not tried an induction hob

        Off grid homes I've visited use bottled gas for cooking. Even the "low impact" hippies. That's what I'd do, too.

      2. Dave 126 Silver badge

        Re: Not tried an induction hob

        Fires after earthquakes when gas mains have been ruptured.

        Releasing combustion fumes at power station, instead of in heavily populated areas.

      3. phuzz Silver badge

        Re: Not tried an induction hob

        A large gas fired power station can be optimised for efficiency, so you get more useful energy out of each litre of gas, rather than wasting it making a pretty blue flame that mainly heats your kitchen.

        1. sabroni Silver badge

          Re: Not tried an induction hob

          You have to optimise a lot to make up for the losses of transmission from station to house and the two conversions, heat to electric and electric back to heat. Got any numbers or references?

        2. Anonymous Coward
          Anonymous Coward

          Re: Not tried an induction hob@ phuzz

          "A large gas fired power station can be optimised for efficiency,"

          In the old world yes. But in DECC's brave new world, few if any UK CCGT are covering their cost of capital plus running costs. And because they're regularly shut down at the whim of subsidy-driven solar and wind, it is uneconomic to run them in combined cycle mode. So they're being either mothballed, or downgraded to run as open cycle plant. What this means is that all those lovely wind turbines and PV plant reduce the efficiency of gas generation to that of a 1970s coal fired station.

          Factor in 13% parasitic loads and grid losses, and distributing gas is far more efficient than electricity.

    2. Anonymous Coward

      Re: "the horrors of an electric stove"

      Came here to say the same thing - I moved into a house with no gas, so stumped up for induction hobs and pans. I'm never going back - the heat is so well spread out and finely controllable that I rarely ever bother using a double-boiler any more.

      1. Hairy Spod

        Re: "the horrors of an electric stove"

        not only that, as the surface of an induction hob is smooth glass and never really gets that hot, its an absolute doddle to keep clean which is just as important to a lazy arse like me, no more messing around taking things apart or scrubbing away at burned on food

        1. John H Woods Silver badge

          Re: "the horrors of an electric stove"

          "its an absolute doddle to keep clean" --

          Yes, and if you want you can even heat your pan through a layer or two of kitchen towels! I have no gas and always complained until I got my first induction hob. When I did, I was only hoping for it to be less of a disappointment than a conventional hob, but within a few hours I realised it was far superior to gas.

          1. Will Godfrey Silver badge

            Re: "the horrors of an electric stove"

            Also the looks on friends' faces is a picture when you have a plate sat millimeters from a nest of hot pans while you casually dole out the food, then hand the barely warm plate to them.

          2. sabroni Silver badge
            Thumb Up

            Re: Yes, and if you want you can even heat your pan through a layer or two of kitchen towels!

            That is something I have always wanted to do.

    3. FlatSpot

      Re: "the horrors of an electric stove"

      Considerably safer than gas as well for old people with limited mobility. Once you've tried induction you will never go back.

  10. Winkypop Silver badge


    So that would be roughly eleventy-million once 'converted' to Australian currency....

  11. This post has been deleted by its author

    1. Gordon 10

      Re: For a car...

      Oh Really? and how many of them are in Consumer levels of production and price?

      1. This post has been deleted by its author

  12. Richard_L

    Much needed publicity for energy storage at last!

    It's great to see Elon Musk giving renewable energy storage a publicity boost - it's the one thing that is essential yet never seems to be considered by any of the politicians who are egging each other on to drive us all faster and faster towards a zero-carbon, green-energy-only car crash.

    Ban coal - coal is dirty! Ban gas - fracking is immoral! Ban nuclear - think of the children! Oh and ban onshore wind while you're at it too, it might be green think of the house prices!

    Great. Now where's the capacity to supply a 24hr base load gone? Where's the surge capacity in the grid?

    Making an offering of Waitrose essentials cous-cous to Gaia in the hope of making the sun to come out on a wet December night so we can all put the kettle on and have a cup of tea when Eastenders finishes just isn't going to cut it.

