Energy Quality Returned On Energy Quality Invested (EQREI) - Part 1

Contents

1. Introduction

2. What Is Energy Quality

3. EQREI

4. Wind Turbine Example

5. Concluding Remarks

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Bitesize Edition

• Efficiency and cost metrics are always analysed as two of the driving metric groups that drive policy decisions on energy and electricity generation sources.

• However, a topic that isn’t covered as often is energy quality. This refers to how easy it is to convert one form of energy into a useful form of energy. Today, the useful form of energy I’ll discuss is electricity.

• High-quality sources are electrical energy, mechanical energy, or chemical energy from fuels. Lower-quality energy often means low-temperature heat energy. When exploring energy quality, these higher-quality sources can often easily be converted into low-quality energy. However, doing this in reverse is difficult.

• The metric we’ll use to explore energy quality is energy quality returned to energy quality invested. This ratio explores the energy invested in processing or extracting a certain energy resource, in our case electricity, versus the useful energy we obtain from a process while accounting for the quality. EQREI is often closely compared to energy return on investment.

• However, EROI looks great when we go from a high-quality energy form to a lower-quality energy form but with a larger quantity of useful energy. EQREI highlights this issue as the energy returned is of a lower quality.

• Through the example of a wind turbine, we’ll explore how a calculation of EQREI would look.

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Introduction

As I continue to deep-dive the mathematics behind our electricity generation methods, today we’re going to explore the little-known metric of energy quality returned on energy quality invested (EQREI). The first question to answer is what energy quality actually is.

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What Is Energy Quality?

Energy quality is referred to as the ease with which a form of energy can be converted to another useful form.

The theory of thermodynamics states that to frame energy quality, we can use quantity entropy. So, what is entropy?

Entropy is a measure of the thermal energy of a system that is unavailable for useful work. This is calculated through the movement of molecules, and so can also be used to measure randomness or disorder in a system.

Some processes are reversible, and others are irreversible. These irreversible processes lead to more energy becoming unavailable for conversion into useful energy, which results in high entropy. The universe is predicted to be undergoing an increasing entropic process, albeit over an incredibly long time.