Solar Panels

Submitted: Friday, Jun 04, 2004 at 13:38
ThreadID: 13454 Views:3795 Replies:5 FollowUps:5
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Can any one advise what is the best solar panel to purchase to top up second battery running lights of a night a 1 x engel fridge.

Thanks in advance
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Reply By: Magnus - Friday, Jun 04, 2004 at 15:40

Friday, Jun 04, 2004 at 15:40

Before you can decide on a panel size you need to know your daily amperage draw. This is the amount you will need to replace in the 8 hours or so of sunlight you get during the day.

Add up your individual light draw and multiply by the hours they are on eg 2 x 10 watt lights will draw 20 watts in an hour and that is 1.6 amps approx. on for say 3 hours and you have a total evening draw of 4.9 (say 5 amps). This is the amount you will need to replace the next day. A 20 watt panel puts out just under an Amp and would be enough to recover a 5 amp per night draw. How does 20 watt convert to only 1 amp. For a start Solar panels put out not 12 volts but 16.8 volts giving a theoretical output of 1.2 amps (20 divided by 16.8) and by the time system losses are taken into account the panel is rated ot only .95 amp.

Now as for the fridge. You need to know the draw. i understand that some of the newer 12 Volt fridges are quite advanced in their power management. Consult your handbook or talk to an Engel dealer.

This draw will be a lot higher than the lights and of course has to be added to the lights.

If you have an older Engel you may find that you will need a whole heap of solar panel output to replace the current drain.

I use, and have for last 30 years, 3 way gas fridges (12, 240 volt and Gas). The first unit lasted 25 years before it spat the dummy. My new one, also a Finch, works just as well as the old one did. As a plus, it cost half the price of an Engel. But no freezer. Don't need one. Have to watch it does'nt freeze things in any case especially working on Gas. My wife won't carry eggs or lettuce in the fridge. Frozen fresh eggs sort of never recover. As for frozen lettuce, forget it.

That way I get by with just a 20 watt solar panel costing $260 and not needing a regulator. And up till April was using only a 27 amp hour sealed lead acid battery arrangement. That gear reached the end of its life cycle in April and I replace it with a 70 amp hour SLA deep cycle unit.

Have never run out of power with the 20 watt panel and the Gas fridge.

By way of comparison an 80 watt solar panel costs $720, measures approx 1200 x 540 and will require a regulator costing between $90 and $230 depending on how many bells and whistles you want on it.

A new gas fridge starts to look decidely cheap.!!

Whatever you do, do the current draw sums carefully or you could find yourself unable to recharge and with a flat battery real quick.

Also make sure your battery is fully charged before you leav home.

I was camped beside a new off raod camper trailer in late April and his unit came with 100 watt solar panel on the roof. However he leftt home without fully charging the deep cycle battery and was without power within 24 hours with a flat battery


AnswerID: 61699

Reply By: The Banjo - Friday, Jun 04, 2004 at 16:13

Friday, Jun 04, 2004 at 16:13
Goona - the maths from Magnus is all good advice - you should be calculating what the real needs are, but another few factors to ponder might be:
BP solar make a range of panels - ring them in Sydney for your local agent. The articulated (hinged) panels cost a lot more than the fixed jobs, $ per watt. A regulator only costs about $45 which avoids cooking batteries if the sun is blasting down.
IMO, its impractical to plan only for solar supply - it may be overcast at times, and anyway, you are likely to run the battery down even if you have al ot of sun.
People I know that use solar see it as an aid - they have a genny, or run the car, or top on on daily drives, while camped.
Quality gennies are great, but who wants to camp by one ? Its 3 way for me, but this might be revised when I head into the far north.
AnswerID: 61700

Follow Up By: Magnus - Friday, Jun 04, 2004 at 17:38

Friday, Jun 04, 2004 at 17:38

Your 3 way will work fine in the Far North especially as I assume u are going in Winter. Different story in Summer, but then no-one goes to the Far North in Summer by choice!!.

I use a BP Solar panel, and I do plan for only Solar supply to charge my battery. But I suppose I am an optimist and count on the sun shining.

Helps that we don't go away if the sun isn't going to shine. Make a lot of use of the Weather Chanel on cable and stay home if the weather is not just so. Also being retired helps a huge amount. We do have flexibility, that's for sure.

Got my panel from Whitworths, the Marine Outfitters. Surprisingly, they consistently have the best price on Solar Panels. Heaps of Yachties use them on their moored boats to keep their cranking batteries charged.

They also have the best range of 12 volt gear you will see in a long day's march!!

Hope u manage to get to the Far North. It is a great place. Lived in Darwin in 1979 and got round a fair bit. U will enjoy it.


FollowupID: 323176

Reply By: The Banjo - Friday, Jun 04, 2004 at 17:44

Friday, Jun 04, 2004 at 17:44
Note re Whitworth's Magnus....thanks....I'm getting a camper soon and will need something to top up the deep cycle within, when static for awhile.....a panel may well be the go.
AnswerID: 61720

Follow Up By: Magnus - Friday, Jun 04, 2004 at 19:57

Friday, Jun 04, 2004 at 19:57

I use a 20 watt Panel. Current Whitworth Catalogue price is $269. No Regulator needed.

I made up a little frame from light pine that is adjustable for angle. Simple A frame held by two small bolts at top. Like an easel. Panel rests on it. Allows me to adjust the angle to suit the Sun.

Run it straight into the battery in the camper. Also have an ammeter wired in so I can see the charge rate. Flip a switch at night and the same meter reads the discharge rate in amps. The meter is a 0 to 5 amp 2 inch square one that I slavaged out of a defunct battery charger.

