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"" Influences on Solar Power
Sunlight
Solar irradiation is measured in Peak Sun Hours (PSH).
* With three-way fridges, solar is practicable at 2 PSH.
* With an efficient chest fridge it becomes practicable at 3 - 3.5 PSH.
* For a medium-sized door-opening electric fridge you really need 4 PSH.
It's also advisable to have generator back up ""


As I read this, it's suggesting that with a "three-way fridge, solar is practicable at only 2 Peak Sun Hours" and "an efficient chest fridge it becomes practicable at 3 - 3.5 Peak Sun Hours"

To me it appears to suggest that an "efficient chest fridge" is much therefore LESS efficient than a 3 way fridge when used on 12 Volt... or said another way, a 3 way fridge is MORE efficient than an EFFICIENT chest type fridge.

Maybe I just don't understand it at all, I believe a 3 way fridge runs @ ~10 Amps, whereby a Efficient chest fridge would be as low as ~5 Amps.

It's claimed the article is written by: Collyn Rivers and was last Updated: 10 Jun 2008, assumingly by him also.

Need some-one to clarify it please...
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Reply By: GerryP - Tuesday, Mar 24, 2009 at 21:40

Tuesday, Mar 24, 2009 at 21:40
Hi Mainey,

I see (and share) your dilemma. PSH is a measure of the daily available sun energy measured in kWh/m².

If you were to run the fridges mentioned somehow from solar power, then the 3 way would be either 12V direct or 240 through an inverter. Either way, it would have to draw a lot more than a chest type or medium size fridge.

Further, when you look at the two different refrigeration systems quoted, the 3 way uses an absorption principle which has a COP (see below) of around 0.6 whereas a vapour compression system would probably be around 3.

COP or Coefficient of Performance is the ratio of energy input to refrigerated heat energy transferred from the product to outside. Hence you can see straight away that the absorption system used in the 3 way is far less efficient to start with.

Mainey, I'm with you - just does not compute.

Cheers
Gerry
AnswerID: 355965

Follow Up By: Maîneÿ [wa] - Tuesday, Mar 24, 2009 at 21:56

Tuesday, Mar 24, 2009 at 21:56
Gerry,
it's just too difficult or I would suggest, impossible for me to believe Collyn Rivers has posted it, makes me wonder who really did the "update" ??

Mainey . . .
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FollowupID: 623979

Reply By: Member - Robert R1 (SA) - Tuesday, Mar 24, 2009 at 21:48

Tuesday, Mar 24, 2009 at 21:48
Hello Maîneÿ [wa],

I have just looked in Collyn Rivers' book "Solar That Really Works - Motorhome addition". When working out the amount of power used he assumes the three way fridge is run on 12v from the starter battery/alternator when the car is running, 240v when it is availabe, and gas when you are camping so there is no draw on the solar panels. The three way fridge draws so much power (approx 18 Amps) that you would have to have a huge solar setup to run it. The 2-3 peak sun hours is for the other electrical appliances e.g. lighting, water pumps, tv, radio etc.

With an efficient chest fridge it is feasible to use solar because the current draw is so much less and within the range of an average solar setup.

Regards,
Bob
AnswerID: 355969

Follow Up By: Maîneÿ [wa] - Tuesday, Mar 24, 2009 at 22:22

Tuesday, Mar 24, 2009 at 22:22
Bob,
I fully agree with what you have read in Collyn's book, that's why I have 'implied' he did NOT write the update at all.

What I'm referring to is the reference that a 3 way fridge is some-how MORE efficient when run on 12 Volt or/and Solar than an 'efficient chest fridge' which any-one will suggest is just absolute total rubbish when comparing current draw by each type of fridge mentioned.

