home router battery backup

Mark Tinka mark at tinka.africa
Wed Jan 19 06:11:00 UTC 2022

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.


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