Weight and stowage
volume are two of the major challenges facing spacecraft
designers today, so device efficiency is one of the
more critical aspects to space-based PV. With emerging
near-space vehicles (High Altitude Airships) requiring
hundreds of times more power than a typical spacecraft,
efficiency is very critical to minimize the area and
weight of the solar cells.
Thin-film PV – Recent
advances in thin-film PV are beginning to gain interest
in space and near-space industries. Thin-film PV uses
thin-film coating technologies, similar to those used
for putting metallic and transparent coatings on plastics
and glass for food processing, architectural glass,
mirrors, eyewear, etc.
The three most common thin-film technologies are amorphous
silicon (a-Si), cadmium telluride (CdTe) and copper-indium-gallium-diselenide
(CIGS). Of these, CIGS currently has demonstrated the
highest laboratory efficiency at 19.5% (NREL,
measured in earth conditions) with CdTe close behind.
CIGS thin-film technologies can be placed on a wide
variety of substrate materials making it is possible
to manufacture very lightweight, flexible solar cells
on metals and plastics. To put it into
perspective, the thickness of a flexible CIGS device
is approximately the same as the thickness of a human
hair, making it very flexible and lightweight.
CIGS on Metal Foils – While CIGS
on metallic foils are a good first step, this class
of thin-film product does not fully address some of
the basic needs of the space and near-space industries.
First, while the performance of these devices are good,
they are not competitive with the existing PV
technologies for space applications when taking into
account the mass of the metallic foils. Second, metallic
foil substrates generally require that each cell must
be interconnected in series and/or in parallel (similar
to how flashlight batteries are stacked) to meet the
desired voltage and current output. While this is merely
an inconvenience for earth applications, space applications
require significant quality control for each process
step of the PV array, thus adding to the cost and complexity
of the power system. Finally, many of the metallic
substrates can interact with the magnetic fields around
the earth. While not a concern for earth applications,
any outside forces in addition to gravity that act
on the spacecraft means that additional onboard fuels
and other resources must be used to maintain proper
spacecraft alignment so that sensors and antennas work
properly.
The Ascent Solar Solution – Ascent
Solar believes that a system-level solution
is needed to provide the space and near-space industries
with better performing products than currently available.
Ascent Solar is developing processing techniques to
take CIGS to production using high-temperature
plastic substrates. These plastics can survive
the manufacturing temperatures associated with thin-film
CIGS processing while remaining flexible and electrically
insulating. The insulating features of the plastics
make it possible to connect individual cells into modules
during processing. These advances in CIGS processing
significantly reduce the weight, cost, and complexity
of PV products making this latest technology uniquely
suited for space and near-space applications.
By close interaction with 'early adopters'
and established prime contractors in the space and
near-space industries, Ascent Solar plans to develop
a power solution that provides a system-level advantage
over traditional technologies and other thin-film vendors.
By combining our new manufacturing facility currently
under construction with over a decade's worth of R&D
in this area, our long term vision is to lead the emergence
and acceptance of thin-film photovoltaics in the space
and near-space industries.
(Play video to watch how our Flexible
Photovoltaic Module is manufactured)
