Chapter 10 : Energy Storage

Question 1

State one problem associated with generating electricity from ocean waves (1)

Answer 1

Any one from;

• Intermittency of wave energy sources. (1)

• Reliability of wave energy sources. (1)

Question 2

Renewable energy sources have the potential to deliver a significant proportion of our energy needs in the future. State one main reason why energy storage facilities are needed in order for us to make optimum use of renewable energy sources such as wind, solar, wave and tidal. {1}

Answer 2

Energy supplies from renewable energy sources (e.g. wind, solar, wave, tidal) tend to be unreliable or intermittent. {1}

Question 3

There are significant wind energy resources available in and around Northern Ireland. State one main reason why we need good energy storage facilities if we are to make optimum use of the available wind energy resources. {1}

Answer 3

Energy supplies from renewable souorces (wind/solar/tidal) tend to be unreliable and/or intermittent {1}.

Question 4

Identify the type of energy storage facility shown in the figure above and describe how the system operates. {4}

Answer 4

Pumped hydro storage. {1}

It utilises renewable energy to pump water up to the high dam / reservoir. {1}

It uses the gravity fed water supply to turn turbines {1} whenever there is a lull in renewable power {1}.

Question 5

State one other method of energy storage. {1}

Answer 5

Compressed air energy storage (CAES) {1}

Question 6

(ii) With reference to Fig.4 describe a Compressed Air Energy Storage (CAES) system operates. {4}

Answer 6

At times of low demand (off peak) electrical energy from a renewable energy source {1} compresses air for storage in an underground store / tavern.

At times of high demand air is released to the surface and heated using gas to expand its volume {1}; and is then used to drive a turbine creating electricity {1}.

Question 7

With reference to Fig. 2, describe how a pumped hydro system operates. (3)

Answer 7

Potential energy is stored in the upper reservoir in the form of water. [1]

During periods of peak demand for electricity this water is released to flow through the generator to produce electric power. [1]

Water is pumped back to the upper reservoir during periods of low demand in readiness for the next cycle. [1]

Question 8

Discuss two features of locations for pumped hydro energy storage that are required to make it cost-effective. (4)

Answer 8

1. Availability of existing water facilities (lakes/reservoirs) [1] to avoid the
   need for excavation with associated costs and environmental impact. [1]
2. A suitable head height [1] so that there is sufficient potential energy stored in the upper facility to drive a turbine and generate electricity. [1]
3. Proximity to transmission lines. The facility needs to connect to the grid as cheaply as possible. [1] Installing new transmission networks
   causes environmental and social issues as well as adding to cost. [1]

Question 9

State three factors that would make a potential location both beneficial as well as cost effective for the type of energy storage facility shown below. {3}

Answer 9

Any three factors from;
• Availability of existing lakes / reservoirs. {1}
• Suitable topography – good height difference (‘head’) between lower and upper reservoirs. {1}
• Proximity to high voltage power transmission network. {1}
• Accessibility for construction, operation and maintenance. {1}
• Lack of environmental concerns / objections. {1}