At Creativeit Group we offer specialized services for the analysis of photovoltaic cells, in accordance with IEC 61215, ISO 9488, ASTM E948, and ASTM E1036. In recent years, reducing fossil fuel consumption and using photovoltaic energy have become popular ways to prevent global warming and preserve the environment. The main advantage of solar cells is that an unlimited amount of energy can be obtained anywhere exposed to sunlight without harming the environment. For this reason, and because the efficiency of power generation does not depend on the scale of the equipment, demand for photovoltaic energy is growing, so at Creativeit we have state-of-the-art specialized equipment for the analysis and characterization of your photovoltaic system.
The most important elements in the analysis and characterization of a photovoltaic cell, module, or set of photovoltaic modules (arrays) are the characteristic behavior curves of voltage versus current (I-V) and voltage versus power (P-V), and the maximum power point (MPPT). These curves are nonlinear; given this condition, there is a point on the panel’s characteristic curve at which maximum power can be obtained. For this reason, an electronic circuit capable of detecting and tracking the maximum power point generated by the solar panels is necessary.
We perform analysis of:
- Solar inverter efficiency.
- Direct (front) irradiance measurement with a reference cell.
- Cell and ambient temperature measurement.
- Summary table of the main electrical parameters.
- I-V curve measurement range / VOC-ISC 1000V / 15A
- Measurement category
Operating principle, structure, and energy conversion efficiency of solar cells
The main solar cells available today are silicon solar cells and compound semiconductor solar cells. Although silicon solar cells are the most widely used, the market share of compound semiconductor solar cells is increasing because they have an advantage in terms of production costs. Below we explain the basic operating principle and structure of solar cells, as well as the typical materials and energy conversion efficiencies of silicon and compound semiconductor solar cells.
Operating principle of solar cells
Silicon solar cells, which are commonly used, have an internal junction of two types of semiconductors, p-type and n-type, each of which has different electrical properties.
When a solar panel is exposed to sunlight, electrons (negative) and holes (positive) are generated. The holes are attracted to the p-type semiconductor, while the electrons are attracted to the n-type semiconductor. For example, when a load, such as a light bulb, is connected to the electrodes on the front and back, electric current flows through the junction as shown in the figure below.
Structure of solar cells
- Cell: A cell is the smallest unit.
- Cell string or cell array: A single cell generates a low voltage. A cell string contains multiple cells connected in series to generate the required voltage. A cell array contains several cell strings connected in series or in parallel to further increase the output.
- Module: A module, also called a solar panel, is a package containing several cell arrays for outdoor use. A module is coated with resin or tempered glass to protect the internal cells and is secured with an outer frame to increase its strength.
- Array: Several modules are connected to form an array.
Energy conversion efficiencies and materials of solar cells
An important indicator of solar cell performance is energy conversion efficiency. Energy conversion efficiency is a parameter that shows the fraction of incident sunlight energy converted into electrical energy. Module energy conversion efficiency and cell energy conversion efficiency are two representative indicators of photovoltaic energy conversion efficiency. The two energy conversion efficiencies are explained below.
Module energy conversion efficiency
Module energy conversion efficiency is commonly used to indicate the power generation capacity of a solar module (solar panel). Module energy conversion efficiency is the percentage of electrical energy converted from approximately 1 kW of light energy per 1 m² (10.76 ft²) of solar module.
With continuous research and development, the energy conversion efficiencies of modules and cells improve year after year. However, modern technology cannot absorb 100% of the incident light energy or convert 100% of the absorbed light energy into electricity due to various factors, such as light reflection on solar panels and cell resistance.
Materials and characteristics of solar cells
Solar cells use various materials depending on the functions required by the application and the expected costs. Energy conversion efficiency varies accordingly. For this reason, manufacturers are working on research and development of materials and manufacturing processes to achieve higher energy conversion efficiency and lower costs.
Below, solar cells are classified into silicon and compound semiconductor types; representative materials and their characteristics are explained for each type.
Silicon solar cell
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Monocrystalline: Solar cells that use monocrystalline silicon are expensive, but have high conversion efficiency and reliability.
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Polycrystalline: Polycrystalline silicon cells are the most widely used because polycrystalline silicon is cheaper than monocrystalline silicon.
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Amorphous silicon: Since amorphous silicon is a non-crystalline silicon, solar cells that use amorphous silicon are cheaper than those that use polycrystalline silicon, but have low energy conversion efficiency.
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Multijunction cells: Several types of solar cells, such as amorphous silicon and thin-film polycrystalline silicon, are laminated to form a tandem structure. This type of solar cell has high energy conversion efficiency.
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Compound semiconductor solar cell
Copper indium selenide (CIS): CIS solar cells are made of copper, indium, and selenide. This type of solar cell can be manufactured at low cost and has relatively high energy conversion efficiency.
Copper indium gallium selenide (CIGS): CIGS solar cells use four elements, with gallium added to the three elements used for CIS. This type of solar cell has slightly higher energy conversion efficiency than CIS solar cells.
Cadmium telluride (CdTe): CdTe solar cells are made of cadmium and tellurium. This type is mainly used in Europe.
Gallium arsenide (GaAs): GaAs solar cells are made of gallium and arsenide. This type of solar cell has high energy conversion efficiency, but is expensive. It is used in satellites and similar applications.
Problems in the measurement, analysis, and evaluation of solar cells
In the photovoltaic industry, with the need to preserve the environment and growing demand for renewable energy, manufacturers compete to develop solar cells that deliver higher energy conversion efficiency at lower cost. In addition, high levels of quality assurance and control are necessary to provide stable photovoltaic and energy storage products and maintain reliability in the aftermarket.
Solar cells have surface irregularities to increase surface area. Each section has a mixture of various materials with different colors and glossy surfaces. This makes it difficult to accurately observe, measure, and analyze the microscopic parts, such as the electrodes, of defective products and prototypes, making these operations very time-consuming.
A great deal of time, effort, and a high level of expertise are required for measurement and analysis. Even when experts use a scale for visual measurement, the measured values can vary from one operator to another.
