Smart Cities - Transition Engineering
Climate Change
Since the industrial revolution started in the 1800s humanity has been steadily raising the level of carbon dioxide in the atmosphere. The level of carbon dioxide in the atmosphere is expressed in parts per million (ppm). At the start of the industrial revolution the level of carbon dioxide in the Earth's atmosphere was 290 ppm.
The info graphic shows the increase in carbon dioxide from the start of the industrial revolution up to the present.
- 100 Gt-C between 1800 - 1960 to reach 310 ppm
- 100 GT-C between 1960 - 1980 to reach 340 ppm
- 350 GT-C between 1980 - 2014 to reach 400 ppm
- 250 GT-C between 2014 - ?? to reach 500 ppm (2 degC global temperature warming)
The global temperature rise can be calculated based on the level of carbon dioxide and other Green House Gases in the atmosphere. The variability is associated with probability calculations. Since the risks associated with climate change are so high it is best to take a conservative approach and aim to keep carbon dioxide at the lowest value range.
- 425-785 ppm for 1.5 °C
- 489-1106 ppm for 2 °C.
- We are currently at 412.5 ppm in 2020.
To keep the global temperature at 1.5 degC the release of carbon dioxide needs to be limited to 100 GT-C from 2014 until 2050. The average amount of carbon dioxide release each year is approximately 10 GT-C per year. To keep within the 100 GT-C budget we would need to reduce carbon dioxide emissions by 10% per year. Climate Change Victoria estimates that the remaining budget is closer to 800 GTCO2-eq.
Transition to 100% Renewables
The world is steadily progressing to reduce the burning of fossil fuels and transition to 100% renewables to reduce GHG emissions. The transition to renewables can be modeled by engineers. Several assumptions are used in the model, such as how quickly to reduce fossil fuels, and how quickly renewable technology can be rolled out. In the model presented below the time period of interest is from 2020 to 2050 where the world transitions to between 80-100% renewables. This graph and others similar to it are widely used to demonstrate to the public and policy makers that transition is possible with current renewable energy technologies. The yearly reduction in GHG emissions are achieved by not burning fossil fuels (6.5% GHG emission reduction per year).
100% renewable energy scenario assumptions
- Fossil fuels reduced by 6.5% per year
- Coal power plants are decomissioned
- Oil and natural gas energy production plant outputs decline
- No new hydro
- Wind increases by 4% each year and levels off at 21% of energy mix
- Solar PV increases by 10% per year and then levels off. Panels need replacing after 30 years.
- No more biofuels
- Biomass energy increases to use as heating fuel
- Geothermal and landfill gas increases 10 fold.
Transition to 100% renewables using a percentage plot. This modelling was conducted for the USA.
Total Primary Energy Production
The graph above can also be presented as a plot of Total Primary Energy production in the US economy. You can think of Total Primary Energy as the sum of all the energy used to run the economy. The chart shows that in order to achieve 80% renewables the Total Primary Energy of the US economy must decrease from today's levels (2020) by approximately half. What does this mean?
In simple terms it means that we will need to run the economy using less energy. The last time the global economy was running on this level of Total Primary Energy was in the 1950s and 1960s.
But how can this be so given that policy makers are adamant that renewables will replace fossil fuels?
The current suite of renewables have different properties to fossil fuels. Fossil fuels, by comparison provide our cities with a stable base electricity supply (with the exception of nuclear and hydro). Fossil fuels are also energy dense (e.g. oil) that is why we can use them in airplanes to cover travel distances. Fossil fuels are also relatively cheap to extract, store and transport.
Energy Return on Investment EROI
To compare different energy sources we can present them based on their Energy Return on Investment (EROI). The lower the EROI the more energy needs to be invested before we get useful energy. The higher the EROI the more favourable the energy returns.
For example, an EROI of 40 means that for every 1 unit of energy invested, 40 units of energy are produced. This is within the range of thermal coal used for electricity production (EROI of 30-50). If translated to the whole economy it means that 2.5% (1/40) of the economy needs to be dedicated to energy production, with the remainder of the economy able to enjoy excess usable energy for other goods and services.
If the EROI drops to 10 (e.g. solar PV panels), then for every 1 unit of energy invested in energy production, only 10 units of useful energy are produced. If viewed across the entire economy, approximately 10% (1/10) of the economy now needs to be allocated to energy production, with less excess usable energy to run other services.
Bioethanol has an EROI of 1. This means that for every unit of energy invested only 1 unit is returned. Yes we can produce bioethanol to use in our cars, but this level of energy investment could not support any other services in an economy (e.g hospitals, schools, manufacturing, etc). In fact, once the EROI drops below 5 it means that society is in decline.
Australia is leading many developed countries in the installation of solar PV power. Solar PV has an EROI of 5 to 10. In comparison to coal this energy source has a low EROI. It is also intermittent because it can only produce power when the sun shines (low Usable Energy). Take away the high emitting coal power plants producing a stable base load supply, and large solar PV panels on houses become useless (e.g. try using an electrical induction cook top at night).
Yes, we can install batteries to store electrical power during the day, but there is a heavy penalty.
While the Usable Energy of the solar PV panel / battery setup has increased (we can use electricity most of the time), the production of batteries and the storage and recovery of electricity from the batteries extracts a penalty of 20%. The EROI for the solar PV/battery system drops to less than 5%. An economy based on solar PV and battery storage would need to dedicate 20% of the economy to Primary Energy production. Remember that for a fossil fuel based economy only 2.5% was dedicated to energy production.
EROI comparisons
- Hydro = 35 to 50
- Thermal coal = 30 to 50
- Wind = 5 to 30
- Solar = 5 to 10
- BioEthanol = 1
- Intensive (industrial) agriculture = 0.1
Battery Storage
Example of EROI for Wind power with and without batteries. Using the batteries in an electric car would return an enen lower EROI.
Wind will also be more expensive to build (lower EROI) for the following reasons:
- noise complaints and forced shutdowns at night
- infrasturucture upgrades to the electricity grid
- expensive offshore installations
- rare earth metals used in constuction of electricity generators
- addition of expensive storage options
- Less usable energy than base load supplies (at scale)
Climate Change preparation
