Grid integration of PV plants in Germany

Transcription

1 Grid integration of PV plants in Germany Stefanie Koch, scientific assistant Department for High Voltage Technology and Electrical Power Systems elenia University of Braunschweig Institute of Technology

2 University of Braunschweig Institute of Technology Department for High Voltage Technology and Electrical Power Systems (elenia) Braunschweig Components of energy supply ~ ~ = = Electro-mobility Facts and figures: inhabitants in Braunschweig Located near to Hannover and Wolfsburg TU Braunschweig founded in different courses of study ca students ca employees Stefanie Koch Grid Integration of PV plants in Germany Page 2 Active distribution grid

3 Agenda Introduction Requirements of grid friendly utility scale PV plants Frequency control Voltage control Grid restoration System management Limitation of rate of change Selected utility scale PV plants Summary & outlook Stefanie Koch Grid Integration of PV plants in Germany Page 3

4 Germany leads the way in solar energy World map of global horizontal irradiation Countries with the largest installed PV capacity in ,1% 21% 1000 kwh/m² 2200 kwh/m² Source: BMWi Annual sum Daily sum Germany Mexico Stefanie Koch Grid Integration of PV plants in Germany Page 4

5 Source: Fraunhofer ISE Power Over 40 % electrical energy production from PV possible Temporary, high amounts of renewable energies are feeding in PV systems are essential and they On sunny weekdays, PV power can cover 35 % of present German electricity demand at peak times, and on weekends and holidays up to 50 % can be a significant part of the energy production! In some regions installed PV capacity far outstrips demand 70 GW Mo Tu We Th Fr Sa Su Example for the feed-in of renewables and conventional power plants in the June of Stefanie Koch Grid Integration of PV plants in Germany Page 5

6 German grid structure and integration of renewables In the past all major power plants were TSO connected to the transport network operated by the TSO Now wind parks and solar plants are connected G 380/220 kv G GG to the distribution grid of the DSO Wind mainly in MV and HV grid 110kV G GG Solar parks in MV grid and in HV grid Mainly residential solar plants in the LV grid 10/20 kv G Paradigm shift: From unidirectional to fluctuating bidirectional load flows 400V TSO: Transmission System Operator DSO: Distribution System Operator Stefanie Koch Grid Integration of PV plants in Germany Page 6 DSO households

8 Requirements of grid friendly utility scale PV plants Utility scale PV plants are increasing in power and number Their feed-in could be limited in the future due to conventional must-run-units and their ancillary services To minimize must-run-units, a behavior of PV plants similar to conventional generation is needed Ancillary services are strictly necessary for the function of the power system. These services are provided for the network user by the system operators. Thus they define the quality of supply: frequency control voltage control grid restoration Stefanie Koch Grid Integration of PV plants in Germany Page 8 system & operation management. Source: Distribution Code 2007, VDN

9 Control reserve for frequency control Absorbing / releasing energy (in case of over- / under-frequency) by rotating masses is called instantaneous power reserve ( spinning reserve ) Primary control reserve (PCR) is activated directly by a controller at the power plant f P P Frequency 5 s 10 s 15 min 1 h Demand and Supply 5 s 10 s 15 min 1 h Secondary control and minute reserve, activated by the TSO, are relieving the PCR Stefanie Koch Grid Integration of PV plants in Germany Page 9 P Primary and secondary control reserve 5 s 10 s 15 min 1 h Source: Verstege

10 Prequalification procedure and market conditions TSO announces demand of control reserve Prequalified suppliers are able to bid on control reserve So far, conventional power plants provided control reserve Market-opening for renewables slowly but surely Primary control reserve Secondary control reserve Minute reserve Time slice 24 h for one week Two slices (peak and off-peak) Six slices each 4 h Minimum Power ±1 MW ±5 MW ±5 MW Auction period weekly weekly daily (except Sat., Sun. & on public holiday) Activation time Full power after 30 s After 30 s reaction measurable, full power after Stefanie Koch Grid Integration of PV plants in Germany Page 10 min Max. duration 15 min 4 h Replaced by intra-day-market Tech. requirements Announcement 7,5 min before activation, full power after 15 Automatic (on frequency-change) Automatic, external signal from TSO Automatic, external signal from TSO Payment Capacity price ( / MW) Capacity-( / MW) and energy-( / MWh)price Capacity-( / MW) and energy-( / MWh)price Pooling Only inside the control area Only inside the control area to achieve the minimum power also across control areas min Only inside the control area to achieve the minimum power also across control areas Current demand 628 MW (+ and -) (DE, CH, NL) 1906 MW (-) and 1992 MW (+) (DE) 2208 MW (-) and 2476 MW (+) (DE)

11 Control reserve with PV plants Source: Energietechnisches Symposium, SMA Challenges for participation: and solutions: Minimal size of the system Solution: pooling of PV plants to a virtual power plant Reliable forecast despite volatile feed-in Solution: pooling of different plants to balance the forecast error Not only negative but also positive control reserve Solution: PV plants with reduced active power feed-in Solution: storage systems P AC t Event Currently fed-in power tsource: oekostromschweiz.ch Stefanie Koch Grid Integration of PV plants in Germany Page 11

12 Contribution of renewable energies to the frequency control Previously PV systems in Germany had to shut down at a frequency of 50,2 Hz With the big increase in PV generators in Germany, this effect could cause a simultaneous shut down of >10 GW danger of under frequency and system instabilities Since 2011 inverters need to have a linear degradation of active power by over frequency. characteristic-curve method More than PV power plants had to be retrofitted 50,2 Hz issue 51, Hz f 51.5 Hz P = 40 % per Hz Stefanie Koch Grid Integration of PV plants in Germany Page 12

