[LibreQoS] solar powered internet

dan dandenson at gmail.com
Sat Apr 15 12:56:01 EDT 2023

I run a number of solar sites in the frozen north as well as have built and
continue to monitor and advise on a number in tropical latitudes.  This
formula holds up in multiple climates and has been learned the hard way
including snowmobile rides with generators to power under built sites.  I
also build RV solar plants.  Once had a solar installation company until
the market fell out in early 2017.

battery sizing is the typical watts of all gear * 24 * max number of
overcast days in a row.
60W site in Montana where we see 7 straight days of overcast is
60*24*7=10080Wh of usable battery
Lipo/lifepo4 batteries can be used at about 100% of rated, while lead acids
are about 1/3 of rated.
so about 4x 24V100Ah lifepo4 batteries, or about 12x of the same in lead
acid for this particular area.

Panel sizing is recovering 2 days of power every day.  So a 60W site needs
1500Wh to operate, and we need to recover 2 days, so we need use+2 days or
4500Wh per day.

Take the sun hours on the 'winter' solstice and divide that.  Montana's
winter solstice for example is 3.5hours of sunlight.  4500/3.5=~1300W
array.  so 4x 325W panels will do it.

Always MPPT, and sized for that 1300W or higher if you like.  Battery bank
needs enough charge rating to take the 1300W.  say 4x 24V lifepo4 in
parallel and you need about 12A of charge rating each for example.   No
reason to over size this by much unless you have high hopes for expanding
the site.  Lead acid batteries are much harder to charge and you might have
to overbuild the array a bit in the cold because you have to push amps in
to get them going.  Just don't lead acid unless you're in a developing

Special consideration for snowy climates.  Tilt panels up at 60 degrees
facing south for a heavy winter bias and to encourage snow to fall off.
Add additional panels facing south east and south west in parallel.  Could
be 2 panels south east in series, 2 south west in series, 2 south in
series, and then the 3 sets in parallel (2S3P layout) and the e/w panels
tilt up very aggressively, that way you can collect maximum sun right away
in the morning as well as be running the site off solar until sunset vs
being on battery for 3-4 extra hours.  Snow buildup is the primary issue in
winter obviously.  If you are at a site that gets feet of snow, then run 2
separate arrays, a 'normal' array at the latitude's optimal tilt, and then
a separate 2S3P or similar style array but stood straight up at 90
degrees.  We're experimenting heating the back of panels when there is snow
on them via a relay.  early results are really promising.  I had about 2
feet of snow on a panel at 60 degrees and it took 5 minutes and about 50Wh
to convince it to slide off.

Main conceptual issues I've had to push people through:
-100% usable vs 33% usable on lifepo4 vs lead acid is worth the up front
cost and the need to get self-heating batteries or put them in a climate
controlled box.   battery performance and life is so much better that
you're UP about 50% in value over 8-10 years.
-Solar efficiency is irrelevant.  This is all for off-grid uptime. Solar
panels are one of the cheaper parts of the kit. Charge controllers don't
have to match panel amps, just volts.  ie, 2 panels w/ 80V8A output and a
100V10A controller is a match, but so is 20 panels at 80V80A, solar doesn't
'push' amps in so you can overbuild solar without increasing the other
-the '7 days of overcast' number is the maximum amount of battery that's
useful.  It may sound great to double this up 'just to be sure' but that is
almost always a far worse decision than doubling up on panels.
-wind is a costly addition that the same $ on more solar panels would
likely double output and not require maintenance. Wind is terribly
inefficient at low blade diameters.  Leave wind to wind farms.
-Solar panels produce about 5% output when covered in a few inches of
snow.  up to 10% on overcast days.  1300W in solar should be able to handle
the 60W site for about 1/3 the day without drawing from batteries.  Again,
more solar is the primary way to juice the system, not adding wind or more
batteries.  Overbuilding solar is really just building appropriately for
overcast conditions.  Forget efficiency when it comes to solar panels,
stack 'em up!

Always put a camera up.  I've seen too much bird crap take down an array so
you want to be able to see charts of production to see that build up
happening.  or if it's covered in snow you want to know what you fix ahead
of time you need visuals.

For equipment:
We use victron.  My preferred kit is the smart MPPT 150/35 plus a Cerbo GX
and Shunt.  All of these devices connect together for monitoring.
Monitoring is king.  We then use a 24>48 DCDC to get dual voltage at the
We use quite a few ubiquiti edgerouter 10XP and similar for airmax sites,
but those are being replaced mostly with mikrotik's Netpower16P unit w/
dual voltage input.   We're still waiting for a 4 pair power multi-voltage
switch from someone other than Netonix (extreme failure rate, I'm OVER 50%
on these, they are banned on my networks).

I could add more, but this post is long enough.

On Sat, Apr 15, 2023 at 5:58 AM Brian Munyao Longwe via LibreQoS <
libreqos at lists.bufferbloat.net> wrote:

> If the radios are POE, DC-Netonix, with enough batteries for 2-3-4 days
> and a MPPT + Charge Controller to handle the voltage from the solar panels
> On Fri, 14 Apr 2023 at 12:07 AM, Dave Taht via LibreQoS <
> libreqos at lists.bufferbloat.net> wrote:
>> I am not going to buy into the level of hype here:
>> https://www.linkedin.com/in/davidtheodore/recent-activity/all/
>> But I am curious as to what extent solar power (how many watts?) can
>> be used nowadays for heavier duty backhaul radios, and what forms of
>> long term battery storage now exist?
>> Most UPSes sold in stores are designed for a high load, for a short
>> time, where aiming for 2-3 days of backup power would be better in
>> this case.
>> --
>> AMA March 31: https://www.broadband.io/c/broadband-grant-events/dave-taht
>> Dave Täht CEO, TekLibre, LLC
>> _______________________________________________
>> LibreQoS mailing list
>> LibreQoS at lists.bufferbloat.net
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