Pumped Thermal Exergy Storage Past, Present and Future Alexander White Josh McTigue, Pau Farres-Antunez, Haobai Xue Caroline Willich, Christos Markides (Imperial), Chris Dent (Durham) Department of Engineering UK Energy Storage Conference. 1 st December 2016
What is Pumped Thermal Exergy Storage? Heat pump Storage Heat engine Work Thermal exergy Thermal exergy Work +? The literature uses several names PHES: Pumped Heat Electricity Storage TEES: Thermo-Electrical Energy Storage CHEST: Compressed Heat Energy Storage SEPT: Stockage d Electricité par Pompage Thermique
Possible embodiments of PTES T h T h Q h Cold Storage Q h W p CHP Q 0 W p CHP Q 0 W p CHP T 0 Q c Hot Storage Q c T c T c Combined
Possible embodiments of PTES (red = Isentropic s PHES) Storage type: - hot / cold / combined - sensible heat / latent heat - packed bed / liquid tank / other (e.g., concrete) Thermodynamic cycle: - Rankine / Joule-Brayton / other (e.g., transcritical CO 2 ) Compression & expansion: - turbomachinery / reciprocating / other Heat exchange: - direct (packed bed) / intermediate HX
A (very) brief history of PTES 1852: Kelvin s Heat Multiplier 2007: (Oct): Isentropic s PHES patent
A (very) brief history of PTES 1924: Thermodynamic steambased storage device (Marguerre) 1978: First solely thermal energy storage system (Cahn) 1852: Kelvin s Heat Multiplier 1977: Forerunner of LAES (Smith) 2007: (Oct): Isentropic s PHES patent 2007: (Jan): PHES patent (Wolf) Last Thursday: Isentropic s SVS engine is turned over
Whole-system analysis (Strbac et al 2012) Annual saving, bn/y Bulk storage (2020) Distributed storage (2020) Storage cost, /kw.y Storage cost, /kw.y 1.2 46 31 25 1.2 111 75 41 1.0 1.0 0.8 savings 0.8 0.6 cost 0.6 0.4 0.4 0.2 0.2 0.0 0.0-0.2-0.2-0.4-0.4 2 5 10 2 5 10-0.6-0.6 Installed capacity, GW Installed capacity, GW Annual saving, bn/y Savings from distributed storage are greater for a given storage cost Benefits are relatively insensitive to storage efficiency
Cost minimisation and endoreversible stuff (Thess, Guo et al) A crude model of costs: Total cost = Engine cost + Cost of heat exchange + Storage cost C = k e W e + k x A x + k s E s ρ e C A W = k e + k x t x + k d s e W e η e ρ e endoreversible analysis minimises this
Cost minimisation and endoreversible stuff (Thess, Guo et al) A crude model of costs: Figure courtesy of Markides Total cost = Engine cost + Cost of heat exchange + Storage cost C = k e W e + k x A x + k s E s ρ e C A W = k e + k x t x + k d s e W e η e ρ e endoreversible analysis minimises this
Endoreversible analysis: maximum power of CHE T 4 T h Q 1 = α h (T h T 1 ) Chambadal-Novikov efficiency: η e * = W p Q 1 = 1 T 0 T h T 1 Ẇ p RHP RHE Ẇ e Maximum normalised power: T 2 Q 2 = α 0 (T 2 T 0 ) ψ e = W e = ( T h / T 0 1) 2 (α h + α 0 )T 0 4 Occurs at T 1 / T 2 = T h / T 0 and α 0 = α h T 0 T 3
Endoreversible analysis: efficiency for hot storage T 4 Q 4 = k Q 1 T h Q 1 = α h (T h T 1 ) T 1 k = discharge time, t d charge time, t c Round-trip efficiency: Ẇ p Ẇ e RHP RHE χ = COP p η e = (k + 1)θ k (k + 1)θ + 1 T 2 Q 2 = α 0 (T 2 T 0 ) where: θ = T h / T 0 T 0 T 3
Endoreversible analysis: efficiency for hot storage T 4 Q 4 = k Q 1 Storage temperature, o C -250 0 250 500 T h 0.6 Hot storage Q 1 = α h (T h T 1 ) 0.5 Ẇ p Ẇ e RHP RHE T 1 T 2 Round-trip efficiency, 0.4 0.3 0.2!! Q 2 = α 0 (T 2 T 0 ) 0.1 T 0 0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 T 3 Temperature ratio, T s / T 0
