[Cerowrt-devel] solar wifi ap designs?

[Cerowrt-devel] solar wifi ap designs?

[Dave Taht]

I keep finding nicely integrated solar/battery/camera/wifi designs

https://www.amazon.com/s/ref=nb_sb_noss_2?url=search-alias%3Delectronics&field-keywords=solar+wifi&rh=n%3A172282%2Ck%3Asolar+wifi

But what I want is merely an solar/battery/AP design well supported by
lede... and either the ath9k or ath10k chipset - or mt72 - that I can
hang off a couple trees. I've not worked with solar much in the past
years, and picking the right inverter/panel/etc seems like a pita, but
perhaps there are ideas out there?


-- 

Dave Täh
Let's go make home routers and wifi faster! With better software!
http://blog.cerowrt.org

Re: [Cerowrt-devel] solar wifi ap designs?

[Aaron Wood]

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I'd pick an AP that works off of a 12vdc supply, and then try to setup a
12vdc solar supply (which should get you lots of stuff for automotive/rv
use).

Are you planning on deep cycle lead acid or lithium ion for storage?

-Aaron
On Sun, Jun 4, 2017 at 17:49 Dave Taht <dave.taht@gmail.com> wrote:

> I keep finding nicely integrated solar/battery/camera/wifi designs
>
>
> https://www.amazon.com/s/ref=nb_sb_noss_2?url=search-alias%3Delectronics&field-keywords=solar+wifi&rh=n%3A172282%2Ck%3Asolar+wifi
>
> But what I want is merely an solar/battery/AP design well supported by
> lede... and either the ath9k or ath10k chipset - or mt72 - that I can
> hang off a couple trees. I've not worked with solar much in the past
> years, and picking the right inverter/panel/etc seems like a pita, but
> perhaps there are ideas out there?
>
>
> --
>
> Dave Täh
> Let's go make home routers and wifi faster! With better software!
> http://blog.cerowrt.org
> _______________________________________________
> Cerowrt-devel mailing list
> Cerowrt-devel@lists.bufferbloat.net
> https://lists.bufferbloat.net/listinfo/cerowrt-devel
>

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Re: [Cerowrt-devel] solar wifi ap designs?

[Dave Taht]

lithium ion... although I admit a fondness for edison batteries.

On Sun, Jun 4, 2017 at 6:54 PM, Aaron Wood <woody77@gmail.com> wrote:
> I'd pick an AP that works off of a 12vdc supply, and then try to setup a
> 12vdc solar supply (which should get you lots of stuff for automotive/rv
> use).
>
> Are you planning on deep cycle lead acid or lithium ion for storage?
>
> -Aaron
> On Sun, Jun 4, 2017 at 17:49 Dave Taht <dave.taht@gmail.com> wrote:
>>
>> I keep finding nicely integrated solar/battery/camera/wifi designs
>>
>>
>> https://www.amazon.com/s/ref=nb_sb_noss_2?url=search-alias%3Delectronics&field-keywords=solar+wifi&rh=n%3A172282%2Ck%3Asolar+wifi
>>
>> But what I want is merely an solar/battery/AP design well supported by
>> lede... and either the ath9k or ath10k chipset - or mt72 - that I can
>> hang off a couple trees. I've not worked with solar much in the past
>> years, and picking the right inverter/panel/etc seems like a pita, but
>> perhaps there are ideas out there?
>>
>>
>> --
>>
>> Dave Täh
>> Let's go make home routers and wifi faster! With better software!
>> http://blog.cerowrt.org
>> _______________________________________________
>> Cerowrt-devel mailing list
>> Cerowrt-devel@lists.bufferbloat.net
>> https://lists.bufferbloat.net/listinfo/cerowrt-devel



-- 

Dave Täh
Let's go make home routers and wifi faster! With better software!
http://blog.cerowrt.org

Re: [Cerowrt-devel] solar wifi ap designs?

[Aaron Wood]

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Lithium will definitely render what I said about 12v stuff less useful (and
out of where I have any experience).  I will say for panels, that location
matters a ton, especially in the winter.  Are you in chaparral and oaks,
madrone, or redwoods?

-Aaron

On Sun, Jun 4, 2017 at 7:03 PM, Dave Taht <dave.taht@gmail.com> wrote:

> lithium ion... although I admit a fondness for edison batteries.
>
> On Sun, Jun 4, 2017 at 6:54 PM, Aaron Wood <woody77@gmail.com> wrote:
> > I'd pick an AP that works off of a 12vdc supply, and then try to setup a
> > 12vdc solar supply (which should get you lots of stuff for automotive/rv
> > use).
> >
> > Are you planning on deep cycle lead acid or lithium ion for storage?
> >
> > -Aaron
> > On Sun, Jun 4, 2017 at 17:49 Dave Taht <dave.taht@gmail.com> wrote:
> >>
> >> I keep finding nicely integrated solar/battery/camera/wifi designs
> >>
> >>
> >> https://www.amazon.com/s/ref=nb_sb_noss_2?url=search-alias%
> 3Delectronics&field-keywords=solar+wifi&rh=n%3A172282%2Ck%3Asolar+wifi
> >>
> >> But what I want is merely an solar/battery/AP design well supported by
> >> lede... and either the ath9k or ath10k chipset - or mt72 - that I can
> >> hang off a couple trees. I've not worked with solar much in the past
> >> years, and picking the right inverter/panel/etc seems like a pita, but
> >> perhaps there are ideas out there?
> >>
> >>
> >> --
> >>
> >> Dave Täh
> >> Let's go make home routers and wifi faster! With better software!
> >> http://blog.cerowrt.org
> >> _______________________________________________
> >> Cerowrt-devel mailing list
> >> Cerowrt-devel@lists.bufferbloat.net
> >> https://lists.bufferbloat.net/listinfo/cerowrt-devel
>
>
>
> --
>
> Dave Täh
> Let's go make home routers and wifi faster! With better software!
> http://blog.cerowrt.org
>

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Re: [Cerowrt-devel] solar wifi ap designs?

[Dave Taht]

so am I the only one left that likes edison batteries? you don't need
a charge controller... they last for a hundred years....

Re: [Cerowrt-devel] solar wifi ap designs?

[Michael Richardson]

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Dave Taht <dave.taht@gmail.com> wrote:
    > so am I the only one left that likes edison batteries? you don't need
    > a charge controller... they last for a hundred years....

I was ignorant of them until just now when I asked google.
I too want a combined AP + solar + battery solution.

I bought one "car wifi" device from aliexpress, and while it claimed it took
12V in, it was in fact intolerant (blue smoke) of the typical 13.6V that
most car systems run at when unloaded.  Seems dumb to regulate to 12V just
so that the unit can regulate again to 3.3V/5V...   I haven't dared to try
a netgear 3800 yet.

--
]               Never tell me the odds!                 | ipv6 mesh networks [
]   Michael Richardson, Sandelman Software Works        | network architect  [
]     mcr@sandelman.ca  http://www.sandelman.ca/        |   ruby on rails    [


[-- Attachment #2: signature.asc --]
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Re: [Cerowrt-devel] solar wifi ap designs?

[Richard Smith]

On 06/04/2017 08:49 PM, Dave Taht wrote:
> I keep finding nicely integrated solar/battery/camera/wifi designs
> 
> https://www.amazon.com/s/ref=nb_sb_noss_2?url=search-alias%3Delectronics&field-keywords=solar+wifi&rh=n%3A172282%2Ck%3Asolar+wifi
> 
> But what I want is merely an solar/battery/AP design well supported by
> lede... and either the ath9k or ath10k chipset - or mt72 - that I can
> hang off a couple trees. I've not worked with solar much in the past
> years, and picking the right inverter/panel/etc seems like a pita, but
> perhaps there are ideas out there?

