Energy plays an essential role in placing humans in orbits and on other planets. Electrical energy is needed to maintain the satellite in orbit, communicate, provide electrical power to the satellite payloads and is also going to be needed for a human base on other planets. With solar as the primary energy source, the lunar bases’ power system can be considered very similar to the renewable-based terrestrial microgrids (MGs).

A lunar MG system consists of generation units based on solar power, energy storage systems (ESSs), and loads. Similar to terrestrial MGs, frequent changes of load and generation in a lunar MG may create voltage (and frequency in case of AC) fluctuations, creating the power system’s stability issues and reducing its reliability. ESSs such as batteries and regenerative fuel cells (RFCs) can mitigate these fluctuations and are also critically important to supply loads at the night-time or eclipses. An efficient and reliable operation can be achieved by connecting multiple MGs together to form a multi-microgrid (MMG) system.

MULTI-MICROGRID SYSTEMS

Adopting an MMG system brings many advantages like sharing power and resources among MGs and enhancing power supply reliability. MMG increases peak power exchange, while two MGs with complementary loads (and maybe generation) profile can reduce the total aggregated peak power. At the time of unexpected events like transmission faults resulting in power loss, MMG systems can have the ability to supply critical loads. The management of MMG involves controlling power converters, power-sharing among the distributed sources, controlling the ESSs, and maintaining the voltage (and frequency for AC supply) at the point of common coupling (PCC).

The rim of the “Shackleton crater” near the lunar south pole is considered the most preferred location by the researchers to establish a lunar base because of its high solar power availability. It has some highly illuminated areas with an average irradiance of 86% and receives continuous sunlight for over six months. At the time of eclipses and dark periods, the loads are to be supplied by ESSs. Other than the “Shackleton crater”, the “Peary crater” rim near the lunar north pole also receives continuous sunlight and instigated interest among the researchers.

LUNAR BASES AND ENERGY NEEDS

There exist various types of loads on a lunar base. The most apparent load is the crew habitat and base camp, which needs 30 to 60 KW of power, consisting of critical life support systems (LSSs), computers, lights, and experiment tools. The energy needs are directly proportional to the number of crew members and mission duration. The different communication systems, such as the lunar surface low rate communications, spacecraft/orbiter relay, and other human outposts, require power ranging from 0.3 to 1 KW per transmitter. Other than this, In-Situ Resource Utilisation (ISRU), an establishment that can produce propellants and oxygen using the lunar regolith, needs 10s of KW to 100s of KW of both thermal and electrical energy depending upon the process and production rate. Other equipment such as long-range rovers or heavy equipment vehicles, electrostatic radiation shielding, water ice exploration, stand-alone geology and astronomy observatory also needs power.

During the night-time or eclipse, the loads are supplied by the ESSs. For planetary base missions, the ESSs with high specific energy (more than 500 Wh/kg), long life (more than 5 years), long cycle life (more than 1000 cycles), and high specific power (500 W/kg) are desired. The ESSs that can satisfy these needs are batteries and RFCs.

In this PhD project, a lunar MMG system based on solar power and ESSs is to be developed by identifying a suitable location with abundant solar energy and thereby reducing ESSs size. The MG sizing is to be done considering the power availability and loads, considering mass, size and efficiency of ESSs and other power system components. The energy management system (EMS) of the MMG is to be implemented considering the several technical constraints related to power equipment for safe, reliable, and autonomous operation of the lunar MMG system.