Sineglazov Viktor Mykhailovych
Head of the Department of aviation computer integrated technologies
National Aviation University
Doctor of technical Sciences, professor, laureate of the State prize of Ukraine, Honored scientist and technician of Ukraine
Renewable energy is the energy generated by a resource that quickly fills up (restores) as a result of a natural process that is not interrupted.
From an economic point of view, renewable energy sources can be considered as an effective means of stimulating innovation and business activity in national economies, creating additional jobs, and creating significant new sources of revenue from the import of equipment.
UN experts suggested the following RES classification:
- solar and wind energy;
- energy from the use of peat, biomass, including waste from the agricultural, forestal, industrial and municipal sectors;
- energy of incoming water, including hydroelectric power stations, with capacity less than 1 MW;
- geothermal energy;
- wave energy, including the energy of currents, ebbs and floats, as well as the energy of the temperature fluctuations of the ocean;
- energy of the residual heat of the earth (low potential energy).
One of the key vectors of sustainable development of high-tech countries was the choice of clean energy future, which includes :
- application of innovative principles of the development of renewable energy, which promotes its effective use, will give an additional impetus to environmental protection, provide reliable energy supply and increase the competitiveness of the economy;
- energy saving for the benefit of an environmentally clean future, given that fossil fuels will be demanded by the world's energy for a long time, will give priority to those innovative technologies that will be aimed at reducing its harmful effects on the environment;
- stimulation of research and development aimed at the introduction of environmentally friendly energy;
- creation of sources of financing RES by means of improvement of market instruments, including tax;
- mitigating the effects of climate change by developing the necessary measures for the development of clean energy technologies markets, and increasing their accessibility for developing countries.
According to the forecast of the International Energy Agency  (IEA), by 2025 the world's electricity consumption will reach 26 trillion kWh, while the installed power of power plants will reach 5500 GW, by 2035 - 32 trillion. kW / h, the installed capacity of the power plants will reach 5900 GW. The leading role (about 44%) in the achievement of the declared parameters is given by the front-runners of the leading states, as traditional methods of electricity generation, having limited initial resources, cause certain damage to the environment .
In 2014, according to the annual UNEP investment survey , global RES investments reached 290 billion euros, and in 2015 this figure exceeded 329 billion US dollars .
The availability of technological innovations has led to the introduction of improved production and consumption products with low RES costs. In conditions of sufficient wind and solar potential and not always predictable oil prices, as well as expensive infrastructure for their application, RES are beginning to successfully compete with traditional energy.
During the last five years of the development of innovative technologies in the RES sector, the cost of generation has decreased by almost twice (Table 1).
Table 1 Comparison of average generation costs for different types of RES in the EU in 2010, US $ / tons of oil equivalent (TOE)
Thus, an increase in the production of RES and their share in energy balances contributes to increasing the efficiency of economic activity in the different volume of energy consumers and strengthening confidence within the country - between the state, business and civil society.
The world community has chosen the path to the new power industry RES, acknowledged that there is no alternative to its innovative development; the projected global spending on RES by the year 2030 will amount to 7 trillion dollars .
The policy of a non-alternative innovative choice of RES in the world's energy sector provided the introduction of a total capacity of 500 GW of RES, which was one and a half times the power of all nuclear power plants in the world. By 2020, the power generation capacity of renewable sources to be introduced will be 700 GW. It is proved that the increase of production of RES and their share in energy balances contributes to increasing the efficiency of economic activity in different energy volumes and confidence-building among countries that have included RES in the list of strategic priorities of their development.
Autonomous renewable energy systems are not reliable due to unsteady availability and changes in climatic conditions. In recent years, systems with renewable energy sources, such as autonomous solar photovoltaic systems, have been propagated worldwide on a relatively large scale. These autonomous systems can not provide a continuous energy source because they are seasonal in nature, the photovoltaic power system can not provide reliable power on non-sunny days, the autonomous wind system can not meet the requirements of constant load due to significant fluctuations in the velocity of the wind from an hour to an hour during the year. Obviously, the combination of two or more renewable energy sources is more effective than a single-source system in terms of price, efficiency, and reliability. Such a system is called the Hybrid Renewable Energy System (HRES) and becomes an element of the fastest-growing market in the world.
