Converting to Powerwall 2 off grid

[Sodamo]

Coming from a pure off grid background, perhaps my perspective has been a bit skewered, wondering how the PW2 will fit into my off grid environment. Took a bit of time to learn more about grid tied systems and now see things a bit differently. Whereas what I have seen is along the lines of off grid systems being tweaked to be grid tied, perhaps the PW2 is somewhat opposite - a purposely built grid tied system tweaked for off grid. This could be as simple as feeding my solar panel DC into the inverter to charge the battery, either at low voltage thru my current MPPT chargers or more likely reconfiguring to higher voltage with MPPT optimizers. I'm guessing something as simple as a software setting would bypass the need to sense grid presence. Perhaps another setting would allow a back up generator to function via same connection.
Someday all this mystery will be replaced with know facts, but until then...
Was hoping that the approval last Thur would lead to release of more info.

 

[Sodamo]

Any chance somebody reading this has knowledge of how the solar side of an installed PW1 is configured.
For example ____ strings of ___ VOC x ___ number of panels? If multiple strings are they to some sort of "box" prior to the PW1? If there a min/max PV wattage?
Is there a PW install manual available anywhere?

Anyone contacted yet as to PW2 installation?

 

[miimura]

Any chance somebody reading this has knowledge of how the solar side of an installed PW1 is configured.
For example ____ strings of ___ VOC x ___ number of panels? If multiple strings are they to some sort of "box" prior to the PW1? If there a min/max PV wattage?
Is there a PW install manual available anywhere?

Anyone contacted yet as to PW2 installation?

PowerWall 1.0 is completely dependent on the SolarEdge Inverter. You can look up their specs and manual for the information above.

 

[Sodamo]

Yep, found the max PV wattage (STC) and amperage in the brochure.

 

[macpacheco]

Powerwall 1.0 uses high voltage DC input/output.
It would make sense that Powerwall 2.0 DC would require high voltage DC in, 110 or 220V AC output.
I think it was something like 380Vdc-440Vdc or something similar.
So your panels would need to be wired in series enough to produce Vdc in the target range. If you have more panels, make multiple series strings and connect them in parallel in the powerwall input.
You must take your temperature ranges and wiring losses to arrive at the powerwall with the right voltage levels. Temperature matters (the colder=lower resistance, hotter=higher resistance) for Kona I would imagine the temperature ranges are more modest (but a solar PV system in Boston this makes a big difference).
I live in a medium size sunny city in Brazil, latitude much like Hawaii, but I have the grid. We have net metering. I've been searching for a solar solution, but find that inverters like Powerwall has (high VDC input, standard VAC output) are as expensive as the panels I need for my installation (3-4kWp). I live in a 8 story building and have to bring AC voltage to the meters and use two meters. So it sounds insane to install the inverter in the roof and incur losses when I could use something like a 400-500Vdc string, and install the inverter next to the meter. I've been delaying purchasing a solution due to both lack of qualified installers and the inverter cost. I have cheap inverters that would require all panels be wired in parallel.

PS...: I'm not an electrician nor an electrical engineer. I'm just thinking out loud. Please consult an actual certified professional that actually does this.

 

[Sodamo]

Well time has run out. Unable to find a good source of PW info, even the local installers. So while I had great hope in using PW2 in my off grid environment, not going to happen. Have a contract for installation of Aquion (salt water) batteries in Feb. My current batteries are failing, generator usage increasing so time is a factor. Being truly off grid isn't quite the same as those who chose to flip a switch or experience short term grid failure. Will also increase my solar panel wattage by about 40% by replacing my original smaller panels with new larger panels. No need to replace my current Outback system, just add another MPPT charge controller. I'll be installing the PV myself, but the Aquions are dealer installed.
Now if I can only get my deposit back...

 

[Chris TX]

PW2 has built in invertor and can be used without solar as a power backup system. This means 120/240VAC in and 120/240VAC out. There should also be taps for DC input from solar or wind, as well. If you're wanting to use a PW2 for off-grid storage, just fill it with PV DC or some other source of AC.

