Solar water heating installations. Thermodynamic converter of solar energy. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Alternative energy sources

 Comments on the article

The sharp rise in prices and tariffs for electricity and heat, the desire of consumers to improve the reliability and use of their own autonomous energy sources, as well as the increased interest in the use of environmentally friendly renewable energy sources are leading to the rapid development of the domestic market for solar water heating installations (SWH), in their own way. technical and economic indicators and technological sophistication of the most prepared for wide commercial use not only in the southern regions of Russia, but also in its middle zone and even in the northern regions.

At the same time, the development of this market in Russia is constrained by a number of factors, among which the high cost of IEDs, their insufficient reliability and durability are the most significant. Long-term observations of the operational reliability of solar collectors have shown that most designs do not provide the minimum service life established by the Russian standard - 10 years.

The cost of solar collectors of Russian manufacturers today lies in the range from 100 to 200 dollars per 1 m2 of their heat-receiving surface. Taking into account the cost of installation and the necessary additional equipment and components, solar water heating installations cost the consumer $ 200 - 500 / m. Foreign analogues of IEDs offered on the Russian market turn out to be even more expensive.

Thus, the task of improving the design of solar collectors, reducing their cost while increasing the period of reliable operation is extremely relevant.

The thermodynamic solar energy converter must contain the following components:

a) a system for capturing incident radiation;
b) a receiving system that converts the energy of solar radiation into heat, which is transferred to the coolant;
c) a system for transferring the coolant from the receiver to the accumulator or to one or more heat exchangers in which the working fluid is heated;
d) thermal accumulator;
e) heat exchangers that form hot and cold sources of a heat engine.

Systems for capturing solar radiation and designs of thermal converters

Systems for capturing solar radiation provide different degrees of concentration (Fig. 3.1).

Fig.3.1. Solar Energy Capture Systems

A small degree of concentration (of the order of 100) is obtained by using reflective surfaces that concentrate energy in any direction of arrival of sunlight. Observation of the Sun is carried out in this case using a simplified control system. Devices of this type include parabolic trough reflectors, the axis of which is either horizontal or perpendicular to the plane of motion of the Sun. Such an installation is controlled only in accordance with the change in the position of the Sun in the sky during the day. The change in the position of the Sun during the year is not taken into account, and measures are taken only to ensure that the focal image does not go beyond the surface of the concentrated radiation receiver.

The average degree of concentration (of the order of 1000) is obtained by using focusing heliostats controlled by two rotational degrees of freedom. Such a heliostat can be a mirror in the form of a paraboloid of revolution, the axis of which is oriented towards the Sun.

A high degree of concentration is carried out by a single optical system (flat heliostats and a paraboloid reflector). It allows you to reach very high temperatures.

The concentrated solar radiation is absorbed by the surface of the receiver and converted into heat. To reduce heat losses associated with radiation from a heated receiver in the thermal region of the spectrum, the surface of the receiver is covered with a thin film of selectively absorbing materials. This allows you to significantly increase the efficiency of the system.

Designs of thermal converters. Two principal schemes are possible. In the first one (Fig. 3.2A), the coolant is heated in the receiver, in connection with which the thermal load of the battery is ensured. At the same time, the working fluid is heated by the battery, which smooths out changes in the intake of solar radiation. Thus, the battery constantly plays the role of a buffer, and the connection of the "receiver-accumulator" system with the heat engine is carried out using at least one heat exchanger.

In the second scheme (Fig. 3.2B), the working fluid is directly heated in the receiver. The battery is charged by removing part of the heated body, and the connection with the heat engine occurs without intermediate devices.

In the first scheme, in comparison with the second one, there is on average a greater decrease in the temperature difference, i.e. temperature difference between the heater and the cooler of a heat engine. In the second scheme, heat is lost only during accumulation and return. However, in the first case, the heat engine and its auxiliary devices are not subject to random temperature fluctuations even in the absence of a control system. In addition, in many cases, the coolant itself plays the role of a heat accumulator.

Fig.3.2. Scheme of thermodynamic conversion of solar energy: A - scheme with a heat exchanger; B - scheme without heat exchanger

heat accumulators

Currently, energy storage is carried out by heat storage.

The heat accumulator is an expensive element. Depending on the temperature of the system, energy storage is usually divided into low temperature (up to 100°C), medium temperature (from 100 to 550°C) and high temperature (>550°C).

Low-temperature batteries, in particular water batteries, are widely used in solar technology for building heating and hot water supply. For low-temperature accumulation, reversible reactions of hydration and solvation of salts and acids, as well as phase transition processes, are also used. For these purposes, paraffins and emulsions consisting of paraffin and water are used as heat storage substances. The latent heat of melting of paraffin is about 44 cal/g, and the melting point is 35 - 50°C.

A new type of thermochemical storage systems "Tepidus" is being developed in Sweden. This plant uses a process of heat release during the hydration of sodium sulfide.

For medium-temperature accumulation, as well as as a coolant, salts and their eutectics are used, characterized by a melting point of several hundred degrees and a large latent heat of phase transition.

