[RE-wrenches] AGS quiet time

[Jason Szumlanski]

You're making the case for multiple AGS start setpoints. There should be a
quiet time override SOC for AGS.


Jason Szumlanski
Principal Solar Designer | Florida Solar Design Group
NABCEP Certified Solar Professional (PVIP)
Florida State Certified Solar Contractor CVC56956
Florida Certified Electrical Contractor EC13013208




On Sat, Apr 11, 2026 at 9:10 AM Zeke Yewdall via RE-wrenches <
re-wrenches at lists.re-wrenches.org> wrote:

> A recent thread included Quiet Time in the list of non-included features
> with newer inverters.  And I too have had customers asking for this. But,
> in many cases, I find that quiet time is not actually a useable feature for
> many current off grid houses with lithium batteries, and this is why.
>
> With lead acid battery banks, we typically designed for the generator to
> start around 50% SOC.  But, occasionally we could discharge down to 20% SOC
> without damaging the batteries long term.  And, typical off grid houses
> were usually designed with fewer nighttime loads, compared to nowadays.
>  So, if the battery bank hit 50% SOC at 9pm, but quiet times extended till
> 8am, we still usually had plenty of reserve left to wait till 8am before
> starting the generator without any additional failures or battery damage.
>
> But a lot of current off grid systems with lithium batteries are sizing
> for a lower days of autonomy (because of the higher cost of lithium
> batteries, though that's changing now), and deeper regular depth of
> discharges.  Generator start is often set at 20 or 30% SOC instead of 50%.
> If we are planning for regularly discharging below 50% SOC overnight, which
> I do commonly see, there's not nearly so much reserve capacity to wait for
> a generator start.  If we hit 20% SOC at 9pm, with a smaller battery bank
> relative to the load, and a higher nighttime load from more things
> remaining on all night that we never used to have (routers, internet,
> heating system controls/pumps/etc), then the chances of us making it till
> 8am to wait for the generator start is a lot lower -- we risk a BMS
> shutdown of the battery sometimes betwen 0% and 10%, before 8am, which
> depending on the particular equipment can be a difficult situation to
> recover from.  Many AIO's will only black start batteries from solar, not
> generator, and most (though not all) older charge controllers and inverters
> will not black start batteries from either solar or generator.
>
> So, because we are using deeper discharges, using more energy overnight,
> and waiting longer before a SOC based generator start, we often don't have
> the option of waiting 4 or 8 hours or such to start the generator.  It
> needs to start very soon after the call for it, or we run into further
> problems.
>
> What would be ideal is a system that looks at SOC before quite times would
> start, and if it's not sufficient to make it through a typical night
> because it's been a cloudy day, starts and runs the generator a bit before
> quite times start, rather than hoping to make it to morning before running
> it.  An experienced off grid owner can do this automatically, topping the
> batteries off before going into the night if they are too low.  But
> unexperienced owners or ones who just don't watch their battery SOC all the
> time, will not.  Perhaps we'll come up with AI driving controls that watch
> the typical batery use patterns and look at the weather forecast, and can
> do this, just like the experienced off grid operator does.
>
> Zeke
>
>
> --
> Zeke Yewdall
> PV Engineer
> NABCEP #031508-89
> zeke at darkforestsolar.com
> 303-523-3592
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