Desalination systems powered by solar energy

Desalination systems powered by solar energy International Conference on Renewable Energy Desalination Tunis, 11.06.2012 Dr. -Ing. Joachim Koschikowski Fraunhofer Institute for Solar Energy Systems ISE Heidenhofstr. 2, 79110 Freiburg joachim.koschikowski@ise.fraunhofer.d e Dipl.-Ing. Marcel Wieghaus SolarSpring GmbH Hanferstr. 28, 79108 Freiburg marcel.wieghaus@solarspring.de

Outline Introduction Solar driven desalination PV-RO CSP-MED Small thermally driven units Membrane distillation Conclusion

Introduction Decrease of fresh water resources due to: Deepwelling ground water levels Intrusion of salt water Draining of fossil ground water reservoirs Pollution of surface water Potential of solar energy e.g. 6kWh/(m²d) 0.6 l oil /(m² d) 220 l oil /(m² y)

Introduction Grid connected systems Stand alone systems 4

Introduction Stand alone systems Challenging approach because: Energy supply is not constant during the course of a year, during day and night time and during daytime even within seconds intensity can change Qualified technical staff for operation and maintenance is not available

Solar driven desalination Solar energy for desalination Different approaches for the utilization of solar energy as the prime mover for desalination processes Desalination Filtration and Disinfektion Pumping UF MF RO: Reverse Osmosis UV ED: Electro Dialysis MSF: Multi stage flash MED: Multi Effect Distillation Well / circul. c VC: Vapor Compression STIL: Simple Solar Stil MEH: Multi Effect Distillation MD: Membrane Distillation 6

Complexity Solar driven desalination Correlation between efficiency and complexity: As higher the efficiency as higher the complexity of the system high low low Efficiency high

System efficiency Solar driven desalination Correlation between energy costs and system efficiency: As higher the costs of energy are as higher the efficiency (investment costs) can be high low low Energy costs high Solar energy is not for free because of significant investment costs!!! Costs for water distribution must be considered (savings for distributed systems)!!!

Solar driven desalination Solar energy for desalination Different approaches for the utilization of solar energy as the prime mover for desalination processes Modular technology for wide range of capacities and different applications RO: Reverse Osmosis ED: Electro Dialysis MSF: Multi stage flash MED: Multi Effect Distillation c VC: Vapor Compression STIL: Simple Solar Stil MEH: Multi Effect Distillation MD: Membrane Distillation

Solar driven desalination PV-RO PV-RO - stand alone system configuration Systeme solar Challenging approach under development at ISE: stand alone PV-RO systems without batteries Advanced pressure exchangers 10

Solar driven desalination PV-RO Development of PV-driven stand alone RO-systems without batteries an chemical pre-treatment Capacity: 5 m³/d from seawater 28Tppm Location of pilot plant : Cyprus Number of RO mudules: 3 Pre-treatment: UF No of PV-modules : 34 PV peak power = 7.65 kwp

Solar driven desalination PV-RO Advantages of PV-RO High performance density low energy demand with pressure recovery (3.5-6 kwh/m³ for SWRO) Modular set up applicable for a wide range of capacities PV and RO system can be separated for long distances Comprehensive R+D on RO membranes, modules and system components Disadvantages of PV-RO Significant sensitivity of RO-membranes against scaling and fouling Limitation in salt concentration Operation with alternating energy supply is not proven Batteries as energy storage are expensive and very limited in lifetime Product water quality is poor in single stage systems

Solar driven desalination Solar energy for desalination Different approaches for the utilization of solar energy as the prime mover for desalination processes Large scale but also small units are available c 13

Solar driven desalination CSP-MED Concentrating solar power combined with MED: Vapor of 60 to 69 C from the steam turbine is condensed in the first stage of the MED plant Fraunhofer ISE: System simulations Fischer Ecosolutions 20-100m³/day MED plant Source: Veolia Source: Fischer Ecosolutions

Solar driven desalination CSP-MED Advantages of CSP-MED Utilization of low grade waste heat from CSP or other industrial sources Low thermal energy demand is possible with a certain number of effects Very robust system design Components for large scale systems are state of the art Product water is of very high quality Disadvantages of CSP-MED Energy demand is high compared to RO (1.5-2.5 kwhel/m³ +~60kWhth/m³) Limitation in salt concentration due to scaling and corrosion Cooling is necessary - air cooling for inland locations is inefficient Mismatch of geographical and metrological site conditions for CSP and MED Efficiency of the power plant is reduced by about10%

