Sesto Val Pusteria, June 26 th 2015 Electrical Storage for Low Voltage Distribution Networks Dipartimento di Elettronica, Informazione e Bioingegneria Politecnico di Milano
Applications Peak Shaving Time Shift Storage can contribute to shift and/or level the electric energy demand, making it somehow asynchronous with respect to production There are two kinds of applications: Power applications Energy applications The benefits of (power) peak shaving are the reduction of the components cost (sizing, lowest used power) and the increase of the load factor of the used power. Example: switching loads The (energy) time shift enables optimal use of the renewable energy sources 2
Electrical Storage Parameters and Features Basic parameters: specific energy and energy density specific power and power density efficiency (round-trip efficiency) lifespan (in terms of number of cycles and of the discharge depth) Maximum depth of discharge 3
Electrical Storage Parameters and Characteristics Lead acid batteries Lithium-ion batteries Supercapacitors Flywheels Specific Energy [Wh/kg] Specific Power [W/kg] 30-50 90-190 2-5 10-50 10-100 200-800 100 4,000 500 3,000 Life Cycles 200-300 500-2,000 1,000,000 20 years A combination of different technologies may be considered 4
Applications Peak Shaving Example 50 40 30 20 AC current (without flicker compensation) Welder current without storage i AC [A] 10 0-10 -20-30 -40-50 0 0.1 0.2 0.3 0.4 0.5 Time [s] 50 AC current (with flicker compensation) 40 30 20 i AC [A] 10 0-10 -20-30 -40 Welder current with storage for flicker reduction -50 0 0.1 0.2 0.3 0.4 0.5 Time [s] 5
Applications Time Shift Example Parameters Residential Photovoltaic plant (1/3) Grid connection power: 3kW Average consumption: 2,700kWh Investment lifespan: 25 years Net metering Tax deduction: 50% Overnight capital cost (without storage): 1,900 /kwp Photovoltaic plant nominal power: 3kWp Yield Location Energy [kwh] North 3,900 Center 4,200 South 4,500 6
Applications Time Shift Example Residential Photovoltaic plant (2/3) Economic results without storage Self-consumption: 30% 8 PBT [years] 7 + 0 % + 2 % 6 North Center South + 4 % 15.000 NPV [ ] 10.000 + 0 % 5.000 0 North Center South + 2 % + 4 % 7
Applications Time Shift Example Economic results with storage Self-consumption: 47% Lithium-ion batteries: i) gross capacity: 2kWh ii) lifespan: 5,000 cycles (DoD 80 %) 15 Residential Photovoltaic plant (3/3) PBT [years] 13 + 0 % 11 9 North Center South + 2 % + 4 % 10.000 8.000 6.000 4.000 2.000 0 North NPV [ ] Center South + 0 % + 2 % + 4 % 8
Applications Time Shift Example Commercial photovoltaic plant (school rooftop) with swimming pool (1/3) Parameters Average consumption: 250,060kWh Investment lifespan: 25 years Net metering Overnight capital cost (without storage): 2,000 /kwp Photovoltaic plant nominal power: 120kWp Location: Rome Yield: 184,796kWh 9
Applications Time Shift Example Commercial photovoltaic plant (school rooftop) with swimming pool (2/3) Economic results without storage Self-consumption: 68 % PBT [years] 10 9,5 9 8,5 NPV [ ] 8 450.000 + 0 % + 2 % + 4 % 300.000 150.000 0 + 0 % + 2 % + 4 % 10
Applications Time Shift Example Commercial photovoltaic plant (school rooftop) with swimming pool (3/3) Economic results with storage Lithium-ion batteries: i) gross capacity: 50 150kWh PBT [years] ii) lifespan: 5,000 cycles (DoD 80%) 19 16,5 14 11,5 9 50 kwh 150 kwh + 0 % + 2 % + 4 % 450.000 300.000 150.000 NPV [ ] + 0 % + 2 % + 4 % 0 50 kwh 150 kwh 11
Applications Time Shift Example Results and remarks The case studies presented above show that the self-consumption rate increases when storage systems are used. Nevertheless, it is not economically convenient The results obtained for the two case studies can be generalized for most applications However, the use of storage brings benefits to the distribution network: o o The energy produced can be stored when the sun is shining and released in the evening, thus bringing benefits to thermoelectric power production Levels the network power fluxes, thus reducing losses and enhancing voltage regulation The storage systems could also enhance power quality in the active users network 12
Applications Increasing the Fault Level CASE STUDY AC Grid with a low fault level Possile loss of selectivity Coordination of the conventional protection system for maximum current INTRODUCTION OF AN ENERGY STORAGE SYSTEM IN ORDER TO TEMPORARILY INCREASE THE FAULT LEVEL No changes in the conventional grid protection system No need for communication among the protection devices 13
Applications Rising the Fault Level Current control strategy GRID VOLTAGE Currents from battery and main PECs (Power Electronic Converter) Fault: t = 0.1s Load 1 Currents from battery and main PECs Maximum current relay opens after 60ms The switchgear opens for a current 3 times the load nominal current 14
