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Research

Solar Energy & Desalination

Solar Energy research is conducted within the context of international collaborations (principally EU) and in in-house programs. In the past significant activity was conducted with the context of the CyI – MIT collaboration and in particular in collaboration with the MIT Energy initiative (MITei). The development of the program of the Institute and in particular of the Solar Thermal Energy component has been selected by the Institute for fast track development with significant investments in infrastructure. A very important enhancement of the research activities and associated personnel is programmed as a result of the award of the ERA chair (CyI Solar Thermal Energy Chair for the Eastern Mediterranean: CySTEM – Chair). Activities of the CySTEM Chair started in July 2015 and will last for five years.

 

Solar Harvesting

 

Solar Energy Receivers

Solar-thermal receivers are the entry point of solar energy to the overall solar power plant. Low-capital cost and overall efficiency of such a receiver are the first design optimization targets to ensure excellence in the design of the solar power plant. In particular, the optimization of concentrated solar power (CSP) receiver technology for the Mediterranean islands has been at the centre of research and development at the EEWRC.

The adopted design optimization philosophy is based on the Integrated Storage Receiver or ISTORE concept [1]. As the name suggest, the innovation of the design lies on the fact that it allows for merging the solar-plant thermal storage and receiver as one unit, thereby, minimising capital cost as well as minimising the pipeline network size and pump operational costs.

The figure depicts the isometric view of a first realization of this device (ISTORE-MkI). Solar radiation is directed from the heliostat field onto the internal surface of the cavity of the ISTORE. The principal cavity is of cylindrical shape expanding in four secondary cavities on the backside. The secondary cavities help to improve the capturing efficiency of the device and provide a larger surface area for heat transfer between the absorber and the heat transfer/storage fluid. The external surface of the cavity is in contact with the molten salt in the storage tank that surrounds it. The receiver is made of AISI SS321H and uses solar salt as the heat transfer fluid and storage medium. In this first realization of ISTORE the energy storage capacity of the device is small and molten salt is recirculated to a separate storage tank. It is admitted to the device through a set of nozzles located at the backside and bottom of the cavity external shell.

isometric left isometric right

 

Figure 1. Isometric view (left) and typical CFD simulation (temperature distribution in K, right) for ISTORE.

Research and development work this far dealt with the light absorption capability and thermo-fluid aspects of the design. In figure 2, a sun-ray tracing visualization using the Monte Carlo technique is shown. Sample data from the computational fluid dynamics, CFD, modelling is also illustrated in this figure.

 

eewrc energy research srt full

Figure 2: Typical sun-ray tracing results (left) using the Monte Carlo technique and OpenFOAM CFD simulation data (temperature distribution in Kelvin) for the ISTORE.

The ISTORE is currently installed at the Cyprus Institute solar facility PROTEAS. Future experimental work will be concerned with inferring the solar flux and temperature distribution across the receiver surface. The experimental data bank will then help establish the measure receiver efficiency and validate the mathematical models employed in the design development of the ISTORE.

References:

[1] ISTORE: C.N. Papanicolas, patent application, US20130074826 and EP2573484, March 28 2013.

 

Thermal Storage: TESLAB Facility

The principle drawback of renewable energies is the fluctuations of the availability of the resource. This stands also for Concentrated Solar Power (CSP). In order to overcome this issue, the Cyprus Institute (CyI) leads experiments on Thermal Energy Storage (TES) of molten salts like in the PROTEAS Facility, but in a lower scale (Figure 1). Thermal Energy Storage permits to store energy as heat and to useable in cloudy conditions or during the first hours of the night. The hot molten salts converts water to steam thanks to a serpentine coil inside for electricity production via a turbine (Rankine cycle). 34 thermocouples are welded along the wall of the tank (Figure 2) and some of them on the different insulation layers. This permits the control and monitoring of the full system, ensured by a Visual Instrument in Labview (Figure 3).


