Marine Renewable Energy

Question 1

What are the main sub-categories of marine renewable energies?

Answer 1

wave energy
tidal energy
offshore wind
ocean thermal energy

Question 2

What is the formula for levelized cost of energy?

Answer 2

(OPEX + CAPEX) / E

exes over E in £/kWh

Question 3

Ocean waves a re a concentrated form of what energy?

Answer 3

solar energy

Question 4

the characteristics of waves depends on what two factors?

Answer 4

fetch

duration of wind

Question 5

what is wind fetch?

Answer 5

length that wind acts on ocean surface

Question 6

What is a wave?

Answer 6

a disturbance travelling through a medium

Question 7

The total power of a regular wave in deep water is measured by what unit?

Answer 7

per unit length of wave front

Question 8

What is the formula for total wave power?

Answer 8

P=(1/8pi )rhog^2a^2*T

a=amplitude
T=wave period

Question 9

Closer to shore, the magnitude of harvested wave power is usually . .

Answer 9

less than in the sea

Question 10

Seasonal variations in the potential energy gained from wave energy are much larger in which hemisphere?

Answer 10

north - stormy winters can generate more wave energy

Question 11

What is a WEC?

Answer 11

wave energy converter - a floaty boi

a.k.a PTO (Power take off), transforms mechanical energy into electricity.

Question 12

how does as WEC work?

Answer 12

piston compress fluid that is stored in a high-pressure accumulator.

pressure diff between high and low pressure accumulators is used to drive electrical generator

Question 13

wave energy absorption can be defined as a [] process

Answer 13

wave interference

Question 14

what is the saying which describes wave interference?

Answer 14

“to destroy a wave means to create a wave” - placing a WEC system in a wave causes destructive interaction and therefore waves of its own

Question 15

energy gained from WEC is maximised when it experiences what phenomenon?

Answer 15

resonance?

Question 16

WEC technologies are classified using:

Answer 16

WEC working principle
dimension/configuration
location - offshore, nearshore, shoreline

Question 17

Which three main types of WECs can be defined based on their working principle?

Answer 17

oscillating water columns
oscillating bodies
overtopping devices

Question 18

oscillating water columns can exist in which two types?

Answer 18

floating or fixed

Question 19

WECs can be either

Answer 19

heaving or pitching

Question 20

what is the difference between heaving or pitching WECs?

Answer 20

heaving - bob up and down
pitching - pivot back and forth

Question 21

How does an overtopping device operate?

Answer 21

Waves approach the device and climb up its slope to be stored.

This water can then be released and harnessed for its kinetic energy

Question 22

In what area are overtopping devices best suited?

Answer 22

Areas with large amounts of land to build on with tall oncoming waves

Question 23

What is a limitation of overtopping devices?

Answer 23

They are costly and large and must be optimised to their environment

Question 24

What are some types of overtopping devices?

Answer 24

fixed or floating

Question 25

What is the main difference between the two types of overtopping devices?

Answer 25

Fixed ones are either anchored or built into the land Floating ones float whilst being connected to the sea bed via mooring lines or cables. - more expensive but better for deep sea and less prone to damage as it floats with the water

Question 26

The periodic rise and fall of water in the oceans is know as

Answer 26

tide

Question 27

The difference in sea level between high and low tide is known as

Answer 27

tidal range

Question 28

Incoming flow of water is called

Answer 28

flood

Question 29

outgoing flow of water is called

Answer 29

ebb - bye bye

Question 30

The flow of water is known as

Answer 30

tidal current/tidal stream

Question 31

why do we observe two tides per day?

Answer 31

cause by rotation of the Earth along its own rotation axis and not the rotation of the moon around the Earth.

Question 32

The existence of two low-tides and two high-tides per day is called what?

Answer 32

semi-diurnal cycle - 2 full periods every day

Question 33

What happens when the sun and moon are aligned(and therefore their gravitational forces)?

Answer 33

spring tide - heightened tide paired with orthogonally placed lowest tide

Question 34

What happens when the sun and moon are perpendicular (and pulling 90 degrees apart)?

Answer 34

neep tide - lowest high tide, tallest low tide

Question 35

The cycle of neap/spring tide has a period of how many days?

Answer 35

14

Question 36

What is tidal range defined as?

Answer 36

difference in sea level between high and low tide

Question 37

what does electricity generation from the tidal range utilise?

Answer 37

the gravitational potential energy an artificial change in height produced by an built obstacle has

Question 38

in nearshore locations tidal currents are [] around headlands or through constrictions

Answer 38

accelerated

Question 39

Electricity generation from tidal currents capitalizes on what form of energy which is found in free flowing water?

Answer 39

kinetic energy

Question 40

Which two forms do tidal range power plants normally take?

Answer 40

tidal barrage or tidal lagoon

Question 41

What are the main components of a tidal range power plant?

Answer 41

sluice gates bulb turbines impoundment

Question 42

What kind of structure might a tidal barrage have?

Answer 42

hundreds of metres long, spanning entire river estuaries

Question 43

What kind of structure might a tidal lagoon have?

Answer 43

encloses an area of coastline with high tidal range behind a breakwater

Question 44

What are the types of tidal stream devices?

Answer 44

horizontal axis turbine vertical axis turbine oscillating hydrofoil Archimedes screw tidal kite

Question 45

what is the main advantage of the tidal kite?

Answer 45

relative velocity felt by the turbine attached to the kite is increase, good for low energy sites

Question 46

what are some environmental consequences of tidal energy shcemes?

Answer 46

disturbance to marine life must coexist with fishing industry large installations can affect: sediment transfer paths, tidal currents water quality might be affected

Question 47

How is the flow of water at the sea bed affected by the sea bed itself?

Answer 47

friction provided by sea bed slows the flow down

Question 48

what is the main difference between first and second generation tidal stream devices?

Answer 48

first generation sit on the sea bed second generation are floaty bois

Question 49

how were 1st gen support structures for horizontal-axis turbines designed?

Answer 49

with extremely heavy weights to resist sliding along the sea bed and bending on the vertical lever arm

Question 50

1st gen structures of tidal stream devices were . .

Answer 50

expensive limited to use on shallow sites

Question 51

2nd gen support structures include:

Answer 51

buoyancy modules (large floaty pills) mooring systems under tension

Question 52

why can't a turbine extract all the kinetic energy from a flow?

Answer 52

the flow would stop