Solar Storage Technologies Part of the BRE Trust

Transcription

1 Solar Storage Technologies Steve Pester Part of the BRE Trust Smart Solar NSC 2015

2 Overview of next few minutes Challenges Some solutions Types of storage Main battery technologies How batteries behave (esp Li-ion) Factors for technology selection Power diverters Further info

3 Main challenges Peaks and troughs in demand predictable, but quite large expensive peak capacity Grid resilience & security Variability of renewable sources Predictable in short term, but not controllable

4 PV generation potential daily sun path Source: PVSyst

5 Solar resource versus national demand A typical day in winter GW Domestic buildings NonDomestic buildings Source: BRE Does not include industrial processes, street lighting, agriculture, etc

6 Overall daily demand Source: Gridwatch,

7 The worst football & royal weddings!

8 The solutions Demand side management International interconnectivity (Supergrids) Storage o Building-level o Grid-level Storage offers: o Spinning reserve o Peak shaving o Load shifting o Voltage & frequency stabilisation

9 Image: Bine Informationsdienst

10 Types of non-fossil storage Electromagnetic / electrostatic Supercapacitors Superconducting magnets Heat Ground o Heat pumps: inter-seasonal? o Geothermal Water o Domestic hot water o Underground tanks Heat Engines Mechanical Pumped Water Flywheels Compressed air Chemical Batteries Static Vehicle batteries for static use Many chemistries Hydrogen Electricity via fuel cells Heat via fuel cells Heat by combustion Make methanol Possible by photosynthesis?

11 Main battery types of interest at present Type Pro s & Cons Maturity Lead-acid (Pbacid) Proven Nickel-Cadmium (NiCd) Higher energy density than Pb-acid Improved cycle & calendar lifetime over Pb-acid Memory effect Toxicity of Cd - banned in EU for many applications now Proven Nickel-metalhydride (NiMH) Largely replaced NiCds for small portable applications Have been used in electric cars Poor self-discharge characteristics Being superseded by Li-ion Proven Cheap Can deep cycle VRLA types Limited cycle life Vented last longer than VRLA Low energy density (~40Wh/kg)

12 Types (cont) Type Pro s & Cons Maturity Various Sodium chemistries (sulphur, metal hydride, nickel chloride) GWh installed, but continue to develop Redox Flow Liquid electrolytes flow over membrane exchanging electrons Decouples capacity and power More from Green Acorn later High temperature (300 C) Grid-level Energy density 3-5 x Pb acid Overall good reliability & service life 1 infamous fire in Japan

13 Types (cont) Type Pro s & Cons Maturity Lithium-ion (Li-ion) Fastest developing battery technology because of EV market Costly, but large price reductions imminent Possibility of using 2nd hand EV batteries ~200Wh/kg energy density ~ cycle life Low self-discharge Most promising in short term for renewables Care and safety precautions required! Thermal run-away & fire under fault conditions Several different chemistries Widely used in EVs, but still developing There are many others!

14 Mistreated Li-ion batteries

15 How batteries behave Discharge Charge X kwh X kwh Not quite

16 Round trip efficiency Charge X * Ec kwh Charge losses Discharge Y * Ed kwh Discharge losses

17 To make matters worse losses are time-dependent Lead-acid discharge curves Faster discharge = lower efficiency Rate of 1C = charge / discharge full capacity in 1 hour, e.g. 0.2C discharge = full discharge in 5 hours

18 Li-ion cycle lifetime v. depth of discharge Lifetime taken to be 70% capacity remaining Cycles % 20% 30% 40% 50% 60% 70% 80% Depth of discharge per cycle 90% 100%

19 Thermal stresses affect performance & lifetime Temperature Hot or cold Lead-acid affected more than Li-ion All chemical reactions slower at low temperature, so charge / discharge reduced, but shelf life extended

20 Balloon analogy Pressure Voltage Volume State of charge

21 Self-discharge balloons are porous so are batteries

22 Limited charge / discharge rates y kwh X kw Internal resistance affects voltage & current seen at the terminals

23 Key factors for technology selection Understanding the above factors is essential for correct design Key characteristics to match to application: Power Capacity Energy density Cycle life Self-discharge rate Technology development status Reliability Safety check safety record and handling/installation precautions Manufacturer bankability

24 Power diverters PV Solar power always supplies house & appliances first Diverter The diverter senses any surplus & directs to the immersion heater, until the set water temperature is reached. Without a diverter, if there is surplus solar power, it goes out to the electricity grid

25 How diverters interface to building CT sensor around L or N only PV inverter Consumer unit N L Existing household circuits E Cable from meter Immersion circuit Energy Diverter Hot water cylinder 2 pole isolator Immersion heater

26 Loads for diverters DHW cylinder is the standard load Thermal stores Battery chargers Towel rails Storage heaters better with wind turbines U/floor heating - supply/demand mismatch with PV Some diverters have secondary load output

27 Diverters - Points to note No combi-boilers Power delivered to load must match that available from PV Watch out for interference generated (EMI)! Common switching approaches Phase angle control Burst mode control Pulse-width modulation Ask to see EMC report (CE) EN (harmonic current emissions) EN (voltage fluctuation and flicker) Issues with heat pump compatibility

28 Where to get further info IET Code of Practice to be published April Training on the CoP will be available A Good Practice Guide on Electrical Storage, EA Technology

29 For more information contact: Steve Pester NSC (Watford Office) Mob: Office: