ALTERNATIVE ENERGY -
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Alternative energy sources are usually framed as those sources that are alternative to fossil fuels, or sources which when employed, generate low levels of GHG emissions.
Alternatives include renewable energy, however, some alternative energy sources can be exhaustible, and therefore not renewable. Current alternative energies include, Wind, Solar, Nuclear, Hydroelectric, Hydrogen, Tidal, Biofuels, Geothermal, and Biomass. Nuclear fision, for example is an alternative energy; however, it is not strictly renewable as it's fuel, such a Uranium, cannot be easily replentished in a human lifetime.
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Nuclear
Energy wise, nuclear fuel is extremely dense. It’s about 2 million times more energy dense than coal; hence, the amount of used nuclear fuel is quite small and likewise little waste is produced. [AE-1]
We might falsely imagine huge piles of radioactive waste, yet all of the spent nuclear fuel produced by the U.S. nuclear energy industry in one year is about 2,000 metric tons. This volume of the spent fuel assemblies is actually quite small considering the amount of energy they produce. The amount is roughly equivalent to less than half the volume of an Olympic-sized swimming pool. [AE-2]
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Figure 1.
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At it's current wordwide rate of use nuclear energy sourced from Uranium could continue for over 200 years. As the technology improves and safety issues are addressed, nuclear may be a viable alternative as renewables are increased in the energy mix.
Enforcing fire and earthquake regulations, addressing flood risks, and safer on-site storage for nuclear waste are just a few of the ways we can help prevent nuclear accidents.
The critical downside of nuclear is the long timeframe required to get a nuclear plant safely designed and built. Uranium, the currently common nuclear fuel, is dissolved in seawater at very low concentrations, only about 3 parts per billion (3 micrograms/liter or 0.00000045 ounces per gallon).
But there is a lot of ocean water - 300 million cubic miles or a
bout 350 million trillion gallons (350 quintillion gallons, 1,324 quintillion liters). So there's about 4.5 billion tons of uranium in the ocean at any one time.
According to the U.S. Department of Energy, the oceans contain at least 500 times more uranium than in all known terrestrial reserves. Nuclear fuel made with uranium extracted from seawater would enable nuclear power to be considered almost renewable. The 4.5 billion tons of uranium in seawater now would fuel a thousand 1,000-MW nuclear power plants for many centuries. Hence, with the procurement issues resolved, it is a viable future alternative.[AE-3]
Ocean Thermal Energy Conversion
An unsual, yet potentially viable alternative energy form is OTEC (ocean thermal energy conversion). Effectively, it is a seawater based heat exchanger that draws cold water from 3000 feet below the surface and exchanges it with warm surface water. Why it hasn't been widely employed is that salt in the water is highly corrosive to the metal in the heat exchanger. Research into this problem is underway by Ocean Energy Research Center (OERC) in Kailua-Kona, Hawaii. As much of the world's population is urban and often ocean side, OTEC has a lot of potential. [AE-4]
Biofuels
The substitution of conventional transportation fuels (gasoline, diesel) by biofuels is being done to reduce GHG emissions and support sustainable agriculture. However, the production of biofuels may cause sufficiant pollution to overide the reductions attained in burning the biomass fuel vs fossil fuel equivalents. The two most common biofuels are biodiesel and ethanol. Life-cycle assessment is a scientific evaluation method to investigate the net environmental impacts of biofuels over fossil fuels. [AE-7]
It's not merely a matter of substituting biofuels for fossil fuels to gain an emission reduction. In fact, it's a very complicated comparison under life-cycle assessment to determine the overall benefit, if any, of biofuels.
The environmental benefits of biofuels occur during the fuel combustion in the vehicle engine. The use of biofuels results in a closed carbon cycle, [AE-5] since the emitted amount of CO2 is as much as the plant (rapeseed, corn, wheat, soybean, etc.) absorbed during its growth. Due to the low or zero content of pollutants such as sulfur in biofuels, the pollutant (SO2 etc.) emission of biofuels is much lower than the emission of conventional fuels.
Environmental degradation may come in what may be various detrimental agricultural methods used to grow or enable growth of the raw materials of biofuels - plants. Moreover, plant processing in the production of biofuel has negative environmental impacts.
