Re: [RE-wrenches] Powerwall 2 AC PV regulation

[Darryl Thayer]

Regarding 3 Power Walls PWs, more solar modules, and inverters.   I hope
this is helpful, I am always going to first principles.  You did not
mention what the customer expectations are.  I see three common
possibilities, 1) For backup power, in which case you need generation
control, such as the AC Diversion control that Magnum solar used to make,
or the frequency shift of the master PW shutting down the inverters.  I
have no idea how the PWs synchronize.  Depending upon the model and age of
the inverters they will back down until they shut off by frequency shift.
>From full power to shutoff is about 0.6 Hz.  If the inverters do not have
frequency shift power correction the inverters will shut down.  Then stay
down for 5 min until time to restart.   2) TOU or TOD (time of day energy
pricing)  with and without full net metering.  The grid is connected the
solar inverter can export when the battery is full.  When the solar is
insufficient the gateway programming directs the PWs to carry enough of the
load to prevent power import. excessive charges.  If you have two different
pricing a study by Egauge or similar should be done to full fill the
highest cost energy needs.  This study should reveal the lowest price
period and the amount of off-peak energy to buy.  If you have data from the
SMA or Egauge as to the past records you can modify your program using the
probability of sun.  3)  No export, this is similar to backup power except
the grid provides synchronization and the inverters must have non-frequency
power limitation.  This is very tricky..  not sufficient power is


On Sat, Apr 17, 2021 at 2:26 AM Jason Szumlanski <
ja...@floridasolardesigngroup.com> wrote:

> I think the limit is now stated as 7.6kw if memory serves me right.
>
> Jason
>
> On Fri, Apr 16, 2021, 12:11 PM Matt Partymiller  wrote:
>
>> They used to advocate 7.9kW AC/DC per Powerwall.  That number may have
>> gone down recently.  Coupling an inverter on the line side of the backup
>> gateway will resolve your issue of meeting homeowner demand.  Tesla will
>> want you to add a CT to that inverter to ensure it does not mess up their
>> monitoring system, though that may already be incorrectly configured and
>> not monitoring the whole home if the system is backup only.
>>
>>
>>
>> Matt
>>
>>
>>
>>
>>
>>
>>
>> Matt Partymiller
>>
>> General Manager
>>
>> Solar Energy Solutions, LLC
>>
>> Lexington | Louisville | Bloomington | Cincinnati | Evansville |
>> Indianapolis
>>
>> 859-312-7456 (Office)
>>
>> 877-312-7456 (General)
>> m...@sesre.com
>>
>>
>>
>> Check out our amazing new website and social media updates: www.sesre.com
>>
>> 
>> 
>> 
>> 
>> 
>>
>>
>>
>> *From:* RE-wrenches  *On
>> Behalf Of *Kirk Herander, VSE
>> *Sent:* Friday, April 16, 2021 11:13 AM
>> *To:* re-wrenches@lists.re-wrenches.org
>> *Subject:* [RE-wrenches] Powerwall 2 AC PV regulation
>>
>>
>>
>> Hello all,
>>
>> I am adding more PV to an orphaned Powerwall 2 AC system (which is all
>> new to me), -3- PW's stacked to total about 40kwh of usable storage. it
>> presently has about 13kw of PV, though -2- SMA inverters, feeding into it
>> through a common subpanel between the PW gateway and the main panel. I'm
>> wondering if there is a limit to the amount of PV the powerwall can
>> regulate/backoff (or use for battery charging) during a utility outage.
>> What is the max PW charge rate? I need to add about 10 kw of PV to produce
>> the owners goal of 100% coverage of electrical demand.
>>
>> If necessary for safety, i assume the extra pv inverter can be routed to
>> the main panel, and then won't participate in battery charging if the grid
>> goes down. Am I correct? Thanks. The PW manuals are of little use here.
>>
>>
>>
>> *Kirk Herander / kirkh@vermont.solar *
>>
>> *Owner|Principal, VT Solar, LLC*
>>
>> *Celebrating our 30th Anniversary 1991-2021!!*
>>
>> *www.vermont.solar*
>> 
>>
>> dba Vermont Solar Engineering
>>
>> 802.863.1202
>> ___
>> List sponsored by Redwood Alliance
>>
>> List Address: RE-wrenches@lists.re-wrenches.org
>>
>> Change listserver email address & settings:
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Re: [RE-wrenches] Powerwall 2 AC PV regulation

