Large Energy Storage SystemEduard Heindl

Hochschule Furtwangen University, Germany

Renewable Energy needs storage

wind 60%solar 40%

supply change

source: Lueder von Bremen, EWEC 2009

storage for up to seven days

required!

Electicity: Daily Production

Base load: coal, nuclear daily production: 1600GWh

Problem: how to use this energy

70GW

280GW

Hydro Storage capacity in Germany: 40GWh

0h midnight 24h time

„priceless energie“

solar power,wind power

Consumption in Germany

12h high noon

Energy demand: Joe Public

• 21kWh electricity a day

• 147kWh electricity a week

• Battery pricing– Car lead battery 150$/kWh – Lithium 1000$/kWh

• Storage per person for one week

25.000$ (2,2t) ... 130.000$

1km

Think Big!

1km

500m 1700GWh

capacitypower converter h

Basic Principle

•Water is pumped into a subsurface cavity, using cheap electrical power•The rock above is lifted by hydraulic forces•The storage is discharged when the energy price is high, using a power converter

power gridc

on

ne

c

t

Construction

1km

mine shaft

base tunnel, water intake

blast hole

1. tunnel

1km

construction road

deep well drilling plant

blast hole

Construction work

1km

1. tunnel

lower saw mill

construction road

wire saw

upper saw mill

Diamond wire sawing

Surface

1. Tunnel

traction

cut surface Diamondwire saw

rock

drilling holes

r

Diamond wire sawing

surface

1. tunnel

traction

Diamond wire saw

rock

drilling holes

r

cut surface

Baseplate seperation

base-tunnel

2. tunnel

traktion

sawing string

rock

drilling holes

r

cutted rock

remaining rock

top view!

Rock Bottom Area SeparationThe remaining rock granite: • Tensile strength: Ts = 11,3N/mm²= 11,3MN/m²• Burst strength : Bs = 214 N/mm² = 214MN/m²• Mass above : ma = ρ h a0 • Pressure by ma : pm= Fm/a0 = g ρ h• Neccesary remaining rock: Fm = Bsar

• Sepparating Force: Fs = Fm + Ts ar

Sepparating pressure ps

ps = Fs /(a0 –ar)ps = (Fm + Ts ar)/(a0 –ar)ps = (g ρ h a0 + Ts ar)/(a0 –ar)ps = (g ρ h a0 + g ρ h a0 Ts/Bs)/(a0 – g ρ h a0/Bs)ps = g ρ h a0 (1 + Ts /Bs)/(a0 – g ρ h a0/Bs)ps = g ρ h (1 + Ts/Bs)/(1 – g ρ h/Bs)

ma

Fm

ar

a0=ar+as

hρ

Fs

ps Bs;Ts

ps=304barh=1000m:

Cutting completed

1km

1. tunnel

2. tunnel

construction road

the wall and the floorof the cylinder are separated from thesurrounding rock

h=r

D=2r

l=2r

Energy Storage CapacityGenerated surface:M = 2 * π * r * l = 4 * π * r² (1)

Real densityρ2 = ρ1 – ρ3 (2)

Potential energy in gravitation fieldE = g * m * h (3)

Real mass of cylinder m = π * r² * 2 h * ρ2 (4)

Eq. 4 and eq. 3 using h = r results in:E = g * π * r² * 2 * r * ρ2 * r (5)

Eq. 5 condensed: E = 2 π g ρ2 * r4 the power

V=4πr³

Energiespeichervolumen als Funktion des Radius

1

10

100

1.000

10.000

100.000

1.000.000

10.000.000

100.000.000

10 100 1000 10000

Radius r [m]

En

erg

ie [

GW

h]

500

1.700

Beispiel

Daily electrical power production in Germany

Energy storage capacity depends on the Radius r

Example

Source: www.eia.doe.gov/cneaf/electricity/epm/table1_1.html

Daily electrical power production in USA

800

Sealing

• The piston has to be sealed against the wall

• The stone walls have to be free of cracks (or the cracks must be closed)

• The sealing needs to function during the movement of the piston

• The sealing has to be positioned above the centre of gravity (half of piston height)

Sealing the Walls

rock mass piston

1. tunnel

platform

sealed wall

support column

sealing

water under pressure

Saw line

Closing the Cracks

rock mass piston

piston1. tunnel

water under pressure

wall with sealant

ad sealant

seal

crack

Complete the Sealing

rock mass piston

piston 1. tunnel

water under pressure

wall with sealant

ad sealing

seal

crack

Sealing

rock mass

piston

pin joint with sensor

seal

steel

podest

water pressure

Water Volume

• Amount of water in the case of 500m radius: 390 Mio m³

• Inlet with one month filling time: 152m³/sFor comparison:

