Submitted: Tuesday, Mar 29, 2005 at 20:35

ThreadID: 21602
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Replies:6
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Ok boys and girls ., its real time question time ; I want to know how big/watts a pair /suitcase style of solar panels + regulator I would require to run my Waeco 80lt + my 15lt engle ,,,combined draw = 6/7 amp per hr ,,Run off AGM batts x 240amps all up ,,,so how much solar to keep fridges on 24/7 and batts topped up for peak longevity,,,,bring out the calculators !!!!!

Tuesday, Mar 29, 2005 at 20:50

Now I don't know the answer and will not be getting the calculator out. But wouldn't you need to know the refrig load needed?? What is ambient temp? Temp of "load" and amount of "load" (read food and drink) in and required temp out. These things surely determine the load which then determines the time compressor runs, which them determines........ and etc. Or do your fridges just run continuously?

I guess some assumptions are required.

Rusty

AnswerID:
104213

Tuesday, Mar 29, 2005 at 21:18

Try the yahoo campertrailers site. http://groups.yahoo.com/group/campertrailers/If you join and go to the 'files' section there is a spreadsheet aclled fridge calculator that allows you to try quite a number of variables. You will be able to add the info you have and have it calculate how things may go. I found it very useful when selecting my power source (2 x 65W) to provide power for my 70L Trailblazer.

Let us know how you go with this!

Bundy

AnswerID:
104217

Tuesday, Mar 29, 2005 at 21:33

Hello Undertaker,From your supplied information your load is 7Ah * 24hrs = 168Ah per day.

Therefore you need to replace that as an absolute minimum for the system to remain in equilibrium. Factor in a minimalistic over capacity charging of 10% and your looking at supplying 185Ah per day to your batteries to stay ahead of the load.

Given you'll get say at best 6 hours of useable sunlight per day, you've got to shove that 24 hour load back in a 6 hour period. Or 25% of a day.

From that we can see you'll need to charge at 185Ah * 4 = 740Ah in that 6 hour period or roughly 124Ah every hour.

If we do it at 14volts, that works out at 124Ah / 14 = 8.9Amps.

From that we can say the following, 14volts * 8.9Amps = 125Watts of theoretical panel capacity.

I've deliberately not used the battery capacity in any of the calculations, your chosen batteries if fully charged are more than sufficient to carry you through the night.

If you think you'll get more or less sunlight than my expectations, just plug your numbers into my calc's.

Note: In all my calculations I've rounded the answers to a safer value, producing a slightly larger theoretical panel than using numbers to 2 or 3 decimal places.

Hope that helps,

Geoff.

Geoff, Landcruiser HDJ78, Grey hair is hereditary, you get it from children. Baldness is caused by watching the Wallabies. Lifetime Member |

AnswerID:
104220

Wednesday, Mar 30, 2005 at 00:03

Questionis the figure of 7 A/h correct?

just seems a hell of a lot of power to run two fridges.

Would the power consumption be less during the night as the fridges would be only running a few times during the nite, wouldn't they ? ?

I think it would be far more efficient, electronically speaking, and possibly financially also, to have only one large fridge/freezer!

FollowupID:
361699

Wednesday, Mar 30, 2005 at 05:46

Geoff,You will have to recalc with the dutycycle figures when Undertaker supplies it?

Guessing here : 7A/h for 8hrs[100% DC].......3.5A/h for 16hrs[50% DC] would represent pretty extreme conditions

ergo: 56+56 =112Ah/24hr cycle

cheers

FollowupID:
361701

Wednesday, Mar 30, 2005 at 18:38

Mainey ,6/7 amps per hr average over a 24hr period ,80lt Waeco ,4 lights = 3.5 amps per hr, ambient temp 10 to 34c....Engle 15lt no2 on dial = 3.2 amps per hr ,ambient temp as for Waeco ,,,,,ever tried lifting a full 80lt Waeco ? use the baby Engle for drinks in camp and away from camp.

FollowupID:
361759

Wednesday, Mar 30, 2005 at 19:56

Geoff M , so 2x 65watters should be enough , 2x 75s having some to spare ,, thanks for the info.
FollowupID:
361771

Wednesday, Mar 30, 2005 at 20:48

Now that I am sober........I calc it this wayBased on your 185Ah [usage + extra] for the 24hrs

In 6hrs of unchanging output from the panel, it would require

185Ah/6h = 31A [30.83A] ie the panels must supply 31A for 6hrs.

At the suggested voltage of 14V it would require 14 x 31 = 434W

What do you think?

cheers

FollowupID:
361777

Wednesday, Mar 30, 2005 at 22:13

Hello Wok,No, I don't calculate it your way,

I've come up with the idea of 740Ah in the 24 hour period, distilling that down to 6 hours of useable sunlight per day I've calculated 124Ah (or 124 Watts) for every hour of that useable sunlight.

My calculations are fairly well supported by the best test yet, real world results from members such as Jimbo and others who have put the wallet next to the calculations.

