On Apr 11, 2026, at 9:35 AM, Jason Szumlanski via RE-wrenches
<[email protected]> wrote:
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
<[email protected]> 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
[email protected]
303-523-3592
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