How efficient are energy systems?

No process or reaction is 100% efficient. When a number of inefficient processed are placed in series the losses can render the process pointless. Generating electricity is never efficient. Burning fossil fuel and generating electricity is about 33% efficient. The First law and Second law of Thermodynamics always work against renewable energy systems.

Burning fossil fuel to create usable heat is 85% efficient eg making steam to power a turbine.  Burning fossil fuel and generating electricity is about 33% efficient. The drop in efficiency comes from the Second Law limitation which states that not all heat (a disordered form of energy) can be converted to work (an ordered form of energy).

Some polymer photovoltaics’ are now reported as having an efficiency of more than 35%.  This is close to the limit of silicon technology.  The high efficiencies that are quoted relate to new panels receiving full solar radiation.  Output from photovoltaic panels is usually restricted to a few hours a day.

The process of storing electrical energy in a battery and recovering it is 90% efficient.

Converting electrical energy into mechanical energy with an electric motor is 85% efficient.

Fuel Cells are up to 60% efficient.  Theoretically they can be 92% efficient.  Electrochemical processes are limited in their efficiency by the enthalpy of the electrochemical reactions.

Internal combustion engines are 30% efficient due to Second Law limitations.

Wind energy is about 60% efficient.  Wind turbines convert the kinetic energy of the wind to rotational shaft energy which can be used to create electrical energy.  The limit of wind energy conversion comes from the residual kinetic energy still present downwind of the blades.  Wind turbines only generate electricity 25% of the time due to the requirements of the grid.

First law of thermodynamics (conservation) Energy is neither created nor destroyed, it changes from one form to another.

Second law of thermodynamics (entropy) The energy available after a chemical reaction is less than that at the beginning of a reaction; energy conversions are not 100% efficient