    If we're to make a renewables-only solution work with the drastic cuts to carbon emissions that politicians are promising by 2020 or 2030 then energy storage on a massive scale and in a number of different forms needs to be very seriously, very quickly and very thoroughly considered.

    1. Dan Paul

      Re: Much needed publicity for energy storage at last! @Richard L

      I agree with your comments.

      Energy storage devices such as Tesla's can only be considered "Green" when charged during the day because the power from Solar and Wind only occurs during daytime hours.

      Almost the same amount of traditional generation capacity will still need to be available to replace renewable energy as most of the world just does not get enough sunshine and wind every day.

      Apparently the "Greens" and politicians still don't understand that the wind does not blow all the time and sometimes it is dark outside.

      1. Sir Runcible Spoon

        Re: Much needed publicity for energy storage at last! @Richard L

        "..because the power from Solar and Wind only occurs during daytime hours."

        I'm pretty sure I've woken up to a missing shed roof before now, and I don't think it was the pixies!

        1. Anonymous Coward
          Anonymous Coward

          Re: Much needed publicity for energy storage at last! @Richard L

          Somebody nick your solar panels in the night?

      2. mgumn

        Re: Much needed publicity for energy storage at last! @Richard L

        Wind only blows during the day?

    2. JP19

      Re: Much needed publicity for energy storage at last!

      Because power generation and distribution is some kind of celebrity driven contest?

      If only facebook likes and tweets could boil my kettle......

      1. Richard_L

        Re: Much needed publicity for energy storage at last!

        No, I'm not talking about just amassing idle 'tweets' and 'likes' for energy storage solutions. I'm hoping that the extensive news coverage generated by this relatively unremarkable battery's association with Elon Musk - that nice man from the Iron Man films with the fancy suit and the sports cars and space rockets - will go some way to making people realise that the mad dash to renewables-only national power generation is not as simple as a lot of people think it is.

        You can't just turn off all gas, coal and nuclear power stations and expect solar panels and wind turbines to do the same job.

        It's popular policy for all politicians wanting to capture the green vote to commit to quite alarming cuts in carbon emissions that will require a huge reduction in power generation from fossil fuels. Add to that a growing demand to reduce air pollution by removing the Evil Diesel vehicles from the roads - preferably by replacing them with electric vehicles - and you end up in a situation where demand for electricity is likely to rise sharply at the same time as our generating capacity becomes subject to large weather-based fluctuations.

        At the moment, electricity demand governs supply. But if you turn decommission nearly all gas, coal and nuclear power stations then people need to understand that with nothing left but wind turbines and solar panels then the situation will reverse and electricity supply will govern demand. (And the billions wasted on over-hyped smart meters won't do a damn thing to help either.)

        Storage of surplus solar and wind energy needs to be incorporated, on a massive scale, into any future where the majority of energy generation depends on solar and wind. As supply will not usually be able to match demand, we must find ways of storing energy that is surplus to the level of demand at its time of generation and releasing it when there is a deficit.

        Whether it's through battery installations or flywheels on a domestic level, compressed air plants on industrial estates to serve small towns, pumping water up to old slate quarries on Welsh mountainsides on a regional level or something else entirely, we need to invest in some combination of them.

        How many people, unquestioningly supporting the politicians carbon reduction targets on the basis that anything green must be good assume that we'll all be OK if we just build some more wind turbines and install some more solar panels, appreciate this?

        How many of those people realise that in a house with a bog-standard domestic solar installation today, solar panels don't generate any power if there's a power cut? How many people realise that you need batteries and additional control equipment to maintain power to a property with solar panels fitted if the grid goes down on a sunny day, let alone to provide a reservoir of energy that can be tapped into throughout the night? How many of those people realise that renewable energy supply is poorly matched to demand?

        Hopefully there are a few more after today's news.