[Chris Sparadeo]

Keep in mind that 7.5kW is max charge/discharge for 10 sec...it is NOT the
continuous rate. This comes into play in the following scenario:

Let’s say a single Powerwall 2 is at 50% SOC and there is a utility outage
on a sunny day. The inverter is outputting 7kW AC and loads in the house
are below 2kW. The Powerwall will force the PV inverter to turn off via
frequency shift and the inverter sit in a holding pattern, trying to
reconnect every 5 minutes. If PV continues to be above 5 kW, then it will
be turned off until the battery shuts off at its designated cut off %. Not
an ideal scenario. This is why I like to use 5kW of PV per Powerwall as a
general rule, to avoid this worst case scenario.

Best,

Chris

On Sun, Apr 18, 2021 at 1:53 PM Barton Churchill 
wrote:

> You can just land the new PV to the same "generation" panel that already
> hosts the 3 Powerwalls and existing PV inverter output breakers. There
> should be no loads on this panel. The Powerwall AC coupled solar limit is
> 7.5 KW AC per Powerwall, note AC not DC. The DC rating is irrelevant here.
> If the combined PV AC inverter output is less than 22.5 kW the system will
> work fine. Tesla does have a list of approved PV inverters but unless
> you're looking to connect something over 3 years old it should be fine.
>
> *Barton Churchill*
> *Director, Power Division*
> 2042 Stadium Drive Suite 2 • Bozeman, MT 59715
> 
> • (O) 406-587-2917 • (D) 406-589-4493
> 235 E. Broadway • Jackson, WY 83001 • (O) 307-200-2210
> bchurch...@energy-1.net|www.energy-1.net
>
> --
> *From:* RE-wrenches  on behalf
> of Kirk Herander, VSE 
> *Sent:* Friday, April 16, 2021 9:13 AM
> *To:* re-wrenches@lists.re-wrenches.org  >
> *Subject:* [RE-wrenches] Powerwall 2 AC PV regulation
>
> Hello all,
> I am adding more PV to an orphaned Powerwall 2 AC system (which is all new
> to me), -3- PW's stacked to total about 40kwh of usable storage. it
> presently has about 13kw of PV, though -2- SMA inverters, feeding into it
> through a common subpanel between the PW gateway and the main panel. I'm
> wondering if there is a limit to the amount of PV the powerwall can
> regulate/backoff (or use for battery charging) during a utility outage.
> What is the max PW charge rate? I need to add about 10 kw of PV to produce
> the owners goal of 100% coverage of electrical demand.
> If necessary for safety, i assume the extra pv inverter can be routed to
> the main panel, and then won't participate in battery charging if the grid
> goes down. Am I correct? Thanks. The PW manuals are of little use here.
>
> *Kirk Herander / **kirkh@vermont.solar *
>
> *Owner|Principal, VT Solar, LLC*
>
> *Celebrating our 30th Anniversary 1991-2021!!*
>
> *www.vermont.solar*
> 
>
> dba Vermont Solar Engineering
>
> 802.863.1202
> ___
> List sponsored by Redwood Alliance
>
> Pay optional member dues here: http://re-wrenches.org
>
> List Address: RE-wrenches@lists.re-wrenches.org
>
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> --
Chris Sparadeo


C_802-369-4458
H_802-728-3059
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Re: [RE-wrenches] Powerwall 2 AC PV regulation

[Barton Churchill]

You can just land the new PV to the same "generation" panel that already hosts 
the 3 Powerwalls and existing PV inverter output breakers. There should be no 
loads on this panel. The Powerwall AC coupled solar limit is 7.5 KW AC per 
Powerwall, note AC not DC. The DC rating is irrelevant here. If the combined PV 
AC inverter output is less than 22.5 kW the system will work fine. Tesla does 
have a list of approved PV inverters but unless you're looking to connect 
something over 3 years old it should be fine.


