The paper presents the main results of the MODENER research project ("Energy model based on an intensive use of renewable energy applied to Jaen province") that is aimed to assess the production capacity of olive pruning biomass, and PV massive grid integration, that will be usable for electricity generation and its distribution across the province of Jaén, in a realistic way.
The methodology, based on the intensive use of GIS tools, includes the development of a distribution map of olive trees whose pruning residuals are likely to be exploited for energy purposes, including information on major agroclimatic variables characterizing them. Furthermore, an extensive field experience based on sampling data in different parts of the region (weighing of pruning olive residuals and characterization of olive trees) has enabled us to determine the variables affecting olive pruning biomass production and to develop a biomass generation predictive model. The application of this predictive model to the distribution map characterizing olive trees will has also allowed us to generate a realistic distribution map of olive pruning biomass
Results arisen from the project highlight that more than 750.000 biomass tons can be yearly generated from olive pruning, which means that more than 90 MW of power can be installed, and that Solar PV can also be extensively used to cover up to 44% of the electricity demand in the region.
1. ModEner Research project
ModEner Research Project ("Energy model based on an intensive use of renewable energy applied to Jaen province"), that is currently being developed at University of Jaen under the sponsorship of Andalusian regional government, is intended to research, analyze and develop an energy model based on an intensive use of renewable energy for generating electricity, applied to the province of Jaén (Andalusia, southern Spain).
The project is focused on biomass and solar photovoltaics, since they are the most promising renewable resources in the region ([1], [2]). On one hand, olive grove is a huge source of biomass resources in Andalusian region, southern Spain, since most of its territory is dedicated to that crop. In this way, pruning residuals are quantitatively the most important fraction of those resources and they are proved to be an excellent raw material for renewable energy generation. Currently, they do not present any alternative use and are considered by olive growers as a waste for disposal, whose most common destination is to be burned in the field [3]. On the other hand, solar radiation is the other main renewable resource in the region, as it is able to provide a mean production of more than 1,500 kWh per kWp of PV electricity [4].
In order to fulfill project objectives, twenty four work packages were planned and executed. We can quote the followings: Project management, Web site implementation, Regional electricity system analysis, Commissioning of a support GIS tool, Design of an experimental procedure to achieve a biomass predictive model, Extensive field experience to quantify olive pruning biomass, Biomass potential determination, Assessment of biomass electricity generation, Regional solar radiation assessment, Assessment of PV electricity generation, Design of regional energy model, Analysis of the impact on electricity grid, and Assessment of socioeconomic and environmental issues.
2. Biomass potential assessment
A stepwise methodology, based on the intensive use of GIS tools, has been used to assess the olive pruning biomass potential in the region. The procedure includes the development of a distribution map of olive trees whose pruning residuals are likely to be exploited for energy purposes, including information on major agroclimatic variables characterizing them, and also includes an extensive field experience based on sampling data in different parts of the region.
It is worth to mention that more than nine million hectares of olive trees are cultivated all over the world, especially in the Mediterranean countries. As an essential operation, pruning of olive trees produces a huge amount of biomass which is currently lacking of industrial applications and must be, in a yearly basis, eliminated from fields to prevent propagation of vegetal diseases. The biomass produced from pruning is usually eliminated by direct burning or by grinding and scattering.
The quantification of the yearly available biomass is an issue that has not yet been properly established. The published reports estimate the production of biomass in a range as wide as between 1 and 5 tons per hectare [5]. This is the main justification of the work done under ModEner Research Project dealing with the estimation of the real biomass production from olive tree pruning by using statistical methods, and applying it to the province of Jaén (Spain), the main olive tree region in the world.
For this purpose, an extensive field experience was performed. It was based on weighing pruning residuals of olive trees in plots with different combinations of factors that could influence the residues generation, in different parts of the province. At the same time, several important factors relative to the pruning location were also recorded, among them: slope, irrigation, tree density, water soil retention, soil capability, altitude, soil depth, number of trunks of the tree and density (number of trees per ha). The region to be studied, Jaén province, was divided in six homogeneous agroclimatic zones of olivestrees, which were treated as strata in a stratified sampling. Weighing of pruning olive residuals in 38
different areas and taking measures from 151 samples, and the characterization of olive trees involved, has enabled us to determine the variables affecting olive pruning biomass production and to develop a biomass generation predictive model. The application of this predictive model to the distribution map characterizing olive trees will also allow us to generate a realistic distribution map of olive pruning biomass.
