Solar Panel Charging: How To Regulate The Charge?
 

Hi Guys,

So on our overland truck we want to fit a solar panel. It will not be permanently attached to the roof as we go through alot of dense jungle and worries it will get damaged. We will hook it up whilst stationary and camping via a plug.

Question: We pull into camp with leisure batteries fully charged. Plug in the solar panel charger.

How do I ensure that this solar charger does not overcharge the batteries? For instance, the split charger we have cuts the charge to the batteries when it senses they are at maximum charge (when driving).

But with the solar panel they will be constatly pumping in energy, and I'm worried about it overcharging the batteries. What is the best solution for ensuring this doesn't happen? Is there a simple way to cut the charge without having to constantly check the battery voltage and manually having to unplug the thing every few hours?

Thanks for any advise.

David

All solarcell dealers, sell a smal box that regulates the charging of the battery.

Here is an example

Wholesale New 20A Solar Panel Charge Controller Regulator 12V 24V Autoswitch, Free shipping, $17.33-21.83/Piece | DHgate

Thanks very much for the link just what I will need! Much appreciated.

Depending on where you are in the world a mppt controller is better as it gives a better charge output and will allow charging even on a cloudy day have a look at the bimble solar Web site

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Thanks Trix I will check that out too, appreciate the advice!

an MPPT tracker is fitted to inverters controlling multiple panel set ups. Under normal circumstances the output will drop to the level of the worst performing panel, say if one is in partial shade. An MPPT tracker helps minimise this effect by balancing the output better to the best performing panels.

However, an unshaded, or predominantly unshaded, system will perform better without the MPPT activated.

There is no value to having an MPPT tracker fitted to a single cell system.

Installation dependent.

Incorrect. A good MPPT will adjust the load demand on a single panel to obtain maximum power out of the panel. As that maximum power point will change as the day progresses (changing angle of sun hitting panel, shading, temperature) you cannot have a simple load that matches the panel all the time.

All this MPPT stuff sounds a bit over the top. No matter what you do, the panel can only give so much energy as is produced by the sunshine hitting it. The only way a controller can the increase working voltage of a panel, is by lowering the load but then you get a lower charge.

If you had several in series, thus giving a much higher voltage than 12V, there could be some benefits.

BUT to me the greatest advantage using the controller from Bimble is that you can get a meter that: "Displays Voltage, Current, Amp-Hours, Watt-Hours and Percentage Charge".
That will be a big help for administering your solar power in a vehicle.

Optional MPPT meter for Tracer Charge Controllers

Mppt controllers give a 30 % better charge overall because the base pwm controllers switch the charge on and off you lose some of the valuable charge , that is a very basic outline of the difference but all you need to know without getting to technical , mppt is better but a little more costly

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Also not true in all, or even most circumstances, but MPPT does certainly usually result in some gain over PWM controllers and are rapidly becoming the standard as costs of the extra circuitry come down.

No, also a bit simplistic. An MPPT controller does - assuming the right algorithms are programmed in (and this is what separates the good MPPT from the bad) - work to maximising the operating conditions to extract the maximum possible power out of the panel if the battery condition is such as to allow it.

Not always appreciated that for largish batteries and smallish panels used as an add-on, no controller is really needed unless your demands are low and you have the panels deployed for long periods. HOWEVER, it does need the operator to keep an eye on the battery voltages and disconnect the panels once the battery reaches closer to fully charged, so the smartest idea is to add a reasonable regulator to take away the guesswork.

Hi David,

I searched the internet very thoroughly last year when I was looking for a good solution for my Defender 110, which I'm preparing for a circumnavigation of Africa next year. It seems that most overlanders - especially on a longer trip - prefer a panel that is fixed to the roof, instead of one that you put up on the ground. To compensate for the loss of efficiency (up to 30% because it is lying flat on the roof) I fitted a panel of 140 watt. During my 2-month shakedown trip
in southern Morocco in March/April this year, I was able to test the setup, and it works like a treat. I can stay off the grid for as long as I want, and comfortably use the Engel fridge, and power cameras, laptops, radio, compressor, etc.
Have you thought about fitting a reliable battery monitor? I can recommend the Victron BMV-602 from my own experience.

http://www.geehurkmans.com/blogs/victron.jpg

Happy trails,

Gee

[QUOTE=Tony LEE;427208]Also not true in all, or even most circumstances, but MPPT does certainly usually result in some gain over PWM controllers and are rapidly becoming the standard as costs of the extra circuitry come down.
we will have to agree to disagree I live on a boat mppt is 30% better, certainly in my set up .