– Schluchseekraftwerk: 80m³/s– Rhine at Speyer: 1 200m³/s mean

• Inlet with one week filling time: 650m³/s

• The amount of water is manageable, especially if the system is for long term storage

Speed of movement

• Depending on the speed of filling and emptying, the piston will move with different speeds

• If we fill the cavity within a month

v = s/tvm = 500m / 2 592 000s

vm = 0.19mm/s

(filling within one day: vd = 5.8mm/s)

• The speed seems to be very low, an advantage for the sealing system

Piston position fine tuning• using a four sector pressure control

piston

low pressure sealing about

1 bar

x x

Seal low pressureseal low

pressure

seal high pressure

exchange pump

Thermal effects

• Due to the water that is pumped into the system, the stone will cool down

• This will reduce the radius of the piston• Calculation: The temperature at the bottom of

the system will be about 50°C* and the temperature will be reduced to 10°C due to the cold water, ΔT=40K, 50m depth of penetration, resulting in 6mm contraction of the granite piston

• This seems to be no problem, in addition, the sign of the change is with the proper direction

*Quelle: Regierungspräsidiums Freiburg www.lgrb.uni-freiburg.de

Price of the system

• Tunnel 50 000€/m

• Sawing 10€/m²

• Coverage 100€/m²

• Sealing 1 000€/m

• Turbines

• Generators not included

• Pumps

Kosten pro kWh Speichervolumen(ohne Konverter)

0,00

0,01

0,10

1,00

10,00

100,00

1.000,00

10.000,00

10 100 1.000 10.000

Anlagenradius r [m]

Pre

is [

€/k

Wh

]

pump storage power station

0,39

500100 1.000

example system

Price per kWh storage volume

(excluding the energy converter)

pri

ce

system radius [m]

Kosten pro kWh Speichervolumen(Verschiedene Konverter)

0,00

0,01

0,10

1,00

10,00

100,00

1.000,00

10.000,00

10 100 1.000 10.000

Anlagenradius r [m]

Pre

is [

€/k

Wh

]

0,39

500100 1.000

day

week

month

year

200€/kW

pump storage power station

example system

system radius [m]

pri

ce

Price per kWh storage volume

(using different converters, 200€/kW)

Calculation

Building cost per unit Mio €

Tunnel 50 000€/m 464

Drilling 1 000€/m 157

Sawing 10€/m² 39

Seal shield 100€/m² 157

Sealing 1 000€/m 3

Total 821

Calculation

Cost Mio €

Storage system

821

Pumps and

Generators

200€/kWh

(T=7d)

2 040

Total 2 861

Return on Investment

Turnover Mio €

Power buy per year

20€/MWh

(T=100d)

490

Power sell

Per year

70€/MWh

(T=100d)

1 200

(Q=70%)

Total 710DRAFT!

Assumption: there are 100 days (2,400h) where the power could be bought with a mean price of 20€/MWh and there are 2400h where it could be sold for 70€/MWh, the other times of the year, there is no activity. The conversion efficiency is 70% (worst case)

Return on Investment

• Under the presented assumptions, the system will be completely depreciated within 4 years

• In the future, a growing market share of regenerative energy sources, like wind and solar, will widen the spread of the price

Requirements: Storage Systems

☺Energy and power density 2MWh/m²☺Lifetime unlimited☺High current acceptance yes☺Fast response to demand for power yes☺Simple request to storage current yes☺Wide temperature range yes☺High safety standards yes☺High efficiency 70-80%☺Low service cost yes☺Simple load measurement yes☺Simple and cost efficient recycling yes

source Dirk Uwe Sauer

Maintenance Steps

• Empty system with pumps

• Open supply tunnel

• Assess sealing

• Replace sealing if necessary

• Assess wall surface

• Replace wall surfacing if necessary

Worst case scenario

• Complete broken sealing– Water exits the system along the sawing slit– Using simple assumption, about 600m³/s leek– This amount of water could be managed by

the hydro system

• Preparation– Drainage along the sawing slit– Back up sealing ring – Usage of a high viscose cover liquid

Research Topics

• Search for good places• Understanding of rock properties• Drilling deep, aligned holes• Configuration of long sawing strings• Coverage of rock for sealing• Sealing ring• Removal of ground plate• Temperature effects• High viscose material sealing• Optimal system size• High pressure pump

Thank you for your interest!Questions?

eduard-heindl.de/energy-storage