* With three-way fridges, solar is practicable at 2 PSH.
* With an efficient chest fridge it becomes practicable at 3 - 3.5 PSH.
* For a medium-sized door-opening electric fridge you really need 4 PSH

It clearly states, with-out any assumptions:

Solar is practicable at 2 'Hours' for a 3 way fridge
Solar becomes practicable at 3 - 3.5 'Hours' for a chest fridge (almost twice as many hours of sunlight than the 3 way fridge, but still a realistic number, only IF the solar system capacity is large enough)
NOTE: -have used 'Hours' to indicate "PSH" to make it simple-

Mainey . . .
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Follow Up By: Sigmund - Wednesday, Mar 25, 2009 at 06:46

Wednesday, Mar 25, 2009 at 06:46
Why not email him?

Address is in his book IIRC.
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Follow Up By: Pete Jackman (SA) - Wednesday, Mar 25, 2009 at 13:25

Wednesday, Mar 25, 2009 at 13:25
Maîneÿ

You need to read the whole article, not just pull one paragraph out and criticise it. :o)

If you look at the "Fridges" section near the bottom it clearly states the assumptions that support the 2PSH claim at the top:

"If money is tight a better choice may be a Domestic Climate Class 'T' three-way fridge. These fridges run on 12-volts whilst driving, 240-volts where mains is available and gas at all other times. The 'T' indicates the fridge is designed to run in ambient temperatures up to 43 degrees C. Use this type of fridge and you may need only a single 120-165 watt module (see later for specifics). "

So if you use a 3 way as described then you only need to support lighting and other domestic use - hence the 2 PSH.

Refirgeration is the big user of power.

Having said all that we survive with 90 watts of panels and 75 AH of gell cells for extended stays running a Waeco CF50 as a fridge, a water pump, various lighting and chargers and the occasional DVD onthe laptop.

If it is going to be cloudy we take the 3 way and leave the Waeco behind

Cheers

Pete

Any mug can be uncomfortable out bush

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Follow Up By: Maîneÿ [wa] - Wednesday, Mar 25, 2009 at 22:07

Wednesday, Mar 25, 2009 at 22:07
Pete,
This IS the whole section relevant to my post:

"Influences on Solar Power
Sunlight

Solar irradiation is measured in Peak Sun Hours (PSH)
The concept is like that of a rain gauge in that fluctuations are averaged: replace rainfall by sunlight and you have the general idea.

* With three-way fridges, solar is practicable at 2 PSH
* With an efficient chest fridge it becomes practicable at 3 - 3.5 PSH
* For a medium-sized door-opening electric fridge you really need 4 PSH
It's also advisable to have generator back up."

This clearly states a three-way fridge will run on just 2 Peak Sun Hours per day.

To suggest "an efficient chest fridge" requires MORE current to run than a "three-way fridge" is absolutely ludicrous.

A "three-way fridge" uses at least double the current to run from 12v than a "chest type fridge" so why does it require only HALF the Peak Sun Hours?

Mainey . . .
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Follow Up By: get outmore - Wednesday, Mar 25, 2009 at 22:37

Wednesday, Mar 25, 2009 at 22:37
hes right mainey - its all right there in the article
albeit a bit ambigously written


there is the first bit which you have quoted
and further down is the info on fridges which rates the relative efficiencys of electric only fridges where the shest fridge is stated to be most efficient

he then mentions the 3 way fridge which effectivly has no 12 volt current draw while stopped


Personally i would have made it a bit clearer but i guess he assumes all fridges being used for there desighned purpose.
he does actually mention this for a 3 way

12 volt while driving, 240v when stopped if available and gas if not

at no stage does it require 12 volt solar input under these conditions
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Follow Up By: Maîneÿ [wa] - Wednesday, Mar 25, 2009 at 23:39

Wednesday, Mar 25, 2009 at 23:39
The point I'm making is the comparison between the 12v current required to run each of the 3 different types of fridges can be 'replaced' by the nominated number of PSH as nominated for each fridge.

