Repsol YPF

Hydroelectric plants use the power of water in order to obtain mechanic energy that is later on transformed into electric energy. Their functioning is simple: water is channelled by means of pipes from a dam or a reservoir, regulating its flow in order to control power and in order to action a series of turbines connected to a generator as it passes by. There are three main types of plants: the run-of-river plants, which do not reuse the flow of the rivers; the mix-pump stations and the regular hydraulic stations. 

They all use the water jumps built on the river basins as provided by nature. Thus, the electricity produced by hydroelectric plants is a renewable type of energy, scarcely polluting and with low maintenance costs. Besides, dams are durable premises for water supply from which agriculture benefits too, among other areas. 

Among its drawbacks we should point out the fact that their availability depends on climatic factors, besides, the cost per megawatt is high and transporting the energy is expensive. 

Availability depending on the climate
It is evident that drought affects negatively the production of electricity. When water reservoirs in dams present critical figures there are negative consequences on hydraulic energy production. During dry seasons dams only let off a very limited amount of water, most of which is used to supply drinking water, water for irrigation and to keep up the ecological flow. This is the result of the deficiencies that are affecting the rain levels in some areas of the country. 

Thus, for example, once more drought provokes a decrease in the hydroelectric production in the region of the river Ebro. Last year, energy production did not reach 30% of the potential production of the more than 250 plants placed in the different rivers of the region, from January to August. Some remained out of service due to the fact that there was not enough water flow in the rivers. 

Hydroelectric plants in the region of the Ebro generated only 4,000 million Kilowatts/hour in 2006, whereas, under normal pluviometric conditions they should have exceeded 12,000. The decrease of the volume of energy produced was observed even in reverse-cycle plants, where water goes through the turbines more than once after having been pumped out. In the case of Extremadura, water jumps in the last few years have produced only 5% of the electric energy consumed.

Another piece of information: The drought Spain is going through, in general, made hydroelectric production decrease 35.6% during 2004, from 29,777 GW/h to 19,170. The lack of rain is responsible for the fact that the working possibilities of hydroelectric plants, in theory, are 55% inferior to the average historical value.

Sustainable demand 
This decrease in hydroelectric production takes place in a context where the tendency is that of a growing demand. While production decreases energy needs at home, at the industry and at different types of commercial entities grow or keep being very high. Nuclear plants and thermal stations, together with the each time more usual contribution of wind electricity, are the ones that make up for this lack of hydraulic energy.

The absence of rain has influenced the evolution of electric companies, whose production by means of fossil fuels is increasing in order to compensate the fall of hydroelectric energy. But the growth of the production at thermal stations and nuclear plants implies a subsequent increase of pollution and the emission of hot-house effect gases. 

The impact of drought calls our attention if we take into account the fact that the existing hydroelectric power is, in regions such as Extremadura, higher than that of nuclear plants under ordinary conditions. As to the future, solar and wind energy projects seem to be the solution to the energetic dependence on nuclear and thermal energy.