 

[Sodamo]

Thanks Chris.
You make it sound so simple and straight forward. Please tell us about your off grid system. If using a PW, the DC side details, if not then how you would convert for PW2.

 

[Chris TX]

I'm saying you can have grid connect 240VAC or PV connect for DC input, or both. I do not have a PV setup, but have a PW2 coming in a few months (referral program) and will use it as a backup and to augment daytime power use, since my 9PM-6AM power is free. The PW2 will be taken with me to my new house, next year that will have PV. I could see being off grid with a full-sized house in maybe 2-3 years for me.

 

[Sodamo]

Chris, my apologies if I come off in a negative way, not my intent, just my frustration coming through.

The problem is you don't know same as I don't know, what Tesla may know, but is not sharing. We can only guess.

Most current off grid systems and many grid tied (all Tesla) are apple and oranges. Are they coming to a future convergence? I hope. My system is based on 48vdc. Simply put, my panels are configured to supply a MPPT charge controller appropriate DC to charge a 48vdc battery bank which in turn supplies 48vdc to my inverters, 120/240 to my house. If I use my generator or grid tie those inverters have a 48vdc charger to my battery bank. 24vdc and 12vdc systems are also common but most of the inverters and some of the charge controllers are not interchangeable, in other words changing from say 24 to 48 volt system requires new equipment.

Will the PW2 accept dc from my current charge controllers? Unknown. If the solar panels connect directly to PW2 can they do so at current configuration? Unknown. Would they need to be reconfigured to a high vdc configuration? Unknown. If so, could that reconfiguration be done at the combiner box or must it be done back at panels? Unknown. If my current MPPT charge controllers are bypassed should/must Optimzers be incorporated? Unknown. A grid tied has convenient backup, how does my generator get incorporated? Unknown. How to go from a 48vdc system to a high voltage dc system? Unknown.
So, just a start on my frustration of what's not known and not being able to find out other than others interpretation of same stuff I read.

Now, to be honest, if I were grid tied, there would be less urgency. If my batteries die, I get to run my generator at $4/hr until they are replaced. My FLA batteries are 10 years old.
If I was simply writing the check and had no role in the actual configuration (see earlier post on expansion) or future maintenance then I'd have little concern either as long as it performed when the the check cleared.

You mention the possibility of going "off grid" in future. I'm guessing what you really mean is having a grid tied system where you choose not to use the grid. Not exactly the same but a common misconception according to my installer. I would recommend that you be up front with your installer and chose one with off grid experience, design accordingly. The couple of installers locally I talked with that had Tesla PW experience had no off grid background and were not comfortable when I said I was off grid.

Perhaps I should add for clarity. Tie to grid is NOT an option. Too expensive to get it to house.

 

[miimura]

@Sodamo I think you are making a logical choice. Dropping in a different 48VDC pack into your current system is by far the most straight forward way to keep your system running. I saw the "pallet style" multiple stack Aquion pack at the July Solar show in San Francisco. It looks like a good solution, but at the time, they told me that the ballpark cost to install one of those was $20k. At that price, it's not a viable solution for ~26kWh. To me, any solution over $500/kWh can be completely ignored as being impractically expensive. However, since that time, they have been talking about significant cost reductions. I see that the same pack is listed online now for $15k. Still high, but at least in the ballpark of other solutions.

When you have the new batteries installed, I would be interested to read about your impressions. Maybe the Energy, Environment, and Policy sub-forum would be more appropriate for that.

