Tesla Home Battery Hype

Tesla announced a big battery that can fit in your garage along a wall and is supposed to be earth shaking (or at least earth saving…)

The whole idea being we all become nice little power company subsidized consumers of Tesla batteries and that lets the percentage of solar / wind / whatever go up on the grid, saving Gaia from nasty {something – not clear…}.

So is this a giant breakthrough in $/kWh of storage? Let’s see…

From https://shawglobalnews.files.wordpress.com/2015/05/tesla-battery-specs.jpg

Tesla Battery Specs

Tesla Battery Specs

There are two models. One for “backup” only at 10 kWh for $3500.00 each. It can give a 2 kW continuous, so that’s about 5 hours and you are dry. Lets compare that to a nice 2 kW Honda generator:


Now this is the California Draconian CARB compliant model of THE best generator I’ve ever found, Honda. Not your “low ball” path.

Price: $1487 with 2 kW nameplate power, runs for 9.6 hours on 1.1 gallons of fuel. (Those are often quoted at 1/2 power, so figure about 5 hours at full output, or about the same as the battery)

Personally, I’d rather have the small 46 lb generator (about the size of a tool box) and a couple of gallon can of gasoline (or a connection spliced off of my car fuel line to drain a gallon if ever needed) than a huge battery at over 2 x the price. (And, oddly, I do… though I found the little brother at 1 kW fine for most needs). Oh, and notice that the Tesla does not include the inverter. You will need to buy one of those (and likely not the cheap $200 one either as this will need to be grid connected and all, and don’t forget to add the cost of installation, permits, and inspections).

Honda manual with specs on page 68 here:

Click to access 00X31Z077000.pdf

Now how about the “cycle” battery?

It is $3000, but only 7 kWh. That’s $428.57 / kWh of storage. (And you still get to buy the inverter… charger not mentioned. And don’t forget the rest of the logistical / install etc. tail.) Now what is the cost of bulk batteries for deep cycle use per kWh for other tech?


I randomly picked the UPG 85980/D5722 Sealed Lead Acid Battery (12V; 35 AH; UB12350) simply because it was clearly marked as deep cycle and the power specs were on the listing (so no need to go hunting). Take 12 VDC x 35 AH = 420 Wh, or 0.420 kWh Price at $65 makes it $65/ 0.42 = $155 / kWh.

I can buy 2.76 times as much battery storage per dollar with small retail deep cycle marine batteries. So even if they only last 3 to 4 years each, my life cycle cost at 10 years is the same or lower. Hmmmm….

Somehow I’m not feeling the love…

Other Bits

The Tesla is warrantied for 10 years. I’ve not got any laptop with a 10 year life on the LION battery in it. Since they use COTS cells, I think that is very optimistic and likely similar to car tire warranties where the goal is to have the device die at about 80% of warranty and then sell you a replacement based on the warranty allowance.

The Lead Acid cell will not burst into flames. LION not so sure.

The Lead Acid is heavier, less likely to take extensive cycles, and will look clunky. Then again, I doubt that a LION cell can get 3650 cycles without issues.

In both cases you will need a charger / inverter / grid connect (and inspections and installation and…) with the commercial Tesla being already approved and your DIY Lead Acid getting a hairy eyeball. No idea what other commercial options would do in a price comparison.

There are MUCH cheaper ways to buy bulk batteries than one at a time from Amazon. In particular, a large DIY wet cell Edison cell can be easily made from relatively cheap materials (iron, nickle, potassium hydroxide aka drain opener) and have been known to last for many decades. So my price compare is NOT to the cheapest alternative. There are many suppliers and this is a well proven (and better than lead acid) alternative. I’m just too lazy to cost it out per kWh at the moment. See: http://ironedison.com/ as one example.

Ok, with all that out of the way, I’m just not particularly impressed. This looks to me like yet another Subsidy Farm for Musk. Yeah, he will sell them; largely to the same uber-rich folks who can buy his toy cars, some to true believers who will get a little benefit from the subsidy structure. But from a $/result point of view, I’m not seeing much to make my heart go pitty-pat.

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About E.M.Smith

A technical managerial sort interested in things from Stonehenge to computer science. My present "hot buttons' are the mythology of Climate Change and ancient metrology; but things change...
This entry was posted in Economics - Trading - and Money, Tech Bits and tagged , , . Bookmark the permalink.