This is something I was up against constantly when I worked for OLPC. 
There's a big gap for products that use more power than a cell phone but 
less than an RV or a off-grid cabin.

For the XO itself we worked around it by designing the front end of the 
XO to be able to handle the range of output voltages from "12V" panels 
(open circuit voltages up to 20V) and to implement an MPPT algorithim in 
the EC firmware.  You can plug up any solar panel with a Voc of 20V or 
less to an XO-1.5 to XO-4 and it will DTRT.

Figuring out what to do with the deployment's APs though was always a 
struggle.

Solutions exist but you need to get a good estimate of what sort of 
power budget you need.  It makes a big difference in what equipment you 
need.

Unless its a really low power device the numbers can get large fast.

My WNDR 3700v2 power supply is rated at 12V 2.5A which is a peak of 30W.

Lets assume your average is 30% of peak.  That's 9W.  Your 24h energy 
requirement is 216Wh.  A reasonable input to usable efficiency for a PV 
system is 70%.  Given average 5 hour window of full sun you need a PV 
output of at least 62W.  It only goes up from there.

Realistically you need to survive a 2-3 day period of terrible solar 
output.  So your storage requirements should be at least 2-3x that. 
When you do get sun again you need excess PV capacity to be able to 
recharge your batteries.  You would probably need a PV output in the 
100W-150W range to make a system you could count on to have 100% 
availability 24/7.

That's going to be a pretty big chunk of hardware up in a tree.

If the average power draw is more in the 3W or 1W range then things look 
a lot better.   That starts to get down into the 40 and 20W range.

> so am I the only one left that likes edison batteries? you don't need
> a charge controller... they last for a hundred years....
> _______________________________________________

I've never used this battery type but it looks like the resistant to 
overcharge assumes you replace the electrolyte.  All the cells I've 
looked at on a few sites seem to be flooded which means maintenance. 
Are there sealed maintenance free versions?

For discharge nominal is 1.2V but charging is listed as ~1.6V/cell so 
you are going to need 16V to charge.  I don't really see how you can 
build a workable system with out some sort of setup that can isolate 
your 12V loads from a 16V charge.

Perhaps undercharge them at a lower voltage and live with the capacity 
loss?

-- 
Richard A. Smith

Re: [Cerowrt-devel] solar wifi ap designs?

[dpreed]

"Deep discharge" batteries work in LEO satellites for such applications. But they are extraordinarily expensive, because the designs are specialized, and that use case doesn't have the 2-3 day solar outage problem.

You are not going to put a good enough system for an AP up in a tree. Maybe on an antenna mast structure with solid base and guy wires. Roofs and ground are better choices.

But I would wonder whether redesigning the AP itself to be power-conserving would be the place to start. They are not designed to be "low power" - they are designed to be inexpensive.

So, for example: why 12V??? No logic needs 12V. Integrate the battery into the AP and run it at 3V, eliminating multiple conversion losses.

You can use 12/20 V off the solar panel to charge the 3V battery system (high current only while charging).

Pay lots of attention to the duty cycle of the radio. If you really expect the radio to be on 100% of the time, you may have to power it all the time. Otherwise, minimize uptime.  Similarly, the processor need not be on most of the time if it is mostly idle while accepting and sending packets from memory. (ARM BIG.little might be helpful).

Get rid of Linux if possible. Linux is not a low-power OS - needs a lot of work in configuring or rewriting drivers to cut power. (there's a need for an LP Linux, but like Desktop Linux, Linus, and his coterie, isn't terribly interested in fixing his server OS to optimize for non-servers, so "server power saving" is the only design point for power).




On Monday, June 5, 2017 12:01pm, "Richard Smith" <smithbone@gmail.com> said:

> On 06/04/2017 08:49 PM, Dave Taht wrote:
>> I keep finding nicely integrated solar/battery/camera/wifi designs
>>
>> https://www.amazon.com/s/ref=nb_sb_noss_2?url=search-alias%3Delectronics&field-keywords=solar+wifi&rh=n%3A172282%2Ck%3Asolar+wifi
>>
>> But what I want is merely an solar/battery/AP design well supported by
>> lede... and either the ath9k or ath10k chipset - or mt72 - that I can
>> hang off a couple trees. I've not worked with solar much in the past
>> years, and picking the right inverter/panel/etc seems like a pita, but
>> perhaps there are ideas out there?
> 
> This is something I was up against constantly when I worked for OLPC.
> There's a big gap for products that use more power than a cell phone but
> less than an RV or a off-grid cabin.
> 
> For the XO itself we worked around it by designing the front end of the
> XO to be able to handle the range of output voltages from "12V" panels
> (open circuit voltages up to 20V) and to implement an MPPT algorithim in
> the EC firmware.  You can plug up any solar panel with a Voc of 20V or
> less to an XO-1.5 to XO-4 and it will DTRT.
> 
> Figuring out what to do with the deployment's APs though was always a
> struggle.
> 
> Solutions exist but you need to get a good estimate of what sort of
> power budget you need.  It makes a big difference in what equipment you
> need.
> 
> Unless its a really low power device the numbers can get large fast.
> 
> My WNDR 3700v2 power supply is rated at 12V 2.5A which is a peak of 30W.
> 
> Lets assume your average is 30% of peak.  That's 9W.  Your 24h energy
> requirement is 216Wh.  A reasonable input to usable efficiency for a PV
> system is 70%.  Given average 5 hour window of full sun you need a PV
> output of at least 62W.  It only goes up from there.
> 
> Realistically you need to survive a 2-3 day period of terrible solar
> output.  So your storage requirements should be at least 2-3x that.
> When you do get sun again you need excess PV capacity to be able to
> recharge your batteries.  You would probably need a PV output in the
> 100W-150W range to make a system you could count on to have 100%
> availability 24/7.
> 
> That's going to be a pretty big chunk of hardware up in a tree.
> 
> If the average power draw is more in the 3W or 1W range then things look
> a lot better.   That starts to get down into the 40 and 20W range.
> 
>> so am I the only one left that likes edison batteries? you don't need
>> a charge controller... they last for a hundred years....
>> _______________________________________________
> 
> I've never used this battery type but it looks like the resistant to
> overcharge assumes you replace the electrolyte.  All the cells I've
> looked at on a few sites seem to be flooded which means maintenance.
> Are there sealed maintenance free versions?
> 
> For discharge nominal is 1.2V but charging is listed as ~1.6V/cell so
> you are going to need 16V to charge.  I don't really see how you can
> build a workable system with out some sort of setup that can isolate
> your 12V loads from a 16V charge.
> 
> Perhaps undercharge them at a lower voltage and live with the capacity
> loss?
> 
> --
> Richard A. Smith
> _______________________________________________
> Cerowrt-devel mailing list
> Cerowrt-devel@lists.bufferbloat.net
> https://lists.bufferbloat.net/listinfo/cerowrt-devel
> 

Re: [Cerowrt-devel] solar wifi ap designs?

[dpreed]

It doesn't jump to mind, but a radio carrying bits near the edge probably won't be used near capacity most of the 24 hours it is operating. Just as Iridium was designed to quiesce most of its electronics on the dark side of the earth, extending its battery life, you can probably assume that a radio in a tree won't be heavily used most of the hours of a 24 hour cycle. 



