20kWh of Tesla Home Storage < 5k ?



Is it safe to say that the ideal (all things considered) a battery that could power the average home for say 24 hrs of "darkness."

On could say 72 hours in certainly locales; hence the modular design.

That said; financially, a goal like 24 hours is unnecessary to realize the majority of the benefits of storage.

So what is it? 6hrs? 10? 12.7? 2? *grin*

Say it's 10 hours; considering metering economics and a theoretical (mental/intellectual) threshold for broad adoption.

The average home in the US uses an average of 32.05 kWh per day. (11,700kWh(yr)/365=32.05)

Lets say the majority of use happens at night; its cold in Philadelphia @ night.

Assume (kinda randomly) 20kWh is consumed AFTER the sun goes down; what if PV array on roof could power the home and "fully" charge the batteries daily.




assuming 153 dollar per kwH that's 3060 for 20kWh for cells. Throw on another 1000 for carriage, inverter, etc.

I think Tesla could easily offer a (nearly closed system) "home storage" solution that meets or exceeds the needs of most for 4k.

What a fun package to offer.

A down payment that gives the home/business owner immediate full ownership of the Tesla Storage system, and they finance, by preferred means, the panels.

(of course you could just roll the cost of the storage in the financing...but I think that immediate sense of ownership of something that is tangibly very valuable; cool, but also relatively accessible financially for not so corporate green types, and young professionals/families; is a neat thing to offer.


Apologies for the ramble.

FRAT version.

How many kWhs will the Tesla storage need to be to be most efficient (cost/metering etc); and how many kWhs to be completely self-sufficient? How big do you think the system will end up being?




  • Yeah, so the efficiencies of those panels are gonna play a pretty big role.

    (off to read more about Silevo; I think I recall something about a target efficiency of 23% on their first production run?)
  • Also...what is the load like? ...


    I can't wait to hear more about this battery.
  • And...fully charging and discharging isn't optimal...


    Also have to consider what one or two years will do to the cost.
  • edited November -1
    Excellent news. Storage might not need to need that high, nor high charge/discharge. Although the average kWh is one figure, its not constant. Much of house demand is in daytime and could run directly from panels. Overnight after sunset demand, if done right, can be quite low indeed. Its all about 'time-shifting' input versus demand. The devil is in the details.

    I use propane instead of an electric range. I have solar air heating, and also have solar hot water; one sunny day = 3 days of hot water. All it needs is a pump, not BTUs to heat. Warm tone LED lighting indoors and out. 'Vampire draws' shut down via power bars. Just those steps alone take care of 3/4 of the 'average' house electricity demand. I used to use 30 or more kWh. My entire house (with one new exception) runs on 8-10 Kwh average a day, or 3,000-3,500 kWh a year.

    But yes, this is truly excellent news.
  • edited November -1
    While I'm a big fan of Tesla's long term vision and goals, doesn't this undermine the "we're battery constrained" argument as far as car production is concerned? This makes sense after the Gigafactory, but not before unless they lock down the deal with Samsung along with Panasonic for nearly all 18650 production, thereby guaranteeing both companies a long term customer (and volume) for that format.
  • edited November -1
    Bob calvo, the gigafactory is intended to release the battery supply constraint.
  • edited November -1
    Bob - different supplier, doesn't compete with the car cells.

    Long term storage is one of the revenue streams enabled by the GF... you need to start building the storage business now if you want to be ready for the GF.
  • edited November -1
    In any case--please correct if I'm wrong; I'm sure I read that somewhere--I understood that once the Gigafactory building is 'up' that it was going to be finished in parallel start-to-finish modular sections so that production can start in one, while the second is being finished, and so on.
  • edited November -1

    You're all making it sound like thhe Gigafactory will be up and running next Tuesday. You're missing my point.
    Unless they are using completely different cells that are inappropriate for the auto imarket, then they are robbing Peter to pay Paul. If those batteries could have been used in a car, then they could be selling more higher margin cars. One of the recurring themes has been that they were production constrained by batteries. This suggests that this is no longer the case as far as Model S is concerned.

    The only way that this makes sense is to tie up factory volume of lower current capacity battery manufacturing of a vendor and then possibly work with them to upgrade the line so that it could also support the car busineess in the future. The future needs more and better batteries for the X and especially for the E/3.
  • edited November -1
    <b>Bob.Calvo</b> wondered, <i>"...doesn't this undermine the 'we're battery constrained' argument as far as car production is concerned?"</i>

    No. It does not.

    <b>Bob.Calvo</b> mused, <i>"Unless they are using completely different cells that are inappropriate for the auto imarket..."</i>

    There you have it.

