Larry,
Connect the coil of a 240 VAC contactor to the output of the generator
circuit. Have the contacts of the relay break the AC coupled feed.
Drake
---
On 2020-07-20 16:25, William Miller wrote:
Larry:
If you can automate disabling grid-sell when connected to the generator in a fool proof manner then you may have a solution. If the system fails I see a damaged generator but not a life-safety issue.
William
From: [email protected] [mailto:[email protected]]
Sent: Monday, July 20, 2020 1:19 PM
To: William Miller; RE-wrenches
Subject: Re: [RE-wrenches] Tesla Powerwall 2.0 - Experience?/Generator charging
Hi William,
Thank you for your response. I was responding to the question of use off grid and Hiltons
question about generator use. Jason said, "But Tesla is clear in that they do not
allow a generator to interact with the Powerwall in any way." This is true.
Powerwall uses AC coupled inverters for off grid charging. If AC from the
micro-inverters was switched off and the generator provided the 240 Volt to the
Powerwal inverter inputl, would that not be a temporary solution to the
generator prohibition? The power wall would see incoming power and sync. Of
course, the system must be monitored. If the power wall calls for cutback or
disconnect by raising frequency, the generator should be disconnected, if it
indeed works like that. If Powerwall provides an internal disconnect, then it
would be safer for the user. Just trying to think outside the box.
Larry Crutcher
Starlight Solar Power Systems
On Jul 20, 2020, at 12:01 PM, William Miller <[email protected]> wrote:
Larry:
I am not Tesla conversant but allow me to speculate: If any grid-tied system
can be fed from a generator it could also feed back to the generator, which may
damage said generator. The grid-tied system should therefore be connected
upstream of any transfer switching, making it ineligible to be charged from the
generator.
William
From: RE-wrenches [mailto:[email protected]] On Behalf
Of [email protected]
Sent: Monday, July 20, 2020 10:52 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] Tesla Powerwall 2.0 - Experience?
Since the Powerwall is AC coupled, how will it know if the power source is a PV
solar array or a generator if either feed the PV input? It seems simple AC
switching is all that would be needed. I like to think outside the box but I'm
not familiar with Powerwall.
Larry Crutcher
Starlight Solar Power Systems
On Jul 20, 2020, at 9:53 AM, Jason Szumlanski
<[email protected]> wrote:
The Powerwall 2 is now supported by Tesla in an off-grid configuration from
what I heard. It is AC coupled. It cannot interact with generators whatsoever.
You can't charge the battery with a generator and you can't AC couple a
generator to it. If you want a generator, you put a transfer switch on the load
side of the gateway device. If the battery dies, the generator starts. The
generator powers loads, but does not recharge the battery because it becomes
isolated via the transfer switch. The big downside I see with that is there
would be a loss of power to the loads until the generator fires up. I don't see
a way around that.
I'm not a Tesla certified installer, but I have seen some of these batteries out in the wild and
that's just the way it is - it's an integrated unit. I'd call it an "AC Battery," kind of
like an AC PV Module. To answer another point in this thread, if the battery reaches its LBCO it
can only recharge with PV in an off-grid scenario. It reserves battery capacity to turn on
occasionally to see if there is PV input. At least that's how I understand it to work. I don't know
what would happen if the battery actually reached 0%. Seems risky. I'm not sure how you would
"jump start" it. Publicly available details seem scant on this, but there are a few
system owners talking about it if you dig deep on the Interwebs.
It will be interesting to see what Enphase comes up with. There are generator inputs on their Ensemble system, but no software support for this yet. The concept is very similar to Tesla in that there is a gateway device, essentially a transfer switch with battery controls inside. The Gateway acts as the AC point of coupling for everything to tie in together.
I'm not sure why you couldn't use a generator to charge the Powerwall battery
the same way you would charge with the grid. However, you would need a way to
disable PV AC coupling when the generator is running. I can see how Enphase
would be able to do this pretty easily. But Tesla is clear in that they do not
allow a generator to interact with the Powerwall in any way.
Jason Szumlanski
On Sun, Jul 19, 2020 at 11:43 AM Hilton Dier III <[email protected]> wrote:
Greetings, Wrenches,
I have an off-grid client who has been reading the buzz about the Tesla
Powerwall 2.0. I have been reading the data sheets and manual for it and it
appears to be AC coupled only. There was talk of a DC input version, but
apparently that fell by the wayside. I try to be agnostic about technology, and
I'd be willing to subcontract a Tesla-approved installer if, in fact, this was
the best solution.
Does anybody have experience using the Powerwall 2.0 in an off grid PV system?
Is it AC coupled only? Can it take generator power without barfing? What is the
lead time on these?
Many Thanks,
Hilton
--
Hilton Dier III
Missisquoi River Hydro
Renewable Energy Design
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