        Even Eddie Mair, when introducing the news item on PM this evening sounded like he was suggesting that for the first time ever, a new type of battery that could store the sun's energy had been invented!

    3. Red Bren

      Re: Much needed publicity for energy storage at last!

      "we can all put the kettle on and have a cup of tea when Eastenders finishes"

      Then the solution is to ban Eastenders.

  13. MJI Silver badge

    Makes solar power relevant

    Currently solar power is not relevant in the UK, generate power when you don't need it.

    Now you could even be off grid.

    Storing you daytime collected power for the evening seems a good idea to me.

  14. Anonymous Coward
    Anonymous Coward

    Storing excess solar energy

    There are existing alternatives to storing excess solar PV energy such as dumping any excess Kwh into a hot water tank or storage heaters. (I'm not connected to this company, other products are available)

    I've looked into this for my PV set up but as we have an old school meter that is running backwards in the summer I'm holding off as I (effectively) get paid 13p per Kwh I pass back to the grid. Anon of course.

    1. Boothy

      Re: Storing excess solar energy

      I've got an Immersun 2 installed (with a 4kW solar PV system). and am very happy with it.

      It monitors the grid power usage/feed-in (earlier versions were basically a fancy timer).

      If you are producing more power than the house needs, AND if the immersion tank is not up to temp, then it pushes the excess power into the tank rather than the grid.

      It controls the voltage to the element, so the watts is flexible, and tends to be anywhere between 100W, to 2kW, depending on time of day, weather conditions etc.

      While the water is warming up, you have a net of zero Watts on the grid power. (The Immersun 2 will not take power from the grid, not unless you manually override it anyway).

      Once the water it up to temp, the excess power is all pushed back onto the grid again as normal, until the thermostat trips in again, and so on.

      So essentially, free hot water....

  15. Unicornpiss

    This technology has its place

    People that already have alternative energy generation available, such as solar, wind, small hydro, etc. will find this a real boon. It's got to be better than lead-acid and other existing battery technologies in current use for night and off-peak generation times. People living where commercial and residential power is billed at flexible rates depending on the time of day could also set up a timing system where the unit charges during hours of the day where rates are lower and gives you juice when power is most expensive. They also could be useful if you live where power is pretty unreliable, I'm sure.

    But I do not expect you will see these in every home anytime soon. I live in an area where commercial power is very reliable overall, and while I own my home, there are too many trees to make solar practical. (also, I just don't use that much power) Plus, a large percentage of the populace everywhere rents their digs.

    Maybe if this was licensed to Apple, whose marketing department seems to have an uncanny knack for convincing people to buy things they only have a marginal use for.

  16. jb99

    Good as far as it goes.

    I'm still to be convinced that CO2 is the problem that it's being made out to be, and not just an excuse to tax us all.

    But... assuming for a moment it is, this seems like a good practical step to helping with that.

    It makes renewable energy and reducing the expensive peak time capacity needed a little bit easier. And its really good to see someone coming up with an actual step towards the solution rather than just demanding more taxes and laws.

    Not sure how much it will help, and I'm not sure it's needed. But I approve of the idea :)

  17. b166er

    Do these make sense with Economy 7 doing the charging?

    1. Anonymous Coward
      Anonymous Coward

      No. The price differential isn't enough to offset the cost of the battery. If the battery cost fell by 75% it might be, but then you'd rapidly see off peak demand rise and peak demand shrink as everybody did this, the price difference would shrink and thus it would become uneconomic after you'd invested in the battery.

      Also, because the standing charges of the network and central generation wouldn't change by much, the regulator would need to step in and institute the sort of complex charging that businesses are subject to, so you'd have a standing charge, a maximum capacity charge, a maximum actual current charge, and a unit charge, and thus the variable element of the bill would fall and the fixed element creep up (again undermining the price arbitrage).

