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Running a freezer from an off-grid PV system.

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Posted by James Washer on January 2, 2005, 10:06 pm
I thinking about better ways to run a freezer from a PV system.

If memory serves, I think most freezer manufacturers say that freezers
will "keep" for a few days in the event of a power outage, provided one
doesn't stand with the door open trying to decide what to have for dinner.

If they can survive for a few days, they CERTAINLY can survive over
night.  With that in mind, would I be better off running the freezer on
a timer, so that it can ONLY cycle on during the sunlight hours, while
I'm producing PV power?

I supposed an advanced freezer might even take this into consideration,
and only cycle the compressor during daylight hours or under unusual
conditions ( like the owner coming home at 10PM and putting a bunch of
non-frozen items into the freezer).

Is anyone doing this? Has this been discussed here before?

  - jim

Posted by Dale Farmer on January 3, 2005, 12:46 am

James Washer wrote:

    If your energy management system just turns off the power to the
freezer during the dark hours, then the freezer will just run for a longer
time when the power comes back on to bring it down to setpoint.
Balancing this is the varied efficiencies of running it at different times
of the day with different ambient temperatures.  This is going to be a
major consideration in hot weather.  The further that the compressor
has to pump the heat uphill, the more power it will consume.


Posted by j on January 3, 2005, 1:15 am

Dale Farmer wrote:

Yes but.....

During the day, I have excess power from the solar array. Without
buying/maintaining more batteries, this power is simply wasted. My
thought was to just run the freezer during this time of excess power.

Further, in the summer, when the freezer has bigger power needs, I'm
producing even more excess power... so that works out well. In the
winter, I produce much less "excess" power, but then the freezer has low
(near zero?) power needs

I considered the fact that I'll be running the freezer during the day
when the ambient temp is higher, making it harder to "move heat" into
the environment... but then again, the freezer will be less prone to
warming back up at night, as the nights are quite cool here in the
Nevada desert. I'm not sure how the math will work out here.

Thanks for your original comments.. I'd appreciate keeping this dialogue
open, if you have further responses.

Posted by Charles Foot on January 3, 2005, 2:58 am
 Here on Great Barrier Island, where the entire island is off-grid it is
normal to run the freezer via a timer so that it gets 3 1-hour cycles
during the day and none at night.It helps too to keep it as full as
possible either with food or just bottles of water.

j wrote:

Posted by jim washer on January 3, 2005, 3:52 am

Charles Foot wrote:

I've heard this "full freezer" argument before. Thinking about it, I
guess it makes some sense... namely, the more "thermal mass" you have in
the freezer, the more "heat transfer" via the freezers insulation you
must have to raise the temperature some number of degrees.

  - jim

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