Secondary energy

What Is Secondary Energy?

Secondary energy refers to energy forms that have been transformed from primary energy sources to make them more usable and convenient for various applications. It is a fundamental concept within energy markets and energy economics, highlighting the processes by which raw energy sources are converted into forms suitable for consumption. The most prominent example of secondary energy is electricity, which is derived from burning fossil fuels, harnessing renewable energy like wind or solar, or utilizing nuclear power¹³. Unlike primary energy, which is found in nature in its raw state (e.g., coal, crude oil, natural gas, sunlight, wind), secondary energy is the result of human-induced energy conversion processes¹².

History and Origin

The concept of converting one form of energy into another has roots dating back to early human history with the controlled use of fire for heating and cooking by burning biomass¹¹. However, the large-scale production and widespread use of secondary energy sources truly began to transform societies during the Industrial Revolution. This era, starting in the mid-18th century, saw the development and widespread adoption of the steam engine, which ingeniously converted thermal energy from burning coal into mechanical energy to power factories and transportation¹⁰.

Before this period, human and animal labor, along with natural forces like wind and flowing water, were the primary means of generating mechanical power. Waterwheels, for instance, were used for grinding grain and driving various machines⁹. The invention of the practical steam engine by figures like James Watt significantly enhanced the ability to convert primary energy (coal) into a more versatile form (steam, then mechanical work), driving unprecedented industrial growth. Later, the late 19th century marked a pivotal moment with the advent of electricity generation, notably with Thomas Edison's first central power plant in New York City in 1880, which converted coal-powered steam into electricity⁸. This innovation laid the groundwork for modern grid infrastructure and the pervasive use of electricity as the dominant form of secondary energy today.

Key Takeaways

Secondary energy is energy that has been converted from primary energy sources into a more usable form, such as electricity or refined petroleum products.
Electricity is the most common and widely used form of secondary energy, produced from various primary sources including fossil fuels, nuclear, and renewables.
The conversion of primary to secondary energy inevitably involves energy losses due to the laws of thermodynamics.
Understanding secondary energy is crucial for analyzing energy consumption patterns, optimizing energy systems, and assessing environmental impacts.
Improvements in energy efficiency during conversion processes are vital for sustainable energy management.

Formula and Calculation

While secondary energy itself is a classification rather than a single measurable quantity with a universal formula, the efficiency of its production is a critical aspect. The process of converting primary energy into secondary energy involves inherent losses. The energy conversion efficiency (or thermodynamic efficiency) quantifies how effectively input energy is transformed into useful output energy.

The formula for energy conversion efficiency is:

\text{Efficiency} = \frac{\text{Useful Energy Output}}{\text{Total Energy Input}} \times 100\%

Where:

Useful Energy Output represents the amount of secondary energy produced (e.g., electricity generated).
Total Energy Input is the amount of primary energy consumed in the conversion process (e.g., heat content of coal or natural gas burned).

For instance, power generation plants typically lose a significant portion of the input energy as waste heat during the process of producing electricity⁷.

Interpreting Secondary Energy

Interpreting secondary energy involves understanding its role in the broader energy system. It highlights the value added through transformation: electricity is far more versatile than raw coal, and gasoline is more practical for transportation than crude oil. The characteristics of secondary energy, such as its ease of transmission, storage (in some forms like batteries or hydrogen, part of energy storage solutions), and end-use flexibility, are paramount to modern economies.

The quantity of secondary energy produced often reflects the scale of industrial processes and general economic activity. When evaluating energy systems, the focus is not just on the volume of secondary energy but also on the efficiency of its production and the environmental footprint of the conversion processes. Policy and investment often aim to increase the share of secondary energy derived from cleaner primary sources or to improve the efficiency of existing conversion technologies. Understanding the flow from primary to secondary energy helps stakeholders, from utility providers to policymakers, manage demand response and plan for future energy needs.

Hypothetical Example

Consider a coal-fired power plant that produces electricity, a common form of secondary energy.

Primary Energy Input: The plant burns 100 units of coal (primary energy).
Conversion Process: The heat from burning coal boils water to create high-pressure steam. This steam then turns a turbine, which spins a generator to produce electricity.
Secondary Energy Output: Due to the inherent inefficiencies in thermal power generation, only about 30-40 units of electricity (secondary energy) might be produced from the 100 units of coal input⁶. The remaining 60-70 units are lost, primarily as waste heat expelled into the environment, often through cooling towers.
Distribution: This generated electricity generation is then transmitted through high-voltage lines and distributed via distribution systems to homes and businesses.