      The underlying financial case for local battery storage relies on beneficiaries benefiting at the the expense of other users. This isn't apparent at low levels of market penetration, but when a lot of people do it becomes a real problem. In much the same way that poor people in flats currently pay higher electricity prices to subsidise wealth pensioners getting PV or "renewable heat" subsidies.

  18. Caustic tWit

    A Great Innovation...But...

    Elon Musk is no doubt a visionary entrepreneur. My hat is off to him. However the big issue in domestic energy efficiency is not cost reduction and efficiency by load smoothing. The real issue is waste reduction, and there are many pressing issues in that regard, which could and should be addressed as higher priorities and have the potential to produce more rapid cost recovery for householders and less need for expensive and environment degrading energy generation.


    1. Most houses (and apartment buildings) are less-than-optimally insulated. Hurts energy efficiency in all climate zones except those where literally no heating or air conditioning is needed. Insulation upgrades are technologically simple, relatively small one-time expenses that can be performed incrementally if need (financial or otherwise) dictates. They require no maintenance or control systems. There are a plethora of options for non-destructive retrofitting of older dwellings of different construction types in different climates. Windows and doors count here too, not just ceilings/roofs and walls. Choices of exterior wall and roof surfaces can also make a differences, particularly in hot sunny climates. Reflecting heat away entails no further cost once the job is done.

    2. Most houses are draughty. Air leak is sometimes the biggest enemy of residential energy efficiency and cost reduction, exceeding even insulation in importance. Infiltration of undesired outside hot or cold air means exfiltration of desired heated/cooled inside air, which you then have to replace, at your expense. Many sources of air leak are obvious, like the aforementioned windows and doors, also unplugged chimneys, gaps between sills and foundations, and the like. Others are downright arcane, weird, who'd-a-thunk-it sorts of things. First you address the obvious ones, then you formally test, most often by employing a professional, but you could do it yourself.

    3. Household heating (including water heating), refrigeration, cooking, and clothes drying appliances often are working against us in not-so-obvious ways. The gas or oil fired boiler that draws combustion air from inside your house is using air that you've paid to heat or cool, and necessitating the infiltration of outside air to replace it. The technology exists to eliminate this waste of energy. Much the same situation with clothes dryers, be they gas or electric. They exhaust air from within the house, necessitating more outside air being drawn in. I'm not aware of any being made which address this problem, but what's wrong with clothes lines anyway? At least during clement weather. Gas kitchen ranges with pilot lights are both a constant waste of gas and (at least in the warmer seasons, in warmer climates) an unwanted source of heat. The gas waste amounts to about 30% of all the cooking gas a family of four uses. A good argument for ranges with piezoelectric igniters. (Those still with manually lit gas appliances should really consider replacing them for safety reasons). Domestic refrigerators and freezers are another issue. To cool the interior of these you must extract heat, which is then dumped into the room in which they sit, so in the summer you are paying to cool this warm air which you have paid to make because you needed to keep your food cold. I have not yet seen or heard of domestic units which address this issue.

    3. Many houses are larger than the occupants need. I'm not a "Tiny House" advocate, but all those extra cubic feet add proportionately to heating and cooling bills, and all that extra external surface area is radiating or absorbing heat too, and that comes at an energy cost. Architecture figures into this too. Some house styles entail much more entail surface area than others. Again I'm advocating nothing; I appreciate a good looking or interesting looking house. It's just food for thought.

    Addressing some or all of these issues will potentially save far more for both individuals and society, than Musk & Co's very elegant whole-house load leveller/UPS, and if you still want to go that route (and I'd like to), you'll won't need as big a one, or so many.

    1. Justicesays

      Re: A Great Innovation...But...

      "2. Most houses are draughty. Air leak is sometimes the biggest enemy of residential energy efficiency and cost reduction, exceeding even insulation in importance. Infiltration of undesired outside hot or cold air means exfiltration of desired heated/cooled inside air, which you then have to replace, at your expense. Many sources of air leak are obvious, like the aforementioned windows and doors, also unplugged chimneys, gaps between sills and foundations, and the like. Others are downright arcane, weird, who'd-a-thunk-it sorts of things. First you address the obvious ones, then you formally test, most often by employing a professional, but you could do it yourself."

