Energy Storage

Question 1

What are the main types of energy storage?

Answer 1

• pumped water storage
• compressed air energy storage
• thermal energy storage
• liquid air
• battery
• hydrogen and fuel cells

Question 2

Describe the concept of pumped water storage

Answer 2

• Water is pumped to a high storage reservoir during off-peak hours and weekends, using the excess capacity from coal or nuclear sources. During peak hours can be used for hydroelectric generation
• Recovers about 75% of energy consumed
• Requires to nearby reservoirs at considerably different heights and considerable capital expenditure

Question 3

Describe the concept of compressed air energy storage

Answer 3

• off peak electricity is used to power a motor/generator that drives compressors to for air into an underground storage reservoir
• energy density is about 50 x greater than hydroelectric

Question 4

Describe the concept of thermal energy storage

Answer 4

• store heat usually from active solar collectors in an insulated repository for later use in space heating, domestic, energy generator ect.
• molten salt has been proposed as means to retain a high temperature
• the salt melts at 220 degrees and is pumped to the top of a tower were concentrated sunlight heats it in a receiver
• heated salt then flows back down a second insulated hot storage tank and when electricity is needed the hot salt is used to produce superheated steam for a turbine

Question 5

Describe the concept of liquid air energy storage

Answer 5

• converting electricity to liquid air and back again, about 25% efficient
• better heat and cold storage systems have raised efficiency to 70%

Question 6

Describe the concept of battery storage

Answer 6

• used in load levelling for UPS (uninterrupted power supplies)
• used in many off-grid systems
• vanadium redox batteries and other types of flow batteries are being used
• difference in potential between 2 electrolytes and drive a charge through membrane
• vanadium potentially cheaper, but more complicated and material issues (corrosion)

Question 7

What types of energy storage are used for transport

Answer 7

• battery
• supercapacitors
• hydrogen fuel cells