Steam Turbines

There are 3 levels of single block steam turbines, and 2 further multi block steam turbines from Gregtech.

Single Block Turbines
Turbines exist for LV, MV, and HV applications. Steam usage increases and efficiency decreases for each level of turbine. It is recommended to total up the number of EU used by machines at any time and provide sufficient turbines for them. At 100% efficiency, turbines use 2L of steam to produce 1 EU, but as efficiency decreases or increases more or less is needed.

Basic Steam Turbine
Outputs 32 EU/t at 1 A. Max steam consumption is 1600L per second. Efficiency is 85%.

Advanced Steam Turbine
Outputs 128 EU/t at 1 A. Max Steam consumption is 7040L per second. Efficiency is 75%.

Turbo Steam Turbine
Outputs 512 EU/t at 1A. Max steam consumption is 31515L per second. Efficiency is 66%.

Multiblock Turbines
Multiblock turbines are larger, more complex to operate, and more expensive than single blocks, and require rotors, which need to be replaced every so often. In exchange for this they are much more efficient. Before version 2.2.0.0 large turbines EXPLODED if you produced more power than the dynamo hatch can output (I.E. make 2400 EU/t with an EV dynamo hatch), after 2.2.0.0 any excess energy is just wasted causing no harm. Large turbines support GT 1A dynamo hatches and GT++ 4A buffered dynamo hatches. Make sure that nothing is in the empty space 1 block in front of the front face of the turbine (where the "rotor" is visually showing), otherwise it can cause issues with the multiblock formation.

Large Steam Turbine
Large steam turbines are available at HV. While these are far more difficult to set up, efficiencies even over 100% are possible with the right rotor. They also have the advantage of returning as much distilled water as would be used to produce the steam, meaning you can re-use the distilled water in a Large Heat Exchanger which requires it, or store the distilled water to use later for other things.

Large HP Steam Turbine
High pressure steam turbines are available at IV. These use high pressure steam, which is produced in a Large Heat Exchanger. They output regular steam at a ratio of 1:1, which can be put into a regular steam turbine to produce more power. These use rotors in the same way as the regular Large Steam Turbine.

Rotors
Both kinds of large steam turbines require rotors, which need to be replaced occasionally. There are small rotors, available at MV, regular sized rotors, available at late HV, large rotors available in EV, and huge rotors available once you've obtained a fusion reactor. Larger rotors process more steam and are generally more efficient, but are more expensive. Rotors are also used in large gas turbines and large plasma turbines. For steam, rotors have 2 main stats: efficiency, and optimal steam flow. The optimal steam flow represents how much steam exactly the rotor is designed to process- using less makes them less efficient, while using more simply voids the excess steam.

The amount of power produced by a Large Turbine can be obtained by the formula: (nominal output) * efficiency. Nominal EU output will vary depending on what type of Large Turbine you're working with. Keep in mind what units you're working with. Since the in-game tooltip shows optimal flow as Liters per second rather than Liters per tick, you will need to further divide by 20 to get EU/t. For example, an optimal flow 96000 L/s rotor on a regular Large Steam Turbine will generate 96000/2/20 = 2400 EU/t, before efficiency.
 * A Large Steam Turbine will have a nominal output: (Optimal Steam Flow)/2
 * A High Pressure Large Steam Turbine and Large Gas Turbines will both have a nominal output: (Optimal Steam Flow)
 * A Large Plasma Turbine will have a nominal output: (Optimal Steam Flow) * 40.

If provided with less than the optimal flow, proceed with normal EU output calculations as stated above, but multiply the final value by (actual flow)/(optimal flow). In other words, a less-than-optimal flow will give you a fraction of the optimal EU/t.

If provided with more than the optimal flow, the turbine will enter overflow mode. It will accept up to 250%/450%/550% of the optimal flow of steam/gas/plasma, and produce more power (exact value will depend on your rotor's overflow tier). Drawback is overflow causes an efficiency loss based on how far away from the optimal flow you are.

Right-clicking a rotor with a screwdriver will put it into "Loose" mode, which allows it to process a lot more steam, but even less efficiently. If the efficiency of your turbines is more important, you can use more tight-fitting turbines, but if you don't have many resources to make more turbines, you can use less turbines in loose mode.

A Gregtech fluid regulator cover is extremely useful here in controlling the rate at which you feed liquid into a Large Turbine. Large steam turbines consume steam every tick, so setting up flow regulator to anything larger than one tick will cause them to enter overflow mode. Large gas/plasma turbines consume fuel once per second, but gas turbines can work inconsistently unless regulator is set to once per tick value.

The durability of a rotor in time units can be calculated with this formula. Every 50s the rotor will take damage equal to min(powerGenerated/5, powerGenerated^0.6). This is subtracted from the overall durability until it reaches 0, at which point the rotor breaks and disappears. This formula also includes element of random, that depends on multiblock and fuel type, so the value above is just theoretical minimum.

Power Output and Input
Power is output from the dot on the side, this can be changed with a wrench. Power must be output horizontally, cannot go on the top or bottom.

Steam can be piped into the machines, or automatically put in by auto-output from boilers, in any of the other faces, including the top or bottom. If using pipes, keep in mind that a LOT of steam is required per second, and make sure that you've got pipes that can put enough steam through.

Steam Production
Steam for single block turbines can be produced using several different types of boilers. 14 Small Coal Boilers would be required to create 1 amp of LV power, or 6 High Pressure Coal Boilers, or 3 High Pressure Lava Boilers. These are suitable for early-game power production, but would need to be upgraded before MV. One 2x2x2 low pressure Railcraft multiblock boiler can provide 1 amp of LV, while a 3x4x3 low pressure or 3x2x3 high pressure boiler can provide 1 amp of MV power, or 4 amps of LV. A Large Bronze boiler from Gregtech, while expensive, can provide 2A of MV or 10A of LV. Two large bronze or steel boilers, or one large titanium one, can produce 1A of HV.

With multiblock turbines, greater efficiency is possible, and producing power up to EV is viable. With 130% efficiency or higher rotors, 2 large titanium boilers can produce 1A of EV, if lower, 3 or 4 will be required. Large Heat Exchangers can produce lots of high pressure steam when fed hot coolant from a fluid reactor.