 

 

Figure 3. Molten salts tank (TESLAB)

salts tank

 

Figure 4. Drawing of the thermocouples of the tank

tank drawing

TESLAB (Thermal Energy Storage LABoratory) Facility has 2 tons molten salts storage which characteristics are:

 

  • Molten salts quantity : 2160 kg (1.1 m3),
  • Mixture: KNO3 (40%) and NaNO3 (60%),
  • Heat capacity mixture: 1590 J/kg/K (at 500°C)
  • Melting point : 221°C,
  • Freezing point: 238°C
  • Heaters capacity: 2 heaters (9 kW electric each), PID controller.

 

Solar Desalination

Water is at the core of human development and, aside from direct consumption, it is used in agriculture, energy production and various other industrial processes. However, according to the World Bank, more than one sixth of the world’s population does not have access to safe drinking water (80% of which live in rural areas) generating social imbalance. UN projections show that by 2025 2.8 billion people will face water stress or water poverty conditions.
Climate projections for the Mediterranean region predict an increase in both minimum and maximum annual mean temperatures of 3 °C, as well as a decrease in precipitation on the order of 20%. Taking into account that currently 300 million people live in the Middle East North Africa (MENA) region, and that this number is expected to double by 2050, a severe stress is imposed on the available fresh water resources and a bleak picture is painted for the near future.
Although many techniques are available for supplying more water, such as wastewater treatment and reuse, or brackish water treatment, a virtually unlimited water source comes from the oceans and seas (out of 1.4 billion cubic kilometres of water that make up the earth’s water reserve, 97.6% is saltwater). Several seawater desalination technologies have been developed, which can broadly be classified based on the separation technique used into thermal and membrane processes. The former rely on an evaporation process whereas the latter on a separation process through an appropriate selective membrane.
Desalination is inherently an energy intensive process. The minimum energy required for desalination can be estimated theoretically from the thermodynamic work for separation and is 1.12 kWh/m3, assuming an infinitesimal production of fresh water from a 4.5% saline solution. In real processes however, energy requirements in the order of 3-3.5 kWh/m3 (in the form of electricity) for reverse osmosis (RO) and 18-30 kWh/m3 (in the form of thermal energy and electricity) for multi-effect distillation (MED) have been reported, making desalination based on fossil fuels neither sustainable nor economically feasible in the long term.
The Solar Energy and Desalination Group at The Cyprus Institute aims at researching novel ways of combining solar energy and desalination, with the following objectives


• Increase the process efficiency by thermodynamically integrating the electricity and desalination cycles into a single process
• Optimally utilize the available energy to maximize production
• Improve the thermal efficiency of MED units
• Investigate transient behaviour of MED plants
• Designing autonomously powered small-scale desalination plants


The group has two custom-designed novel 4-effect MED units, one operating in a laboratory setting and the other fully integrated with a solar-thermal plant at the PROTEAS laboratory in Pentakomo.

 

Additional Info

Relevant publications:

Techno-economic assessment of a pilot-scale plant for solar desalination based on existing plate and frame MD technology

E Guillén-Burrieza, DC Alarcón-Padilla, P Palenzuela, G Zaragoza

Desalination 374, 70-80, 2015

 

Membrane structure and surface morphology impact on the wetting of MD membranes

E Guillen-Burrieza, A Servi, BS Lalia, HA Arafat

Journal of Membrane Science 483, 94-103, 2015

 

 

Solar Thermal Steam Generation

The production of steam is a typical process in a concentrated solar power plant. It is commonly used as the working fluid for the conversion of solar thermal energy to electricity and/or for driving seawater desalination. Steam power thermodynamics are thus one of the core areas of design and optimization of the EEWRC.

The principal aim is the development of numerical fluid and heat transfer models for the design of a water preheating and steam generation system, namely coil heat exchangers. In-house codes were developed and their results were compared to commercial CFD packages such as Comsol Multiphysics. Prototype performance testing in the 10kW steam power range demonstrated the adequate prediction capabilities of the design methodologies adopted. Further work is currently aiming at producing steam power in the 150 kW range. In figure 1, the preheater and steam generator coils designed for this level of power output are shown.

eewrc energy res heatxfer

Figure 5: An isometric view of the preheater and steam generator coil and blue and yellow colour respectively. The coil heat exchanger is capable of generating up to 150 kW of the saturated steam at 12bar-g for the cogeneration of electricity and desalinated water at the PROTEAS CSP plant.

