2:30 PM - 2:45 PM
[HCG24-04] Energy management of plant production in closed ecosystems
Keywords:Renewable energy, Energy storage, Food production, Plant factory
In artificial closed ecosystems, energy is necessary for food production, temperature control, and other human activities. Electricity is the easiest form of energy for us to handle, and we can expect to use photovoltaic power generation when constructing an artificial closed ecosystem in outer space, and wind power generation in addition to photovoltaic power generation when constructing in polar and arid lands. Energy management to appropriately obtain, store, and use these energies is indispensable for maintaining artificial closed ecosystems. I will discuss the concept of energy management for plant production using renewable energy in artificial closed ecosystems and on Earth in the presentation.
The first option for food production in closed ecosystems is plant cultivation. The report of Lunar Farming concept study working group (2023) assumes the use of sunlight with materials that transmit visible light, or the use of artificial light sources such as LEDs. The report also lists rice, potatoes, sweet potatoes, soybeans, tomatoes, cucumbers, lettuce, and strawberries as candidates for cultivation. To supply the energy necessary for human, a cultivation area of more than 70 m2 is required, and about 800 m2/person of solar cell modules are needed to irradiate this area with LED light. (Calculated assuming LED lighting with a PPFD of 600 µmol m-2 s-1 at a 16h light/8h dark cycle, and a photovoltaic facility utilization rate of 10%). However, in outer space, the photovoltaic facility utilization rate is expected to be several times higher than this, so the required area would be smaller.
On Earth, solar power output fluctuates. Storage batteries can be used to utilize the generated power without loss, but because of the high cost of storage batteries, energy consumption should be adjusted to match the amount of power generated. Conventional plant factories maintain the ideal environment for plant growth at a constant level, but now there is a need for know-how to fluctuate electricity consumption significantly without adversely affecting plant cultivation. In the demonstration project of the plant factory using renewable energy, the self-consumption rate was about 70% under the condition that the amount of electricity generated and the amount of electricity used were at the same level. Complete energy self-sufficiency without relying on grid electricity has not yet been achieved. In human daily life, there is also a need to reduce electricity consumption during times of low renewable energy generation. Life cycles in artificial closed ecosystems should be considered taking into account when power can be generated. Wind power generation is currently more expensive than solar power generation, but the pattern of power generation differs from that of solar power generation. The best mix should be designed to combine solar power, wind power, and other power generation in appropriate sizes according to the power consumption patterns.
Both outer space and on the earth, as mentioned above, the amount of solar and wind power generation fluctuates. Therefore, energy needs to be stored to use energy when power generation is scarce. When energy is finally used as heat, thermal storage can be a less expensive energy storage system than using storage batteries. However, both storage batteries and thermal storage cause losses when storing energy for long periods. For long-term storage, fuel cells such as hydrogen may be used, even if the energy loss during conversion is larger. In addition, when energy is ultimately used as dynamic, there is the option of storing it as kinetic energy in a flywheel, which could be an energy storage method with little storage loss in the microgravity and vacuum of space. The best mix of energy storage methods should be considered according to the amount, type, and duration of energy storage required.
The first option for food production in closed ecosystems is plant cultivation. The report of Lunar Farming concept study working group (2023) assumes the use of sunlight with materials that transmit visible light, or the use of artificial light sources such as LEDs. The report also lists rice, potatoes, sweet potatoes, soybeans, tomatoes, cucumbers, lettuce, and strawberries as candidates for cultivation. To supply the energy necessary for human, a cultivation area of more than 70 m2 is required, and about 800 m2/person of solar cell modules are needed to irradiate this area with LED light. (Calculated assuming LED lighting with a PPFD of 600 µmol m-2 s-1 at a 16h light/8h dark cycle, and a photovoltaic facility utilization rate of 10%). However, in outer space, the photovoltaic facility utilization rate is expected to be several times higher than this, so the required area would be smaller.
On Earth, solar power output fluctuates. Storage batteries can be used to utilize the generated power without loss, but because of the high cost of storage batteries, energy consumption should be adjusted to match the amount of power generated. Conventional plant factories maintain the ideal environment for plant growth at a constant level, but now there is a need for know-how to fluctuate electricity consumption significantly without adversely affecting plant cultivation. In the demonstration project of the plant factory using renewable energy, the self-consumption rate was about 70% under the condition that the amount of electricity generated and the amount of electricity used were at the same level. Complete energy self-sufficiency without relying on grid electricity has not yet been achieved. In human daily life, there is also a need to reduce electricity consumption during times of low renewable energy generation. Life cycles in artificial closed ecosystems should be considered taking into account when power can be generated. Wind power generation is currently more expensive than solar power generation, but the pattern of power generation differs from that of solar power generation. The best mix should be designed to combine solar power, wind power, and other power generation in appropriate sizes according to the power consumption patterns.
Both outer space and on the earth, as mentioned above, the amount of solar and wind power generation fluctuates. Therefore, energy needs to be stored to use energy when power generation is scarce. When energy is finally used as heat, thermal storage can be a less expensive energy storage system than using storage batteries. However, both storage batteries and thermal storage cause losses when storing energy for long periods. For long-term storage, fuel cells such as hydrogen may be used, even if the energy loss during conversion is larger. In addition, when energy is ultimately used as dynamic, there is the option of storing it as kinetic energy in a flywheel, which could be an energy storage method with little storage loss in the microgravity and vacuum of space. The best mix of energy storage methods should be considered according to the amount, type, and duration of energy storage required.