Energía Hidroeléctrica de Navarra has commissioned a 1.2 MW solar energy plant in Spain. The facility represents an investment of g10.85 million and is the only one in Europe with solar tracking in the entire generation field. One third of the plant is dedicated to analysing the performance of eleven different types of photovoltaic panels

In January 2003, Energía Hidroeléctrica de Navarra (EHN) inaugurated a photovoltaic solar energy plant of 1.2 MW, the largest in Spain in terms of installed capacity. Apart from its size, the facility stands out for two reasons: firstly, because it is the only plant of its kind in Europe to have solar tracking in the entire generation field, and secondly, because it allocates part of its capacity to an experimental area where the performance of eleven types of solar panels is analysed. These panels are produced by nine manufacturers using six different technologies.

Tudela (Navarre), located in the north of Spain around 90 km from the French border, is not one of the famous regions of Spain for tourists seeking the sun. Nor was it famous for wind power 13 years ago when EHN started to measure wind speeds in the region. The company was initially created to operate small hydropower stations, but nowadays wind power covers over 50 per cent of electricity consumption in Navarre and EHN has more than 700 wind turbines in operation.

Faithful to its aim of being present in all renewable energies, EHN also decided to develop photovoltaic solar power in the region. This is why it has chosen Tudela, an area in the south of Navarre with high levels of sunshine hours (1600 kWh per m2 per year) to install this plant, which is quite novel in terms of its power and technological characteristics.

Figure 1. The Tudela photovoltaic plant represents an investment of some g10 million
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The new facility represents an investment of g10.58 million. Promoted by EHN, it is also funded (ten per cent) by the Instituto para la Diversificación y Ahorro de Energía (IDAE), an organization that reports to the Spanish Treasury. It has also obtained the support of the V Framework Programme of the European Union and the Scientific Promotion Programme (Profit) of the Spanish Ministry of Science and Technology.

Figure 2. Plant layout diagram of the Tudela photovoltaic plant
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Estimated production from the solar plant is 1.9 GWh per year. The production of electricity, however, is not the only purpose of the facility. The plant will also be an important test-bed for photovoltaic energy and a benchmark for the whole of Europe, where this technology will develop considerably in the future. Specifically, the plant near Tudela uses software that will provide experience in the monitoring and remote control of photovoltaic power plants. Moreover, the existence of very different solar panel technologies on the same site will mean that comparative studies and trials can be carried out with a view to the future.

Following the sun

The photovoltaic solar plant at Tudela covers a surface area of 70,000 m2 on open sloping land, between 380 and 405 m above sea level and with a gradient of between one and eight per cent. The site is located at 42° 10′ north and 1° 40′ west. EHN has installed 400 sun trackers there that, like sunflowers, follow the sun across the sky to get the maximum exposure possible to its rays.

It is the only plant in Europe that has a computerized solar tracking system in all its photovoltaic panels. The trackers were designed by the engineering team of EHN with the aim of obtaining maximum production levels. They are made of robust materials and are easy to maintain.

The structure is made of galvanised steel and consists of a frame and support, with a crown wheel bearing. This is driven by a motor and turns the screen on which the photovoltaic panels are supported. A back tracking system makes the trackers ‘retreat’ slightly to stop them casting shadows on each other towards the end of the day as the sun goes down.

The control programme and the electrical engineering of the plant were developed by the Spanish company Ingeteam, a regular collaborator of EHN, with which it has introduced major technological changes in the field of wind power. The project engineering for the plant was carried out by AESOL, a subsidiary of EHN.

The electronic monitoring and control system has a triple purpose. Apart from continuous supervision of the operation of the facility as a whole, it evaluates the production levels, availability and energy performance of the plant.

Finally, it generates and transmits information on operational parameters, alarms and warning signals, and takes appropriate action in the event of anomalies. The system consists of a range of equipment (computer, PLCs, meters, etc.) and a series of computer applications adapted to the operational requirements of the photovoltaic plant.

The plant also has a meteorological station that measures parameters such as irradiance on the inclined surface of the panels, ambient temperature, the operating temperature of the cells, wind speed and air humidity.

The four hundred sun trackers give a futuristic air to the steppe-like site where the plant is located. The trackers, always facing the sun, support a total of 12 602 photovoltaic panels that convert the sun’s power into electricity.

Centralized area

About 70 per cent of the plant has been designed with the aim of optimizing the electricity that is sent to the national grid. This, the ‘centralized’ area, has an installed capacity of 856.8 kWp and consists of 280 trackers, each of which is equipped with 36 photovoltaic modules, linked in series.

Figure 3. The centralized area is optimized for supplying power to the national grid
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These 10 080 panels (all BP-585 model) are monocrystalline silicon using Saturn technology, and are manufactured by BP Solar. Some 280 branches emerge from the trackers, in 14 sets of 20. They operate in parallel, two by two, to form seven generating sets.

The parallel connection of the branches is made via two field junction boxes that are strategically located in the photovoltaic field. The terminals and intermediate points of 20 branches reach each one of these boxes.

In each box there are two fuses per branch. On the one hand, they protect the photovoltaic modules against overcurrent and on the other, enable the electrical insulation of a branch in the event of a breakdown or maintenance. Each box contains overvoltage suppressors that make an earth connection in the event of lightning strikes.

