Renewable energy resources

Humanity inevitably needs energy. We use a huge amount of energy for preparing our food and for other activities of our everyday life. Our relation with the environment is fundamentally determined by producing and making energy available. It can be stated that our most important energy source is the Sun, its energy is utilized by the plants and indirectly the energy of the Sun can be found in fossil fuels. Throughout the history of humankind, human and animal power, biomass, and from the start of the industrial revolution, coal have been the most significant energy sources. Use of energy from hydrocarbons (oil, natural gas) became the most prevalent source of energy during the last century.

The growing population of the Earth and the increasing hunger for energy gradually leads to a point where hydrocarbon resources peter out or their production becomes uneconomic. This is why renewable or alternative energy resources have started to gain increasing focus. Earth’s population exceeded 7 billion by now, and according to forecasts it attains 9 billion by 2050. The current structure of energy production will not be able to provide such a huge population with sufficient amount of energy, a contribution from renewable energy resources is certainly needed. Use of nuclear energy poses a greater risk than renewable energy resources, and nuclear disasters can cause even greater damages than their share in the production. Recent catastrophes (Chernobyl 1986, Fukushima 2011) showed that necessary amounts of energy have to be produced without nuclear power plants.

Currently, 80% of the produced energy is consumed by the developed countries, but only 20% of humanity lives in these countries. Therefore it is absolutely clear that our energy consumption is unsustainable, it is inconceivable that every citizen of the Earth increases the consumption of energy to the level of developed countries.

According to our current knowledge, such an energy demand cannot be satisfied and there is no definite, obvious solution for this problem. The following efforts shall undoubtedly be made:

- improvement in energy saving,
- improvement in energy efficiency,
- improved use of still unexplored or unused energy resources,
- and these above efforts should be made with full consideration of environmental aspects and the least possible damage to the environment.

All the forecasts on energy consumption show an increase in future use, but also prognosticate the increment in the utilization of renewable energy. Different countries have different opportunities, but in broad lines the following renewable energy resources can be taken into consideration:

  • Biomass,
  • Thermal energy,
  • Solar energy,
  • Wind energy,
  • Water energy.

The greatest problem of renewable energy resources is availability, since their availability changes in time (just consider solar energy for example). Therefore the production of these cannot be sustainable without appropriate energy storing systems. The objectives of the EU 2020 strategy determined strict targets.

  • 20% decrease in primary energy consumption by 2020
  • 20% decrease in the emission of greenhouse gases in the EU by 2020
  • 20% of total energy mix must be covered by renewable energy sources by 2020
  • At least 10% use of biofuels must be attained by 2020.

In case of Hungary, EU specified a 13% share of renewables.

Use of renewable energy resources in Hungary by 2020, total: 186.4 PJ

Use of renewables in the production of electricity in 2020:

9470 GWh (79.7 PJ)

Use of renewables in the production of heat energy in 2020:

87.1 PJ

Total energy of biofuels used in 2020:

19.6 PJ

Domestic energy balance

In the recent 20 years primary energy consumption has not been changing significantly: it was around 1100-1150 PJ in average. Figure below shows the distribution of energy consumption in 2008. There is a general trend towards declining coal and oil use, and the share of output of power plants increased from 25% to 35%.

primerenergia2

63% of total domestic consumption is imported; the proportion of domestic production attains only 37%, which shows Hungary’s significant dependence and vulnerability. A predominant proportion of the import arrives as liquefied and gaseous energy resources, the former is used by chemical industry and transportation and traffic, while the latter is used by households and electricity sector. In the distribution of domestic energy production, the production of electricity is the most predominant (Paks Nuclear Power Plant).

Domestic primary energy usage:

hazaiprimerenergiafelh

Classification of energy sources:

Non-renewable:

  • nuclear,
  • coal-type energy resources (peat, lignite, sub-bituminous coal, bituminous coal, anthracite)
  • hydrocarbons (natural gas, crude oil)

Renewable:

  • water,
  • biomass
  • wind and solar energy

Transitional:

  • geothermal energy (10-100 years depending on local conditions)

Renewable energy sources:

Biomass

In the course of photosynthesis plants bind and build in atmospheric carbon, thus transforming the energy of the Sun into chemical energy. The Hungarian flora binds an amount of carbon nearly three times greater than that of production. So the utilization of remaining biomass for energetic purposes would be quite useful. Annually, nearly 10 million tons of organic by-products could be used and 60-70 MJ of energy could be produced this way. Main types of utilization could be burning, pyrolytic gasification, biogas (methane fermentation), plant oil (biodiesel) and production of alcohol. From environmental protection aspects, the most purposeful utilization in Hungary would be the methane fermentation, because this way useful biofertilizer by-product would be produced beside biogas that could substitute chemical fertilizers in soil remediative treatments.

Biomass types for combustion (burning) purposes

Biomass source for combustion can be of quite various origin: herbaceous (energy grass, energy reed, grain straw, corn stalk, husks, mowed roadside grass residues, litter, etc.) and woody (treebark, forest residues, loppings) biomass as well. The energy content and density of these is very different of course, therefore each type has different setbacks and advantages.

One of the ways of plant production for energy purposes is the use of cultivated plats since their production technology is already elaborated, and these can be produced in a reliable way with a nearly constant yield. However, plant production for energy purposes often clashes with food production; therefore it must not be disregarded that we must produce food on the areas of good conditions and only the remaining, unused lands should be used for energy production purposes.

Grain straw

From the aspect of energy production, it is not the one of the best combustion material, but its accessibility and quantity makes it appropriate for use. Due to the declining animal stocks it is available in large quantities and the technology for mechanical collection (baling) is widely available. It can be transported easily and it is considered an economical solution within reasonable limitations.

szalma

Corn stalk

Approximately 15 million tons per year of corn stalk is produced in Hungary, which provides a good potential for energy production. Its setback is its late collection which means increased humidity that decreases below the 20% utilization threshold only in a few months.

kukoricaszár

Oil plant cakes

Oil plant cakes are by-products of pressing of oil plants, and they make one of the best biomass materials for energy production. Their low dry-matter and high oil content, and high energy density make them very appropriate for use. In the past, they had been used as animal feed, but declining animal stocks rendered their use for energy production a viable option. Their mostly known forms are pellets and meals, the first of which can be used in a technologically easier way.

Vine, loppings

Considering their characteristics, they are extremely good energy resources, but they are produced in smaller amounts in smaller areas, therefore their utilization can be economical only if used locally. Due to its high calorific value, it can be combusted profitably in specific equipment.

venyige

Energy grass ( Agropyron elongatum ), energy reed ( Miscanthus ), energy hemp

The great yield (10-20 t/ha) and low agrotechnical needs make it a viable choice for energy production. Pellets are produced from the harvested plants to be combusted in special furnaces. Industrial level usage is not yet elaborated, but it can be combusted in smaller, local facilities. Energy reed does not produce seeds in Europe; therefore its propagation makes the production expensive. Similarly to energy grass it has a high yield (20-40 t/ha) and recommended to be used in the form of pellets. Energy hemp can be produced on all types of soils except extremely saline soils, its plant protection requirements are low due to its good weed-suppressing ability, and can be used in the form of pellets as well.

Forest byproducts

In Hungary, approximately 6 million m3 of wood is produced every year. Byproducts can be used extremely well due to their high calorific values. Every year, nearly 1 million m3 byproducts are produced (twigs, boughs, bark and other tree residuals that cannot be used for industrial purposes), however, their collection is quite difficult and expensive which makes their collection unprofitable. As a by-product of sawmilling industry, half a million tons of sawdust is produced annually that can be used locally in an economical way.

