Charge Controllers

[mlewis3498]

With reverence to MPPT and PWM charge controllers. Are their advantages one has over the other on a PV system?

[Sunking]

Yes, with MPPT you will generate about 30% more power. A 200 watt panel with MPPT will generate roughly the same power as a 300 watt panel with PWM.

[green]

So if a PWM controller is "wasting" power, where does that "lost" energy go?

Just wondering,
Green

[Sunking]

So if a PWM controller is "wasting" power, where does that "lost" energy go?

Does not go anywhere, just not utilized.

A PWM controller used on solar panels operate a less than Vmp, and above Isc. With any PWM controller Input Current = Output Current. So take a typical 100 watt panel with a Vmp = 18 volts, and Imp = 5/55 amps. Armed with that and assuming the battery is discharge, full bright sun the output current is 5.55 amps @ roughly 12 volts = 67 watts. If you were to measure the input to the controller you would measure roughly 13 volts @ 5.55 amps or 72 watts. Note what is going on at the input. You are pulling down the rated Vmp voltage of 18 volts down to 13 volts. Solar panels are current sources, not voltage.

Take the same conditions except use a MPPT controller. At the input is 18 volts @ 5.55 amps (100 watts), and on the output is 12 volts @ 7.91 amps or 95 watts.

[russ]

So if a PWM controller is "wasting" power, where does that "lost" energy go?

Just wondering,
Green

I wrote some special software to make it go to your "account" - for only a small fee you can access those stored photons.

[mlewis3498]

Charge Controllers

With reverence to MPPT and PWM charge controllers. Are their advantages one has over the other on a PV system?

Thank you for your quick response and answer.

[green]

Thank you Sunking, that actualy makes sence now, but I like Russ' answer better . It's nice to know I have those photons banked for a rainy day.

On a serious note though, do you think the electronics the manufacturers put into a MPPT controlers are really worth as much as they are charging for them. Or is the price justified soley because of demand. There is such a huge difference in price it just seems like they are gouging to me.

Green

[Sunking]

On a serious note though, do you think the electronics the manufacturers put into a MPPT controlers are really worth as much as they are charging for them. Or is the price justified soley because of demand. There is such a huge difference in price it just seems like they are gouging to me.

We could debate this all day. PWM controllers are pretty simple devices, and MPPT is more complex requiring more parts and engineering.

The more important question is economics of a project. Say you want 1.5 Kwh/day in KCY with a winter Sun Hour of 3 hours with 12 volt battery.

PWM Requirements are:
Panel Wattage = 1000 Watts
Charge Controller = 60 amps

MPPT Requirements are:
Panel Wattage = 750 watts
Charge Controller = 60 Amps

Now go price that out and tell me which is less expensive to implement.

[inetdog]

Thank you Sunking, that actualy makes sence now, but I like Russ' answer better . It's nice to know I have those photons banked for a rainy day.

On a serious note though, do you think the electronics the manufacturers put into a MPPT controlers are really worth as much as they are charging for them. Or is the price justified soley because of demand. There is such a huge difference in price it just seems like they are gouging to me.

Green

One big difference is that a PMM controller can be implemented using only discrete analog and digital parts, while by far the easiest way to implement MPPT is to us a microprocessor or microcontroller chip, with all of the additional support circuitry and software, including lots of testing.

The second is that a PWM controller can use just switching elements (FETs these days) while an MPPT controller has to include a DC to DC converter with intermediate energy storage and a buck-transformer or coil.

A third possible factor is that building a good MPPT requires more engineering, and therefore more development costs to recoup.

[green]

Valid points guys, I just wanted some opinions about it. I should have clarified that I am in the market for a small MPPT controller and thats where I have noticed the biggest price jump when opting for an MPPT.

Green