Fig. 1. Olive groves in Jaen province and sample points locations (38 areas, 151 sample points)
Later on, a regression model was developed to predict the dry biomass obtained from the explicative or independent variables. The approach used to fit the regression model was a stepwise regression by backward elimination. The dependent variable is the log of the tons per ha. The results show that significant factors having influence on olive pruning biomass production are (p<0.01, ANOVA): the homogenous area; slope; if it is an irrigated land or not; number of trunks of the tree; soil depth; and altitude.
Once the regression model was fitted, the goodness of fit of the model was checked by the diagnosis of the model showing that there are not violations of the statistical assumptions. The specification of the model was tested by the Ramsey regression equation specification error test (RESET test). The pvalues obtained are greater than 0.01 so there are not statistical reasons to think that the model suffers from mis-specification. In this sense, the regression model fitted is adequate to predict the dependent variable.
The final distribution map of olive pruning biomass that was obtained shows that the overall biomass production is 758.197 tons per year, considering only those land surfaces with a slope below 20%. Considering the biomass potential, biomass characterisation and similar installations already functioning, the exploitation of olive pruning could be the basis for 92 MW of new installed power that could generate more than 690 GWh per year, which is 23,7% of the yearly electricity consumption of the region.
Fig. 2. Biomass potential map
3. Photovoltaics potential assessment
An initial prediction of solar radiation for the region was carried out by means of artificial neural networks models [6]. Perceptron Multilayer model was chosen for the analysis and different solar radiation maps were generated for the different inclinations from 0º (horizontal surface) to 90ª (vertical surface) and grouped by month and an annual average.
Following, a set of criteria was established to determine which areas could be appropriate for PV installation in accordance with project objectives. Due to recent changes in Spanish legislation the best option to consider was the implementation of a great number of small PV building-integrated plants, as smart grids for distributed generation, instead of bigger isolated plants.
The proposal arisen from ModEner Project has been focused on available industrial areas. These areas shows a number of advantages: they have a high percentage of suitable surface for PV, visual impact is improved, there is no need of additional land and the technical installation is easy.
Fig. 3. Average solar radiation
Total capacity for PV power plants has been calculated in three different scenarios, 100%, 33% and 10% of the use of the available surface, and the optimal type of PV plant (flat, inclined or inclined by slope) has also been established. The total amount of suitable surface is 1.641 Ha, and the maximum PV potential is 1289 MWp. In a more realistic scenario, the total PV power to be installed would be 431 MWp, that would generated more than 580 GWh of annual energy. This figure represents 20% of the total electricity consumption in the region.
Table 1. PV power potential and annual PV electricity generation
4. Conclusions and main results from ModEner Project
Results arisen from ModEner Research Project highlight that more than 750.000 biomass tons can be yearly generated from olive pruning in the region, which means that more than 92 MW of power can be installed. Concerning Solar PV, the exploitation of suitable industrial areas can contribute to the installation of 431 MWp in a realistic scenario.
Combination of biomass and PV electricity may provide the regional energy system with more than 1270 GWh, which roughly represents 44% of the annual electricity consumption.
5. Acknowledgements
Authors want to acknowledge the Regional Government of Andalusia for financial support (Proyectos de Excelencia, ref. P09-TEP-5254). MODENER PROJECT.
6. References
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- Terrados J, Almonacid G, Perez-Higueras P. 2009. Proposal for a combined methodology for renewable energy planning. Application to a Spanish region. Renewable and Sustainable Energy Reviews, 2009; 13: 2022-2030.UNEF. 2012. Unión Española Fotovoltaica
- Gallego FJ, Terrados J, Lara PJ, Almonacid G, Castro E (2011). Aprovechamiento masivo para producción de electricidad del potencial biomásico procedente de la poda del olivo de la provincia de Jaén. X Congreso Nacional de MedioAmbiente. Madrid.
- Ruiz-Arias J.A., J. Terrados, P. Pérez-Higueras, D. Pozo-Vázquez, and G. Almonacid. 2012. Assessment of the renewable energies potential for intensive electricity production in the province of Jaén, southern Spain. Renewable and Sustainable Energy Reviews; 16(5): 2994- 3001
- Gallego FJ, Terrados Julio, Ruiz-Ramos E, Romero I, Martínez-Rodríguez AM, Guzmán A, Mesa JL, Castro E (2013). Model for estimating biomass potential from olive pruning in the province of Jaén (Southern Spain). Proceedings of the 2nd Iberoamerican Congress on Biorefineries.
- Hontoria, L. 2002. Generación de series sintéticas de radiación solar combinando herramientas estadísticas y redes neuronales. Tesis Doctoral.
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