Tuesday, August 2, 2011

Role of electricity on primary energy demand

Is electricity hindering primary energy demand to go down in absolute terms? Is electricity a high quality but polluting energy form, that should be only used when there is no alternative? With the increasing conversion efficiency of electricity in generation, increasing share of renewable electricity, the high efficiency at the point of use and the system level efficiencies, there is a lot of supporting evidence for a claim that electricity can save energy.
Growth in electricity consumption can be seen as fuelling GDP growth. Modernising electricity infrastructure increases economic productivity. All over world high growth of electricity's share in the total final energy mix has been steadily increasing.
Electricity is just an energy carrier, which due to its high quality, can be converted with high efficiency into practically any energy service. An integrated resource viewpoint should be taken when evaluating the efficiency of electricity to deliver energy services. For example an electric vehicle can be about twice as efficient in converting primary energy into transport services. Based on the integrated resource view, we can speculate that it is actually the growth in electricity consumption that is pushing down primary energy demand.
Electricity is a product, and just like any other product, it has certain quality characteristics such as voltage level and tolerance, frequency, environmental performance, But it also has very unique features. The main characteristic of electricity is its high quality, and its resulting capability to serve practically any energy service (light, appliances, motion, electronics, heat) from a single system. The price to pay for this high quality is the conversion loss in the thermal power station, a loss that has been steadily decreasing over the past century, and is now approaching its thermo dynamical limit). Serving all energy needs from a single system reduces cost of technical installations to the end-user. The capital becoming available could be used to invest in energy conservation, energy efficiency or renewable generation.
Electricity also has some disadvantages. It cannot be stored in large quantities in a practical way and at reasonable cost. As a result, supply and demand must match at all times in a fragile balance. It's the ultimate just-in-time product, consumed at the moment it is being produced, In fact, its users have as much influence over its quality than its suppliers. Considering this fragile balance, it is all the more amazing that we observe unplanned interruptions frequently in the electricity system . For example 100 minutes lost corresponds to 0.02% of the minutes in a year, or 99.98% availability. The best performance is achieved in the electricity systems of Austria, Germany and the Netherlands, and such high performance may not even be sufficient to power the digital economy. Meanwhile, the question remains whether the emerging electricity system of the future India will be able to achieve the higher goal.
When power stations convert primary energy into heat, and then into electricity, the conversion efficiency varies between 30% (older power stations) and 60% (modern gas-fired combined cycle stations). Therefore, the share of electricity in the energy mix differs dramatically between primary energy and secondary energy (or final energy). When converting this amount back to primary energy, a method called the 'physical energy content' is often used . For example:
Renewables: a factor 1
Nuclear: factor 3
thermal power plants: factor CO2 (e.g. 2.5 for coal, 1.7 for gas)

The average 'physical energy content' of electricity for Europe is around 3, i.e 3 kWh of primary energy is needed for each kWh of electricity. For a (hypothetical) electricity system based on a quarter each of renewables, nuclear, coal-fired and gas-fired combined-cycle stations, the conversion factor would be slightly above below 2.5. When taking transmission & distribution losses into account, the factor should be 4-10% higher. For electricity systems where additional electricity demand is supplied by renewables or combined cycle power stations, the primary energy factors would be respectively 1.07 and 1.8.
The efficiency of appliances to convert electricity into energy services is increasing steadily, and still has improvement potential. For example:

• Losses in refrigeration have been reduced historically by a factor 5, from the levels at the end of the 80's to the best available technology in class A+ appliances (fig 3).

• Energy use for individual lighting applications can be reduced by a factor 5 or more. Modern lighting solutions are 50-100 times more efficient than candles.

• Distribution transformers, one of the most efficient machines ever designed by man, can still reduce losses by a factor 3-4 through the use of amorphous iron

• In motor driven systems (pumps, compressors, fans, washing machines, electric trains), it is possible to reduce losses by 30% on average.

But the above examples just provide a static perspective, whereas electro technologies sometimes have more dramatic impacts at the systems level.

Because of its high quality, using electricity instead other energy carriers can have a boosting effect to save primary energy and reduce greenhouse gas emissions, even when including conversion losses in power generation:

• The use of high speed electric trains instead of air transport reduces primary energy use per passenger.km by a factor 3 and CO2 emissions by a factor 4.

• Using electric trains instead of diesel trains reduces CO2 emissions by a factor 4 and primary energy use by a factor 2 .

• Electric vehicles are twice as efficient as vehicles with internal combustion engines.

• Efficient heat pumps, drawing heat from the underground require 20-40 kWh of electricity to supply 100 kWh of heat; they typically reduce final energy demand for heating by at least a factor 3 and primary energy demand by at least 25%.

• With induction heaters for cooking, 90% of (final) energy goes in the pan, compared to 55% for gas-fired cooking.

• Modern high temperature heating solutions for industrial processes can in some cases save up to 80% of primary energy and up to 60% of CO2 emissions through their efficient use of primary energy

At the next level, electricity - the only energy carrier that can power the digital economy - enables system-level efficiencies, eliminating or drastically reducing the need for certain energy services like:

• Teleworking, Videoconferencing or webconferencing, reducing the need for travel

• Heating controls for building energy management, ensuring buildings are only heated when needed
• Dimmable lighting systems, ensuring exactly the right amount of light in the right place at the right time
• Process control technologies, especially in industry can drastically reduce energy

With the increasing conversion efficiency of electricity in generation, the increasing share of renewable electricity, the high efficiency at the point of use and the potential for system level efficiencies, there is a lot of supporting evidence for a claim that electricity can save energy. Considering the high quality of electricity, its inefficient use and high stand-by losses are a waste that needs to be avoided, without impairing its potential benefits to reduce primary energy and reduce greenhouse gas emissions in many other areas.

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