The Solar Helmet is a piece of armor added by Industrial Craft 2. It is a Solar Panel worn in the Helmet slot of the inventory that recharges the item in the Torso slot of the inventory, such as a BatPack, an Electric Jetpack, or a LapPack, as long as the player is within view of the sun. It will generate EU at a rate of 1 EU/t, which is the same rate of generation as the Solar Panel itself.
There is a bug with the Solar Helmet where it will continue to generate EU during the night, so long as the player is within view of the sky. Similarly, though the upgraded LV Solar Hat and the MV Solar Hat cannot recharge a LapPack, the Solar Helmet is able to.