I still believe a gram of theory is worth a kilogram of practical results.

Geoff.

Geoff, Landcruiser HDJ78, Grey hair is hereditary, you get it from children. Baldness is caused by watching the Wallabies. Lifetime Member |

FollowupID:
361785

Thursday, Mar 31, 2005 at 06:59

Firstly, let me say that a] I am not suggesting a panel size for The Undertaker [that needs the DC values]

b] I am not ' stirring' you .... I apologise if it appears that way...trying to be constructive

=====================

The figures don't add up.

For the panel supplying 8.9A for 6hrs.......8.9 x 6 = 53.4Ah [c.f 185Ah required]

Another approach is,

7A for 24hrs >> 168A

Add 10% >> 185A

For 6hrs charging >> 31A

=====================

I am not disputing Jimbo's experience [or any other Forumites :)]

peace..................:)

FollowupID:
361799

Thursday, Mar 31, 2005 at 07:25

Hey Wok,No arguments mate and I don't see you as a stirrer, your just not seeing my maths and I'm not seeing yours. Simple misunderstanding, would be darn easy to clear up over a beer and a pencil and paper! (I dislike internet forums, e-mail and SMS for the communication confusion they cause, they are not true two way communication, just verbal vomit)

We're both saying fundamentally the same thing,

You've said that 8.9A * 6Hrs = 53.4Ah, spot on for the total over 6 hours.

I've said, 14V * 8.9A = 125 Watts over a single hour, the panel size required to do this for an hour. Then we leave it in the sun for 6 hours.

I'm thinking we are both saying the same thing, one over an hour the other over six hours.

Geoff.

Geoff, Landcruiser HDJ78, Grey hair is hereditary, you get it from children. Baldness is caused by watching the Wallabies. Lifetime Member |

FollowupID:
361801

Thursday, Mar 31, 2005 at 08:09

Hi all,Wok is correct. If the useage is 185 Amps / day and you have only 6 hours to put back 185 Amps then your hourly input is 185 / 6 = 31 Amps per Hour for 6 hours.

An 80W panel has a Peak current input of 7.1 Amps at 17 volts but in reality puts in around 5.5-6 Amps at around 13.5V due to heat losses and not being at the optimum angle for the whole day. Therefore you would need around 5-6 panels.

I have a 90W + 60W Bifacial panel that I bought for a tryout last week. For a moderately overcast day I could produce 14.6 Amps for the day with it and that was changing its position every hour. On a sunny day I can produce 27 Amps for the day.

As I don't stay in the one place for more than around 5 days, I calculated I only need enough charge input to keep me going for that long so I don't need to put in what I have taken out for the day.

I also have a Waeco 80 and with its duty cycle worked out (it is also stated in the manual) and using an electric water pump and fluro light I worked out:

Duty cycle at 20 °C (night) 25% - 7.5A * 25 % = 1.875 A/hr @ 12 Hrs

Duty Cycle at 30 °C (Day) 35% - 7.5A * 35% = 2.625 A/hr @ 12 Hrs

Total Fridge = 54 Amps / Day

Fluro = 1 Amp * 4 Hrs = 4 Amps / Day

Pump = 1.9 Amps * 1 Hr = 1.9 Amps / Day

Total draw = 59.9 Amps per day

So my panel puts back half of what I use in a day. If I bought a second panel then I would be self sufficient providing it doesn't get overcast.

The 6 hours used in solar calculations is peak sun hours ie maximum solar radiation for maximum current production. I noted that at 7.30 in the morning when the sun had just poped up over the trees I was producing 2.9 Amps.

The Engel consumes around 3.5-4.6 Amps (roughly) and with a duty cycle of say 30% (providing it is not left in a hot confined space) then it would draw around 32.4 Amps / Day @ the 4.5 Amp rating (worst case). Adding this to what I get above that would eaqual:

Total = 92.3 Amps / Day which is around half of what you worked out. Add to this a 10% loss for cables etc then a realistic figure would be 101.53 Amps / Day.

That should give a good indication of the number of solar panels to use (just remember that if the solar panel says Peak current is 7 amps - actual figure you will be able to produce is around 75 - 80 % of that figure)

Hope this helps.

Regards

David

FollowupID:
361806

Thursday, Mar 31, 2005 at 13:53

Grungle, Are the power consumption figures too high at 185Amps per 24 hours!

Your post "An 80W panel .... in reality puts in around 5.5 to 6 Amps at around 13.5V due to heat losses and not being at the optimum angle for the whole day"

is fundamentally true, being 5.5wts x 6 hours = 33Amps, or 6wts x 6 hours = 36Amps, however, it contradicts the rest of your post?

