Most renewable energy technologies are directly or indirectly powered by the sun. Earth’s atmosphere system is balanced so that heat radiation into space as incoming solar radiation resulting in a certain energy level in the Earth’s atmospheric system, which roughly can be described as the Earth’s climate. Hydrosphere (water) absorbs a larger proportion of incoming radiation. Most radiation is absorbed at low latitude in the area around the equator, but the energy dissipates in the form of winds and ocean currents around the planet. Motion of the waves could play an important role in the process of conversion of mechanical energy between the atmosphere and ocean through the load caused by wind. Solar energy is also responsible for the distribution of rainfall, which are exploited hidroenergetskim projects, and for growing plants that are required for the production of biofuels. 
Flow of renewable energy include natural phenomena such as sunlight, wind, waves, geothermal heat, such as International Energy Agency explains: 
“Renewable energy is obtained from natural processes that are constantly updated. In its various forms, is supplied directly from the sun or the heat created deep within the Earth. It also includes electricity and heat supplied from sources such as sunlight, wind, ocean, hydropower, biomass and geothermal energy and biofuels and hydrogen derived from renewable sources. ” 
Each of these sources has unique characteristics that affect how and where they are used.

Plants use photosynthesis for growth and biomass production. Known as biomaterija, biomass can be directly used as fuel or for production of liquid biofuels. Biofuel produced in agriculture, such as biodiezela, ethanol or biogas (often as a byproduct of sugar cane cultivation), energy can be used in the process of combustion in internal combustion engines or boilers. It is customary to burn biofuel that released chemical energy stored in it. Actively working to research more effective ways of converting biofuels and other fuels into electrical energy using fuel cells.

Biogas can be easily produced from the current residue, such as paper production, sugar production, sewage, animal remains, and so on. These different remains to be mixed together with natural fermentation to produce methane gas. This can be done by turning the current fecal plant in biogas plants. When plants drop all the methane biogas that can, the remains are sometimes more suitable for fertilizer than the original biomass.
Alternatively, the biogas can be produced with the help of advanced waste processing systems such as mechanical biological treatment. These systems updated elements recycled from household waste and process the biodegradable fraction in anaerobic summarize the content.
Renewable natural gas is a biogas which has improved the quality similar to natural gas.Approaching the quality of quality to that of natural gas, it becomes possible to distribute gas to the mass market with the help of gas distribution network.

Geothermal energy is obtained by removal of heat from the earth, usually miles deep in the Earth’s crust. Expensive to build a power plant, but labor costs are cheap, resulting in low cost energy for suitable locations. Finally, this energy is derived from the heat of the Earth’s core.The government of Iceland states: “It should be pointed out that geothermal resources are not necessarily renewable in the same sense as the water resources.” It is estimated that Iceland geothermal energy could provide 1700 MW for 100 years, compared with current production of 140 MW. The International Energy Agency believes renewable geothermal energy. 
Three types of plants used for energy production from geothermal sources: dry steam, flash and binary (mixed). Dry steam power plants take steam out of parts of the country and used for direct drive turbine, which turns a generator. Flash plants take hot water, usually temperature of 200 ˚ C, from the country, and allowing fermentation and efflux to the surface of the steam separator and steam in the water phase separators through heat exchangers, boiling an organic fluid that spins the turbine. Condensed steam and remaining geothermal fluid in all three types of power plants are incorporated back into the hot rock to collect more heat. 
Geothermal energy is the Earth’s crust in some areas near the surface than in the other. In places where the hot interior of the steam or water can be separated and brought to the surface that can be used to produce electricity. Such geothermal power sources exist in certain geologically unstable parts of the world such as: Chile, Iceland, New Zealand, the United States, the Philippines and Italy. Two of these most important areas in the United States in the Gulf Yellowstonea in northern California. Iceland produced 170 MW geothermal power and heated 80% of their households in 2000. year using geothermal energy. Part of 8000 MW capacity produced in its entirety. 
There is also potential to get geothermal energy from hot, dry rocks. Perforated holes are at least 3 km in the Earth. Some of these holes pump water into the ground, while the other pump hot water out. Heat sources consist of hot underground radiogenih granite rocks that heat up when there is enough sediment between the rock and the earth’s surface. Several companies in Australia investigating the technology.

