At the stage when Solar Cell is researched, player has no heat infrastructure, and therefore must place generators adjacent to the cell in order to make electricity. Diagonal directions do not count, so at most, four generators could benefit from single cell`s output. It`s worth to mention that heat is divited evenly between every single neghboring building that CAN accept heat. So, if Solar Cell is surrounded by one Battery, two Generators and empty cell, Generators will each receive half the heat the cell made.
Vanilla Solar Cell produces 3 x 100 = 300 units of heat in it`s lifetime. Since regardless of method, heat is exchanged for money on 1:1 ratio (Before Bank is constructed, anyways), so fully utilizing the heat output of Solar Cell should give player $100 in profit.