Category Solar Module Packaging

Glossary

Active area: The surface area of the photovoltaic module responsible for the conversion of light into electricity Adhesive: A material used to bond two surfaces together Amorphous silicon cell (a-Si): A classification of thin-film photovoltaic cells composed of noncrystalline silicon that lacks long-range order and uniform lattice structure; typical Eg = 1.7 eV Antireflective coating: Typically an inorganic coating formulated to decrease the reflection and increase the transmission of specific wavelengths of light

Backsheet: A material typically composed of a polymer used as a primary barrier to the backside of a photovoltaic module Balance of Systems (BOS): Components of the installation used to mount the array to the roof and electrically connect it to the home or business

Band gap (Eg):...

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Conversion Factors and Common Units of Measurement

TABLE A.1

Metric System Prefixes, Symbol, and Conversion Factors

Prefix

Symbol

Conversion Factor

Giga

G

1,000,000,000

Mega

M

1,000,000

Kilo

k

1,000

Hecto

h

100

Deca

da

10

1

Deci

d

0.1

Centi

c

0.01

Milli

m

0.001

Micro

P

0.000001

TABLE A.2

Example of Applying These Prefixes to Length Measured in Meters

Prefix

Symbol

Conversion Factor

Gigameter

Gm

1 Gm = 1,000,000,000 meters

Megameter

Mm

1 Mm = 1,000,000 meters

Kilometer

km

1 km = 1,000 meters

Hectometer

hm

1 hm = 100 meters

Decameter

dam

1 dam = 10 meters

Meter

m

1 meter

Decimeter

dm

1 dm = 0.1 meters

Centimeter

cm

1 cm = 0.01 meters

Millimeter

mm

1 mm = 0.001 meters

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Polymeric Photovoltaic Solar Cells

Entire books have been devoted to the niche discipline of polymeric photo­voltaic solar cells, also known as organic solar cells. It is not the intent of this section to cover the expansive research in this area but to provide the reader with an overview of the application’s current feasibility and limitations as it relates to polymeric packaging.

Like CPV, polymeric photovoltaics are a cost-reduction technology. Specifically, the manufacturing costs can be reduced by eliminating inor­ganic chemistry, sourced from precious Earth metals, and using polymers, mainly sourced from petroleum by-products.

Polymeric substrates are flexible and can be formed into a number of dif­ferent geometries, increasing the commercial applications for PV...

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Luminescent Solar Concentrators (LSCs)

The goal of luminescent solar concentrators (LSC) is to simultaneously decrease costs and increase efficiency. Traditionally, LSCs are designed to absorb unusable light and re-emit it at wavelengths with the highest effi­ciency for the underlying PV cell. By increasing the concentration of highest – efficiency light, material costs decrease because fewer PV cells are required for the same power generation. Unlike the aforementioned concentrator tech­niques, there is no required tracker creating odd-shaped array footprints in residential areas.

LSCs are constructed of a polymeric lens that directs the light into the adjacent PV cells. The flat plate geometry is the most widely discussed, but cylindrical concepts have been proposed and patented since the late 1970s [21-24]...

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Metallic Films

Parabolic concentrators and reflectors use metallic surfaces to concen­trate light. Parabolic concentrators are composed of two parabolic mirrors, referred to as the first and the secondary. The first mirror reflects light from the Sun to the secondary mirror elevated above the first. The secondary mir­ror focuses light back onto the underlying PV cell. Parabolic concentrators
often exhibit high concentration factors, and they require a dual-axes tracker to follow the course of the Sun and optimize performance. In contrast, reflec­tors have guidance mirrors on each side of the PV cell. Light rays from the Sun hit the mirror and bounce down to the cell...

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Lenses

There are a number of design considerations to ensure a lens efficiently focuses light rays onto a focal point. The two relevant for this discussion are geometry and material selection. Design considerations include the geomet­ric shape, the wavelength with the highest quantum efficiency for the PV cell, and the refractive index of the materials used for the lens.

Fresnel lenses are the most common geometry designed for CPV concen­trators [16]. A Fresnel lens is composed of a number of Fresnel zones visual­ized as a series of prisms with different steps in thickness cut around the lens circumference. The expected concentration factors in the assembly are typically modeled using ray tracing, specifically the edge-ray principle [17]...

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Concentrated and Organic Photovoltaics

Between 2004 and 2008, silicon supply constraints caused more than a dou­bling of raw material cost [14]. In an effort to further reduce production costs, PV manufacturers have tried to reduce the amount of costly semiconductor material used in the module. These initiatives have generated interest in con­centrated photovoltaics (CPVs).

CPVs use polymeric lenses and packaging components to focus incident light on encapsulated cells, thereby increasing collection efficiency over a smaller cell area. Concentrated photovoltaic modules constituted 125 peak kilowatts, 0.06% of U. S. PV exports, in 2005, and 27,527 peak kilowatts, 2.8% of U. S. PV exports, in 2008 [15]. This explosive growth is the outcome of increased competitiveness due to improvements in cell efficiency...

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High Index of Refraction Polymers

Looking at the cross section of a module, there is a large disparity between the refractive index of PV cells (e. g., silicon) and packaging materials (e. g., glass and encapsulant) (Table 6.5). For instance, soda lime glass is about two units away from silicon. Most PV manufacturers make packaging choices to minimize the refractive index change across the glass-encapsulant interface.

TABLE 6.5

Packaging Function with Corresponding Inorganic or Organic Materials and Refractive Index

Function

Materials

Refractive Index

Superstrate

Optical glass

1.6

Encapsulant

Polydimethylsiloxane

1.4

High refractive index encapsulant

Polyphenylene

vinylene

2.1

Solar cell

Silicon

3.5

They then use an AR coating on the cell to maximize light transmission...

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