Technical sciences/5. Energetics

C.t.s. Bulatbayev F.N., Yakupova O.V.

Karaganda State Technical University, Kazakhstan

Comparative anaysis OF solar cells operating efficiency for selection of reseaRch and object implemeNtation

In the modern world non-renewable energy resources of the Earth, such as coal and oil, are being depleted rapidly. As a result, enormous damage is caused to environment, and the consequences of this are quite hard to avoid.

Alternative and renewable energy sources, such as wind power, wave energy, sunlight and geothermal energy, attract more and more attention all over the world. On the one hand, interest to these sources is caused by environmental considerations, and on the other hand because of limitations of conventional Earth resources.

The sun is an inexhaustible, safe and accessible source of energy. Solar energy is clean, easily used, inexpensive, constant in abundance, don’t have negative impact on the environment and can be used as a standalone power source. The total amount of solar energy reaching the Earth in one hour exceeds the amount of energy consumed by humanity within a year.

For the last 20-30 years growth rates of solar energy production were about 25%. According to the forecasts in the XXI century, the development of solar energy will be the main among all alternative sources. According to assessments, the solar power could provide 20-25% of global energy production by 2050, and by the end of XXI century solar energy should become the dominant source of energy with a share of up to 60% [1].

In the Republic of Kazakhstan every year there comes from 1400 up to 2000 kWh of solar energy per 1 m² of the ground. Accordingly, there is a possibility of large-scale solar radiation usage.

An important place among the alternative and renewable energy sources belongs to photovoltaic converters of solar energy, also called solar cells and solar batteries.

Solar cells assembled into solar batteries are used for solar energy conversion into electrical energy. Solar battery constantly generates direct current which can be immediately used or accumulated, or converted into alternating current with the required characteristics (for example, 220 V, 50 Hz).

History of solar cells development. Photo effect phenomenon was firstly noticed by A. Becquerel in 1839. In 1883 Charles Fritts invented the first solar module. The basis of invention was selenium coated with thing layer of gold. Efficiency of it was about 1%. Only in 30-s of XX century in physico-technical institute under the supervision of Ioffe, it was possible to produce current by means of photo effect. There were invented the first solar sulphur-thallic elements. Efficiency of them we 1%. In the beginning of 50-s XX century American scientists Pearson, Fuller and Chapin invented and patented the first silicon solar cell with efficiency of 6%. In the beginning of 50-s XX century there were started a wide practical use of solar cells. In 1957 year in the USSR launched the first satellite with the use of photovoltaic cells, and in 1958 year in the USA launched Explorer 1 artificial satellite with the silicon solar cell panels.

Zhores Alferov and his colleagues invented the first heterostructure (with the use of helium and arsenium) solar battery with high efficiency in 1970 in the USSR. By the mid 70-s of the last century, it was possible to increase efficiency of solar cells up to 10%. After 20 years stagnation, the world scientists increased the solar cells efficiency up to 15% by mid-90-s, and by the beginning of the XXI century it was increased up to 20%.

The invention of more effective colorosensibilized solar cells was a significant development done by Americans in the 90-s. In 1989 the solar cell with efficiency over 30% were invented. Currently, the majority of industrial solar cells have the efficiency not exceeding 7-15% [2].

Energy photovoltaic converters classification.

The basic material for the solar cells manufacture is crystalline silicon. Nowadays, the proportion of solar cells and modules produced on the basis of crystalline silicon, exceeds 90%, where about 2/3 are polycrystalline silicon and 1/3 is monocrystalline silicon. Such a widespread use of crystalline silicon is based on advanced silicon technology in general and the possibility of manufacturing of solar cells for terrestrial applications with the most appropriate relation of cost – effectiveness on its basis. The rest part of the market is accounted for film elements based on other materials including more than 5% of solar cells based on thin films of hydrogenated amorphous silicon [3].

