This circuit is an implementation of a buck converter power stage that could be used in the MPPT solar battery charger reference design found here: https://www.systemvision.com/design/solar-energy-harvesting-compare-dire...
That reference example is appropriate for "system level" trade-off assessment, where the MPPT (maximum power point tracking) approach can be compared with direct solar panel battery charging. It uses a state-average (non-switching) buck converter model for much faster simulation, so that power tracking performance over long time periods can be observed. However, it does not account for some important aspects of a real converter implementation, such as the predicted power loss in the switching components, or the switching noise on the current and voltage measurements that are needed for power detection.
This circuit confirms the performance of the system at full solar panel irradiance, and with the converter duty-cycle set to a fixed value of 0.8. That value was shown to provide maximum power under full irradiance. The results with this design confirm those of the reference design: The steady-state panel power output is just under 60 Watts (light blue waveform); The corresponding voltage (16 V) and current (3.7 A) into the converter (magenta and green waveforms, respectively); The current into the battery is 4.5 A (red waveform), as expected. Note also that the input L-C filter removes most of the switching noise that would be visible on these signals without that filtering effect.
The average power loss in the P-channel MOSFET is 1.3 Watts (brown waveform). This is important for assessing overall system efficiency, a key factor in the trade-off analysis with direct charging. The user can move the waveform probes around and observe the power loss in all of the other components too, as part of the efficiency analysis process.