help on understanding MPPT for solar panels

[anarion]

Hi! I am studying maximum power point tracking (MPPT), and I have found many setups with buck converter. Buck converters step down the voltage from my understanding, so how can you have the maximum power at load if you step down the voltage? Do you increase the current so you get max power?

I am also confused about what load to use in the output of the buck converter. For example if you step down from a 17V solar panel input to a 5V output, and the max power from the solar panel is 10W, you need 2A current at the output (5V*2A = 10W), so your load should always be 2.5 ohms? So if one changes the load, then the maximum power cannot be reached?

I hope someone can point me in the right direction, and correct me if my understanding is wrong

Thanks

 

[emontllo]

Hello,

A Buck converter with a MPPT control strategy would be focused on changing the current drawn from the solar PV panels dynamically in order to find the maximum power point (V*I).

Typically, these converters are connected to loads like voltage sources (typically batteries or inverters), not resistors. If a battery is connected to the output of this buck converter, the output current will change according to the available power. The same for a properly controlled inverter injecting current to the grid.

In the other hand, if you connect a resistor, you will only be able to track the maximum power point if you allow a variable output voltage. If you fix output voltage it is not possible to reach the maximum power.

If the panels are used for a stand-alone system, MPPT only makes sense if batteries are used. If no batteries are available, control the buck with a fixed voltage output and expect not using all the power available and power outages when there is not enough sun!

 

[anarion]

Hello,

A Buck converter with a MPPT control strategy would be focused on changing the current drawn from the solar PV panels dynamically in order to find the maximum power point (V*I).

Typically, these converters are connected to loads like voltage sources (typically batteries or inverters), not resistors. If a battery is connected to the output of this buck converter, the output current will change according to the available power. The same for a properly controlled inverter injecting current to the grid.

In the other hand, if you connect a resistor, you will only be able to track the maximum power point if you allow a variable output voltage. If you fix output voltage it is not possible to reach the maximum power.

If the panels are used for a stand-alone system, MPPT only makes sense if batteries are used. If no batteries are available, control the buck with a fixed voltage output and expect not using all the power available and power outages when there is not enough sun!

Thank you for answering! Aside from using voltage sources, I was thinking of using a fan from a desktop CPU at the output of the buck converter. Do you think MPPT can be implemented with a fan?

 

[FvM]

Do you think MPPT can be implemented with a fan?

Do you mean transfer the maximum power to the fan? This presumes, that the fan can't be overloaded by the solar panel output power, otherwise you need to implement an additional voltage limiting. Appart from this problem, it's surely possible. MPPT need a controller, that either uses known solar panel characteristic or determines the MPP by continuos small variations of the operation point. In most cases, a microcontroller will be used for this purpose.