Jayco also sell them for $30. Check out their cataloguie, not their on line one but the hard copy.

I fully charge the Camper Battery with a 2 amp charger that I leave on till the battery volts stabilises at about 15.3 volts. Read from a Jaycar voltmeter naturally. Then it is fully charged.

Or should be. The old set would go to 16 volts before stabilising. Haven't had this battery in long enough or left it on charge long enough to confirm. Bought the new battery, went camping and now have the CT in bits painting it as I prepare it for sale. The brand new CT is in the back yard waiting for me to get at it and wire it up etc, etc etc.

I run 2 low draw Fluros with Tri Phosphor 8 watt tubes (two per light) Lucky brand from Whitworths for less than $20 a pop and Halogen cabin lights for boats also from Whit as lights in the Camper. The halogen are for using when I want to listen to the radio at night. Cheap fluros kill radios and there is no guarantee the expensive supposed non inteference won't do the same.

My worst offender is one of those real low amp fluro lights that cost $90. You can take it 100 feet away on a different circuit and the radio still screams something awful. Leaving it home next trip. Wasn't a real flash light in any case. That little experience led me to buying the el cheapos from Whitworths. Better light to use even though they are 16 watts and so 1.3 amps. The halogen cabin lights make great reading lights in bed. 10 watt with swivel fittings etc, so less than an amp draw. Beats a fluro for reading in bed.

Have fun setting all this up!



FollowupID: 323196

Follow Up By: Magnus - Friday, Jun 04, 2004 at 20:08

Friday, Jun 04, 2004 at 20:08

That enough is just a stray left over word.!!

FollowupID: 323198

Reply By: Magnus - Friday, Jun 04, 2004 at 20:06

Friday, Jun 04, 2004 at 20:06

That enough is a stray word!!

AnswerID: 61733

Follow Up By: V8troopie - Saturday, Jun 05, 2004 at 00:02

Saturday, Jun 05, 2004 at 00:02
Magnus, a couple of things you said in your reply above worry me.

Firstly, charging a battery for an extended time with a voltage in excess of 15v is detrimental to it. Cut it back to 14 V and you can leave it hooked on as long as you like. Smart chargers do just that, they hit the battery first with a higher voltage to press more current into it, then throttle the voltage back (or pulse it) to top the battery up, finally settling at around 13.8 - 14V to maintain the battery charge.
However, they sense the 'current' that the battery will accept, if it starts tapering back the charger throttles back also. Watching a volt meter during charging will tell you nothing much useful with regard to state of charge.

Secondly, you cannot get a true 'fully charged' voltage reading from a battery until it had been disconnected from the charger for some hours and no load had been connected meanwhile. If it then reads at least 12.6V it is fully charged.

Thirdly, the best way to measure the output of a solar panel is not by measuring volts at all. Connect an Ampmeter ( set to 10 Amp range or so) directly across the solar panel terminals. Yes, that does practically short circuit it but any solar panel can handle a short circuit indefinitely.
Point the panel at the sun and read of the maximum current by varying the angle of the panel. The maximum available charging current is a little less than that since the battery (and wiring) does have some resistance.

I think that a 20W panel is very much underrated to feed an Engel fridge. I did wreck a good deep cycle battery some years ago - it powered a 15l Engel on a boat - and I only had a 20W solar panel.

Now, my boat has a much more efficient eutectic fridge and 76W of solar panel power. This is sufficient IF the sun shines at least every other day - if not, the genny has to be used as well.
FollowupID: 323239

Follow Up By: Magnus - Saturday, Jun 05, 2004 at 14:00

Saturday, Jun 05, 2004 at 14:00

Thanks for the comments. Seems like I have been getting by more by good luck than by good management. Perhaps I best replace my little $20 and 2 amp charger with a newer better one that does what you describe in the charging process.

However I have been aiming for a 12.6 volt readout at rest to indicate fully charged. So I have been doing that bit right. If I have had 12.6 before I set out camping I have been OK for the duration of the camp. I found that waiting till the voltmeter read 15 plus whist charging gave me the 12.6 at rest. Again, luck and not science. Will definitely fix that. Thanks for setting me straight.

I have an ammeter in my camper circuit so when the panel is in use I can see the amps going in. Interesting to watch on a cloudy day as the meter goes up and down. I only have it to tell me the panel is working and that I have actually plugged it in. There have been times when I have forgotten. It is a small Solarex 20w panel so it is easy to put away at night. Especially so when the National Parks sign say to lock up your goodies as there have been thefts etc.

Even though I have never used a 12-volt only fridge, always 3 way, I suspect you are spot on about 20 watts and Engel fridges. A big mis-match.

Again, thanks for the constructive advice.


FollowupID: 323272

Reply By: Member - MightyQ - Saturday, Jun 05, 2004 at 00:16

Saturday, Jun 05, 2004 at 00:16
G'day Goona, Over the past 20years I've used Solarex solar panels, used 20w and 60w never had any problem. I used a regulator with the 60 w. For 18 months I lived up in the High Country and that was my only source of power, ran 12v drills, fluros and a 12v television. Even in winter I had enough power with only one deep cycle battery 70 amp and a few old car batteries, just one panel.
Now days I used the same 60w panel on the Jayco outback, I don't mount it on the roof I have 2 12volt connections, one on either side of the camper(snap in connectors) so I can move it when the shade is a problem. Battery mounted inside the van, charged while I travel, isolating switch when needed.
The reason i chose Solarex is their robust construction, C-section Aluminium frame
toughened glass(not my choice really, as a glazier I'd use 5mm Laminated--but that's just me)
Good luck
AnswerID: 61781

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