Energy Systems and Sustainable Land Use: The Good, the Bad, and the Unexpected
- May 9, 2021 3:55 pm GMT
An often overlooked element of sustainability engineering and science is sustainable land use or sustainable land management (SLM). The United Nations defines sustainable land use as “the use of land resources, including soils, water, animals and plants, for the production of goods to meet changing human needs, while simultaneously ensuring the long-term productive potential of these resources and the maintenance of their environmental functions.”
It is important to appreciate that virgin ecosystems or lands associated with indigenous peoples are essential for assimilating atmospheric carbon dioxide.
Given the fact that some renewable energy systems have egregious land use requirements, it is prudent to suggest that inordinate land use will mitigate or even ameliorate the emissions control benefits of these technologies. In light of the headlong rush to deploy renewables, it is essential to understand land use characteristics for different systems. This knowledge becomes part of the deployment calculus and enables engineers and planners to design and implement systems that are mindful of land use sensitivities. Clearly, given the complexity of sustainability challenges and the wide variety of renewable energy options that are available, it is crucial that clean energy be economically and strategically deployed at large scale and with a distributed resource strategy, if feasible. Repurposing land for some renewable energy systems with a consequential reduction in biodiversity which is crucial for assimilating atmospheric carbon dioxide is counter-productive. The twin challenges of reversing biodiversity declines and mitigating anthropogenic climate change with renewable energy systems must be addressed in concert.
The productivity and sustainability of a land-use system is determined by the interaction between land resources, climate change, and human activities. In the face of climate change and variability, selecting the right land uses for given biophysical and socio-economic conditions, and implementing SLM, are essential for minimizing land degradation, rehabilitating degraded land, ensuring the sustainable use of land resources (i.e. soils, water and biodiversity) and maximizing resilience.
Power Densities per Area for Various Renewable Sources
A graph showing area power densities for various energy sources is shown below. The energy sources picked represent a mixture of both renewable and fossil fuel sources.
It is clear that there is quite a range for power production per area for the various sources.
It needs to be emphasized that these ratings do not either disqualify, or for that matter, guarantee, the use of a particular energy source. This is stated because the key metric for this analysis is land use or sustainable land management.
For example, solar and wind are less desirable for large production systems because they will displace large tracts of land. On the contrary, both of these technologies are nimbler by the fact that they can be deployed relatively easier at small, even single household, levels.
The Good and the Bad
Three technologies, nuclear power, natural gas power plants, and anaerobic digesters to make RNG (renewable natural gas), all provide an option to coal, with less land management issues. It is noted that these options are not all renewable, particularly nuclear power which has its own challenges. Although natural gas (which consists primarily of methane) is a fossil fuel, it is more environmentally friendly than coal when used in power plants. However, natural gas must be transported long distances where leaks can occur. Natural gas losses during transportation can significantly contribute to global warming because methane is 25 times more potent as a greenhouse gas than carbon dioxide.
Large scale wind and solar technologies installations will be hampered by the large land requirements. However, deployment of these platforms in smaller energy generation scenarios is often ideal. Another constraint with wind and solar is that there is usually only one source of revenue generation which is the sale of electricity as AD generation of methane which can monetize multiple renewable product streams such as energy, fertilizer, and even water.
Methane production using anaerobic digesters (AD) is potentially very green and since the methane is generated on-site, the risk of GHG leaks to the atmosphere is significantly reduced. However, there are other obstacles for anaerobic digestion. Most concerns about anaerobic digestion concern issues such as odors, performance, and process control. Proper design and operation can address these aspects. There is also a sense in the environmental space that AD systems cannot be large-scale players in the renewable space and this concern is related to the fact that most AD's are unable to achieve much more than 45% conversion of solid biomass feedstock. However, a new generation of AD's with high conversion rates (90%) and multiple renewable products is in the deployment phase which will prove to be a game-changer for sustainable resource production as we know it.
The land use analysis really did not reveal anything new with solar and wind platforms.
But it somewhat unexpectedly shows that BOTH natural gas and RNG systems are the predominant favorable technologies from a land use perspective.
Nuclear systems also score well from a purely technical and land use perspective. Unfortunately, even though public opinion has become somewhat more favorable, these plants also require lengthy times to design and install which is on the order of 10 years.
RNG AD high conversion systems have several advantages that are not readily obvious.
- In many cases, high conversion RNG plants can installed at existing AD systems without minimal or no additional land required.
- Existing operational AD systems can be upgraded to a high conversion mode using a "plug and play infrastructure" approach that requires far less capital with upgrades implemented in months, not years.
- AD systems can be modified to almost double gas generation as well as generated high-valued products such as green ammonia and water.
- Manufacturing multiple renewable products and associated off-take agreements facilitate project financing by using the agreements as collateral.
In summary, in the complicated milieu that is the sustainability and climate change space, one axiom seems to hold sway in that there will always be room for multiple technological platforms. The notion that there is a broad solution that is embodied as a Holy Grail or a universal panacea that may suddenly appear is wishful thinking. Practicing sound science and engineering and utilizing structured mass and energy balances appropriately in concert with judicious economic assumptions will take one far in devising insightful and elegant solutions for even the most challenging problems.
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