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High Temperature Energy Storage in a Rock Bed

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High Temperature Energy Storage in a Rock Bed

Kurt Engelbrecht, Stefano Soprani, Loui Algren, Kenni Dinesen, Thomas Ulrich, Ole Alm, Eva Sass Lauritsen, Fabrizio Marongiu, Allan Schrøder Pedersen

(2)

DTU Energy, Technical University of Denmark

Project Description (HT TES project)

2

Source: SEAS-NVE

Heat is stored at high temperature (600 ⁰C).

The heat is used to produce high pressure steam to expand in a turbine.

Funded by EUDP

(3)

DTU Energy, Technical University of Denmark

Project Challenges and Research Areas

3

• Choose suitable rock material

• Design of the rock bed

• System testing

• Model rock bed operation, both thermal and economic aspects

(4)

DTU Energy, Technical University of Denmark

Brief summary of thermal rock storage

4

• Low cost electricity is stored as heat in a rock bed then used to produce electricity or district heating when prices are high

• Due to the reduced efficiency associated with thermal conversion to electricity, the technology relies on relatively high electricity price fluctations

• The main advantages are low cost and easy scalability

• Storage period is a few days up to several weeks, depending on the insulation and thermal losses

(5)

DTU Energy, Technical University of Denmark

Rocks…the very basics

‘Monomineralic’ rocks (>90% one mineral)

‘Polymineralic’ rocks:

(several minerals)

Quartzite (Hardeberga, Sweden) Magnadense (Kiruna, Sweden) Dunite (Norway)

Ansite (Norway)

Granite (Bornholm)

Norite/Gabbro (Telnes, Norway) Diabas (Finland, Sweden)

Basalt (Germany/Austria) Hyperite (Norway)

Rock texture

Mineral 1

Mineral 2 Mineral 3

(6)

DTU Energy, Technical University of Denmark

Dunite

before after

After heating

1000um

olivine

Microscopic textur e

1000um

Before heating

olivine

(7)

DTU Energy, Technical University of Denmark

Rock selection for first experiments

7

• We chose Swedish diabase as the first rock material

• Cheap and available day-to-day in Denmark

• Available in different sizes

• Able to withstand cycling to 600 C

• First rocks tested were sieved between 20 mm and 40 mm

• We are looking at different rock types and sizes for future experiments

(8)

DTU Energy, Technical University of Denmark

Experimental setup “shoebox”

8

Heater

Fan Thermal

insulation

Hot end Cold end

Containment grids

20 October, 20 October, 2017 2017

(9)

DTU Energy, Technical University of Denmark

Experimental setup “shoebox”

9 20 October,

20 October, 2017 2017

(10)

DTU Energy, Technical University of Denmark

Experimental setup “shoebox”

10

Fan Hot-end

16 x temperature sensors To the chimney

(outside)

Heater (behind the ”shoebox”)

Cold end

Size = 1.5 m3 of rocks ~ 450 kWhth ΔT=600C Max. charging rate = 25 kW

20 October, 20 October, 2017 2017

(11)

DTU Energy, Technical University of Denmark

Experimental result - charging

11

Heater power 25 kW

(12)

DTU Energy, Technical University of Denmark

Experimental result - discharging

12

(13)

DTU Energy, Technical University of Denmark

Experiment status

13

• Initial testing indicated that heat losses were a problem and more insulation has been added.

• Our first heater is broken and we are waiting on its replacement

• Next step is to fully test the 20-40 mm Swedish diabase

• Future tests will investigate the effects of varying the rock size

(14)

DTU Energy, Technical University of Denmark

Modelling efforts in the project

14

• Inside the project we have both economic models of the Danish electricity market and the cost of the thermal storage and a numerical model of thermal interactions in the rock bed.

• A goal of the project is to couple the two models to give accurate performance predictions and a prediction for how a company might invest is such a storage based on realistic market conditions

(15)

DTU Energy, Technical University of Denmark 15

15

EL-1

High temp.

air El

DK1

HT-TES Charger (heater+fan)

HRSG Steam Turbine

Steam

04-12-2017

Economic model: electricity storage

• Model considers both a scenario with a higher mix of renewables for 2035 and actual market

prices for Denmark in 2015.

