[Server-devel] NUC and solar power questions

George Hunt georgejhunt at gmail.com
Fri Jun 20 12:07:56 EDT 2014

On Fri, Jun 20, 2014 at 7:09 AM, Ben Burrell <baburrell at gmail.com> wrote:

> George:
> I have a physics student who will be assembling and testing a solar setup
> similar to that described on the Unleash Kids site (
> http://www.unleashkids.org/2014/02/21/off-the-grid-suitcase-solar-solutions-for-power-in-haiti/).
>  I understand that the system can re-charge about 10 xo1's each day with 6
> hrs of sunlight where the battery is discharged no more than 50% (one of
> the things she'll test).
> Can you give me some estimates about what is needed to power the NUC
> you're testing, a hard drive with iiab, and an access point?

The average NUC power is about 9 watts, and the AP that I have running from
village telco draws 1.5 watt (and runs on 9-15 volts -- good for lead acid
batteries).  I don't think village telco units are easily available from
amazon.  Maybe someone else knows.

> 1. Approx what # of watts per hour do the panel(s) need to generate to run
> the system for, say, 3 hours per day...assuming 6 hours of sunlight and
> maintaining a proper discharge of the battery.
Well, if you need 300 whr for  10 XO's, and 30jwhr to run the NUC for 3
hours, the bar minimum is 330 watt hours per day. Then you need to factor
in losses in charging of battery, overcast days, etc.  So if you had a 100w
solar panel working for 6 hours per day, with clouds, overhanging trees,
lack of proper sun orientation, you'd probably be lucky to get 330 watt
hours per day

> 2. Is the 10 amp charge controller (described on the website) sufficient
> or would a 20 amp be better?

depends a lot on the size of your solar panel. In my fixed single 100 watt
solar installation, I've never seen more than 65 watts (5Amp).

> 3. Is more than one 12V battery needed?
batteries come in different capacities.  If you want to handle a few cloudy
days the trojay 105 AHR 12v battery should really only be used to store 600
watthours (use half). With losses, that's not really enough for 2 days
overcast. So probably two 6 volt trojan t-105's, which are rated at 225AHr,
might be a better choice

> 4. Can you power an access point from DC  (please pardon my ignorance)  If
> not, is there a low cost true sine wave inverter that you can recommend?

It's worth your time to find a 12 powered AP I think. I've been impressed
with the support we can get for village telco units.

> Thanks.
> Ben
> On Fri, Jun 20, 2014 at 6:10 AM, George Hunt <georgejhunt at gmail.com>
> wrote:
>> Tony,
>> I'm currently running the i3 NUC off of a solar charged LA battery. Boots
>> fine. Per Richard Smith's analysis, I'd say that the NUC can handle the 14+
>> charging/equalizing cycles, but might not get a full 12v in really cold
>> climates (with the internal 2.5 hard disk running on the 5 volt rail, and
>> the motherboard probably using buck converters to much less than 12, I'd
>> expect it to work well).
>> On Fri, Jun 20, 2014 at 12:42 AM, Tony Anderson <tony_anderson at usa.net>
>> wrote:
>>> George,
>>> Great news! It sounds like this may turn into the hardware of choice for
>>> a school server in the coming
>>> year. I'll try to see how to get one in EU - may have to wait until I
>>> get back to Germany in a few weeks.
>>> If possible, could you verify that it boots and operates from a 12v
>>> battery? This is the environment in the Kokobe school in Lesotho. I would
>>> like to swap out the MSI and operate a server directly from the battery.
>>> Tony
>>> On 06/20/2014 01:54 AM, George Hunt wrote:
>>>> the i3 NUC arrived, has an upgraded bios, and is running the hard drive
>>>> that I removed from the MSI, successfully headless. The annoying thing is
>>>> that they changed the video output to micro hdmi.  Fortunately I had an
>>>> adapter.
>>>> the Documentation is specific that it will run on 12-19.  I was
>>>> concerned that lead acid batteries might go lower than that during deep
>>>> discharge, but referring to the charts suggests that at capacity in amp
>>>> hours divided by 20 gets down to 12 volts at 30% remaining charge. Docs at
>>>> http://downloadmirror.intel.com/23089/eng/D54250WYB_
>>>> D34010WYB_TechProdSpec05.pdf
>>>> The NUC idles at 8 watts, spiking to 16 when it's doing anything
>>>> intense.
>>  --
>> Unsung Heroes of OLPC, interviewed live @ http://unleashkids.org !
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