# Solar MPPT charging circuit

I'm new to this solar stuff. I bought an 20W solar panel. I'm planning to upgrade to 100W. But the problem is I've searched about mppt systems and get bit of confused. So please correct me if I'm wrong. So the voltage of the solar panel changes depending on the light. So with mppt we are tracking maximum available power could get from the panel. What is the power(V.I) in this method. I mean which I or which V. V=open circuit? I=short circuit? If like that how can we measure them at the same time and put a result(power) and decide at which voltage the power is the max ? Also , let's say we have found a the peak of power. So we set the voltage to that voltage level via mosfets. And what next , we put it into an DC-DC converter and after that to battery ? Here I've tried to make a circuit. Could you also tell what is wrong with that circuit. Many thanks..

• There is always place between open and short circuit. Google up some graphs Apr 19, 2016 at 6:50
• I've searched a little bit, around 17 volts I see the maximum power for 40-50W panels. How do I get Imp and Vmp ? Apr 19, 2016 at 7:07

MPPT algorithms work something like this.

If you don't take any current from the panel, the voltage is maximum, but the output power is zero.

If you take maximum current from the panel by short circuiting it, the output power is zero.

At any intermediate level of current, power is finite.

At some specific intermediate level of current, the MPPT, power is maximum. At levels of current above and below the MPPT, the power is less.

The actual level of current drawn to achieve MPPT depends on the present lighting level, which will change throughout the day and from second to second, so cannot be predetermined.

So the MPPT controller makes a guess of an initial current, and measures the output power. If the load is a relatively constant voltage like a battery being charged or an inverter into the grid, then it's simply a matter of measuring the current output into the load, no need to multiply Vin by Iin.

Now the MPPT increases Iin a little, and measures Iout. If it increases, it does it again. If it decreases, it drops Iin and tries again. Rinse and repeat all day.

To work like this, the MPPT controller must be able to dump any level of output current into its load. Batteries or the grid-tie connection must be sized to allow this given the size of the panels connected. If the panels are upgraded, then the load capability must be rechecked.

• I got it thanks. I've searched Google to find mppt circuits which controlled by arduino. Can you suggest one ? Apr 19, 2016 at 8:46