* With three-way fridges solar is practicable @ . . . 2 PSH
* With an efficient chest fridge is practicable @ . . . 3 - 3.5 PSH
* For a medium-sized door-opening fridge @ . . . 4 PSH


This clearly states a three-way fridge will run on just 2 Peak Sun Hours per day.

A "three-way fridge" uses at least double the current to run from 12v than a "chest type fridge" numbers range from 10 Amp up to 18 Amp.

So why does it require only HALF the Peak Sun Hours to replace more than DOUBLE the 12v current used by a "chest type fridge" which nominally uses only ~5 Amps ?

Mainey . . .
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Follow Up By: get outmore - Thursday, Mar 26, 2009 at 02:52

Thursday, Mar 26, 2009 at 02:52
??

this is now a non issue
its been pointed out to you that lower in the article it explains how that is possible

for some reason you seem to be unable to read this part of the article

An electric-only fridge gobbles 60%-80% of daily electrical draw. Chest-opening types are the most efficient; door-opening types use more power. A realistic maximum is 170 litres. This will need three (ideally four) 120-watt modules. If money is tight a better choice may be a Domestic Climate Class 'T' three-way fridge. These fridges run on 12-volts whilst driving, 240-volts where mains is available and gas at all other times

if you stop obsessing over just that paragraph and read the article in its entitirety it will make sense to you
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Follow Up By: Maîneÿ [wa] - Thursday, Mar 26, 2009 at 08:59

Thursday, Mar 26, 2009 at 08:59
Mr. outmore,

Can I ask you one question and receive a 'yes' or 'no' reply?

Do you believe the power usage *COMPARISON* statement, as shown below, is technically correct ??

* With three-way fridges solar is practicable @ . . . 2 PSH
* With an efficient chest fridge is practicable @ . . . 3 - 3.5 PSH
* For a medium-sized door-opening fridge @ . . . 4 PSH


Simplistically written:
Do you believe a three-way fridge uses almost ½ (~HALF) the 12v current required to run an efficient Chest type fridge?


Or maybe I should ask; do you believe a three-way fridge is more efficient on 12v battery power than a similar sized Engal fridge, when run ONLY on 12v ?

On 12v the maths are very simple
# a three-way fridge uses . . 10 to 18 Amps
# a chest type fridge uses . . 3 to 8 Amps


Obviously the question is in reference to the number of Peak Sun Hours of Solar power that's required to recharge a 12v battery when powering each of the three different types of fridges nominated.


We are specifically talking about the number of PSH required to RECHARGE the 12v battery, by a Solar panel, when running each of the three fridge types nominated.
The fact that a three-way fridge can also run off 240v or gas is not relevant.

Mainey . . .
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Follow Up By: Pete Jackman (SA) - Thursday, Mar 26, 2009 at 15:05

Thursday, Mar 26, 2009 at 15:05
Hi Maîneÿ,

I too have Colin's book "solar that works" where it is quite clear that he assumes a 3 way would be on gas in camp - a the article on here also clearly states if you read it as a whole rather than just pull small quotes out of context..

Most of us seem to read that this:

"* With three-way fridges solar is practicable @ . . . 2 PSH
* With an efficient chest fridge is practicable @ . . . 3 - 3.5 PSH
* For a medium-sized door-opening fridge @ . . . 4 PSH

Was never a fridge power use comparison - that is only what you are trying to read into it.

If you are using a 3 way fridge as described further down in the same article (ie on gas when stopped) then a solar setup is feasable at 2 PSH as most other battery drwas are quite low. This is my experience as well. If I take my 3 way and run it on gas then my 90W of panels can easily keep up with the other power draws, even in overcast weather.

I agree that on 12V a 3 way is a power pig and no reasonable solar system (one that could be transported in the typical 4by) could keep up with it. I measured my 3 way pulling over 12 amps which would flatten my batteries in under 5 hours and need arounf 400W (nominal) of panels to keep up with it. But only a dope would run a 3 way off batteries (as I did once when I left it plugged into the car while stopped and had to jump the Pajero off my gell cells)

"Obviously the question is in reference to the number of Peak Sun Hours of Solar power that's required to recharge a 12v battery when powering each of the three different types of fridges nominated. "

No, obviously the question is in reference to the number of Peak Sun Hours of Solar power that's required to recharge a 12v battery when powering each of the three different types of fridges nominated in their most efficient operating mode.

