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The number of small ones is expanding

New hydroelectric power plants of up to 30 megawatts and the recovery of power plants that were closed down expands generation capacity

miguel boyayanLow environmental impact and a fall in electric power transmission losses, because of the proximity to centers of consumption, have made the small hydroelectric power plants/PCHs an attractive venture to expand the country’s generation capacity. In addition to attracting the interest of Brazilian conglomerates to build electric power plants of this kind because of tax exemption on transmission fees and the guarantee of electric power sales for 30 years, they are also being focused on by researchers. They have evaluated a great, low-cost energy potential resulting from the recovery of hydroelectric power plants that had been closed down, as shown in a recent study conducted at the Paulista State University/Unesp. The functioning principle of a small power plant is the same as that of a conventional power plant – the force of the water turns the blades of the turbines which, connected to the generators, produce electric power. But while the big power plants depend on the damming of rivers and the formation of enormous lakes, the small ones operate without any reservoirs and only on running water, and generate up to a maximum of 30 megawatts (MW).  This is enough to light 6 thousand middle-class homes.

Although this generation power might seem insignificant, an analysis of the numbers of the Agência Nacional de Energia Elétrica/Aneel regulatory agency shows that the market of the PCHs is expanding. At present, 67 small power plants are being built in the country and will aggregate another 1.112 MW to the existing 2.489 MW generated by the 333 power plants in operation. In other words, when these power plants are ready, the PCHs will account for a quantity of electric power equivalent to that produced by the Jirau power plant, currently under construction on the Madeira River in the State of Rondônia.  The Jirau power plant is a source of controversy, which has delayed the beginning of the construction and involves the flooding of forests, the impact on the native fauna and flora and the displacement of people who live in the surroundings. “Considering that the current electric power demand in Brazil corresponds to approximately 70 gigawatts, these small power plants account for approximately 5% of the total need”, says professor José Luz Silveira, from the energy department and the post-graduation program in energy studies at the Unesp School of Engineering in the city of Guaratinguetá, State of São Paulo. Aneel data for February shows that another 152 concessions have already been granted by the regulatory agency for the construction of small power plants with power of 2.255 MW; construction has not started yet.

A study on the PCH Sodré in Guaratinguetá, inaugurated in 1912 and closed down since 1992, shows that it is possible to significantly increase the small power plants’ capacity to generate electric power without the need of any major structural renovations. “A survey of the hydraulic potential of the Piagui River, which feeds the power plant, showed the possibility of increasing the generation capacity by approximately 75%”, says Silveira, one of the advisors of the research study on this matter, together with Oscar Maldonado Astorga, also from Unesp. This study also included an evaluation of the components that had to be replaced to adapt the power plant to new generation conditions, such as the generators, transformers and voltage and speed regulators.

CERPCHLuiz Dias power plant, in the city of Itajubá, State of Minas Gerais: laboratory on a real scaleCERPCH

All these interventions, however, took into account the preservation of the power plant’s existing characteristics, in order to prevent any significant environmental impact. This data was used as the basis for the analysis of the project’s economic feasibility which took into consideration not only the cost of the work and the price of electric power, but also the environmental benefits from the commercialization of carbon credits obtained by re-starting the PCHs, that is, by increasing the capacity of  the production of electric power by replacing or modernizing components and systems. When the credits for the emission of 1,919 tons of carbon are accounted for, the investment amortization time is reduced. “Instead of four years and four months, the return period is three years and six months, which increases the economic attractiveness of the venture”, says Dinara Silva Gyori, who headed the research project.

According to the existing calculations, the re-starting of the Sodré power plant will increase the generation capacity to 2 MW per day. Although this is not an impressive figure, in view of the demand for a total of 40 MW by Guaratinguetá, a city with a population of 100 thousand people, this capacity will be enough to meet the needs of approximately 400 middle-class homes. “Although they represent a small generating potential, if the PCHs that are inactive because of technical problems are not repaired and reactivated, Brazil will have to invest in the construction of new power plants”, says Silveira. “As the thermal power plants that run on natural gas are the main target of current investments, we may have serious problems ahead”.