 

[Sodamo]

Thank you Miimura, not an easy decision. I've been very excited about the Tesla PW2 and was quite willing to be on the bleeding edge.
My Aquion contract is just a few thousand more than my Tesla reservation. Unfortunately, that reservation has changed since I made it and I truly suspect it would increase significantly by the time it was completed. Simply adding taxes and transportation to Hawaii would make it even. So I saw this as a nearly equal cost tradeoff.
Part of the challenge is to determine how to compare choices.
To replace my current batteries with exact same would be directly comparable. What originally cost me $200/kw are now $400/kw plus installation. I get same capability but also same lifespan, so in another 10 years I get to replace again, perhaps at $600/kw. One overriding concerns was to break the replacement cycle. I really want this to be my last set of batteries. The attractiveness of Aquion/Tesla is less kw may also equal longer lifespan. Does Tesla equal Aquion lifespan? Unknown, but indications are Aquion may outlive Lithium. I will rarely take these new batteries below 50% DOD so I think I can expect 20 years plus.
Based on what I spent on diesel for my generator this year I'll recoup cost of my solar upgrade is a little more than a year.

I will post in the other forum when installed.

 

[neroden]

The Tesla Powerwall 2 is clearly designed to be A/C coupled primarily; the DC version seems to be an afterthought and specs are quite unclear. So basically the only Tesla option you have which doesn't have "unkonwns" attached would be to get a normal solar inverter instead of charging your batteries with DC, and then charge the batteries with AC. Probably not a great choice technically, so I think you're doing the right thing with the Aquion.

 

[Sodamo]

OK, I'm going to agree but perhaps different reasons. It seems that most grid people really don't have a clue what truly off grid means. Any AC power I produce is either via my inverters (powered by my batteries) or my generator, my only choices. A common theme I read in many forums seems to be that "off grid" means either the public utility has an outage or a switch was thrown choosing to disconnect. Trust me, that is not truly off grid. Should I lose power in middle of the night, the problem resides totally within MY equipment. Unless I get up and troubleshoot, the likelihood that power will be restored come morning is slim to none. The only other switch to can throw is my generator. Fortunately, that happens far less than our grid tied friends and neighbors. There is a very sizable air gap between me and the public utility.

 

[Chris TX]

Sodamo, I understand that you have a 48VDC PV system with 48V battery storage. You're wondering if PW2 would be a good replacement for your aging 48V storage. Right now, the DC version of PW2 expects HVDC input. The only way you could use the DC PW2 is to reconfigure your PV array to be HVDC. Whatever cost that is to reconfigure (if possible) might be a good option, considering the $/kWh of the PW2 and its newer tech and smaller footprint vs new batteries for your existing setup. Do you know what the DC-AC invertor efficiency is of your existing unit? You might also be able to sell your older 48VDC for some cost recoup.

 

[Sodamo]

Good thoughts Chris. Unfortunately, I'm running out of time. Due to winter clouds, less sun, and degradation of my batteries, I'm having to run my generator every day. The Tesla configuration calculator suggested I should increase my PV and that would be beneficial with any battery so that is my plan. As I decided to replace my older 125w panels with 280w panels in same location increasing my 10kw to 14kw. Reconfiguring from 48 to HVDC would not have been a problem. I will just depend on generator charging on days my panels aren't available. Unfortunately, I still don't know if those panels would direct connect or go thru optimizers for the PW2. If I could have taken my 48v arrays and recombined to HVDC just by creating higher series at the combiner box, I would have been interested. Unfortunately, no follow up info at all from Tesla or an installer so last Thu I pulled the plug and cancelled my PW2 reservation. My math, depending on the installation hit, being able to recoup some $$ from my current hardware may have made the PW2 a more cost effective option. Certainly something I found attractive. Unfortunately, I don't dare wait longer, my my batteries will be installed in Feb. Diesel here isn't cheap.
An interesting aside, my battery installer is also the local rep for another name brand Lithium battery, but recommends the Aquion especially in off grid. they anticipate their PW2 installs will be more gridtied unless there is some unknown starting fact as yet nknown. They still sell mostly lead acid types due to initial $$.

 

[neroden]

I think there will probably be more PW2 off-grid installs once the *installation manuals and detailed specs are actually released* but of course they haven't been yet, and that's your problem. There's enough information to know how to do an AC coupling but not a DC coupling.

