Amorphous module

An amorphous silicon solar cell (a-Si) is made when silicon atoms are deposited to a substrate material. During solidification the atoms cannot connect to other atoms and hence remain disordered without a crystalline structure.

Deposition can be performed onto rigid or flexible substrates. By an intelligent selection of the encapsulation material the flexibility of the solar cells can be maintained when hence flexible modules can be build. These can be applied to flexible substrates.

Alternating current (AC)

Electric current whose direction reverses cyclically. The frequency is the number of electric waves per second and varies by country. Unit: Hertz (Hz).

BIPV (Building Integrated Photovoltaic)

 

Bypass-Diode

Within a serial photovoltaic system, the photovoltaic element receiving the least sun light always determines the current flow. Thus a slight shadow means a significant reduction in power generation. Shading in an area acts like a resistance in an electric circuit. Consistently unequally spread sun light might even cause damages to the solar cell as a shaded module could be compared with an obstructed water pipe. The other, non-shaded modules then try to pass their nominal power through the "obstruction" which irreparably damages the cell. In order to prevent a decrease in efficiency caused by shading (also through leaves and dirt), a bypass diode can be switched with every single cell. There are also shadow-sensitive solar modules already integrating a bypass diode. The bypass diode passes the flow around the shaded module and provokes a short-circuit within the shaded area. This prevents damages to the modules. In modern modules up to 24 cells are protected by a bypass diode, allocated within the module or the module connection device. The PV elements used by Solar Integrated have an integrated bypass-diode in every cell.

Degradation

Degradation is the decrease of module performance caused by aging. Generally, manufacturers guarantee 80% of the nominated performance after 20 years. However, on good modules the real decrease in performance is less, e.g. 10% after 20 years.

Diffuse radiation

The flux of light is scattered when passing through clouds or dust in the atmosphere etc. and not directed straight to the Earth or an object.

Direct current (DC)

Direct current is a one way, consistent flow of electric charges, distinguishing it from alternating current. Typical sources of direct currents are electric cells, rectified power units and direct current generators. Also solar systems produce a direct current flow. In order be used for typical 120 or 220 volt household appliances, it must be converted to AC (alternating current). For this conversion an inverter is being used.

Direct radiation

The sun is directed straight to an object without any scattering or obstruction.

EPC

Engineering, Procurement and Construction – a common form of contracting arrangement within the construction industry.

Under an EPC contract, the contractor will usually design the installation, procure the necessary materials and construct it, wither through own labour or by subcontracting part of the work. The contractor carries the project risk for schedule as well as budget in return for a fixed price, depending on the scope of work.

Feed-in tariff

The feed-in tariff is a government incentive program to increase the usage of solar energy and to allow the solar industry to grow and develop to a level that allows it to become competitive in the general energy market. The feed-in tariff usually provides a higher remuneration for kWh produced and fed into the electricity grid of a utility company than for kWh used and bought from the utility company. Once installed, the feed-in tariffs are usually kept at same level for 20 to 25 years, allowing for long-term planning and assurance in the investment decision.

Generator

The PV modules as a whole are called generator.

Global radiation

Global radiation is the direct irradiation from the sun to the earth, which is absorbed by a horizontal area within a specific time unit.

Hours of sunshine

Hours of sunshine are a definition for the amount of hours per year, in which the sunlight reaches the surface of the earth without being obstructed by clouds or any atmospheric pollution. The average amount of hours of sunshine in Europe ranges, depending on the geographical location, between 1300 - 1900 hours per year. The midpoint is 1550 hours of sunshine per year.

Inverter

Device converting continuous current into alternating current, classified into devices working with and without transformers.

ISPRA-guidelines

Guidelines for the evaluation of photovoltaic systems, published by the Joint Research Centre (JRC) of the European Commission in Ispra, Italy.

kWp

Kilowatt peak, i.e. peak performance measured in kilowatt
This unit describes the optimal performance of a solar cell in a standardized test environment (1000W/m2 irradiation, 25°C module temperature, 1.5 air mass). Under a clouded sky or heating of the module, the performance of the solar generator is lower.

Laminate

Flexible solar modules encapsulated in special materials, e.g. Tefzel. Flexible solar modules are produced by laminating the modules with transparent membranes.

Monocrystalline

Mono-crystalline cells are made from a solid mono-crystal, in which the lattice of the entire cell is without grain boundaries. Mono-crystalline PV cells are considered to render the highest efficiency due to the pureness of the material.

MPP

Maximum Power Point - the power at the point on the current-voltage characteristic, where the product of current and voltage is at its maximum. Unit: watts (W)

Open-circuit-voltage (Voc)

The voltage across a photovoltaic cell or module in sunlight when no current is flowing; the maximum possible voltage. Unit: volt (V)

Polycrystalline

Poly-crystalline cells are a solid material composed of many crystallites of varying size and orientation. Poly-crystalline cells can be recognized by visible grains, a “metal flake effect”.

PNOCT

Power of PV-cell/module at Normal Operating Cell Temperature.

