History of Abengoa Solar
Abengoa began its involvement in the development of solar technologies in 1984 with the construction of the Solar Almeria Platform in Spain. The company supplied heliostats and glass facets and worked on the construction of the Cesa Tower. Later, in 1987, Abengoa supplied the facets for the heliostat field of the Weizmann Institute in Israel.
This initial work was undertaken by the Abengoa company, Inabensa as part of its construction department.
In the 1990’s, a new department was created devoted to solar R&D projects. In 1983, Abengoa Solar IST (then Industrial Solar Technology) was founded by Ken May with the purpose of developing trough technology that was economically feasible for commercial and industrial applications.
The 90s: Concetrated Solar Power and Photovoltaic R&D Projects
In 1993, Abengoa built Toledo PV, a 1MW turn-key photovoltaic plant, that is owned by Union Fenosa, Endesa and RWE. The project was built with a subsidy from the European Union.
In 1994, several tower R&D projects were initiated. These projects were partially subsidized by the European Union under Framework Programs IV, V and V. R&D focused on different types of receivers. One of the projects, Solgas, focused on steam generation while the other, Colon Star, focused on electricity generation. Between 1995 and 2000, several R&D projects involving troughs began under by the EU Framework Program s IV and V. The following are highlights of the late 90’s R&D projects.
* The Theseus Project: The Theseus Project studied the feasibility of a parabolic trough plant in Greece.
* Eurotrough: Abengoa Solar was one of the leaders in developing the Eurotrough. The purpose of this project was to develop a parabolic trough with improved optical efficiency, and better manufacturing and assembly processes compared to existing designs.
* DISS: A research project investigating the direct generation of steam in the trough receiver. The research goal was a major technical advance leading to a 30% increase in the efficiency of parabolic trough electricity generation.
In the 1990’s Abengoa Solar also collaborated on dish-Stirling projects involving the production of the Eurodish and Envirodish.
Abengoa Solar worked on concentrated photovoltaic projects. The outcome was the low-concentration dishes (Sevilla PV) now installed at the Sanlucar Solar Platform.
During this time, Abengoa Solar IST worked with some of the world’s best labs and institutions to improve and install solar trough systems for industrial and commercial applications.
2004 to Present: Transition from R&D to Commercial Plant Construction
Based on the economic and technical foundation provided by investments in R&D, Abengoa Solar has transitioned into a pioneer in the construction of commercial CSP and PV plants.
In 2007, Abengoa Solar inaugurated the world’s first commercial solar tower plant, the 11 MW, PS10, and the world’s largest low-concentration PV plant ( Sevilla PV, 1.2 MW). These two plants are part of the Sanlucar Platform, which when complete in 2013 will have a total capacity of 300 MW. Such output can supply the needs of 18,000 households in Seville, while eliminating 600,000 tons of CO2 per year. Besides the Sanlucar Platform, Abengoa Solar is building additional plants in Spain, the USA, Algeria and Morocco.
Abengoa Solar New Technologies (NT) is the R&D company of Abengoa Solar in Spain. Abengoa Solar NT collaborates with institutions such as NREL, Ciemat and Fraunhofer, as well as research universities to develop CSP and PV technology. In addition, Abengoa Solar NT performs internally-funded R&D to develop new proprietary knowledge aimed at improving performance and reducing the cost of solar technology.
Photovoltaic (PV) cells use semiconductors to produce electricity. The cell absorbs solar radiation, which excites the electrons inside the cell. A semiconductor must have at least two electric fields. When an electron excited by solar energy leaves its electric field, it seeks to return to its original electric field. In order to do so, it must pass through an external circuit, producing electricity. This is referred to as the photovoltaic effect.
The following are the primary components of PV technology.
- Optics: Different optical elements, such as mirrors and Fresnel lenses, are used to concentrate solar radiation onto a point where a PV cell is located.
- Photovoltaic Cell: The photovoltaic cell is the semiconductor used to produce the photovoltaic effect.
- Inverter: Since the photovoltaic effect produces direct current (DC), an inverter must be used to change it to alternating current (AC).
Types of Photovoltaic Cells
There are two predominate PV systems on the market. Each has their own pros and cons regarding application, efficiency, and cost.