[cid:f7580fd8-6285-4e79-9ad8-512cb4416200]Barton Churchill
Director, Power Division
2042 Stadium Drive Suite 2 • Bozeman, MT 59715 • (O) 406-587-2917 • (D) 
406-589-4493
235 E. Broadway • Jackson, WY 83001 • (O) 307-200-2210
bchurch...@energy-1.net   |
www.energy-1.net



From: RE-wrenches  on behalf of Kirk 
Herander, VSE 
Sent: Friday, April 16, 2021 9:13 AM
To: re-wrenches@lists.re-wrenches.org 
Subject: [RE-wrenches] Powerwall 2 AC PV regulation

Hello all,
I am adding more PV to an orphaned Powerwall 2 AC system (which is all new to 
me), -3- PW's stacked to total about 40kwh of usable storage. it presently has 
about 13kw of PV, though -2- SMA inverters, feeding into it through a common 
subpanel between the PW gateway and the main panel. I'm wondering if there is a 
limit to the amount of PV the powerwall can regulate/backoff (or use for 
battery charging) during a utility outage. What is the max PW charge rate? I 
need to add about 10 kw of PV to produce the owners goal of 100% coverage of 
electrical demand.
If necessary for safety, i assume the extra pv inverter can be routed to the 
main panel, and then won't participate in battery charging if the grid goes 
down. Am I correct? Thanks. The PW manuals are of little use here.


Kirk Herander / kirkh@vermont.solar

Owner|Principal, VT Solar, LLC

Celebrating our 30th Anniversary 1991-2021!!

www.vermont.solar

dba Vermont Solar Engineering

802.863.1202
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Re: [RE-wrenches] Powerwall 2 AC PV regulation

[Jerry Shafer]

Wrenches
This customer with an orphan PW, not to compromise the factory warranty on
the batteries, it would be safest to just grid tie any additional PV and
not touch the existing system from the gateway down.
Jerry
NABCEP PV Inspector

On Fri, Apr 16, 2021, 8:38 AM Kirk Herander, VSE 
wrote:

> Hello all,
> I am adding more PV to an orphaned Powerwall 2 AC system (which is all new
> to me), -3- PW's stacked to total about 40kwh of usable storage. it
> presently has about 13kw of PV, though -2- SMA inverters, feeding into it
> through a common subpanel between the PW gateway and the main panel. I'm
> wondering if there is a limit to the amount of PV the powerwall can
> regulate/backoff (or use for battery charging) during a utility outage.
> What is the max PW charge rate? I need to add about 10 kw of PV to produce
> the owners goal of 100% coverage of electrical demand.
> If necessary for safety, i assume the extra pv inverter can be routed to
> the main panel, and then won't participate in battery charging if the grid
> goes down. Am I correct? Thanks. The PW manuals are of little use here.
>
> *Kirk Herander / **kirkh@vermont.solar *
>
> *Owner|Principal, VT Solar, LLC*
>
> *Celebrating our 30th Anniversary 1991-2021!!*
>
> *www.vermont.solar*
> 
>
> dba Vermont Solar Engineering
>
> 802.863.1202
> ___
> List sponsored by Redwood Alliance
>
> List Address: RE-wrenches@lists.re-wrenches.org
>
> Change listserver email address & settings:
> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
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> There are two list archives for searching. When one doesn't work, try the
> other:
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