Why a 130W solar module does not produce 130 W when connected to battery?

[Sunking]

Exactly right! Very similar to what a transformer does for AC, just harder to implement.

Not exactly as there will always be power losses in the conversion process. Transformers can be up to 99% efficient and MPPT controllers as high as 98%. It a moot point though so the concept is correct.

Now if the output voltage of the panels were exactly right at any given moment during charging, a PWM CC could be slightly more efficient than an MPPT controller simply because there is less electronics between the panels and the batteries.

Nah. If the panel voltage were always correct there would be no need for a controller. Regardless a PWM will always have a forward bias voltage drop of approx 1 volt in the FET junction. So say 13 volts @ 7.69 amps (100 watts) comes out at 12 volts @ 7.69 amps (92 watts) 0r 92% efficiency which is lower than MPPT 95 to 98%.

This is what makes MPPT controllers so much better. When using a PWM controller on a 12 volt battery you are forced to use panels made for 12 volt batteries that have a Vmp of 17 to 18 volts. It has to be to be able to supply a charging voltage up to 16 volts + 1 volt for forward bias voltage.

MPPT allows you to use much less expensive Grid Tied Panels and much smaller less expensive wiring between panel and controller. There are some MPPT controllers that you can use up to 100 volts on a 12 volt battery. In that case you input 100 volts @ 1 amp and out with 12 volts at 8.16 amps.

[inetdog]

Regardless a PWM will always have a forward bias voltage drop of approx 1 volt in the FET junction.

With a MOSFET, there is no need for a forward bias. This is one reason that circuits which must have polarity protection but cannot afford the voltage drop use active circuitry with FETs instead of a diode. Not that any particular PWM CC does that, but that is the theory.

[ckhorne]

Thanks for the clarification, but I thought that is what I said. Did I articulate it incorrectly? Would not surprise me if I did lol...

Well, yes and no... You said "Though it only has the Voltage and amps the Panel(s) provide." - this is incorrect in that it doesn't have the constituent voltage and current to work with (ie- only 12v and only 8amps), but rather any combination of the two that provides the maximum power to the battery. It's a technicality, but an important one when comparing MPPT vs PWM controllers...

[RageFury]

Well, yes and no... You said "Though it only has the Voltage and amps the Panel(s) provide." - this is incorrect in that it doesn't have the constituent voltage and current to work with (ie- only 12v and only 8amps), but rather any combination of the two that provides the maximum power to the battery. It's a technicality, but an important one when comparing MPPT vs PWM controllers...

Understood.

[Sunking]

With a MOSFET, there is no need for a forward bias. This is one reason that circuits which must have polarity protection but cannot afford the voltage drop use active circuitry with FETs instead of a diode. Not that any particular PWM CC does that, but that is the theory.

All PWM controllers use FET's. All FET's have a voltage drop between Drain and Source of approx 1 volt when operated as a DC Switch or relay.

[inetdog]

All PWM controllers use FET's. All FET's have a voltage drop between Drain and Source of approx 1 volt when operated as a DC Switch or relay.

It all depends on the type of FET and the available Gate to Source voltage. Take a look at the upper left graph on page 3.

The Source to Drain voltage shown there has a purely resistive characteristic as long as a high Gate to Source voltage is applied.
It may be that design economics result in a working configuration in which a 1 volt drop under full current load it tolerated, but it is by no means a "diode drop" which produces a constant voltage offset independent of current.
If you use a big enough FET (or enough in parallel) you can reduce the offset to as small a number as you want.

If you want to make the statement that all known PWM CCs are designed around a one volt drop, I do not have any information to contradict that. But that would be an engineering decision rather than a requirement imposed by the technology.

Since an MPPT controller uses either rectifier diodes or synchronously switched FETs on its output, the losses there would be the same as the losses in a PWM CC, and you would then have the additional input stage and transformer losses to contend with. What the MPPT controller does always have available is a source for high Gate voltages.

[Sunking]

Who is going to pay $200 for a $40 10 amp controller? To do what you suggest has already been done in decades past in the 8-Track Tape days. A relay with a voltage comparator circuit to operate a relay. DOH! That is exactly what Coleman controllers did.