Solar energy-battery storage optimization for satellite-to-ground communication
Authors:   , Ntlela Simphiwe A. 
Published: April 2024

The creation of ubiquitous broadband systems has piqued the interest of both academics and industry to fulfil the exponential growth in demand for multimedia services on mobile devices and to support access anywhere on the earth. The implementation of such systems is anticipated to heavily rely on satellite networks in general and Low Earth Orbit (LEO) satellite constellations. Therefore, increasing their service life has become a significant engineering and scientific challenge. The main finding of this thesis is that by sharing the power of a satellite's batteries with another spacecraft that is still in the sun, one may considerably extend the service life of a satellite. Over 30% of the time that LEO constellation satellites are in the earth's shadow, they are powered by batteries. Although the batteries are replenished by sunlight, the depth of discharge they experience during an eclipse has a major impact on their lifetime and, consequently, the service life of the satellites. A 15% increase in the DoD can almost halve the service life of the batteries. The major section of this thesis includes a variety of strategies we think may help LEO constellations' batteries last longer. The market's demand for satellite communication networks has changed recently. Low-EarthOrbit (LEO) satellite constellations have therefore received increased attention because they are expected to address these needs. In the current LEO satellite constellation-based communication system, the satellite close to the satellite terminal that submits the communication request answers to it regardless of the state of its battery. However, in cases of significant battery deterioration, this communication technique reduces the lifetime of the satellite. This means that in big satellite constellations when operating costs are a concern, this communication mechanism is unsuccessful. To extend the battery's lifespan, we design a communication mechanism in this work that regulates the transmission power and transmission gain of a satellite antenna based on the battery's state of deterioration. Large-scale LEO satellite constellations can be created and used thanks to the decrease in operating expenses that results from extending battery life. Future demands for satellite communication should be met by the system that has been put in place. Through simulation, the usefulness of the suggested approach is confirmed. The use of solar energy for satellite power is an attractive option due to its sustainability and cost-effectiveness. However, satellite communication requires a constant and reliable power supply, which is challenging to achieve with solar energy alone, particularly in periods of low solar activity or during eclipses. This is where battery storage optimization comes into play. In this study, we propose an optimization model for the use of solar energy and battery storage in satellite-to-ground communication systems. The model takes into account various factors such as solar irradiance, battery capacity, and communication power requirements. The optimization objective is to maximize the utilization of solar energy while ensuring uninterrupted communication. We apply the proposed model of Q-theory to a case study of a Low Earth Orbit (LEO) satellite. The simulation results show that the proposed optimization model can significantly improve the performance of the satellite power system. Specifically, it can reduce the reliance on battery power during periods of low solar activity, leading to longer battery life and more reliable communication.