Project: Desert Trinity, Masdar, United Arab Emirates
Architects: Midori Architects, Chennai
Solar electricity generation is one of the very few low carbon energy technologies with the potential to grow extensively. The challenges faced with solar power generation are reducing cost of installed capacity, addressing intermittency of power and grid parity. Though the cost curve of solar photovoltaics has declined rapidly over the last decade, its intermittent nature of energy production is a limitation. On the other hand, Concentrated Solar Power (CSP) produces electricity using the heat of the sun, and is known to be a source of deployable power as it includes a Thermal Energy Storage System (TES). This system allows delivery of power regardless of the position of the sun and carries a zero-fuel cost risk, making it an alluring alternative energy option. Apart from the cost of materials, investment in thermal energy storage and solar field size requirements contribute to the high capital costs involving solar energy plants.
The project represents the three parabolic elements; two solar elements and one wind element that work synergistically to provide a clean and sustainable source of energy. The two concentrated solar paraboloids (solar elements) harness solar energy and the other paraboloid (wind element) comprising helical shaped vertical axis wind turbines (HWT) harness wind energy. The elements have a diameter of 35m each. The weight of the parabolic structure is supported by a concrete pylon in the shape of a hand, which is a representation of the hand of Gaia, the Goddess of the Earth in Greek Mythology. The project’s large energy generation potential with minimum environmental impact is harmonious with preserving nature’s beauty and serves as an example to future generations on sustainable coexistence.
The geographic location of Masdar has high annual solar irradiance (0.265 KW/sqm) with an average annual sunlight of 10 hours per day1, making concentrated solar power an attractive solution. Optimum orientations have been considered (south from east to west) when placing the solar parabolas on the site (300m x 90m) to capture the maximum solar power. The wind parabola consisting of HWTs has been oriented towards north-west, to take advantage of the prevailing winds that blow with an average wind speed of 5.4 m/s. The concentrated solar elements harvest
sunlight to make thermal energy from a strategically designed curved mirror surface onto a focussed collector. Compared to other geometries, a parabolic dish is said to have a higher conversion efficiency2. The concentrated solar element consists of a lightweight polyethylene base film over which a polymer and silver layered mirror film reflects concentrated sunlight onto the receiver.
The mirror film has a reflectivity of 94% which ensures high optical efficiency. Within an airtight chamber, compressed air makes the mirror film take the shape of the parabola over which an Ethylene Tetrafluoroethylene (ETFE) membrane serves as a transparent protective layer tethered by a steel framework. The elements are structurally sound due to the steel framework and pressurised air yet is lightweight permitting ease of installation and portability. The thermal receiver is situated on a parabolic steel outer ring containing the heat transfer fluid flowing in an absorber tube surrounded by vacuum within a glass tubular structure. The elements are tilted at an angle of 24° taking into consideration the optimum tilt angle in summer and winter.
Considering the availability of sand in the region, fluidised sand was proposed as the Heat Transfer Fluid (HTF)3 which is pumped through the parabolic absorber tube from the cold storage tank to the thermal receiver which is placed at the focal point of the paraboloid at a distance of 8.5m from the vertex. The HTF gets heated by reflecting sunlight from the mirror film onto the thermal receiver and once the sand attains a temperature of 550°C, it flows down to the hot storage tank through displacement. This heat is transferred to the steam generator or stored for later use.4 The
backend power block works similar to a thermal plant where steam runs the turbine generators which produces electricity. The HTF runs through a closed loop through the outer ring where it flows back to the elements and gets reheated. The thermal energy storage system ensures that heat is transferred to the steam generator after dusk, by storing energy for a period of four to six hours.
The wind element of the structure holds 53 small Helical Wind Turbines (HWT) within it, which has a paraboloidal configuration, rotating on the vertical axis. The blades of the HWT are attached to multiple central vertical ribs which run parallel, supported by a steel frame. The blades of the HWT can utilize wind from any direction. The system of HWT has a rotor diameter of 2m and a blade length of 5.6m. Carbon fibre reinforced polymer is used for the wind blades to ensure its lightweight which allows the blades to spin faster and capture winds at low velocities. The solar elements are relatively low maintenance because it uses simpler lightweight technology and is a passive system that has no moving parts. The primary materials used are ETFE, mirror film, steel, PET base film, local sand and concrete. The total cost of the two concentrated solar paraboloids is $2.7 million approximately. The cost of constructing the wind paraboloid is approximately $24,000.
The total cost/Watt of the entire installation is $4.94. Balancing solar with wind power eliminates the intermittency issues and combining the two technologies reduces overall delivered power cost. Conventional CSP, require enormous quantities of steel and glass with heavy foundations. The ETFE used here is recyclable and 1/100th the weight of glass, providing a substantial cost benefit as the structural framework requirements are significantly reduced. This makes it an ideal replacement for glass since it transmits approximately 95% of natural light onto the mirror film5. Further weight reduction is facilitated by usage of a polymer mirror film with a silver reflective layer which is 1/3rd the weight of a 4mm glass mirror. The embodied energy of ETFE Foil is less than a 6mm float glass due to its thickness.
An approximate estimate of 2,388 MWh/year electricity is generated through the solar and wind elements. The bridge paved with piezoelectric tiles, also generates energy additionally. The nameplate capacity of a concentrated paraboloid is 267 kWp. Considering a capacity factor of 50%, energy generated through the solar paraboloids is 2,343 MWh/year. The nameplate capacity of
an individual HWT is 0.3 kWp and together generates 45MWh/year, considering a capacity factor of 32%. The amount of electricity consumed by a typical house in Masdar is 10 MWh/year6. Hence, the net energy produced annually can supply peak load demand to more than 238 homes in the UAE. Initial capital investment for solar power is quite high; however, the lifecycle cost is minimal.
In the event of a sandstorm, the residual sand which gets collected on the protective layer of the ETFE membrane can be cleaned using compressed air, thereby reducing the amount of water (a scarce resource in UAE) which would otherwise be required for cleaning. The solar element is a membrane-based solution that can be inflated and deflated making installation and transportation easy, so that it can be erected in an alternate location. CSP remains a land intensive resource. A benefit of vertical design is that it can take advantage of the wind and at the same time facilitates land use for prime agriculture more effectively than urban sprawl. The technology’s ability to produce large-scale generation is an advantage for regions that utilize a centralized electricity distribution system like the UAE.
The project showcases that the transition from an exclusive energy generation system to an enhanced convergence of renewable energy technologies which bypasses the environmental snags of both systems results in a better economic utilisation of nature’s environmental processes. The project is envisioned as the energy park of the future in a public realm that spreads awareness of the need for sustained reduction in energy utilization. As a step further, the pedestrian bridge that unifies the Trinity (three elements) is composed of low carbon concrete with piezoelectric tiles, enabling visitors to contribute towards the generation of energy during their visit to the power plant of the future.
Client: Masdar City
Design team: Architect Suraksha Acharya
Built-up area: 13457sq m (3 paraboloids of 35m height)
Architectural design credit: Suraksha Acharya, Midori Architects
Visualization credit: Suraksha Acharya & Lucid Dreams
Cost of project: $2.7 million