      Go ahead, make your house airtight and then get back to me if you survive the monoxide poisoning!

      1. Caustic tWit

        Re: A Great Innovation...But...


        Valid point, but not an issue really. Firstly when retrofitting it is not possible to achieve "airtightness." What you do manage to do is reduce the air exhange somewhat. With new house construction of the most energy efficient sort you replace inadvertent air exchange with a heat-and-air exchanger. This replaces the air but reduces the associated heat loss 60-80% (with better units). That said, if you have any sort of combustion appliance, be it boiler, furnace, dryer, range, heater, or whatever, you are always at some small risk and must be careful to maintain and replace these things at approriate intervals.

    2. Boothy

      Re: A Great Innovation...But...

      You need ventilation in the house.

      I live in a new build (two years old), and the house is A rated on the EPC, all the latest regs etc.

      And most of the windows include air vents, to enable a constant through draft into the house.

      The only time they get closed is in the middle of winter, or if it's storm conditions outside. Otherwise the house would get far too stuffy too quickly.

    3. Anonymous Coward
      Anonymous Coward

      Re: A Great Innovation...But...@Caustic tWit

      Some interesting and relevant points.

      To clarify a couple of points, most boiler installations shouldn't be drawing combustion air from inside the house, they'd have a balanced flue or separate air intake. But your point is valid for vented tumble dryers, which should be banned with immediate effect (a good condensor works well, and all the heat stays in the thermal envelope of the house).

      On energy efficiency, the majority of cavity wall houses have CWI, most lofts have at least a minimal level of insulation, and the remaining opportunity is therefore the 7m solid wall properties. Unfortunately solid wall insulation is expensive, and has a circa 20-40 year cash payback in most cases. You can subsidise it (as government do) but that's still a very expensive way of saving money or emissions.

      As for air tightness, that's a real bug bear. Without expensive, well specified and installed heat recovery ventilation systems, greater air tightness leads to worse air quality, damp and mould, along with measurably worse health problems (some good Dutch studies available, published to the web in English if you want to look this up). In conceptual terms good air tightness is easy enough, in practice it is difficult to achieve, and requires a balance with air quality that reduces the initial benefits.

      1. Caustic tWit

        Re: A Great Innovation...But...@Caustic tWit


        You are quite right about boiler installations, but at least in North America, many are still be installed which do draw combustion air from within the house, and many, many older units are still in service.

        As regards CWI, it all depends on the depth of the cavity and the type of insulation. Loft insulation is far and away the most important part, hereabouts ~20in (50cm) of glass fibre or equivalent is optimal. Most older construction has 6in or less. And it is usually an easy job and cheap.

        For air tightness, yes there is such a thing as too little air exhange with the bad effects you describe. However, and again I qualify with "around here", northern North America, the best you can achieve with older homes is substantial draught mitigation, with resultant air exchange which is still much more than adequate. With new construction the additional cost of a good heat and air exhanger should not exceed 0.5% of the overall cost of construction.

  19. This post has been deleted by its author

    1. Boothy

      Re: I really don't want to go back to a gas oven.

      One of the issues here is to get people like yourself to stop running all the high power usage items at once. This helps reduce your peak usage hugely, and helps level out overall demand.

      i.e. Don't do laundry at the same time as you're cooking, use the dish-washer after your finished eating etc.

      I've got Solar PV, so I obviously try to do as much as possible during the day. I turn the laundry and the dishwasher on, in the morning on the way out the house, the dishwasher has a 3 hour delay, so comes on after the laundry is finished. Unless it's a really bad day, the day time power usage never exceeds the PV generation.

      And whilst the oven (which is electric) does go on generally in the evening when the PV output is low, so does take from the grid, I never use the dishwasher or do laundry at the same time. (If I need to wash something in the evening, I'll do it in the sink by hand).

