 ### Network # Maximum Power Point Tracking for solar photovoltaic ??

#### forever074

Mar 14, 2014
22
I am studying the solar converter which converts voltage of solar photovoltaic module to constant voltage of about 24V (the current can be customized). This converter uses Maximum Power Point Tracking (MPPT).
When the load need power Pload =240W for example, with Uload=24V, then Iload =10A. The power of solar photovoltaic module at maximum Power Point (Pmpp) change depending on solar insolation and temperature. Thus, if this Pmpp=350W, so where does Delta_P of 110W (=Pmpp-Pload) lost ? Do we need another resistor load to dissipate this energy (Delta_P) and how to do that??
Thank you. #### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,505
You misunderstand what MPPT does.

It simply adjusts itself so that the power passing through the load is maximised for any particular set of operating conditions under which the solar cells are experiencing.

Typically the output goes to a constant voltage sink (i.e. you're charging a battery). Whilst this is not quite a constant voltage, it is close enough for the purposes.

With such an output, the maximum power corresponds to the maximum current through the load. So the MPPT charger adjusts the current drawn from the solar panel in small steps. It that step provides an increase in power to the load (i.e. output current) then the next step is in the same direction. If not, the next step is in the reverse direction.

The maximum current may well be zero (at night), so even with a 1,000,000 watt array, you may experience times when you can't supply a 250W load.

Practical MPPT chargers will detect the full charge on the battery and change their program so as not to dump maximum power any longer.

Other MPPT devices (grid linked inverters) have other criteria to stop supplying power. Typically this is when the grid exceeds some range of voltages, frequencies, or impedance.

#### forever074

Mar 14, 2014
22
You misunderstand what MPPT does.

It simply adjusts itself so that the power passing through the load is maximised for any particular set of operating conditions under which the solar cells are experiencing.

Typically the output goes to a constant voltage sink (i.e. you're charging a battery). Whilst this is not quite a constant voltage, it is close enough for the purposes.

With such an output, the maximum power corresponds to the maximum current through the load. So the MPPT charger adjusts the current drawn from the solar panel in small steps. It that step provides an increase in power to the load (i.e. output current) then the next step is in the same direction. If not, the next step is in the reverse direction.

The maximum current may well be zero (at night), so even with a 1,000,000 watt array, you may experience times when you can't supply a 250W load.

Practical MPPT chargers will detect the full charge on the battery and change their program so as not to dump maximum power any longer.

Other MPPT devices (grid linked inverters) have other criteria to stop supplying power. Typically this is when the grid exceeds some range of voltages, frequencies, or impedance.
If load is a battery 12V. the limit charging current is 10A. Is the maximum power from solar PV moule 120/conversion efficiency(W) ??? On the sunny day, the converter doesn't work at maximum power point, does it???

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,505
An MPPT charger will (all other things being equal) ALWAYS work at the maximum power point. That's what they are designed to do.

It may be producing 10A into a 12V load, and at that particular instant the maximum power point of your panels may be 18.2V at 6.6A (Let's say they're a 200W array, the figures are reasonable for that)

A moment later some wispy clouds partially obscure the sun and the maximum power point of the panels is 14.3V at 3.25A -- the current into the 12V load drops to 3.78A.

A while later the clouds suddenly clear, and the panel being a little cooler now has a maximum power point of 18.4V at 6.75A, so 10.35A into 12V. As the panels heat up, the maximum power point shifts back to 18.2V at 6.6A and again the 12V load is getting 10A.

These calculations assume a 100% efficiency which won't happen in real life, but it makes the calculations easier for demonstration purposes.