Renewable resources - Solar and Wind Energy in Serbia

EnergyTechnical ArticlesSouth-East European INDUSTRIAL Мarket - issue 5/2005

by prof. Petar Gburcik

Mankind is today confronted with a great challenge. The most extensively used energy resources are fossil fuels and nuclear energy and they brought a fast progress during the past two centuries. But their reserves are limited and they are on the way to be exhausted, or at least to become unbearably expensive. On the other hand, the use of these resources leads to the degradation of environment and climate changes, as well as to intensification of dependency and poverty in countries not disposing with these resources.

In order to preserve the environmental equilibrium, the growth should not have the characteristics of unsustainable processes, which end with collapse. The sustainable progress can be achieved only by the use of renewable energy resources. Renewable energy is the energy of the sun that in combination with the atmospheric water transforms in a new quality – climate resources. The inevitable activity on the way to introduction of climate resources in the energetic system of a country, is the assessment of solar and wind energy resources.

Climate resources

The resources indispensable for the existence and progress of mankind, are present in our world. Resources are divided on renewable and non-renewable (Fig.1). They may be also divided on material and energetic. Some of them (like oil and wood) can be at the same time material and energy resources. The main components of the climate resources are solar energy and water in the atmosphere. The life is a product of climate and at the same time is a part of the climate (as biomass).

The climatic system is formed in the lower part of the atmosphere (troposphere). In this layer all weather processes take place. Weather is a daily manifestation of the climate. The system Earth-Atmosphere-Water is shown on Fig. 2. The energetic input is the solar energy. 30% of the total energy is reflected from clouds and earth surface back to the universe, and does not participate in the energy conversion inside of atmosphere. Solar energy, on its way to the earth surface, is subject to the selective absorption. The absorption of x and g rays occurs at a height of about 100 km, and leads to the formation of ionosphere. In the layer between 50 and 20 km greater part of UV radiation is absorbed (stratosphere). Formation of ionosphere and stratosphere does not take significant part of energy. In the lowest layer (troposphere) 25% absorb clouds and different aerosols, while the ground absorbs about 45% of the initial solar radiation. The soil, heated in this way, emit infrared radiation, which is absorbed by water vapor and other greenhouse gases. The energy (consisting of short and long range radiation), that atmosphere obtains in this way, serves as input for all weather processes (sunshine, wind, rain, etc.) and for creating of biomass. All this constitutes the climate. This energy (per year) is about 15000 times larger than the actual yearly energy consumption of the mankind.

Solar energy in the atmosphere in all four possible forms: as radiation (light), heat, as well as potential and kinetic energy. The visible part of solar radiation (light) contains the most energy of the radiation arriving on the earth surface, and it is commonly named "solar energy".

  • The part constituted through a process in which the light, heat and water included, is named "biomass".
  • The potential energy derived from the heat trough the process of water circulation in the atmosphere (evaporation – rain – sources) is named "hydro energy". The same process produces the water sources (cold or warm).
  • Kinetic energy of the wind is due to the process of general circulation induced by inequalities of temperature distribution over the globe and Earth rotation.
  • The only energy which is generally treated as renewable and can not be treated as climate resources is the energy stored in the underground reservoirs of thermal water. Pumping of such water can mean a potential danger for the energetic balance on the earth surface. The other handicap is that such reservoirs are not always renewable.

Solar and Wind Energy Resources in Serbia

One important phase in preparation the plan of solar and wind resources utilization, as well as in concrete projects of utilization, is assessment of these resources on global and local levels. In order to prepare and enable Serbia to implement EU programs and standards, the Ministry for science and environment adopted National Energy Efficiency Program. A part of this Program is the "Study of solar and wind energy potential in Serbia" (SWEPS) which presents assessment of solar and wind energy resources on national (global) level.

  • Solar energy resources. Mean values for January are in the range from 1.1kW/m2 in the north of the country, to 1.7 in the south. Map for July indicates the least energy in the west part of the country and maximal energy in the southeast. Such spatial distribution is caused by the influence of daily cloudiness, which is most pronounced in the mountainous regions. Mean values for July are in the range from 5.9 to 6.6 kWh/m2. Mean values for the year are in the range from 3.3 to 4.3 kWh/m2.
  • Wind energy resources. Two approaches to the wind energy assessment were applied. The first one was the mapping of wind power and wind energy and the second was analyzing of annual course of power and energy in some characteristic locations. Here will be discussed only the mapping of wind power. Maps were created for the height of 10 m (measured values) and 100 m (assessed values). For the time being the maps were not elaborated for all months, but only for January, July and year. Here is presented only the wind power map for January for the height of 100 m.

Maximal values of wind power for January occur at the territory of lower Danube (this territory is characterized by the wind Kochava) and Eastern Serbia.

The area closed by the line indicating 300 W/m2 is the optimal area for the prospective wind parks. In this area were already identified some locations were the wind profile measurements will be conducted and experimental windmills mounted.