Biomass from energy plantations

In Hungary, plantations of at least 3000m2 area are considered energy plantations. Their production cycle can be very short (max. 5 years); short (max. 15 years and long (20-25 years). The most important woody energy plants are: poplar, black locust and different kinds of willow. Main energetic characteristics of the most important solid types of biomass suitable for combustion are listed in the table below:

Name

Yield (t/ha)

Calorific value (MJ/kg)

Gross energy content (MJ/ha)

Tonne of oil equivalent (toe/ha)

Wheat

3-5.2

15.32-17.57

45960-92360

1.097-2.205

Rye

1.5-2.7

14.96-17.43

22440-47060

0.535-1.124

Corn

3.5-7.6

16.5-17.87

57750-135810

1.379-3.243

Cornstalk

5.2-11.4

16-17.5

83200-199500

1.987-4.764

Corn cob

-

16.16-17.4

-

-

Grain straw

1.5-3.5

15-16.77

22500-58690

0.537-1.401

Rape straw

2.5-5.8

13-15

32500-87000

0.776-2.077

Rape cake

0.6-1.3

19.57-21.5

11740-27950

0.280-0.667

Sunflower stalk

1.9-3.5

15.2-17.45

28880-61070

0.689-1.458

Sunflower cake

1.1-1.5

16.6-23.75

18260-35620

0.436-0.850

Grape vines

1.0-2.0

15.23-17.23

15230-34460

0.363-0.823

Orchard loppings

1.0-2.0

8.4-14.7

8400-29400

0.200-0.702

Energy grass

10.0-15.0

14.78-16.84

147800-252600

3.530-6.033

Energy reed

20-25

14.67-16.8

293400-420000

7.007-10.03

Energy hemp

12.1-15.0

16.03-17.25

193960-258750

4.632-6.180

Sweet sorghum

20.0-26.2

14.73-16.28

294600-426530

7.036-10.187

Black locust

8.0-23

16.325-18.411

130600-423450

3.119-10.113

Oak

11.0-20.0

9.046-18.075

99500-361500

2.376-8.634

Beech

11.0-20.0

10.530-18.156

115830-363120

2.766-8.672

Poplar

15.0-21

11.778-18.472

176670-387910

4.219-9.265

Birch

11.0-20.0

12.933-18.917

142260-378340

3.397-9.036

Pine

11.0-20.0

14.226-18.659

156480-373180

3.737-8.913

Willow

15-25

14.34-17.98

215100-449500

5.137-10.736

Forest loppings

8.0-9.0

11.6-16.7

92800-150300

2.216-3.589

Logging residue

1.5-2

11.3-14.6

16950-29200

0.404-0.697

Sawdust

-

12.4-17.2

-

-

Wood chips

-

11.8-17.8

-

-

 

Biogas systems

Biogas systems produce biogas by fermenting different kinds of organic materials and on one hand utilizes the energy of the produced gas and on the other hand the remaining biofertilizer is reused in soil cultivation. Biogas systems have advantages in numerous areas. They help in the neutralizing of biological wastes and during they anaerobic way of operation the environmental load presented by waste materials is decreased, and they also facilitate carbon neutral energy production. All the used materials remain in the closed cycle of complex biogas systems, only the energy is delivered. In Hungary, organic waste from animal husbandry can be used for energy production purposes in the greatest quantity. This means mainly manure, primarily pig slurry. Currently, slurry management is still considered as an activity resulting in heavy pollution, but this load could be decreased by operating biogas systems while also producing energy.

