Solar Thermal Energy Storage Technologies Doerte Laing, German Aerospace Center (DLR) ENERGY FORUM, 10,000 Solar GIGAWATTS Hannover, 23. April 2008 Folie 1
Energy Storage for Concentrating Solar Power Plants KONZENTRIERENDER CONCENTRATING SOLAR COLLECTOR SONNENKOLLEKTOR Fossil fuel (optional) Solarheat ENERGIE- ENERGY SPEICHER STORAGE WÄRMEKRAFT- POWER BLOCK MASCHINE Electricity Heat Higher solar annual contribution Reduction of part-load operation Power management Buffer storage Energy storage necessary for successful market implementation of CSP technology Doerte Laing, Folie 2
Thermal Energy Storage Challenges Highly specific design specifications regarding: primary HTF - pressure - temperature - power level - capacity Storage system ONE single storage technology will not meet the unique requirements of different solar power plants Doerte Laing, Folie 3
Storage concepts for parabolic trough power plants Classification Heat transfer fluid as storage media Direct active thermal energy storage Two tank oil storage Steam Accumulator Dual medium storage system Passive thermal energy storage liquid solid phase change Molten salt sensible heat storage Solid media sensible heat storage Latent heat storage Doerte Laing, Folie 4
Thermal Energy Storage for CSP Plants Status und Development Commercially available storage systems Steam Accumulator 2-Tank sensible molten salt storage based on nitrate salts Alternative materials and concepts tested in lab and pilot scale Solid medium sensible heat storage - concrete storage Latent heat - PCM storage Combined storage system (concrete/pcm) for water/steam fluid Improved molten salt storage concepts Solid media storage for Solar Tower with Air Receiver (e.g. natural rocks, checker bricks, sand) Future focus for CSP Higher plant efficiency => Increase process temperature New fluids: steam, molten salt, gas/air Doerte Laing, Folie 5
Steam Accumulators Storage of sensible heat in pressurized liquid water Steam Charging Isolated Pressure Vessel Steam Steam Discharging Charging process: raising temperature in liquid water volume by condensing steam Liquid Phase Liquid water Charging / Discharging Discharging process: generation of steam by lowering pressure in saturated liquid water volume Buffer storage for peak power Inefficient and economically not attractive for high pressures and capacities Doerte Laing, Folie 6
Steam Accumulators PS10 Saturated steam at 250 C 50 min storage operation at 50% load Doerte Laing, Folie 7
Steam Accumulators PS10 Doerte Laing, Folie 8
Steam Accumulators PS10 Doerte Laing, Folie 9
Molten Salt Storage - Solar Two Storage capacity (3h) 1400 t of nitrate salts (60% NaNO3 + 40% KNO3) 2 tanks: 12 m Ø, 8 m high Doerte Laing, Folie 10
Molten Salt Storage Andasol 1 Syn. Oil Collector field NaNO 3 -KNO 3 Molten salt storage H 2 O Conventional steam turbine Doerte Laing, Folie 11
Molten Salt Storage Andasol 1 Storage capacity 1010 MWh (7.7h) Nitrate salts (60% NaNO3 + 40% KNO3) Salt inventory 28.500 t Tank volume 14.000 m³ 6 HTF/salt heat exchangers 292 C 386 C 14 m Ø 38,5 m Doerte Laing, Folie 12
Molten Salt Storage Andasol 1 Source: ACS Cobra Doerte Laing, Folie 13
Solid media concrete storage Dual medium indirect storage system with regenerative heat transfer Preferred for single phase HTF up to 400/500 C Modular and scalable design from 500 kwh to 1000 MWh Economic and reliable TES Cost target < 20 / kwh TES capacity Flexible to large no. of sites and construction materials Doerte Laing, Folie 14
Solid media concrete storage Current Status 2 year operation of 2 modules 350 kwh castable ceramic 350 kwh concrete Second generation concrete 400 kwh storage module developed with Current investment cost ~ 30 /kwh (large scale, 6 h cycles) Concrete storage is ready for scale-up and demonstration System integration and operation strategy is an important issue Doerte Laing, Folie 15
Solid media concrete storage Storage Design 134 mm Basic storage module 4 m 18 m 2,6 m Doerte Laing, Folie 16
Solid media concrete storage Storage Design Set-up of storage units Storage Package Storage Package Insulation 25 m 50 m Doerte Laing, Folie 17
Solid media concrete storage Storage Design Piping Doerte Laing, Folie 18
Solid media concrete storage Integration into power plant 50.000 m³ Concrete Storage Material 6 h Storage for 50 MW-Power Plant Doerte Laing, Folie 19
Phase Change Storage Why using Phase Change Material (PCM)? Working fluid water/steam: => Evaporation phase (T=const) Phase change storage medium => Melting phase (T=const) temperature pressurized water superheated steam temperature solid phase liquid phase wet steam two phase solid / liquid spec. enthalpy spec. enthalpy Significant advantage of PCM technology in steam production due to constant temperature Doerte Laing, Folie 20
Phase Change Storage Selection of Phase Change Materials 400 350 300 For industrial process heat LiNO 3 Enthalpy [J/g] 250 200 150 KNO 3 -LiNO 3 LiNO 3 -NaNO 3 NaNO 2 NaNO 3 100 KNO 3 -NaNO 2 -NaNO 3 KNO 3 -NaNO 3 KNO 3 50 0 100 150 200 250 300 350 Temperature [ C] For solar power generation Doerte Laing, Folie 21
Approaches to realize PCM with superior thermal conductivity liquid solid Fluid Heat transfer coefficient is dominated by the thermal conductivity of the solid PCM Low thermal conductivity is bottleneck for PCM Finned Tube Design effective Lamda >10 W/(mK) Doerte Laing, Folie 22
On-sun demonstration of a 200 kwh PCM storage Dimensions: 5 x 0,6 x 0,5 m3 PCM: 2 tons nitrate salt - 120 kg graphite plates Maximum pressure: 40 bar Charging/discharging power 100 kw Thermal capacity 200 kwh Estimated investment cost: 45 /kwh th Doerte Laing, Folie 23
Combined Concrete / PCM Storage for direct steam generation in parabolic troughs evaporation/ condensation from solar field to solar field preheating C superheating D from power block A concrete storage module B PCM storage module concrete storage module to power block A feed water inlet / outlet B liquid water C saturated steam D live steam inlet / outlet Doerte Laing, Folie 24
Conclusions Energy storage is a key issue for CSP Steam accumulators only economic as buffer storage Molten salt technology is available, further improvements for cost reduction needed Concrete storage technology is attractive alternative demonstration in pilot scale needed PCM storage technology is the most promising technology for DSG plants Continuous research and development effort is needed especially for higher process temperatures (> 400 C) and for further cost reduction Doerte Laing, Folie 25