Module 2.5 Wind Energy 2.5.2 Grid Integration Gerhard J. Gerdes Workshop on Renewable Energies March 11, 2005 Majuro, Republic of the Marshall Islands Grid integration levels Large network Micro grid Stand alone system The main question for grid integration is the penetration of wind energy in the grid 2
Energielabor 1983 vs. German grid today PV (solar) 6kW wind turbine 4,5kW 6kW Renewable share wind/solar Storage diesel generator 10kW 80% 110 000 MW wind farms PV (solar) 16 000 MW 300 MW 6% 3 Integration of wind energy into power systems Integration into large networks national or continental interconnected systems grid connection is only a question of available grid capacity or grid reinforcement small grids separate isolated distribution systems not connected to large networks grid integration is a matter of adapting the wind farm size to the capacity of the existing power generation and consumption stand-alone systems no connection to a grid most difficult case: production has to meet consumption at any time on a small scale 4
Large network, example Germany 380 kv Extra-high voltage 110 kv High voltage consumer 10 or 20 kv 400 V Medium voltage Low voltage 5 Example: Scandinavian network 6
Connection to different voltage levels of the electrical network Voltage System Low voltage system Feeder to the medium voltage system Medium voltage system, at transformer substation to high voltage High voltage system Extra high voltage system Size of wind turbine For small to medium sized WTs For medium to large WTs and small wind farms For medium to large wind farms Clusters of large wind farms Large offshore wind farms Transmittable power up to 300 kw up to 2 5 MW up to 10 40 MW up to 100 MW > 0.5 GW 7 Grid connection of a single WT Rotor G Generator low voltage line mean voltage ring station Transformer energy counter mean voltage sepera te Rotor G Generator low voltage line mean voltage branch station Transformer Transfer from WT owner to network operator energy counter Transfer from WT owner to network operator mean voltage 8
Grid connection of a wind farm in ring configuration 9 Example of grid connection of a wind farm in radial configuration 110/20kV SN=31,5MVA uk=17,5% Consumers 2000m 240² PN=500kW asynchronous stallcontrolled fixed speed 20/0,4kV SN=630kVA uk=4,1% A5 200m 150² A4 170m 150² A3 260m 150² A1 170m 240² A2 P1 200m 95² P2 260m 150² 170m 95² P3 260m 95² all cables: 3x1xNA2XS(F)2Y with different cross sections P5 170m 95² P4 10
What does Power Quality of Wind Turbines mean? power factor (reactive power) power variations (10min,1min, instantaneous) switching operations (current spike factor) flicker and voltage fluctuations harmonics (Integer harmonics and interharmonics) 11 Standards for Power Quality Measurement Procedures of Wind Turbines and Assessment IEC-Standard 61400-21, CDV: Measurement and assessment of power quality of grid connected wind turbines Measurment quality ensuring guidelines like MEASNET National guidelines for keeping power quality limits (like VDEW, Connection of independent power production units to the medium voltage system ), typically based on IEC-standards 12
Micro grid and stand-alone alone In principle Micro grid and stand-alone are quite similar The main question is the amount of renewable energy in a system, the penetration An often economic viable solution for existing diesel supply is the extension to a wind-diesel-system The most simple systems for stand alone operation is the fuel saver 13 Wind-Diesel Diesel-Systems Consumer G Households and public Wind turbine SG Diesel generator Trade and craft 14
Fuel consumption of a diesel generator and fuel saver operation Fuel consumption [gal/h] 3,5 3,0 2,5 2,0 1,5 1,0 0,5 0,0-20 -10 0 10 20 30 40 50 Diesel power [kw] measured curve Minimum consumption of a 35kW diesel-generator at idle speed (power = 0kW) is 3 litre per hour (0,7923 gal/h), which means 25% of the consumption at rated power. For fuel saver operation this means still a high consumption even in times when high renewable power is available In fuel saver operation a maximum of 30% of fuel can be saved (rule of thumb) 15 Efficiency of a diesel generator Normalized fuel consumption / power. 400% 350% 300% 250% 200% 150% 100% 50% 0% 0% 20% 40% 60% 80% 100% Normalized by relation to values at rated power Normalized diesel power 16
Sizing a wind diesel system For design of a wind diesel system there are some basic questions: what is the average and what is the peak load? how low can the security of supply (availability) be? is load management or load shedding possible and to what amount? For availabilities far below 100% a combination of WTG and diesel is a simple solution, the availability can be influenced by the rate of wind power / diesel power. For 100% supply availability a storage and/or an efficient load management system is required in case of high penetration. 17 Penetration level depending on system configuration System low medium high small stand alone, e.g. single house stand alone, e.g. small village micro grid diesel PV diesel wind turbine Penetration level diesel wind turbine (PV) diesel some wind turbines PV (wind charger) Battery diesel wind turbine (PV) Battery diesel some wind turbines storage e.g.: low penetration level means small share of renewable energy supply related to total 18