30 Responses to Tesla Home Battery Hype

  1. p.g.sharrow says:

    I saw the Musk presentation article. Another sell the sizzle and collect the subsidies. Not something I would buy at his prices!
    I have an old 1200 watt UPS that I hooked up to 12 – 80AH deep cycle lead acid batteries that protects my electronics, gives us lights as well as computer and television. About 10 to 12 hours of heavy use. It will even run the micro wave for quick needs but a bit small for the refrigerator. About $1,200 worth. It has earned it’s keep several times during voltage surges and power outages. I bought a 5Kw generac 12 years ago but have not needed it. Not even sure it will start! pg

  2. M Simon says:

    p.g. The proper care for an emergency generator (EG) is to fire it up once a month. When your EG is a 1 MWe diesel (nuke plant) it is an event. Anyway – you test them regularly so if you need them the odds are you are good to go.

  3. nzrobin says:

    It is presumptuous to say that it’s both single and three phase compatible if they don’t provide the inverter.

  4. Richard Ilfeld says:

    Those little deep cycle marine batteries seem to be able to take a licking and keep on ticking. Have a small solar panel that wont quite turn over my trolling motor. On the battery as an extender, charging in the Florida sun, it pushes a pirot for longer than my bladder or butt cares to be out — 5 hours plus. If i run it down till the battery can’t turn the motor over any more it comes back fine. Lost about .08 volts since new (cute little LED Voltmeter I put into the rig when I built it.
    Never tried it in cold weather — but worry about Tesla — the house — given that Tesla the car doesn’t like cold. So Its 10 below (not here, of course). The power failed overnight. I need to get warm. The batter lived in the garage. ?????????

  5. E.M.Smith says:

    @Richard Ilfeld:

    I’m sure they can keep the battery warm while on standby with a nice electric blanket ;-)

    I lived on a sailboat for a couple of years. Had 2 deep discharge marine batteries that could be (with one switch) put as A or B or A+B. You were supposed to run on just one (usually A) most of the time, with B available when you discovered you had completely drained A and needed to start the marine Diesel (that DID have a manual crank on it, but hell if I could do it…). You were encouraged to swap between A and B to assure recharging (when motoring around or plugged into the dock). On only one occasion did I need to resort to A+B when A was nearly dead flat and B was too long since charge. It started, though at a slow crank.

    In two years of live aboard, and about 3+ of docked weekend-warrior (harder on batteries, really) I never changed a battery. They were in the boat when I bought it…

    Don’t know the A-hr, but they were relatively big. About the size of 2 car batteries. At the limit of what one mechanic could likely carry and position into a battery box in a hold… Would easily run the electrical needs of the 27 foot live-aboard for a couple of days on one battery, then start the engine (or if that didn’t work well, swap battery and start engine, then switch back to charge – though often I’d charge in A+B mode and let the two batteries figure out the split by their own voltage differential…) and putter around for a while to recharge if needed. As it had a 40 gallon Diesel tank, and the Diesel, though it looked about the size of a car engine, was a very heavy very overbuilt 10 Hp Volvo Penta Marine Diesel, it hardly used any fuel at all. Typically I’d fill the tank at least once a year, whether it needed it or not. (No joke!)

    If plugged into dock power, they could float charge on a built in charger. For the live-aboard years, that was pretty much all the time I was not actively out sailing around on weekends. For the weekend-warrior period it was only on occasional weekends when I would visit, clean, do repairs, etc. Then sometimes sail a half day. Charging from Diesel only while in the “motor out of dock area” and “motor back in” – maybe 10 minutes each way? Or 20 when I was up in Port Sonoma (that has a VERY long channel out to open tacking depth…)

    Yup. Some of those batteries are VERY sturdy. Have to be. If tide and wind are against you, and you NEED that auxiliary engine, it can all come down to how resilient is the battery. (On more than one occasion, a ‘start on A’ would fail. I’d just “let it rest” with all drains turned off – fish more or have another beer – then try again and have it start. Just letting it rest could often recover ONE start from an apparently dead battery. Yes, I was curious and had a full B Batt available, but wanted to know…

    Sidebar on AwShit Diesel Starts:

    Once I was paying too little attention while sailing a circle around Angel Island in the San Francisco Bay (where Alcatraz sits). This has Raccoon Strait on one side, and the Golden Gate in/out flow toward the west. Currents can be strong, and tricky. My boat was a fat shoal draft keel (27 inches! of depth) that could maybe make 4 knots with the wind at your back, and often could not tack “up current” in Raccoon Straits. (More than a few times I’d be tacking back and forth like crazy and just going back and forth across the strait until the tide slacked. Fun, but not good if you wanted to actually get somewhere. For that, you watched those tide tables…) So turning on the Diesel to get through the Strait was something I got in the habit of doing and accepting. I know, bad sea habits, but there it was.

