Quoted from Prof. 9:

All-new Boktai solar sensor patches written from scratch, with features not found in many other solar sensor patches.

• Button activators chosen to interfere with button combinations used by the game as little as possible.
• Adjust sunlight by 1 bar per button press instead of a continuous increase/decrease as long as the button is held down.
• Does not affect save format or Real Time Clock.
• Boktai 1 patch does not have the sensor blocking bug.
• Boktai 3 patch affects all game elements that require sunlight.
• Works with effects that modify the sun gauge, such as Rising Sun.

These patches 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 or defeat half of the bosses. 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, a continuous increase/decrease of sunlight or the faked sunlight not affecting all in-game elements that it should. So, having played all the Boktai games, I tinkered with those patches a bit to fix things I didn't like; later, I wrote my own patches from scratch which are what you'll find in this archive.

In addition to supporting more regions, my patches differ slightly from other patches available on the web. Mine generally fake the solar sensor value at a lower level, so they should have the best effect. Furthermore, they do not change the save format or Real Time Clock. You can find some of the other differences below:

Boktai 1:
• Uses R+A+D-pad button activator instead of L+D-pad.
• Doesn't have the bug where setting the solar gauge to empty does not actually block out all sunlight that some other patches have.
• Works with Rising Sun grenades, Sunny Clogs and Mr. Rainnot/Tonniar .Rm.

Boktai 2:
• Uses Select button activator instead of R+D-pad.
• Updates solar gauge graphics when changing the sunlight level while the game is paused.
• Changes the sunlight level one bar per button press instead of a continuous increase/decrease.
• Works with Rising Sun/Black Sun magic, Sunny Clogs and Mr. Rainnot/Tonniar .Rm.

Boktai 3:
• Uses Select button activator instead of L+D-pad.
• Affects all game elements - Skylights, motorcycle sequences, Solar Stations - instead of only a few.
• Updates solar gauge graphics when changing the sunlight level while the game is paused.
• Changes the sunlight level one bar per button press instead of a continuous increase/decrease.
• Works with Rising Sun magic, Sol Trance, Sunny Clogs and Mr. Rainnot/Tonniar .Rm.

History:
v1.0.0 - 11 August 2010:
• Initial release. Contained revised patches for European Boktai 1 and 2, and Japanese Boktai 3.

v2.0.0 - 25 July 2012:
• Wrote new patches from scratch for all known Boktai ROM dumps.

v2.1.0 - 7 February 2015
• Fixed solar sensor deterioration bug for Boktai 3.

v2.2.0 - 21 March 2015
• Patches now work properly with effects that modify the solar gauge such as Rising Sun, Sol Trance, Sunny Clogs and Mr. Rainnot.
• Changed the button combination for Boktai 1 to R + A.

Credits:
• Prof. 9: modified Boktai 1 and 2 patches, created Boktai 3 patch.
• Hiei-YYH: save fix for Eternity's Boktai 2 patch. I also used his Sun Meter Mod code for Bokura no Taiyou 3 to make the new Boktai 3 solar sensor patch.
• The release groups that made the original solar sensor patches for Boktai 1 and 2 (E): Rising Sun and Eternity.

For further details see the following threads:
• New Version - Boktai 1 Solar Sensor Hack
• New Version - Boktai 2 Solar Sensor Hack
• New Version - Boktai 3 Solar Sensor Hack