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.

Each 12 volt solar panel you add in series is going to increase the voltage
by 12 volts i.e. 2 panels=24 volts, 3 panels=36 volts. If you want to
increase the current you need to connect the panels in parallel.

Take for example an exide 15 watt panel. Under optimum conditions this
panel can supply 12 volts at 1.25 amps. In reality, you should expect .7
to 1.0 amps from a typical 15 watt panel. To get 12 volts at 5 amps, you
would have to wire 5 or 6 panels together in parallel. If you want 24
volts at 5 amps, you wire 2 sets of six panels together in parallel and
then connect the 2 sets together in series. This would provide 24 volts at
5 amps which would get you about 120 watts of power.

Most of the 12 volt refigeraton units require between 2 and 8 amps depending
on the model.

lisa
www.ultimatepassage.com

Richard Kollmann wrote:

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.

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.

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.

Richard, I know this is a bit late, but I just arrived back home after
a couple of months on the boat (and I'm away again for another month).

A 50" by 20" solar panel (rated at 80 watts, for example), will
generate about 20 amp-hours per day if the panel is not adjusted to
face the sun as the sun (or the boat) moves. If you optimize the
panel's alignment, perhaps twice that - 40 amp-hours. The panel will
provide about 5 amps in full sun when properly aligned, less when the
sun's angle to the panel and the light intensity change.

If you connect panels in series, the voltages add, as another poster
pointed out. If you connect them in parallel, the current's add up.
(E.g 5 amps per panel gives 10 amps for two)

However, most panels are affected by shadows falling on the individual
cells; this reduces the output of the panel. Putting two panels in
series, where one is slightly shadowed and the other is in full
sunlight will affect the output of BOTH. You are better off connecting
them in parallel to avoid this.

Just as a note on my system: I have a cold-plate system (EZ-Kold)
that uses a Danfoss BD35 compressor. I have a 4.5 cubic foot box, with
roughly R20 insulation. About 1/4 of this is a freezer section, with
an insulated partition and spillover of cold air from freezer to
fridge section.

In Lake Ontario (43 degrees north) in the spring and fall, when air
temp is moderate (75 degrees or so), I use about 50 amp-hours per day
- the compressor runs about 50% of the time - on for about 3 hours,
off for about 3 hours.

I would need three "randomly oriented" panels to keep the batteries up
if solar were my only charging method.

(Richard Kollmann) wrote:

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


Larry Bradley VE3CRX
Remove "removeme" from my e-mail address for direct mail
Ottawa, Canada

(use the e-mail address above to send directly to me)

Larry, Thanks for providing information on solar power and
refrigeration at 40 degrees north. There are new BD35 compressors with
controllers that no longer need a battery's narrow voltage range to
operate. These new controllers are reported to be able to maintain
compressor speed with solar panel voltages from 10 to 45 volts, as
long as there is sufficient amperage. So the question will be, will
these new units use less amp hours, if three 12 volt panels are
connected in series.

I was surprised by your 50 amp-hrs per day until I saw that you were
using an EZ Kold unit. A 4.5 cu. ft. refrigerator with three inches of
good insulation in your cruising area, should consume no more than 30
amp-hrs per day.
Try this the next time you go cruising, disconnect the power to the
speed-up unit and use air cooling instead of water. The speed-up unit
destroys the coefficient of performance (COP) of the BD35 condensing
unit and the water pump current drain is not necessary. The compressor
may run longer but will only draw ½ the current.
Let us know what you find out.

http://www.kollmann-marine.com

Larry Bradley wrote in message . ..
Richard, I know this is a bit late, but I just arrived back home after
a couple of months on the boat (and I'm away again for another month).

A 50" by 20" solar panel (rated at 80 watts, for example), will
generate about 20 amp-hours per day if the panel is not adjusted to
face the sun as the sun (or the boat) moves. If you optimize the
panel's alignment, perhaps twice that - 40 amp-hours. The panel will
provide about 5 amps in full sun when properly aligned, less when the
sun's angle to the panel and the light intensity change.

If you connect panels in series, the voltages add, as another poster
pointed out. If you connect them in parallel, the current's add up.
(E.g 5 amps per panel gives 10 amps for two)

However, most panels are affected by shadows falling on the individual
cells; this reduces the output of the panel. Putting two panels in
series, where one is slightly shadowed and the other is in full
sunlight will affect the output of BOTH. You are better off connecting
them in parallel to avoid this.

Just as a note on my system: I have a cold-plate system (EZ-Kold)
that uses a Danfoss BD35 compressor. I have a 4.5 cubic foot box, with
roughly R20 insulation. About 1/4 of this is a freezer section, with
an insulated partition and spillover of cold air from freezer to
fridge section.

In Lake Ontario (43 degrees north) in the spring and fall, when air
temp is moderate (75 degrees or so), I use about 50 amp-hours per day
- the compressor runs about 50% of the time - on for about 3 hours,
off for about 3 hours.

I would need three "randomly oriented" panels to keep the batteries up
if solar were my only charging method.

(Richard Kollmann) wrote:

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


Larry Bradley VE3CRX
Remove "removeme" from my e-mail address for direct mail
Ottawa, Canada

(use the e-mail address above to send directly to me)

Richard, I don't have water cooling - Marvin didn't recommend it for
northern waters. The 50 AH is my total load, including lights, etc.
It's hard to tell what the compressor load on its own is, but it
appears to run about 50% of the time, perhaps somewhat less. I've
built a microprocessor-controller thermostat that records run times,
etc, for use next season, so I'll have more information and better
control than the mechanical thermostat.

I disabled the "speed control" on the EZKold soon after I installed
the system, as I found that the compressor ran more or less forever.
But I think I was trying to keep things too cold back then. I replaced
it with a 1500 ohm resistor, to let the compressor run at full speed.
But I gather from reading your web site that effeciency may increase
by matching the compressor speed to the box. I think I will install a
variable resistor in the new controller (or maybe have the computer
switch in different values) so that I can try to optimize things.

Given the situation for my system, any suggestions as to what level I
should try to run the BD35 at?


(Richard Kollmann) wrote:

Larry, Thanks for providing information on solar power and
refrigeration at 40 degrees north. There are new BD35 compressors with
controllers that no longer need a battery's narrow voltage range to
operate. These new controllers are reported to be able to maintain
compressor speed with solar panel voltages from 10 to 45 volts, as
long as there is sufficient amperage. So the question will be, will
these new units use less amp hours, if three 12 volt panels are
connected in series.

I was surprised by your 50 amp-hrs per day until I saw that you were
using an EZ Kold unit. A 4.5 cu. ft. refrigerator with three inches of
good insulation in your cruising area, should consume no more than 30
amp-hrs per day.
Try this the next time you go cruising, disconnect the power to the
speed-up unit and use air cooling instead of water. The speed-up unit
destroys the coefficient of performance (COP) of the BD35 condensing
unit and the water pump current drain is not necessary. The compressor
may run longer but will only draw ½ the current.
Let us know what you find out.

http://www.kollmann-marine.com

Larry Bradley VE3CRX
Remove "removeme" from my e-mail address for direct mail
Ottawa, Canada

(use the e-mail address above to send directly to me)