At present, 34 thermoelectric power plants are under construction, with total power of 3.383 MW.  Another 156 concessions of the same kind have been granted by Aneel, with total power of 11.215 MW. Silveira points out that Brazil depends on other countries, such as Bolivia, for its natural gas needs.  Last year, a political crisis in Bolivia interrupted the supply of this input. When natural gas is not available, the thermoelectric power plants have to run on diesel oil, which is highly polluting. ‘When they run on natural gas, the power plants emit a huge amount of carbon dioxide; but when they burn diesel oil, they pollute much more, because they release huge quantities of carbon dioxide, sulfur dioxide, nitrogen oxides, and particles”,  says Silveira, whose article on the ecological efficiency of thermoelectric power plants has already been published.

In addition to less environmental impact  provoked by the construction of the PCHs, because they do not form lakes bigger than 13 square kilometers, the 3% loss in the transmission of electric power, from generation to delivery to the end consumer, are lower than the 10% loss faced by the big energy transmission systems in Brazil. According to international standards, the loss limit must correspond to approximately 6%.

An estimate prepared by the Centro Nacional de Referência em PCH/CERPCH reference center, linked to the Federal University of Itajubá/Unifei, in the State of Minas Gerais, shows that if the more than one thousand existing inactive PCHs were put into operation again, they could generate approximately 300 MW, enough to meet the electric power demands of 60 thousand homes. “At the time these power plants were built – approximately 80 years ago – there was no hydrological data available”, says professor Geraldo Lúcio Tiago Filho, executive secretary of the CERPCH. “As the demand was small, power plants were customized according to the required loads.”

miguel boyayanEnvironmental bottleneck
The interest in reactivating these power plants has increased because the environmental permit process is simpler.  “Nowadays, the environmental permit is the major bottleneck for the construction of a new PCH”, says Tiago. “It’s easier to obtain the permit for a new thermoelectric power plant than it is for a PCH”. The shorter time necessary to reactivate a power plant is also an advantage for investors. “It takes up to two years to build a new PCH, while reactivation takes one half of this time”, says Silveira.

The first hydroelectric producing system in Brazil was implemented in the Santa Maria mining company, in the city of Diamantina, in the state of Minas Gerais in 1883. The process expanded swiftly in the 1920’s, up to 1930, when the number of PCHs went up from 186 to 519 and the power from 310 to 655 MW. Historically, the country has grown on the basis of generation in isolated systems. This tendency lasted until 1960, when construction began on the big hydroelectric power plants, in line with a more centralized model. Federal and state government electric power companies were established to manage these big power plants; the isolated generation plants merged into the big companies and were later deactivated. “The movement to reactivate these small power plants began in the 1980s, when most of these small plants were non-operating”, says Tiago.

One of the actions taken by the government in this respect was the creation of a laboratory at Unifei for the development of hydraulic machines, for the purpose of holding specialization courses in the field of small power plants, and for the preparation of manuals with regulations for the construction of micro, mini and small power plants. “This program did not move forward because the government was the only buyer of the electric power, and, as inflation had to be controlled, the government would freeze the utility rates”, Tiago explains. This model prevented the private sector from investing in the small power plants. The creation of the lab at Unifei opened up the possibility for the university to become responsible for the operation and maintenance of the Luiz Dias PCH, in 1998.  This PCH was commercially run by the Companhia Energética de Minas Gerais/Cemig electric power utility.  This power plant functions like a lab on a real scale for studies and research into the field of electric power generation.

At the end of the 1990’s. the creation of Aneel and the restructuring of the electric power sector, which included the freedom to negotiate consumption in the market, led to the resurrection of the PCHs.  Some advantages, such as the tax exemption on the transmission rate and payment for flooded areas, were crucial for the expansion of the market. “These advantages were granted because the operating costs of a PCH are higher than those of a big hydroelectric power plant”, says Tiago. The creation of the Programa de Apoio Financeiro em Fontes Alternativas de Energia Elétrica/Proinfa funding program in 2002, the objective of which is to increase the participation of biomass, wind energy and PCHs in the Brazilian energy matrix, was important for the consolidation of the small power plant market. “But the private sector is the biggest development agency for PCHs”. Tiago emphasizes.

According to government data, Brazil has 17 thousand MW available in scheduled power plants and PCHs inventories, that is, detected potentials, evaluated and registered with Aneel. A study conducted by CERPCH estimates that the theoretical potential for the small power plants,  not yet  inventoried, corresponds to approximately 14, 8 mil MW. The Southeast Region, the biggest consumer market, has the highest available hydrological potential, followed by the South and Central-West Regions.

Scientific Article
SILVEIRA, J. L.; VILELA, I. A. C. Ecological efficiency in thermoelectric power plants. Applied Thermal Engineering. v. 27, p. 840-847, 2007.