On Monday, June 5, 2017 1:52pm, dpreed@reed.com said:

> "Deep discharge" batteries work in LEO satellites for such applications. But they
> are extraordinarily expensive, because the designs are specialized, and that use
> case doesn't have the 2-3 day solar outage problem.
> 
> You are not going to put a good enough system for an AP up in a tree. Maybe on an
> antenna mast structure with solid base and guy wires. Roofs and ground are better
> choices.
> 
> But I would wonder whether redesigning the AP itself to be power-conserving would
> be the place to start. They are not designed to be "low power" - they are designed
> to be inexpensive.
> 
> So, for example: why 12V??? No logic needs 12V. Integrate the battery into the AP
> and run it at 3V, eliminating multiple conversion losses.
> 
> You can use 12/20 V off the solar panel to charge the 3V battery system (high
> current only while charging).
> 
> Pay lots of attention to the duty cycle of the radio. If you really expect the
> radio to be on 100% of the time, you may have to power it all the time. Otherwise,
> minimize uptime.  Similarly, the processor need not be on most of the time if it
> is mostly idle while accepting and sending packets from memory. (ARM BIG.little
> might be helpful).
> 
> Get rid of Linux if possible. Linux is not a low-power OS - needs a lot of work in
> configuring or rewriting drivers to cut power. (there's a need for an LP Linux,
> but like Desktop Linux, Linus, and his coterie, isn't terribly interested in
> fixing his server OS to optimize for non-servers, so "server power saving" is the
> only design point for power).
> 
> 
> 
> 
> On Monday, June 5, 2017 12:01pm, "Richard Smith" <smithbone@gmail.com> said:
> 
>> On 06/04/2017 08:49 PM, Dave Taht wrote:
>>> I keep finding nicely integrated solar/battery/camera/wifi designs
>>>
>>> https://www.amazon.com/s/ref=nb_sb_noss_2?url=search-alias%3Delectronics&field-keywords=solar+wifi&rh=n%3A172282%2Ck%3Asolar+wifi
>>>
>>> But what I want is merely an solar/battery/AP design well supported by
>>> lede... and either the ath9k or ath10k chipset - or mt72 - that I can
>>> hang off a couple trees. I've not worked with solar much in the past
>>> years, and picking the right inverter/panel/etc seems like a pita, but
>>> perhaps there are ideas out there?
>>
>> This is something I was up against constantly when I worked for OLPC.
>> There's a big gap for products that use more power than a cell phone but
>> less than an RV or a off-grid cabin.
>>
>> For the XO itself we worked around it by designing the front end of the
>> XO to be able to handle the range of output voltages from "12V" panels
>> (open circuit voltages up to 20V) and to implement an MPPT algorithim in
>> the EC firmware.  You can plug up any solar panel with a Voc of 20V or
>> less to an XO-1.5 to XO-4 and it will DTRT.
>>
>> Figuring out what to do with the deployment's APs though was always a
>> struggle.
>>
>> Solutions exist but you need to get a good estimate of what sort of
>> power budget you need.  It makes a big difference in what equipment you
>> need.
>>
>> Unless its a really low power device the numbers can get large fast.
>>
>> My WNDR 3700v2 power supply is rated at 12V 2.5A which is a peak of 30W.
>>
>> Lets assume your average is 30% of peak.  That's 9W.  Your 24h energy
>> requirement is 216Wh.  A reasonable input to usable efficiency for a PV
>> system is 70%.  Given average 5 hour window of full sun you need a PV
>> output of at least 62W.  It only goes up from there.
>>
>> Realistically you need to survive a 2-3 day period of terrible solar
>> output.  So your storage requirements should be at least 2-3x that.
>> When you do get sun again you need excess PV capacity to be able to
>> recharge your batteries.  You would probably need a PV output in the
>> 100W-150W range to make a system you could count on to have 100%
>> availability 24/7.
>>
>> That's going to be a pretty big chunk of hardware up in a tree.
>>
>> If the average power draw is more in the 3W or 1W range then things look
>> a lot better.   That starts to get down into the 40 and 20W range.
>>
>>> so am I the only one left that likes edison batteries? you don't need
>>> a charge controller... they last for a hundred years....
>>> _______________________________________________
>>
>> I've never used this battery type but it looks like the resistant to
>> overcharge assumes you replace the electrolyte.  All the cells I've
>> looked at on a few sites seem to be flooded which means maintenance.
>> Are there sealed maintenance free versions?
>>
>> For discharge nominal is 1.2V but charging is listed as ~1.6V/cell so
>> you are going to need 16V to charge.  I don't really see how you can
>> build a workable system with out some sort of setup that can isolate
>> your 12V loads from a 16V charge.
>>
>> Perhaps undercharge them at a lower voltage and live with the capacity
>> loss?
>>
>> --
>> Richard A. Smith
>> _______________________________________________
>> Cerowrt-devel mailing list
>> Cerowrt-devel@lists.bufferbloat.net
>> https://lists.bufferbloat.net/listinfo/cerowrt-devel
>>
> 
> 
> _______________________________________________
> Cerowrt-devel mailing list
> Cerowrt-devel@lists.bufferbloat.net
> https://lists.bufferbloat.net/listinfo/cerowrt-devel
> 

Re: [Cerowrt-devel] solar wifi ap designs?

[Jim Gettys]

[-- Attachment #1: Type: text/plain, Size: 7499 bytes --]

On Mon, Jun 5, 2017 at 2:01 PM, <dpreed@reed.com> wrote:

> It doesn't jump to mind, but a radio carrying bits near the edge probably
> won't be used near capacity most of the 24 hours it is operating. Just as
> Iridium was designed to quiesce most of its electronics on the dark side of
> the earth, extending its battery life, you can probably assume that a radio
> in a tree won't be heavily used most of the hours of a 24 hour cycle.
>

​Turns out that (at least in OLPC days), the signal processing in the WiFi
module dominated power consumption (relative to the radios themselves). At
the time, power consumption was of order 1 watt and the radios themselves
consuming only a fraction of that.

I don't know what the current chips/modules consume, however.

Another big consumer turns out to sometimes be ethernet chips; gigabit
nic's often take/took a watt of power.

So your mileage varies, and you cannot easily presume its one thing or the
other, but need to measure (which we did extensively for OLPC, to get its
power consumption down to where it is) and fix lots of software.

Linux itself is pretty decent for power management these days: but all it
takes is a single chip/subsystem or stupid applications to blow that up.
So the whole bus structure has to be understood and properly done, and some
technologies are pretty hopeless.

