Lecture 6 – Large Scale Centralised Energy Storage Systems

Question 1

În which undercategory of Storage of electricty can we assign the Pumped Hydro Storage Systems?

Answer 1

Under Mechanical Energy Storage System

Question 2

What is the diffrence between Pumped Hydro Energy Storage System (PHESS) and Hydro Power Stations

Answer 2

Hydro Power Stations themselves are using water coming from rain or snow and generating electricty from them.

PHESS stores the energy with the surplus with puming it up. In most cases it doesnt even have a natural water feeder. Its just get filled water that pumped up.

Question 3

If there is a water inflow to upper resoirver we can speak from ……

If there is no natural water inflow we speak from a ……

If there is dam present but no pumping its a ……

If there is no (large) storage reservoir it is a …..

Answer 3

Pump-Back Hydroelectric Power Plant* Does not count to the regenerative energies (use of electricity mix for pumping)*

Pumped hydro storage power plant. Does not count to the regenerative energies (use of electricity mix for pumping)

Storage reservoir power plant (SpeicherKW) I*t is regenerative energy production *

Run of river power plant(LaufwasserKW) *It is regenerative energy production *

Question 4

1. Why does the PHSPPs not belong in the category of power plants?
2. What is a Black start capability

Answer 4

1. Since there is no net electricty production takes place
2. It means you can start the system without having electricty from the grid.

Question 5

Proporties PHSPP

• Energy density is …..
• ….. power and energy capacity possible
• Efficiency** …..%**

Answer 5

• Energy density is low: if you bring 1 L water up to 360 m height difference you get 1Wh of stored energy
• High power and energy capacity possible
• Efficiency 60% - 80%

Question 6

Main types of water turbines:

Answer 6

Pelton Turbine
Francis Turbine
Kaplan Turbine

Question 7

Pelton Turbine Properties

■ Free-jet turbine, constructed by engineer Lester Pelton (1879)
■ Water flows in a jet (in einem Strahl) of very high speed from one or more nozzles (Düsen (Wasserstrahlkopf)) onto the blades of the impeller.
■ Control over 1 to 6 surrounding nozzles(Düsen (Wasserstrahlkopf))
■ Suitable for ….. drop heights and ….. flow rates
■ Efficiency _ - _ %.
—-> Not suitable for ……

Answer 7

large
low
85-90
pumping operation

Question 8

Francis Turbine Properties

• Developed in 1849 by the American James Bicheno Francis
• Reaction turbine: At the impeller inlet, the pressure is higher than at the impeller outlet
• Universally usable turbine type
• Low pressure and high pressure application
• Turbine capacities up to 1 GW
• Impellers up to 150 t weight
• Efficiency up to 90 %.
• Use as** pump turbine possible**

Question 9

Kaplan Turbine Properties

• Particularly suitable for run of river power stations
• Suitable for large and fluctuating flow rates
• Efficiency 80 95%
• Can be used at drop heights of 2 30 meters

Question 10

Comparison of efficiencies

Answer 10

The Pelton and Kaplan turbines have very similar efficiency curves depending on the flow rate. They quickly reach 80% efficiency after 20% flow and go up to 90% for larger Watervolumes. The Francis turbine, on the other hand, reaches the 80% line only at a higher flow rate of about 45%.

Question 11

Operation Aspects

-> conflicting aspects, getting more difficult to build new ones (Inevest cost is also too high)
- Efficiency up to 80% -> turbine usually works at higher efficiency than pumps.
- Require ramp up times since large masses needs to be moved
- Not fast enough for primary control reserve
- Extreme fluctuations on construction costs

Question 12

Operational Characteristics

Explain the Concept of Hydraulic Short
Circuit

Answer 12

• if there is a overcapacity of 100MW in the grid, but the pump is only available at 150MW or 0MW of pumoing power due to power electronics
• Part of the water is pumped up, the rest is still operating through
  the turbine (150MW for pump,100MW from grid, 50MW from
  turbine)
• Turbine is controllable

Question 13

Under which category can we assign the Compressed Air Storage Systems (CASS)

Answer 13

With PumpedHydro and Flywheel under Mechanical Energy

Question 14

How is the working principle of diabatic CASS?

Answer 14

It has two phases:
in the first phase of Energy storage en electical motor drives a compression turbine which presses the air into a preasure vessel. The air gets hot due to pressure and we need Coolin Mechanisms.
in the second phase energy is extracted: Air flow from the vessel drives a nexpansiuon turbine which then drives a generator. Heating or a Fuel burner is needed for extraction in order to prevent ice building.

Question 15

Which components of a compressed Air Storage is there and what are their features?

Answer 15

• Compressor
• Air is compressed with energy
• Pressure increase to 70-100 bar
• Air temperature increase up to 1000°C
• Salt Cavern
• Cool air is stored in cavern
• Pressure resistant
• Lossless
• Turbine
• Flow of air through turbine -> air must be reheated prior to expansion
• Depending on technology, gas turbine or air turbine à used for grid stabilization
• Generator
• Synchronous generator: kinetic to electric energy

Question 16

Why is it hard to calculate the efficienies of these CAES?

Answer 16

Because we need external gas turbines in the system for the waste heat to use in the Extraction Phase

Question 17

Cavern serves as isovolumetric mass storage for compressed air. Technically safest and most cost-effective
geological formation are salt cushions or salt domes, into which the required storage volume is introduced
by means of extraction
- Suitable salt structures available in wide areas of Norther Europe
- No leaks from cavern and safe to use
- No risk of corrosion due to salt
- Current main application as minutes reserve

Question 18

Whats the diffrence between Compressed Air Energy Storage (CAES) and Adiabatic Compressed Air Energy Storage (A-CAES)

Answer 18

Now we have a heat storage installed. when charging compressed air
storage, the produced heat of compression is not released to environment, but caught to reheat the air coming out again
- No fossil fuel is needed anymore (so no extra gasPP)!
- Efficiency about 70%
-> sensitive heat storage with solid Material to store heat

Question 19

SWOT analysis for A-CASS

Answer 19

Strengths
CO 2 neutral
High efficiency (70 75 %)
Fast start up time (15 min)
High energy and power density
Black start capability
Low full costs for daily use

Weaknesses
High full costs for weekly storage
High investment costs (depreciation approx. 30years)
Salt caverns are expensive

Opportunities
Provision of control energy
Provision of reserve capacity
Storage of offshore energy (salt caverns in the North Sea)
CO 2 Reduction through support of fossil power plants

Risks
Limited availability of salt caves
Environmental impact of cavern excavation

Question 20

Diabetic compressed air storage
Efficiency max. ….%
Additional requirements of an energy carrier (mostly natural gas)

Adiabatic compressed air storage
Efficiency approximately …..% (predicted)
No additional …. requirement
Autonomous operation as pure storage possible
Additional …. storage necessary

Isobaric compressed air storage
Pressure in the storage is kept largely constant by water column
….. and ….. variant possible
Installation e.g. on the sea or lake bottom or in old pits

Answer 20

Diabetic compressed air storage
Efficiency max. 55%
Additional requirements of an energy carrier (mostly natural gas)

Adiabatic compressed air storage
Efficiency approximately 70% (predicted)
No additional fuel requirement
Autonomous operation as pure storage possible
Additional heat storage necessary

Isobaric compressed air storage
Pressure in the storage is kept largely constant by water column
Diabetic and adiabatic variant possible
Installation e.g. on the sea or lake bottom or in old pits