Solar System Sizing...

Submitted: Thursday, Mar 31, 2005 at 21:06
ThreadID: 21673 Views:5218 Replies:5 FollowUps:11
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Wonder if anyone could help me 'size' a solar set up for my Landcruiser to run a fridge and a freezer ?

My Deep cycle battery ( second ) is a Century N70T 75 amp Hours ..20 hrs..It has isolator switches and was installed by a competent electrical person who does this all the time..

Now I intend stretching the holiday to around 2 months and will be using a little Engel 21 litre as a freezer, and a 39 litre one as a cool/ fridge for salads etc !!...and we want to go to the Kimberleys June -July -August ( from Sydney) and stop wherever we wish...and have enough power to keep everything as it should be ..for a couple of days or so , ...without running the engine all day to keep up !
My sparky checked out my fridges consumption and when cold both draw approx 3.6 total.. when both running, less of course individually man however admits he has no ideas/ experience with solar panels etc....and I have very little idea anyway !!!

Hopefully someone out there with experience can fill me in on what I should consider / buy in the line of suitable panel(s) a good controller, and a battery monitor ???... that will let me see the state of charge etc.of my battery .?? and do I need all these things ??
Wondering also what the difference is between an Amorphous, Polycrystalline and Monocrystalline panels is !!!..its all a bit of a mystery at the moment !

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Reply By: Rosco - Bris. - Thursday, Mar 31, 2005 at 21:39

Thursday, Mar 31, 2005 at 21:39

From my limited investigations I reckon you'd probably need an 80 watt job. That should run the fridges and top up your battery during a good day's sunshine. 80W should give you 6.6 amps when full on so there's a fair safety margin.

That's the way I considering heading ... when I have the spare ching ching $$$.

AnswerID: 104590

Reply By: Member -Dodger - Thursday, Mar 31, 2005 at 23:50

Thursday, Mar 31, 2005 at 23:50
Engel fridges usually draw about 2.5 to 3 amps each when running so maybe your sparky got it wrong. You can check each one individually with a multi meter that has a 10amp plug on it.
I would suggest that you would need about 120watt panel total to build the battery up when stopped as the draw overnight from both units would lower the battery considerably.
I have a 64 watt panel and it manages to run the my engel during the day and when the fridg cycles it puts the power into the battery. Just enough to keep the battery going when stopped for a couple of days.
I used to have a handle on life, but it broke.

Cheers Dodg.

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AnswerID: 104613

Follow Up By: Member -Dodger - Thursday, Mar 31, 2005 at 23:55

Thursday, Mar 31, 2005 at 23:55
Forgot to mention, my panel is a unisolar panel, however I would recomend the Kycero panels as they are smaller for the power output.
The unisolar are supposed to be unbreakable and shade tolerant.
The others are glass and can be broken however if looked after properly will give goodservice for many years.
I used to have a handle on life, but it broke.

Cheers Dodg.

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FollowupID: 361945

Reply By: Mainey (WA) - Friday, Apr 01, 2005 at 01:07

Friday, Apr 01, 2005 at 01:07
I believe an 80 watt panel will only give you 'realistically' 5 Amps, times 5 hours at full sun = 25 watts, PLUS the few hours each side of 'full sun' will give you a further (maybe) 10 to 22 Amps daily. I have noticed some Isolator systems nowadays state they are suitable to be used with Solar panels, what this means I am not sure, maybe some are not ? I don't know the answer.
A 75 watt DC battery I believe is too small to do the job you are asking of it on a three month trip, yes, only my opinion, I had one 80 a/h and then added another in parallel, giving 160 a/h total and now don't have battery problems.
I don’t use a regulator as the power 'in' is a similar number to the power 'out' and the batteries are Calcium which can take the extra current when offered.
I also believe the 3.6 amp current draw of your two fridges combined to be a bit low!
(Quote) Hopefully someone out there with EXPERIENCE can fill me in on what I should consider/buy in the line of:
suitable panel(s)-> I use Solarex
a good controller-> depends on how deep your pockets are… do you NEED one?
battery monitor that will let me see the state of charge etc. of my battery-> a $30, 30 amp in/out gauge wired between the battery and the fridge shows the battery power to the fridge, also if the panel is wired via the fridge it will show the Solar power going to the battery.
(plug) if you want a good Isolator and Monitor I have both presently for sale, as I have recently upgraded...
AnswerID: 104615

Follow Up By: Steve - Friday, Apr 01, 2005 at 10:00

Friday, Apr 01, 2005 at 10:00
As for the experience comment...well have been to a couple of places who tell me that all I need is what they sell !!! ....but none have been able to explain why !!!...I have spent a few hours trawling the net to get some ideas and have bumped an article (the same) in 3 different places ...and countries !!!! am a bit hesitant to rush out and spend the beer money at the mo...
I do ask myself if i really need all this but in reality its almost a definite yes as I have had the 39 Engel flatten the battery in a couple of days when we were sheltering in 50C+ degrees end last year ...and a tad difficult when food starts to smell and the nearest 'shop' is 200 kms away ....thats when you toss the beer money !!
FollowupID: 361974

Follow Up By: Mainey (WA) - Friday, Apr 01, 2005 at 15:10

Friday, Apr 01, 2005 at 15:10
I can only say from my own experience, I don't believe you need a regulator if you have a large battery system, and I believe your battery system is far too small for a three month trip!