    So I’m just rounded Angel Island having gone up the Strait with slack water, and out into the bay and then played a while. Then rounded back down like I was headed toward The Golden Gate on that side, and turned “final” across the Gate side of Angel Island back toward Sausalito where I was berthed at the time. End of a long lazy day. Just drifting in light winds to home. And the winds became near nothing. And I thought about beer supplies and would it last until the winds picked up… my bad. I ought to have been looking at tides and currents. After a couple of minutes, playing with sails and trying to get somewhere, I noticed that Angel Island was getting bigger. The tide was inbound from the Gate and shoving me right toward the island, and the rocks on that shore. No Worries, I’ll just start the Diesel…

    No Joy. It would crank, and occasionally give a “sput”, but not start. Now this thing was VERY cold blooded. On cold days it could take bit of cranking to get started anyway. Open the fuel up about 1/2 throttle and let it “sput” a dozen times and in about 30 seconds it would start to sput-sput-sput and in a while longer it would be running. This time it was only the rare “sput”. As though there was nearly no fuel (that took me a while to conclude). Meanwhile Angel Island is looking VERY much larger. I can see the white as waves crash on the rocks and I’m thinking what color does a boat make?… But it was clear that the Volvo would have benefited from glow plugs ( I’m pretty sure it didn’t have any) and was a marginal start even with lots of fuel. And Something Was Wrong.

    So I head below decks, open the engine hatch and do the ‘hang torso into engine area while hips and butt counterbalance’ engine maintenance position to try to figure out “what is wrong”? Since nearly nothing can go wrong on these beasts, I’m not sure what I can fix…

    The very good news was that I quickly found the throttle cable had pulled loose from the injector control lever. One screw loose. Put the metal block end back in place, turn screw tightly, up the ladder, crank crank “sput-sput-sput-skip-sput-sputteerrr-rrrrroomm” and point bow toward The Gate…

    Later I closed up the engine compartment and resolved to stock more tools in the tool box aboard.

    I was at least 100 yards and maybe 200, and likely a good 5 minutes away from the rocks. Maybe. A couple of other boats looked like they were looking at me, and I might have been able to ‘arm wave’ in a tow in time. While the bottom comes up rather steep, there, I had enough anchor line I THINK I could have drug an anchor and stayed off the rocks (that was my ‘last ditch’ plan) One boat that was ‘headed my way’ turned off when I cut a line away from Angle Island, so I THINK I would have been ‘saved’. But still, it was definitely a “pucker moment”.

    Several things came from it. For one, I started paying a LOT more attention to “time and tides” and especially when going “cross tides” near land, knew which tide, how fast, and when; and gave much more leeway at all times. I also learned to sail with far less use of the Diesel as I wanted to hone the “get me out of here” skills even in light winds. (Though in no-wind you are stuck). I came to appreciate the (at least) 3 generations of Merchant Seamen on my Mom’s side of the family. (We know of three, but it likely goes back to the original Viking arrival, just not recorded in the books…) Dealing with that kind of thing every day for years, with only an oar as your auxiliary engine… well, it would make for much better sailing instincts. I also started taking a regular look at the engine, a pre-flight if you will, before heading out. Even if it did mean a bit of work (hatch was under furniture) and being head down for a while. Special attention to fuel system (well, really it was about the only thing that could be inspected…) And a battery check.

    I’d never really had much issue with the batteries, but after that time (and I’d run A down quite a bit on the first long series of ‘grind and no start’ and was wondering if it would ‘go flat’ and was B any more fully charged and..) I made sure both were charged before heading out or that I was going to run long enough to charge them…

    “Lessons Learned”…

  6. John Silver says:

    About the 10 year warranty; he is not planning to stay in business that long, he will take the money and run when the subsidies dries up.