In this scenario, electricity is the secondary energy form that is ultimately consumed by end-users for lighting, heating, cooling, and powering devices.

Practical Applications

Secondary energy is the cornerstone of modern life and industry, appearing in numerous practical applications:

Electricity Grids: The most ubiquitous application, electricity, powers homes, businesses, and public services. It enables communication, computing, and a vast array of electrical appliances.
Transportation: Refined petroleum products like gasoline and diesel, which are secondary energy forms derived from crude oil, fuel most vehicles globally. Biofuels are another example of secondary energy used in transport.
Industrial Heating and Processes: Many industries use secondary energy forms, such as processed natural gas, refined coal products (like coke), or high-temperature heat generated from primary fuels, for manufacturing and industrial processes.
District Heating/Cooling: In urban areas, centralized plants convert primary energy into heat or chilled water, distributing these secondary energy forms to multiple buildings for heating or cooling purposes.

The widespread use of secondary energy, particularly electricity, facilitates the operation of diverse economic sectors and contributes significantly to quality of life. However, it also presents challenges related to energy efficiency and environmental impact, especially when derived from carbon-intensive primary sources⁵.

Limitations and Criticisms

Despite its essential role, secondary energy and its production processes face several limitations and criticisms:

Conversion Losses: A major drawback is the unavoidable loss of energy during the transformation from primary to secondary forms. For example, over 60% of the energy consumed for electricity generation in the U.S. was lost in conversion in 2019⁴. These losses represent inefficiency in the overall energy system and contribute to higher energy consumption of primary resources.
Environmental Impact: The production of secondary energy, especially from carbon-intensive primary fossil fuels, is a significant contributor to greenhouse gas emissions and other air and water pollutants. For instance, electric power generation is a major source of carbon dioxide emissions and toxic metals, impacting human health and ecosystems³. Addressing these environmental concerns requires transitioning to cleaner primary energy sources and improving conversion technologies.
Infrastructure Dependence: The efficient delivery of secondary energy, like electricity or refined fuels, relies heavily on extensive and costly grid infrastructure and distribution systems. Maintaining and upgrading this infrastructure, particularly for aging systems, can be a significant economic and logistical challenge.

Secondary Energy vs. Primary Energy

The distinction between secondary energy and primary energy is fundamental to understanding energy flows and balances.

Feature	Primary Energy	Secondary Energy
Definition	Energy found in its natural, raw state.	Energy derived from the transformation of primary sources.
Examples	Coal, crude oil, natural gas, sunlight, wind, uranium, hydropower.	Electricity, gasoline, diesel, hydrogen, processed heat, synthetic gas.
Source	Extracted or captured directly from nature.	Produced through human-engineered conversion processes.
Usability	Often not directly usable by end-consumers in its raw form, or less convenient.	Generally more convenient, versatile, and suitable for direct end-use.
Energy Losses	No conversion losses at this stage.	Inherent energy losses occur during transformation from primary to secondary.

Confusion often arises because some renewable primary energy sources, like solar photovoltaic (PV) and wind, directly produce electricity. In some energy accounting frameworks, this electricity is considered primary at the point of generation, while electricity produced from thermal generation (e.g., burning coal or gas) is always considered secondary². However, the core differentiating factor remains whether the energy has undergone a significant human-induced transformation process from its original natural state¹.

FAQs

What is the most common form of secondary energy?

The most common and widely used form of secondary energy is electricity. It is produced by converting various primary energy sources, such as coal, natural gas, nuclear power, wind, and solar, into electrical power through power generation processes.

Why is secondary energy important?

Secondary energy is crucial because it provides energy in forms that are much more convenient, versatile, and widely applicable for everyday use than raw primary energy sources. For example, electricity can easily power countless devices, while gasoline makes modern transportation possible. The transformation makes energy accessible for industrial processes and domestic needs.

Does secondary energy have environmental impacts?

Yes, the production of secondary energy can have significant environmental impacts. These impacts are largely dependent on the primary energy sources used and the efficiency of the energy conversion process. For instance, generating electricity from fossil fuels leads to greenhouse gas emissions and other pollutants. Efforts to promote renewable energy and improve energy efficiency aim to reduce these impacts.

What are "losses" in secondary energy production?

Losses in secondary energy production refer to the portion of the primary energy input that is not converted into useful secondary energy but is instead dissipated, usually as waste heat. These losses are inherent due to the laws of thermodynamics and vary depending on the conversion technology and the type of energy being transformed. Minimizing these losses is a key goal of improving energy efficiency.