How to store/use energy that could be generated from a solar cell duing the off stage of a buck converter?

Question

I am trying to design and build a MPPT charger to charge a battery from a solar cell. From what I understand, an MPPT controller is basically a buck converter where the output voltage is optimized such that the current being drawn from a solar cell is I_mp, which will cause the voltage to be at V_mp.

Ideally, the current should be drawn constantly at I_mp to maximize the power, but during the off stage of a buck converter, no current is being drawn from the solar cell when it could have been producing power. Is this really the case, and is there a way to store/use that power during the on stage? Would adding an inductor and capacitor (L2 and C2 as shown below) to the input of the buck converter effectively store the energy from the off stage of the buck converter such that it will be used during the on stage?

Answer 1

Is this really the case [?]

Yes. Without \$L_2, C_2\$ there is no input current when the transistor is off and the solar cell doesn't deliver power other than for its own heating up.

...and is there a way to store/use that power during the on stage?

Yes, your \$C_2\$ can do that for you.
And if you're not concerned about EMC, your \$L_2\$ can be the parasitic inductance of the cables. What I mean to say is that \$L_2\$ isn't necessary for the functioning of the circuit.

Would adding an inductor and capacitor (L2 and C2 as shown below) to the input of the buck converter effectively store the energy from the off stage of the buck converter such that it will be used during the on stage?

Absolutely.
And if the switching period is short enough, but not too short, you can see a current and voltage ripple on the clamps of the solar panel, which enables you to track the Maximum Power Point (MPP). If the ripple is too large, i.e.: influencing the 'average MPP' too much, then your switching frequency is too low.

Answer 2

By off state, I'm assuming you mean the part of the cycle where the buck converter is not feeding current into the buck converter.

If you look at the circuit you've shown above, you see two similar sections on the input and output, formed by an inductor in series and a capacitor to ground. This is a low pass filter, which basically lets DC through, but the high frequency AC from the switching section is heavily attenuated. What this means is that while to the transistor in the middle, it looks like the load on the supply is a high frequency square(ish) wave, to the solar cell it looks like a steady load, with only a minor ripple. The same thing happens at the output, the load receives an almost constant current or voltage, while the middle of the circuit sees high frequency AC.