ESA Document - Emits - ESA

s
4.3.5.4.1.2 Solar dynamic
HMM
Assessment Study
Report: CDF-20(A)
February 2004
page 302 of 422
This option consists of a lens or a mirror that focuses the sunlight onto a receiver. In this
receiver, the collected sunlight provides heat to a thermal-conversion unit.
The NASA demonstrator has a low specific mass: 4.2W/kg with 17% of efficiency.
Moreover, this system may be more interesting by using thermal storage instead of batteries.
This system is interesting for high power needs, but the disadvantages that disqualified this
concept are:
• the dust deposit of the mirror/lenses
• the need of a Sun-tracking system
4.3.5.4.1.3 Wind generator
This design could be performed on the Martian surface by mounting a wind generator on a
hydrogen balloon.
It may be interesting during a dust storm when solar energy is not possible. Otherwise, this
design is not reliable since it depends on the local wind strength.
4.3.5.4.1.4 Solar photovoltaic
The conversion of solar energy to electricity by solar cells is the most reliable way to generate
power on the Martian surface. Moreover, it is the only power generation system already qualified
in a Martian environment.
In addition to the severe environment constraint that affected the solar cells (See 4.3.5.3), the
solar panels would have to be very large for being able to generate the required daily energy
(more than 100m²).
To limit as much as possible this area, the most efficiency cells should be considered.
Currently, the efficiency of AsGa TJ cells is (in AM0 28°C conditions) 27%. For 2015, 30% is
expected.
The inconvenience of these cells is that they are rigid and therefore mounted on a heavy rigid
panel (total weight estimated: 3.33 kg/m 2 ).
Various developments are currently performed for optimising solar panels weight by using
flexible structure or thin films. In 2015, a mass of 0.53 kg/m 2 can be expected with cells having
an efficiency (AM0 28°C) around 15%. With that technology, the solar panels could consist of
one (or several) blanket to unroll on the surface.
4.3.5.4.1.5 Other technologies
The following list shows the most promising other technologies with the rationales of their
rejection in this study:
• Microturbines: Technology extremely immature and need to bring fuel
• Thermionic converters: Not European strength
• Thermoelectric generators: Low efficiency and still theoretical concept
• Photocatalytic decomposition of CO 2 : Considerable further research required
None of these technologies is kept for this design. Nevertheless, if there are important
improvements in the coming years, they should be reconsidered.