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Modern societies consume huge amounts of energy for heating (homes and offices), transportation, electricity production and industrial use. Due to economic progress and a rising standard of living, the demand for energy is continually increasing. At present, the largest amount of energy we use is derived from conventional sources of energy which are petroleum, gasoline and coal. These are non renewable sources of energy which, sooner or later, will be exhausted. The production and use of energy derived from these sources create a series of environmental problems, the most serious of which, as we all know, is greenhouse effect.
On the other hand, renewable energy sources (RES) are continually renewed by the cycle of nature and are considered to be practically inexhaustible. The sun, wind, rivers, organic material such as wood and even household and agricultural waste are energy sources which are always available and are never exhausted. They are plentiful in our natural environment and they are the first sources of energy used by man, almost exclusively, until the beginning of the 20th century, when humankind turned to the intensive exploitation of coal and hydrocarbons.
Interest in the broader exploitation of RES, as well as in the development of reliable and economically profitable technologies to use their potential appeared, in the beginning, after the first oil crisis in 1979 and became permanent in the following decade after public awareness of global environmental problems. For many countries, RES are a significant domestic energy source, with great development potential on a local and national level. RES make an important contribution to their energy balance, helping to reduce dependence on expensive and imported petroleum and strengthening the security of their energy supply. At the same time, RES have a share the protection of the environment because their use does not burden it due to the fact that they do not produce pollution or gases which increase the danger of climate change. It has also been established that the energy sector is mainly responsible for pollution of the environment, as nearly 95% of atmospheric pollution is due to the production, refining and use of conventional fuels.
Greece has considerable RES potential which can provide a practical alternative solution to meeting its energy needs.
TYPES OF RENEWABLE ENERGY SOURCES
Wind Energy: the kinetic energy which is produced by the power of the wind and is converted into usable mechanical energy and/or electricity.
Hydroelectric Power: Small hydroelectric projects (up to 10 MW) make use of falling water in order to generate electricity or to convert it into usable mechanical energy.
Biomass: is the result of photosynthesis which converts solar energy into a series of processes in both land and water based plant organisms.
Solar Energy consists of the following:
Active Solar Systems: convert solar radiation into heat.
Bioclimatic Design and passive solar systems:
Concern architectural solutions and the use of suitable construction materials for the maximization of the direct use of solar energy for heating, air conditioning or lighting.
Photovoltaic Solar Systems: convert solar energy directly into electricity.
Geothermal Energy: is thermal energy which is produced in the Earth’s interior and manifests itself in natural steam, in surface or underground hot water and hot dry rock.
Hydrogen: Hydrogen makes up 90% of the Universe and will be the new fuel which we will use in the future.
ADVANTAGES OF RENEWABLE ENERGY SOURCES
The main advantages of RES are as follows:
 They are practically inexhaustible sources of energy and contribute to reducing dependence on conventional energy resources.
They are an answer to the energy problem for the stabilization of carbon dioxide emissions and other greenhouse gases. In addition, by replacing energy generation plants which use conventional resources, they lead to a reduction in the emission of other pollutants, such as sulfur and nitrogen oxides which cause acid rain.
They are domestic sources of energy and contribute to increasing energy independence and security of energy supply at the national level.
They are geographically dispersed, leading to the decentralization of the energy system, making it possible for energy needs to be met at a local and regional level, thus relieving infrastructure systems and reducing losses from energy transmission.
They provide opportunities for the rational use of energy sources because they cover a wide range of users’ energy needs (i.e. solar energy for low temperature heat, wind energy for electricity production).
They usually have low operating costs which are not influenced by fluctuations in the international economy and especially in prices for conventional fuels.
RES investments create a significant number of new jobs, especially at the local level.
In many cases, they can be a catalyst for the renewal of economically and socially depressed areas and a magnet for local development through the promotion of relevant investments) for example, greenhouses using geothermal energy).
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