Phase II Final Report - NASA's Institute for Advanced Concepts

Chapter 3.0 Vehicle Design
3.6 Power System
16
14
12
10
CdS/Cu2S
CuInSe2
CuGaSe2
CuInS2
CdTe
a-Si
CASCADES
8
6
4
2
0
1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996
Figure 3-172: Historical Progress of Thin-film Solar Cell Efficiency. Experimentally
Achieved Efficiencies (Extrapolated to Air Mass Zero Spectrum, in Percent)
[293]
The Kapton or other polymer substrate is capable of serving a double duty as the substrate for
the cells and skin for the wing. The thin films are quite flexible and can easily accommodate the
curved shape and flapping motion of the wing.
Thin film cells tend to have a high optical absorption constant; therefore, active material may be
as thin as 1 to 2 µ, yielding inherently lightweight cells. A very conservative projection of thinfilm
solar cell technology would be a 5% efficient thinfilm cell fabricated on a 25 µ thick Kapton
substrate. This yields a PV blanket specific power of 1.7 kW/kg. An optimistic projection
might be a 15% thin film cell on a 7 µ thick Kapton substrate, leading to a PV blanket specific
power of 15 kW/kg. These numbers compare favorably to current state-of-the-art spacecraft
solar blankets (e.g., 67 W/kg at the array level for the flight-tested SAFE array) and 130 W/kg at
the array level for the experimental APSA array using thin silicon solar cells.
Preliminary results also indicate thin film solar cells may be inherently radiation-tolerant and not
require a glass cover for radiation protection. They are highly tolerant of small damage areas
from debris impact and any tearing.
211