The world’s first molten salt concentrating solar power plant  

Carbon Commentary has a post on the new solar thermal power demonstration plant that has started operation in Italy -
The world’s first molten salt concentrating solar power plant.

On 14 July 2010 the Italian utility Enel unveiled “Archimede”, the first Concentrating Solar Power (CSP) plant in the World to use molten salts for heat transfer and storage, and the first to be fully integrated to an existing combined-cycle gas power plant. Archimede is a 5 MW plant located in Priolo Gargallo (Sicily), within Europe’s largest petrochemical district. The breakthrough project was co-developed by Enel, one of World’s largest utilities, and ENEA, the Italian National Agency for New Technologies, Energy and Sustainable Economic Development.

Several CSP plants already operate around the world, mainly in the US and Spain. They use synthetic oils to capture the Sun’s energy in the form of heat, by using mirrors that beam sunlight onto a pipe where pressurised oil heats up to around 390°C. A heat exchanger is then used to boil water and run a conventional steam turbine cycle. Older CSP plants can only operate at daytime – when direct sunlight is available -, an issue that has been dealt with in recent years by introducing heat storage, in the form of molten salts. Newer CSP plants, as the many under construction in Spain, use molten salts storage to extend the plants’ daily operating hours. Archimede is the first plant in the world to use molten salts not just to store heat but also to collect it from the sun in the first place.

This is a competitive advantage, for a variety of reasons. Molten salts can operate at higher temperatures than oils (up to 550°C instead of 390°C), therefore increasing efficiency and power output of a plant. With the higher-temperature heat storage allowed by the direct use of salts, the plant can also extend its operating hours well further than an oil-operated CSP plant with molten salt storage, thus working 24 hours a day for several days in the absence of sun or during rainy days. This feature also enables a simplified plant design, as it avoids the need for oil-to-salts heat exchangers, and eliminates the safety and environmental concerns related to the use of oils (molten salts are cheap, non-toxic common fertilizers and do not catch fire, as opposed to synthetic oils currently used in CSP plants around the World). Last but not least, the higher temperatures reached by the molten salts enable the use of steam turbines at the standard pressure/temperature parameters as used in most common gas-cycle fossil power plants. This means that conventional power plants can be integrated – or, in perspective, replaced – with this technology without expensive retrofits to the existing assets.

I have published some more data from ENEA on my blog, regarding their expectations from this technology once it’s fully developed: http://www.opportunityenergy.org/?p=94 :

For a typical 100MW stand alone plant in Egypt, it should look like this:

Annual direct solar radiation: 2.900 kWh/(m2 year)
Total area occupied by the solar collectors: 67 ha
Total area occupied by the solar field: 134 ha
Nominal power output: 100 MW (Peak 485 MW)
Thermal storage capacity: 1.800 MWh
Net annual electricity produced: 369 GWh/year
Plant load factor: 42 %

Total Cost : 157 M€
Specific cost : 1.570 €/kWe
Service life: 25 years
Interest rate: 7%
Annual operating (O&M) costs: 2% of investment cost
Levelized Cost Of Electricity (LCOE): 4,5 €cents/kWh

Obviously, this can be scaled down or up according to needs, as much as the technical data can be changed. Some clients might want more storage to achieve a higher load factor, some might prefer a lower storage capacity, and just modulate the plant according to peak prices (which tend to be matched quite well by nature in this case).