Production of electricity using photovoltaic solar cells 
 Production of hydrogen using fotoelektrokemijskih cells 
 Production of electricity using concentrated solar energy 

Production of electricity by heating the air that was caught turning turbines in the solar tower 
 Heat buildings, directly through the construction of passive solar buildings 
 Heat food with the help of solar oven 
 Heat water or air for domestic hot water and heat 
   space using solar thermal panels 
 Heating and cooling air through the use of solar fire 
 Production of electricity using solar geosinkronoj orbit satellites 
 Solar air-conditioning unit.

Solid biomass is mostly commonly used sagorljivo directly as fuel, producing 10-20 MJ / kg of heat. 
Its forms and sources include fuel derived from wood, the biogenic fraction of municipal solid waste or unused share of field crops. Field crops can be cultivated must not intentionally as an energy crop, and the rest of the plant is used as fuel. Most types of biomass contain energy.Even cow manure contains two thirds of the original energy used by the cow. Collecting energy using a bioreactor is cost-effective solution for the disposal of waste faced by dairy industry and it is possible to produce enough biogas to run these farms. 
With current technology, it is not ideally suited for use as transport fuel. Most transportation vehicles require power sources with high power density such as those used in internal combustion engines. These engines require clean sagorljivo or fuel that is usually in liquid form and small dimensions, compressed gaseous phase. Liquids are more portable because they have high energy density and can be pumped, which allows for easier handling. This is why most of the liquid transport fuels. 
Non-transport application  can  tolerate the density of low-power engine with external combustion engine that can run directly on less expensive biomasenim solid fuels for heating and combined operation. One type of biomass is wood, which is used for millennia in different quantities, and in recent times his invention increased use. Two billion people currently cook every day and heats their homes during the winter using sagorljivu biomass which is a major contributor to climate change global warming caused by human hand. Black soot, which is spread from Asia to polar regions caused by their faster melting in the summer. In the nineteenth century, steam engines driven by combustion of wood were common, contributing to such air pollution in the industrial revolution. Coal is a form of biomass that komprimirao millennia to produce neobnovljivog high zagađujućeg fossil fuels. 
Wood and its by-products can now be converted through processes such as rasplinjavanja in biofuels, such as gas obtained from wood, biogas, metanolno or ethanol fuel, although further development may be required to make these methods available and practical. The rest of the sugar cane, wheat chaff, corn cob and other vegetable matter can be successfully and is burning. Pure carbon dioxide that are added to the atmosphere of this process comes only from the fossil fuels that are used for planting, fertilizing, collection and transportation of biomass. 
The process of collecting the biomass from poplar and willow seasonal and permanent grasses such as wild millet, water and svjetlice Asian reeds require less frequent cultivation and less nitrogen than the typical annual crops. Making pellets from Asian and her cane burning is being studied and could become economically viable.

Airflow can be used to run turbines. Newer wind turbines have a power range from 600 kW to 5 MW turbines, although the output power of 1.5 to 3 MW have become typical for commercial purposes; turbine power output is a function of cubic wind speed, so with increasing wind speed dramatically increases the power output. Areas where winds are stronger and more frequent, such as coastal and high altitude sites, are recommended for the construction of wind. 
Since wind speed is constant, the energy produced by wind park in the year was never as great as the sum of the nominal value of the generator multiplied by the number of working hours. The ratio of actual energy produced in the year to the theoretical maximum is called the capacity factor. Normal capacity factor of 20% to 40% with the values in the upper limits of the suitable places of production. For example, a 1 MW turbine power with the capacity factor of 35% will produce 8760 MWh per year, but only 0.35 x24x365 = 3066 MWh, which on average is 0:35 MW. With the help of data available on the Internet for some locations, the capacity factor can be calculated on the basis of annual output. 
Globally, it is considered that the long-term technical potential of wind energy is actually five times higher than the final world energy production, ie, that is 40 times higher than the current demand for energy. This could require a large amount of land to build wind turbines, especially in areas with higher wind resources. Experience with coastal sources indicate that there is a wind speed ~ 90% higher than those on land, so that coastal resources could contribute substantially more energy. This number should also be able to increase with increasing altitude wind turbines located on land or in the air.

Liquid biofuel is bioethanol, or otherwise, such as fuel ethanol, or bioulje, such as biodiesel and pure vegetable oil. Biodiesel can be used in modern diesel vehicles with little or no modification to the engine and can be produced from the remains or pure plant or animal oils and fats (lipids).Pure vegetable oil can be used in modified diesel engine. In fact, the diesel engine was originally designed to drive vegetable oil, and not drive on fossil fuels. The main advantage of biodiesel is a little radiation (emission). Using biodiesel emissions of carbon monoxide and other hydrocarbons is reduced by 20% to 40%.In some areas corn, corn stalks, sugar beet and millet are grown specifically for ethanol production (also known as granular alcohol “or” of grain alcohol), liquids that can be used in internal combustion engines and fuel cells. Ethanol is gradually used in the existing energy infrastructure. E85 is a fuel composed of 85% ethanol and 15% gasoline that is sold to consumers. Biobutanol developed as an alternative to bioethanol. Increased international krizitiranje biofuels produced from food crops due respect to issues such as food security, environmental impacts (deforestation) and energy balance.

Germany, the US, Spain, Denmark, and India are among the world’s leading nations in the acquisition of wind energy. According to Chris Flavin, a speaker at the World Oil Forum held in Denver, Colorado, on October 30, 1998, “Navarro, Spain, is utilizing wind power to generate 23% of its electricity needs.” Denmark now generates 8 percent of its electricity from wind power. Flavin, a vice president and senior energy policy analyst at the Worldwatch Institute, reported that wind generated energy is growing in leaps and bounds.

In fact, according to Worldwatch Institute Online, “The world added 2,100 megawatts of new wind energy generating capacity in 1998, a new all-time record, and 35% more than was added in 1997. Wind power is now the world’s fastest growing energy source and has also become one of the most rapidly expanding industries, with sales of roughly $2 billion in 1998.” Major offshore developments are likely in northern European waters in the early part of the next century.

This will be the next major step for this technology and will result in a dramatic increase in decentralized electricity generation. Offshore wind has the potential to deliver substantial quantities of energy at a price that is cheaper than most of the other renewable energies, as wind speeds are generally higher offshore than on land. But there is increasing energy being put in finding many other alternative sources of power and making them viable, such as geothermal and wave energy and biomass. Just as there are many types of systems for home  there will soon be many choices for home power.



CROATIAN CENTER of RENEWABLE ENERGY SOURCES (CCRES)• was founded in 1988 as the non-profit European Association for Renewable Energy that conducts its work independently of political parties, institutions, commercial enterprises and interest groups, • is dedicated to the cause of completely substituting for nuclear and fossil energy through renewable energy, • regards solar energy supply as essential to preserve the natural resources and a prerequisite for a sustainable economy,• acts to change conventional political priorities and common infrastructures in favor of renewable energy, from the local to the international level, • brings together expertise from the fields of politics, economy, science, and culture to promote the entry of solar energy, • provides the opportunity to play a part in the sociocultural movement for renewable energy by joining the association for everyone, • considers full renewable energy supply a momentous and visionary goal - the challenge of the century to humanity. Zeljko Serdar Head of CCRES association

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