      1. This post has been deleted by its author

        1. Boothy

          Re: I really don't want to go back to a gas oven.

          I wasn't trying to be patronising, you specifically stated that you run high power items at the same time, and nothing you posted indicated that you might have thought this was a bad idea, or that it could be better managed. Not everyone considers peak usage.

    2. Anonymous Coward
      Anonymous Coward

      Re: I really don't want to go back to a gas oven.

      "I think Musk's obsession with electricity only has prevented him from coming out with a really good vertically integrated solution. "

      That really good vertically integrated system already exists. In the UK it's call the national grid, and it uses a network of wires to connect a vast range of alternative sources of power to a vast range of varying demands. This novel system enables users to benefit from the large economies of scale in power generation, to have a fair degree of redundancy and reserve capacity, and to have the system professionally managed 24/7.

      Shame that the hippy dog-f*ckers want to throw all this away.

  20. johnnymotel

    Back in 1995 I visited some friends up in the Pyrenees on the Spanish side. All they had for leccy, were PV cells and lead batteries. They just about managed day to day. The cost of bring mains power to their house was not cost effective. This is where I can see the advantages, almost anywhere the cost of bringing power lines is not cost effective. I don't know the numbers, but there must be a very large population who don't have mains power and to bring it in is not cost effective. It could be sold by the utility as a package of PV+battery.

    1. Boothy

      Would be good for anyone with Solar PV, not just off grid.

      I've got a 4kW system (in the UK), and around 70%+ of the generated power goes onto the grid each day, especially during the week, when I'm not at home.

      With one of these, I could put the excess power into the battery during the day, and then feed off the battery in the evening.

      This would greatly reduce the need to take power off the grid. (Likely still be needed for high consumption devices, like the leccy oven).

      Could also be used to charge a leccy car at night, as at the moment, I'd have to charge a car from the grid, (if I had one), which seems rather silly when I have PV energy to spare during the day!

  21. Fred Flintstone Gold badge

    Does it fit in the boot?

    I can see this as an extra range facility for the Tesla :).

  22. Alistair

    Like the idea

    Sadly in our area we're dealing with over regulation of consumers and no regulation of the (grid) providers -- and possibly no regulation of the source provider in the near future.

    Quite literally - we're *not* allowed to store power locally. Not, at least in the residential space. We cant touch the stuff we generate on our roofs or in our backyards - it goes *back* to the grid first, then we have to buy it at the current rate if we want to use it. - There are of course credits - but they pay out quarterly only and you get billed monthly anyhow. (Nah, there's no screwing over the end user is there?)

    Seriously though - two, perhaps three of these in a shed off to the side, with relevant controlling/cooling system, Solar on the roof and wind *in* the roof (look it up - thermal values etc) , geothermal heating with a bit of gas backup and gas for the BBQ, and a big black marble wall to heat the pool. I'm happening.

    Just - that the damned government here would figure out a way to charge me 0.11/hr/l for the water running through that black marble pool heater, amongst 12 different other "surcharges" even IF I was pushing 40% of my production back into the grid.

    And I still want my goddamn Tesla S. But I'll have to get all that set up on the QT so I can stop paying $550 to $600 a month in the winter for electric heat.

    It friday and I'm wrapping a project. I have to stop being grumpy, have a beer on me Elon.

  23. BitDr

    I think this will work out...

    A 10KWh unit + inverters & charge controller and a budget of $12K should do the trick for us. We can add another later if need be.

    When we built our home we were aiming at being off grid, unfortunately, like many things, there was too much project left at the end of the money. What we did manage is to get an 11KW generator (LPG fueled) installed, as well as the all-important generator/cutover controller (a GE unit). The entire home is easily run from the backup generator, including all motor start loads, of which the Air Con is the worst.

