Renewable Energy Quiz 3

Biomass

mass of plant material formed from solar energy, water, and air, or any organiz material that is renewable

Biosphere

thin layer on the Earth’s surface in which its total biomass exists

Composition of biomass

75 percent carbohydrates 25 percent lignin forms woody cell walls of plants

Bagasse

sugar cane refuse left after pressing the juice from the cane

Co-fire

to burn an additional fuel with primary fuel, such as bagasse or sawdust with coal

IWS

Industrial Waste Stream (waste wood, plastics, fiber, etc.)

MWS

Municipal Waste Stream (Trash, plant trimmings, garbage (batteries, heavy metals, etc.)

hydrogen to oxygen ratio in carbs

2:1

4 types of carbs

glucose, starch, cellulose, hemicellulose (starch and cellulose different structures of same numbers)

3 thermal biomass energy convrsion pathways

combustion, gasification, pyrolysis

combustion process

excess oxygen produces heat (boiler, steam turbine generator)

gasification process

partial oxygen produces fuel gases (catalytic converter to alcohol and chemicals)

Pyrolosis process

no oxygen produces char, gases, aerosols (uses bio-oil)

What are the biochemical energy conversion pathways

fermentation —> ethanol, anaerobic digestion —> methane

What is the physical biomass energy conversion pathway

hydrolysis (heat/pressure) —> liquid

What is yield of a crop

mass of biomass produced per hectacre per yr

what is the typical energy output and conversion efficiency for common energy crops

15-400 Gjoule per hectacre per yr, low solar—>bioenergy conversion efficiency (not even 1 percent)

biofuel

materials from which useful energy can be extracted via combustion

equation for combustion of methane

methane + oxygen = carbon dioxide + water + heat energy

heat energy output of reaction is called the ….

heating value of the fuel (energy or heat content)

Low heating value

water vapor produced in reaction is not condensed

high heating value

water vapor produced in reaction is condensed hence giving off useful heat energy

List 7 biomass sources

• sustainable energy tree farms (bagasse)

• forest waste

• municipal waste streams (requires energy to remove pollutants)

• industrial wastes (requires expensive drying process)

• animal waste (anaerobic digestion —> methane gas recovery)

• biodiesel fuels (processed, strained, canola oil)

• gaseous biomass (methane and landfill)

direct combustion

burning biomass with excess air to produce steam

co-firing to electricity conversion

part of coal replaced with biomass

gasification

heat biomass without oxygen to produce calorific gas

what size of modular system can biomass power

small, 5 MW (for small communities)

Challenges of biomass

• too much energy required to collect, dry, and transport materials to power plants

• reduce soil nutrient replenishment

• raising wood and food price

• large areas required

biomass environmental concerns

• deforestation —> soil erosion

• biomass fuel produces waste

• more series air pollution

• emit carcinogens

• emit toxic ash and gas

What are the two energy sources behind hydroelectricity

• gravity of falling or flowing water

• potential energy of dammed water

what percentage of solar energy reaching the earth’s atmosphere is consumed in the evaporation of water (energy stored in water vapor)

25 percent

where does the energy in water vapor go when it is condensed

• most released as heat into atmosphere and re-radiated into space

• small fraction (200,000 TWh per yr) into rain or snow —> 1/5 of this into streams and rivers (40 TWh per yr)

• “Total hydro resource” of the world

What is the top country in hydropower

China

what is the conversion of energy equation, applied to hydropower, ignoring other constants

potential energy = potential energy + kinetic energy + work

Energy is stored in a water reservoir by virtue of its…

height (z)

How does pumped hydro energy storage work

stores as potential energy by virtue of height (bulk electrical energy)

• plant has reversible pump turbine that pushes water uphill (during low energy demand with excess energy) flows down when energy needed

Pressure head

elevational difference between the forebay and the after bay

High-head dam

100+ meters

Medium-head dam

10-100 meters

Low-head dam

less than 10 meters

Two factors that dictate hydroelectric power output

flow rate, head

Flow is proportional to …

area x velocity

power is proportional to

head x flow

energy produced by mini, micro, and pico hydroplants respectively

100kw-1MW, 5kw-100kw, few hundred watts to 5kw

what is the typical ratio between effective and gross head

effective is 75-95 percent of gross head

Where do energy losses occur (hydropower inefficiency)

• friction and turbulence in penstock and piping

• turbine and generator equipment (small)

Power output of a hydroelectric plant is regulated by controlling the…

flow rate (and therefore frequency of rotation - 60 hz)

reactive turbines (sea shell shape)

• totally immersed in water

• derive power from pressure drop accross turbine

• angular and linear motion converted to shaft power

impulse turbines

• convert kinetic energy of water jet hitting buckets

• no pressure drop across turbines

what is the most common type of turbine for medium to large scale hydro plants, and is it reactive or impulse

francis turbine - reactive

Itaipu dam

Between Brazil and Paraguay, providing a large portion of both countries’ power

What is the world’s largest hydroelectric power plant

Three Gorges Dam - China

Environmental impacts of hydropower

• loss of habitat

• upstream inundation and degradation

• rotting vegetation emits ghg

• loss of aquatic diversity

• cumulative impacts on water quality + flooding

• disrupt energy transfer among water and sediment

• sedimentation reduces reservoir life

What does hydrokinetic technology do?

converts energy from waves, tides, and river/ocean currents into electricity

What is the most ideal characteristic of a tidal power plant site

narrow channe;s means high variation in tide level

what are the two types of tidal plant facilities

• tidal barrages

• tidal current turbines

What is the primary source of tidal power

the moon!

Describe the ocean’s response to the moon’s gravitational pull

• side of earth facing moon bulges out, as does other side due to centrifugal force

• so as the earth turns there are two high and low tides per day (tide reaches high or low approximately every 6 hours)

When a land mass is 90 degrees from earth to moon line…

low tide occurs

What are spring tides and when do they occur

spring tides are high tides that occur when the earth moon and sun are all in a line (strong gravitational pull)

What are neap tides and when do they occur

neap tides are low tides that occur when sun is perpendicular to earth-moon alignment (weak gravitational pull)

what is the approximate period between spring and neap tides

7 days (1/4 of lunar cycle)

flood currents

currents moving in the direction of the coast

ebb currents

currents moving away from coast

How do bays and inlets amplify the height of the tide

narrower channel, same volume of water in smaller space, greater head height behind sluice gates

what is the minimum required head height for practicality

5 meters

how many sites around the world meet the minimum head height requirement for a tidal barrage

around 40

what is the approximate power output of harnessed tidal power

3000 gigawatts

tidal range (R) is the same as…

head height (between maximum high and low tide - every 6 hrs)

average power output of tidal barrage is proportionate to…

R squared

Differential work done by water is proportional to what

potential energy

Tidal current turbine

extracts kinetic energy from currents

parts of a tidal current turbine

rotor, gearbox, generator, and support structure

three types of tidal current turbine support structures

• gravity

• piled

• floating