To get more data you should look at the charging PMIC data sheet which shows the max voltage input of 17v 
Particle recommends you keep it below 12v due to heat build up from the PWM conversion of converting the higher input voltage down to the battery voltage. Particle is playing it safe and is unoffocially recommending 12v via engineers on the form in past discussions.
Make sure to pay attention to the “symbol” column which shows the associated pin. The ratings differ because they are for different pins. Although the Vin pin rating doesn’t match the Electron now that you point it out… which @RWB just clarified above.
@peekay123, shouldn’t that be “reverse-voltage” not reserve-voltage?
I believe reserve voltage is otherwise known as a battery 
MORE DATASHEETS!!!
Arghhhhh!!!
Been there and done all this reasearch years back.
Just take our word that the Vin max input voltage is 12v and if you want to use
Solar it’s most efficient to use 6v solar panels and the code we use above.
pmic.setInputVoltageLimit(5080); or 4840 until we get some response from the Powers That Be.
Correct, use the 4840 for now since we know for sure that works.
My full code with low soc sleep mode that will not work on the Boron right now is included.
Hi @Rftop, I think I’ve read through the entire post and replies (which are all fantastic by the way), but haven’t seen the make/model of panel and controller that you’re using? Can you share that?
For my Electron+Asset Tracker Shield build, I used the Voltaic/Ada 2W panel and the Adafruit LiPo Solar charge controller, and connected to the 5-12VDC screw terminal block on the Asset Tracker (which I assume is connected to the VIN pin of the Electron). This SEEMED to work fine, though nowhere near the performance you are getting.
For the Boron on its own, I was assuming I’d have to move the battery to the BATT JST of the Adafruit charge controller and then connect the LOAD JST to the Boron LiPo+ JST. Trying to maintain a ‘pluggable’ build for quick assembly/disassembly. I have no idea if this works in practice because I haven’t even had time to unbox the shiny new Boron.
I noticed that you mention the USB port for solar power input, which I’m confident is technically correct and a lot simpler, so that made me wonder what controller you are using?
Thanks for any tips. I really appreciate you and @RWB contributing so much detail in one post to an area that is foreign to me.
You do not need a external charge controller for the Electron or Boron since there is a built in charging chip.
The code I posed above is what you run to make these charging settings take effect for best performance.
These are really good outdoor ready panels
These are the two panels used in my Boron Trials.
1-Watt SeeedStudio,
2-Watt Voltaic Systems,
The Voltaic Panel ships with the USB connector.
I swapped the SeedStudio panel to a USB connector.
@Mister, I assume you're not limited on weight/size for a weather station ?
Have you considered a 12V SLA battery and a 12V panel ?
Those are much cheaper and way more storage capacity than Li-Po's and 6V (ie: this thread).
How much cheaper are we talking?
There are cheaper 2w Epoxy solar panels if you don’t want to spend on the Voltaic panels.
How much cheaper can a 12v AGM battery + solar charge controller be compared to a LiPo battery?
I have never bought a AGM battery except for my truck so I’m interested to see what your buying and how much it cost if you don’t mind sharing.
If size and space are not design constraints, this is a great combo for a "no-worries" install:
12V, 10-watt Panel, with controller
12V, 12aH SLA battery
I've used these w/ Electrons. Add a voltage divider to monitor SLA voltage and never worry about a couple weeks in a row of cloudy weather.
Haha yep. I have thought about it for multiple reasons
The good thing about CO though is cloudy weather is typically maxed out at 2 days. Sometimes its worse but I’m out in wheat fields so there are no other obstructions except snow and clouds
this is my set up currently (stolen from a presentation I gave recently). The plan is to install 25 of these.
But…
Excellent info fellas, thanks much. Simpler and still pluggable - win win!
Update: Trial stopped for 2-watt panel w/ 2,000 mAH Li-Po.
A full day of rain has dropped the SoC to less than 50%, since the Li-Po never got a chance to recover from the previous Night.
SoC projections put the 2,000 mHA Li-Po ~ 20-25% tomorrow morning, so I’m pulling the plug.
Here’s the last 7-days:
However: The Boron with the tiny 1-watt panel & 5,000 mAH Li-Po is happily cruising along at 70% SoC after the same day of missing out on Solar Recharging.
If you had those sleep modes available you would be perfectly fine.
@RWB,
No Joy on trying pmic.setInputVoltageLimit(5080)
The Boron’s Charging LED still lights when I applied 4.20V to the USB connector.
I also just tried pmic.setInputVoltageLimit(4840);
The Boron’s Charging LED lights when I reached 4.25V to the USB connector.
Has anyone ever confirmed the PMIC operations actually work?
The variable Power Supply I’m using isn’t Lab Grade at ALL, but it’s not that bad.
The charging led will still turn on when the input voltage is below 4.84v, the solar input will behave differently than a power supply because the voltage will not rise above where you have the output set on the power supply.
The PMIC will basically lower the charge current until the panels voltage is at 4.84v.
Hook up a solar panel and put it under the brightest light you can find and test the panel voltage if there is enough current to start charging.
Also note the main firmware overwrites it to the default settings every time it powers on.
And yes this was working on an Electon just fine.
Wish I could, it's night time 
Using pmic.setInputVoltageLimit(4840)
It's only drawing 2.5 mA @ 4.20V (so yeah the Charging LED is just pranking)
Actual Charging started at 5.05V, Li-Po resting at 3.83V, Current Measured w/ a µCurrent GOLD
23mA @ 5.10V
42mA @ 5.15V
80mA @ 5.20V
105mA @ 5.25V
150mA @ 5.30V
200mA @ 5.40V
310mA @ 5.50V
I'll repeat w/ pmic.setInputVoltageLimit(5080)
LED lights at 4.25V, 2.6mA,
22mA @ 5.30V
50mA @ 5.40V
170mA @ 5.50V
240mA @ 5.60V
I suppose this test is the opposite of how Solar Panels work, since they are current producing devices?
I'm testing by supplying a Voltage and measuring the current.
