Biomass and photovoltaic power stations


    Comparison of land use and efficiencies Authors: Dr. Mirco AndreottiElisa Samorì Abstract: In this article we present a summary of the studies undertaken to evaluate the energy balance in energy production from renewable sources. We report the evaluations, their pros and cons, and their potential solutions for the production of energy from biogas, vegetable oil and photovoltaics. The results have been assessed by analysing power station designs and presentations, and data from Terna and ARPA. The study concludes by illustrating that photovoltaics are clearly more efficient than biomass energy production and recommendations are made about careful exploitation of the environment.

    Introduction

    The use of fossil fuels undoubtedly gives rise to a variety of problems: an increase in carbon dioxide in the atmosphere, the emission of harmful substances and the inevitable exhaustion of the fuel itself.

    Many technologies for electricity production have been considered in order to tackle these problems. Among the various solutions we would like to examine and compare are biomass and photovoltaic technologies.

    Biomass

    The technology of biomass energy production is based on the production of fuels that come from plant and/or organic sources which enable an electricity generator to function. Biomass is considered to be a source of renewable green energy.

    It is renewable because the fuel is produced from annual cultivation cycles, therefore the production cycle is limited for only a brief amount of time (as opposed to petrolium production which requires geologic time scales).

    It is also a green technology because the carbon cycle does not contribute to the increase of carbon dioxide in the atmosphere. This is due to the fact that the carbon released by burning is then reabsorbed by growing plants. Among the various sources of biomass that are spreading across Italy we consider as examples a biogas station and vegetable oil.

    In biogas plants, the agricultural product is used to produce biogas from fermentation and then used as a fuel for the generators. In vegetable oil plants, combustible oil is extracted from the agricultural product in order to fuel the generators.

    It is easy to understand that being a source of renewable energy, biomass is no more than a conversion of solar energy, which is the only inexhaustible source of energy that originates outside of the earth.

    Solar energy is used by plants to synthesise organic material through the photosynthesis of chlorophyll. Fuel is extracted from this in order to power generators.

    Photovoltaics

    A photovoltaic plant directly converts solar energy into electricity through the photoelectric effect. This technology is therefore part of renewable energy production. These power plants do not emit any type of substance into the atmosphere because the process is not based on a combustion cycle.

    Problems associated with biomass

    Among the inherent problems that can arise from biomass are the use of fossil fuels for cultivation and the use of fertilisers.

    With regard to the first problem, the studies undertaken demonstrate that biogas and vegetable oil use 2% and 13% respectively of the diesel oil that would be needed to produce the same energy with a traditional thermoelectric station operating exclusively on fossil fuels.

    Therefore, we can conclude that incidence in the use of fossil fuels for land cultivation can be considered minimal, if not nonexistant.

    A bigger problem arises with the inevitable use of fertilisers. This leads to the emission of nitrogen and its various compounds into the atmosphere, which are harmful to health and the environment.

    Problems associated with photovoltaics

    The fundamental problem of a photovoltaic plant is that it produces electricity according to the solar cycle, be it daily or annually. This means that a power plant could produce energy surplus to requirements in certain periods and be lacking at other times.

    This problem could be resolved with photovoltaic systems that store energy, as has been proposed by some experimental power plants.

    Already in the experimental stage are, for example, plants with hydrogen storage that use energy in excess of the demand to produce hydrogen and re-use it to produce energy during periods in which photovoltaics fail to meet the demand for energy.

    Other problems could be the use of some highly toxic substances such as Cadmium Telluride, the disposal of used solar panels, changes to the environment caused by the installation of photovoltaic cells with the subsequent change in albedo and potential creation of microclimates that are different from the original environment.

    Studies demonstrate that these effects seem to be minor. With regard to disposal there are two pilot plants in the world that recycle used solar panels by restoring them and rebuilding new panels from old parts.

