[Power] Haiti power questions

[scott at solarnetone.org]

Hi Richard,

I concur that our previous discussion represents our maximum 
load in terms of XO's.  Are there other loads to account for, such as 
lighting, network server/access point, printer,etc?


On Mon, 6 Dec 2010, Richard A. Smith wrote:

> On 12/05/2010 12:05 AM, scott at solarnetone.org wrote:
>
>>>
>>> Assuming you are only going to 50% DoD I'm guessing your minimum battery
>>> voltage is about 11.5 to 11.6V.
>>
>> 12.2 is the lowest I have seen my battery array drop in 5 years of
>> operation.  That was during a weak but especially large and slow
>> moving tropical storm a couple of years ago.
>
> That would suggest that your normal DoD is much lower than 50%.  What
> average DoD did you design for?
>

Here is the datasheet for the batteries I generally use:
http://www.surrette.com/pdf/S-530.pdf?phpMyAdmin=0610e516bf803196b5feee0b1ad65c08&phpMyAdmin=3jSJ-jdC5E7b53DHgV8TGvpSCF6

Not sure if there are DoD curve charts available, but we designed at the 
C-20 rate.

> I must have been looking at the wrong curve when I said 11.5-6 thats  a
> C/5 number rather than a C/20 or C/100.  12.2V is approx 50% on some of
> the generic curves I found on the web.

Discharging at C-5 rate will greatly reduce the lifespan of your 
batteries, from my experience.

>
>> either way... I spread it out over 24h, while you need it in a 3h span.
>> That dictates a few changes to accomodate a slightly different load
>> profile.  That being said, I will put together a parts list for an exact
>> replication of the power system for you, and a list of parts slightly
>> better tuned to the 50 XO load.
>
> Thank you.  That way someone wanting to implement such a system has a
> starting point.  Each site is different and will need customisation for
> their specific workflow and geographical location.
>

Correct, and no problem.  I will try to be as generic as possible so we 
are not particularly bound to any given vendors products.

> Did you run any HOMER simulations for your existing setups?

I did not.  In the design process of the SolarNetOne, once we decided on 
ultimate functionality of the network, we derived the load that would 
present.  Dr. Cerf then put me in contact with Mr. Freling at self.org. 
We discussed load structure and my optimization methods, and self.org sent 
some gear for us to prototype with after mutual deliberation.  I am still 
in posession of, and use daily, that prototype unit, and have been 
observing its performance daily over the intervening years.

>
> What sort of logs do you have for the performance of the system  Do you
> log things like PV output or Wh consumed on a periodic basis?

Alas, I have not kept any hard data logs, mainly because that 
functionality was not built into the pwm charge controller.  With the 
advent of MPPT charge controllers, this would be pretty easy work.

Our main design consideration was that we could power a 100W load 
continuously.  In that, it has never failed.


>
> It would be interesting to compare a HOMER simulation against real world
> data.
>

Indeed.  There are likely some minor optimizations that would result from 
that.

Cheers,
Scott

> -- 
> Richard A. Smith  <richard at laptop.org>
> One Laptop per Child
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