Renewable Energy Laws

Certainly the most important economic development for the photovoltaic industry is the Renewable Energy Laws passed in various countries (e.g. the EEG in Germany or the Conto Energia in Italia). Objective of these laws are to foster the installation of energy plants supplying energy to the grid from renewable sources. It has been designed to protect the climate and being less dependent on fossil fuel like oil, natural gas or coal. An amended version, as decided by the German Federal Parliament on June 6th, 2008, will be effective as of January 1st, 2009.

Return

The annual return of a PV installation divided by the installed PV performance, depending on location, direction towards the sun and climate, is a way to calculate its profitability.

SC

Abbr.: Short Circuit

Protection class

Describes with two figures the kind of protection against mechanical load and penetration of water.

Series connection

A wiring configuration used to increase voltage. Series wiring is positive to negative (+ to -) or negative to positive (- to +), opposite of parallel connection.
Series connections are applied by manufacturers of large dimension modules with thin-film technology. During the manufacturing process large scale solar cells are cut into single stripes. A connection between the front of one solar cell and the back of another adjacent cell results in a serial connection. Together with material savings, the possibility of an integrated serial connection is the main advantage of the thin-film technology.

Short circuit current

The current flowing freely from a photovoltaic cell or module through an external circuit that has no load or resistance; the maximum current possible. Unit: Ampere (A)

Silicon, Si

Right after oxygen the most common chemical element. Silicon is the basic material of most beach sand and can be found in nature mainly as quartz SiO2. It is sensitive to light and capable of transforming light into electricity and therefore the raw material used to manufacture most photovoltaic cells.

Solar

Lat. referring to the sun.

Solar-Module

Entity formed by solar cells in order to produce electricity. Better described as photovoltaic module or just PV-module.

Solar Cells

The basic photovoltaic device, which generates electricity when exposed to sunlight. Solar cells can be classified in different groups. The most common criteria is the material thickness, differentiating between thin-film and crystalline cells. Another criteria is the material itself: in use are e.g. semiconductor materials such as CdTe (cadmium telluride), GaAs (gallium arsenide) or CulnSe (or CIS, copper-indium-diselenide), most frequently however silicon.

There are different types of silicon solar cells which differ according to application, performance and manufacturing process of the silicon layer:

• monocrystalline silicon cell
• polycrystalline silicon cell
• amorphous silicon

Photovoltaic installations mainly use crystalline cells as they have a higher efficiency grade. When used in roof-top installations, higher weight and additional wind loads are frequently disadvantageous for the roof static, especially for industrial low slope roofs.

Thin-film cells are produced in several variations, depending on the substrate used and vacuum metalized materials. The range of physical characteristics and efficiency grade varies accordingly. The module efficiency grades normally range between 7-9%. Amorphous silicon, copper-indium-diselenide (CIS) or Cadmium telluride (CdTe) are used as cell material.

Stand-alone installations

Stand-alone installations are not connected to the grid; they do not feed their generated electricity into the grid. From an economic point of view they are mainly used in areas without any possibility of connection to the power network, e.g. mountain shelter, as a mobile device on ships or countries, which do not have sufficient electricity net.

STC

Standardized Test Conditions, which are:

• insolation intensity of 1000 W/m2 on module level
• constant solar cell temperature of 25 °C
• global irradiation spectrum of AM 1,5

Modules are tested and their efficiency rated at STC, however real performance under actual conditions may vary - please check out our chapter Efficiency versus Energy Output for more information.

Temperature coefficient

Describes the deterioration of a PV cell/module in relation to the temperature increase.

Thin-film modules

Thin-film solar cells or modules vary according to their composition and substrate material coated with amorphous silicon or other photovoltaic material like copper-indium-diselenide (DIS) or cadmium telluride (CdTe). The range of their physical characteristics and performance depends on the same variety. The efficiency factor of the modules normally ranges between 7-9%. Nowadays there are even thin-film cells with the same efficiency as crystalline cells. CIS thin-film modules e.g. have an efficiency of 11-12% and are being used for wide-spread areas. The encapsulation of thin-film solar cells in synthetic materials often still complicates the production of flexible PV laminates considerably. That's why United Solar Ovonic is at present the only manufacturer ready for mass-production of flexible solar modules.

Tilt angle

A fixed angle measured from the horizontal to which a solar array is tilted. The tilt angle is chosen to maximize the array output and varies in its optimal position depending upon latitude, season and time of the day.

Tracking system (e.g. Solar Integrated's Follow The Sun™)

An array of photovoltaic modules mounted on a movable structure that has been designed to follow the path of the sun. In this way, it is possible to obtain the best insolation angle for the sun and a constant power supply.

Turnkey

Turnkey describes something that is built or installed for a customer ready to use.

The concept is commonly used in the construction industry and refers to the bundling of materials and labor by sub-contractors.

A turnkey installation can very much vary in its complexity and can involve everything from project design,  administration & engineering up to operation & maintenance.

W, Wp

Watt. Watt peak. The nominal power of a solar cell under standard conditions (formula: P.P=U*l).
1 Wp ~ 20 kWh