1 Crystallized Silicon (~200 µm)
A double layer antireflection coating is used to reduce reflection losses on the front surface of crystalline silicon wafers. The wafers are about 400 µm thick to ensure near-complete absorption of all photons having energy greater than the band gap. At the bottom of the wafer, a SiO2 layer is inserted between the wafer and the aluminum backing to achieve reflectance back toward the cell.
- Single-Crystalline Si
The semiconductors of most PV cells are made from single-crystalline Si. This requires highly purified silicon to be crystallized into ingots. The ingots are then sliced into thin wafers to make an individual PV cell.
- Polycrystalline Si
Polycrystalline Si cells are produced in a way very similar to single-crystalline cells. The primary difference is that silicon of less purity is used for polycrystalline cells. The result is reduced cost and increased ease of production, but a loss of efficiency.
- Ribbon Si
Ribbon type PV cells are produced in a similar fashion to single- and polycrystalline silicon cells. The primary difference is that a ribbon is grown from molten silicon instead of an ingot. These cells often have a prismatic rainbow appearance due to their antireflective coating.
Thin film (~5 µm):
Thin film semiconductor technology may not be as efficient as traditional semiconductor technology, but its light weight and low cost make it an ideal solution for certain applications.
- Amorphous Si
Unlike crystalline semiconductors which have a band gap of 1.1 eV, by manipulating the alloy of amorphous silicon semiconductors the band gap energy can be tuned between 1.1 eV and 1.75 eV. Additionally, because they have a much greater absorbance than crystalline silicon, amorphous silicon semiconductors can be much thinner (less than 1 µm). Although amorphous Si cells can be manufactured at low temperatures (200-500 C) and at low costs, a major drawback is their light-induced degradation.
- 3 Copper Indium Gallium Diselenide Solar Cells (CIS Cu In Se2)(CIGS Cu(InGa)Se2)
Due to its relatively high efficiency and low material cost, this technology has emerged as one of the most promising thin films. By adjusting the ratio of In to Ga in CIGS cells, the band gap can be tuned between 1.02 eV and 1.68 eV. The absorption elements of CIGS cells are incredibly high, allowing more than 99% of incoming radiation to be absorbed within the first µm of material. Although this technology has a relatively low material cost, the complicated and capital-intensive manufacturing methods remain as significant drawbacks.
- Cadmium Telluride (TeCd)
Cadmium Telluride is another thin film technology that has been available longer and undergone more research than any other thin film technology.
Although there are diverse manufacturing techniques that can be used to produce the films, many of which are promising for large scale production, the cost and potential health concerns remain as drawbacks for this technology.
- Micro Si
Micro silicon cells are expected to surpass the efficiency and performance of amorphous silicon cells and become a competitor with other thin film technologies. The high efficiency and negligible degradation of Micro Si cells has been widely reported.
- Titanium dioxide (TiO2)
Instead of the semiconducting materials used in most cells, TiD cells use a dye-impregnated layer of titanium dioxide to generate voltage. Because of their relatively low cost, TiO technology has the potential to significantly reduce the cost of solar cells.
Offers the best efficiency but requires high direct concentration, and is therefore only viable in some geographies.
- Fresnel point focus (High concentration-GaAs) (GC~500)
Fresnel point lenses concentrate direct solar radiation onto a focal point. Since Fresnel lens can provide concentration ratios of up to 500, the necessary surface area for PV cells is greatly reduced. Since fewer PV cells are needed, it is possible to use high quality, more expensive materials like Gallium Arsenide for the semiconductors.
Gallium Arsenide (GaAs) multi-junction semiconductors: Multi-junction semiconductors is a relatively new technology that offers significantly higher efficiencies than traditional, single-junction semiconductors. Each electrical field junction within a semiconductor has only one band gap energy. Incoming solar radiation will either have less energy than the band gap (and therefore will not be used), more energy than the band gap (and therefore some energy will be wasted), or the exact energy as the band gap. By having multiple junctions, GaAs semiconductors are able to utilize more energy from the incoming solar radiation.
- Fresnel line focus (medium concentration-Si) (GC<500)
Fresnel line lenses are flat cylindrical lenses that condense or diffuse light in a linear direction. This technology has lower concentration ratios than Fresnel point lenses, so high efficiency silicon semiconductors are used instead of expensive GaAs semiconductors.
- Low concentration (2-4 times)
Low concentration (2-4 times) Low concentration technology uses mirrors instead of lenses to concentrate solar radiation. Since the solar radiation is much less condensed, conventional silicon semiconductors are often used because of their affordability.