[aprssig] Shack backup power

Bob Bruninga bruninga at usna.edu
Fri Jun 3 16:45:54 EDT 2011

>> Economical solar runs 99.9% of the time

> Just how long does the sun stay up where you live?

Actually, it's the coffee machine that keeps me up ;-)  But the point is
that the grid is all part of a home solar energy system and is as important
as any other part of shack power.

> Anyway, I wasn't thinking of using it for a "true emergency"
> installation, more of an augmentation that would allow... 
> 1 - non-emergency solar use. Something along these lines:
> 2 - I need batteries for emergency backup.
> 3 - Since I need batteries, I may as well charge them with solar power.
> 4 - If I've got them running on solar power, 
>   - I may as well power the rig that way all the time.
> 5 - Now that I've got the radio on solar, 
>   - can I move the rig computer to solar/battery?

It is that combination of #1 and #3 as an assumption that is my recent
"revelation" that I am sharing (ad nausium) with everyone else...  Nothing
wrong with the plan, but just making sure people are chosing the plan with
full knowledge of the impact of their choice, and are aware of a better way
to do it..

For example, given #1 (non emergency use), then it is far cheaper to charge
the batteries from the grid for a few pennies than to spend $$$ hundreds on
solar panels.  Next, it is far cheaper to run these APRS shack items on grid
power (at 100% efficiency 99.5% of the time) and only run on the inefficient
battery (60 to 70% efficiency) only the 0.5% of the time that the grid is

The above 5 step plan (which was also my original thinking) 1) has a huge
investment in solar (which is not needed 99.5% of the time) and 2) throws
away 30 to 40% of all that solar power through chemical losses going into
and out of the battery every single day, and 3) requires added cost and
hassle of replacing the battery every few years.  And finally, for every
good sunny day that the battery is fully charged, then 4) all the rest of
the solar power goes now where and is simply lost.

So the solar makes no economic sense (in this case specific set of

In fact, solar with battery energy storage makes no economic sense in any
other case except for two cases:  1) one has no access to the grid, or 2)
One wants to invest in Armageddon power outages longer than several days.
In all other cases, solar-with-grid storage is what has made solar so
economical on a daily basis these days.

Of course, it is not all about economics.  It is about Peace of mind to many
of us.  Fortunately, now we can now have the best of both worlds.  With
these small plug-in grid-tie inverters in the 250 Watt class, now it is
possible to run our shack:

1) On a battery
2) But Economically Float supplied by the grid (99.5% of the time)
3) With solar back-up charging (if needed 0.5% of the time)
4) But with the solar power actually providing full pay-back power ALL the
rest of the time, even when the battery is fully charged.
5) Now you only lose the 30/40% of battery energy losses ONLY during the
0.5% of the time the power is out, not every day 365 days a year.

IN other words, during the 99.5% of the time the grid is up, we get to run
our shacks on cheap grid power AND during this same 99.5% of the time when
the sun shines we are getting full retail electric value from our solar
panel(s) because it is injecting those few watts into our home consumption.
The only time we are operating inefficiently is during those 0.5% of the
time the grid is out.

Contrast that with the typical 5 step approach we all originally think about
and as you proposed.  In that case we are operating inefficiently (60 to 70%
efficient use of power) every day, 99.5% of the time.  And most of the
investment in solar is unused on every sunny day beyond the point where the
battery is fully charged.

So that is the "revolution" that has recently taken place in solar, and that
is the availability of micro-grid-tie inverters that make sure that every
penny of your solar investment is working for you all the time that the sun
shines..., not just heating batteries.

See www.aprs.org/off-grid-maybe.html

Hope that helps.  It was a revelation to me.  YES, I have batteries, but I
do not use solar to charge them everyday, and I do not use them, except
during an outage. Not daily.  Much more efficient.

Something like that.

Bob, Wb4APR

 99.5% of the time case of assumptions if one has access to the grid but
chooses to store the energy in a battery and one does not

#2 that combined with the first 3 line assumptions (non-emergency) that is
what I am stressing so muchs the enlightening point that I have recently
learned (and beating everyone over the head with)... and that is

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