(Quote) I have a 90w + 60w Bifacial panel that I bought for a tryout last week. For a moderately overcast day I could produce 14.6 Amps for the day with it and that was changing its position every hour. On a sunny day I can produce 27 Amps for the day.(end quote)

Your sunny figure of only 27 Amps for the entire day from 150w of Solar panels (90w plus 60w) I believe, is far too low when you can obtain as you have stated above, 5amp from one 80wt panel, in the same conditions, that equates to 25 amps in 5 hours, plus the 2 or 3 hours prior and also after the peak sunshine hours, (10 to maybe 22 amps) as the panel works from the time it is in the sunshine till it is out of the sunshine creating power, as you have posted above; “The 6 hours used in solar calculations is peak sun hours, ie maximum solar radiation for maximum current production. I noted that at 7.30am when the sun had just popped up over the trees I was producing 2.9 Amps.”

--> Not seeking an argument, just some clarification of the numbers<--

I use a 80w Solarex panel and obtain the same numbers you have quoted, being 5 amp in peak sun, and starting as the sun hits the panel at lower numbers, it ran a ‘power hungry’ fridge without hassles, now I have ordered a new larger fridge, still of the same design, that due to more efficient electronics, will run at even lower figures than those quoted here!

FollowupID:
361835

Thursday, Mar 31, 2005 at 20:33

Sorry - you are right that it doesn't add up as there is a typo "80W" should read "120W". A 120 W solar panel generates 7.1 clamed as seen here.Actual solar figures is explained well here.

My Bifacial Solar Panel I have had for a week but Easter gave me a great deal of time to really test it. Yes it is 90W + 60W = 150W ( 5.29 Amps + 3.52 Amps = 8.81 Amps) but this is claimed and I could generate nothing close to this.

Over the weekend and in a mixture of rain, over cast and perfect conditions I managed to generate a maximum of 5.8 Amps (64% of claimed) on a cloudless sky with our duchess mirror 2 meters behind the panel directing perfect sunlight onto the reverse of the panel. Now this is not practical out bush but using white card I could generate 5.1 Amps (57% of claimed) and with no reflective material I could generate 4.8 Amps (54% of claimed) at best (this was utilising only the 90w side of the panel).

During rain I could generate around 0.2 Amps and on a moderately overcast day I could generate between 1.9 - 2.4 Amps.

The Bifacial compared to the output of a 120W panel generates around the same Amps (roundabouts) but when you factor in cost then the Bifacial comes out on top (120W $1050 - Bifacial $770 on special). If you manage 5 Amps from a 80W panel then that would be better cost wise than both the 120W and Bifacial.

The Bifacial could be improved a great deal by moving the connection box on the reverse side to the outside edge as it does shade around a quarter of 2 cells. I did a test using a Fluke Amp Meter in series with the load to see how much shading affects these panels. At full production single side if I moved my hand over a cell slowely, current production would drop from 4.8 Amps to 2 Amps when 1 cell was a a third shaded to under 1 Amp when 1 cell was three quarters shaded. This is a big drop.

Also using say a polished stainless steel backing would improve the 5.1 Amps I got with white card but not to the extent of using a mirror a couple of meters away at an angle.

I don't know if I am happy with the Bifacial until I get to test a 64W, 80W or120W panel under the same conditions to see what produced the highest Amp / Watt at the lowest Cost / Watt.

As stated in my previous post we are camping in one spot for no longer than 5 odd days so its output is enough to keep everything going without damaging batteries long term through over discharge but I am interested how it stacks up in reality (with definitive test figures) against single sided panels and cost wise.

Regards

David

FollowupID:
361905

Wednesday, Mar 30, 2005 at 01:24

Get a gennie LOLOLOLOLOLOLOL

AnswerID:
104258

Wednesday, Mar 30, 2005 at 18:26

Have a generator already ,works magic, but comes a time when solar may be a prefered option.
FollowupID:
361758

Wednesday, Mar 30, 2005 at 05:29

Mr. Undertaker,The dutycycles for the two fridges is required for calculation. This varies according to load,ambient temp,usage pattern etc.

cheers

AnswerID:
104259

Wednesday, Mar 30, 2005 at 07:32

Hey Wok,You are correct on re-calculating for Duty Cycle, but we don't have that number. (Or maybe we do, just that Undertaker called it 7A/hr)

See what the man comes back with for a duty cycle.

Best way to do this is charge the batteries to full (good 3-stage) run the system for 24 hrs in your typical camping scenario.

Then work out how much charge is left in the batteries and work backwards from their adding say a 10 or 20% loss/overcast factor to your panel size.

Geoff.

Geoff, Landcruiser HDJ78, Grey hair is hereditary, you get it from children. Baldness is caused by watching the Wallabies. Lifetime Member |

FollowupID:
361705

Wednesday, Mar 30, 2005 at 17:01

I have a single panel 100W Suntech which puts out - the best so far- 6.5amp via a PL20 regulator.I tested it out in the Murray Sunset park a bout two weeks ago and to get it to maintain the 6.5amps was a bitch in that it had to be positioned (moved regularly) and angled correctly to get that 'mother of all mothers' 6.5 amp.

In view of that I will be very interested in seeing what sort of 'briefcase folder' panel you end up with that suits your requirements.

Please keep us all posted.

Regards

Ken Robinson

AnswerID:
104345