It's a lot cheaper to buy a 'decent' battery system initially than buy a 'decent' regulator, with a few cloudy days your "regulator" will not keep the fridge cool and the good woman happy, decent batteries will.
FollowupID: 362013

Follow Up By: Steve - Friday, Apr 01, 2005 at 16:13

Friday, Apr 01, 2005 at 16:13
Agree with you on the battery size: my problem is that I cant fit a larger one into the second battery box in my LC 80 Station Wagon space....unless someone knows of something that will fit that spot..?? anything with serious capacity is much larger and I have not come across one that fits..maybe you can help me on this one too!!
FollowupID: 362019

Follow Up By: Member - Jimbo (VIC) - Friday, Apr 01, 2005 at 17:10

Friday, Apr 01, 2005 at 17:10

Try the bloke at Federal Batteries in Sydney. Great for advice and has distributors all around Australia, 13.... no in yellow pages.


FollowupID: 362022

Follow Up By: V8troopie - Friday, Apr 01, 2005 at 18:31

Friday, Apr 01, 2005 at 18:31
Mainey, your follow up is a bit misleading, IMO.
"It's a lot cheaper to buy a 'decent' battery system initially than buy a 'decent' regulator, with a few cloudy days your "regulator" will not keep the fridge cool and the good woman happy, decent batteries will."

The function of a regulator is to make sure that a battery which is connected to a solar panel gets charged optimally.
This would apply to any size battery IF sufficient charging current is available.

The function of the solar panel is to provide that charging current.
If there is insufficient charging current available ( solar panel too small or battery is too large, then the regulator will most likely be always full on (not doing anything) while the fridge is switched on.

The function of the battery is to store this charge, so that its available whenever the fridge cuts in.

Its a balancing act, a bit like a wallet that would soon run empty if more is taken out as is put back in. However, wallets, unlike batteries, would not suffer from over charging ;-), which never happens - at least not to mine :-)

FollowupID: 362029

Follow Up By: Mainey (WA) - Friday, Apr 01, 2005 at 23:21

Friday, Apr 01, 2005 at 23:21
Klaus, I did not intend to make my post misleading, to clarify it more I think may complicate it even further……
I believe it is less expensive to buy a good Deep Cycle battery ($220) than a plasmatronic PL20 at $320, because as you have posted the regulator is only effective when the battery is at, or very near its full capacity, the regulator does not actually add power to the battery system, only regulating the power that is being produced by the solar panel, and then as you have stated, only when the battery system is somewhere near fully charged, they are mainly effective on wet cell batteries to avoid them gassing, boiling and running dry, whereby a sealed calcium DC battery can accept added power supplied by the solar panel on the few times it is available, because the fridge is drawing on the battery power almost constantly during the day light hours as power is being supplied by the panel.
A regulator is less effective on larger/oversized battery systems simply because they infrequently receive full charge from the panel when the panel is undersized by comparison and the fridge is running.

By doing the maths and also checking out previous solar panel tests on the forum, I believe you will find an 80wt solar panel will keep up with or exceed the power demands of an ‘average’ fridge, even by the numbers quoted of ~4amp (which I believe to be low) for 6 hours and a few extra amps each side of the 6 sunhours, because when the sun is on the panel it gives out some amperage, as you can see the numbers will quickly add up.
FollowupID: 362057

Reply By: V8troopie - Friday, Apr 01, 2005 at 01:10

Friday, Apr 01, 2005 at 01:10
Steve, rather than rehash what's been said many times over here, why not google for the answers re the different types of solar panels? The 'net is absolutely full of info about them.
About your panel wattage, it also depends how you are going to use the panel(s). Like, are they going to be fixed onto the roof rack and remain oriented flat? Are you going to site them at each stop so they face the sun for maximum output?
It *will* make a difference. Having them fixed on the roof is the least hassle but it also means you'll have to park the cruiser in the full sun every time you stop.