The organic part of municipal waste can also be used for biogas production. A significant, 30-40% of municipal waste is organic material, however, a larger proportion of this is not utilized, but stored in expensively maintained waste deposits or becomes incinerated. Organic wastes placed in waste deposits not only decrease the storage capacity of the waste disposal site, but as a consequence of precipitation and rainfall, harmful materials can leak into the soil and can pollute groundwater. Besides, sludge of high organic material content remaining from municipal sewage can also be considered as a significant waste source, it’s handling still unresolved. The same applies to the wastes of animal origin from slaughterhouses. These, beside considered as hazardous waste materials, pose a significant animal health risk.

biogázmukodes

Biogas production

Biogas is produced from the organic materials of biological origin mentioned above at an appropriate temperature, by fermentation with the help of different kinds of bacteria. Energy content of the produced gas is 70% that of natural gas, approximately 18-23 MJ/m3. Depending on composition and pollutants, 50-75% of biogas is methane, 50-25% carbon-dioxide. In Hungary, nearly 30 million tons of organic waste is produced every year. From this, approximately 2 billion m3 biogas can be produced annually. Biogas can only be produced in the reactors if the conditions below are simultaneously met:

  • anaerobic storage ;
  • constant high temperature;
  • presence of appropriate bacteria.

In the course of biogas production, organic materials are decomposed into simpler molecules, eventually to methane and carbon dioxide. Biogas is produced from the organic material in 25 days at 35°C, and in 15 days at 56°C. Appropriate setting of these systems is a difficult task, bigger systems may require as much as 3 months until the system operates at a maximum efficiency producing appropriate amounts of gas.

Biogas utilisation

Biogas is a renewable energy resource that can be used in multiple ways. It is possible to produce electric and heat energy. By producing electric energy, biogas is used primarily to drive gas motors driving an electricity generator. Gas motors produce mechanical energy which is transformed to electric energy in a generator. Generators generate an alternate current of 50 Hz and 500 V, which is transformed and supplied into the public mains. By producing electricity, the efficiency of the process is around 30-40%, the rest of energy is heat. A further utilisation of this heat energy, it is possible to utilize as much as 90% of total energy produced. By burning (combusting) biogas, heat can be produced directly as well, however this can be economic only when used locally (heating the site, central heating). During indirect utilisation, biogas is transported to the users in a pipeline. Prior to direct utilisation, the gas must be purified and smelled; afterwards it can be supplied into the public mains or used as a fuel for vehicles using gas.

Remaining materials of biogas production can be utilised for soil improvement measures as a replacement of chemical fertilizers. Operation of the system is not economic in every case due to the high initial investments, but on sites where appropriate amounts of organic waste is produced, a system like that can turn profitable in a short period of time. Considering all the above mentioned factors, utilisation of organic wastes as a resource for biogas production has economic, environmental, waste management and renewable energy production benefits.

Geothermal energy

Geothermal energy is stored in Earth’s high temperature masses. According to the law of thermal conductivity, energy per unit of mass is greater in lower depths. In the course of exploiting thermal energy, it must be considered that energy storing masses should be nearest to the surface. Therefore geothermal energy can be produced in those areas where these conditions are met, and where geothermal energy is of great relative energy content, cheap and can be utilised in great amounts, available and can be handled well. Considering these assumptions, water meets the conditions best from an economic aspect. Industrial geothermal heat stock stored in the rock layers of Hungary is around 8.55×1019 kJ, available energy produced is around 4.085×10 17 kJ of which 30-40% can be utilised.

Exploitation of thermal energy, i.e. surfacing Earth’s core energy, shows a relationship with the production of fossil energy resources considering the methods and necessary tools and equipment. Main conductor of thermal energy is water; therefore the most abundant current of energy can be surfaced by utilizing its physical characteristics. Water or steam of appropriate temperature can be surfaced by drilling wells and the expansion of water or steam. Formerly the water of high saline content was directed into nearby natural water currents causing significant environmental damage. The yield of wells decreased continuously and the temperature of the water also decreased, so the cooled water was injected back to the wells in order to maintain constant production of appropriate amount of energy. This could only be done by coping with a number of technological problems, pressure differences emerging in the system, turbulent streams and two-phase mixed streams. In the course of reinjection, changes have to be considered both in the medium and the energy distribution in the medium. Therefore energy production with reinjection requires appropriate prudence, careful planning and knowledge of quantitative and qualitative context of partial processes.

