MPPT controller - voltage sensing without separate wires?

I think about it this way:

In MPPT your system losses are mostly around the distance your solar controller input voltage is away from the instantaneous Vmpp of the panel, the efficiency of the DC-DC voltage conversion, and the voltage drop over the wires coming into the controller (P=IE).

In PWM you sacrifice voltage as part of the design, and the power you drop is the difference between Ppwm = ~Isc * Ebatt and Pmpp = Impp * Vmpp. The big voltage drop due to direct connecting to the battery usually subsumes any drop on the trip from the panels over the wires (except for near sunrise, near sunset, and possibly in lower light conditions). In PWM you are using the solar panels as a current source, and that current does not vary much with voltage drop most of the time (e.g. to the left of Vmpp on the solar current vs. voltage curve).

A typical example might be Vmpp of a panel is 18V, you have .5v drop over the wires. in MPPT that is lost power. In PWM since you are going to pull down the voltage on the panels below 17.5v to something between 10.5 and say 14.8v, the loss does not hurt you much at all. You are into the part of the IV solar panel curve where the amps produced are essentially Isc whether at 14.8v at the panel, or at 15.3 because of the .5v drop due to wiring. There *is* a small drop since the curve is not flat, but it does not usually add up to much unless Vmpp under current conditions gets close to Vbattery.

Jim

"Do you understand how PWM works?

A controlled serial connection from the array to the battery
Ignoring the older cheap junk controllers that did shunt operation

PWM is not that concerned about voltage drops.

Voltage drop equates to a loss of power to the battery which is always a bad thing

As mentioned, PWM can deal with a 5% line drop without performance loss (most of the time).

5% from my POV is a poor system design; anything more than 2 or 3% total line loss is poor design.

MPPT will have a 5% performance drop.

Please explain - some details please
It works like the simple PWM the buck conversion is not needed at lower input voltages. The MPPT controller should not be used in that specific example anyway

Please offer up some specifics - convince me - right now I do not believe

It's all relative, but MPPT needs the big cables."

Again - I need specifics as to WHY you believe this
Personally I do not believe it

Thanks again for taking the time to explain it, even if I need a two by four over the head first.

I also forgot we are talking controllers that do 24v panels but do the amps out to a 12v battery, so the Voc limit and the amps limit are for different things.

Yes, I will stick to my 12v PWM set-up. Less brainwork! :) Thanks again!

Do you understand how pwm works? PWM is not that concerned about voltage drops. As mentioned, pwm can deal with a 5% line drop without performance loss (most of the time). MPPT will have a 5% performance drop. It's all relative, but mppt needs the big cables.

BTW, I do like mppt, but need to keep the facts straight. Was getting 10A from 130W after clouds cleared in Bend this noon.

Sal

Sal

You are going to have to explain your reasoning a bit better
For me to consider your statement anything other than an off the wall remark

I guess I am happy if that is the only thing from the past several posts you can pick on - I expected something sooner

smkettner wrote:
^^^^

6x 24v panels about 200W each. 3 series, 2 parallel.

Actually 2 series and 3 parallel would work same.

Exactly. It is not series or parallel, it is series and parallel. You have the freedom to work with any permutation of combining panel watts up to the voltage limit.

Jim

Or configure for higher voltage and have the best of both worlds. Just go series for low drop on smaller wires.

Jim

Not correct! Why does pwm require massive wires? PWM can easily afford a 5% drop between controller and panels. MPPT can't afford that kind of drop.

When you think about it, mppt needs the huge wires! Big wires or lose performance.

Sal

KJINTF wrote:


4 - Finally the PWM gets to play in the game - a 12 VDC array with a MASSIVE 50 amps of current and requirement for HUGE wires to compensate for extensive line losses

"but you want to stay inside the 45amps limit.

Not really
You want to stay within the WATT limit on the input side for the operational voltage 12, 24, 36, or 48" - the controller will stay with the 45 amp limit input watts output amps

Argggh! But you said if you go close to the 45 the controller will heat up and you want to stay well below that limit.

Me personally I would go with the 60 amp controller if I had 600 watt array in a 12 VDC system - yes I said they heat up etc.. I design my systems on the conservative side. AM Solar and many others do not they sell 600 watt arrays (6 of their 100watt panels) hooked up in parallel with a 20Voc using the 45 amp version controller. For me that's not a good design

Sticking with our discussion the rated max array size for the 45 amp 12 Volt operation systems is 600 watts - so we have been using that as the figure

Now you don't care if you go over the 45?

You cannot go over the 45 amp it is limited by the controller
Remember input watts out amps

I meant just use bigger panels at the same Voc to get more wattage as one choice.

I understood buy had to comment - thought you had some magic powers and could make a larger panel

^^^^

6x 24v panels about 200W each. 3 series, 2 parallel.

Actually 2 series and 3 parallel would work same.