The Geothermal Generator is an Industrial Craft 2 generator. Geothermal Generators use the heat from Lava Cells or Lava Buckets to generate EU. The primary benefit of the Geothermal Generator is that it will only provide EU when a machine requires it, whereas the standard Generator will burn fuel as soon as it's provided to it.
During operation, the Geothermal Generator will output 20 EU/t. At maximum output, the Geothermal Generator will consume a Lava Bucket every 50 seconds and produce 20,000 EU per-item. The Geothermal Generator has its own internal lava storage and can hold up to 24 Lava Buckets or Lava Cells. Internally, the Geothermal Generator can store 480,000 EU in lava, but it has to consume that lava before it can be used.
Along with Lava Cells and Lava Buckets, the Geothermal Generator will accept lava pumped in from BuildCraft Waterproof Pipes. Lava can be pumped in from any side of the machine. Lava source blocks crafted from UU-Matter cannot be directly used with the machine and have to be placed in a Bucket or an Empty Cell before processing.
The Geothermal Generator's GUI features two slots. The top slot can be used for recharging tools and batteries. Lava is placed in the bottom slot of the GUI.