Solar driven desalination Solar energy for desalination Different approaches for the utilization of solar energy as the prime mover for desalination processes Technologies which are adapted particularly to solar thermal low grade heat supply c 16

Solar driven desalination small thermal Simple solar still Systems without heat recovery loose the latent heat to the ambient very low efficiency <~4 l/m² day

Solar driven desalination small thermal Simplified Solar thermally driven MED system developed by Soalrinstitut Jülich 6-10 effects recover latent heat, All effects are operated at ambient pressur GOR ~3 Output about 10-15 l/m²

Solar driven desalination small thermal Multi Effect Humidification unit MEH Developed by ZAE Bayern, TAS and Tinox-MAGE

Solar driven desalination small thermal Performance optimization The performance of solar thermal collectors is decreasing with operation temperature, the performance of thermally driven desalination processes is increasing Range of operation

Solar driven desalination small thermal Advantages of adapted thermally driven small and medium size systems Potential for good compromise between low complexity and good efficiency Adapted system design for transient operation Robustness Up and downscaling is possible Disadvantages of adapted thermally driven small and medium size systems No real long term experience Expensive compared to output (Solar system is about 50% of total costs) Still not perfect match between complexity and efficiency Development does not profit from improvements in large scale technology Market for small units is not developed yet

Membrane distillation Driving force: Difference of water vapor pressure between both membrane boundary layers q 22

Membrane distillation condenser outlet condenser inlet external heat source permeate distillate outlet outlet evaporator inlet evaporator outlet

Membrane distillation condenser outlet condenser inlet external heat source permeate distillate outlet outlet evaporator inlet evaporator outlet 1. preheating of cold feed water 2. temperature gain by external energy 3. evaporation through membrane into permeate gap cooling by latent heat of vaporisation and sensible heat losses concept of internal heat recovery GOR~ 3-8

Membrane distillation Test cell for the investigation of: Membrane performance Channel configurations Validation of single node simulation models

Membrane distillation MD-module production at SolarSpring

Membrane distillation Development of MD-pilotdesalination systems for sea and brackish water using solar or waste heat

Process design: Solar driven systems MD Compact system Collector area: 6.8m² Capacity: 150 l/day Specific capacity: 17-22 l/m² d

Solar driven desalination Basic design of stand alone two- loop systems

Membrane distillation Installation at Etosha Basin North Namibia Nuber of Modules: 12 Hot Ready Water installed Storage: MD Volume System 12m³ Collector Area: 225 m² Target Capacity: ~5000 l/d

Membrane distillation Waste heat driven MD system in Pantelleria, Italy Start of operation October 2010 Prime mover: Waste heat from power plant Target capacity: Raw water source: Operation mode: 5m 3 /day Sea water 28.000ppm 24h / day (no heat storage)

Membrane distillation Solar thermally driven MD system in Gran Canary, Spain Start of operation, March 2011 Prime mover: Target capacity: Raw water source: Operation mode: Solar only (180m² flat plate collectors) 3.5 m 3 /day Sea water 35.000ppm <16h / day (with heat storage)

Solar driven desalination Advantages of Membrane Distillation MD Good compromise between efficiency and complexity Feed temperature, depending on MD configuration, can be between 50 and 90 C low grade waste heat or solar thermal collectors can be used Low sensitivity against fouling and scaling due to membrane properties and flow configuration Transient operation in temperature and flow rate is possible in a wide range High salinities can be treated depending on system configuration (zero liquid discharge) Disadvantages of Membrane Distillation MD Specific energy demand is high compared to RO (2kWh/m³el, 80kWh/m³th) Specially developed MD membranes are not available Long lifetime is still not proven No large scale industrial systems in the market today

Conclusion All desalination technologies have advantages and disadvantages and must be chosen with respect to particular boundary conditions Small and medium size-, in particular stand alone solar driven desalination systems, are still in the developing ore pilot phase Long term experience for realistic life time estimations must be conducted also with respect to the calculation of realistic water production costs Today solar driven desalination systems are almost not on the market because they are considered as too expensive but there is already a huge demand Cost savings due to decentralized production (no transportation, no grid, no subsidies for conventional energy) must be considered more carefully for the comparison of water production costs

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