Correct Answer - Option 1 : 27%

__Concept:__

The overall efficiency of the power plant is given as

\(Overall\;Efficiency\;\; = \frac{{Electrical\;energy\;output}}{{chemical\;energy\;input}}\)

Overall efficiency is also expressed as

\({\eta _0} = \;\frac{{Thermal\;Energy}}{{Chemical\;Energy}} × \frac{{Mechanical\;Energy}}{{Thermal\;Energy}} × \frac{{Electrical\;Energy}}{{Mechanical\;energy}}\)

So, the overall efficiency of the power plant is equal to the multiplication of the efficiencies of the boiler, turbine, and generator.

**Overall Efficiency = Boiler efficiency × turbine efficiency × generator efficiency**

**ηpower plant = ηboiler × ηturbine × ηgenerator**

Where,

Boiler efficiency = Thermal efficiency

Turbine efficiency × Generator efficiency = Electrical efficiency

∴ Overall Efficiency **= ****Thermal efficiency × Electrical efficiency **

__Calculation:__

Given-

Thermal efficiency = 30%

Electrical Efficiency = 90%

Overall efficiency of the plant = (0.30) (0.90) = 0.27

Overall efficiency of the plant in percentages = 27%.