Grid Efficiency: An Opportunity to Reduce Emissions

By District Energy posted 08-10-2017 00:00


Malcolm Metcalfe, The Energy Collective


Current efforts to conserve energy and reduce emissions are significant. Some governments in Europe have set targets of 50% for the energy conservation.  But is this the whole story?  The overall efficiency from primary energy to delivered work is about 33% for energy in the US. Almost 2/3 of the energy that is consumed as primary energy is released as waste.

There are two key areas where waste occurs. Fossil fuels are delivered to users with a relatively high efficiency, but when it is burned or used to create other forms of useful energy the waste grows rapidly. Electricity, which is a carrier or proxy for energy, is generally used efficiently, but the generation and delivery of electric power consumes almost 2/3 of the primary energy delivered to the grid, leaving les than 40% of the primary energy to be converted to useful work.  These areas of loss are opposite for the two types of fuel. Electricity loses a large amount of energy in the production and delivery stages, while fossil fuel losses occur mostly at the end of the line; in user systems.

There may be opportunities in the electric system to improve efficiency. One is to displace coal fired steam turbine generating plants with newer distributed technology, such as gas turbines or solar and wind power. Combined cycle gas turbines are capable of generating electricity at over 60% efficiency, while the maximum theoretical efficiency of the steam turbine alone is about 42%, and it is likely less because the turbines are not operated continuously at maximum efficiency. Combined Heat and Power systems (CHP) systems have the potential to increase efficiency to more than 80%;  by using almost all waste heat for other purposes.

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