As a result, the use of wind and solar photovoltaic energy generation becomes a reality. However, other renewable energy (RE) sources / alternative energy (AE), generation technologies such as ocean waves and floats, osmotic, geothermal, fuel cells (FCs) and microturbines (MTs) can not be left with no attention.
In general, hybrid systems will convert all the received energy into one kind, usually electric and / or accumulate energy in some form (chemical, compressed air, thermal, mechanical flywheel, etc.) and the aggregated output is used to feed a variety of loads.
Hybridization leads to increased reliability of the RES system, but it provides optimal choice of sources of energy and technologies for their selection, which will determine the methodology of designing such systems for improving performance, dispatching solution and management tasks. Different generation sources can contribute to one another in achieving higher energy efficiency and / or improve performance.
The accumulative element is a component of the hybrid RE and AE of the energy generation system. High-capacity energy storage technologies such as a pumping hydroelectric power station, storage of compressed air energy and hydrogen storage generally have no response time and are used for long-term energy storage / slow load variation control. On the other hand, high-speed storage devices such as batteries, flywheels, supercapacitors, and superconducting magnetic energy storage (SMES) are used to respond to short temporary obstacles such as fast transient processes during loading and to accelerate loading. A brief overview of different energy generation technologies of RE / AE and various energy storage schemes that can be used in hybrid systems is given in Table 2.
Table 2 A brief overview of different RE / AE energy generation technologies and various energy storage schemes
Any combination of RE / AE energy generation technologies for proper storage and, possibly, in combination with traditional generation technology, such as a diesel generator, may form a hybrid power system. For example, a hybrid system can have any combination of systems: wind power, photovoltaic solar panels, micro-hydro, micro turbines, conventional diesel generator, battery and hydrogen storage based on electrolysis, in a network or autonomous configuration.
The outputs of different sources of generation of the hybrid power system should be coordinated and monitored to obtain the maximum amount of energy.
In order to maximize the efficiency of the whole system, while simultaneously contributing to the maximum reduction of emissions to the environment while minimizing energy production costs, it is necessary to use methods of multicriteria optimization and control to determine the structure of the system and the optimal distribution of the received energy from different sources.
The sources of RE / AE have different performance characteristics; therefore, it is important to have a clearly defined and standardized structure / procedure for their connection in order to create a hybrid system or, more broadly, a microgrid where a local cluster of sources of distributed energy sources, energy storage and loads are integrated together and capable of autonomous operation. The robust microgrid should also have the ability to implement and enable the "plug and play" technology, according to which the device (DG, energy storage or controlled load) can be added to the existing system (microgrid) without requiring reconfiguration of the system to perform its developed function, namely: generating power, providing energy or controlling the load.
In order to choose the optimal configuration of the hybrid system that meets the load requirement, the assessment should be based on the reliability criteria of the power supply and the cost of the life cycle system.
Hybrid systems may also include heat sources (biogas units, solar thermal collectors) and sources of organic fuels (diesel generators) that serve as a backup power supply. Technological configurations can be classified according to the type of voltage in the network: constant, alternating current or mixed lines.
In the hybrid DC system, all components of the electricity generation are connected to the DC lines from which the batteries are charged. Batteries must have protection (controller) from recharging and full discharge. The voltage from the alternating current sources (wind turbine, diesel generator) will be converted into constant using converters. The voltage which is produced according to demand is applied to the DC load. AC loads are fed through the inverter.
In hybrid AC systems, the main voltage sources can be connected directly to the AC line or through additional converters to provide the necessary characteristics of the AC (actual in the case of connection of the system with a centralized power supply system). In both cases, the bi-directional inverter controls the supply of energy for charging batteries as well as from accumulators to AC loads. Direct current can be supplied with battery voltage.
Based on the peculiarities of work, hybrid systems are classified as serial, changeover and parallel.
