Solar Panel Question...

Submitted: Monday, Jan 02, 2012 at 08:41
ThreadID: 90947 Views:2206 Replies:5 FollowUps:9
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My van has a 100amp/hr calcium battery with a 240v Electro 3-stage charger. I have a 2kva Honda genny which I use to re-charge the battery - usually every 2nd night.

The 12v items in the van are - 3 fluro lights (usually only have one on at a time), water pump, spark-lighter for gas and the TV which I don't usually watch when camping except for perhaps an hour to catch up on ABC News and 7:30 Report. I run the fridge on gas.

I am considering installing solar panels on the roof of the van. I have had advice that two 80W panels - each panel producing 18V nominal voltage and 4.4Amps nominal current would be what I require to keep the battery charged.

The panels will have a solar panel controller/regulator which shows current battery voltage , solar panel output volts , current input current in amps , current charge type (Bulk, Absorb, Float) and the usual 'management' stuff.

Would appreciate any advice/comment by those who have knowledge/experience with solar panels.


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Reply By: Battery Value Pty Ltd - Monday, Jan 02, 2012 at 09:17

Monday, Jan 02, 2012 at 09:17
Hello John,

your panels are good for 25Ah~30Ah per day. That's taking into account some losses caused by mounting them flat, and temperature effects which I estimate to be around 30% all up.
I'd be surprised if your telly and other small loads would exceed 20Ah per day, so the proposed panel wattage is sufficient.
And if the need arises, you can always boost solar output by up to 20% by purchasing a true MPPT solar regulator.

And if you rather park your van in the shade, you might want to look into a pair of folding solar panels. Here, a true MPPT solar regulator is also very useful in that it can take 24V on the input side, so you can wire the pair of folding panels in series for minimum voltage drop in the long wire (series configuration of solar panels reduces the max current hence voltage drop by 50%) - resulting in another charging amps gain of another several percent.

cheers, Peter
AnswerID: 473836

Follow Up By: Member - Daryl N (NSW) - Monday, Jan 02, 2012 at 12:03

Monday, Jan 02, 2012 at 12:03
Hi Peter
Could you explain what a MPPT regulator is, why it is different and why is it more efficient than a more typical regulator that John has described?
FollowupID: 748700

Follow Up By: Member - Ed C (QLD) - Monday, Jan 02, 2012 at 13:41

Monday, Jan 02, 2012 at 13:41
@ daryl

What the heck is an MPPT??


Confucius say.....
"He who lie underneath automobile with tool in hand,
....Not necessarily mechanic!!"

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FollowupID: 748709

Follow Up By: Battery Value Pty Ltd - Monday, Jan 02, 2012 at 13:49

Monday, Jan 02, 2012 at 13:49
Hi Daryl,

yes no worries.
Think gearbox in a car.

An ordinary solar regulator (PWM, or on/off type) acts like a single speed box.
As long as the clutch is disengaged the motor revs up freely, but the moment the clutch comes on the motor revs drop depending on the actual speed of the car.
Because max motor power has a peak somewhere up high, this power usually won't be available during cruising.
On the other hand, a multi speed gearbox allows the driver to shift the motor revs to the max power point, independent of vehicle speed.

Solar panels, not unlike combustion engines also have a peak in the output power which is visible in the EI diagram of the panel. The panel's operating Voltage could be likened to the motor RPM, and the panel current to the motor torque.

So motor revs are equivalent to the panel's operating voltage, the gearbox is the DC/DC converter inside the MPPT regulator, the driver is the microcontroller, the clutch are the wires between solar regulator and battery, and the vehicle speed is the SOC (battery terminal voltage).

Because in a solar panel, the maximum power point shifts up and down with temperature and insolation, the microcontroller constantly regulates the current through the panel. The algorithm looks for the maximum in the ExI product.

Hope this isn't too confusing.

cheers, Peter
FollowupID: 748710

Follow Up By: Member - Daryl N (NSW) - Monday, Jan 02, 2012 at 14:44

Monday, Jan 02, 2012 at 14:44
Hi Peter
Many thanks. What is a good brand to purchase?
FollowupID: 748713

Follow Up By: Battery Value Pty Ltd - Monday, Jan 02, 2012 at 14:51

Monday, Jan 02, 2012 at 14:51
Hi Daryl,

a link to a very good unit can be found on our EO profile page:

If I can be of assistance please send us a member message.

regards, Peter
FollowupID: 748715

Reply By: The Bantam - Monday, Jan 02, 2012 at 11:50

Monday, Jan 02, 2012 at 11:50
The big question is how long do you need to run without alternative charging.