    Land requirements for biomass and photovoltaics

    In order to compare the amount of land required for a photovoltaic power station and for the growing of crops needed to fuel a biomass station, let us also consider a solar power plant with hydrogen storage. This gives three model plants that produce energy according to the pattern of demand of a hypothetical community.

    Assuming an average electricity demand of 1MW, a biogas plant, vegetable oil plant and photovoltaic plant with hydrogen storage located in the Ferrara region require 400, 1000 and 15 hectares respectively, as outlined in the following table:

    Photovoltaics = 15 ha

    Biogas = 400 ha

    Vegetable oil = 1000 ha

    Comparison of efficiencies

    As we have already explained, the technologies discussed here convert solar energy into electricity.

    By studying the incident solar energy measurements (supplied by ARPA) in the city of Ferrara over the past 5 years we have been able to determine the efficiency of converting solar energy into electricity i.e. the fraction of electricity that can be obtained from incident solar energy over the course of one year.

    From analysis of the data we can verify that photovoltaic, biogas and oil technologies have the following efficiencies: 4%, 0.14% and 0.06%, as summarised in the table below:

    Photovoltaics = 4%

    Biogas = 0.14%

    Vegetable oil = 0.06%

    Analysis of results

    The results demonstrate that photovoltaic technology is decidedly more efficient than biomass: 30 times more efficient than biogas systems and 70 times more efficient than vegetable oil systems.

    This implies that the land dedicated to growing biofuels is actually unnecessary because photovoltaics require far less surface area to meet the same demand.

    General considerations

    The results obtained here are not meant to be used as an argument against biomass, but are more of a starting point to reflect on land use and better organisation in the management and production of electricity.

    The location of power plants must be carefully chosen and evaluated based on the existing settlements and characteristics of the particular territory.

    Therefore biomass technology should also be exploited. However, it would be wise to locate it in areas where the fuel can be grown without taking over agricultural land.

    As regards photovoltaic plants, it is fair to say that having vast expanses of land occupied by such plants would be undesirable for the surrounding environment. Nevertheless, as in the case of biomass, it is best to carefully assess the location and size of the project.

    Considering the small area of land required for photovoltaics in relation to that required by biomass, it is clear that a solar energy plant would have very little impact on the area in which it is located.

    Furthermore, it is only right to add that photovoltaic energy does not have to result in one-off plants concentrated in a limited area.

    In fact, it would be sensible to consider the possibility of utilising all those surfaces that have already been modified by humans, for example, roofs of buildings, car parks and any infrastructure that is more or less exposed to the sun.

    Organising a reasonable number of micro power plants that are all linked together in a network could have many advantages. First of all, many micro power plants offer the possibility of producing electricity in situ that can be used directly by consumers in the surrounding area. This eliminates the need to create substantial transport lines. Moreover, placing photovoltaic plants in locations where the albedo and environment are already altered by existing structures should only create minor changes in the environment.

    Final observations

    The evaluations summarised in this article are estimates and therefore further thorough studies should be conducted to be able to assess a series of complex factors, such as the energy necessary to build infrastructure and power plants.

    These studies should be carried out by a team of experts in different fields in order to get a more comprehensive vision of energy systems and the correct use of resources.

    Obviously, the research and development of new and more efficient technologies must continue and be more incentivised.

    Lastly, we would like to stress that this work has been carried out according to a scientific rather than political economic line.

    Acknowledgements

    Thanks to the Bondeno municipality (FE), Energy Renew S.r.l., ARPA and the University of Ferrara.

    Bibliography

    [1] Degree thesis in Natural Sciences by Elisa Samorì, title of thesis “Evaluation of the Energy Balance in the Production of Energy from Renewable Sources” (“Valutazione del Bilancio Energetico nella Produzione di Energia da Fonti Rinnovabili”), AA 2009/2010.

    The complete text is available online at: index of thesis - italian language

    [2] For the complete bibliography, refer to that of the aforementioned thesis.