Hydrates of oxides of alkaline earth metals are very promising for medium temperature accumulation. The use of the processes of accumulation of oxide hydration reactions has a number of advantages. These are a high density of stored energy, simple long-term accumulation at ambient temperature, compactness of a solid energy storage substance, its low cost, and obtaining sufficiently high-potential heat at the hydration stage.

High-temperature accumulation is carried out using reversible exo-endothermic reactions. In this case, the reactions can be divided into two groups: catalytic decomposition reactions, the products of which can not be separated and stored together, and reactions occurring without catalysts, the products of which must be separated at the temperature of the solar receiver in order to prevent a reverse reaction.

The choice of the type of thermodynamic cycle and the nature of the working fluid is determined by the operating temperature range of the heat engine, i.e., the characteristics of the concentration system, accumulator and cycle parameters are closely interconnected. In solar installations with concentration, steam-water cycles are preferred.

Author: Magomedov A.M.

See other articles Section Alternative energy sources.

Read and write useful comments on this article.

<< Back

Latest news of science and technology, new electronics:

Alcohol content of warm beer 07.05.2024

Beer, as one of the most common alcoholic drinks, has its own unique taste, which can change depending on the temperature of consumption. A new study by an international team of scientists has found that beer temperature has a significant impact on the perception of alcoholic taste. The study, led by materials scientist Lei Jiang, found that at different temperatures, ethanol and water molecules form different types of clusters, which affects the perception of alcoholic taste. At low temperatures, more pyramid-like clusters form, which reduces the pungency of the "ethanol" taste and makes the drink taste less alcoholic. On the contrary, as the temperature increases, the clusters become more chain-like, resulting in a more pronounced alcoholic taste. This explains why the taste of some alcoholic drinks, such as baijiu, can change depending on temperature. The data obtained opens up new prospects for beverage manufacturers, ... >>

Major risk factor for gambling addiction 07.05.2024

Computer games are becoming an increasingly popular form of entertainment among teenagers, but the associated risk of gaming addiction remains a significant problem. American scientists conducted a study to determine the main factors contributing to this addiction and offer recommendations for its prevention. Over the course of six years, 385 teenagers were followed to find out what factors may predispose them to gambling addiction. The results showed that 90% of study participants were not at risk of addiction, while 10% became gambling addicts. It turned out that the key factor in the onset of gambling addiction is a low level of prosocial behavior. Teenagers with a low level of prosocial behavior do not show interest in the help and support of others, which can lead to a loss of contact with the real world and a deepening dependence on virtual reality offered by computer games. Based on these results, scientists ... >>

Traffic noise delays the growth of chicks 06.05.2024

The sounds that surround us in modern cities are becoming increasingly piercing. However, few people think about how this noise affects the animal world, especially such delicate creatures as chicks that have not yet hatched from their eggs. Recent research is shedding light on this issue, indicating serious consequences for their development and survival. Scientists have found that exposure of zebra diamondback chicks to traffic noise can cause serious disruption to their development. Experiments have shown that noise pollution can significantly delay their hatching, and those chicks that do emerge face a number of health-promoting problems. The researchers also found that the negative effects of noise pollution extend into the adult birds. Reduced chances of reproduction and decreased fertility indicate the long-term effects that traffic noise has on wildlife. The study results highlight the need ... >>

Random news from the Archive Winkel Board Developer Board 14.12.2016 Mintbox Technologies has launched a fundraising campaign for the release of the Winkel Board, designed for development and prototyping. The upcoming novelty features a high degree of integration and support for the main wireless interfaces that may be required in such projects. The Winkel Board is based on an Atmel Atmega128 microcontroller with 128 KB flash and 4 KB SRAM. The controller is compatible with the Arduino IDE development environment, but unlike the boards of the same name, the new product already has an Espressif ESP8266 wireless module with Wi-Fi 802.11 b/g/n support and an Itead HC-05 module that supports Bluetooth 2.0 with EDR. Atmel and Espressif controllers are connected by UART bus and can execute code independently from each other. There is a Nordic nRF24L01 radio transceiver operating in the ISM band, as well as a DS3231 real time clock. MPU-6050 accelerometer and gyroscope daughterboard can be connected. The Winkel Board has a total of 38 digital and 8 analog input/output connectors; a microUSB port is wired for power and programming. The minimum fee for owning a board with two microcontrollers is $21, the Atmega128 version is priced at $12.

Other interesting news:

▪ robot citizen

▪ Graphene helps get into the brain

▪ ELG-200/240 - powerful LED drivers with wide dimming options

▪ Smart brake light for bicycles

▪ quantum spin liquid

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the site Protection of electrical equipment. Article selection

▪ article by Henri de Toulouse-Lautrec. Famous aphorisms

▪ What was the impetus for the Latin American Wars of Independence? Detailed answer

▪ article Mechanisms of occurrence and development of fires

▪ article Generator ZCH. Encyclopedia of radio electronics and electrical engineering

▪ article Power regulator for electric heaters. Encyclopedia of radio electronics and electrical engineering

Leave your comment on this article:

All languages ​​of this page

Arabic	Hebrew	Polish
Bengali	Hindi	Portuguese
Chinese	Italian	Spanish
English	Japanese	Turkish
French	Korean	Ukrainian
German	Malay	Vietnamese

Home page | Library | Articles | Website map | Site Reviews

www.diagram.com.ua
2000-2024