"We are specifically talking about the number of PSH required to RECHARGE the 12v battery, by a Solar panel, when running each of the three fridge types nominated. "

Agreed, but the 3 way is on gas as noted further down in the article.

"The fact that a three-way fridge can also run off 240v or gas is not relevant."

That is very relevant. You could equally argue that the lighting might be 240V 75W incandescents run through an inverter - equally stupid as running a 3 way on 12V when camped.

Pete

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Follow Up By: get outmore - Thursday, Mar 26, 2009 at 15:09

Thursday, Mar 26, 2009 at 15:09
I dont believe this

its all in the article

why would you use a 3 way fridge on 12V solar power? he never says you would - its not desighned for this

given the assumption is the fridge is used for iits purpose as he states


then yes

the 2 psh is to power the rest of the requirments

it really is all in the article. others have read it and come to the same concluson

I can only assume you are attempting to discredit the author but have failed due to lack of reading comprehension or selective reading.

its stuff like that why the Author got sick of the forum and left


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Follow Up By: Maîneÿ [wa] - Thursday, Mar 26, 2009 at 18:49

Thursday, Mar 26, 2009 at 18:49
the entire section RELEVANT to the post is:

"Influences on Solar Power

Sunlight
Solar irradiation is measured in Peak Sun Hours (PSH).
The concept is like that of a rain gauge in that fluctuations are averaged: replace rainfall by sunlight and you have the general idea.
With three-way fridges, solar is practicable at 2 PSH.
With an efficient chest fridge it becomes practicable at 3 - 3.5 PSH.
For a medium-sized door-opening electric fridge you really need 4 PSH.
It's also advisable to have generator back up"


Using the analogy the nominated "2 PSH" is NOT used to power the three-way fridge, but ONLY the accessories, obviously you will also have to ADD the same "2 PSH" to both the other two fridge numbers also, for a realistic direct comparison.

Unless of course the "2 PSH" is already added to both the fridge numbers?

If that's the case, 1 PSH to 1.5 PSH will definitely run a chest type fridge daily?

With the three-way fridge running on gas, it's NOT relevant to battery recharging with a Solar panel, only the accessories are, but they are NOT mentioned, the fridge is and I have to believe what I read, not what I think it may mean and have it clarified on another page.

Yes, I believe it's very poorly written, as I've misunderstood the heading "Influences on Solar Power" to actually be inclusive of ALL the 3 fridge types nominated because it mentions the three-way fridge, it does NOT mention any accessories.
(maybe the other two fridge's were run off 240v anyway)

If you look further up I've stated I DON'T believe Collyn R wrote the update, as I'm definitely NOT attempting to discredit Collyn in any way, but to understand how a three-way fridge runs on 2 PSH.
( Yeahhh, I know it won't )

Mainey . . .
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Reply By: Best Off Road - Thursday, Mar 26, 2009 at 06:39

Thursday, Mar 26, 2009 at 06:39
Mainey,

It's very clear to me, and others above.

Collyn is saying if you run a three way fridge there is no need for it to draw on your solar system, you run it on gas when camped.

Hence you only need solar to run lights, pumps, TV's etc. And that need is less without the need to run a 12V compressor fridge.

Cheers,

Jim.

AnswerID: 356232

Follow Up By: Pete Jackman (SA) - Thursday, Mar 26, 2009 at 15:14

Thursday, Mar 26, 2009 at 15:14
Jim,

You forgot the latte machine, cigar humidor, temperature controlled wine storage, hair dryer for SWMBO, hair straigthener for the bush princess, play station etc etc.

:o)

Pete
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