One MPPT or Two?

[temptress]

If you connect the solar panel to a variable load together with a voltmeter and an ammeter

Record volts and amps as the load is varied , multiply volts by amps to get the power in watts and plot a graph of power against volts you will get a curve which rises to a maximum and then falls again.

The peak is the maximum power point at which an MPPT controller tries to control the solar panel. the corresponding volts is V_MP

Thanks finally see what's happening there but still need to know if multiple Mppt controllers are needed?

 

[noelex]

I have my panels connected is parallel to a single Mppt and they work fine.

They will work fine this is how most solar arrays are connected including mine, but that does not mean it is the way to extract the most power.

Let me try explaining it another way. Let's suppose you have two identical panels one is in full sun and the voltage that this panel produces the most power is 16v (the Vmp). The second identical panel has small shaddow from one of the shrouds falling across a couple of cells, as well as decreasing the output from that panel the shadow also drops the voltage at which it produces the most power, lets call its Vmp 15v. This is quite a common and realistic situation.

With two controllers one for each panel they can be operated at different voltages by their individual controllers. One at 16v the other at 15v. This will by definition extract the most power.

With only one controller for both panels they must be operated at the same voltage (if in parallel). The controller would probably pick something like 15.5v. Both panels would be running at 15.5 v which is not the voltage that they produce the most power. Because neither panel is operating at its optimum voltage the output will be lower.

Whether or not the difference great enough to warrant separate controllers is another matter, but I hope the practical example makes it easy to understand why the output is greater with a controller for each panel (ignoring self consumption of the controllers).

NOW, how about wiring the panels is series to increase the input volts to say 60? Assuming the controler can handle the input would this be better?

Series or parallel connection is way more complicated to analyse.
The mathematical modelling of what hapens with isolated shade is very complex. The consensus seems to be that on a boat parallel connection is superior. I agree with this and this is how my panels are connected, but I would like some firmer evidence before I was certain.

 

[MikeBz]

As other posters have said, multiple MPPT controllers are not NEEDED but will yield more charge if the panels are in different amounts of light/shade or at different angles to the sun. Whether the improvement is worth the expense is unknown - I bet the money would be much better spent on another panel (if you have somewhere to fit it).

 

[temptress]

They will work fine this is how most solar arrays are connected including mine, but that does not mean it is the way to extract the most power.

Let me try explaining it another way. Let's suppose you have two identical panels one is in full sun and the voltage that this panel produces the most power is 16v (the Vmp). The second identical panel has small shaddow from one of the shrouds falling across a couple of cells, as well as decreasing the output from that panel the shadow also drops the voltage at which it produces the most power, lets call its Vmp 15v. This is quite a common and realistic situation.

With two controllers one for each panel they can be operated at different voltages by their individual controllers. One at 16v the other at 15v. This will by definition extract the most power.

With only one controller for both panels they must be operated at the same voltage (if in parallel). The controller would probably pick something like 15.5v. Both panels would be running at 15.5 v which is not the voltage that they produce the most power. Because neither panel is operating at its optimum voltage the output will be lower.

Whether or not the difference great enough to warrant separate controllers is another matter, but I hope the practical example makes it easy to understand why the output is greater with a controller for each panel (ignoring self consumption of the controllers).



Series or parallel connection is way more complicated to analyse.
The mathematical modelling of what hapens with isolated shade is very complex. The consensus seems to be that on a boat parallel connection is superior. I agree with this and this is how my panels are connected, but I would like some firmer evidence before I was certain.

Yes I like that. Will experiment with panels is series over the next couple of months and see what I get then perhaps start another thread.

 

[charles_reed]

Solar panels were and are still designed to charge a 12v battery with a direct connection. The design here means the number of cells cosen to make the panel. Cells giving about .4 volt each and are wired in series (then banks in parallel. The number of cells was chosen to give a useful charge voltage say about 13v on a relatively dim day. This means that in real full sun the voltage is higher than needed. hence a 12v panel will usually produce 18 to 20 volts with no load. As said the cells have a significant internal resistance. This means that as current is drawn the voltage falls. Now a regulator is usually fitted to stop the panel overcharging or boiling the battery. hence not a concern for a small panel large battery.
An MPPT controller both stops the battery being overcharged but more importantly takes current from the panel at the rate for amx power (transfer) for that particular level of sun shine.
As for the OP question I would mostly guess that while as said 3 controllers might extract a little more power from the whole system it would mostly improve the sellers sales figures. olewill

Way out of date William - domestic panels are being being produced that put out (usually) 48v and some @ 72v nominal. They're far more rewarding to use than those manky little 12v PV panels.

 

[William_H]

Quite correct domestic panels are typically much higher voltage and ina size generally limited to easy handling on a roof. ie about 200watts.
nteresting that the switching input circuits of a domestic 240v inverter would be similar to input circuits of an MPPT controller. Domestic panels are usually connected in series to give around 300 or more volts in to inverter. Higher voltage to switching transistors means lower current being switched and any volt drop in the switching transistors (FETs) being less significant . So theoretically series panels into an MPPT controller should be more efficient. (ultimately only a small change in efficiency overall of course) olewill

 

[William_H]

Quite correct domestic panels are typically much higher voltage and ina size generally limited to easy handling on a roof. ie about 200watts.
nteresting that the switching input circuits of a domestic 240v inverter would be similar to input circuits of an MPPT controller. Domestic panels are usually connected in series to give around 300 or more volts in to inverter. Higher voltage to switching transistors means lower current being switched and any volt drop in the switching transistors (FETs) being less significant . So theoretically series panels into an MPPT controller should be more efficient. (ultimately only a small change in efficiency overall of course) olewill