Energy Efficiency Introduction

Overview

This page will provide you with a general understanding of the term efficiency and the concept of energy efficiency.

You also can check out the video lecture on energy efficiency by Prof. Ramchandra Bhandari, TH Köln – University of Applied Sciences:

Further information on the mentioned MOOC on "Powering Agriculture - Sustainable Energy for Food" and related materials you can find here.

Efficiency in general

The term efficiency is used in many different fields, for example in engineering, economy, medicine as well as in sociology. However, quite often the word is used ambiguously. Therefore, we start by having a look at the meaning of this term.

Generally, efficiency is defined as the ratio of the desired output (useful effect) to the required input (used resources) of any system (Pérez-Lombard , et al., 2012). Efficiency can easily be expressed as:

The equation highlights that efficiency always involves both used resource and provided services. Therefore, efficiency can be improved if the same service is provided using fewer resources, or if a better service is achieved with the same resource consumption as before. These two scenarios are often referred to as minimization and maximization strategy, respectively.

Energy Efficiency

Now that we know about the general concept of efficiency, let us turn our focus to energy systems. Assessing their efficiency is classically achieved by looking at energy conversion efficiency (η), (Greek letter Eta).

The most common example of calculating Energy Efficiency is a conventional power plant where heat is converted into electricity by using a turbine and a generator. In such thermal power plants, energy input would refer to the heat we feed into the process and electricity we get as a useful output. Both elements are energy flows and can be quantified by using thermodynamic calculations which result in an absolute value for efficiency.

Unfortunately, such a straight forward procedure is not always applicable: For example modern light bulbs with LED technology are able to provide a light with brightness or more accurately, with visible light of 1000 lumen with electricity input of 20 Watt. On the other hand, the old incandescent light bulb technology needs five times more electricity input to provide the same brightness of visible light.

The LED uses the input resource in a more efficient way. However, we have to be aware that this comparison is only acceptable when the output or service is really the same in both technologies. In the case of a light bulb, some people might say that brightness is the only important factor, but others might argue, the LED provides a different light colour and therefore a different or less valuable service than the incandescent bulb. “Therefore, it is worth distinguishing between quality and quantity of output service. Evaluating the quality of services is generally difficult, especially when multiple services are provided by the system subject to analysis (Pérez- Lombard , et al., 2012)“.

 In addition, it is important to closely look at the denominator of the efficiency equation (the energy input). When comparing different technologies with another, not only the end use appliances (like a light bulb) might be changed but also the form of energy input. For example, changing a system in which power and heat are conventionally generated in separate generation cycles while waste heat remains unused to a a) more efficient system with heat reuse and heat recovery or b) even to a combined heat & power supply (co-generation facilities) system. Now the energy production itself should be incorporated into the evaluation of efficiency.

Energy Efficiency – Global Dimension and Co-Benefits

The International Energy Agency (IEA) considers energy efficiency as „the world´s first fuel“. On global level more than half of the worldwide consumed primary energy is lost in production processes, by transport and general energy consumption. The resulting global high energy efficiency has hardly been captured. Facing this situation, energy efficiency has also gained high attention on the international political agenda: e.g. energy efficiency is incorporated in the new global agenda of „Sustainable Development Goals” (SDGs), and as 2/3 of global Greenhouse Gas Emissions (GHG) derive from energy consumption (of power, fossil fuels etc.), energy efficiency is also a key for climate protection and will play a major role in international processes for realizing global climate goals (after COP 21 in Paris). Besides high climate relevance, energy efficiency increase also addresses various so-called co-benefits (or multiple’ benefits): security of energy supply, import improvements, increased productivity & economic growth, modernization of facilities and more.

Overview on common energy efficiency measures & technologies for agricultural value chains: As the agri-food sector heavily dependents on fossil fuel inputs (for production, transport, processing, and distribution – remember Reader 1), and as this energy demand will even increase due to growing global food demand, opportunities for real energy savings are numerous along many agri-food chains – by increasing energy efficiency and using energy more wisely to avoid wasting it.

The following table gives a short overview of typical energy demand occurring in many agricultural value chains (due to applied energy intensive processes and technologies), and of common technologies and measures for increasing energy efficiency well as other co-benefits.

Which Energy(Service)	Demand? Which agri-food Processes/ Value Chains?	Which common energy efficiency technologies/ measures?
Heat supply	Greenhouse farming Processing (dairy production, drying fruits & vegetables, canned food etc.)	Waste heat recovery (e.g. by heat exchangers that use ‘waste’ heat for pre-heating other processes) Insulation of networks/ pip line, building facilities
Cooling & air conditioning / cold storage / cooling chains	In all agri-food sectors where food quality needs to be maintained after harvesting, while processing and for transporting food/ agri products => dairy/ milk production, rice production, vegetable production, beverage industry, drinking water treatment and processing etc.	Insulation of networks/ pipeline, building facilities Minimizing heat load at the end of the processing phase of the cold chain Efficient and ‘climate friendly’ refrigeration systems (also with new/ renewable technologies are available, such as solar absorption chillers)
Fertilizer	In many agri-food sectors/ processes	Reducing heavy energy inputs in fertilizer manufacturing, but also by more accurate application methods.
Water supply/ pumping	Greenhouse farming Irrigation for all agri-chains Beverage industry & drinking water treatment Food processing in general	For irrigation: using gravity supply Maintaining all equipment regularly; Drip irrigation in row crops; Alternative fuels/ energy sources for driving pumps (e.g. solar and wind-powered pumps)
Machinery (also tractors etc.)	Many agri-food processes (growing, harvesting, processing)	Correct gear and throttle selection Efficient automation (efficient electric drives & motors, as well as automate monitoring & control systems) for production and processing
Transport and distribution of food	Transport of food commodities (such as milk powder, rice in bulk, fruits etc.), partly under controlled atmosphere or refrigeration	See as under cooling/ air conditioning
Processing & packaging of food	Many agri-/food chains and their sites for processing agro-products or food/ beverages	Efficient automation (efficient electric drives & motors, as well as automate monitoring & control systems) for production and processing
Renewable energy and stable energy supply	All along the value chain in many agri-food sectors Where good local energy resources exist Where stable power/ energy supply is need	Using grid electricity with a growing share of renewables (solar, bioenergy, geothermal etc.) Improving & modernization of power grid (centralized and decentralized networks)
Lighting	Greenhouses Production, processing and storage sites	Energy saving lighting technologies (e.g. LED) Efficient automatisation of lighting (matching real demands)

Conclusion

• Generally, efficiency is defined as the ratio of the desired output (useful effect) to the required input (used resources) of any system.
  
• Efficiency measures can be targeted at both used resources and provided services. Energy efficiency is a way of managing and restraining the growth in energy consumption. However, a process can become more efficient even though the input resources are not decreased.
  
• Assessing energy efficiency is only possible when the systems to be compared are examined within the same system boundaries.
  

Further Readings

Energy Efficiency in Powering Agriculture

Energypedia Portal of Powering Agriculture

FAO Study: Opportunities for Agri-Food Chains to become Energy-Smart

Reader of the MOOC "Powering Agriculture - Sustainable Energy for Food"