The first generator that is available to a player. Becomes an option as soon as Solar Cell is researched. Initially, it`s matched exactly to Solar Cell - three heat produced, three heat consumed. This, however, quickly changes as the upgrades start to roll in.
As a rule of thumb, when it`s employed, player lacks any means of heat dissipation of cooling, so if it does start heating up, then the good idea would be to pause and consider the design critically, then either add additional generators or cut down on heat sources. Or invest in some productivity upgrades. Just to make it clear - upgrading heat capacity of this generator only prolongs the inevitable until player researches some alternate means of utilizing or wasting the heat.
This generator does not have the provisions to use water.