Overview of the Photo Voltaic Energy System (PVES) for the CHILL-ICE mission

Introduction; In the summer of 2021, the analogue astronaut mission “CHILL-ICE” shall be carried out inside the Stefanshellir cave system. This short term 2-night emergency mission has the objective to put up an inflatable habitat inside a Lunar-analogue Lava tube, while wearing simulated space suits. For all extra-terrestrial missions, power is mandatory for survival of the crew. Therefore, this is likewise introduced in the CHILL-ICE analogue mission. A lot of devices such as; the short and long communication system, lighting, cooking area, equipment, Lunar Zebro rover and research projects all depend on this power system. 

 

System requirements; For the CHILL-ICE mission, a solar power system for remote areas has been developed by our partner Blinkinglights. The system with acronym PVES (Photo Voltaic Energy System) needed to fulfil the following mission requirements:

• 8H put up/ Take down
  • Essential for the astronauts to stay alive.
• Portable for 2 persons to carry around the selected lava tube
• Free standing
  • Fidelity for an analogous mission and no reliance on ground conditions.
• Peak power (W_p) of 2200W
• Re-deployable
  • Needs to be used for recurring phases of analogue missions.
• Easy to handle while wearing simulated space suits.
  • Fidelity in simulating the usage of a power system in an emergency situation in a extra-terrestrial environment.
• Weather resistant

Interior needs to stay dry. The caves on Earth can be subject to high humidity and cave rain.

For this analogue mission and the usage of PVES, the influence of gravity and space vacuum has been neglected. In addition, PVES shall have an automatous function to shut down when a spike in current is measured above a certain threshold, preventing possible fires and/or harmful situations.

Furthermore, as the Stefanshellir cave system consist of a rocky basaltic terrain, the cable going from PVES to the habitat, needs to be able to withstand possible ruptures.

 

PVES; The PVES (Photo Voltaic Energy System) is designed to provide an electrical power supply for use in a remote location where no grid-power is available. It has to be portable and should be able to be set up with two persons in a limited timeframe. Because of the rough terrain in Iceland care was taken, to design a ruggedized system that should be able to withstand impact with sharp rocks and outdoor weather conditions (complying roughly with IP54 specifications).

The system is built from different components that can each be carried into the lava cave area by foot. These components can then be connected together using interconnect cables with locking connectors. Different types of connectors have been chosen to discern between different types of electrical connections, as to prevent accidental misconnections and reduce the risk of electrical shock to the operator.

There are four main components to the PVES (fig. 1): PV panels (2x), SolarBox MPPT solar charge controller, PowerBox Lithium battery + power inverter and an additional ChargerBox that can be used to charge the battery from a regular power socket or a generator when solar energy is insufficient.

 

(Figure 1: Overview of the PVES and its subsystems.)

There are three different voltages present in this system: PV output voltage (~ 30 VDC), DC battery voltage (12 VDC) and AC voltage (230 VAC). The 12 V connections to the PowerBox are fused to protect the wiring and connectors from overheating in case of a short or overcurrent situation. The AC output power is automatically protected by the inverter in the PowerBox. When excessive power is drawn (and the inverter heats up too much) it will shut down automatically. It will have to be reset manually after this.

 

It is important that all devices that will be connected to the AC output of the PowerBox are doubly insulated (IEC 61140 Class II, indicated by the symbol ⧈ (a square inside a square)), as there is no proper safety earthing provided by the PVES. The system will operate in what’s called an unearthed IT AC system. Currently no provision is made to monitor insulation resistance in accordance with IEC 61557-8 because of the short timeframe of preparations for the CHILL-ICE mission.

Care is taken to choose a cable type that is suited for use in these rough environments. The cable type used throughout the PVES is H07BQ-F polyurethane sheathed cable with an orange jacket for visibility. This cable is designed to withstand abrasion and specifically use around sharp objects. It is UV and moisture resistant. The technical specifications of the PVES are given in table 1 below.

 

(Table 1: PVES technical specifications.)

PVES technical specifications
Peak power (Wp)	3000 W
Continues Power (Wc)	1200 W
Dimension	Standard Euroboxes
Output	230 V
Type solar cells	60 cell Poly-crystalline
Battery type	Lithium (LiFePo4) 2kWh stored
Expected solar yield	1 kWh/day [4]

 

Acknowledgements;

First, we would like to thank Jaap Elstgeest from Blinkinglights for his amazing work in researching and developing the PVES system for the CHILL-ICE mission, during this difficult COVID period. He has been the key factor for the success of the power system and therefore contributed significantly to this mission.

In addition, we would like to thank the whole CHILL-ICE team for their remote support during the development of PVES.

Lastly, we acknowledge the ILEWG EuroMoonMars manager B.  Foing for making this research possible.

 

References;

[1] M.V. Heemskerk et al., EGU2020-901-1, (2020)

[2] 2021LPI....52.2762H2021/03 CHILL-ICE (Construction of a Habitat Inside a Lunar-Analogue Lava Tube): Building and Testing of a Deployable Habitat in Icelandic Lava Tubes for Space Exploration Purposes Heemskerk, M. V.; Pouwels, C. R.; Heemskerk, R. S.; Kerber, S.; Foing, B. H.

[3] 2021LPI....52.2502F2021/03 Life and Research at SouthPole Moonbase: EuroMoonMars Campaigns Results 2019-2020 Foing, B. H.; Rogers, H.; Musilova, M.; Weert, A.; Mulder, S.; Kerber, S.; Castro, A.; Pouwels, C.; Das Rajkakati, P.; Heemskerk, M.; et al

[4] Calculated with https://www.victronenergy.com/mppt-calculator