The details matter.  Unfortunately, home routers have generally been plug
in devices, and the vendors haven't paid much attention.
                                                          - Jim


​

>
>
>
> On Monday, June 5, 2017 1:52pm, dpreed@reed.com said:
>
> > "Deep discharge" batteries work in LEO satellites for such applications.
> But they
> > are extraordinarily expensive, because the designs are specialized, and
> that use
> > case doesn't have the 2-3 day solar outage problem.
> >
> > You are not going to put a good enough system for an AP up in a tree.
> Maybe on an
> > antenna mast structure with solid base and guy wires. Roofs and ground
> are better
> > choices.
> >
> > But I would wonder whether redesigning the AP itself to be
> power-conserving would
> > be the place to start. They are not designed to be "low power" - they
> are designed
> > to be inexpensive.
> >
> > So, for example: why 12V??? No logic needs 12V. Integrate the battery
> into the AP
> > and run it at 3V, eliminating multiple conversion losses.
> >
> > You can use 12/20 V off the solar panel to charge the 3V battery system
> (high
> > current only while charging).
> >
> > Pay lots of attention to the duty cycle of the radio. If you really
> expect the
> > radio to be on 100% of the time, you may have to power it all the time.
> Otherwise,
> > minimize uptime.  Similarly, the processor need not be on most of the
> time if it
> > is mostly idle while accepting and sending packets from memory. (ARM
> BIG.little
> > might be helpful).
> >
> > Get rid of Linux if possible. Linux is not a low-power OS - needs a lot
> of work in
> > configuring or rewriting drivers to cut power. (there's a need for an LP
> Linux,
> > but like Desktop Linux, Linus, and his coterie, isn't terribly
> interested in
> > fixing his server OS to optimize for non-servers, so "server power
> saving" is the
> > only design point for power).
> >
> >
> >
> >
> > On Monday, June 5, 2017 12:01pm, "Richard Smith" <smithbone@gmail.com>
> said:
> >
> >> On 06/04/2017 08:49 PM, Dave Taht wrote:
> >>> I keep finding nicely integrated solar/battery/camera/wifi designs
> >>>
> >>> https://www.amazon.com/s/ref=nb_sb_noss_2?url=search-alias%
> 3Delectronics&field-keywords=solar+wifi&rh=n%3A172282%2Ck%3Asolar+wifi
> >>>
> >>> But what I want is merely an solar/battery/AP design well supported by
> >>> lede... and either the ath9k or ath10k chipset - or mt72 - that I can
> >>> hang off a couple trees. I've not worked with solar much in the past
> >>> years, and picking the right inverter/panel/etc seems like a pita, but
> >>> perhaps there are ideas out there?
> >>
> >> This is something I was up against constantly when I worked for OLPC.
> >> There's a big gap for products that use more power than a cell phone but
> >> less than an RV or a off-grid cabin.
> >>
> >> For the XO itself we worked around it by designing the front end of the
> >> XO to be able to handle the range of output voltages from "12V" panels
> >> (open circuit voltages up to 20V) and to implement an MPPT algorithim in
> >> the EC firmware.  You can plug up any solar panel with a Voc of 20V or
> >> less to an XO-1.5 to XO-4 and it will DTRT.
> >>
> >> Figuring out what to do with the deployment's APs though was always a
> >> struggle.
> >>
> >> Solutions exist but you need to get a good estimate of what sort of
> >> power budget you need.  It makes a big difference in what equipment you
> >> need.
> >>
> >> Unless its a really low power device the numbers can get large fast.
> >>
> >> My WNDR 3700v2 power supply is rated at 12V 2.5A which is a peak of 30W.
> >>
> >> Lets assume your average is 30% of peak.  That's 9W.  Your 24h energy
> >> requirement is 216Wh.  A reasonable input to usable efficiency for a PV
> >> system is 70%.  Given average 5 hour window of full sun you need a PV
> >> output of at least 62W.  It only goes up from there.
> >>
> >> Realistically you need to survive a 2-3 day period of terrible solar
> >> output.  So your storage requirements should be at least 2-3x that.
> >> When you do get sun again you need excess PV capacity to be able to
> >> recharge your batteries.  You would probably need a PV output in the
> >> 100W-150W range to make a system you could count on to have 100%
> >> availability 24/7.
> >>
> >> That's going to be a pretty big chunk of hardware up in a tree.
> >>
> >> If the average power draw is more in the 3W or 1W range then things look
> >> a lot better.   That starts to get down into the 40 and 20W range.
> >>
> >>> so am I the only one left that likes edison batteries? you don't need
> >>> a charge controller... they last for a hundred years....
> >>> _______________________________________________
> >>
> >> I've never used this battery type but it looks like the resistant to
> >> overcharge assumes you replace the electrolyte.  All the cells I've
> >> looked at on a few sites seem to be flooded which means maintenance.
> >> Are there sealed maintenance free versions?
> >>
> >> For discharge nominal is 1.2V but charging is listed as ~1.6V/cell so
> >> you are going to need 16V to charge.  I don't really see how you can
> >> build a workable system with out some sort of setup that can isolate
> >> your 12V loads from a 16V charge.
> >>
> >> Perhaps undercharge them at a lower voltage and live with the capacity
> >> loss?
> >>
> >> --
> >> Richard A. Smith
> >> _______________________________________________
> >> Cerowrt-devel mailing list
> >> Cerowrt-devel@lists.bufferbloat.net
> >> https://lists.bufferbloat.net/listinfo/cerowrt-devel
> >>
> >
> >
> > _______________________________________________
> > Cerowrt-devel mailing list
> > Cerowrt-devel@lists.bufferbloat.net
> > https://lists.bufferbloat.net/listinfo/cerowrt-devel
> >
>
>
> _______________________________________________
> Cerowrt-devel mailing list
> Cerowrt-devel@lists.bufferbloat.net
> https://lists.bufferbloat.net/listinfo/cerowrt-devel
>

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Re: [Cerowrt-devel] solar wifi ap designs?

[Aaron Wood]

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As for why 12V: it's a common standard regulator that allows all the
various internal voltages to be derived from (5, 3.3, 1.8, etc). So that's
why a lot of designs use that. Especially since the 5v for USB can be
isolated corrected against being pulled too low by devices that are plugged
in.

That's harder with a 5v supply (although I tend to see designs using those
simply let an overloaded USB bus reset the whole device)

IIRC, a 5354g took about 1 watt, pretty much regardless of what it was
doing. But I haven't looked at any of the current APs.

Measure, and measure under full load on all interfaces. And measure a 24
hour cycle to see the watt hours used.

-Aaron
On Mon, Jun 5, 2017 at 11:22 Jim Gettys <jg@freedesktop.org> wrote:

