I came across a .zip with refined solar sensor patches for all three Boktai (1-E, 2-E, 3-J version) games some time ago (I actually forgot where I got this).
To quote the readme:
The patches in this archive are solar sensor patches. They allow you
to play the Boktai or Bokura no Taiyou games without a solar sensor,
so that they can be played on a flash card or emulator that doesn't
support it. The retail cartridges have a solar sensor built in,
which affects many things in the game. Sunlight is crucial to
playing the games; without sunlight, you cannot recharge your energy
and thus cannot use a large part of your weaponry. Some puzzles are
also impossible to do without sunlight.
There were solar sensor patches for all three games already, but
some of them (the patch for the third game in particular) had some
faults like inconvenient button activators or a continuous
increase/decrease of sunlight instead of one bar at a time. I took
those patches and improved on them a little in order to make them
a bit easier to use in combination with in-game functions.