    When power goes off the generator auto-starts within 30 seconds and power comes on a couple of seconds later when it and the AC stabilize. The cutoff unit 'sees' power from the generator, disconnects the grid side and connects the generator with a loud CLACK! When the grid power comes back on the controller unit slowly synchronizes the two AC signals, reconnects the mains, and shuts down the generator. The electronics in the house are never aware of the switch back to grid power.

    The generator has been used for 80+ hours in the last 10 years, saving much in what would have been spoiled food during one particularly long outage, and running the central heat, stove/oven, and hot water heater. The LPG for all of these is stored in a 2000 Litre tank.

    To take this system and turn it into what we want we need to mimic the utility company, putting our "mimic" in-between them and us, and electrically moving the generator so it can feed either the charging system OR replace the mimic should the need arise. The utility company OR the backup generator could be used to "top-up" the batteries, which one gets chosen for the task would depend on the time of day or if the grid is even alive at the time (it has been known to go off-line). If we then add a few solar panels to the battery maintenance mix the usage of the grid would begin to decrease.

    As of this writing our electrical bills are $220/month, ten years ago they were $100/month. In one year we spend $2600+ on electricity. The house has CFC lights, LPG Hot water heater, LPG oven & stove-top, and an LPG clothes dryer. There are four desktop PCs running 24/7, 2 of which are servers, all have their own UPS so they don't go dark during the 35 seconds or so that it takes the generator to start powering the house. Electrical outlets to the entertainment stack are switched, allowing us to power off those parasitic loads when not in use.

    A budget of $12K should do it. If we borrow the money @ 5% over 5 years it results in a bi-weekly payment of $104.41 (annual payment of $2714.66), replacing an existing $220 monthly payment (annual payment $2640) . We pay 74.60 more per year for the next 5 years, after that we earn $2640 a year. During the term of the loan and beyond the cost of electricity will continue to increase, so these are conservative numbers.

  24. Andy Christ

    Here's a link to the presentation Musk gave last night.

    Have to say I was dissappointed. If the technology is open source, why were just about no details given about how the battery bank works and what is actually innovative about it, other than price? Makes me sadly suspect there is nothing all that new and revolutionary inside, or he'd have had plenty of reason to flaunt it.

    Richard Widmark fails at show and tell. :(

  25. Art Esian

    There has been no alarming global warming for 18.5 years. It may in fact have rolled over into cooling based upon a profound drop in solar magnetic shielding. I was in graduate school when computers were invented. We made models of everything. If they were not predictive or could not hind-cast we threw them out and the hypothesis with them. If we failed a second time, the student was thrown out. This is a model based upon numerous models that do not work. Who is going to be the first to toss out the students and the professors? Garbage in garbage out!

  26. Anonymous Coward
    Anonymous Coward

    Elon is hoping that you are really gullible

    As a charlatan...consumers are seen as an entity to be exploited. Buying a 10KW brick for your residence makes as much sense as buying ocean front property in Arizona. I'm sure that you'll enjoy the mid-night fly-over to view the ocean front property almost as much as a 10KW brick.

  27. LB45

    Can't be for real

    No mention of graphene in any form being used in the product!

    Sounds like a scam to me. ;-)

  28. el rekrab


    Isn't Musk's cousin the one who started Solar City that place that charges you for hosting their solar panels?

  29. crayon

    You have 92% efficiency on an exchange rate?

    Actually that's a pretty high efficiency. For products priced in USDs it's around 64% efficiency right now since they miraculously translate to dollar-sterling parity once they swim across the pond.

    +1 for induction cooking - clean, efficient and no more hot kitchens.

  30. Hurry home

    New tech?

    Is it actually a new kind of technology Musk has invented/presents or is it only a new way to pack the already existing battery technology?

  31. Shovel

    simplify what you are getting.

    I'm not even going to bother with back of a napkin. Let me use 1rst-grade math

    10 KWh battery

    2 KW constant output or 8.6 Amps constant output

    10 divided by 2 = 5

    This product can supply 1 house circuit with 5 hours continuous use

    And if it is like other Lithium Ion batteries, you won't get any warning..., it will just stop.

    so when the power goes out, you get one 20A circuit(under load) for 5 hours, for $3500.