Energetic utilisation of thermal waters

Utilization of thermal water consists of two large sectors: production of electricity (energy produced using heat) and direct use (utilisation without transformation). When electricity is to be produced from thermal water, then the thermal water must be cooled and the energy produced using this temperature difference can be transformed into electricity. Unfortunately, this process can be characterized with a very low efficiency. Production of electric energy production can only be profitable where geological and thermal conditions are appropriate for this task. In Hungary, there are suitable areas, mainly the Southern areas of the Great Hungarian Plain where thermal waters of 100-200°C are available. In Hungary, it must also be considered that reinjection results in significant costs, therefore without the reutilisation of the resulting low temperature water, this way of energy production cannot be profitable. It might be reasonable to use linked electric and heat production. When purely electricity is produced, efficiency remains as low as 10%, but if heat energy is further utilized, efficiency can approach 100%.

For the purpose of direct utilisation, cooler waters, with temperature of less than 100°C can be considered. Use of natural gas can be replaced by direct utilisation; thermal water can be used to produce warm water that can be used to heat residential and industrial buildings. In Hungary, the industrial use of thermal water began in the 1920’s, Hungary becoming one of the leading countries in thermal water utilisation for the 1960’s. The most important sectors utilising thermal energy are horticulture, animal husbandry and central heating. Unfortunately, the legal aspects of thermal water utilisation are still not appropriately settled in Hungary, and only 1% of domestic energy production comes from this energy resource.

Heat pump systems

22% of world’s thermal energy utilisation is made with thermal pump systems. These systems utilise energy with an extremely high efficiency. Therefore, significant improvements and development have been carried out in Hungary during the recent decades. Waters of 60-90°C temperature are the most suitable for heat pump application. For industrial purposes, mainly waters of low temperature resulting from electricity production can be considered, while in public use, heating of buildings can be the most reasonable application. As for the efficiency of these systems: there are great variations, but obviously these systems can be profitably applied in areas where significant temperature differences are present and different media have good heat conductivity.

Heat pump systems are basically quite simple systems, their structure does not differ significantly form industrial or household refrigerators. During their operation, refrigerators draw heat and through a heat exchanger, heat energy is transferred to the environment. The principle is quite similar, but heat pumps draw heat from the environment and this energy will be transferred to the medium to be heated. More up-to-date equipments can be set to reverse operation and work as air-conditioners in summer.

As a heat source, a so-called geothermic probe is used. It is a probe bored to 100m depth, this layer keeps a 10-15°C temperature all year round, independently from the change of seasons. This media of constant temperature is the source of heat. In winter, when the system is used for heating, heat pump delivers the heat from the deep towards the buildings, and in summer, when it is used for cooling, the heat is transported from the buildings into the probe. The circulated medium transfers the heat through a dual heat exchanger. Formerly freon was used as a conveyor medium, but due to its ozone damaging effects; currently environment friendly, non-polluting gases are used. Under appropriate circumstances, current up-to-date equipment are able to produce 4-5kW heating energy from the 1kW electric energy used.

Since the decrease of CO2-emission became a significant factor in industrial energy usage, a growing interest can be observed towards the utilisation of geothermal energy, because it is relatively cheap and most importantly, is associated with low levels of air pollution. In Hungary geothermal heat sources are primarily utilised by agriculture, therefore mainly such modes of utilisation must be found which satisfy the needs of agriculture, such as cooling and drying. A significant variation can be observed in the utilisation of heat pump systems: most important periods are the winter heating season and the summer cooling period. With appropriate planning and careful design, the unutilized capacities can be exploited, and the energy source can be linked to energy production systems.

Utilisation of solar energy

The most important energy source of Earth is the Sun. The surface of the Earth receives energy many times the needs of the entire global energy consumption, 1353 W/m2 on average. The radiation reaching the surface consists of two parts: direct and scattered radiation. The extent of actually utilisable solar radiation is affected by geographical location, seasons, parts of the day and a number of other meteorological factors, so the actually utilisable energy maximum is around 1000 W/m2. Of course, only a small part of this amount can be utilised in reality.