  7. bruce says:

    what a pleasure to read about your sailing life. In an odd coincidence, I lived on a sailboat anchored out in a sea connected lake. The battery life determined how pleasant life was, tempered by diesel level. I too have a story, I’ll just say its nice to hear that even the smartest have to learn from experience from time to time.

    As for the tesla, the car itself is a hit with its owners, so I give it more credit. There is a bit of heaven in every corner of hell, just need to love a special thing.

  8. E.M.Smith says:

    This site has a DIY Edison Cell design that looks to be in a pint Mason jar. Specs are
    1.2 V
    1 A-hr

    It also looks to me like the jar is about 3/4+ of unused space just holding excess electrolyte. I suspect it would be terribly easy to make a many cell version in the same jar just by adding more sets of plates, perhaps with a baggie plastic separator layer between them. Or just use something other than the jar… The design is clearly for “demo” and not for “efficient space use”… Still, it shows that this isn’t a hard tech to do. And the batteries are known to last for decades while being very happy with deep discharge cycles.

    http://noonco.com/edison/improvements.htm With links to “white papers” on howto.

    Click to access white_paper_01.pdf

    Click to access white_paper_02.pdf

    These folks sell larger Edison batteries. The 6kWh one is more expensive than the Tesla at $7,500 ( 24 V ) and I’d expect them to see some pricing pressure from the Tesla. OTOH, see the quote on lifetime maintenance…



    Dimensions of the 250 Ah 1.2V nominal cell:
    10.5″ x 6.25″ x 22″

    When maintaining your Zapp Star Battery, it is important to add a 1/4″ layer of consumable grade mineral on the electrolyte and keep the water level between the two level lines by adding distilled water when indicated. If the water level drops below the lower level line, carbon can build up on exposed plates. This will weaken the battery capacity. If this happens, flushing the battery with distilled water and refilling with new electrolytes will return the battery to 100% capacity. Changing the electrolytes can be expected every twenty years (20) years. By rule of thumb only change the electrolytes when the battery capacity drops. With proper maintenance a two-year warranty is provided.

    Just as a humorous point of comparison, if you pessimistically assume a 1 V lifetime voltage on that jar based cell, then it is a 1 W-hr cell. So it would only take about 6000 pint jars to make the same capacity as their 6 kW-hr battery. I think the experimental cell can be improved ;-)

    Looks like Stanford has been playing with them too. Got a 1000 x increase in charge speed (and discharge if the story reads right..)


    Edison’s original battery used a cathode made of nickel and an anode made of iron, and bathed the lot in an alkaline solution. Back in Edison’s day, the conductive elements contained some carbon to help them work, but the Stanford engineers thought it would be fun to see what replacing that with graphene would do. Hailiang Wang, one of the researchers, explains to the BBC:

    “In conventional electrodes, people randomly mix iron and nickel materials with conductive carbon… Instead, we grew nanocrystals of iron oxide onto graphene, and nanocrystals of nickel hydroxide onto carbon nanotubes.”
    Usually, Edison’s battery takes hours to charge; the Stanford version takes minutes. In fact, it’s 1000 times faster. Though still very firmly in the lab-based stages, Wang suggests that in the future they could be used alongside lithium-ion batteries in electric vehicles, to give them “a real power boost for faster acceleration and regenerative braking”. Is there anything graphene can’t do? [Nature Communications via BBC]

    Not to besmirch the graphene and nanotubes, but it looks like they didn’t bother trying a plating onto simple carbon. It would be interesting to get a couple of simple very porous carbon rods and try plating them with the reactants… Basically replace all that nickle plated steel in the typical cell with pressed carbon…

    Carbon fibre mat. Apply paste, form electrode. Stack electrodes with plastic separators and immerse in KOH. Seems easy to me…

  9. DocMartyn says:

    Go to ebay and look at Forklift Batteries; heavy duty and with all the tech you need to support them

    You can buy a used reconditioned unit for $2500

  10. cdquarles says:

    I’ve seen lead-lead dioxide, sulfuric acid batteries catch fire before from excessive hydrogen production. Sure, that was about 35 years ago; but, yes they can and have caught fire. The sealed ones are less likely to suffer from hydrogen related failures; but, still.