Geez, another Tesla problem which is basically communications. It's their weak point.

 

[Sodamo]

'Tis a shame. I would have been a very good advocate. I think I would have been a very good beta site

 

[MarcEMarc]

You could look at Pika Energy's 380v islanding inverter. Probably just what you need because I'm looking for the same thing. In addition, another vendor was coming out with a 380v inverter, sma? solar edge? Can't remember. Anyway, Pika seems to have nailed the things I'd like. I'm just a year away unfortunately or fortunately as the case will turn out to be. Not many options but Pika is one of them. Oh, the only issue with them is that they can't use Sunpower panels (grounding issues).

That said, if Tesla is bundling up lots of the power electronics into the pw2 than my life might have become a bit easier to manage, combined with the new roofs it's a very compelling option for new builds.

First off STAY AWAY from Pika Energy!
I have the Pika X7601 system that had promises of sophisticated off-grid operation with PV Link optimization and automatic switching from battery pack to panel to grid (if there). That's all true - EXCEPT you can ONLY use Pika batteries
(at double or triple the $/kwh here's the calcs)
- Tesla Powerwall 2 14 KWh at $7584 installed or $541.71 /KWH compared to the
- Harbor 15P which is $1230/KWH. That’s more than 100% higher.

and their quotes on other Pika compatible batteries:
"Fri, Aug 4, 2017 at 2:52 PM Some of these are not yet available but planned to begin shipping in January. Here is current pricing shipped and installed:
Harbor10P: $14,250

Harbor15P: $18,450

Coral: $11,100

and Pika will NOT sell you any pieces (charge controller or battery interface) for you to add say another battery to their system. I was told they would support DIY lithium batteries by the sales engineer only to find out after install they will not. AND, they will not talk to customers - they only talk to the installer/rep.

To cloud the waters even more, I ordered a PowerWall 2 and ask if they would interface with Tesla PowerWall.
They will NOT even talk to Tesla to interface with the Powerwall and responded:

"On Thu, Jul 20, 2017 at 4:09 PM, Chip Means <[email protected]> wrote:

Hi Marc,

First and foremost, I completely identify with your concern and fully appreciate your candid feedback. I am happy to help explain further.

REbus (our core architecture) is designed as a common gateway for clean energy devices (generation, storage, loads, etc.), combining them on a common DC-bus with built-in control. The advantage this provides is that when you’re using REbus devices (i.e. Pika products), you don’t need additional comms boxes, switches and autotransformers that other manufacturers’ products require to integrate features like islanding and battery storage.

To be clear, the AC-coupled Tesla Powerwall 2 is designed to work on the AC side of the inverter and therefore would not be a desirable design for functions that are built into the DC side of our system — the Powerwall is a product that contains another inverter inside of it, designed for AC-coupling. We are not supporting or integrating our products with the Tesla Powerwall batteries at this time and are making no claims of compatibility with that product.

There is a level or propriety in all clean energy power electronics products (you can’t connect a SolarEdge optimizer to an SMA inverter, for example). That said, the Energy Island system is compatible with two DC-coupled smart batteries (Coral and Harbor, more to come in the future), whereas the other inverter platforms on the market are mostly only compatible with AC-coupled options that have limited performance features compared to the Pika/REbus operating system.

Thanks again for your support,

Chip


Chip Means
Director of Marketing, Pika Energy
M: (207) 749-6570
O: (207) 887-9105"​

If anyone out there wants to buy a used Pika x7601 and two PV Links let me know :O

 

[miimura]

I talked to a Pika Energy rep at the solar show in San Francisco in July 2017. They were quite clear that they only supported their own battery systems. I expressed the advantage of their system architecture to accommodate other battery systems, especially the fact that they use DC/DC converters to allow mixing of battery types and native pack voltages on their DC bus. I asked if they would be willing to work with other integrators to allow interfacing with other battery packs, particularly salvage EV packs, and the rep said he doubted that would ever happen. Sorry you were misled to believe that they would allow other batteries.