David:
You are right holding plates store energy the same as batteries, but
they do not have the problems with maintenance and regular replacement
that batteries do. A full time cruiser or live aboard with twelve
volt refrigeration can wear out cheap batteries in less than three
years. Over the years when I was building holding plates I sold
hundreds of them with dual coils. Many of those plates were designed
as hybrid refrigeration 12 volt and engine driven. With the hybrid
system energy could be stored in both the batteries and in the holding
plates. When there were several no sun days the engine alternator and
engine driven compressor could replenish the stored energy. There is
a very small market for 12 volt solar powered refrigerators without
batteries. The hardware is available; motor controllers, soft start
variable speed and variable voltage compressors so why not use it. I
have many design upgrades in the 12 Volt Refrigeration Manual but they
all require battery support this one will not require batteries.

Richard Kollmann
http://www.kollmann-marine.com


It sounds like you are designing a refrigeration system that runs only
on
solar panels with no batteries in the system. Presumably a holding
plate
stores energy when there is no sunlight. If that is your plan, it
doesn't
make much sense to me. A couple of cheap golf cart batteries can store
as
much energy as a holding plate at a fraction of the cost. But back to
your
question.

If you look at solar panel specs you will see that typical "12 V"
panels
have an open circuit voltage of 15 or so volts and a voltage vs
amperage
curve that peaks in wattage at about 14 volts.



"David&Joan" wrote in message news:xvyKc.2985$_K2.2391@lakeread02...
Richard:

It sounds like you are designing a refrigeration system that runs only on
solar panels with no batteries in the system. Presumably a holding plate
stores energy when there is no sunlight. If that is your plan, it doesn't
make much sense to me. A couple of cheap golf cart batteries can store as
much energy as a holding plate at a fraction of the cost. But back to your
question.

If you look at solar panel specs you will see that typical "12 V" panels
have an open circuit voltage of 15 or so volts and a voltage vs amperage
curve that peaks in wattage at about 14 volts.

So, if your motor can stand 45 volts and can efficiently use power at that
voltage then you could have three standard 12 volt panels in series. If your
motor draws 5 amps then you need 5 X 14 = 70 watt panels assuming full
sunlight at 90 degrees incidence. But what happens if the motor stalls if
the panel's voltage/current drops as the sun moves past vertical? If the
motor needs a minimum of 5 amps at all voltages, then you probably need a
minimum of three 100 watt panels to assure that you have at least 5 amps for
most of the day.

OTOH if your motor can efficiently operate at 12 v and 5 amps then one 100
watt panel will work, but may not provide enough watthours for your daily
refrigeration load.

It all depends on how many watt hours you need to run the compressor and
store enough refrigeration when there is no sun. A good rule of thumb at low
lattitudes such as the Bahamas is that a solar panel of X watts will put out
3X to 4X watthours on a sunny to partly cloudy day.

You probably know this better than me, but a well insulated small icebox
will require about 50-75 amphours each day or 600-800 watt hours. Using the
rule of thumb above would indicate somewhere between 2 and 3 100 watt panels
will be required.

David


"Richard Kollmann" wrote in message
om...
Solar Panel Question
A motor had an expectable voltage range from 10 to 45 volts DC
without the use of batteries and required three amps minimum current
to run. The voltage must stay below 45 volts with a maximum current
draw of 5 amps.
How many 12 volt solar panels connected in series would provide the
most daily motor running hours? And what wattage panels would fit this
load requirement?
I know the size of panels will depend on sun hour days, but say it is
a sailboat in the Bahamas.