The most important limiting factor of utilising solar energy is the number of hours of sunlight and the angle of incidence of solar radiation. The latter can be greatly influenced by physical placement, but the intensity varies greatly during the year. Energy utilisation is of higher level in the summer than in winter and in the transitional months. Solar radiation can be utilised in many ways. Active utilisation of solar energy can be realized with photothermal (simply thermal solar radiation collector) or photovoltaic (solar cell, often abbreviated as PV) methods.

Passive utilisation of solar radiation can be realized with the design and orientation of buildings.

Thermal utilisation

In the course of photothermal utilisation, solar radiation is transformed into heat with the help of some energy receiving medium (collector). It is used mainly for producing warm water, but other technological purposes can also be considered, like heating of buildings, swimming pools, greenhouses etc. A very important element of the thermal collectors is the storage medium, since solar energy is usually not available when required. Very good thermal insulation is a primary requirement of heat storages which result in low heat loss, and they must also be easily fulfilled and emptied.

napkollektor

Photovoltaic utilisation

In the course of photovoltaic utilisation, solar radiation is transformed directly into electricity. This kind of equipment (solar cells) produces direct current in general, which can be converted into alternating current directly or with the help of inverters. The produced energy can be supplied into the public mains, or stored in chemical or other types (e.g. hydrological) of energy storages. The most important applications of photovoltaic system can be as follows:

  • Facilities located far away from public mains,
  • Farms, buildings, stables,
  • Electric supply of storage facilities (lightning, ventilation, security, etc.);
  • Irrigation, water pumping (inland drainage),
  • Water supply of animal husbandry farms;
  • Electric supply of telecommunication devices,
  • Energy source of equipment of public needs.

napelem

Several ways can be applied for the storage of electricity. A differentiation has to be made between the stand-alone (not linked to public mains) and systems connected to the electricity network. In systems connected to the electricity network it is reasonable to supply the energy to the network and get it back if needed. The disadvantage of this is that it requires a two-way electricity meter and the permission of the power supplier. During stand-alone operation, produced energy must be kept in storages. This is possible by storing the energy as chemical energy (accumulators, hydrogen production) or physical storage (hydrological, flywheels, etc.)

Passive utilisation of solar energy

Passive utilisation of solar energy can be put forward primarily in construction solutions. With appropriate orientation and shading, solar energy can heat the buildings in winter, and does not significantly warms them up in summer. A basic aspect of design is that in residential buildings, rooms with the greatest heating requirement should be oriented towards S-SE-E direction due to the light the energy that can be gained from solar radiation. Simultaneously, rooms of lower heating requirement are designed to insulate, protect rooms with greater heating requirement. Slanted glass surfaces greatly enhance the insolation of buildings. Passzívházakról bővebben.

Utilisation of wind energy

Wind is one of the longest used renewable energy source. Recently its utilisation – besides producing mechanical energy – facilitates the production of electricity. Despite a number of technical improvements, wind turbines with horizontal axis have been spread widely. The reason for this is the significant surplus in electricity production compared to other technical solutions.

Efficiency of wind turbines is greatly affected by meteorological condition, location of deployment and the relative location of wind turbines to each other. Based on geographical location, basically sea (offshore) and inland wind turbines can be differentiated. From the aspect of energy production, a wind turbine can be stand-alone, or linked to the mains. Also wind turbine parks, as complex energy producing units can be differentiated. Dynamic improvements can be observed in all fields of related technologies, from new constructional aerodynamic solutions to computer software development. Currently, world’s wind turbine capacity is around 160000 MW. New blade profiles, greater generators with higher efficiency, higher towers, new material structure solutions, lighter constructions, more efficient and reliable control solutions characterize the modern wind turbines these days.

