Assessment on the Technical Feasibility of Using Solar Energy to Power the Legion in 86
Preliminary analysis of how an entire army can be powered by solar energy
The Legion in 86 uses solar energy as its main energy source. It is mentioned in chapter 3 of volume 1 that units of the Legion “would remain in the areas they controlled and received energy packs. Once those ran out, they would deploy solar panels and recharge that way.” For units that are energy intensive (such as Morpho), supplementary units (such as the Edelfalters) are deployed to provide additional energy. The Legion can thus be considered powered by a fleet of distributed energy resources of solar photovoltaic and a certain form of energy storage.
It has been revealed in the later volumes of the light novel series that the Legion does not rely only on solar energy. Volume 4 introduces us to a nuclear fusion generator type Admiral underground and volume 6 revolves around the destruction of a geothermal generator type Admiral. However, as in our world, due to possible limitations such as technical maturity level, generation and system cost, resource availability, scalability, or safety concerns, solar generator type Admirals remain the norm (as mentioned in chapter 2, volume 4) and one can safely assert that solar photovoltaic provides the main bulk of energy demand for the continual operation of the Legion.
In this thread I will qualitatively discuss some challenges that might arise for an energy system that is based almost entirely on solar energy, and counter measures to cope with them. Quantitative analysis will be more difficult since I then need to estimate the total number of operational units and the energy intensity of different types of units, although it can be done easily for units which has clear parameters (for example, after a back-of-the-envelope calculation, the saturated operation of Morpho is estimated to require 27 GW of solar photovoltaic [1]). In any case, I will try to do one once I figure out a reasonable methodology and also when I have the luxury.
I will divide the challenges into 3 types: the first type troubles our world but not the Legion, the second type troubles both our world and the Legion, and the last type troubles only the Legion.
Type 1 Challenges
Land use conflicts
In our world, this might be a challenge for the deployment of solar energy if a nation is densely populated. The increase of photon-to-electricity efficiency of solar cells and optimal designs such as agrophotovoltaic or aquaphotovoltaic can ease this challenge and in some cases even provide synergies for multi-purposes of land use. This challenge does not trouble the Legion that much because they do not have to face multi-objective conflicts in a human society and can deploy solar panels wherever they want. The fact that their solar generator extension types Edelfalters can fly in the sky also means that they can optimize energy yield by always pointing their tilting angle directly at the sun while maneuvering around to avoid shadowing each other.
Short term flexibility requirements due to uncertainty of solar power output
The unpredictable part of the power output from solar energy, namely the fluctuations that occur in the timescale of seconds to minutes due to cloud movement, can be problematic on the microgrid or distribution grid level. In addition, in our world where the energy system is still dominated by incumbent conventional energy sources, solar PV systems are inverter-based and higher penetration of them in the power system can cause larger frequency swings of the conventional generators in case of a contingency [2].
These concerns are not relevant for the Legion because they build their energy system with electronic-based technology from the scratch, and therefore smart electronic control algorithms must have already been implemented within every unit of the Legion to deal with these types of issues. There is probably no need to even use alternative current in many of the units, which can avoid energy losses of inverters and problems accompanied with frequency control.
It is also important to acknowledge that each unit of the Legion is basically an isolated microgrid, and in our world inverter-based PV-battery systems can already easily outperform the conventional diesel generator systems in isolated microgrids regarding performance of short term flexibility requirements.
Type 2 Challenges
Flexibility requirements due to hourly and diurnal variability of solar power output
Obviously, the sun does not shine at night, and flexible resources are required to smooth out the demand and supply imbalance due to this variability nature of solar energy. In our world this is currently done mostly with hydropower plants, pump storage, and conventional gas power plants (especially open cycle gas turbines), but batteries and demand side management are becoming more and more important in the power system.
On the other hand, energy storage and demand side management are the 2 main measures mentioned in the light novel. The capability of nighttime operations in the first wide network area of the Legion (where only solar generator type Admirals are observed) in volume 2 and 3 implies that the Legion can allocate sufficient solar energy into energy packs so that major offensives and defense can still be carried out at night.
This is not surprising since probabilistic operation research is not rocket science and the Legion must be familiar with the same mathematics used to design reliable grids 100% based on variable renewables (the mathematical formulation of its operation problem will be similar to a grid with a large fleet of electric vehicles, although the requirement for spatial flexibility will be significantly higher for the Legion). Nevertheless, it is mentioned in chapter 3 of volume 1 the Legion tends to avoid nighttime operations, which can be viewed as a type of demand side management based on availability of renewable resources.
Long term flexibility requirements due to seasonal variability of solar power output
Solar radiation exhibits strong seasonal variability, especially in higher latitudes. In our world, 4 strategies can be deployed to cope with the challenge. First, overbuilding variable renewable capacity; second, long duration storage (currently green hydrogen or other synthetic gas are most promising); third, adjust industrial production according to the seasonal variation of renewable resource availability; last, renewable energy trade with other energy systems through direct grid connection or transportation of energy carriers (again green hydrogen or other synthetic gas are most promising).
Seasonal variability should also be a challenge for the Legion. If the Legion wants to have the same operational capability in summer and winter, it has 3 options: it can overbuild its solar photovoltaic fleet, adjust the production schedule to an extent that will not affect the readiness of its combat units, or have storage type units that provide seasonal storage (renewable energy trade is not an option for the Legion because it does not negotiate terms with humans). The optimal solution will probably be a combination of the 3 options. To my best knowledge, however, there is no mentioning of large scale seasonal storage units in the light novel.
Type 3 Challenges
Mass and Volumetric Energy Density Requirement for Energy Storage Devices
Energy density requirement for energy storage devices is not that relevant in our world since most units in our energy system will not be moving around. Of course, volumetric energy density will still need to be optimized for the transportation of hydrogen, while mass energy density can hinder the progress of decarbonization of the aviation sector, but the energy producing units in our world will remain stationary at one place so the size and weight of the storage material does not affect their efficiency.
In contrast, solar generator extension type Edelfalters are implied in the light novels to be able to fly in the air. Unless the energy packs they are charging are light enough, flying may consume a significant portion of the energy they produce during daytime. This may well offset any advantages flying in the air can provide regarding energy yield gain previously mentioned. I am not aware of any concrete description of the material used to store the solar energy, so I am not sure how severe this challenge poses to the Legion.
The observation control type Rabe might suffer from the same shortcoming if it operates independently without supply from the ground. However, similar designs in real life are emerging, providing evidence of feasibility.
[1] How much electricity is needed to power Morpho in 86?
https://medium.com/re-members/49ab41a56bef
[2] Inertia and the Power Grid: A Guide Without the Spin, NREL, 2020