  11. Tech Editor says:

    I have used twin Optima D31T 75 ahr batteries to power my Toyotomi L73 Vented Kerosene Heater when the power goes out. They will operate the heater for over 23 hrs. with the heater running at full power. I control the batteries with an SEC America SF606 Heater Sentry inverter/charger/switcher. The oldest battery is now 9 yrs old and still going.

  12. John de Melle says:

    What about house insurance ? When I told my insurance company that I was going to install solar-heating for my domestic hot water I received a panic phone call from them wanting to know if the heating was from PV or ‘wet’ solar panels. I could hear a sigh of relief that it was the latter system. Their experience with PVs were a considerable worry.

    Similarly, the Fire Department are very worried about PVs as there is no way of switching them off and fighting the fire until nightfall. http://www.bishop-hill.net/blog/2015/4/21/solar-heat-illustrated-josh-322.html

  13. punmaster52 says:

    It’s Elon Musk! He is a magician with electricity! Everyone says so.

    And then I come here . . . ;-)

  14. p.g.sharrow says:

    Prices for Tesla’s residential battery will range from $3,000 for a 7 kilowatt-hour unit to $3,500 for a 10 kwh unit, not including the cost of installation and an inverter. Orders will begin shipping in three to four months.

  15. p.g.sharrow says:

    Think I would rather build my own Iron-Nickel battery. Wonder how difficult creating the plates would be. The case would be no problem for me, pg

  16. RobL says:

    The key metric for diurnal battery storage is $/kWh stored and extracted. Currently there is little around that can do better than about $0.10/kWh eg $250/kWh nameplate capacity (I can buy Liion battery packs (18650 cells) from Taobao in China for $200-250/kWh retail.) used for 3000 cycles, add some cost to cope for net present value and capacity decline.

    A really efficient IC engine generator can do about 30% efficiency, giving about 12 kWh per gallon. Or about $0.30 per kWh electricity.

    Installed pv is probably slightly cheaper than $0.20/kWh in california.

    LED lighting, large thermal masses in fridges/refrigerators, solar thermal hot water and storing heat pump created cold water for AC can relatively cheaply alleviate the need for most large nighttime electrical power, aside from some cooking, washing and hair drying needs.

    I think the economics are probably just about there for household pv and diurnal battery storage to cover say 95-98% of days, with an IC genset to cope with conditions outside of that range – getting off grid saves a lot of utility connection costs.

    So this Tesla deal is probably just the forerunner of what will become a much larger trend.

    [Reply: It is traditional to leave the cents in when doing fractional dollars, so $0.20 rather than $0.2 so I put the final zero in. It also saves me from needed to scrutinize each number to figure out who’s a what ;-) -E.M.Smith]

  17. Serioso says:

    I can confirm RobL’s numbers, although I doubt 30% efficiency on an IC engine unless run at full throttle (which would probably destroy it in rather short order). And I agree that the Tesla story is the beginning on a new paradigm in electrical power generation. Within 5 years we’ll know for sure, I think. Maybe less.

  18. janama says:

    In order to get down the price of the Tesla car they have to reduce the cost of the battery which to replace is currently $45,000! half the cost of the car.
    They have just built a massive new battery factory and this venture will give them the increased scale to bring the cost down.

    this is the competition coming out of Europe.


    It’s a battery where the charge is stored in the electrolyte which is salt water! Charge the salt water, pump it into the car battery, remove and replace when discharged. i.e = pull into a servo and recharge with a simple transfer of fluid, just as it is now.
    The car has 4WD using 4 electric drive motors. 0 – 100 km/h: 2.8 S
    top speed: 380 + km/h


  19. E.M.Smith says:


    Man those are heavy “page weight” links. BIG high def images AND video… to bad they had nearly nothing technical on them (and with that page weight and little obvious menu for the tech stuff, I didn’t feel like exploring). The concept looks right to me, though. High perf cars with a FUEL that can be changed. Yeah, you can call it an electrolyte battery, but it acts like a regular refueling stop.


    It’s the gas that burns, not the battery (unless the plastic case gets involved, which is easily prevented with the right plastics). Yes, all sorts of things can have oxidations, but the lithium battery is in an entirely different class.

    A wooden box is higher fire risk than a lead / acid battery on a matched charger.