> On Mon, Jun 5, 2017 at 2:01 PM, <dpreed@reed.com> wrote:
>
>> It doesn't jump to mind, but a radio carrying bits near the edge probably
>> won't be used near capacity most of the 24 hours it is operating. Just as
>> Iridium was designed to quiesce most of its electronics on the dark side of
>> the earth, extending its battery life, you can probably assume that a radio
>> in a tree won't be heavily used most of the hours of a 24 hour cycle.
>>
>
> ​Turns out that (at least in OLPC days), the signal processing in the WiFi
> module dominated power consumption (relative to the radios themselves). At
> the time, power consumption was of order 1 watt and the radios themselves
> consuming only a fraction of that.
>
> I don't know what the current chips/modules consume, however.
>
> Another big consumer turns out to sometimes be ethernet chips; gigabit
> nic's often take/took a watt of power.
>
> So your mileage varies, and you cannot easily presume its one thing or the
> other, but need to measure (which we did extensively for OLPC, to get its
> power consumption down to where it is) and fix lots of software.
>
> Linux itself is pretty decent for power management these days: but all it
> takes is a single chip/subsystem or stupid applications to blow that up.
> So the whole bus structure has to be understood and properly done, and some
> technologies are pretty hopeless.
>
> The details matter.  Unfortunately, home routers have generally been plug
> in devices, and the vendors haven't paid much attention.
>                                                           - Jim
>
>
> ​
>
>>
>>
>>
>> On Monday, June 5, 2017 1:52pm, dpreed@reed.com said:
>>
>> > "Deep discharge" batteries work in LEO satellites for such
>> applications. But they
>> > are extraordinarily expensive, because the designs are specialized, and
>> that use
>> > case doesn't have the 2-3 day solar outage problem.
>> >
>> > You are not going to put a good enough system for an AP up in a tree.
>> Maybe on an
>> > antenna mast structure with solid base and guy wires. Roofs and ground
>> are better
>> > choices.
>> >
>> > But I would wonder whether redesigning the AP itself to be
>> power-conserving would
>> > be the place to start. They are not designed to be "low power" - they
>> are designed
>> > to be inexpensive.
>> >
>> > So, for example: why 12V??? No logic needs 12V. Integrate the battery
>> into the AP
>> > and run it at 3V, eliminating multiple conversion losses.
>> >
>> > You can use 12/20 V off the solar panel to charge the 3V battery system
>> (high
>> > current only while charging).
>> >
>> > Pay lots of attention to the duty cycle of the radio. If you really
>> expect the
>> > radio to be on 100% of the time, you may have to power it all the time.
>> Otherwise,
>> > minimize uptime.  Similarly, the processor need not be on most of the
>> time if it
>> > is mostly idle while accepting and sending packets from memory. (ARM
>> BIG.little
>> > might be helpful).
>> >
>> > Get rid of Linux if possible. Linux is not a low-power OS - needs a lot
>> of work in
>> > configuring or rewriting drivers to cut power. (there's a need for an
>> LP Linux,
>> > but like Desktop Linux, Linus, and his coterie, isn't terribly
>> interested in
>> > fixing his server OS to optimize for non-servers, so "server power
>> saving" is the
>> > only design point for power).
>> >
>> >
>> >
>> >
>> > On Monday, June 5, 2017 12:01pm, "Richard Smith" <smithbone@gmail.com>
>> said:
>> >
>> >> On 06/04/2017 08:49 PM, Dave Taht wrote:
>> >>> I keep finding nicely integrated solar/battery/camera/wifi designs
>> >>>
>> >>>
>> https://www.amazon.com/s/ref=nb_sb_noss_2?url=search-alias%3Delectronics&field-keywords=solar+wifi&rh=n%3A172282%2Ck%3Asolar+wifi
>> >>>
>> >>> But what I want is merely an solar/battery/AP design well supported by
>> >>> lede... and either the ath9k or ath10k chipset - or mt72 - that I can
>> >>> hang off a couple trees. I've not worked with solar much in the past
>> >>> years, and picking the right inverter/panel/etc seems like a pita, but
>> >>> perhaps there are ideas out there?
>> >>
>> >> This is something I was up against constantly when I worked for OLPC.
>> >> There's a big gap for products that use more power than a cell phone
>> but
>> >> less than an RV or a off-grid cabin.
>> >>
>> >> For the XO itself we worked around it by designing the front end of the
>> >> XO to be able to handle the range of output voltages from "12V" panels
>> >> (open circuit voltages up to 20V) and to implement an MPPT algorithim
>> in
>> >> the EC firmware.  You can plug up any solar panel with a Voc of 20V or
>> >> less to an XO-1.5 to XO-4 and it will DTRT.
>> >>
>> >> Figuring out what to do with the deployment's APs though was always a
>> >> struggle.
>> >>
>> >> Solutions exist but you need to get a good estimate of what sort of
>> >> power budget you need.  It makes a big difference in what equipment you
>> >> need.
>> >>
>> >> Unless its a really low power device the numbers can get large fast.
>> >>
>> >> My WNDR 3700v2 power supply is rated at 12V 2.5A which is a peak of
>> 30W.
>> >>
>> >> Lets assume your average is 30% of peak.  That's 9W.  Your 24h energy
>> >> requirement is 216Wh.  A reasonable input to usable efficiency for a PV
>> >> system is 70%.  Given average 5 hour window of full sun you need a PV
>> >> output of at least 62W.  It only goes up from there.
>> >>
>> >> Realistically you need to survive a 2-3 day period of terrible solar
>> >> output.  So your storage requirements should be at least 2-3x that.
>> >> When you do get sun again you need excess PV capacity to be able to
>> >> recharge your batteries.  You would probably need a PV output in the
>> >> 100W-150W range to make a system you could count on to have 100%
>> >> availability 24/7.
>> >>
>> >> That's going to be a pretty big chunk of hardware up in a tree.
>> >>
>> >> If the average power draw is more in the 3W or 1W range then things
>> look
>> >> a lot better.   That starts to get down into the 40 and 20W range.
>> >>
>> >>> so am I the only one left that likes edison batteries? you don't need
>> >>> a charge controller... they last for a hundred years....
>> >>> _______________________________________________
>> >>
>> >> I've never used this battery type but it looks like the resistant to
>> >> overcharge assumes you replace the electrolyte.  All the cells I've
>> >> looked at on a few sites seem to be flooded which means maintenance.
>> >> Are there sealed maintenance free versions?
>> >>
>> >> For discharge nominal is 1.2V but charging is listed as ~1.6V/cell so
>> >> you are going to need 16V to charge.  I don't really see how you can
>> >> build a workable system with out some sort of setup that can isolate
>> >> your 12V loads from a 16V charge.
>> >>
>> >> Perhaps undercharge them at a lower voltage and live with the capacity
>> >> loss?
>> >>
>> >> --
>> >> Richard A. Smith
>> >> _______________________________________________
>> >> Cerowrt-devel mailing list
>> >> Cerowrt-devel@lists.bufferbloat.net
>> >> https://lists.bufferbloat.net/listinfo/cerowrt-devel
>> >>
>> >
>> >
>> > _______________________________________________
>> > Cerowrt-devel mailing list
>> > Cerowrt-devel@lists.bufferbloat.net
>> > https://lists.bufferbloat.net/listinfo/cerowrt-devel
>> >
>>
>>
>> _______________________________________________
>> Cerowrt-devel mailing list
>> Cerowrt-devel@lists.bufferbloat.net
>> https://lists.bufferbloat.net/listinfo/cerowrt-devel
>>
> _______________________________________________
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> https://lists.bufferbloat.net/listinfo/cerowrt-devel
>

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Re: [Cerowrt-devel] solar wifi ap designs?

[David Lang]

On Mon, 5 Jun 2017, Richard Smith wrote:

> My WNDR 3700v2 power supply is rated at 12V 2.5A which is a peak of 30W.

don't forget that this includes providing power out to the USB port as well.

yet another reason to measure things :-)

David Lang
k

Re: [Cerowrt-devel] solar wifi ap designs?

[Jim Gettys]

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On Mon, Jun 5, 2017 at 4:20 PM, David Lang <david@lang.hm> wrote:

> On Mon, 5 Jun 2017, Richard Smith wrote:
>
> My WNDR 3700v2 power supply is rated at 12V 2.5A which is a peak of 30W.
>>
>
> don't forget that this includes providing power out to the USB port as
> well.
>
> yet another reason to measure things :-)


​USB places (placed?) multiple second ​latencies on suspend/resume as well.

This makes it really hard to do decent high speed power management on an
operating system.  Linux itself we measured on an iPAQ at 20ms latency to
suspend resume.  Then when you had a USB port, it took of order a second
(to get the best power management on OLPC we had to disable USB entirely).

Have I said how much I hate USB?
                       - Jim


>
> David Lang
> k
>
> _______________________________________________
> Cerowrt-devel mailing list
> Cerowrt-devel@lists.bufferbloat.net
> https://lists.bufferbloat.net/listinfo/cerowrt-devel
>

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Re: [Cerowrt-devel] solar wifi ap designs?