Wind-Diesel Diesel-System with battery storage Consumer G Households and public Wind turbine SG Diesel generator Battery Storage Trade and craft Ideally the battery storage has to cover 10 minutes of full load. Battery and inverter have to be dimensioned accordingly. 19 In case of a stall WT in a small system SG Stall controlled WT WT = wind turbine controllable dump load for excess power 20
Wind-Diesel Diesel-System with flywheel storage Consumer G Households and public Wind turbine SG Diesel generator M Flywheel Storage Trade and craft 21 Grid-parallel and stand-alone alone operation grid-parallel operation, 100 kw (a.c. generator) stand-alone operation, 50 W (DC battery charger) 22
Operation strategy, WTG dimensioning and fuel consumption 23 Reduction of fuel consumption by storage size 24
Diesel starts for various system layouts, no storage 25 Reduction of diesel starts by storage implementation 26
Rule of thumb for small system sizing Load, per year: L year [kwh] Load, per day: L day [kwh] Electric energy delivered from PV-generator and wind turbine per year: E W+S [kwh] Chose size of PV and wind turbine such that: E W+S 2.0 L year Battery nominal capacity: C nom [kwh] Chose battery size such that: C nom = 1.5 L day C nom = 3 L day or larger for systems with diesel back-up for systems without diesel back-up 27 Example of a micro grid integration Example of integration into a 2MW local grid for power supply of a small town For design of wind farm size a model calculation was performed, to find the optimum wind turbine size and number 28
Average Power [kw] Mean average production and consumption in a wind-diesel diesel-systemsystem 1400 1200 1000 800 600 400 200 0 Turbine Load Diesel Generator Surplus 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Average Hour of day 29 Power production and consumption in a wind-diesel diesel-system system 1400 1200 1000 Power [kw] 800 600 400 200 0 2001.3.27 0:0 2001.3.28 0:0 2001.3.29 0:0 2001.3.30 0:0 2001.3.31 0:0 2001.4.1 0:0 2001.4.2 0:0 Time Turbine Load Diesel Surplus 30
1400 1200 1000 Power [kw] 800 600 400 200 0 2001.9.26 0:0 2001.9.27 0:0 2001.9.28 0:0 2001.9.29 0:0 2001.9.30 0:0 Time Turbine Load Diesel Surplus 31 Surplus production with increasing number of wind turbines Energy Yield [kwh] 2'000'000 1'600'000 1'200'000 800'000 400'000 0 3 4 5 6 7 8 10 15 Production of Turbines 358'776 478'368 597'960 717'552 837'144 956'736 1'195'920 1'793'881 Surplus 3'200 4'358 7'447 13'568 24'791 42'243 94'795 308'909 Surplus / Production 0,9% 0,9% 1,2% 1,9% 3,0% 4,4% 7,9% 17,2% Number of Turbines 20% 18% 16% 14% 12% 10% 8% 6% 4% 2% 0% 32
Grid connected renewable energy system Example of a wind solar and biogas powered sewage plant Turbine: Solar: Biogas: electric: thermal: Consumption peak: average: 250kW 140kW 30kW 60kW 106kW 47kW 33 Energy exchange with the grid and system design With the ratio wind energy / solar energy the energy required from the grid varies. PRG means the share of energy by renewables related to the consumer load of the sewage plant 34
Seasonal energy exchange 1.2 In winter time 200% (normalized to the annual consumption) of required power is produced, of which 120% is fed to the grid, while still 10% have to be imported from the grid. In summer time 180% of required power is produced, of which 70% is fed to the grid and 20% are still imported from the grid. CHP = Combined Heat and Power (biogas plant) WEC = Wind Energy Converter PV = Photovoltaic 35 Summary The design of a stand-alone or micro-grid system has to be done carefully with respect to the renewable input, existing diesel system, consumer average and peak load, supply security, load management capabilities A high penetration means a high logistic effort (control), taking into account load management and storage strategies and capacities For new systems a specific design of the diesel generators would be valuable (cascaded rated power) 36
What information is required for micro grid or stand-alone alone integration? Diesel generator sets: Number and size specific operation conditions, if any Load: Maximum and minimum demand average consumption best: hourly data of demand for minimum one year load shedding or management possible? what size? Wind speed: hourly data for minimum one year 37 Turbines available Vergnet: 5, 10, 15, 20, 60, 250kW AOC: 10, 50kW Enercon: 330, 800, 2000, 4500kW Vestas: 850, 1650, 2000, 3000, 4500kW Bonus: 1000, 1300, 2000kW GE-Wind: 1500, 2000, 3600kW Nordex: 1300, 1500, 2500, 2300kW 38