How is wind caused?

Basically, because the level of solar radiation absorbed by the surfaces at the Equator is greater than that around the poles, in a simplified approach, air masses flow from the poles towards the Equator. This is modified by the rotation of the Earth which results in many vortexes both at the Northern and Southern hemispheres. In Eastern wind belts the atmosphere gains impulse momentum, and in the Western wind belts the atmosphere delivers impulse momentum.

Energy production

The more energy is utilised by a wind turbine, the more it decreases the mechanical energy of the wind. If all the energy were utilised, windspeed would drop to zero behind the wind turbine, therefore air mass should be immensely condensed. If the air masses could pass without any braking effect, energy would not be produced. It can be deducted from the statements made above, that there should be an optimal point of energy exploitation somewhere between the two extremes. An ideal wind turbine decreases windspeed by 2/3, so it utilizes 2/3 of all available energy. To be very precise, Betz’s law states that no turbine can capture more than 16/27 (59.3%) of the kinetic energy in wind.

szél

Energy storage

Utilisation of renewable energy sources cannot be separated from the need to (transitionally, or for a longer period) store and transport energy. Alternative energy sources have several disadvantages compared their fossil counterparts. They possess a way lesser energy density, poorer availability, transportability and in many cases they can be utilised only in certain periods, their energy production often being not reliable. Therefore it is necessary to store produced energy. Some types of energy storages used in practice

  • mechanical accumulators;
  • heat accumulators;
  • electric and electromagnetic energy storages;
  • electrochemical accumulators, fuels, energy resources.

Mechanical accumulators

Mechanical accumulators store produced energy basically in potential or kinetic energy. Potential energy can be stored in the gravitational space of the Earth or a flexible deformation of a solid body. Kinetic energy is mostly stored as the rotational energy of a flywheel. In a larger scale, mechanical energy storage is realized by pumped storage power plants. This kind of power plant consists of two storages with great difference in their elevation. In the empty period, water i pumped upwards, to the upper storage, while in case of energy need, the change in the potential energy of the water is used: the water flows downwards and drives a generator, producing electricity.

Heat accumulators

Heat accumulators accumulate energy by heat intake. Two types of heat accumulators can be distinguished. In the first type, temperature increases in the course of heat intake, and in the second type, the heat taken in causes some kind of state change (mostly melting). In the case of the first type, stored specific energy is defined by the heat capacity of the storage medium and the affordable change in temperature, while in the second case, stored specific energy is defined by the latent heat of the state change. Type, structure and cost of heat accumulators depend primarily on the desired duration of storage. In heat accumulators, heat must be stored at the highest possible temperature, possibly near to the temperature of the heat source the energy of which is desired to be stored.

Electric and electromagnetic storages

Electric energy can also be stored in condensers (capacitors). Theoretically, condensers with infinite resistance keep 100% of the electric energy, however, in reality these are of low capacity, and they also slowly lose their energy in time. To resolve this problem, supercapacitors have been developed that are able to store huge energies with very low losses compared to their conventional counterparts. Also an advantage of theirs that they are able to take and deliver the energy very quickly. On of the most important areas of application is the electric car, where supercapacitors are used for quick energy storage and delivery secondary energy storage. This way the conventional accumulator can be protected from the impulse-like energy demands which result in increased lifetime of the accumulator.

Electrochemical accumulators

Electrochemical accumulators (everyday accumulators, batteries) belong to the group of chemical energy storages which store, gain or deliver electricity as a direct consequence of a chemical reaction. The accumulator consists of electrodes separated by liquid, gel, sometimes solid state electrolytes. Electrodes make up the two electric outputs of the accumulator. The materials of the electrolyte and the electrodes are able to produce chemical reactions associated with the change of electric charges. In the course of charge and discharge, the active substance of the cells becomes transformed in a chemical reaction, without the addition of any external material, delivers energy and is rebuilt later.