Seems te standard resposne for salesmen is to recomend 2 x 80 watt pannels regardless of needs...probably because that is where the customer flinches.

if ya only stopping a few days at a time and are prepared to run the genny for longer stops, you may be better off increasing your battery capacity and forgetting the solar.

I notice you have not mentioned a that gas.

AnswerID: 473852

Follow Up By: Member - JohnBee (VIC) - Monday, Jan 02, 2012 at 12:03

Monday, Jan 02, 2012 at 12:03

Hidden in the original post - "I run the fridge on gas."

I often stop for 4, 5 or 6 days - I run the genny every 2nd night, or every night depending how much 'light' I used the night before, and how amenable other campers are.

I always feel guilty using the genny in camp (when others are within 100metres of me). The Honda is very quiet, but I used to dislike people playing music loudly in the bush. We all go bush to get away from noise etc. So I thought solar might alleviate some of my guilt hangups :-)

FollowupID: 748701

Reply By: The Bantam - Monday, Jan 02, 2012 at 12:21

Monday, Jan 02, 2012 at 12:21
A MPPT regulator is a Maximum Power Point Tracking regulator, it is in essence an inverter or switch mode device that takes what ever the pannels put out and produces the maximum charging effect possible.
More efficient tha a basic regulator.

Mate if ya running a week at a time and with no fridge drain, 160 watts of pannels should be reasonable as long as ya not wastefull...are all ya lights LED?

AnswerID: 473853

Follow Up By: The Bantam - Monday, Jan 02, 2012 at 12:24

Monday, Jan 02, 2012 at 12:24
Sorry I note you have fluro's.

Thay arent too bad, maybe a little hungry...replacing them with LED strips will probaly increase yor run time.

FollowupID: 748704

Reply By: Member - JohnBee (VIC) - Monday, Jan 02, 2012 at 14:45

Monday, Jan 02, 2012 at 14:45

Thanks to all replies. Sounds like it should all be OK.

I would prefer the panels mounted on the roof of the van - saves having to figure out where to carry the portable ones and less likely to be knocked off by enterprising visitors :-)

Downside is need to keep them clean every month or so ... but that's a small problem

AnswerID: 473866

Reply By: Ross M - Tuesday, Jan 03, 2012 at 12:35

Tuesday, Jan 03, 2012 at 12:35
Lots of good info here in the replies.
just a note to people who use a Honda generator to charge batteries.

If you use the Honda 12v outlet which is 8amp max, then the recharge time will be longer and therefore motor/gen runs far longer than if you use a switchmode battery charges off the Gens 240 v.
A good size 240v Switchmode charger will output near 20 amps into the battery and make the run time required to charge the battery much shorter than the Honda std method.
I think both systems can be used at the same time if you need quick action for car battery flat and need to start the engine asap.
Eg, Honda leads to battery and switchmode battery charger leads to battery = both connected to the battery.

A 100ah battery will not like more than 20 amps flowing during recharge, gets too hot, tends to cook battery and shortens its life.

Most switchmode chargers monitor the charge rate and cut back and float charge when battery is charged unlike old transformer based chargers that are dumb and just keep pumping electrons. If you use one of the old chargers you have to be the battery monitor. You stuff up, so does battery.


Ross M
AnswerID: 473940

Follow Up By: jimreevescairns 1 - Tuesday, Jan 03, 2012 at 16:31

Tuesday, Jan 03, 2012 at 16:31
I was thinking of getting one of those Bushmaster chargers that put out 50 amps allegedly allowing you to minimize charging times when connected to your generator but if what you say about 20 amps being the maximum then that would be a waste of time ! Are there batteries that can take larger charging currents ?
You are right there is good info in this thread
FollowupID: 748781

Follow Up By: Ross M - Tuesday, Jan 03, 2012 at 21:59

Tuesday, Jan 03, 2012 at 21:59
I know my 100ah deepcycle gel types only like a max of 20 amps per battery.
If you pump too many amps into them the plates don't like it as they overheat and shorten the batt life dramatically

This usually happens when the charger tries to a discharged battery and the charge rate continues for some period of time.

So if you have two batteries and they are both discharged to some degree then the larger charger may be ok. They usually have a dual setting on them so a lower charge rate may be selectable while the full 50 Amps is also available.
If you go the switchmode type then make sure it has a dual option , it is then more flexible for your needs when the solar isn't able to keep up. eg weather.

The average cranking battery does take more charge current flow because the alternator just tries to bring up the charge as quickly as it can and this can last for some time. These batteries are not as suited to caravan and solar setups as the deep cycle types.

With this stuff, I see it as trying to cover all bases so you are not inconvenienced in what you do while out on the track.
Ross M
FollowupID: 748816

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