36v Panel, multiplies amperage

[UptownSport]

A thread fifty some pages back where Denver Jim described successfully using grid-tie solar panels interested me-
I didn't want to add to the thread as it veered into other topics.
I assumed his grid panels were something like this:

SolarWorld 340 Watt Sunmodule XL Monocrystalline Panel with Black Frame & Backsheet


And, then, saw this;

... MPPT ...

When it steps DOWN the voltage of a 36 volt panel three times to 12 volt, it also steps UP the amperage and triples the amperage. It does appear to be magic, but it's simply Ohms law meeting some great electrical engineering.
...

The panel, or one similar to the one linked would end up with 800-900 Watts at 12v, or so?? (Not to be contrary, but sounds a little too good to be true, between you and me!)

I'm confident that there'll be a problem even with moderate loads* and 200-300W of 12v panels, as there's long overcast periods here.

Maybe my thinking's wrong that high watt panels will charge more in sub par light, but I did see one of Bob's interviews where that was mentioned.


I understand from what I've read the controller will need to be rated for the full open circuit voltage.

So my question is, would a 36v panel produce double or even near triple the effective watts at 12V? I understand theory is different than real life. Anyone who's still using them?
Thanks in advance!

* Fridge, fans, etc

 

[tx2sturgis]

There is no 'free lunch' in electronics.

If you halve the voltage but double the current, its still the same amount of power. Doing creative math does not change this.

12 volts at 2 amps is 24 watts.

And 24 volts at 1 amp is....24 watts.

The power output that is possible for the panel is always about the same, no matter how the volts and amps are juggled around, within reasonable limits.

1 volt wouldn't work very well, neither would 20,000 volts. But within normal ranges, the power and performance are similar.

The MPPT controllers can extract a bit more of the panels total power output over a day of charging, so thats why they are used.

 

[John61CT]

Yes watts are watts, no matter the voltage, power stays constant.

Only amps vary with voltage

 

[UptownSport]

LoL, thanks! No free lunch.

 

[jimindenver]

Gris tied panels work great and cost a lot less too. I started with a 230w panel that was rated for under 9 amps and on a MPPT controller it put out 15a to the battery. A MPPT controller does not boost anything, it allows you to use 100% of the panels output. It seems like a boost when you are use to a PWM controller but that is because a PWM controller dumps any excess voltage meaning you do not get to use 100% of your panels production.

 

[jonsun]

...unless you bought panels at the proper voltage from the get go

 

[akrvbob]

...unless you bought panels at the proper voltage from the get go

EXCEPT, THEY DON'T EXIST. Every solar panel produces more volts than a 12 volt battery can take. If you buy a PWM controller, all the power above the voltage the battery can take and the voltage the panel is rated at is lost. Flushed down the toilet. 

But... if you buy a MPPT controller it will step down the voltage, just like the PWM does, but it will also increase the amps. That way, all the power your panel makes gets into the batteries. 

There is no proper voltge for solar systems, only proper controllers that can efficiently handle that voltage. 

A PWM controller NEVER efficiently handles the voltage any solar panel on the market makes.

 

[jonsun]

you charge your battery at 12v?

 

[highdesertranger]

well actually you charge your battery from 13.6-14.8 depending on battery chemistry. and the don't make solar panels in that range that's why you need a controller. if the made 12v panels your battery would never get charged. highdesertranger

 

[jonsun]

so would you say a 17v panel is much closer to that 14.8v than a 36v panel?

Do you get more current from a 100w panel at 17v or 36v?

 

[jimindenver]

As long as you are using a MPPT controller, they both produce the same.