Electricity Production from Renewable Energies

Benoit Robyns, Arnaud Davigny, Bruno François, Antoine Henneton, Jonathan Sprooten

• Publisher: Wiley-ISTE
• Year: 2012
• ISBN:
  9781118563069
• Edition: 1
• Topic: Tecnologia e ingegneria
• Subtopic: Risorse energetiche

Energy and environmental issues have caused a marked increase in electricity production from renewable energy sources since the beginning of the 21st Century. The concept of sustainable development and concern for future generations challenge us every day to produce new technologies for energy production, and new patterns of use for these energies. Their rapid emergence can make the understanding and therefore the perception of these new technologies difficult. This book aims to contribute to a better understanding of the new electricity generation technologies by addressing a diverse audience. It presents the issues, sources and means of conversion into electricity using a general approach and develops scientific concepts to understand their main technical characteristics.
Systems of electricity generation from renewable energy resources of small to medium powers are presented. The basic electrical concepts necessary for understanding the operating characteristics of these energy converters are introduced, and the constraints and problems of integration in the electrical networks of those means of production are discussed. Several exercises are provided to the reader for evaluation purposes.

Contents

1. Decentralized Electricity Production from Renewable Energy, Benoît Robyns.
2. Solar Photovoltaic Power, Arnaud Davigny.
3. Wind Power, Bruno Francois and Benoît Robyns.
4. Terrestrial and Marine Hydroelectricity: Waves and Tides, Benoît Robyns and Antoine Henneton.
5. Thermal Power Generation, Jonathan Sprooten.
6. Integration of the Decentralized Production into the Electrical Network, Benoît Robyns.

Chapter 1

Decentralized Electricity Production from
Renewable Energy ¹

1.1. Decentralized production

There is no clear official definition of decentralized production. Generally, decentralized production is defined as the opposite of centralized production [CRA 08, JEN 00]. To simplify, let us say at first that decentralized units:

– are not planned in a centralized way;

– are not controlled (or dispatched) in a centralized manner;

– have a power, which does not exceed 50 to 100 MW;

– are generally connected to the distribution network and not to the transportation network.

Another characteristic of decentralized production is that it is scattered over a territory, in contrast to conventional production, which is concentrated on a limited number of well-defined sites.

The development of decentralized production over the last few years has been especially favored by the opening of the electricity markets (which has spread in Europe from the beginning of the 2000s) and the development of renewable energies, especially wind energy, driven by a real commitment to the environment on a European scale. Decentralized production is thus developing in many countries on the basis of cogeneration units, renewable energy systems or conventional productions, which have been installed by independent producers.

The development of this type of production can contribute to solving technical, economic and environmental problems [CRA 08, JEN 00], even if it is not the only answer to these multiple challenges.

Let us make a list of elements favoring decentralized production:

– the desire to reduce greenhouse gas emissions (mainly CO₂) encourages the development of renewable energies;

– the energy efficiency increase, which has been obtained thanks to cogeneration systems;

– the opening up of the electricity market enabling the emergence of independent producers;

– the desire to widen the range of energy supply, in order to limit the energy dependence of the European Union, which results from the use of fossil fuels;

– technological progresses contributing to the reliability and availability of 100 kW to 150 MW units;

– the greater facility to find sites able to accommodate a reduced power production;

– shorter construction periods and lower investments than for large conventional power plants;

– a production that can be carried out at the proximity of its use, thus reducing transportation costs.

Depending on the profile of the historical generation system of each country, the structure of their transport and distribution network and the organization of the electrical system, these various points can be more or less important, depending on the countries, especially within Europe.

1.2. The issue of renewable energies

1.2.1. Observations

The growing interest in the development of renewable energies is caused by several elements: climate change, increasing energy demand, limits of fossil fuel reserves, low global efficiency of the energy system and energy dependence, especially in the case of Western countries [CHA 04].

Climate change

The growing “greenhouse effect” leads to the increase of the global temperature at the surface of the planet. And yet, because of human activities, the concentration of greenhouse gases has soared since the pre-industrial era (1750–1800). Carbon dioxide concentration (CO₂) (the main greenhouse gas) has increased by 30% since the pre-industrial era. The combined effects of all the greenhouse gases (CO₂, methane, ozone, etc.) nowadays amounts to a 50% CO₂ increase compared with this period.

Since 1860, the mean temperature at the surface of the Earth has risen by 0.6°C. Several prospective scenarios are predicting that by 2100, this temperature will increase further between 1.5 and 6°C, if energy systems and current consumption habits do not change. This significant increase would be accompanied by a sea level rise from 20 cm to 1 m. If the climate change seems non-reversible, this evolution can however be slowed down, by significantly reducing greenhouse gas emissions.

