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Powerwall solarpowered off grid

Discussion in 'Tesla Energy' started by JEU, Apr 16, 2017.

  1. zag2me

    zag2me Member

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    Thats totally awesome, love the plug in and play design.

    Lets hope this kind of system becomes more popular over time and the price reduces.

    For info, they do a 4kWh system as well for not much more money.
     
  2. Ampster

    Ampster Member

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    #22 Ampster, Apr 20, 2017
    Last edited: Apr 20, 2017
    You can't legally and for safety reasons send any thing to the grid when it is down. However behind a transfer switch you could spoof the grid and get a grid tie inverter working just fine.
     
  3. miimura

    miimura Active Member

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    In order to have a stable off-grid AC coupled system, even if it's usually grid tied, you usually have to have a larger battery inverter than solar inverter. However, if you use solar charge controllers to charge the batteries directly, then you don't have that limitation. The small 1,500 Watt inverter in the linked PowerOak system does not seem suitable for AC coupling.
     
  4. Tim

    Tim Member

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    Miimura,

    I appreciate your reply. I'm pretty sure greater than 99% of the population would have no idea what you're talking about. And I'm pretty sure that 99% of the people that are interested in solar wouldn't even know what you're talking about. I'm not trying to be insulting, because you clearly seem to know quite a bit, but I think your response is illustrative of the general problem with solar right now. It's way too complicated.

    I also think you're wrong about that PowerOak box. Which isn't surprising, because I still don't really know what it is. I've never seen anything quite like it. I'm currently using fully-islanded microgrid appliance, but I'm not sure that's the best description. It's really a unicorn afaict and is much more complicated and functional than a powerwall. I looked up Poweroak and they're a Shenzhen ODM that apparently started by making lipoly batteries and powerbricks to charge phones and other USB devices. That's clearly the DNA of this device and its a thoroughly interesting evolution(at least to me!). The box is marketed as a solar generator or ESS, but its not that at all. It's not an AC battery either. It only has 3 plugs and 3 operating modes. It's super simple. AC IN, DC IN, and AC OUT. The 3 modes are 1 - Off grid Solar using DC IN and AC out), 2 - UPS using AC IN and AC OUT, and 3 - Grid assist(they call it something like peak avoid, but it's basically grid assisted solar). Importantly the AC IN and AC OUT are two separate busses(islanded) and none of the inputs or outputs are bidirectional. IE this thing would always be a load on the electric grid. I think(but am not positive) that every component(the solar charge controller, the battery charge controller, the ac input and PWM output) are coupled to a common DC bus internal to the box. Which makes since since that's by far the easiest way to manage load sharing in a microgrid. The closest analogy I can think of is to take a Radian, 4kwh of 18650s, and a user friendly touch screen HMI and put it and put it in a box the size of a computer case. Which sounds super obvious except when you realize that no one has done that before. This is truly an engineering marvel imo. One of their marketing people has a couple useful presentations on slideshare. Vivian Yan

    But like I said up-thread, that's the least interesting thing about this thing. I was trying to think of how it would be classified and I think that this thing is for all intents and purposes a programmable UPS. A big one, that includes optional DC(solar) input, but that's what it is. So, the genius of this design is that it no longer has anything to do with article 690 of the NEC and really falls under article 702. But since it's an appliance it really it falls under UL 1778. I think. Anyways, the point being that if this thing was UL listed as such it would be code compliant and could be installed most places without pulling a permit and without asking or informing your power company. And given the size, weight and complexity an average homeowner could do it. Just like any other UPS. That is an absolutely huge change from the status quo. And since its a tiny box in your garage or basement even if they wanted to regulate its use it would be pretty much impossible. The fact that it is user-installable is key to reducing system cost and increasing adoption.

