[LibreQoS] solar powered internet

Dave Taht dave.taht at gmail.com
Sat Apr 15 20:21:18 EDT 2023

Really wonderful information. I last tried to accomplish this using
edison batteries (in the warmer climes) due to how long they last and
the simpler solar controller. But they were bulky, and needed

On Sat, Apr 15, 2023 at 9:56 AM dan <dandenson at gmail.com> wrote:
> 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 country....
> 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 components.
> -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 site.
> 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
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AMA March 31: https://www.broadband.io/c/broadband-grant-events/dave-taht
Dave Täht CEO, TekLibre, LLC

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