Skip to 0 minutes and 11 seconds Let’s return to our systems view and decomposition of our fossil energy system, and use our new knowledge on efficiencies and inevitable losses in the first analysis. In the diagram I’ve listed numbers that are indicative of first law efficiencies of state of the art technologies and systems. What can we learn from this? First, I’ve not put a number on the outer right boxes. Here energy is put to use to fulfil a need. The consequence of all energy use here is that it eventually is dissipated as low level heat into the environment and increasing total entropy.
Skip to 0 minutes and 54 seconds Transport equipment, industrial and home spaces, machines, and appliances therefore should be designed and produced in such a way that they require a low level of net energy input per unit of need fulfilled.
Skip to 1 minute and 10 seconds The systems between resource and end use should be efficient. Here we can already observe some interesting differences. Delivering heat from gas is the most efficient system. The overall efficiency is between 65% and 73%. This view hints at reduced energy use for heating requires more energy efficient buildings, or as building space per person or activity. Providing automotive is the least efficient system. At best, some 30%, worst case, only 16% efficient. Providing electric power for coal is only marginally more efficient at 28% to 32%.
Skip to 1 minute and 54 seconds Here on the left side I’ve added the so-called research to product ratio. The amount of known resources that can be produced divided by the annual production, which equals consumption they’ve not used. On the right side, the amount of gigatons of carbon emitted from the total use of crude oil, natural gas, and coal, respectively are listed. Together these convey the message that improving our current energy systems will not suffice to overcome the global energy challenges as outlined in the lectures of the first week by Professor Andre Faaij.
Skip to 2 minutes and 32 seconds In order to prevent dramatic consequences of climate change induced by carbon dioxide emissions, and to ensure security of supply in the long-term, we require an energy transition where we develop and implement energy systems with much higher efficiency, switch to renewable resources that can replace fossil, and reduce our end use demand by energy efficiency at home, at the office, and the factory. We need better energy system combinations. One example is to use the waste heat of power plants before shedding it to the environment. A coal-fired power plant, for example, can be connected to a district heating system. The supply of heat, typically at 60 to 90 degrees centigrade, will sacrifice some electric power production, however.
Skip to 3 minutes and 22 seconds In power plants running on natural gas or other gaseous fuels, better combinations can be made because we can include gas turbines which employ the Brayton cycle. In a gas turbine, gases combusted with air at elevated temperature. The resulting flue gas directly drives the turbine. In a so-called open cycle gas turbine, or OCGT system, the exhaust of the turbine, at some 500 to 600 degrees centigrade is discharged into the atmosphere as wasted heat. It’s efficiency is only 30% to 35%. In a so-called combined cycle gas turbine, or CCGT power plant system, the gas turbine exhaust is used to replace air input to the [INAUDIBLE] furnace, thus recouping more of the heat liberated from the gas.
Skip to 4 minutes and 12 seconds These plants have efficiencies up to 60%. Finally, many a combined heat and power, or CHB system, deploys a gas turbine to generate electricity, while the exhaust heat is used for raising steam for industrial or space heating. In modern CHBs, thus over 90% of the fuel input is used effectively. This is only one example of a more efficient energy system. In the next lecture, we will explore the challenges of the energy transition– how to develop new energy sources such as solar, wind, and biomass, and new energy systems that integrate with and which replace our legacy energy systems.
Energy system performance
We will return to our system’s view and decomposition of our fossil energy system, and use our new knowledge on efficiencies and inevitable losses in an analysis. It will become clear that improving our energy systems may not be sufficient in the energy transition. Additional actions are required, such as efficiency improvements, development of renewable sources, and reducing our energy demand.
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