Energy Transformation

Energy Conversion Sequence in a Device

Energy transformation is the change of energy from one form into another. The word "transformation" does not mean energy is created from nothing. Energy still follows the law of energy conservation, but its form and transfer path change.

Energy changes form during use, but the total amount remains constant. In a real device, part of the input usually becomes the desired output, while another part is transferred to the surroundings as heating, sound, vibration, or reflected light.

An energy technology's conversion path shows how it changes energy:

\text{energy source} \rightarrow \text{initial form} \rightarrow \text{conversion device} \rightarrow \text{useful output}+\text{energy to surroundings}

The energy sent to the surroundings still counts in the energy balance. Its form may be heat, sound, vibration, or reflected light.

Conversion Paths in Power Plants

The diagram shows the forms of energy supplied by different sources and how power plants convert them for use.

Power Plants Convert Energy in Stages

In hydropower, water flows through a penstock and spins turbine blades. The turbine drives a generator that produces electricity.

In wind power, wind turns the turbine blades, the rotor drives a generator, and the generator produces electricity.

Wind Turbine Energy Conversion

Change the wind speed, observe the rotor, and compare how the kinetic energy of the air is converted into electrical energy.

Wind speed

7\ \text{m/s}

Conversion path: Wind turns the rotor, the rotor turns the generator, and electricity flows out.
Physics meaning: Higher wind speed can make the rotor spin faster, but output is still limited by turbine capacity, the control system, and site conditions.

In a photovoltaic panel, cells convert sunlight directly into electricity. Only photons absorbed by the semiconductor material contribute energy to electricity generation.

Technology	Main conversion path	Energy often transferred to the surroundings as
Hydropower plant	gravitational potential of water → kinetic energy of water → turbine → generator → electricity	heat from shaft friction, sound, vibration
Wind turbine	wind kinetic energy → turbine → generator → electricity	sound, vibration, heat from components
Photovoltaic solar panel	solar radiation → electricity	reflected light and heat
Biomass	chemical energy → combustion → heat → turbine → generator → electricity	waste heat, exhaust gases, sound
Biogas	chemical energy → combustion in an engine or turbine → shaft motion → generator → electricity	waste heat, exhaust gases, sound
Geothermal power	reservoir thermal energy → flowing steam or working fluid → turbine → generator → electricity	waste heat and system friction

Biopower technologies convert biomass into heat and electricity through combustion, bacterial decomposition, or conversion into gaseous and liquid fuels.

Geothermal power plants use hot fluid or steam from below Earth's surface to drive turbines and produce electricity.

Because not all input energy becomes the output we need, we use efficiency. Efficiency compares useful energy with input energy.

\eta=\frac{E_{\text{useful}}}{E_{\text{input}}}\times 100\%

Symbol guide:

Symbol	Meaning
$\eta$	efficiency
$E_{\text{useful}}$	energy delivered as the intended useful output
$E_{\text{input}}$	energy received by the device

Suppose a panel receives $800 \text{ J}$ of light energy and produces $160 \text{ J}$ of electrical energy. Its efficiency is:

\begin{aligned} \eta &= \frac{E_{\text{useful}}}{E_{\text{input}}}\times 100\% \\ &= \frac{160 \text{ J}}{800 \text{ J}}\times 100\% \\ &= 20\% \end{aligned}

The energy that does not become useful electricity is:

\begin{aligned} E_{\text{surroundings}} &= E_{\text{input}}-E_{\text{useful}} \\ &= 800 \text{ J}-160 \text{ J} \\ &= 640 \text{ J} \end{aligned}

So, an efficiency of $20\%$ does not mean the remaining $80\%$ disappears. The remaining $80\%$ is transferred to the surroundings, for example through heating or reflected and transmitted radiation.

Energy efficiency measures the share of input energy converted into useful output by a device.

Comparing Conversion Paths across Devices

Solar panels, wind turbines, generators, and biogas reactors convert existing energy from one form to another. The device name alone does not state the source, conversion path, useful output, or energy transferred to the surroundings.

When you see this device	Ask this question
Solar panel	How much radiant energy becomes electricity?
Wind turbine	Is the wind fast enough to rotate the rotor?
Hydropower plant	How large are the water flow rate and height difference?
Biomass	Is the feedstock sufficient and managed sustainably?
Geothermal power plant	Does the site provide sufficient underground heat, fluid, and flow for power generation?

The conversion path records the source, initial energy form, output form, useful energy, and energy transferred to the surroundings.