Portable Solar Panels

So Steve, Can you please answer this question for me? We have a 24 amp battery pack and if we were to hook up an 80 watt solar panel to this to run the fridge, would this not be sufficient??
Cheers
JO

Jo ,

Within 2 hours - 3 hours after sundown your fridge will stop !! 24 aH battery is not big enough to get you through the night .. You need a minimum of 75 aH preferably 100aH to give you enough running time overnight ..
All a solar panel should do is fillup the overnight battery loss and run the fridge at the same time during the sunlight hours .. depending on the Amps your fridge draws the 80 watt panel may not be big enough either ...

SO - I suugest a 100 aH AGM battery and a 100 watt solar Kit should see you OK until about day 4 of cloudy weather !!

Cheers

Steve

Hi Steve,
Thank you very much for your response!! I can under stand exactly what you are saying. Thanks for keeping it simple!!! And your patience!!
Cheers

Jo ,

I had better qualify that a bit -

There are a lot of assumptions and guesswork involved -
How often do you open the fridge ?
Ambient temperature ? If its hot fridge works harder uses battery quicker ..

If its cold then the fridge will not work as much etc etc ...

Rule of thumb is NOT to let your battery discharge to under 50% as this will eventually ruin it permanently .. so you really only have a 12aH battery to run a fridge at 4-5 aH - 3 hours flat out and fridge will stop as it cuts out when the voltage from the battery drops below a certain set amount ...

By way of example I have a Waeco 50 Litre powered by a 100aH battery attached to a 140 watt Solar panel .. Even after 6 cloudy days the fridge was still running and the battery voltage was 12.8 volts...

Cheers

Steve

From my experience with solar and fridges that is very sound advice.

Jim.

Hello Jo and Steve,

I reckon Steve is on the money in terms of battery capacity recommendations, but the solar panel of 100W won't go very far either.

Here are my calcs, pls correct me if I'm wrong:

80W times 4.5h equals 360Wh per day, equals 26Ah @ 13.8V. Add 30% to this output if you are constantly adjusting the panels to point to the sun.
So in average you'd think that you may get some 34Ah into your battery, every day.
But because you're not going to adjust your panels constantly and due to losses of your regulator, and panel (max power point at 17.5V instead of 13.8V) this figure will be lower, say around 30 Ah.
Now if according to Steve, the fridge requires 40 to 50Ah, your 80W panel isn't going to be sufficient.

And if your battery has to power the fridge for 16 hrs while there is no or little sun, it'll have to provide 67% of this daily Ah requirement, or 45Ah before it slowly gets recharged.
Your 24Ah battery is not sufficient for this, you want at least a 60Ah deep cycle battery, which you then will deplete to around 80% every day before it gets fully recharged by f.e. 2x80W panels.
A 100Ah deep cycle VRLA AGM battery's even better because it'll give longer service life compared to the 60Ah battery (plus you've got some leeway in case it's a cloudy morning...)

Hope this clears it up?

hi batt/world so would 2x120 amp deep cycle batt and a 175 watt solar panel be enuff to run a engel 60lt and 2 led lights for a cpl of days


cheers mick

.......... yes

Maîneÿ . . .

Hello Mick

I second Maîneÿ...
If fridge uses 45Ah per day, this is an energy equivalent of about 600Wh per day, and your LEDs another 30Wh or so.
Your solar panel will give you 175W times 4.5h equals about 780Wh per day, so yes that's fine.

Just one question:
what happens after a couple of days out in the sticks?
I'm asking this because just in case you're home by then, you most likely would use a 240VAC mains charger to fully recharge your two 120Ah batteries?

In this case, I wouldn't bother with the solar panel (unless you've got them installed already), because you only would discharge your batteries to about 40 to 50% during these two days.

Best regards, Peter

"Here are my calcs, pls correct me if I'm wrong: 80W times 4.5h equals 360Wh per day, equals 26Ah @ 13.8V. "

WHOA !

An 80 watt panel puts out 4.5 amps max. So with 4.5 hours of sunshine you have 4.5 x 4.5 = 20.25 amphours.

I thought it was common knowledge that an 80 watt panel ONLY puts out 80 watts at around 19 volts - there was no mention of an MPPT controller being used here.

