| |
Layers
with Photovoltaic Modules
Photovoltaic modules (PVs) are
a special topic. They enable the active use of solar
radiation by turning it into electrical energy;
in addition they can also represent a form of passive
solar protection.
The most well known PV products
are silicon solar cells, available in three types:
monocrystalline, poly- or multicrystaffine, and
amorphous, ie: non-crystalline solar cells. The
monocrystalline solar cells are opaque, blue or
dark grey to black, and they have a high efficiency
(14-16%). They are expensive because they are made
from silicon crystals in a complicated manufacturing
process.
|
 |
The
polycrystalline solar cells are mostly blue or opaque.
These are cheaper because they are made from poured
silicon blocks, but they have a lower efficiency (14%).
Crystalline solar cells are produced as 0.4mm thick
discs in sizes from 10 x 10cm to 15 x 15cm. These
discs are then put together to form modules and embedded
with resin in the cavity in a laminated glass unit. |
|
According
to composition, the result can be either a transparent,
translucent or non-transparent module. Light transmission
through transparent and translucent modules can be
set from 4% to 30% according to the choice of spacing.
Polycrystalline silicon cells were used in 1991 in
Aachen by the architect Georg Feinhals for the renovation
of the glass façade of the Stawag administration
building. Special light-scattering and insulating
glass elements were developed in order to meet both
the needs in terms of lighting and insulation, as
welI as the desire to maintain and exploit the corporate
image as protected through the façade.
In the exterior
laminated glass the PV cells have a gap of 5mm between
them (SGG Optisol Façade). On the inside a
laminated glass with an opaque interlayer was used.
The glazing lets through approx. 0.08 of the incident
light and provides an even illumination of the interior
space.
|
 |
Amorphous
solar cells are attracting great interest at present,
because of their potentially lower costs. Thanks to
thin-film technology they can be manufactured using
less material and at lower temperatures. The films
can be applied to various carriers such as glass,
plastics or steelfoils. Unfortunatelv the efficiency
is still relatively low, values of 5 - 7% are typical.
Large areas of amorphous silicon cells are mostly
red-brown-ish, or, when transparent, slightly reddish.
Also available are
semi transparent amorphous solar cells They are produced
by removing partial areas of the thin film by means
of a laser separation process, in order to create
narrow transparent strips between the opaque surfaces,
which allow up to 12% of the incident light to pass
through. The impression gained is that of looking
through a half-open louvre blind (Asi-Glass). |
|
As
alternatives to amorphous silicon solar cells other
materials are attracting increasing interest - materials
such as CdTe and CuInSe2. These cells can be built
using established thin film technologies or even by
a dipping process. In smaller areas up to l6% efficiency
has been reached under laboratory conditions. Production
values, however, do not exceed 8% so far.
Optimised exploitation
of solar energy can be achieved by combining several
thin film layers with different spectral responses.
So-called tandem cells have reached up to 12% efficiency
under laboratory conditions, slightly higher values
seem possible. Further possibilities are offered by
triple cells which consist of a succession of three
thin film layers Efficiencies of 10% in production
quantities are becoming realistic.
Although PV
cells cannot yet compete economically with other ways
of generating energy, they are gaining ground due
to a generally increasing concern for the environment,
supportive regulations and financial help from public
funding.
|
|
