[Soekris] solar power

[David Smead]

Greetings,

I design remote energy systems for a living, and my book, "Living on 12
Volts with Ample Power" is the origin of the 50% discharge rule for
batteries, misquoted more often than not, including recently on this
list.

Accounting for all the variables in a remote energy system requires a
lot of planning, and what works in one place may not be viable
elsewhere.

Properly managed, batteries are inexpensive.  Ten year life cycles can
be achieved with the right charging and monitoring gear.  Perhaps
you're putting up amateur solar sites which you can trek to and don't
mind replacing batteries every six months, but try to tell the owner of
a mountain top site that they have to rent a helicopter every six
months to replace batteries.  Even in less severe circumstances,
sending a tech out to replace batteries is a costly endeavor.

For many of our users, (sailors cruising the seven seas), a power
failure could be deadly. A failure at a telcom site may not be deadly
to the owner of the site, but could indirectly result in a fatality to
a user of that site.  Needless to say, installing a relay site without
a thorough understanding of the power needs, and without a high degree
of confidence that the power system is adequate, may leave you open to
serious legal repercussions later  -- the word negligence comes to mind.

\/
Sincerely,

David Smead
http://www.amplepower.com

On Sun, 28 Mar 2004, Dave wrote:

> Hi All,
>
> I thought it might be helpful to toss in my solar-soekris experiences....
>
> We are in Central Coast California...stats say anywhere from 3 - 5 hours of
> sunlight....winter is not too nice and we get plenty of rain and clouds for
> week+ long.
>
> We have 2 self-sustained soekris repeaters...
>
> (#1) Early 2003 we did solar calcs with a local solar pro and he recommended
> 200W of PV and 200ah+ SLA battery...he demanded a charge controller. All
> this for a single Soekris 4521....I assumed since he was a pro we should
> listen and we did except we opted for a 110W PV instead of 200W...needless
> to say we have had absolutely no power problems and we ran another 4521 and
> a 4511 for a couple months at that location on same power supply during
> June/July 2003...no problems. 30+ associations to a PCMCIA radio at any
> given time and plenty of data running through the board at any given time.
>
> (#2) December 2003 I decided to do it myself since the previous seemed a
> little overkill to me. I wanted to do it as inexpensive as possible and with
> as little of a PV footprint as possible...for curiosity reasons and since
> this repeater was not planned to be a heavy usage repeater.
>
> On #2 I chose a Kyocera 60W PV (KC60) and thought I would try some small
> batteries and NO charge controller (I didn't care if I fried batteries). I
> started with a 20ah SLA and it lasted for 48 hours...next I replaced the
> 20ah with a 35ah SLA (all fully charged) and it lasted for about 10 days...I
> then dropped in a second 35ah SLA and paralleled it to the previous...uptime
> on the 4521 is now at 82 days and currently has 10 active associations to
> the distribution PCMCIA radio...this box also has a second PCMCIA radio
> doing WDS to another repeater and a miniPCI doing WDS toward the gateway...
>
> The 35ah SLA's I picked up at a surplus battery store for $15 each...I
> bought 10 of them...if I have to replace them every 6 months because I am
> not using a charge controller I consider it a fair investment.
>
>
> In short...I recommend whatever you can afford up to a maximum of what I am
> using for #1 above for a 4521...In my experience and in our area I have
> found that #1 is way more than sufficient for our needs.
>
>
>
> -Dave
>
>
>
>
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