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elaborate 'installation dependant'
If in series, the panels will default to the current of the worst performing panel, if in parallel they will drop to the worst voltage. Short of individual inverters or power optimisers your stuck with that as far as I am aware

I am used to multiple panel installations. Under those installations using MPPT trackers in inverters can reduce the output of the system due to the varying characteristics of the panels. The best way of negating this is microinverters or power optimisers.

Another configuration that is becoming more popular as the prices of all components comes down is to have two completely separate systems, panel, regulator and batteries - one supplying the need-to-have items such as refrigeration and the other for the nice-to-have stuff. This also fulfills the "mandatory" requirements for providing two way and even three-way redundancy in expedition vehicle systems.
One really important feature of solar systems is if you are ever silly enough or unlucky enough to stall the engine somewhere where a push start is impossible, and all of your batteries are too depleted to crank the battery (does happen in even the most anally-maintained systems) then having a decent area of panels does mean that getting mobile again is just a matter of a few hours of sunshine.

As for the 30%-guaranteed-no-matter-what claim for MPPT over PWM. Normally you only see that in duplicitous MPPT adverts on eBay, or by consumers with a bad case of confirmation bias, or from those who spend their entire life above the arctic circle where getting 30% more than just about zero isn't all that much of an achievement.

Guys, what's your thoughts on this panel? A big wattage, will be used in West Africa so plenty of sunshine, should easily trickle enough juice in to keep the leisure batteries topped up:

Solar panel 250W ~ 24V ~ Mono ~Made in EU~ | eBay

personally I would never buy from a seller that spouts such tosh!

NO panel is 100% efficient. the best on the market at the moment are about 18% efficient and cost double the price of this panel.
This panel is a domestic panel, it is not designed for vehicular use. Now, you can use domestic panels, that in itself isn't a problem. I supplied one for my uncle to use on his yacht, but I made sure it was one man enough for the job, and a yacht is a very different environment to a truck.
It isn't 24V. Not that this matters especially, the regulator can deal with that, but it's still more tosh.
I have never heard of this panel. that may or may not be a problem as there are so many you can't know them all, but I am instantly suspiscious of panels with names I don't recognise, because there is a lot of tosh out there.

Now of course, it's entirely possible I don't know what I am talking about, but my company is Dorset Solar Power Ltd

Thanks for your thoughts Moggy! Will have a look for another, did seem very cheap for the wattage when compared to others.

More reading - where efficiency counts is in a race ...

AERL - Solar Charge Controller - MPPT solar car controller

Thanks for all the information guys.

Just one question: Is there actually such a thing as a 24V panel? Alot of them say 12v/24v?

I take that to mean that it's basically a 12v panel that can be used via an MPPT controller to charge 2x12v batteries wired in series (ie a 24v system).

If so, I can buy any panel described as 12v, and use it with an MPPT controller to charge my 24v system? Or am I missing a trick?

Cells within a panel can be connected together to form close to a desired voltage. Panels can also be connected together to form larger voltages (series connection) or connected together to form larger currents (parallel connection) at the same voltage ...

MPPT can be designed to BUCK (reduce) the voltage OR to BOOST (increase) the voltage.

The variations are large. What works best depends on the installation;
all panels lit to the same degree all the time?
load is best at what voltage?
money?

And of course what is available

Hi Warin,

THanks for your thoughts.

Basically want to make sure our fridge can keep working, as it has an internal regulator that cuts the fridge off when it senses the batteries are down to 22.8volts.

Load of the fridge is 4.5 amps per hour, but presume this is if running continuously.

I have some LED lights too but the draw these make is very small.

So all up a panel capabale of 5 amps per hour charge.

I really don't want to have 2 panels wired together. Ideally want one panel that can charge the 2x12v batteries wired in series.

David