4.5 Hours of sunshine - Hobart maybe ?

Try upping that to 6 or 7 hours per day for most of mainland Oz ..

I think Mainey went down this track a few threads ago ...

Cheers

Steve

Mike,

if you read my post a second time, you may or may not notice that I've allowed for that. Concentrate on line number 5 in my calcs.

Best regards, Peter

Steve,

there are maps for this.

Sydney: 4.5
Brisbane: 4.5
Perth: 4.0 (just)
Melb: 3.0 (just)
Alice: 5.5
Hobart: 2.6
somewhere south near Kimberleys: 6.5

So 4.5 PSH for the whole continent is a good average.

As a side note, you owe me one for this because compared to your 6.5 hrs average, you can now start selling 1.4 times more solar panels to your clients ;)

Best regards, Peter

Here's the BOM map link Annual Average .

Which clearly shows from Victoria at 6 to Port Hedland at 10 the average annual sunlight hours in Oz ..

If people wish to use 4.5 - I'll be a very happy solar panel seller !!

Whats 1.4 times my miniscule profit margin - about 2.8 stubbies - LOL

Cheers

Steve

Steve,

thanks for the offer, I'll have one - you drink the rest ;)

Steve, I was referring to the concept of 'peak sun hours'.
This forms the base for PV output calculations.

cheers mate!

For Mike to suggest there are only 4.5 sun hours it obviously refers to his own inefficient solar panel ??

I suggest this because Mike has previously posted on the forum his panel does not work in low light conditions, but he has refused to admit what brand and model it is the three (3) times I've asked him.

So again..
Mike please tell us what brand of panel you have recently bought, as you have previously stated it's inefficient - just so others don't get caught out too :)

Maîneÿ . . .

"For Mike to suggest there are only 4.5 sun hours "

Mainey, do please continue with your Reading classes. The quotation marks mean I was copying what Batteryvalue wrote - his example used 4.5 sunhours, so I continued with that assumption.

Mike,
now I have your attention, will you please inform me as to what brand of solar panel you recently bought that your unhappy with because it's inefficient in low light conditions

Maîneÿ . . .

Member - Mike DID posted:
"Here are my calcs, pls correct me if I'm wrong: 80W times 4.5h equals 360Wh per day, equals 26Ah @ 13.8V. "

WHOA !
An 80 watt panel puts out 4.5 amps max. So with 4.5 hours of sunshine you have 4.5 x 4.5 = 20.25 amphours. I thought it was common knowledge that an 80 watt panel ONLY puts out 80 watts at around 19 volts - there was no mention of an MPPT controller being used here.
Mike R
. . . . . . . . . . . . . . . . . . . . . . .


Mike,
you posted just as I've copied for you above, then you tell me I need to 'continue with my Reading classes' however if you look back at your own post, I've copied it here for you

# WHOA !
An 80 watt panel puts out 4.5 amps max. So with 4.5 hours of sunshine you have 4.5 x 4.5 = 20.25 amphours #

Mike, See you have placed NO quotation marks at all around the words or indeed the sentence at all, maybe it is you who needs to continue with your reading class's and not me after all.

Mike your only human, you make mistakes too :)

Maîneÿ . . .

Where to shop? I think you need only scroll up.

Both Steve and Peter offer VERY competitive pricing and they wouldn't last five minutes on this forum if they weren't reputable.

Cheers,

Jim.

So very true Jim!! At least they will know what my needs are!!
Cheers
JO

I would suggest that a 100ah, or 120 ah, and 100w of solar would get you by.
So many factors include how much sun, do you move the panels during the day, how often the fridge is opened, ambient temp etc.

Basic ball park is that 100ah, and 80w will keep a 40l fridge going.
120ah, and 100w solar will keep a 60 going.
However if your only going to stay put for 2- 3 days, using say 35ah/ day, or more depending on if its freezer, or fridge, and is it 25 or 45 deg ambient.
So 80w will get you thru, but the state of charge of the battery will drop during those days of use.
100w should keep you topped up at full charge, 120w gives you some buffer for less sunlight/ day.

Basic calcs to go by, Steve has a great calculator on his site to use for what you might need.
His gear and service is also top notch too.

Hope that helps

Trains