Peculiarities and advantages of solar cells from crystalline silicon:

- solar cells from polycrystalline and monocrystalline silicon have high efficiency;

- best combination of high quality raw materials and components;

- lightweight solar cell built on an anodized aluminum frame;

- high reliability level even in extreme weather conditions.

Applications of crystalline silicon solar cells

1. Power stations connected to common power supply.

2. Solar systems of street lighting.

3. Solar systems of accommodation lighting.

4. Solar modules of electric power.

5. Other autonomous systems.

6. Pressure water supply system.

Standard monocrystalline solar modules. In solar cell of this type, the silicon layer is used as the semiconductor. To produce module of that type, the silicon have to have a very high level of purity, so the production of solar cells of this type is expensive. Advantage of solar cells based on monocrystalline is reliability and high efficiency level.

Standard polycrystalline solar modules. To produce elements from polycrystalline silicon, the liquid silicon is poured into blocks which are then sawn into plates. With this method of solar cells production, there is a degradation of the silicon crystals characteristics, consequently decreasing their efficiency. However, the production of elements of this type is easier and cheaper.

Solar cells based on thin films of amorphous silicon.

While thin film technology based on materials with a high absorption coefficient used in the form of polycrystalline films, the hydrogenated amorphous silicon (a-Si: H) allows to reduce consumption and cost of the material used. When using these materials, the technology is highly efficient, less energy-consuming and requires lower investments. The low efficiency of about 6-8% and poor parameters stability of these solar cells can be considered as the disadvantages.

Peculiarities and advantages of thin film solar cells:

- higher conceived technology;

- they generate more power compared to solar cells from crystalline silicon;

- thin film solar cells have excellent performance even under high temperature in summer, and in cloudy conditions;

- high stability of output power for a long period of time;

- environmentally safe – it is 1/600 of silicon used in compare with polycrystalline silicon type; as a results, power consumption decreases and high productivity can be achieved in the mass production of solar batteries;

- due to high energy output there is a reduced payback time of the solar panel.

Basic parameters and characteristics of solar cells and modules. A set of parameters and characteristics is used to describe solar cells, allowing performing a comparative evaluation of different types of solar cells. Volt-ampere and spectral ones are referred to the specific parameters of solar cell. Specific parameters of solar cell are efficiency, filling factor, open circuit voltage, SC current or current intensity of SC current [4].

Current-voltage characteristic shows the dependence of the solar cell current output from the voltage on its output.

Current-wavelength characteristic (spectral response) depends of the quantum efficiency (solar cell efficiencies while irradiating by monochromatic light at a specific wavelength) from the wavelength of incident radiation.

Solar cells efficiency shows, what portion (in percentage) of the solar energy incident on it can be turned into electricity.

Open circuit voltage is maximum voltage generated across open findings of solar cell during its irradiation by sunlight.

SC current is the maximum current flowing through solar cell outputs when they are shorted.

Filling factor shows how much power generated by the solar cell is used in the load.

Comparing these parameters and characteristics, the most appropriate solar battery for technical and economic aspects can be determined.

Conclusions. Thus, there are no doubts on the prospect of solar modules and autonomous power installations on their basis using. The widespread implementation of solar power in real life is associated nor with the level of problem development, but firstly and foremost, with the economic feasibility and the cost of energy obtained in this way.

Bibliography:

1. Ryazanov К. V. Prospects of the solar energy development //КАБЕЛЬ −news. 2009. № 12–1. P. 81–85.

2. http://www.creeed.net/wp-content/uploads/2013/06/Hystory%20and%20

classification%20of%20solar%20energy.pdf (reference date 1.02.2014).

3. Afanasiev V.P., Terulov E.I., Sherchenko A.A. Thin film solar cells based on silicon. 2-nd ed. SPb.: Pub. house СПбГЭТУ “ЛЭТИ”, 2011. 168 p.

4. Gremenok V.F., Tivanov M.S., Zalesskiy V.B. Solar cells based on semiconductor materials. Minsk. Pub house БГУ. 2007. 222 p.