In serial systems, the batteries are charged from the solar photovoltaic module (in the presented configuration) or from the diesel generator of direct current (if there is no solar radiation). From the batteries using the inverter, the AC load is fed. The system can be operated manually or automatically in the presence of battery charging sensors and a diesel generator controller. The consistent configuration of the system has a relatively simple scheme and is currently widely used.
There are a few deficiencies such as frequent recharging of the battery, which leads to a shorter lifetime, the need for high-capacity batteries (to reduce the depth of discharge). Failure of the inverter results in the complete disconnection of consumers from the network.
In switched hybrid systems, alternating voltage can be supplied to consumers through an inverter from batteries, renewable sources, or alternators. Charging of batteries is carried out from renewable sources or from a diesel generator (through rectifier). When operating in automatic mode, controllers create the necessary configuration of the system, which ensures uninterrupted power supply for consumers and the required level of battery charge.
Compared to the serial, changeover hybrid system has more reliability in power supply, but, of course, it also has more complexity.
In the parallel configuration of the hybrid system there is the possibility of supplying the energy to consumers independently of each source entering the system (for small and medium loads), as well as at the same time from all - at peak loads. In the latter case, it is necessary to synchronize the voltage form at the output of the inverter and alternator. A bi-directional inverter ensures the charging of batteries from the alternator and the conversion of direct current from solar panels and accumulators to alternating current. It should be noted that efficient operation of the parallel hybrid system requires a complex control system. However, based on the increased capabilities of reliable power supply, the latter configuration has the prospect of practical application, especially when several types of renewable energy are connected to the system.
On the basis of the above, one can note the following features of the hybrid systems that make them highly efficient and competitive:
- flexibility of choice of fuel, reliability (use of excess technologies and / or energy storage), efficiency, reduction of harmful emissions;
- the possibility of including thermal, high-power and highly effective devices (fuel cells, modern materials, cooling systems, etc.) in their composition;
- the possibility to simultaneously improve the quality and availability of electricity;
- the ability to include the maximum amount of renewable energy sources depending on the location;
- ensuring a significantly lower level of harmful emissions in comparison with traditional technologies that use mineral resources;
- achieving desirable characteristics at the lowest acceptable cost, which is the key to market acceptance.
The block diagram of a typical hybrid power system with an open contour based on the use of wind and sun energy is shown in Fig. 1
Fig. 1 Block diagram of a typical hybrid power based on the use of wind and sun energy
This hybrid power system consists of solar and wind power plants. The power generated by the wind power plants is an alternating current, but has a variable amplitude and frequency, which can then be converted into a direct current to charge the battery. The controller protects the battery from excessive charge or deep discharge. Since high voltage can be used to reduce system losses, the inverter is usually used to convert low voltage DC to AC 220 V, with a frequency of 50 Hz.
The controller provides the following functions:
- maximizing the value of electric energy produced by electric panels or wind turbine by determining and monitoring the position of the operating point corresponding to the maximum energy (MPPT task);
- accumulation of electric energy in storage batteries to ensure continuous and uninterrupted operation;
- managing the processes of charge and discharge of batteries;
- protection of the wind turbine from excess speed, connecting the fictitious load on its output;
- initiating the operation of a diesel generator or connecting the system to an power network (if there is any) when renewable energy sources can not provide sufficient electricity;
- ensuring the accumulation and preservation of information on local solar radiation: high, low and average daily solar radiation, calculated over one year.
The block diagram of a typical hybrid power system based on the use of solar and hydro energy sources is shown in Fig. 2
Fig. 2 Block diagram of a typical hybrid power system based on the use of solar and hydro energy sources
As a source of hydropower, a small reservoir for the accumulation of water is used. The location of this system depends on the geographical location of the available sources (reservoirs) of water, which are kept at a sufficient height. The power of the system depends on the amount of water and solar radiation.
The block diagram of a typical hybrid power system based on the use of energy from biofuels, solar energy and diesel generator is shown in Fig. 3
Fig. 3 Block diagram of a typical hybrid power system based on the use of energy from biofuels, solar energy and diesel generator
It is assumed that biofuels use waste (dead trees, branches, mowed grass, crop residues, wood chips, bark and shavings from saw mills, etc.).