[Michael Richardson]

Such an interesting thread.
But, is the 3800 tolerant of spikes of 13.6V?  Has anyone tried?
I haven't many left :-)

--
]               Never tell me the odds!                 | ipv6 mesh networks [
]   Michael Richardson, Sandelman Software Works        | network architect  [
]     mcr@sandelman.ca  http://www.sandelman.ca/        |   ruby on rails    [

Re: [Cerowrt-devel] solar wifi ap designs?

[Joel Wirāmu Pauling]

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I've installed several 3800's into Fibre Install van's attached to
Inverters and LTE Dongles to provide in-van wifi. One has been going for
the last 5 years without issue so spikes seem to be well tolerated.

On 6 June 2017 at 09:51, Michael Richardson <mcr@sandelman.ca> wrote:

> Such an interesting thread.
> But, is the 3800 tolerant of spikes of 13.6V?  Has anyone tried?
> I haven't many left :-)
>
> --
> ]               Never tell me the odds!                 | ipv6 mesh
> networks [
> ]   Michael Richardson, Sandelman Software Works        | network
> architect  [
> ]     mcr@sandelman.ca  http://www.sandelman.ca/        |   ruby on
> rails    [
>
> _______________________________________________
> Cerowrt-devel mailing list
> Cerowrt-devel@lists.bufferbloat.net
> https://lists.bufferbloat.net/listinfo/cerowrt-devel
>

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Re: [Cerowrt-devel] solar wifi ap designs?

[Michael Richardson]

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Joel Wirāmu Pauling <joel@aenertia.net> wrote:
    > I've installed several 3800's into Fibre Install van's attached to
    > Inverters and LTE Dongles to provide in-van wifi. One has been going
    > for the last 5 years without issue so spikes seem to be well
    > tolerated.

With Inverters?  You mean, going to 120V and using the brick to bring it back
to 12V?

Or are you connecting directly to the "12V" auto bus?

I'm trying to put this in my VW Westfalia, which has a second "house" battery
for stuff like this.

    > On 6 June 2017 at 09:51, Michael Richardson <mcr@sandelman.ca> wrote:

    > Such an interesting thread.
    > But, is the 3800 tolerant of spikes of 13.6V? Has anyone tried?
    > I haven't many left :-)

    > --
    > ] Never tell me the odds! | ipv6 mesh networks [
    > ] Michael Richardson, Sandelman Software Works | network architect
    > [
    > ] mcr@sandelman.ca http://www.sandelman.ca/ | ruby on rails [





--
]               Never tell me the odds!                 | ipv6 mesh networks [
]   Michael Richardson, Sandelman Software Works        | network architect  [
]     mcr@sandelman.ca  http://www.sandelman.ca/        |   ruby on rails    [


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Re: [Cerowrt-devel] solar wifi ap designs?

[Jim Gettys]

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On Mon, Jun 5, 2017 at 6:49 PM, Joel Wirāmu Pauling <joel@aenertia.net>
wrote:

> I've installed several 3800's into Fibre Install van's attached to
> Inverters and LTE Dongles to provide in-van wifi. One has been going for
> the last 5 years without issue so spikes seem to be well tolerated.
>

​There is the converse problem: I've recently had two USB hubs fail
 (serially) on a telescope system.  My theory is that their 12V supplies
really don't like to be fed 13.8V (to get rid of a pile of dongles and
wires on the telescope, we replaced them all with a common regulated power
supply that is ​at 13.8V, which is what most car batteries *actually* put
out when fully charged).  The hubs would have to dissipate a lot more power
to keep the USB port voltages at spec'ed voltages, shortening the hub's
lives.

Basically, while OLPC was carefully designed to be very tolerant of input
voltage as Richard Smith pointed, many devices are not and you cannot
presume no problems may occur.

Care is in order.




> On 6 June 2017 at 09:51, Michael Richardson <mcr@sandelman.ca> wrote:
>
>> Such an interesting thread.
>> But, is the 3800 tolerant of spikes of 13.6V?  Has anyone tried?
>> I haven't many left :-)
>>
>> --
>> ]               Never tell me the odds!                 | ipv6 mesh
>> networks [
>> ]   Michael Richardson, Sandelman Software Works        | network
>> architect  [
>> ]     mcr@sandelman.ca  http://www.sandelman.ca/        |   ruby on
>> rails    [
>>
>> _______________________________________________
>> Cerowrt-devel mailing list
>> Cerowrt-devel@lists.bufferbloat.net
>> https://lists.bufferbloat.net/listinfo/cerowrt-devel
>>
>
>
> _______________________________________________
> Cerowrt-devel mailing list
> Cerowrt-devel@lists.bufferbloat.net
> https://lists.bufferbloat.net/listinfo/cerowrt-devel
>
>

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Re: [Cerowrt-devel] solar wifi ap designs?

[Richard Smith]

On 06/05/2017 04:20 PM, David Lang wrote:
> On Mon, 5 Jun 2017, Richard Smith wrote:
> 
>> My WNDR 3700v2 power supply is rated at 12V 2.5A which is a peak of 30W.
> 
> don't forget that this includes providing power out to the USB port as 
> well.
> 
> yet another reason to measure things :-)


Ah. Yeah good point.  Thats .5A.

-- 
Richard A. Smith

Re: [Cerowrt-devel] solar wifi ap designs?

[Richard Smith]

On 06/05/2017 05:51 PM, Michael Richardson wrote:
> Such an interesting thread.
> But, is the 3800 tolerant of spikes of 13.6V?  Has anyone tried?
> I haven't many left :-)

OpenWRT has some hardware info here:

https://wiki.openwrt.org/toh/netgear/wndr3700#tab__hardware_details

Which has a pointer to the data sheet for the onboard regulators.

http://www.st.com/stonline/stappl/st/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/CD00169322.pdf

The datasheet says those are good up to 18V input so that's promising. 
It will depend on what they did with protection circuitry (if any) and 
the thermal design.

I'd be surprised if it 13.8V made it smoke but depending on the thermal 
design it might be a problem at higher temperatures.

That said, an automotive electrical system is a _very_ harsh place. 
13.8-14.2V is just the nominal output of the voltage regulator for 
charging the battery.  It's by no means the limit of the spikes that can 
occur.

I would not recommend any electronics not designed to work in a car be 
used without some sort of external protection.  Load dump can cause very 
large voltage swings for extended periods.

Here's an app note that talks about some of the hazards.

www.st.com/resource/en/application_note/cd00181783.pdf

-- 
Richard A. Smith

Re: [Cerowrt-devel] solar wifi ap designs?

[Richard Smith]

On 06/06/2017 08:04 AM, Richard Smith wrote:
> On 06/05/2017 04:20 PM, David Lang wrote:
>> On Mon, 5 Jun 2017, Richard Smith wrote:
>>
>>> My WNDR 3700v2 power supply is rated at 12V 2.5A which is a peak of 30W.
>>
>> don't forget that this includes providing power out to the USB port as 
>> well.
>>
>> yet another reason to measure things :-)
> 
> 
> Ah. Yeah good point.  Thats .5A.
> 

I wired up my WNDR3700v2 running a fairly newish version of LEDE to my 
power supply.

Idle with 5G and 2.4G active, upstream link (GibE) connected and 1 sta 
attached to 5G:
	5.2 - 5.3 W.

Running some upload/download tests:
	5.2 - 8 W.

On boot however there are brief spikes that required the current limit 
of my supply to be set up in the 1A zone.

Given the info I saw in the buck regulators datasheet I suspected that 
the only reason it needs 12V is to run the +5V USB supply.  12V wall 
warts are super cheap so 12V is a reasonable choice from a BOM cost 
perspective.

