@Ryan R I think you have to do a .print statement after the .tran line, and run ngspice as a batch operation (in xschem: select ngspice batch in Simulation->configure Simulators and tools). the listing goes in the output log file (*.out file). This file can be easily read by excel: .print tran v(vgs) v(vds) result in log file will be something like:

No. of Data Rows : 5662
      ** sch_path: /home/schippes/share/doc/xschem/ngspice/solar_panel.sch
      Transient Analysis  Sat Jul  2 15:02:18  2022
--------------------------------------------------------------------------------
Index   time            v(panel)        v(led)          
--------------------------------------------------------------------------------
0       1.000000e-11    6.300000e-06    -1.25000e-09
1       2.000000e-11    1.260000e-05    -2.50000e-09
2       4.000000e-11    2.520000e-05    -5.00000e-09
3       8.000000e-11    5.039999e-05    -1.00000e-08
4       1.600000e-10    1.008000e-04    -2.00000e-08
5       3.200000e-10    2.015999e-04    -4.00000e-08
6       3.807335e-10    2.398619e-04    -4.75917e-08
7       4.365831e-10    2.750472e-04    -5.45729e-08
8       4.659514e-10    2.935491e-04    -5.82439e-08
...
...