Slide 1: Large Energy Storage System Eduard Heindl Hochschule Furtwangen University, Germany

Renewable Energy needs storage: 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: 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: 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$

Slide 5: 1km

Slide 6: Think Big! 1km 500m 1700GWh

Basic Principle: capacity power 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 grid connec t

Construction: Construction 1km mine shaft base tunnel, water intake blast hole 1. tunnel 1km construction road deep well drilling plant

Construction work: blast hole Construction work 1km 1. tunnel lower saw mill construction road wire saw upper saw mill

Diamond wire sawing: Diamond wire sawing Surface 1. Tunnel traction cut surface Diamondwire saw rock drilling holes r

Diamond wire sawing: Diamond wire sawing surface 1. tunnel traction Diamond wire saw rock drilling holes r cut surface

Baseplate seperation: Baseplate seperation base-tunnel 2. tunnel traktion sawing string rock drilling holes r cutted rock remaining rock top view!

Rock Bottom Area Separation: Rock Bottom Area Separation The remaining rock granite: Tensile strength: T s = 11,3N/mm²= 11,3MN/m² Burst strength : B s = 214 N/mm² = 214MN/m² Mass above : m a = ρ h a 0 Pressure by m a : p m = F m /a 0 = g ρ h Neccesary remaining rock: F m = B s a r Sepparating Force: F s = F m + T s a r Sepparating pressure p s p s = F s /(a 0 –a r ) p s = (F m + T s a r )/(a 0 –a r ) p s = (g ρ h a 0 + T s a r )/(a 0 –a r ) p s = (g ρ h a 0 + g ρ h a 0 T s /B s )/(a 0 – g ρ h a 0 /B s ) p s = g ρ h a 0 (1 + T s /B s )/(a 0 – g ρ h a 0 /B s ) p s = g ρ h (1 + T s /B s )/(1 – g ρ h/B s ) m a F m a r a 0 =a r +a s h ρ F s p s B s ;T s p s =304bar h=1000m:

Cutting completed: Cutting completed 1km 1. tunnel 2. tunnel construction road the wall and the floor of the cylinder are separated from the surrounding rock

Energy Storage Capacity: h=r D=2r l=2r Energy Storage Capacity Generated surface: M = 2 * π * r * l = 4 * π * r² (1) Real density ρ 2 = ρ 1 – ρ 3 (2) Potential energy in gravitation field E = g * m * h (3) Real mass of cylinder m = π * r² * 2 h * ρ 2 (4) Eq. 4 and eq. 3 using h = r results in: E = g * π * r² * 2 * r * ρ 2 * r (5) Eq. 5 condensed: E = 2 π g ρ 2 * r 4 the power V=4πr³

Slide 17: 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: 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: Sealing the Walls rock mass piston 1. tunnel platform sealed wall support column sealing water under pressure Saw line

Closing the Cracks: Closing the Cracks rock mass piston piston 1. tunnel water under pressure wall with sealant ad sealant seal crack

Complete the Sealing: Complete the Sealing rock mass piston piston 1. tunnel water under pressure wall with sealant ad sealing seal crack

Sealing: Sealing rock mass piston pin joint with sensor seal steel podest water pressure

Water Volume: Water Volume Amount of water in the case of 500m radius: 390 Mio m³ Inlet with one month filling time: 152m³/s For 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: 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/t v m = 500m / 2 592 000s v m = 0.19mm/s (filling within one day: v d = 5.8mm/s) The speed seems to be very low, an advantage for the sealing system

Piston position fine tuning: Piston position fine tuning using a four sector pressure control piston low pressure sealing about 1 bar x x Seal low pressure seal low pressure seal high pressure exchange pump

Thermal effects: 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: Price of the system Tunnel 50 000€/m Sawing 10€/m² Coverage 100€/m² Sealing 1 000€/m Turbines Generators not included Pumps

Slide 28: pump storage power station 0,39 500 100 1.000 example system Price per kWh storage volume (excluding the energy converter) price system radius [m]

Slide 29: 0,39 500 100 1.000 day week month year 200€/kW pump storage power station example system system radius [m] price Price per kWh storage volume (using different converters, 200€/kW)

Calculation: 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: Calculation Cost Mio € Storage system 821 Pumps and Generators 200 €/kWh (T=7d) 2 040 Total 2 861

Return on Investment: 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 710 DRAFT! 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: 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: 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: 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: 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: 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