Mega Joules

BuildCraft's system of power.
MJ (Mega Joules) can be generated with BuildCraft Engines, Thermal Expansion Engines or the Blulectric Engine from RedPower 2,  these engines produce MJ when recieving a redstone input and consuming fuel. It's recommended not stay on Redstone Engines too long (or not at all) because they are very slow. Stirling Engines however is very potent early in the game as it produces 1600 MJ per coal at 1 MJ/t and can be connected to machines with Conductive Pipes unlike the Redstone Engine. The Blulectric Engine is a good option if you have a lot of Nikolite, it's able to produce 32 MJ/t at peak performance (depends on the machine it's powering) and can run without the need for maintenance if hooked up to some Solar Panels.

NOTE: MJ to EU is not a 1:1 ratio but rather a 1:2.50 MJ to EU ratio

Using BuildCraft Power (MJ)
MJ can be used to power BuildCraft machines such as the Quarry, and Machines from the Thermal Expansion Mod.

Storage
Currently the only way to store MJ without conversion is with the Redstone Energy Cell, capable of holding 600 000 MJ. The Redstone Energy Cell can also accumulate power by filling it with Molten Redstone.