EUCLIDES™ photovoltaic plant

Should you think this web site needs improvement, don't hesitate to let me know. I'll be happy of any constructive criticism. Any comments on terminology and web site content are appreciated. E-mail them to:

Demonstration power plant based on the EUCLIDES^TM (European Concentrated Light Intensity Development of Energy Sources) photovoltaic concentrator

It is said that when Euclides was asked his opinion concerning the gods, he replied, "I know nothing more of them than this, that they have inquisitive persons."

Tracking control unit View of an array Central wheel Connection to the inverters

Euclides System
(courtesy: ITER)

ITER, IES and BP Solarex have carried out the project for the installation of the world largest PV concentration grid connected power plant, the EUCLIDES^TM-THERMI plant. The plant has been installed in the south of Tenerife in the grounds of ITER. This plant is rated 480 kWp and is composed of 14 parallel arrays, each 84 meters long. The arrays are North/South oriented and close to the ground. Each array carries 138 modules and 140 mirrors. The modules are series connected in each array. The geometric concentration ratio is x38,2, 1,2 times the one in the prototype. The mirror technology is based on metallic reflective sheets shaped with ribs to the parabolic profile. Three different materials have been tested to be used as reflective material. The fully encapsulated receiving modules are made of 10 concentration LGBG BP Solarex cells, series connected. The modules are cooled with a passive heat sink. Every two contiguous arrays are connected, in parallel, to one inverter sized 60 kVA. The output voltage at standard operating conditions is 750 Volts. The inverter, without intermediate transformer, was designed and manufactured by ITER. The concentrating optics are mirrors instead of Fresnel lenses used previously in all PV concentration developments. The tracking system is one axis, horizontal, as it is thought that the one-axis solutions are cheaper than the two-axes tracking ones. The concentrating schemes present a more constant output than the flat panels, so they might present some advantage in the value of the electricity produced.

EUCLIDES^TM plant construction details

The plant is composed of 14 arrays 84 meters long, and its nominal power is 480 kWp. Each array has 138 modules and 140 mirrors. The 138 modules are series connected in each array. They provide a minimum acceptable voltage over 700 Volts at the worst conditions, in order to use a "true" three phase inverter without intermediate transformer. The solution adopted for the DC/AC conversion is not conventional. Following common practice, the installation of one single inverter for the whole plant could be considered. However, for the sake of modularity, it would be preferable that every EUCLIDES^TM concentrator unit were delivered provided with its own inverter. Although such an approach guarantees the maximum modularity of the system and also gives very good reliability (the failure of an inverter affects only one unit), economical considerations and marketing advised that two arrays could share the same inverter. Modularity is then kept at the level of 68 kWp.

EUCLIDES concentrator prototype

EUCLIDES^TM Concentrator
(courtesy: ITER)

Therefore, this EUCLIDES^TM plant has seven modular inverters 68 kWp, for every two arrays. Another novelty of the solution adopted is the connection of all inverters in parallel on the primary of the transformer (380V/20KV) used to connect the whole plant to the grid. Avoiding the intermediate transformer saves around 4% of the overall energy of the plant. The module is composed of 10 LGBG cells from BP Solarex. The cells are fully encapsulated on a module. The length of the module is 1.20 meters like in the prototype, but now the cells are larger and only 10 are included on it, instead of 12. The new size of the cells provides several advantages as saving material and cell fabrication costs, decrease the optical mismatch losses between mirror and receiver and reducing the overheating of any reverse biased cell because only 10 cells are now by-passed by a diode, instead of the 12 cells in the prototype. In the new modules the series resistance of the interconnection tabs has been reduced: the 13.2 mohm with the old tabs becomes only 10 mohm with the new ones. The effect in the total efficiency at STC, 25^oC is to pass from 16.9% to 17.4%. Another improvement achieved in the new modules is the reduction of the thermal drop between the cell and the aluminium substratum, affecting significantly the efficiency. The size of the array, 84 meters long and 250 m²of aperture, has been optimised to share the structure and the tracking system costs. The design of the prototype structure has been revised to reduce components, to simplify the fabrication, to withstand the larger forces on the system and to easy the transportation and field installation. The concentrating optics consists on parabolic mirrors mounted in a continuous way along the 84 meters array in order to avoid shadows in the cells. The mirror will cast the energy in a strip 26 mm wide (the active cell width is 40 mm). The mirror aperture is 1.2 times larger than the prototype, so the energy output is increased about 1.16 times. The mirrors are made of reflective sheets glued on aluminium plates that are shaped to a parabola profile using two ribs. The reflective surface used in the prototype, the acrylic silvered film ECP305 from 3M seemed to be the best reflective material for our mirror technology. But 3M retired the material from the market, and we were forced to research on alternative materials. Finally, three different reflective films were selected: (a) 4 arrays with aluminium sheets with a thin dielectric coating to increase its reflectivity, laminated on an aluminium substratum 1.5 mm thick. (b) a Sylverlux film from 3M. It consists on a polyester substratum with an acrylic adhesive and a thin silver coating, protected with two transparent weather-resistant acrylic films. This option was used in 9 arrays (c) 1 array with a factory-made sandwich of a weather-resistant silvered plastic film on 1.5 mm thick aluminium substratum. The reflectivity of the options b) and c) are practically the same than the ECP305 film, but the reflectivity of the polished aluminium is only 82%. Due to the associated decrease of the cell temperature, the annual energy produced is reduced 7%. As this affects only to 4 arrays, the percentage of losses for the total plant due to the lower reflectivity is only 2%.

EUCLIDES power plant

Tracking structure

EUCLIDES^TM Power Plant
(courtesy: ITER)

Text and pictures published with kindly permission of ITER - Instituto Tecnológico y de Energías Renovables, Polígono Industrial de Granadilla, E-38611 S/C de Tenerife, Islas Canarias, Espana

PV Module Tracking Structure
(courtesy: ITER)

Literature and more information

Polytechnical University of Madrid - The Institute of Energía Solar (IES): History of Modern Concentrators (678 kB).
Sala, G., Antón, I., Arboiro, J.C., Luque, A.: Instituto de Energía Solar UPM, Madrid, Spain; Camblor, E., Mera, E., Data, P., BP Solar, Espana; Gasson, M., Mason, H., Heasman, K., Bruton, T.: BP Solar Ltd Sunbury - on Thames, UK; Cendagorta, M., Valera, P., Friend, M.P., Monedero, J., González, S., Dobon, F., Perez, F.: ITER; Luque, I.: INSPIRA, Madrid, Spain: 480 kWpeak EUCLIDES™ Concentrator Power Plant Using Parabolic Troughs (1,51 MB).
Sala, G., Antón, I., Arboiro, J.C., Luque, A.: Instituto de Energía Solar UPM, Madrid, Spain; Camblor, E., Mera, E., Gasson, M.: B.P.Solar Ltd Sunbury - on Thames, UK; Cendagorta, M., Valera, P., Friend, M.P., Monedero, J., González, S., Dobon, F.: ITER; Luque, I.: INSPIRA, Madrid, Spain; The 480 kWp Euclides-Thermie Power Plant: Installation, set-up and first results (168 kB).
Instituto Tecnológico y de Energías Renovables - ITER