[Energy] Spec-ing solar panel donation?

Sage Radachowsky sage.radachowsky at gmail.com
Wed Nov 30 12:26:06 EST 2011


Well the way it works is that a panel is called "nominal 12V" but provides
peak power at a voltage significantly higher than 12V, like 16V or so.  The
peak power point varies a bit based on lighting conditions, but panels are
called by a nominal voltage that allows them to charge a battery at that
voltage.

Here is an example:
http://www.amazon.com/Ramsond-Nominal-Output-Battery-Charging/dp/B005RUUNFA
This is a little 20 Watt panel with these specs: 12V Nominal Voltage Vmp:
17.6V Voc: 21.8V Imp:1.14A Isc:1.25A
That is 12V nominal, 17.6V maximum power, 21.8V open circuit, Current at
max power of 1.14A, Current at short circuit 1.25A.

I always recommend an MPPT charge controller. This means "Maximum power
point tracking" and this lets the charge controller convert the current &
voltage as needed to maximize the power extracted from the panel, and
pushed into the battery.  Here is the Wikipedia entry for
MPPT<http://en.wikipedia.org/wiki/Maximum_power_point_tracking>
.


And by the way, here's the same type of MPPT charge controller that I
brought to the camp to charge batteries:
http://www.amazon.com/SolarTorrent-STCMPPT10-Solar-Regulator-MPPT/dp/B0030H5ABY

- - - -
Let the sun shine in!

Sage



On Wed, Nov 30, 2011 at 12:06 PM, Douglas Breault <GenKreton at gmail.com>wrote:

> A 12 V panel is not ideal for charging a 12 V battery. Peak voltage is
> only obtained in good sunlight (a fraction of the hours available) and
> ideally you want more than 12 V to charge a 12 V battery anyways. Say you
> snag an 18 V panel, then you're only at 18 V during noon sun and you may
> actually be at 12 V during the first hours of day light. Also, keep in
> mind, a 400 W (440 W?) panel is working very well for us so if they are
> willing to get us larger ones maybe we should just take larger ones.
>
> - Doug
>
>
> On Tue, Nov 29, 2011 at 13:04, Sage Radachowsky <
> sage.radachowsky at gmail.com> wrote:
>
>> I would say 100 to 200 watts is a decent power though whatever is
>> available. 12v nominal is best though 24v works too. Higher voltage makes
>> it hard to find a good MPPT charge controller.
>>
>> Sage
>> On Nov 29, 2011 12:59 PM, "Dana Moser" <dana at occupyboston.org> wrote:
>>
>>> Greetings.
>>> Can anyone give specifications for a solar panel? I'd like
>>> to answer this message from Eric Broadbent (ebroadbent at me.com)
>>> -D
>>>
>>> ==============================**=========================
>>> Hi Dana - this is a response to my request for panels from
>>> a person who runs a solar firm.
>>> I should have known to be more specific. Let me know
>>> if you can get any specs - and I'll relay them back to him
>>> Thanks,
>>>
>>> -Eric
>>>
>>> Begin forwarded message:
>>>
>>> > How many do they want / need?  What power?  What operating voltage?
>>> > As you may know the vast majority of PV modules out there are set up
>>> for grid connected systems – not battery charging and thus, run at ~35
>>> volts Vmp.
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