The coils consists of AISI 40S 316 Φ0.5” piping. The preheater (top coil) is suspended over the molten solar salt surface while the steam generator (bottom) coil is immersed in the salt. The produced steam power aims at rendering the PROTEAS plant self-sufficient, that is, produce enough power for solar salt pumping, pipeline heat tracing, drive various instrumentation, as well as for driving the Multi-effect desalination unit.

 

Solar Thermal Electricity Production

One of the techniques in raising the overall solar-thermal efficiency in a CSP plant is through polygeneration. In the EEWRC, considering the needs for water desalination in the Middle Eastern Mediterranean region, the conventional steam power (Rankine) cycle has been combined with Multi-effect desalination, MED.

Current work demonstrated the successful commission of each subsystem for electricity production and MED. Figure 6 is a schematic of the combined Rankine cycle and MED unit.

eewrc energy research rankine cycle

Figure 6: A simplified schematic illustrating the hybrid power station for the co-generation of electricity and seawater desalination at the PROTEAS CSP plant (arrow-heads indicate the direction of steam or liquid water flow).

Further work aims at establishing the combined efficiency and further optimization of this type of polygenerative system. This work will also involve sizing-up the output capacity of the plant from 1.5 kWe to 15 kWe to ultimately allow for self-sufficiency of the PROTEAS facility.

 

 

Energy Futures-Sustainability -Built Environment

Smart, Energy Efficient Buildings

Microgrids

Natural resources integration

The Energy Division has worked together with the MIT Energy Initiative (mitei.mit.edu) to produce a series of reports on the monetisation potential of Natural Gas for Cyprus

Energy Systems modeling

Modelling systems is crucial in order to take decisions like supporting HVAC of a building with a Fresnel collector in order to reduce the dependency to fossil fuels/electricity. Simulations with models permit to size components to achieve objectives of energy reduction. The Cyprus Institute (CyI) leads simulations in solar energy fields at CFD level (Fluent, COMSOL, ANSYS) used for the PROTEAS facility and system level (EES, TRNSYS) used for STSMED project.

Solar cooling under STMED project was first designed using TRNSYS software suite. It started with the identification of the power units of the HVAC system of the Novel Technology Laboratory (NTL) such as heat-pump, chillers, fan coils units, heat recovery units, air handling units… Then each of these elements was implemented in the software model with their corresponding technical specifications. Integration of a new power unit on this previously implemented HVAC system, like a Fresnel collector for instance can be evaluated (Figure 5). The results permit to check the added value gained (energy consumption avoided, efficiencies…) even before taking the decision of installing a Fresnel collector (Figure 6).

Further work is currently aiming at producing steam power in the 150 kW range. In figure 1, the preheater and steam generator coils designed for this level of power output are shown.

Figure 1: An isometric view of the preheater and steam generator coil and blue and yellow colour respectively. The coil heat exchanger is capable of generating up to 150 kW of the saturated steam at 12bar-g for the cogeneration of electricity and desalinated water at the PROTEAS CSP plant.

The coils consists of AISI 40S 316 Φ0.5” piping. The preheater (top coil) is suspended over the molten solar salt surface while the steam generator (bottom) coil is immersed in the salt. The produced steam power aims at rendering the PROTEAS plant self-sufficient, that is, produce enough power for solar salt pumping, pipeline heat tracing, drive various instrumentation, as well as for driving the Multi-effect desalination unit.

 

 

 

 

Figure 5. Model of the Solar air-conditioning system at CyI under TRNSYS

 

solar air condi system

 

Figure 6. Energy balance, results from TRNSYS Simulation

energy balance results

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