Figure 2 - source: https://www.homeowner.com/energy-science/resources
Figure 3 - source:
Biofuels - continued
Making truly carbon neutral biofuels is a big challenge. Why? Because many steps used to create biofuels may emit CO2 and other greenhouse gases even before the fuels are burned. These steps are fermentation, the energy for processing, and transportation. As well, the fertilizers used to grow the source plants were made under intensive CO2 emitting processes, and excess fertilizers leach into the soil and runoff into streams with harmful impacts. Changes in farmlands used to grow biomass can also have climate impacts, particularly if it is created from CO2-storing forests
A 2022 study questions the effectiveness of biofuel programs, "The US Renewable Fuel Standard is the world’s largest existing biofuel program, yet despite its prominence, there has been limited empirical assessment of the program’s environmental outcomes. Even without considering likely international land use effects, we find that the production of corn-based ethanol in the United States has failed to meet the policy’s own greenhouse gas emissions targets and negatively affected water quality, the area of land used for conservation, and other ecosystem processes. Our findings suggest that profound advances in technology and policy are still needed to achieve the intended environmental benefits of biofuel production and use." [AE-56] In the United States, the Renewable Fuel Standard (RFS) specifies the use of biofuels and, according to this study (Lark, 2022), guides nearly half of all global biofuel production, It states, "...yet outcomes of this keystone climate and environmental regulation remain unclear. Here we combine econometric analyses, land use observations, and biophysical models to estimate the realized effects of the RFS in aggregate and down to the scale of individual agricultural fields across
the United States. We find that the RFS increased corn prices by 30% and the prices of other crops by 20%, which, in turn, expanded US corn cultivation by 2.8 Mha (8.7%) and total cropland by 2.1 Mha (2.4%) in the years following policy enactment (2008 to 2016). These changes increased annual nationwide fertilizer use by 3 to8%, increased water quality degradants by 3 to 5%, and caused enough domestic land use change emissions such that the carbon intensity of corn ethanol produced under the RFS is no less than gasoline and likely at least 24% higher. These tradeoffs must be weighed alongside the benefits of biofuels as decision-makers consider the future of renewable energy policies and the potential for fuels like corn ethanol to meet climate mitigation goals." [AE-6]
Biofuels can be a low-carbon alternative in challenging sectors such as heavy transport, steel, cement, and aviation and can assist in decarbonizing light-duty transportation alongside vehicle electrification in the near-term. When combined with capture and storage (CCS) of high-purity CO2 streams made available during the conversion of biomass to liquid fuels, the carbon intensity of biofuels can be driven lower or in some cases achieve net removal of carbon from the atmosphere.
So, you see that there are pros and cons pf trying to reduce GHG emissions, by lessening the use of fossil fuels by other means such as biofuel substitution. Even our sense of being environmental stewards, by using a hybrid fuel with ethanol, may deter us from going full out and replacing the fossil burning chariot with an EV (electric vehicle).
Footnotes
[AE-1] Dr. Nick Touran, Ph.D., P.E., 2017-12-17. A primer on energy, greenhouse gas, intermittency, and nuclear. https://whatisnuclear.com/primer-on-energy.html . See - Dr. Nick Touran - https://partofthething.com/
[AE-2] https://www.energy.gov/ne/articles/5-fast-facts-about-spent-nuclear-fuel
[AD-4] Makai Ocean Engineering completed the construction of a heat exchanger test facility in 2011 and has since received funding to install a 100 kW turbine. http://nelha.hawaii.gov/energy-portfolio/
[AE-5] Biomass is carbon neutral, because when plants are grown, through the photosynthesis process, they absorb carbon dioxide which is then released during the combustion process. Therefore, with burning biomass, its net emissions are zero, the photosynthetically absorbed CO2 offsets the CO2 emissions from burning.
[AE-6] Lark, T. J., Hendricks, N. P., Smith, A., Pates, N. J., Spawn, S. A., Bougie, M., … & Gibbs, H. K. (2022). Environmental Outcomes Of the US Renewable Fuel Standard. Proc. Natl. Acad. Sci. U.S.A., 9(119). https://doi.org/10.1073/pnas.2101084119
[AE-7] The life-cycle concept is a ‘cradle-to-grave’ systems approach for thinking about technology. The concept is based on the recognition that all life-cycle stages (raw material acquisition; manufacturing, processing, and formulation; transportation and distribution; use, reuse, and maintenance; and recycling and waste management) along with all life-cycle phases (pre-operation, operation, and post-operation) result in economic, environmental, and energy impacts. Without consideration of life-cycle concepts, unforeseen negative consequences may be overlooked.