"Low cost storage technologies are indeed a key aspect for CSP plant exploitation"

At the time of planning of the Archimede Project, Enel had stated that its main objective was to acquire top level of expertise in concentrating solar technology. 

The project is based on a technology devised by ENEA (Italian Governmental Agency for Energy Research).

ENEL's power plant at Priolo Gargallo (Siracusa, Sicily) has been deemed apt to host the project deployment both due to its very high values of insolation (incoming solar radiation) and to the site morphologic features (orography). The concentrating solar system will be totally integrated with the thermodynamic cycle and with the equipment and services already existing in the power plant.

Recently, Enel begun testing of solar thermal generation with the Archimede project.

Providing an insight into the current status, Gianluca Gigliucci, head of renewable energy research, Enel told CSPToday.com: "After a long period necessary to get the construction licences, the plant is now under construction. Civil works as well as procurement are in an advanced phase of development. Plant commissioning is planned for the middle of 2010."

According to the company, this is the world's first example of a combined-cycle gas plant integrated with a solar plant. The new solar energy system by concentrating the direct sunlight through parabolic mirrors can convert solar energy into high temperature heat, which, due to the properties of the salt fluid being used, can be stored and made available at any time of the day when needed, thus avoiding supply discontinuit typical of other renewable sources. The thermal energy will be used to produce steam at high temperature (535°C or so) and high pressure (110bar), suitable for combined cycle steam turbine.

Gigliucci shared that the solar plant is designed to produce high quality steam, 540°C temperature with respect to 390°C of diatermic oil-based plants, that can be directly used in the high pressure stage of the steam turbine of the combined cycle plant.

"This has implied the use of molten salts not only for storage, but also as heat transfer fluid and the consequent development of innovative components,  first of all the heat collection elements of the solar troughs," said Gigliucci.

"Moreover the use of molten salts as HTF allows to avoid the presence of heat exchangers between the solar field and the storage system, thus increasing plant efficiency," said Gigliucci. "Finally, the use of molten salts gives Archimede plant a further environmental advantage compared to the oil-based plants, due to the environmental compatibility of the molten salts."

In the past, it has been shared that this thermoelectric plant is composed of two units of 380 MWe capacity each (250 MWe gas turbine line and 130 MWe steam line) and the "Solar Field" will consist of 72 parabolic solar collectors with a total active surface of about 40,000 square meters.

Providing an insight on designing and achieving optimal results from cost for produced energy perspective, Gigliucci said in the final configuration the solar plant consists of 54 parabolic solar collectors and an active surface of about 30,000 square meters. The storage system is of about 100 MWh thermal.

"The possibility to increase HTF temperature up to 550°C is the key aspect, together with hybridisation, allowing a very high efficiency to be reached (i.e. almost 16 percent net average annual sun-to-electricity conversion)."

"High efficiency together with cost reductions predicted both for the heat collecting elements and storage systems  allow  very  promising perspectives on the cost of the produced energy."

According to Gigliucci, hybrid plants with existing combined cycles will therefore constitute a very effective mean to increase CSP plant penetration even in case of sites that would not allow investment proficiency for stand-alone plants.

Also, Gigliucci mentioned that low cost storage technologies are indeed a key aspect for CSP plant exploitation and should be regarded as one of the key R&D topics, as their availability would allow reliable power production forecasting, avoiding instability problems for existing grids in case of high fraction of renewable energy production and allowing higher investment proficiency thanks to energy dispatching on actual peak hours along the whole year.

Birth of Enel Green Power

Enel recently announced the birth of Enel Green Power, a group company which will focus on developing and operating power generation from renewable resources in Italy and around the world. 

Enel Green Power is currently analysing the benefits of the various options available, such as semiconductor alternatives to silicon that can achieve very high levels of efficiency, as well as concentration systems with heat recovery.

The new company's business incorporates all of Enel's activities in the wind, solar, geothermal, run-of-the-river hydroelectric and biomass fields in Europe, North America and Central and South America. Enel Green Power also controls Enel.si, anoperator in photovoltaic and solar thermal power, with a market share of 35 percent.

As far as the CSP industry is concerned, Gigliucci said Enel Green Power is concentrating on the development of a portfolio of renewable energy diversified by technology as well as by country.

"CSP can play a significant role in this portfolio, in particular in countries where high levels of solar radiation can be captured. At the same time, the selection of projects on a world-wide basis follows, independently from technologies or countries, one simple rule: the most efficient and economic solution will always prevail," said Gigliucci.