AIRLIGHT ENERGY Innovations
ALE innovative technology is based on flexible pneumatic mirrors combined with concrete frames, a receiver that adds a second concentration axis, which integrates multi-junction cells in the case of CPV, which uses air as thermal fluid combined with a heatstorage system based on the simple heating of gravel for the CSP.
AIRLIGHT ENERGY innovations include:
- Multiarc pneumatic mirror
- Pre-casted fiber reinforced concrete collector
- Two axis receiver
- Pebble bed storage (CSP only)
Multiarc Pneumatic Mirror
The pneumatic mirror systems is composed by a long lasting transparent ETFE foil on the upper side, a silicon fibreglass fabric on the bottom side, and a flexible mirror foil (made of polyester film with a reflective aluminized mirror coating on upper side) well protected inside.
InflaTech is inflated with air at a few mbar overpressure. The result is a 2-volume pillow: the upper volume given by the ETFE and the mirror and the lower volume resulting from the mirror and the silicon fabric. By controlling the pressure difference between the two volumes, it is possible to stretch the mirror foil perfectly, and elastically deform it into a perfect parabolic shape. The pressure difference is being produced by a ventilator system which also filters and de-humidifies the air to preserve the mirror life.
The major benefits are:
A large collector aperture of 9.5m, resulting in increased sun concentration (120-160x) and higher thermal energy for the CSP or electrical energy for CPV.
Significant rigidity at low internal pressure of 2 to 4 millibars to withstand wind loads in excess of 160km/h.
Both mirror and the secondary axis receiver are enclosed in controlled atmosphere with filtered and de-humidified air and do not come into contact with atmospheric agents, dust or dirt.
External ETFE film has excellent self cleaning properties (Teflon). The configuration of the enclosure allows for recycling of 95% of wash water during cleaning. The whole solar field can also be used as a huge water collector in rainy days.
An Automatic self re-alignment of the mirror parabolic shapethrough differential air pressure control.
ETFE and polyester film membranes are produced in large quantities by various suppliers, are delivered in pre-cut rolls with a 1m diameter containing approximately 2’000m2 of mirror and are easy to install.
Precasted Fiber Reinforced Concrete Collector
The membranes are supported on their edge with a simple precast concrete frame. The frame infrastructure can rotate on a single-axis placed at the centre of gravity of the collector. The rotation is controlled by a precomputed solar position based sun tracking system. All frames are manufactured with custom designed concrete mixtures incorporating synthetic fibers to increase tensional strength and additives to accelerate curing time resulting in a very compact and durable concrete. Although specifically designed for a sophisticated air or CPV receiver, the ALE collector is also ready to be equipped with others kind of receivers (thermal oil, direct steam).
Major benefits of concrete structure versus metallic structures are:
- Pre-cast fiber-reinforced concrete structure increases stiffness avoiding mirror shape variations (defocusing) under wind loads and therefore allowing for a larger trough, greater concentration and solar energy.
- Concrete reduces material, construction and logistic costs through the use of local skill and materials, and improves longevity (>60yrs) and durability, reducing maintenance costs.
- Use of fiber reinforcements versus steel rebars reduces corrosion problems.
- Precasting allows accurate and modular production of components.
High dead weight of superstructure eliminates need for underground foundation.
- Because the superstructure is more than 5 meters high,fouling is greatly reduced and less dust/sand reaches the mirror in windy conditions.
- Precisely balanced frame rotates around center of gravity using small, low power, inexpensive asynchronous electric motors.
ALE innovative 2 axis receiver, combined with the primary concentration of pneumatic mirror, allows for a global concentration factor well above 500 suns.
CSP system, by using air as thermal fluid, can reach temperatures in excess of 650°C. To ensure good efficiency, having air as low thermal transport capacity, it is necessary to use a big receiver. Thanks to the large mirrors of ALE technology, this is possible without the shadow generated by the receiver affecting the total efficiency of the system.