If you use mono or poly crystalline panels you have to make sure no part of the surface is shaded, a shade from a branch or something means the panel output drops to zilch. Amorphous panels give you a proportional output, shade half the panel and you get roughly half the current of the full panel in sun. These panels are also near twice the size of the other tyes, for comparable outputs.

If it was my trip I would use at least 120W of solar power AND make sure the panels get lots of sunshine whenever the engine is not charging the battery.

The best thing you can do is getting a little needle type Ampmeter ( rated for the maximum panel output current), fit it into a plastic project box and let it monitor the panel output all the time. It will give you a *very* good idea what's going into your battery. If you get a three stage solar regulator ( recommended) the meter will also show you when the battery is getting near full as the needle will start 'pulsing' rather than showing a steady charge current. When the battery is almost completely full the 'pulses get gradually shorter and the pauses longer until the charging current drops down to the trickle value which is most likely lower than the meter will register.
A simple Ampmeter is *much* more useful than a voltmeter for this purpose. It also draws virtually no power for itself and requires no batteries to work.
AnswerID: 104616

Follow Up By: Rosco - Bris. - Friday, Apr 01, 2005 at 07:22

Friday, Apr 01, 2005 at 07:22

Is the ampmeter connected in series in the +'ve wire from the panel ?

If so, does that mean all current flows through the meter ?

FollowupID: 361954

Follow Up By: Mainey (WA) - Friday, Apr 01, 2005 at 15:00

Friday, Apr 01, 2005 at 15:00
I have recently had a similar system installed as troopie has described.

The 30 Amp needle type -/+ Ammeter shows charge/discharge and goes 'in line' between the battery and the actual fridge socket which is mounted into the inside wall of the vehicle, allowing all wiring to be out of site inside the panels, the solar panel lead is also connected direct into the back of this socket with the lead from the battery, the power from the solar panel flows only one way, to the battery, via the fridge connection.
I think it is a 'HTM' brand, grey in colour and similar in design to a household power socket in appearance, but with only two connections (-/+).

It shows current flowing either, TO -> or <- FROM the battery...
investment $30
FollowupID: 362010

Reply By: Grungle - Friday, Apr 01, 2005 at 08:14

Friday, Apr 01, 2005 at 08:14
Hi Steve, I have just gone through the same thing myself.

If your fridges draw 3.6 Amps for the 2 running at the same time and you work out a conservative duty cycle of approximately 40% on 60% off then over 24 hours you will consume around 35 Amps / Day. Now the duty cycle does change quite a bit depending on ambient temperature.

A solar panel has a max current rating and for an 80W panel this is 4.55 Amps @ 17.6 Volts (4.55 * 17.6 = 80W). This is what the manufacturers claim.

In reality however a solar panel will only produce around 75% of the claimed current. This is because a panel is rated under test conditions and things such as panel temperature, atmospheric conditions, orientation, cable loses etc will have an impact. Also the fact that we are using the panel in a 12.8 Volt system (even though this contradicts ohms law of power = voltage x current) will add to the problem.

So for an 80W panel you will most likely get around 3.4 Amps. You may get more or less but there is no way of exactly working out what you will get until on the day.

Now work out what you will get for the day by multiplying the panel output (3.4 Amps) by the number of Peak Sun Hours in the day. This will vary on things such as Latitude and season. During Summer 6 PSH is usual and Winter around 3 PSH.

Therefore an 80W panel will produce around 21 Amps (3.4 x 6) on a sunny day. If you plan to stay in one spot indefinately then 2 panels should do the trick (providing it stays sunny) but if you only plan to stay in the one spot for a few days you should get away with one.

Regarding regulators I would recommend a 3 stage and the best I believe is the Plasmatronics PL20. This has everything but is around $350. I bought a Manson SBC-7120 off ebay for $130 and it does the same thing as the PL20 except does not show Ahrs out. The PL20 may have a couple of addition features but these are options which cost $. Do a search on the Solar sites in Australia for a better understanding of features, costs etc but also setups.

AnswerID: 104630

Follow Up By: Steve - Friday, Apr 01, 2005 at 09:49

Friday, Apr 01, 2005 at 09:49
This all makes a lot of sense to me last !!!....I see my real 'problem' as having a battery that is a tad I need to know if a battery monitor is different to a super dooper regulator or should i get a 'standard' regulator and a monitor ? I really will need to know how much 'fuel' is in the battery each which point I could turn down the fridges and conserve a bit over the night...
Thanks for your info..
FollowupID: 361973

Follow Up By: CT - Tuesday, Apr 05, 2005 at 18:35

Tuesday, Apr 05, 2005 at 18:35
An excellent reply that does the sums correctly too!

I've listed the performance of my system and all the relevent tech. in previous post 7531 if you wish to search the archives.

FollowupID: 362414

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