Endoreversible analysis: efficiency for cold storage T 4 T 0 Storage temperature, o C -250 0 250 500 Q 1 = α 0 (T 0 T 1 ) 0.6 Cold storage Hot storage T 1 0.5. W p RHP RHE. W e T 2 Q 2 = α c (T 2 T c ) Round-trip efficiency, 0.4 0.3 0.2 T c 0.1 Q 3 = k Q 2 0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 T 3 Temperature ratio, T s / T 0
Endoreversible analysis: efficiency vs. power density 0.6 500 Round-trip efficiency, 0.4 0.2 100-75 -125 300-175 Hot Cold 0.0 0.00 0.05 0.10 Normalised power output, e
Endoreversible analysis: combined hot & cold storage 0.6 T c = -150 o C 500 Round-trip efficiency, 0.4 0.2 100-75 -125 300-175 Hot Cold Combined 0.0 0.00 0.05 0.10 Normalised power output, e
Exergetic storage density (kwh / m 3 ) Exergetic density, kwh / m 3 250 200 150 100 50 0 PTES cold liquid N 2 CAES PHS hot water PTES hot -250-125 0 125 250 375 500 Storage temperature, o C
Isentropic s SVS (Scaled Validation Model of PHES) Hot and cold layered thermal stores for a 120 kw system HOT (500 o C) COLD ( 150 o C)
Efficiency-cost optimisation (packed-bed reservoirs) 100 Open symbols = layered stores 98 valves Efficiency (%) 96 94 92 90 88 R1: Hot (Argon) R2: Cold (Argon) 86 0.75 1.00 1.25 1.50 1.75 Normalised cost per unit returned energy Isentropic s layered store concept GA optimisation for different packed-bed thermal reservoirs (Josh McTigue, 2015)
Isentropic s SVS : The Engine Double-acting reversible reciprocating compressor / expander HOT side COLD side (below gallery)
PTES is sensitive to all loss parameters (low work ratio ) heat exchange effectiveness χ = fn( P i, T i, η j, ε k, f l ) polytropic efficiencies pressure loss factors 100 = 0.99 100 Thermodynamic efficiency, 90 80 70 60 = 0.95 = 0.90 Thermodynamic efficiency, 90 80 70 60 = 0.99 = 0.95 = 0.90 50 0 5 10 15 50 0 25 50 75 100 Pressure ratio, Pressure ratio, Liquid PTES 2-stage A-CAES
Compression & Expansion Losses: Valve Losses Early prototype piston / valve arrangement for a heat pump P-V diagram from an off-the-shelf compressor Isentropic s cunning valve design P-V diagram from Isentropic s device
Compression & Expansion Losses: Thermodynamic Losses 10 1 isothermal adiabatic 10 0 10 1 Loss 10 2 10 3 CFD Air r v =6.8 CFD Helium r =6.8 v CFD Helium r v =2.0 Exp. Helium r v =2.0 10 2 10 0 10 2 10 4 Pe slow fast
Load-Integrated Energy Storage (LIES) Electricity in Low-grade heating Refrigeration and / or cooling Electricity out
More LIES T-s Diagram T-s Diagram 600 Charge Discharge 2 600 Charge Discharge 2 400 400 Temperature, C 200 3 Temperature, C 200 3 0 q out < 50 o C 1 0 1-200 4 q out < 50 o C -200 4 q out > 75 o C -0.4-0.2 0-0.4-0.2 0 Specific Entropy, KJ/kgK Specific Entropy, KJ/kgK Optimised for work output Lower discharge pressure
The UK s Energy Storage Inventory (data from DOE) 3.5 PHS Mechanical Batteries 3.0 Installed capacity, GW 2.5 2.0 1.5 1.0 0.5 0.0 1963 1965 1974 1984 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016
SUMMARY q PTES has good potential for distributed storage q High power density and efficiency go together for (hot + cold) storage q Possible scope for load integration (cooling / heating) q Low temperature PTES is probably best used for low-grade heat q High compression and expansion efficiencies need to be demonstrated q To reap the benefits of a whole-system approach it s probably best to have a whole system