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Renewable energy technologies (R.E.T.)

Dr. Sam C. M. Hui

Department of Mechanical Engineering

The University of Hong Kong

E-mail: [email protected]://web.hku.hk/~cmhui Oct 2015

CCST9016 Energy: Its Evolution and Environmental Impacthttp://me.hku.hk/bse/CCST9016/

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Contents

Overview Solar Energy

Wind Energy

Biomass Energy

Geothermal Energy

Small Hydropower

Ocean Energy

R.E.T.

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Overview

Renewable energy (RE)

Energy that comes from resources which arecontinually replenished such as sunlight, wind,rain, tides, waves and geothermal heat

Derives from the sun or from heat within the earth

Three main types of RE:

1. Traditional biomass Woodfuels (forests), agricultural by-products and dung burned

for cooking and heating purposes (in developing countries)

2. Hydroelectricity (large hydropower from dams)

3. New renewables (small hydro, modern biomass,wind, solar, geothermal, and biofuels)

Have

significantsocial &

ecological

impacts!

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Overview

Contribution of RE

For the worlds final energy consumption (2010)

16.7% from renewable resources: 11.4% fromtraditional biomass, 3.3% from hydroelectricity and 2%from new renewables

For the worlds electricity generation

About 16% from hydroelectricity and 3% from newrenewables

Application of RE

Large-scale projects (hydropower, wind farms) Small-scale (e.g. for rural and remote areas)

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Contribution of renewables in total world energy consumption

(Source: http://en.wikipedia.org/wiki/Renewable_energy)

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Overview

Renewable energy technologies (R.E.T.)

Produce sustainable, clean energy

RE resources exist over wide geographical areas

(unlike oil and coal, which are concentrated in alimited number of countries)

Energy security and economic benefits

Applied in four distinct areas: 1. Electricity generation

2. Hot water/space heating

3. Motor fuels 4. Rural (off-grid) energy services

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Solar energy can be converted into heat or

electricity using various technologies*

1. Solar thermal (e.g. solar water heating)

Also solar space heating in colder climates

2. Solar photovoltaic (PV)

PV modules made of solar cells (semiconductor

devices); can be connected to form small or large arrays

3. Concentrating solar power (CSP)

Use reflective materials such as mirrors to concentratethe suns energy to convert it to high-temperature heat

Solar Energy

(See also: http://re.emsd.gov.hk/english/solar/solar.html )

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1. Solar thermal (solar water heating)

Harness the solar heat to produce hot water

Domestic solar water heating system usually

comprises of solar collectors and a water tank

Types of solar collectors:

(a) Flat-plate

(b) Evacuated-tube

Glass-glass type

Glass-metal type (direct flow-through type and heat-pipe type)

Storage tank and ancillary equipment

Solar Energy

(See also: http://re.emsd.gov.hk/english/solar/solar_wh/solar_wh_to.html )

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Examples of solar thermal systems

Flat-plate solar collector

Evacuated-tube solar collector

H f fl l l ll

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Heat transfer processes at a flat-plate solar collector

(Source: http://www.volker-quaschning.de/articles/fundamentals4/index.php)

P i i l f d b ll i h h i

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Principle of an evacuated tube collector with heat pipe

(Source: http://dogstarsolar.net/about/solar-evacuated-tubes/)

S h ti di f l t h ti t

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Schematic diagram of a solar water heating system

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2. Solar photovoltaic (PV)

Converts the light energy in sunlight into

electricity by means of photoelectric phenomenon

Types of solar cells: Crystalline silicon cells

Monocrystalline (efficiency: 15%-18%)

Polycrystalline (efficiency: 13%-16%)

Thin layer/film cells

Amorphous silicon (efficiency: 5%-8%)

Copper indium diselenide (CIS) (efficiency: 7.5%-9.5%) Cadmium telluride (CdTe) (efficiency: 6%-9%)

Solar Energy

(See also: http://re.emsd.gov.hk/english/solar/solar_ph/solar_ph_to.html )

Structure and processes of a solar cell

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Structure and processes of a solar cell

(Source: http://www.volker-quaschning.de/articles/pv-basics/index.php)

Photovoltaic system on a convention centre rooftop (1 MW)

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(Source: www.eeremultimedia.energy.gov)

Photovoltaic system on a convention centre rooftop (1 MW)

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Video: Energy 101: Solar Power (3:24)

http://youtu.be/NDZzAIcCQLQ

An inside look at solar-power technology; breaks

down the different types of solar devices and howthey work, detailing the pros and cons of this

renewable energy source

Video: Photovoltaics: a diverse techno. (4:26)

https://www.eeremultimedia.energy.gov/solar/vide

os/photovoltaics_diverse_technology

Solar Energy

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2. Solar photovoltaic (PV) (contd)

Emerging PV technologies

High-concentration PV (by using mirrors/lenses)

SILVER (thin and bifacial moncrystalline) Organic/polymer PV

Microcrystalline and micromorphous cells

Hybrid HIT (heterojunction w/ intrinsic thin layer) cells

Perovskite solar cells

PV systems Standalone vs Grid-connected (or grid-tied)

Solar Energy

(See also: http://re.emsd.gov.hk/english/solar/solar_ph/solar_ph_to.html )

http://en.wikipedia.org/wiki/Perovskite_solar_cell

A standalone PV system supplying DC and AC loads

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(Source: http://re.emsd.gov.hk/english/solar/solar_ph/solar_ph_to.html )

A standalone PV system supplying DC and AC loads

d.c. = direct current

a.c. = alternating current

Grid-connected solar photovoltaic (PV) systems

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(Source: http://re.emsd.gov.hk/english/gen/grid/grid_int.html )

