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A question of power

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Posted by Jack Russell on July 5, 2005, 1:32 am
I just need to get this straight, I think have it though, so bear with me...

I am running a small 12v 9a water pump, 108w...so far so good...I have 95w
of solar on top of my trailer. At maximum output, the panels will replace
about 87% of the energy used by the pump...Correct? I will run the pump
twice a day for ten minutes for watering needs, so with a total of twenty
minutes run time, it will require, theoretically, about 23 minutes of
sunshine to replace what is used. Am I on track or is there more I need to

Thanks, Paul...

Posted by Richard P. on July 5, 2005, 5:39 am
Pretty darn close.  The one thing to consider is that is under the ideal

Consider the actual output of your PV when it heats up in direct sunlight.  It
will probably put out
a little bit less depending on the PV.  Second, if you are charging a battery
then consider the
losses caused by the charge controller.  For example, if the panel puts out 16
volts @ 4 amps =  64
watts.  But a charge controller will drop the voltage to say 13.8 volts @ 4 amps
which will only
give you 55.2 watts.

Just a couple of things to consider.  Perhaps the wire run from the panel to the
battery and on to
the pump might also have to be considered.  But otherwise I would say you aer on
the right track
with your calculations.

"Jack Russell"

Posted by Jack Russell on July 6, 2005, 3:02 am
 Thanks Richard, Here is some background:

I have a 2400gal storage tank that I fill using my generator. This little
pump/timer setup is for watering a small patch of grass in front of my
travel trailer that is our "Cabin". After much experimentation I just have
to use a Rainbird that requires a 4gpm Sureflo pump. It was the only way
that I was able to get water on the grass and not be there. The other thing
that was brought up was the need for a controller. This I also have. I just
needed to know if I was thinking correct about the recharge rate because we
are sometimes not there for up to three weeks.

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