PWM or MPPT controller for solar

Bigfish,

Nah mate the 2 main cranking N70'S take care of starting and get isolated by the VSR.
Had experience with ya mate Murphy...lol gets around doesn't he...(;-))

Cheers
Pop

Hi Tc,

Now they are well priced, haven't had a look at e bay yet. The Plasmatronics PL 20 PWM was around the $385 mark and the Morningstar MPPT 20 amp job was about double that hence my enquiry. I want to try and get it right first time....I hope.

Cheers
Pop

And yeah you're right about the "experts" not agreeing about which is best value for money. Some say put your dollars into an extra panel which is also worthy of consideration


Cheers
Pop

I meant to say search for the Tracer on ebay.

Quote - "The reason is simple, panels work at about 20V, batteries charge at about 12 to 14V. The difference in the resulting power is thrown away in PWM chargers, where as MPPT's work like an inverter in reverse and preserve the power."

That 20 V is a falacy. Someone has been feeding you duff gen. The peak voltage of 12 V panels is 20 or so volts, generally around 21 V. In that condition no current is being drawn from so they are generating SFA power.

Solar panels are a dynamic device. When you start working them their terminal voltage drops somewhat. When they are producing their maximum power the terminal voltage drops to around 17 V, this is a far cry from your 20 V.

When you charge a battery with a series regulator (PWM is just one form of them) the terminal voltage drops to around 15 V or a little under. When you redo your maths I suggest you also take into consideration that at 15 V the panel is also supplying more current than it does at the MPP voltage. I think if you recalculate your gains on those figures then you will see that an MPPT regulator will only supply 15% more power than a series regulator and then only under the most favourable conditions

Thanks for the info so far guys, I have been trying to edgumacate my rapidly fading grey matter a bit more. Although I inhabit an aging body I am pretty green with regard to solar energy.
I have measured the open circuit or what ever it is called with the 85w (rated??) panel I have at the moment. I am reading 21v with a multi meter. Now as has been pointed out that voltage will drop as a load is applied, this I can understand VxA=W???
I have also read that an extra panel, if I need one can be installed in either series or parallel. Obviously the regulator would have to be capable of handling the now doubled input voltage but some people are saying the higher input voltage with a series connection gives less power loss than a parallel connection.
Now does any of that make sense and does it matter whether the regulator is MPPT or PWM?
I am not trying to get a cheap lesson in electronics (far toooo late for that..lol)

Thanks
Pop

Sorry Peter, you may be a retired radio tech, but as an Electronics Engineer with direct experience with this I can tell you that you are incorrect.

True a PWM will drag the panel down to the charge voltage plus a little, but you have obviously never used or measured the panel voltage when connected to a MPPT controller. If working properly, the panel voltage will be very close to it's MPP level when at full load, and that is about 19 - 20 V generally.

Have you ever tired it? Obviously not.

Pop,

Whether you can series or parallel panels depends upon which style of controller and also the specifications of the controller. If you are using a simple series controller you should parallel your panels. The charge current is not boosted by the controller like it is in an MPPT controller. You will only get an increase in current if you parallel your panels.

With MPPT controllers there are a couple of things to watch. Firstly you have to consider its input rating. If you are using something like a Ctek D250S that only has a maximum input voltage rating of around 21 V, you will zap it if you series the panels. One bloke in CF reported he had blown his, he thought "MPPT, series panels mean less power loss" but forgot to read the specifications of his unit.

The second thing to watch is shading. We all encounter camping in places where our panels get a little shading throughout the day. The current from a series array is dependant upon the output of the weakest panel. If one panel gets a little or complete shading the whole of the arrays power output is reduced by that amount. If you have a parallel array and only one panel is shaded the other will still contribute its full power. You will only suffer the loss of power from half of the array.

In addition if you have panels of different power output the current that is generated in a series array will be largely controlled by the panel with the lesser power rating. You can parallel panels of different capacities but there is little point of connecting them in series.

Pop, the kind of regulator I referred to will cope with inputs up to about 150V ( check the type you buy if you go this way, some are 60V, 100V etc)

All of them would easily handle 2 panels in series or parallel and will deliver a charge at nominally 12v to your batteries with the same power.
The advantage of wiring the panels in series ( ie about 40V input) is that the current is low and you have less losses over the cable from the panel to the charger which can be considerable. However as Peter points out shading is your enemy. You will lose almost all power, even if only one panel is shaded. Bypass diodes will minimise this effect somewhat.


The advantage of putting them in parallel ( ie about 20V in) is that they will operate independently wrt shade so you will still get half power even if one panel is totally shaded. The cost to this is the increased losses due to higher current or the price of thicker wire.

Boobook, quote "If working properly, the panel voltage will be very close to it's MPP level when at full load, and that is about 19 - 20 V generally. "

The MPP voltage for a 12 V panel is around 17 V, not 19 - 20 V. If you use a digital meter you can get all sorts of funny readings when working with pulsing circuits. Try using something like an AVO model 7 to do your readings.

Peter

The MPP of a panel will depend on the manufacturer and construction. 19V is VERY Common and observable. There are literally thousands of panels with 19V plus MPP. I have personally observed it regularly on mine.

Have you ever seen a MPPT controller in action rather than relying on internet based theory?

Better stick to Radios with that Avo :-) Yoiu are trying to argue against facts, not opinions. It is pointless arguing with you on this. Try some real world measurements.

Apologies, for completeness I should mention the other, and probably most significant factor in the maximum power point voltage of a panel, the temperature, Panels have a higher temp when cooler, hence my earlier comment about the effectiveness in the mornings.