Major benefits of the 2 axis receiver are:
- High operating temperature > 650°C (1200°F) at low back radiation losses, allowing higher efficiency of the steam cycle
- Operates near atmospheric pressure enabling use of thin metal piping with no special steel alloys or expensive rotating joints which provide ease of installation and reduced cost.
- Possible leakages will cause efficiency deficits, but doesn’t cause environmental impacts.
- Heat can be easily stored in a packed bed storage system. All such benefits overcoming following traditional inherent issues in using thermal oil, or water as receiving fluids:Thermal oil is expensive and has upper temperature limits of 400°C before degrading and being destroyed. This requires tighter temperature control in each single solar collector.
- Thermal oil operates under high pressure requiring special piping with protection against leakage due to its toxicity.
- Storage options are limited and additional heat exchangers or high pressure vessels are required.
In the CPV system, thanks to the total concentration of 500 suns, the cells are optimally driven. A closed-loop water cooling keeps the cell temperature below 40°C ensuring total efficiency above 25%.
Further advantages are:
- Modular and scalable CPV system, from 1 MW installations, to 100 MW and beyond, taking advantage of the typical cost savings of economies of scale.
- Receiver with 2 axis integrated in a protected and controlled environment and therefore requiring no special maintenance or cleaning.
- Total system efficiency of about 25% with potential to achieve as much as 35% in the future thanks to the evolution of multi junction cell technology.
- Low ambient temperature sensitivity as result of can active cooling system.
- Longer expected cell lifetime due to cell temperature control of the active cooling system.
Pebble bed storage (CSP only)
The use of air as thermal fluid allows the realization of a simple storage system based on the proven (since 1929) packed-bed gravel storage technology consisting of a closed concrete container using silica based pebbles. The energy is stored in stones by a slow, controlled flow of hot air into the tank during the day. Overnight or during peak consumption hours, the process is reversed obtaining hot air out of the storage and being used for power generation. Heat can be released whenever adequate. In ALE design, the release capacity is roughly 3 times higher than the storage capacity and high temperature air can be released until the tank is almost „empty”(cold).
With such concept, the air temperature can be stabilized and grant stable steam parameters for power production.
Major benefits are:
- Continuous operation (7000 h/year) as well as power production on demand to take advantage from electricity price fluctuations.
- Simple, proven and effective technology that has been used for decades (1929). Does not require additional heat exchangers.
- Similar thermal losses as molten salt solutions (thermal losses in the range of 1%/24h)
- Highly competitive, robust, fail safe technology
- Allows steam cycle operation near optimum performance level at higher than competition efficiency due to higher steam temperatures 600°C (1100°F)
- Filler material locally available, non-polluting, non-corrosive and minimal maintenance requirements.
Most traditional CSP plants are operating without storage, but the ones that do have storage face significant limitations:
- Steam storage requires large volumes which inherently limits the obtainable pressures and temperatures and requires high operating and maintenance costs.
- Oil storage is expensive and presents environmental concerns with leakage.
- Molten salt storage is technically complex to handle, highly corrosive, and hazardous in the event of a leak. It requires large volumes of salt which is only available from a limited number of producers, is capital intensive in terms of the auxiliary equipment required and it requires high operating temperatures as it solidifies at 230°C.
Thermodynamic (CSP only)
ALE uses a Rankine cycle to produce electricity from heat stored in the storage. The Rankine cycle is a well known technology installed in thousands of combined-cycle power plants around the world.
Combined with all other ALE innovations, the Rankine cycle provides following benefits:
- The high temperature level achieved with air significantly improves the water-steam cycle, which in turn allows for high steam parameters (>100 bar, >560°C). This is not possible with oil or direct steam systems.
- The ability to store and control the dispatch of the thermal energy allows for the installation of a smaller power block reducing overall CAPEX.
- Because of the higher temperatures and pressures and thus higher water-steam efficiency, ALE is able to use dry cooling (versus wet cooling) of its discharged steam with a lower them competition decrease in thermodynamic efficiency.
- Use of air cooling allows for ALE to strive towards a policy of „zero discharge” in its water use, unlike conventional wet cooled CSP plants.