    OH, and the Inverter is not included in that price. How much is a TSW 2000W inverter these days?

    A quality TSW inverter that you can put in line with your service panel will most like cost another $2,000. You don't want to trust your home to a Chinese POS. They MEANWELLL, I mean,

    1. mrbojanglez

      Re: simplify what you are getting.

      SHOVEL......sorry didnt see your post till after I had sent.

      I follow your basics thank you, but where does the cycle come in.....I have a gerbil in a cage to power mine!

  32. mrbojanglez

    In plain English please!

    Can anyone please kindly explain in simple language....coz I is simple.....what the power output of these two batteries is in practical terms. Why is one quoted as a weekly cycle and one a daily cycle?

    What does the 10kwh mean in practical long would it power a house for?

    Assumably the speed by which they recharge would be dictated by the size/ability of the solar panels?.....Your help is much appreciated.

    "Powerwall comes in 10 kWh weekly cycle and 7 kWh daily cycle models. Both are guaranteed for ten years and are sufficient to power most homes during peak evening hours. Multiple batteries may be installed together for homes with greater energy need, up to 90 kWh total for the 10 kWh battery and 63 kWh total for the 7 kWh battery."

  33. mrbojanglez

    Can anyone please kindly explain in simple language....coz I is simple.....what the power output of these two batteries is in practical terms. Why is one quoted as a weekly cycle and one a daily cycle?

    What does the 10kwh mean in practical long would it power a house for?

    Assumably the speed by which they recharge would be dictated by the size/ability of the solar panels?.....Your help is much appreciated.

    "Powerwall comes in 10 kWh weekly cycle and 7 kWh daily cycle models. Both are guaranteed for ten years and are sufficient to power most homes during peak evening hours. Multiple batteries may be installed together for homes with greater energy need, up to 90 kWh total for the 10 kWh battery and 63 kWh total for the 7 kWh battery."

    1. Shovel

      what you need, is a sh*tload of solar panels

      There is a back-of-the-napkin formula for determining the amount of solar panels you need to generate enough power to recharge 10KWh of battery. It's in 2 parts. Careful now, this is very dirty math, but surprisingly accurate against correct formulas. Here it comes

      Formula 1

      Watts x 4 divided by 2

      Assume that you are using a 300W solar panel, so 300 is our 'Watts'.

      4 = amount of average direct-sun hours shining on a fixed-tilt solar panel, per day.

      Divide that figure in half, to compensate for end-to-end loss to infrastructure (cables, ambient temp, battery temp, panel efficiency-changes with temperature).

      Formula 1: 300W x 4Hrs / 2 = 600 Watts 1 panel would supply to a battery bank in the 4 hours the sun is tracking directly over your panel.

      Here comes Formula 2:

      A 10,000 WHr, or 10KWh battery bank would need to be charged in the 4 hours of direct sunlight hitting the panels. 10KWh / 4 hours would be 2500Watts per Hour. Because we lose half of our electricity in infrastructure, we would need to have twice as many panels to sustain 2500 W an hour. Let's get 5000W of panels:

      Formula 2:

      5,000 W / 300W = 16.6 solar panels to give enough Wattage to the system to charge Mr. Musk's battery in 4 hours of direct sunlight.

      There is a glaring flaw in my simple math, and that is, Mr. Musk is talking in terms of KiloWatt Hours(USEAGE), but batteries are rated in Amp Hours(STORAGE).

      THEY ARE DIFFERENT QUANTITIES, so there is no direct conversion. You can look up many tables in Google to try and figure out how they convert. We can only guess.

      Again, this is all dirty math, but it gives one some insight into what it would take to support Mr. Musk's fancy battery in the event of a complete power outage…, Sixteen 300W solar panels.

      Do you smell that? It's Elon Musk!

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