As previously mentioned, diesel is used in the hybrid system as a backup source during peak load period.
The system uses a hybrid controller that maintains the energy balance during load change, assigns priority among energy sources.
The hybrid controller provides the following functions:
- connecting the power to the consumer from the power source capable of providing the load requirements;
- synchronization of voltage signals from different sources, for example, in case when the instantaneous value of the voltage signal from the source of photovoltaics differs from the value of the signal from another source, say, biofuel, causing a local flow of circulating power.
The block diagram of a typical hybrid power system based on the use of photovoltaic energy, thermal solar energy and electricity is shown in Fig. 4
Fig. 4 Block diagram of a typical hybrid power system based on the use of photovoltaic energy, thermal solar energy and electricity: 1 – hot water; 2 – cold water
Solar heat is one of the cheapest and most practical forms of renewable energy (a source of hot water for the home or commercial use, such as swimming pools, car washes and laundries, simple solar furnaces and cookers are used all over the world, both in commercial kitchens and in living quarters).
The hybrid controller synchronizes various sources, as described earlier.
This system is suitable for places where solar power is available, but other sources such as wind, waves, floats, etc., do not have high energy potential, and other sources of minerals are not economically viable.
Determining the size of the hybrid system RE / AE is an important task. The main approach to solving the problem of determining the size of components of a hybrid system is to minimize the value of a system while maintaining its reliability, which is realized as a result of the use of systems of artificial intelligence.
At the National Aviation University under the leadership of the Head of the Department of Aviation Computer Integrated Systems, Honored Scientist of Ukraine, Laureate of the State Prize of Ukraine in the field of science and technology, doctor of sciences, professor, Victor Sineglazov, there has been developed a hybrid power plant, which is located on the roof of the educational building No. 5 (Fig. 5).
Fig. 5. Hybrid power plant “VS-1.1”
The hybrid power plant consists of a wind turbine unit with a combined vertically-axial rotor of the Darye Savonius type, a solar power plant, a system for accumulating energy based on rechargeable batteries and control systems.
The hybrid power plant is completely autonomous, does not require constant control during operation and maintenance. Overall dimensions are 2 meters high and 2.4 meters wingspread. Rotor wind turbine is made of fiberglass and aluminum.
The wind turbine itself is made according to the direct drive rotor-generator scheme, which provides high reliability and simplicity of construction. The combined rotor ensures the operation of the installation on small winds (at a wind speed of 2 m / s).
The graph of the dependence of the capacity of the power plant on the wind speed is shown in Fig. 6
Fig. 6 Graph of the dependence of the capacity of the power plant on the wind speed
At the moment, the power plant fully provides illumination of the educational building No. 5 at the National Aviation University at night.
Taking into account the study of international experience, for intensifying innovation in the field of RES it is necessary to
1. Develop a state program for the intensification of the use of RES in order to reduce carbon dioxide emissions and improve the ecological state. To form a state vision of strategic parameters and characteristics of RES products.
2. Determine the real targets of renewable energy segments, providing optimal value generation of renewable energy and traditional for a certain period for specific regions of Ukraine taking into account the potential of and demand measures of support depending on their expected role in the energy balance of the region.
3. Identify the regions most suitable for optimum economic production of types of renewable energy for creating new jobs and increasing employment, and for the growth of the tax base at all levels.
4. Generate targeted goverment order as a tool to target the domestic producer to management decisions to invest in renewable energy sources to reduce market risks and financial investors and corporations save time and money for their design.
5. Create an interdepartmental structure managing the development of renewable energy at national and regional level, securing its functions of institutional and legislative support of active development of renewable energy by improving existing regulations and developing new ones.
6. Determine hybrid systems based on renewable energy as a promising solution for decentralized power supply in rural and remote sites, and to ensure the accumulation of surplus electricity, removing peak loads during operation of high power seasonal and weather-dependent renewable energy (wind power plants).
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