Interview by Rikki Stancich

Last week, Fresnel technology developer, Airlight Energy signed a deal with cement producer, Italgen, for the construction of a concentrated solar power plant at Italcementi’s cement plant in Ait Baha (Morocco). 

The solar field, comprising three solar collectors and a storage unit, is to be constructed using Airlight Energy’s proprietary Fresnel technology and air receivers. The solar field will be integrated into the cement plant’s existing heat recovery system, to provide an additional150kw of on-demand electric power. 

The project, which requires an investment of €2.7mn, will be installed within a 12-month period. CSP Today speaks to Airlight’s CTO, Andrea Pedretti, to learn more about this latest Fresnel technology.

CSP Today: Airlight's 'Flaming Air' air-based fresnel receivers can generate temperatures of above 650 degrees celcius. Can you explain more about the low-pressure receiver technology configuration?

Andrea Pedretti: Our primary mirror is a trough configuration, and the primary mirror is 9.5 m net aperture which enables very high concentration compared to existing systems that are typically smaller (around 5 m). With a secondary concentration optic we enter in our receiver which uses air as the heat transfer fluid.

The air pipe is at low pressure like a traditional HVAC duct for air conditioning; despite the higher temperature, the technology is simple. We are able to use air, which requires a large pipe, because our structure is large enough and receiver does not create any shadow on the primary mirror.

Unlike thermal oil, air is not constrained by temperature and the pumping power, (which was our main concern), is not so dramatic as the temperatures are higher compared to thermal oil.

CSP Today:  Airlight Energy has developed proprietary mirror technology: the reflectors are Airlight Energy's 'Inflatech' aluminized polyester foils. These reflectors are housed within a controlled atmosphere, with transparent ETFE foils (above) and a fiberglass membrane (beneath), which protect the reflectors from dust and humidity. To what extent does the outer membrane deflect sunlight that would otherwise be harnessed by the collector mirrors? What is the reflectivity of the Inflatech mirrors?

Andrea Pedretti: ETFE reduces the optical efficiency like any other protective coating. We lose around 8% but the reflectivity of the mirror (96%) and all the components inside (receiver, too) are well protected.

CSP Today: Does the mirror efficiency cancel out the additional cost of the engineering involved with these collectors?

Andrea Pedretti: The collector cost is much less compared to steel or alu frame and current glass or alu mirror. Our mirror foil is 0.5€/m2 compared to 20€/m2 or more for glass mirror. No special materials are used; concrete can be manufactured everywhere.

An accurate steel frame cannot be produced in a low developed country and should be manufactured in Europe and transported to Africa.

CSP Today: Airlight Energy uses pre-cast concrete and plastic fibre reinforced support structures. Why did you opt to use these materials, from a logistics perspective?

Andrea Pedretti: The main innovation is to build the concrete elements on site like any other concrete structure using local, raw materials (sand, gravel, etc), and in this way, avoiding all the transport costs.

The idea is that we transport our molds on site and produce locally with local people.

CSP Today: Why did Airlight opt for concrete over lighter weight materials?

Andrea Pedretti: Costs - concrete costs 0.1€/kg is 20 times less expensive than any other construction material. Logistics were also a major factor, as I have just mentioned. Concrete also provides stiffness, and is maintenance free.

CSP Today: What are the estimated O&M costs for an Airlight solar field designed for a 150MW plant, and what is the water requirement and cost of running the automated mirror washing system?

Andrea Pedretti: The O&M costs are comparable to existing systems.

We have the advantage of being able to collect rain and therefore recycle the washing water.

CSP Today: The ETFE foils are said to be 'self cleaning' and the system comes with an automated mirror washing system. How exactly is the ETFE material 'self-cleaning'?

Andrea Pedretti: ETFE is Teflon; dirt cannot attach to the surface easily.

CSP Today: Airlight Energy is to deploy its air-based fresnel receiver CSP technology in Morocco, to produce energy for a cement plant. Three solar collectors, plus a thermal storage system will be installed, to provide 150kw of energy on-demand, providing a good example of Airlight Energy's modularity. Is this technology better suited to industrial processes, or are there plans for deployment on a utility-scale?

Andrea Pedretti: Both. Waste heat recovery is a plus we have. Basically using air as HTF we are very compatible with many industrial processes, so we may connect to waste heat recovery without any additional heat exchanger.  

CSP Today: What is the estimated LCOE for a 150MW Airlight Energy CSP plant?

Andrea Pedretti: It strongly depends on the location. Every project has its unique economics. Using local resources, the cost of the plant varies dramatically from site-to-site

To respond to this article, please write to the Editor:

Rikki Stancich: rstancich@csptoday.com

Image credit: Images courtesy of Airlght Energy