    There are different grades of 18650 Lithium-ion battery cells. Not all of them charge/discharge at the same rate. The ones used in stationary storage are not as <i>'fast'</i> as those used for powering a vehicle.

    Reduce. Reuse. Recycle.

    Over time it will take fewer individual battery cells to make a vehicle battery pack at a given total capacity, thereby reducing the cost as well.

    As time goes by, older automotive cells may lose their ability to quickly charge and discharge, but can still operate many thounsands of cycles at a lower rate. So they can be repurposed, reused for stationary storage applications for decades after their initial use in cars.

    Ultimately, with the passage of time, even that use will come to an end. So the base materials that make up the battery cell woud be harvested to be recycled into new batteries to start the process anew.
  • edited November -1
    The production constraint was batteries at some points, but is now just factory throughput, AFAIK.
  • edited November -1
    I think Brian's closer on this. Car factory throughput is holding them back now. If you listened to the call Elon alluded to this at one point saying they need to maximize efficiencies so they don't have to hire more as he's not sure where everybody would park!

    You've got to go back to their master plan though. It is to move the world away from fossil fuels toward renewables. Not just in transportation.

    They have always used part of their battery supply for stationary storage. Maybe Red is correct but I've never heard of them using different cells for the stationary packs.
  • edited November -1
    To the original question, I think generally you'll see great -stability- benefits with a 10kWh system, and agree that financial benefits come by matching the battery to the kWh you use in peak, 20kWh seems fair.

    But hopefully it's possible to do far more, and hopefully Solar City and Tesla are looking at a very intelligent system (by today's standards).

    My first thought was that a future system should be aware of your regular usage patterns, and work to move your consumption to make it as cheap as possible for you. If you have plenty of solar and battery then it stores everything and sells any excess in peak time - and recharging at 2am from the grid is also okay as you'll have sold power at a higher price in the evening.

    While from an individual's perspective you ideally want to either pay nothing for electricity (using your own stored solar) or buy the cheapest energy you can overnight (if you can't get solar) - from a solar power company perspective you want to sell your energy to the general market at peak times.

    So my subsequent thought is that really, no matter what size battery you buy, it should charge to full with the cheapest power it can, run your household using grid power most of the time, and then sell everything it can during peak time. Of course your shoulder rates might be higher than what you get wholesale at peak, so the system has to work that out for you - it would have to make sure it keeps enough power stored to get you through your peak and shoulder needs until the cheapest power is available again.

    All of which will be too complicated for the average home owner to work out, but may be possible with an intelligent power management system. However, home owners are far more likely to understand a simple "I use 35 kWh, so I'll buy an 10kW solar panel and 40kWh battery and get myself off grid".

    Solar city can do far more as a distributed storage and solar power generation company, starting with the simplest of adjustments to their supply of power and stabilising the grid. They could just "move" power between solar city customers (some will just have solar panels, some just have battery storage, some both, and some simply power users) using storage to make solar power available to everyone 24/7 without using any external power sources.

    But I'm sure they'd like to produce more power than they use, and sell back to the grid at peak times. And different benefits for customers depending on what they've invested in or allowed on their property.

    So again back to the original question - it can be about self sufficiency, but it could be far better to be part of a nationwide power generation network with cheaper electricity plus offline power when the grid goes down.
  • *grin*

    Great post grega! Thank you. I really like your thoughts re: shuffling power between Solar City customers. *grin*

    Similar to some projects in Hawaii, that SCTY has been participating in (including a neat little tech company - enphase or some such. *grin*

    Exciting times! (once considered somewhat of a curse; there are upsides!)
  • edited November -1
    <b>grega: +1 <i><u>UP</u>!</i></b> Well done! That covers the benefits of such a system very well. I would not doubt that JB Straubel agrees with that concept fully.

    Bear in mind though, that in some states such as Arizona, public utilities are already lobbying state regulators and legislators to effectively tax, if not outright ban, such an action. They don't want anyone using their own batteries to store energy, even if it is gleaned from their own solar system instead of the grid. They have in particular stated they believe it would be <i>'unfair'</i> for a homeowner to <i>'stockpile'</i> electrical energy just to sell it to them at higher rates during peak times. They either want to get the energy for free, or worse yet, charge you for the benefit of them taking it off your hands -- to sell to someone else. This is why we can't have nice things. Greed. Thus, I would probably opt to be completely off the grid.
  • "This is why we can't have nice things."

    Ha! Agreed.

    "Thus, I would probably opt to be completely off the grid."