Fuels

Artificial fuels are such materials that are able to produce energy when entering into a reaction with each other, or other materials usually inorganic materials found in the environment (air, water, carbonic acid). In the majority of cases, these reactions can be renewed, i.e. by necessary energy input the state of the materials can turn back to the original state. Among artificial fuels, hydrogen seems to be the most ideal, as it can be produced by hydrolysis and does not produce pollutants during its use. Hydrogen is the most suitable material to replace fossil fuels like gasoline, oil, natural gas, carbon. The disadvantage of hydrogen is that it can be liquefied in a difficult way; the process requires a very low temperature of -252ºC. Liquefying hydrogen requires great energy input and an expensive and complicated cryostat is needed to keep hydrogen in liquefied form. Therefore, from the aspect of energy storage, local use must be the primary goal. Further disadvantages of hydrogen include dangers of leakage and explosion, therefore equipment used for transport, store and utilisation must be equipped with high level control and safety tools.

References

Bohoczky F.: 2000. Megújuló energiaforrások terjedése Magyarországon, Energiagazdálkodás, 41. évf., 12. sz., 13-15. o.

Boyle G. 1996. Renewable energy. Power for a suitainable future. Oxford University Press. Oxford. ISBN 0-19-856452-X.

Büki G.: 1997. Energetika. Egyetemi Tankönyv, Műegyetemi Kiadó, Bp.

Farkas I. /szerk./: 2003. Napenergia a mezőgazdaságban, Mezőgazda Kiadó, Budapest,

Horváth G. – Tóth L. (2001):A szélenergia hasznosítása. Magyar Tudomány. MTA Folyóirata Budapest, 11.sz.1300-1306.p.

Pecznik Pál szerk.: Megújuló energiaforrások. Mezőgazdasági vállalkozók tanácsadó füzete MGBSZ Gödöllő 2003

Szűcs M.: Passzív napenergia-hasznosítás a mezőgazdasági építészetben, Napenergia a mezőgazdaságban /szerk. Farkas I./, Mezőgazda Kiadó, Budapest, 2003, 207-240. o.

Tóth L. – Horváth G. – Schrempf N. (2004): Energetikai széltérkép készítésének metodikája; MTA AMB, K+F Tanácskozás Nr. 28 Gödöllő, 4. kötet 246-250. p

Tóth L.-Horváth G.: 2003.Alternatív energia. Szélmotorok, szélgenerátorok, Szaktudás Kiadó Ház, Budapest.

Tóth László, Schremp Norbert (2011): Energiaellátás, megújuló energiaforrások hasznosítása. Jegyzet SZIE, Gödöllő.

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Sajtóközlemény

A projekt célja magyar és angol nyelvű digitális tananyagok fejlesztése a Budapesti Corvinus Egyetem Kertészettudományi Karának hét tanszékén. Az összesen 14 tananyag (hét magyar, hét angol) a kertészmérnök Msc szak és a multiple degree képzés keretében kerül felhasználásra. A digitális tartalmak az Egyetem e-learning keretrendszerével kompatibilis formában készülnek el.

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Sikeres pályázat

A projekt célja magyar és angol nyelvű digitális tananyagok fejlesztése a Budapesti Corvinus Egyetem Kertészettudományi Karának hét tanszékén. Az összesen 14 tananyag (hét magyar, hét angol) a kertészmérnök Msc szak és a multiple degree képzés keretében kerül felhasználásra. A digitális tartalmak az Egyetem e-learning keretrendszerével kompatibilis formában készülnek el.

A tananyagok az Új Széchenyi Terv Társadalmi Megújulás Operatív Program támogatásával készülnek.

TÁMOP-4.1.2.A/1-11/1-2011-0028

Félidő

A pályázat felidejére elkészültek a lektorált tananyagok, amelyek feltöltése folyamatban van. 

 

uszt logoTÁMOP-4.1.2.A/1-11/1-2011-0028

Utolsó frissítés: 2014 11. 13.