On 1/18/22 23:17, Joe Maimon wrote:
The inverter in question is the one being utilized in conjunction with
the powerwall, ats, solar array. All nicely done and reliable and
wired in already and with proper capacity.
Being able to call for and get more DC power on demand would make this
a true uninterruptible solution.
Running a gen to support the battery means the gen size does not need
to correlate at all with the peaks and surges of demand and can run at
maximum efficiency and we can avoid unbalanced leg problems and other
voltage variation issues that can happen with portable gens.
Programming comes into play for automated monthly testing, capacity
prediction, even spot costing of utility power. Between the grid, the
solar array, time of day, season, weather, battery level, generator
input, load characteristics, outage duration, grid costs/stresses
there can be a lot of factors that might need a bit more balancing and
programming than you might typically expect available from any half
decent battery inverter, but might find a nice place in a truly fully
integrated home UPS solution.
Integrate it enough and perhaps the gen/rectifier components would
even fit into typical residential facilities spaces and this sort of
setup could be all the more typical and standard.
I use SMA... both for PV and battery inversion. It's an AC-coupled
system, with the battery inverter being at the core of the system.
Both the PV and battery inverters are highly-configurable, and out the
box, will do a lot of things reasonably well.
However, it took me about 8 months to properly set this system up for
our requirements, because, as you say, you need to get a lot of things
right on a number of separate systems (in an AC-coupled design) to get
the most out of your installation.
For us, we have a system large enough to be off-grid 100% of the time.
However, we want to lengthen the lifespan of the battery, by keeping
charge voltage low, and not discharging it too much. So we struck a
balance between using the grid significantly less than we used to before
we could self-generate, and keeping the battery voltage low (charge to
about 78% SoC, discharge to about 65% SoC). Of course, in the case of a
utility outage, we shall charge to 100%. Luckily, during those outages,
we've not had to dip below 35% SoC when the outage is throughout the
night, and into the morning when the sun is out. The pack is a 48V,
33.6kWh, 700Ah system.
So yes, even the most sophisticated inverters may still need some user
input. The most important thing is to understand what you want to get
out of the system (do you want to go off-grid, do you want to stay
on-grid but save a little utility cash or do you just want backup
protection for a couple of hours?), find an inverter that can provide
that, and spend several weeks to a few months fine-tuning the
installation once the installers leave.
Mark.