• Prices of all necessary

components are inputs to the model

• Main output is how large an investment in the system is optimal

(16)

DTU Energy, Technical University of Denmark

Case 1:

electricity storage 2035 prices

04-12-2017 HT-TES WP4 modeling

16

Unit CAPEX [DKK/M W]

OPEX[DKK/M W/y]

Yearly

investment Cost[MDKK]

Invested capacity

Charger 625,000 6250 2.9 MDKK 55.6 MW_el Discharg

er 4,580,000 180,000 2.8 MDKK 5.5 MW_el / 12 MW_th

Storage 2,620 0 0.2 MDKK 1000

MWh_th

Revenue 7.76 MDKK

(17)

DTU Energy, Technical University of Denmark HT-TES WP4 modeling 04-12-2017 17

Unit CAPEX [DKK/MW ]

OPEX [DKK/M W/y]

Yearly

investment Cost[MDKK]

Invested capacity

Charger 625,000 6250 0.34 MDKK 6.5 MW_el Dischar

ger 5.5 MW_el /

12 MW_th

Storage 2,620 0 0.10 MDKK 540 MWh_th

Revenu

e 0.75 MDKK

Case 2:

electricity storage

DK1 2015 prices

(18)

DTU Energy, Technical University of Denmark

Governing Equations of a 1D Numerical Rock Bed Model

          

2 2

f f f f

f f f s c f r f f f c f

h

r disp c

N uR e,P r k T

m tc T T aAT T c T A T

x d t

e n th a lp y flo w h e a t tr a n s fe r to c a p a c ity o f e n tr a in e d flu id r e g e n e r a to r m a te r ia l

k A T x a x ia l d is p e r s io n

 

            

 

 



f

m t p x

v is c o u s d is s ip a tio n

 

 

f f

  

f f scf r c

  1

o effc22r rc

  1

r

h

N u R e , P r k T M T u a A T T A H k A A

d t x t

a x i a l

m a g n e t i c w o r k e n e r g y s t o r e d h e a t t r a n s f e r f r o m f l u i d

c o n d u c t i o n

i n m a t r i x

   

    

  

Fluid:

Regenerator:

x

 

,

oH x t

T

f

(x,t)

T

r

(x,t)

 

m t

(19)

DTU Energy, Technical University of Denmark

Coupling economic model to 1D model

19

• Bed size

• Charge and discharge

characteristics

• Heater power

1D model inputs

• Rock type

• Bed geometry

• Air flow rate etc Run 1D model over an entire

year

(20)

DTU Energy, Technical University of Denmark

Some model constraints

20

• Minimum temperature for steam productin is 530 C

• Charge inlet temperature is 600 C

• Maximum outlet temperature is 300 C

• We use the return temperature from the heat recovery steam generator as the inlet discharge temperature (100 C)

• Initial rock bed temperature is 20 C

(21)

DTU Energy, Technical University of Denmark

Full year rock bed operation for 2035

21

• Economic model calls for a bed that is approximately 3,400 m3 in volume.

First we model a 15 x 15 x 15 m3 rock bed

(22)

DTU Energy, Technical University of Denmark

Full year rock bed operation for 2035

22

• “Skinny” bed 10 x 10 x 33.75 m

(23)

DTU Energy, Technical University of Denmark

Predicted power supplied to power cycle

23

(24)

DTU Energy, Technical University of Denmark

Preliminary model conclusions

24

• Sometimes the temperature in the bed is too low to produce steam, although the economic model expects a power production

– May need a minimum charge energy constraint in the economic model

• System optimization based on rock bed dimensions and rock size is necessary

• We have demonstrated modelling a full year of operation using a detailed 1D numerical model of the rock bed

– System optimization of such a rock storage will be performed in the near future

• Pressure drop can become a major issue for long beds or small rock sizes

• Reducing rock size from 20 mm to 16 mm gives approximately 2% more power production over the full year

• Reducing the length of the bed to 8.4 m while increasing cross sectional area gives a reduction in power production of 5.5% over the full year

(25)

DTU Energy, Technical University of Denmark

Conclusions

25

• At DTU we have a functional 1.5 m3 rock bed storage that can operate at temperatures up to 600 C

– Capable of quickly testing different rock types and sizes and system configurations

• Economic modelling shows that for 2015 prices, the system needs to use an existing steam turbine to be economical

– Using a 2035 scenario with higher renewable mix it can make sense to invest in a new turbine dedicated to a rock storage unit

• We have demonstrated modelling a full year of operation using a detailed 1D numerical model of the rock bed

– System optimization of such a rock storage will be performed in the near future

20 October, 20 October, 2017 2017

(26)

DTU Energy, Technical University of Denmark 26

THANK YOU FOR YOUR ATTENTION

20 October, 2017

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