Applications Increasing the Fault Level Different solutions Oversizing the main PEC Multiple parallel-connected PECs with storage system main PEC DC AC 1 2 3 4 PEC 1 PEC 2 PEC 3 PEC n ESS DC AC DC AC DC AC DC AC 5 Load 1 Load 2 Load 3 Load n Main PEC oversized Load 1 Load 2 Load 3 Load n PEC s operating point corresponds to non optimal efficiency The network must withstand the potential increase of the shortcircuit power during a fault on a load Small storage system The storage PEC is not necessary Better balance between PECs and loads (high efficiencies) 15
Applications Energy Efficiency Storage systems may contribute to enhance the efficiency of systems with electrical drives There are two advantages: Design advantages Energy advantages Chance of modulation Energy recovery in electrical drives 16
Electrical Drives Energy Efficiency Regenerative Brake Design Parallel-connected Electrical drives 17
Storage systems for naval applications Ship s parameters Diesel generators 2 machines: 15.75 MVA 2 machines: 10.5 MVA Total thrusters power = 6.3 MW 2 thrusters: 2.2 MW 1 thruster: 1.9 MW 18
Storage systems for naval applications Diesel generators support during thrusters load step CASE STUDY Need of a quick thrusters load step when entering the port Diesel generators have limited ΔP/ Δt Storage systems enhances faster thrusters load step 100 Diesel load step Andamento della presa di carico dei gruppi diesel P [%] 80 60 40 Curva normale Curva di emergenza 20 0 0 20 40 60 80 100 120 140 160 180 t [s] 19
Storage systems for naval applications Diesel generators support during thrusters load step 7 6 Needed load step Thrusters load step Profili potenze Potenza [MW] 5 4 3 2 1 50% of generators power Load step limited by the generators 0 0 5 10 15 20 25 30 t [s] 20
Storage systems for naval applications Diesel generators support during thrusters load step Design of the Storage System Power of the thrusters = 6.3 MW (2x2.2 MW, 1x1.9 MW) The order of magnitude of the whole storage system is: Power = 1.3 MW Energy = 3 kwh Storage volume: 0.5 m 3 Obtained result: thrusters are fully operating after 12.9s. Without storage system 26.1s are needed. 21
Storage systems for naval applications Grid support after a generation loss CASE STUDY Loss of one or more generators The energy storage system is introduced to compensate the imbalance between the power generated and the power requested to the grid during the period of load reconfiguration. 22
Storage systems for naval applications Grid support after a generation loss CASE STUDY Loss of one or more generators The energy storage system is introduced to compensate the imbalance between the power generated and the power requested to the grid during the period of load reconfiguration. Order of magnitude of the storage system Loss of a diesel generator with a nominal power of 15.75MVA Load reconfiguration time 120ms Power = 7 MW Energy = 0,23 kwh Power Performance Storage volume 1 m 3 23
Applications RSE Test Facility DC Smart Grid Front-End Converter AC-DC (100 kw) 3-phase IGBT inverter manages the power flows between DC and AC grid Storage System 2 Zebra batteries (32 kw, 64 Ah, 279 V) 2 supercapacitors (384 V, 30 kw, 120 kj) PV Emulator (50 kw) Programmable Load (2 x 30 kw smallest step 1 kw) 24
Applicazioni RSE Test Facility DC Smart Grid (power quality) Interruption of the main supply with variable load : behavior of the hybrid storage system High quality of the Voltage 25
Applicazioni RSE Test Facility DC Smart Grid (peak shaving) Switching loads with no grid peak shaving to level the load power Load Battery SuperCap 26
Italian Regulation CEI 0-21 / 2014-09 & CEI 0-21; V1 / 2014-12 Regola tecnica di riferimento per la connessione di Utenti attivi e passivi alle reti BT delle imprese distributrici di energia elettrica. CEI 0-16 / 2014-09 & CEI 0-16; V1 / 2014-12 Regola tecnica di riferimento per la connessione di Utenti attivi e passivi alle reti AT ed MT delle imprese distributrici di energia elettrica. Deliberazione 18 dicembre 2014 642/2014/R/EEL dell Autorità Ulteriori disposizioni relative all installazione e all utilizzo dei sistemi di accumulo. Disposizioni relative all applicazione delle Norme CEI 0-16 e 0-21. 27
Italian Regulation CEI 0-21; V1 Storage system connected to the DC side Storage system connected to the AC side after the energy meter 28
Electrical Energy Storage Design Specific Energy Specific Energy (pu) 0.9 1 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.2 0.4 0.6 0.8 1 Specific Power (pu) Cycle Life (pu) Cycle Life 10 5 0 10 20 30 40 50 60 70 80 90 100 DoD (%) Efficiency 1 Efficinecy 0.8 0.6 0.4 0.2 0.4 0.6 0.8 1 Specific Power (pu) 29
Energy Storage Systems Cost Analysis Tot Storage Cost n Storage Device n r replacements r k 0 Storage Cost Interface Converter Storage System 1 c 1 d r r k l k l storage storage l External System Lifespan (years) plant j 0 1 Energy Cost 1 c 1 d j r j r Size of the storage system Lifespan O&M Costs Exchanged Energy System Efficiency Number of Cycles c r e d r are the inflation and the cost of capital respectively l storage : Life of the storage system Extra Costs Management and Monitoring Systems Interface Converter Maintenance 30
Sesto Val Pusteria, 25/06/2014 Electrical Storage for Low Voltage Distribution Networks THANK YOU