The natural CO₂ wells, such as land, trees and oceans, would only be able to absorb a little less than half of the CO₂ production resulting from human activities (produced in 2000). In order to stabilize the CO₂ concentration at its current level, we thus would have to immediately reduce the gas emissions from 50 to 70%. This drastic reduction is clearly impossible. However, it is urgent to start acting, because this is a cumulative issue. Indeed, the carbon dioxide lifespan in the atmosphere is of about one century and, therefore, the stabilization of the CO₂ concentrations to an acceptable level will take several generations.

CO₂ is produced by the combustion of all fossil fuels: oil, gas and coal. CO₂ emissions from coal are twice as high as the emissions from natural gas. Oil emissions are in-between.

At the beginning of the 21^st Century, the distribution by sectors of CO₂ emissions in the world was as follows: electricity production 39%, transport 23%, industry 22%, residential 10%, service sector 4% and agriculture 2%. This distribution varies however from one country to another. For example, in France where only one tenth of the electricity is produced from fossil fuels, the transport sector is responsible for more than 40% of the CO₂ emissions into the atmosphere.

Increasing energy demand

At the beginning of the 21^st Century, the global energy consumption was about 10 Gtoe (toe = ton of oil equivalent; 1 toe corresponds to the energy produced by the combustion of one ton of oil). Fossil fuels represent about 8 Gtoe.

Many energy scenarios are developed each year by specialized organizations in the energy field. These scenarios plan an energy demand in 2050 of about 15 to 25 Gtoe. These prospective scenarios are based on various parameters, such as economic growth, increased by world population increase, the progressive access to electricity of the 1.6 billion people still without any access to it at present, the growing needs of developing countries and the implementation of energy-saving policies in order to protect the environment. The uncertainties in relation to the evolution of these parameters explain the significant gap between extreme scenarios.

However, it seems quite reasonable to predict that by the middle of the century, the energy demand will have doubled.

Limits of the fossil fuel reserves

The R/P oil ratio (known reserves to the annual production) is about 40 years. This piece of data (which is equivalent to a period) should not be mixed up with the period during which we will still dispose of oil, nor to the one during which it will still be cheap enough. These two periods are completely unpredictable, because they depend on too many parameters. Let us note that since the 1980s, each year we consume more oil than we discover.

For natural gas, the R/P ratio is about 60 years. But if we wanted to replace oil and coal with gas, in order to reduce greenhouse gas emissions, the R/P ratio would then only be 17 years. When some countries give up nuclear energy for the benefits of gas, it could increase the consumption of resources.

Coal is the fossil fuel with the most significant reserves. Its R/P ratio is estimated at more than 200 years.

The R/P ratio of uranium is about 60 years (on the basis of “reasonably assured resources” added to “recoverable resources” at less than $130 per kg of natural uranium and a conventional fission exploiting isotope 235). Let us also note that nuclear fission only contributes up to 2.7% to the final energy on a global scale and that doubling its production will only have a small impact on the reduction of greenhouse gas emissions.

The energy demand until 2050 (then predicted to be between 15 and 25 Gtoe, compared to 12 Gtoe in 2010) could still be met mainly (at present) by nonrenewable raw energy materials. This would have dramatic consequences for the climate in particular, and for the environment and would not really take into account the needs of future generations.

In order to limit the rise in temperature to a range from 1 to 3°C, the total emissions for centuries would have to be only a third of the current emissions, caused the combustion of the accessible resources of gas, oil and coal. Humanity would then have to stop burning two-thirds of a relatively cheap and accessible energy source. It is thus not reasonable to bank on an early exhaustion of the resources, in order to naturally reduce greenhouse gas emissions. This is particularly true, because the relatively low price of fossil fuels (despite regular explosions) are disrupting the emergence of new technologies, which are inevitably more expensive until they become integrated into a mass production process.

Low global efficiency of the energy system

The global efficiency of our energy system is quite low: for example, in 2008, to satisfy the French requirements for final energy (marketed) of 168 Mtoe, 262 primary Mtoe were needed to produce them, which corresponds to a 63% efficiency, all the while knowing that effectively useful energy is much lower. The energy transformation losses alone when making marketable energy are about 27%. 94 Mtoe have thus been lost in energy transformations (refining, electricity production, etc.). These losses of 94 Mtoe, associated with bad uses of the final energy (bad building insulation, low efficiency of the car heat engines, etc.) are the main item of expenditures and finally the most important cause of CO₂ emissions. For example, in 2000, the global efficiency was about 34%.

Energy dependence

About 50% of the energy consumed within the European Union comes from resources located in countries outside the EU. If nothing changes in the energy production field, and taking into account the expected consumption increase, this energy dependence will go up to 70% by 2030.

The global dependence on Middle East countries (which possesses 65% of the known oil reserves) should increase. The dependence is even higher for uranium (100% for France). From 2020–2030, economic and political tensions could arise from the diminution of fossil resources, which are easily exploitable and from their concentration in politically unstable zones. Thi...