    Me too.
  • edited November -1
    Arizona's attitude regarding battery storage reminds me of other states blocking Tesla stores... Interesting how disruptive technology upsets the established mono- or oligopolies. It certainly exposes their fears.
  • edited November -1
    It may end up being the case that Solar City and Tesla can do great things for power generation and management in SOME states, and nothing in others, in the short-mid term. That would be a pity, but still allow a game changing new paradigm to be experienced.

    We do have to make sure the payments are balanced, and I think that is part of the problem. Here we pay too little for "being connected" and then a higher amount for the electricity. Plus people selling Electricity back sometimes get more than they pay for power (not more than wholesale prices, more than retail!). So that doesn't work.

    I suspect that a large majority of people will prefer to be connected to the grid, even at a cost. It gives a backup/safety option, plus if they have more solar panel power than they need they can disrupt the coal-power plant industry even more.

    Ultimately the model of having Solar City as a "distributed power production company" theoretically can bypass individuals selling power entirely. Instead Solar City is providing power to the city grid, it's just that it has its solar panels and energy storage all over the city

    Personally I live in an apartment. I can't add solar cells but I could add batteries. I hope that I'll be able to buy power generated from solar-panels on other people's rooftops one day. Right now I'm actually switching to hydro-power.
  • My word! The implications for the humble yurt! Nigh endless! *grin*

    Really though; imagine burning man; sponsored by Tesla!


    Now THAT is a marketing coup.

    Know for being "green" self-reliant/sustaining, but also a gift giver; other; next; new.

  • One has to be careful about expecting to be able to charge from the utility company at off peak hours and then welling it back at peak. Many Utility companies are very against this for some reason.

    They don't seem to mind charging from the solar array and selling it back during the "duck head" hours, but don't want to make very little at night and then have to pay at premium rates later that day.

    Look up duck head power curves if you need an explanation.
  • Oops, selling it back, not welling it back. My mistake.
  • edited November -1
    I think that falls under the concept that the pricing has to be fair and make sense.

    Theoretically if the energy retailer is paying Xc/kWh at 2am, but Yc/kWh at 8pm, then they're not going to care where they get either from. In fact, if you can sell it back to them such that they make a 1c/kWh savings in peak time they may like the idea. Theoretically.

    I think there are 3 problems
    1) Too many incentives tied to selling electricity back to the grid have been thrown in to the solar panel industry. My brother makes a huge profit on every kWh he sells, he thinks it's great. It needs to be a realistic return in terms of genuine wholesale energy prices, not in terms of encouraging people to put in solar cells or battery packs.
    2) It needs to be manageable. How do you pay someone who profits - do they need to be a registered business? If Solar City co-ordinates as a distributed power supplier it makes it smoother (I hope).
    3) the generating companies see this as competition, which they're not going to want.

    If it's the same company retailing the energy, running the local power lines, running the master power lines, and generating the power... then they really don't want that to change.

    I may be missing something - is there more to it?

    In Australia the energy companies all invested to upgrade their power lines and substations to handle increased demand, but instead the demand has reduced in the last year... and the companies still have to pay back the billions invested. So they don't need any systems to take the pressure away from peak needs on the substations, they can handle that fine.
  • Regardless the writing in on the wall.

    And the more resistance, in places like Florida and Texas that are being held up legislatively (oil money; purchased politicians. Because it certainly isn't economics and public sentiment hold it back) the more it will engender enthusiastic advocacy for COMPLETE grid independence; which is ultimately inevitable as well.

    One way or the other; as the great Sam Cooke once observed "change is gonna come"


    You guys hear about the new 3d printed solar concentrating domes? Basically...instead of having a racking system that shifts the panels east/west to track the sun and raise total efficiency...they've found that you basically put a little dome over the solar cell and have it redirect incoming light at oblique angles...and for equal efficiency you'd have to move the panel something like a centimeter all day...but ever barring that movement....this recent advance alone is a HUGE boost, because this allows residential markets access to drastically improved efficiencies without needing to install much heavier moving "frames/racks"

    Exciting times!!!
  • edited November -1
    Hadn't heard about that. Doubling solar efficiency is good, but I think adding moving parts will be an issue. Found the paper "Wide-angle planar microtracking for quasi-static microcell concentrating photovoltaics" 5 Feb 2015.

    There's a good article at
  • Exactly! These new "domes/concentrators" remove the need for movement. It relies on natural properties of the propagation of light via "synthetic" medium "glass/silicate." A solution Einstein would almost certainly approve of, at least in that it is simple, ergo elegant; beautiful.

    OR: don't move the panel; move the light.


    little printed domes; instant upgrade. HA!
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