    To illustrate how easy an off-grid install would be with the box consider what you'd need.
    The box - includes a 4KWH battery and 2kw/3kw peak inverter
    4 solar panels approx 1kw (I'd go with some maxim optimized Jinko's so I didn't have to worry about mismatch, but pretty much any would do.)
    Enough 10 gauge cable and MC4 connectors to connect the panels in series.

    To install put the panels in a sunny area. Plug the solar panels together in series. Plug the solar cable into the box. Plug the box into the off-grid house. Select Mode 1. Done. (Yeah, I should probably ground the panels too. That will take another couple minutes.)

    Considering all that stuff is about $4K unsubsidized out the door and user-installable in about an hour is insane.

    If you took the same setup and plugged the grid into the AC IN and selected Mode 3 then you could get all the benefits of grid-assisted solar(load shifting, avoidance of grid-tie fees etc) as well as keep the benefits of the full micro-grid islanding not possible with current grid-tie(and tough to achieve with an AC coupled powerwall). To install in an existing house the only wiring modification would be to install a subpanel, generator transfer switch and move all your circuits small enough to be powered by the box to the subpanel. Amazon sells those as kits for about $200-400.

    So, I think this is what the powerwall should have been and probably will become. It needs some upgrades still. The boxes should be able to expand capacity with other boxes in parallel. They need the UL listing. While I understand the universal outlets, it really needs a NEMA L14-30 or something similar. Also, I think it should be smart-device enabled, whether that's SmartThings, IOT, or whatever to properly manage load(weather forecasting, usage etc). And I think Tesla is tantalizingly close to being able to build and sell something like that for $1500 in which case the economics heavily favor everyone installing it. And in the event that Tesla doesn't, well I guess the guys in Shenzhen will. :)
     
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  5. miimura

    miimura Active Member

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    @Tim - I appreciate and understand everything you wrote and I agree with everything you wrote except this:

    The PowerWall is a completely different animal and is designed first and foremost to be grid interactive. That is Tesla's mission - to drive toward sustainability. The big picture for the PowerWall is to become a massive and distributed virtual battery that can help balance the grid and reduce fossil fueled generation. Off-Grid is great and this PowerOak box is definitely useful in a suitable use case. However, there is no place for a battery that small in my home that already has 4.3kW of solar installed. I know that there are people who strive to keep their electrical footprint as small as possible and this small system would be great for them. Heck, it might even be good for the "preppers" out there that want to be prepared for the next hurricane / earthquake / flood / zombie apocalypse. I just don't think this is suitable for very many American homes. A "tiny house" or an RV, sure. Cabin in the woods, maybe with propane or gasoline backup generator - yeah, that would probably work too.
     
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  6. GSP

    GSP Member

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    @miimura,

    NB: The PowerOak systems are available up to 31 kWh, enough for whole house backup, and for more than 4.3 kW solar.

    GSP
     
  7. doubleohwhat

    doubleohwhat Member

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    Pricing on the larger units?
     
  8. miimura

    miimura Active Member

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    Also, how many kW to go with those larger kWh?
     
  9. Tim

    Tim Member

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    You'd probably have to contact them directly for pricing of larger units. I don't see them on Amazon. Though they do advertise the 6kwh units for $3400 on Facebook. That's fob shenzhen so you'd have to factor shipping.

    My big point here was that they're making it possible to install a 2.4kw/4kwh off grid system for $4800. Unsubsidized. That's $2/w installed. The lcoe for that depends on your assumptions, but it's about $0.2/kwh or less. It doesn't take much improvement to get the costs to the low teens. That's a magnitude cheaper than anyone else is talking about. Check out this recent article and price for similar systems.

    How Much Does a Rooftop Solar System With Batteries Cost?

    According to pvwatts, that system would make about 4000kwh/year in Hawaii. That's nearly enough for a median household there to go grid free. That 6kwh system and a 3kw solar array probably does it for over half the state.

    Things are about to change. Not just in Hawaii. But everywhere. I've been waiting for this for a long time. Slow and then really fast.
     
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