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Energy & Environment > Marine Renewable Energy > Flashcards

Marine Renewable Energy Flashcards

1
Q

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

A

wave energy
tidal energy
offshore wind
ocean thermal energy

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2
Q

What is the formula for levelized cost of energy?

A

(OPEX + CAPEX) / E

exes over E in £/kWh

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3
Q

Ocean waves a re a concentrated form of what energy?

A

solar energy

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4
Q

the characteristics of waves depends on what two factors?

A

fetch

duration of wind

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5
Q

what is wind fetch?

A

length that wind acts on ocean surface

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6
Q

What is a wave?

A

a disturbance travelling through a medium

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7
Q

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

A

per unit length of wave front

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8
Q

What is the formula for total wave power?

A

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

a=amplitude
T=wave period

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9
Q

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

A

less than in the sea

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10
Q

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

A

north - stormy winters can generate more wave energy

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11
Q

What is a WEC?

A

wave energy converter - a floaty boi

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

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12
Q

how does as WEC work?

A

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

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13
Q

wave energy absorption can be defined as a [] process

A

wave interference

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14
Q

what is the saying which describes wave interference?

A

“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

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15
Q

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

A

resonance?

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16
Q

WEC technologies are classified using:

A

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

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17
Q

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

A

oscillating water columns
oscillating bodies
overtopping devices

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18
Q

oscillating water columns can exist in which two types?

A

floating or fixed

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19
Q

WECs can be either

A

heaving or pitching

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20
Q

what is the difference between heaving or pitching WECs?

A

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

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21
Q

How does an overtopping device operate?

A

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

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

22
Q

In what area are overtopping devices best suited?

A

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

23
Q

What is a limitation of overtopping devices?

A

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

24
Q

What are some types of overtopping devices?

A

fixed or floating

25
Q

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

A

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

26
Q

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

A

tide

27
Q

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

A

tidal range

28
Q

Incoming flow of water is called

A

flood

29
Q

outgoing flow of water is called

A

ebb - bye bye

30
Q

The flow of water is known as

A

tidal current/tidal stream

31
Q

why do we observe two tides per day?

A

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

32
Q

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

A

semi-diurnal cycle - 2 full periods every day

33
Q

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

A

spring tide - heightened tide paired with orthogonally placed lowest tide

34
Q

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

A

neep tide - lowest high tide, tallest low tide

35
Q

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

A

14

36
Q

What is tidal range defined as?

A

difference in sea level between high and low tide

37
Q

what does electricity generation from the tidal range utilise?

A

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

38
Q

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

A

accelerated

39
Q

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

A

kinetic energy

40
Q

Which two forms do tidal range power plants normally take?

A

tidal barrage or tidal lagoon

41
Q

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

A

sluice gates

bulb turbines

impoundment

42
Q

What kind of structure might a tidal barrage have?

A

hundreds of metres long, spanning entire river estuaries

43
Q

What kind of structure might a tidal lagoon have?

A

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

44
Q

What are the types of tidal stream devices?

A

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

45
Q

what is the main advantage of the tidal kite?

A

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

46
Q

what are some environmental consequences of tidal energy shcemes?

A

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

47
Q

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

A

friction provided by sea bed slows the flow down

48
Q

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

A

first generation sit on the sea bed

second generation are floaty bois

49
Q

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

A

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

50
Q

1st gen structures of tidal stream devices were . .

A

expensive

limited to use on shallow sites

51
Q

2nd gen support structures include:

A

buoyancy modules (large floaty pills)

mooring systems under tension

52
Q

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

A

the flow would stop

Energy & Environment (13 decks)

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