    Making any old plate is easy. Making one the right way is a bit tricky (it is in the links above).

    My speculation is that a very good plate can be made by using a carbon fiber core (make sure it is plain carbon and not coated with plastic … you want electrical conduction, so take a resistance meter to the buy…) and then coating it with the appropriate hydroxide / oxides. (How to make the oxides / hydroxides via a paste is in the links above and in various web pages)

    Putting plates together into a battery, I’d either use a permeable plastic (i.e. a sponge layer) and just roll it up like a lithium cell, or if the oxide is too brittle, the classic alternating plates with space between them design like a lead acid battery. Plastic spacers to prevent touching / shorting.

    The traditional way is to make repeated layers of oxide/hydroxide with ‘bits of metal’ (usually nickle flake) in a nickle tube. The oxide / hydroxide doesn’t conduct well, so the metal flake acts to conduct charge. These layers are packed into a perforated nickle tube that makes the electrode. Lots of steps. Metal fabrication. Seems sub-optimal from an assembly process POV.

    One paper linked above used a ‘carbon nanotube’ adjunct and got outrageously fast charge times, that IMHO demonstrates the limit in the old design. Charge collection and conduction.

    Thus my “put carbon down the middle in a sheet of fabric” idea. Gets rid of the expensive metal fabrication and the fussy lots of steps process. Improves conductivity. Assembly process more like other cells with ‘paste on sheet’ continuous flow. It’s on my “someday” list to try it… feel free to try it first and let me know. ( IFF it works spectacularly, post that it failed and tell me in email and then we can share taking over the battery world ;-)


    Your comment on PV in California got me thinking… Compressed air storage or small site water pumping… I wonder how big a water tank, say 30 feet up a tower, would be needed to store the typical 7 to 10 kWhrs needed to get a California home through the night… Or how small a 3000 PSI compressed air storage / motor system could be… and with what efficiencies… Might be an interesting “Dig Here!”… Question: Is it cheaper to do a micro scale hydroelectric pumping than to do a Tesla battery? May not matter in San Francisco, but on a farm somewhere? Hmmmm…

    At one time, circa W.W.II and after, the US Army had a little portable generator that could be attached to household water supply. Why? While electricity would often be out, the water supply was often intact. Got something like 100 W? from a kitchen faucet…

  20. p.g.sharrow says:

    @janama ; Your links lead only to company promos. How about a link to the science/technology. pg

  21. p.g.sharrow says:

    @EMSmith ;Lol, my to do list is even longer then yours! :-) Still this is very intriguing. Don’t really need fast charge/discharge but do need size,safety and longevity. A “home built” electric energy storage is a real draw to me. So I must study this further. pg

  22. punmaster52 says:

    The car has 4WD using 4 electric drive motors. 0 – 100 km/h: 2.8 S
    top speed: 380 + km/h

    While I realize the point of such a vehicle is to prove what can be done with the technology, what good is a car for the street who will do 200 mph? The average driver these days isn’t paying enough attention to be safe at 60 and doesn’t have the car control skills to drive 70. 100 mph, carry 4 adults, get 35 mpg, quiet enough for conversation at 70, A/C which freezes you ( Florida resident ). Why can’t I get a car that does these things instead of having the ability to send messages to the Mars rover? I had a 1998 Ford Contour which was just short of those things. Not quite large enough for 4, although average size adults would fit in the back seat in moderate comfort. Consistent 32 mpg in town. I could get 35 staying at 70 on the highway, 38 drafting semis at a truck length and a half. ( Crack the passenger window on the driver’s side an inch. When you don’t hear the wind out of it anymore, you are close enough. You are still far enough away not to scare yourself. ;-) ).

  23. E.M.Smith says:


    At 200 mph you can outrun the black helicopters… Very important feature..


  24. punmaster52 says:

    But not the radios. And if your land speed record machine has turbochargers, can you say heat seeking missile lock? I knew you could. :-)

  25. punmaster52 says:

    Besides, they knew from your phone data where you were going. And black helicopters are so 1980s. Electric, solar-powered drones which color change against the sky. And carry heat seekers just big enough, just in case.

  26. Pingback: nightmare of solar … | pindanpost

  27. Thanks for your critical view on the whole Powerwall hype. The overhyped situation is more a result of a huge marketing budget rather than the actual impact it will have.

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