If that is true you don't care about USB then it should run fine at 5V 
Vin, and indeed it runs just fine at 5V Vin.  I needed to up the current 
limit above 1A to allow it to boot.  I set it to 2A and didn't try to 
find the exact spike threshold.

5V gives you a slight savings. Idle at 4.8W.  That's about what I would 
expect. It's pretty easy to get close to 90% on a DC-DC converter these 
days without too much extra effort.

-- 
Richard A. Smith

Re: [Cerowrt-devel] solar wifi ap designs?

[Christopher Robin]

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> <dpreed@reed.com> wrote:
>You are not going to put a good enough system for an AP up in a tree.
Maybe on an antenna mast structure with solid base and guy wires. Roofs and
ground are better choices.
>But I would wonder whether redesigning the AP itself to be
power-conserving would be the place to start. They are not designed to be
"low power" - they are designed to be inexpensive.

Along these lines, would using cellphone chips be viable?

I'm trying to imagine a use case where decade long, maintenance free, tree
mounting would be the preferred solution. The only thing I can think of is
a cheap active repeater in an area with infrequent users. Push as much
logic/processing back to a unit where power is cheap.

-CR

>

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Re: [Cerowrt-devel] solar wifi ap designs?

[Michael Richardson]

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Richard Smith <smithbone@gmail.com> wrote:
    rs> If that is true you don't care about USB then it should run fine at
    rs> 5V Vin,
    rs> and indeed it runs just fine at 5V Vin.  I needed to up the current
    rs> limit

I don't care about USB for now.

I have a spare 12V->5V DCDC adapter, I suspect that it will isolate my 3800
From engine noise and spikes, and if anything is going to blow, it will
be the DCDC adapter...


--
]               Never tell me the odds!                 | ipv6 mesh networks [
]   Michael Richardson, Sandelman Software Works        | network architect  [
]     mcr@sandelman.ca  http://www.sandelman.ca/        |   ruby on rails    [


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Re: [Cerowrt-devel] solar wifi ap designs?

[Dave Taht]

My use case used to be covering hundreds of km in the Nicaraguan
jungle. The prototype for that covers a mere 110 acres in the los
gatos hills, trying to get stuff deep into ravines and so on.

I have at least a dozen areas where a wifi repeater would be useful,
but I tend to meshy route things, so rather than repeaters, I have
routers.

the ubnt radios I presently use tolerate 6-24v, and eat less than 5w -
so some of the things I've been watching rathole here don't apply.
What I'd hoped for was an "all-in-one unit" much like the wifi camera
that kicked off the thread.

I'm NOT going to put a wndr3800 in a tree, and while offering usb
recharging might be a good thing to a campsite, not planning on it at
the moment.

So I'm back to building a custom enclosure for edison batteries, a
solar panel hopefully lacking in charge controller, and a nanostation
m5 or rocket m5 as the gear.

>I'm trying to imagine a use case where decade long, maintenance free, tree mounting would be the preferred solution. The only thing I can think of is a cheap active repeater in an area with infrequent users. Push as much >logic/processing back to a unit where power is cheap.

Re: [Cerowrt-devel] solar wifi ap designs?

[Richard Smith]

On 06/09/2017 10:02 AM, Dave Taht wrote:

> My use case used to be covering hundreds of km in the Nicaraguan
> jungle. The prototype for that covers a mere 110 acres in the los
> gatos hills, trying to get stuff deep into ravines and so on.
> 
> I have at least a dozen areas where a wifi repeater would be useful,
> but I tend to meshy route things, so rather than repeaters, I have
> routers.

> the ubnt radios I presently use tolerate 6-24v, and eat less than 5w -
> so some of the things I've been watching rathole here don't apply.
> What I'd hoped for was an "all-in-one unit" much like the wifi camera
> that kicked off the thread.

I haven't done much of a search in the last 5 years but I've yet to see 
such a product.  I wonder how well the wifi camera stuff actually works 
measured against availability during minimal-sun periods.

Accounting for wost case is always what amplifies the requirements of an 
off-grid system.

NASA Surface meteorology and Solar Energy claims that for Los Gatos 
December is the lowest output.  Given a split-the-middle tilt alignment 
of 37 degrees it will receive average full-sun net of 3.5 hours.

I'll Assume your setup averages at half duty (2.5W) which is 60Wh/day.

Using my .7 number for PV system input-output that's minimum of a 25W 
panel with zero tolerance for low-sun days.

NASA has minimum irradiance across n-day periods.  For for 1, 3, and 7 
day periods in December the minimums are 12, 23, and 42 % of average. I 
did some spreadsheet numbers for those periods using 30, 40 and 50 W 
panels.  I summarized the results into a table of PV wattage, Min 
battery, and recovery time.  PV wattage is your input wattage, Min 
battery is the amount of energy storage you need to stay operational 
during the period, and recovery time is how many days of average output 
you need to recover the battery back to 100%.   Note that this assumes 
your storage device is 100% efficient. Real batteries would need to be 
over sized by some % to net out the required energy.

1-day

PV  Batt  Recovery
--  ----  --------
30   50    2
40   47    0.9
50   43    0.55

3-day

PV  Batt  Recovery
--  ----  --------
30  122    5
40  103    2
50   83    1

7-day*

PV  Batt  Recovery
--  ----  --------
30  173     7.5
40   90     2
50   8.5    0.1

* The 7-day numbers are a bit misleading.  Any 7-day period could 
contain a 3-day period. So even though the period math claims that for 
50W panel you only have 8.5 Wh of deficit you still need energy storage 
numbers from the 3-day period to deal with the worst distribution of the 
worst case.

So looks like a 50W panel and a 90ish Wh battery should do pretty good. 
Unfortunately, this is all average based so it still won't guarantee you 
stay up 100% but it should be pretty close.

Now contrast that with the best month June having 6.8 hours of full-sun 
and min % of 16, 51 and 59.

In the 3-day and 7-day periods the system doesn't go into deficit.

1-day

PV  Batt  Recovery
--  ----  --------
25   39    0.5
30   34    0.33
40   26    0.16
50   17    0.08

Event though the 3 and 7 day periods don't actually go into deficit you 
still need storage for ~2 days @ the 1-day minimum.  The 3 day period 
could be comprised of 2 really weak days and then 1 great one.  So sadly 
you would still need 70ish Wh of storage.

I included 25W to have a item that matched the best recovery in December.

If you aren't sizing for worst case and are ok if things stop when it 
rains for more than 1-day then you can get by with a lot less of a 
system, but for 95%+ uptimes  you need a lot of excess capacity.

> So I'm back to building a custom enclosure for edison batteries, a
> solar panel hopefully lacking in charge controller, and a nanostation
> m5 or rocket m5 as the gear.

If you omit the controller you will need to factor in the additional 
loss of forcing your PV array to operate at a fixed voltage.

You can think of PV as a voltage controlled current source.  At 
different voltages it will produce a different amounts of current 
producing an IV curve.  There exists a point on that curve where the 
voltage * current produces a maximal power output usually denoted in the 
specs as Vmp.  For most "12V" Poly-Si panels Vmp at operating temp is 
15-16V.  The exact value varies by panel makeup and by operating 
temperature.

If you directly connect the panel up to a battery then you will force it 
to operate at the battery voltage and thus its power output will be 
bound to that voltage point on the curve.

It certainly makes for a simpler system but depending on the situation 
the output power reduction of the PV can be significant.