13 Source: echo-online.de Reactive power management for voltage control Capacitive (e.g. cables) or inductive (e.g. transformers, overhead lines, loads) elements generate reactive power demand Network assets have to be designed for the additional reactive power transmission Transmission of reactive power causes active power losses Reactive power should be provided where it is needed Compensation systems are used by the TSO for voltage control Static voltage control Adjustment of the voltage by limited active-power feed-in (P(V)) Dynamic voltage control Supply of short circuit power: For a secure trigger of the protective devices To limit the voltage droop in case of a fault Stefanie Koch Grid Integration of PV plants in Germany Page 13 Phase-shifter in the former nuclear power plant Biblis A

14 Voltage difference at point of interconnection ΔU/Ur Voltage can be influenced by reactive power Voltage difference at the point of interconnection at different grid angles ψ when generation power P through short-circuit capacity S k " is 5% 8,0% 6,0% 4,0% cos φ = 0,95 (ind.): reduction of 50 % 2,0% 0,0% -2,0% -4,0% 0,8 0,85 0,9 0,95 1 0,95 0,9 0,85 0,8 Phase shift cos ϕ Stefanie Koch Grid Integration of PV plants in Germany Page 14

15 Grid restoration after a blackout The current concept after a blackout incorporates a grid restoration via the transmission network level: Power plants with start-up ability (hydro and gas-turbine power plants) build up the supply on the maximum voltage level Thereby they help other power plants to restart Separate island-networks are synchronized to bigger grid system; lower network-levels and loads are gradually connected Up to now: non-open platform for these ancillary services and therefore no economic incentive for PV But: inverter systems are suitable to support grid restoration Greatest challenge will be the complex coordination of all participants Stefanie Koch Grid Integration of PV plants in Germany Page 15

16 Source: fernglasagentur.de System management Monitoring the current network status Continuous monitoring only on the maximum and high voltage levels, partially on the mid-voltage levels In the most low-voltage grids there is no monitoring Congestion management for prevention of local asset overloads E.g. by feed-in management (renewables), re-dispatch (conv. power plant) or other action to influence the feed-in (countertrading) Securing and providing the other ancillary services (frequency control, voltage control and grid restoration) Responsibilities TSO: Responsibilities DSO: Organization of the use of the control reserve and reactive power, congestion management and grid restoration Local voltage control and grid restoration (supporting TSO) Stefanie Koch Grid Integration of PV plants in Germany Page 16

17 Limitation of rate of change Challenge: With PV systems, high rates of change possible due to variations in irradiance Variability of PV generation critical for grid reliability Solution: Ramp rate control to make controlled changes Larger plants have smoother rate of changes MW W/m² :00 05:00 10:00 15:00 Time in minutes Source: First Solar Stefanie Koch Grid Integration of PV plants in Germany Page 17

18 The actual ancillary services of utility scale PV plants Active power reduction due to overfrequency HV (e.g. 110kV) MV (e.g. 20kV) Limitation of rate of change Grid control centre Grid operator Medium-voltage switchgear V actual, f actual, P actual, Q actual, Central power plant controller P target, Q target, Static voltage control Dynamic voltage control Feed-in management 3~ = 3~ = 3~ = 3~ = 80 % 80 % 80 % 80 % Impact of cloud passage Stefanie Koch Grid Integration of PV plants in Germany Page 18 Energy loss due to cloud passage

19 In future: the ancillary services have to be provided by area power plants power plant ancillary flexibility system services security Past: centralized old world: central TSO 380/220kV flexibility ancillary system services security power plant Present: decentralized new world: decentral TSO central central power plant power plants DSO area power plant area power plant DSO 110/20/0,4kV Stefanie Koch Grid Integration of PV plants in Germany Page 19

21 PV farm in Templin, Germany Power: Yearly energy production: 128 MWp MWh Begin of Operation: April 2013 Grid connection via two substations to the 110 kv grid Source: belelectric.com Stefanie Koch Grid Integration of PV plants in Germany Page 21

22 Actual data about utility scale PV projects in Mexico Source: GTM research Announced Approved Under construction Operational Stefanie Koch Grid Integration of PV plants in Germany Page 22

23 Aura Solar Mexico the first utility scale PV project in Mexico Size: 38.9 MWp Yearly energy production: GWh Location: La Paz Operation: 2013 the biggest solar park in Latin America Outlook: Second solar park with 30 MWp In addition: a storage of 11 MW Planned cost: 80 Mio. $ Source: aurasolar.com Stefanie Koch Grid Integration of PV plants in Germany Page 23

24 Summary and outlook Already today PV plants provide grid supporting functions : Frequency control Active power reduction due to overfrequency Rising contribution to control reserve + instantaneous power reserve Voltage control Static and dynamic voltage control Grid restoration Supporting effect, especially in combination with storage systems System management Feed-in management Limitation of rate of change Ramp rate control In future, PV plants and other renewable energies will provide more ancillary services to reduce the amount of must-run-units Future ancillary services will be provided by area power plants Stefanie Koch Grid Integration of PV plants in Germany Page 24

25 Thank you very much for your attention!

26 Energy Production in Germany in 2015 Hard Coal Gas Oil and Ohters Wind 9.1% Renewables Biomass 7 % Uranium Hydro Power 3.3% Solar 5.7% Urban Waste 1% Brown Coal Stefanie Koch Grid Integration of PV plants in Germany Page 26 Source: BDEW, AG Energiebilanzen, Stand Februar 2015