These units, each of 122.4 kWp, are connected to seven 100 kW inverters that convert the direct current to alternating current before it is sent to the grid. These seven inverters are made by two different manufacturers (Ingeteam and Enertron) and are located inside the general services building of the plant.

The inverter outputs are connected in parallel to the input of a transformer, which raises the low voltage electricity (380 V) to medium voltage (20 kV). The 1200 kVA transformer is also located in the inverter room and is equipped with the necessary metering, protection and switching components to ensure the safe operation of the installation.

Experimental area

In addition to the energy producing part of the plant, almost one-third of its capacity is dedicated to experimentation and the comparative analysis of different photovoltaic panel technologies. It is a major research facility, equipped with 2522 solar panels with an overall capacity of 321.1 kWp.

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As in the centralized area, these panels are installed on trackers – 120 to be exact – equipped with the same automatic sun tracking system. The basic difference, however, lies in the type of panels installed. In this case, there are 11 different types of panels by nine manufacturers using six different technologies.

The six technologies present are: polycrystalline silicon, monocrystalline silicon, CIS (Copper Indium Diselenide), triple layer, amorphous silicon (fine film) and EFG. The panels are produced in the plants of some of these manufacturers: Kyocera, Mastervolt, ASE, Siemens, Unisolar, EPV, Atersa, Isofotón and BP Solar.

Given the nature of this area of the plant and the need to compare the performance of the different types and models of panels, each tracker has one or two low-powered inverters (0.13-2.5 kWp). Distributed in six groups of 20 trackers each, they make up a platform for a distributed photovoltaic generation system that enables the evaluation and comparison of a number of technological alternatives.

The commercial and experimental nature of the facility will mean that projects can be carried out in collaboration with entities and organizations dedicated to research in this field, such as the Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (Ciemat), the Universidad Pública de Navarra and the National Centre for Renewable Energies (CENER), among other centres and universities.

Once the inverters have transformed the direct current generated by the solar panels into alternate current, both in the centralized and distributed areas, this is transformed to medium voltage inside the plant. From there, the electricity is transmitted underground to an EHN substation located about 2 km away, where the voltage is increased to 66 kV. From there it is transmitted by pylons for about 600 m as far as the connection with the general grid.

Ambitious objectives

The Tudela plant represents a major milestone in an expanding field. The world photovoltaic market is growing at a rate of over 30 per cent per annum (38 per cent in 2001).

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With approximately 1000 MW of installed capacity worldwide, Japan is the country where it is most applied (46 per cent of the world total). In terms of installed capacity it is followed by Germany, with approximately 20 per cent, the USA (17 per cent) and, farther behind, Australia (3.4 per cent), Holland (2.08 per cent), Italy (2.02 per cent), Switzerland (1.78 per cent) and Spain (1.58 per cent).

The level of solar power in Spain contrasts with the strength of the manufacturing sector of photovoltaic modules in the country, where three manufacturers represent eight per cent of the world market and export 80 per cent of their production.

However, the objectives set by the Spanish government are very ambitious in terms of the development of photovoltaic energy over the next few years. The Plan for Renewable Energies aims to reach 144 000 kW of installed capacity in 2010, in contrast to the 15 600 kW accumulated at the end of 2002. In terms of production, the Plan envisages a rise from the 15.3 GWh generated in 1998 to 218 GWh in 2010.

Reaching these objectives will require a major effort, and the plant constructed by EHN in Navarre has become a clear benchmark for the development of solar energy in Spain. This is also how the Spanish government sees it. In the recent inauguration of the plant the Director General of the IDAE, María Isabel Monreal, said that the Tudela plant was “one of our country’s most important contributions to the use of renewable energies and puts Spain in a privileged position on the international scene”.

The region of Navarre is very much part of this effort. It already has 261 photovoltaic installations connected to the grid (total 2800 kWp) representing 40 per cent of the power connected to the grid in the country. This figure is very important if the region’s location and weather conditions are taken into account: it is not exactly the sunniest place in Spain, and certainly does not have nearly as many sunshine hours as the south of the country.

Furthermore, the objectives set out for Spain are in line with those established by the European Union. In its White Paper titled “Energy for the Future: Renewable Energy Sources”, the EU set itself the objective of multiplying the electricity generated from photovoltaic panels by 100 times, i.e. from 30 GWh in 1995 to 3000 GWh in 2010.

Towards a sustainable model

EHN was created in Navarre in 1989 with the immediate objective of building small hydropower stations. It currently operates 25 of these, totalling 64 MW.

Figure 3. Back of a solar tracker
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Nevertheless, its main activity since then has been wind power. In December 1994 the company installed its first wind turbine in Navarre, and has since put more than 1500 turbines into service in Navarre and Castilla-La Mancha – the latter through the company EEE. It has also built the largest biomass plant in Spain near the town of Sangüesa (Navarre) based on straw combustion. It has an installed capacity of 25 MW and will cover 5.5 per cent of the electricity consumption of the region.

EHN also develops thermal and photovoltaic power plants through its subsidiary Aesol. The Tudela plant is the largest project carried out in this field by the company.

According to its Chief Executive Officer, Esteban Morrás, EHN aims to become a “multinational of clean energies”, whose mission is to “show the world that a change in the energy model is technically and economically viable, moving away from a model based on fossil fuels to another sustainable model that cares for the environment and allows people to gain access to development regardless of their place of birth”.