The 1.6V charing voltage of a NiFe cell seems to align with a 12V
PV panel in that a a 9 cell NiFe would need 14.4V for charge.  But the 
devil is in the details.

If say for example your battery can draw more load than your PV can 
output then there won't be much voltage rise on the battery.  A low NiFe 
battery is 1.2V/cell so say the battery voltage is only 11 or 12V when 
it starts to charge.  Thats going to reduce your PV power output.

An MPPT controller can recovery that lost power by keeping the PV 
voltage at a maximum but that has to be contrasted vs the efficiency of 
the controller.  Depending on the system it may be a wash.

MPPT helps in smaller PV setups where the load is much larger than the 
PV input.  In these cases the load will overdraw the panel and pull the 
voltage way down which decreases the PV output even more.  The PV ends 
up operating way down its power curve.  You can have full-sun on the 
panel and still be no where near the expected output.  MPPT can prevent 
that from happening and keep the panel operating at maximum power.

Are you not wanting a controller due to cost and complexity or because 
you are concerned about conversion efficiency?

-- 
Richard A. Smith

Re: [Cerowrt-devel] solar wifi ap designs?

[Christopher Robin]

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On Tue, Jun 13, 2017 at 8:24 AM Christopher Robin <pheoni@gmail.com> wrote:

>
> On Tue, Jun 13, 2017 at 7:52 AM Richard Smith <smithbone@gmail.com> wrote:
>
>> On 06/09/2017 10:02 AM, Dave Taht wrote:
>>
>> > My use case used to be covering hundreds of km in the Nicaraguan
>> > jungle. The prototype for that covers a mere 110 acres in the los
>> > gatos hills, trying to get stuff deep into ravines and so on.
>>
>> Accounting for wost case is always what amplifies the requirements of an
>> off-grid system.
>>
>> NASA Surface meteorology and Solar Energy claims that for Los Gatos
>> December is the lowest output.  Given a split-the-middle tilt alignment
>> of 37 degrees it will receive average full-sun net of 3.5 hours.
>
>
Dave: With these being tree mounted, how likely is full-sun? I'm not
familiar with the tree type/density. Are you're looking to avoid having
separated solar panels?

Richard: I would presume these calculations are all for "open field"
conditions?

If the panels are under a tree canopy, a lower attack angle may be better
to better utilize morning/evening sun. A higher one may be necessary to get
a useful charge during peak daylight. I've seen some pretty impressive
calculators to work out best guesses for field testing.

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Re: [Cerowrt-devel] solar wifi ap designs?

[Richard Smith]

On 06/13/2017 09:03 AM, Christopher Robin wrote:
> 
> On Tue, Jun 13, 2017 at 8:24 AM Christopher Robin <pheoni@gmail.com 
> <mailto:pheoni@gmail.com>> wrote:
> 
> 
>     On Tue, Jun 13, 2017 at 7:52 AM Richard Smith <smithbone@gmail.com
>     <mailto:smithbone@gmail.com>> wrote:
> 
>         On 06/09/2017 10:02 AM, Dave Taht wrote:
> 
>          > My use case used to be covering hundreds of km in the Nicaraguan
>          > jungle. The prototype for that covers a mere 110 acres in the los
>          > gatos hills, trying to get stuff deep into ravines and so on.
> 
>         Accounting for wost case is always what amplifies the
>         requirements of an
>         off-grid system.
> 
>         NASA Surface meteorology and Solar Energy claims that for Los Gatos
>         December is the lowest output.  Given a split-the-middle tilt
>         alignment
>         of 37 degrees it will receive average full-sun net of 3.5 hours.
> 
> 
> Dave: With these being tree mounted, how likely is full-sun? I'm not 
> familiar with the tree type/density. Are you're looking to avoid having 
> separated solar panels?
> 
> Richard: I would presume these calculations are all for "open field" 
> conditions?
> 
> If the panels are under a tree canopy, a lower attack angle may be 
> better to better utilize morning/evening sun. A higher one may be 
> necessary to get a useful charge during peak daylight. I've seen some 
> pretty impressive calculators to work out best guesses for field testing.

Yes.  All best case there.  Nothing fancy.  I was just trying to show a 
rough relation to the size of the system and uptime given crappy 
conditions without getting too complicated.  As you mention, figuring 
out the best setup can get pretty hairy.

Optimizing for in-tree use is left as a future exercise. :)

Optimum tilt for Dec is listed as 62 degrees but that only increases the 
full-sun from 3.5 to 3.9 so it doesn't change the analysis that much. 
Given there so much leeway in the peak months it certainly makes sense 
to be optimized for maximal production in the low months.

-- 
Richard A. Smith

Re: [Cerowrt-devel] solar wifi ap designs?

[Dave Taht]

If you run the numbers for Nicaragua, you'll find that the solar
coverage is WAY better year round. (share the spreadsheet?) The
problem is the rainy season from late august through november, and I
was aiming for 3 days of battery life, with only 20% sun over those
days.

(yes, the whole bufferbloat project has always sort of been, for me,
about *eventually* having wifi routers you could drop off a truck (or
drone!), that would "just work" in the third world. I didn't do all
this just to solve first world problems!)

I have a new site to try out and IF I get my act together soon enough,
I hope to do a deployment down there before it starts to rain
overmuch. See: http://www.harmonia.life/ .
I might give wind a try, also.

I am heading down there next week or the one following to explore the
possibilities (and get some surfing in!).

Now that my new office space is coming along, I have space and tools
(cnc machine, etc), to try and build something that would work. I'd
always intended local manufacture of the edison batteries.....

AND: speaking of all that, if anyone's bored and wants to camp out for
a week or three, I have spare tent site reserved in los gatos... and
some space down in harmonia, also... and I'm happy to say, I, at
least, am having fun with all this, again, finally.

Re: [Cerowrt-devel] solar wifi ap designs?

[Richard Smith]

On 06/13/2017 01:25 PM, Dave Taht wrote:
> If you run the numbers for Nicaragua, you'll find that the solar
> coverage is WAY better year round. (share the spreadsheet?) The
> problem is the rainy season from late august through november, and I
> was aiming for 3 days of battery life, with only 20% sun over those
> days.

In general is better but I would not call it WAY better.  I looked up 
Harmonia and used Cárdenas, Nicaragua as my data point.

The average is a pretty solid 5-6 hours across the year but the rainy 
season has a large effect.  20% matches the 3-day in Oct which looks 
like it's the weakest month overall, but the 3-day minimum is in Aug @ 
13%.  When you do the math it actually ends up being worse that the 
minimum in Los Gatos.  Los Gatos had a minimum of 2.4 hours where as 
Cárdenas nets out at 2 hours.

Here's the spreadsheet.  'Lowest' and 'Highest' are Los Gatos and 
'Nicaragua' is Cárdenas.

https://docs.google.com/spreadsheets/d/1p6PYBgcTtLR9cwWlVpzRiIt4t2RcjoYVC4_K6WxLmso/edit?usp=sharing

> I might give wind a try, also.

Wind and solar are great complements to each other.  In general one is 
good when the other is bad.

> I am heading down there next week or the one following to explore the
> possibilities (and get some surfing in!).

Nice.  Can't go wrong with some good beach time.

> Now that my new office space is coming along, I have space and tools
> (cnc machine, etc), to try and build something that would work. I'd
> always intended local manufacture of the edison batteries.....

Cool.  I'm interested in seeing what you come up with.  Maybe you can do 
a kickstarter to build a larger quantity of them. :)

-- 
Richard A. Smith