Thermal storage options for CSP

Thomas Roos

Overview

• Introduction: Why Energy storage?

• Options, TES concept and TES classification

• Different CSP systems: different TES

• HTF = oil, steam, molten salt and air

• Conclusion

Why energy storage?

• Mismatch in supply & demand

• Constant supply, variable demand

• Coal-fired baseload & peaked grid: pumped storage

• Domestic hot water geyser

• Intermittent supply

• Cellphone & laptop: charger & battery

• Household scale solar: PV and batteries

• Grid-scale wind or solar?

Energy storage options

• Electrical – batteries, capacitors

• Chemical – reversible chemical reactions

• Potential – clock weights, pumped storage

• Kinetic – flywheels

and

• Thermal – ice, hot water bottles, geysers and thermal storage for CSP

• Heat cheaper than electricity to store!

© OECD/IEA

2010

Source:

SolarMillennium

Thermal energy storage (TES) concept

• Oversize solar field and store excess heat

• Operate in cloud transients and at night

• Increase capacity factor

4 TES concepts, same field

Load Type

Storage

Turb

ine

Production Start

End

Ho

urs

Intermediate S M 08 19 11

Delayed M M 12 23 11

Baseload L S 00 24 24

Peak load L L 11 15 4

© OECD/IEA, 2010

Source: J Octobre & F Guihard, Systèmes Solaires, 2009

TES classification

• Sensible heat

• HTF itself: Steam, oil, molten salt, liquid Na (fire)

• Separate medium: concrete, molten salt, ceramic

• Mixtures: Fe, rocks, sand in conjunction with oil

• Latent heat

• Phase Change Materials (PCM: eg nitrate salts)

• Thermo-chemical storage (not yet)

© RENAC, 2009

Different CSP systems: different TES

• No one single TES type for all CSP systems

Config. HTF TES

Trough Oil MS: 2-tank, or 1-tank thermocline

Solid material (concrete)

Steam Concrete, PCM, Ruths storage

Molten Salt MS: 2-tank, or 1-tank thermocline

Tower Steam PCM, Ruths storage

Molten Salt MS: 2-tank, or 1-tank thermocline

Air Packed bed, solid matrix © RENAC, 2009

HTF = oil, TES = 2-tank molten salt

• Andasol 1 (50 MWel):

• D = 38.5 m, H = 14 m, Vol = 28 000m3, tstore = 7.5h

• Tcold = 292 °C, Thot = 386 °C (Oil T limited)

• 3 pumps in hot tank, 4 pumps in cold tank

© OECD/IEA 2010 Source: SolarMillennium © DLR, RENAC 2009

HTF = oil, TES = Concrete

• Metallic tubes 65 – 75% of cost

• Not yet commercially operational

©DLR, Tamme

HTF = steam, TES = PCM

• Meant for evaporation part of DSG plant

• Advantage: Const. T and ΔT during evaporation

©DLR, Tamme

HTF = steam, TES = PCM

• TPCM must match Tevap

• PCM: Salts >200 °C © DLR, RENAC 2009

Steam HTF, PCM TES

• kPCM controls heat transfer

• But ksalts are poor, so:

• PCM/graphite composite (h = 5-10 W/mK)

• Finned tube sandwich (h > 10 W/mK) © DLR,

RENAC 2009

HTF = steam, TES = PCM & concrete

• Pilot

• PCM evaporator (right)

• concrete superheater (left)

• Litoral power station

• Carboneras, Spain

© DLR 2011

HTF & TES = steam: Ruths storage

PS10: 40bar sat. steam pressure vessel

• Sliding pressure during discharge

• Thermal capacity is proportional to ΔT

• High CAPEX cost due to pressure vessel

• Not for large scale / high P applications

© DLR, RENAC 2009

HTF = MS, TES = 2-tank MS

• No HTF/TES heat exchangers

• Higher ΔT than MS/oil, so:

• smaller volume reqd.

• More efficient cycle

Trough Tower

Name Archimede Gemasolar

Site Sicily Spain

Turb. 5 MW 19.9 MW

Tcold 290 °C 290 °C

Thot 550 °C 565 °C

tstore 8h 15h

HTF = air, TES = solid media

• TSA used 1 MWh packed bed of spherical Al2O3 ceramic pebbles

• KAM use ceramic regenerator storage material at Jülich, 680 °C/120 °C

• Sand receivers and storage, and rock beds are receiving attention due to potential low costs

SUPSI, Switzerland

HTF = air, TES = solid media

• SUNSPOT concept (Stellenbosch University)

HTF = air, TES = solid media

• TES for solar gas turbines (≥800 °C, >4atm)

• Currently no published solutions exist

• DLR have published a simulation of a pressurised packed bed of steel pebbles

• Wilson SolarPower: SolarBatteryTM “dry storage medium”

• CSIR are building a CSP research facility, including storage:

• 100kWel gas turbine

• 500kWth heliostat field

• 3 hours high temperature storage

Conclusion

• Reiner Tamme of DLR says: The question is not

• “What is the best thermal storage technology?”

• but

• “What is the best CSP concept including storage?”

• The TES solution must match the CSP technology (no “one size fits all”)

Thank you for your attention!