Grid connected solar photovoltaic (PV) systems

Hydrid solar photovoltaic (PV) and wind turbine systems

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(Source: http://re.emsd.gov.hk/english/solar/solar_ph/solar_ph_to.html )

Hydrid solar photovoltaic (PV) and wind turbine systems

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3. Concentrating Solar Power (CSP)

A large-scale solar thermal-electric technology

Makes use of mirrors to convert the suns energy

into high-temperature heat Main types of CSP technologies:

(a) Trough System

(b) Dish/Engine system

(c) Power Tower

Small concentrating solar devices, e.g. solar oven

Solar Energy

(See also: http://re.emsd.gov.hk/english/solar/other_st/other_st_to.html )

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Video: Energy 101: Concentrating Solar

Power (2:16)

https://www.eeremultimedia.energy.gov/solar/vide

os/energy_101_concentrating_solar_power From towers to dishes to linear mirrors to troughs,

concentrating solar power (CSP) technologies reflect

and collect solar heat to generate electricity. A singleCSP plant can generate enough power for about 90,000

homes. This video explains what CSP is, how it works,

and how systems like parabolic troughs producerenewable power.

Solar Energy

Concentrating Solar Power Tower Plant

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g

Concentrating solar tower system in California (10 MW)

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g y ( )

Solar Dish/Engine Power Plant

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g

Linear Concentrating Solar Power Plant

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Linear Fresnel Power Plant

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Environmental impacts

Land use (land degradation and habitat loss)

Water use (manufacture of components, cooling)

Hazardous materials (e.g. PV cell manufacture)

Life-cycle global warming emissions

(manufacture, transport, installation, maintenance,

decommissioning)

Visual impact/intrusion on aesthetics

Effect on ecosystem, flora and fauna (for CSP)

Solar Energy

(See also: http://www.ucsusa.org/clean_energy/our-energy-choices/renewable-energy/environmental-impacts-solar-power.html)

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Other solar technologies:

Solar space heating

Active solar space heating

Passive solar space heating Solar cooling

Solar absorption cooling (evaporate the refrigerant)

Solar adsorption cooling (regenerates the silica gel in

adsorption chiller)

Solar lighting (e.g. light pipe)

Sunlight concentrating or transmission

Solar Energy

(See also: http://re.emsd.gov.hk/english/solar/other_st/other_st_to.html )

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Wind

Air movement due to the variation in solar

radiation absorption on different parts of the earth

and the dynamic effects from the earths rotation Considered an indirectform of solar energy

Examples of wind energy:

Wind turbines to make electrical power

Windmills for mechanical power

Wind pumps for water pumping or drainage Sails to propel ships

Wind Energy

Examples of wind turbines

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Vertical-axis wind turbinesHorizontal-axis wind turbines

Small wind turbines Wind farm (off-shore)

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Wind turbines

Large ones: several hundred kW to a few MW

Small ones: up to tens of kW

Offshore wind farms: planting wind turbines onthe seabed

Wind farms Consist of many individual wind turbines which

are connected to the electric power transmission

network

Wind Energy

(See also: http://re.emsd.gov.hk/english/wind/wind.html )

Large wind turbine installation and operation

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(Source: http://re.emsd.gov.hk/english/wind/large/large_to.html )

Wind speedwill affect

the output

power ofwind turbine

Small wind turbine installation and operation

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(Source: http://re.emsd.gov.hk/english/wind/small/small_to.html )

Furling is one

method of

preventing

awind

turbine from

spinning too

quickly simply

by turning the

blades away

from thedirection of the

wind

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Video: Energy 101: Wind Power (2:14)

http://youtu.be/niZ_cvu9Fts

Our animated correspondent Little Lee Patrick

Sullivan explains how the wind can be used togenerate power, including where wind comes

from, its history as a power source, how wind

farms generate electricity and what's likely to bethe first major offshore wind project in the U.S.

Wind Energy

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Video: Energy 101: Wind Turbines - 2014

Update (3:16)

http://youtu.be/EYYHfMCw-FI

See how wind turbines generate clean electricityfrom the power of wind. The video highlights the

basic principles at work in wind turbines, and

illustrates how the various components work tocapture and convert wind energy to electricity.

Wind Energy

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(Source: http://bertmaes.wordpress.com/2009/07/02/part-1-green-technology-wind-turbines-and-cnc/)

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Advantages of wind power

Plentiful, renewable, widely distributed, clean,

produces no greenhouse gas emissions during

operation and uses little land, no fuel required Technology is robust & mature

Economics of wind energy

The monetary cost per unit of wind energy

produced is similar to the cost for new coal and

natural gas installations

Wind Energy

(See also: http://en.wikipedia.org/wiki/Wind_power )

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Noise produced by the rotor blades

Aesthetic (visual) impacts

Birds and bats having been killed by the rotors

Electromagnetic interference (w/ radar & telecom)

Supply and transport issues Wind power is intermittent (need storage/backup)

Good wind sites are often in remote locations

May compete with other uses for the land

Wind Energy

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Biomass Energy

Biomass

Biological material from living, or recently living

organisms, e.g. plants or plant-derived materials

Can be used directly or indirectly (e.g. convertedinto biofuel)

Biomass can be converted to energy by:

1. Thermal conversion (e.g. direct combustion)

2. Chemical conversion (e.g. biofuel/biodiesel)

3. Biochemical conversion (e.g. anaerobic digestion)

(See also: http://en.wikipedia.org/wiki/Biomass )

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Biomass Energy

Biomass energy or bioenergy

Using wood, residues (forestry, agricultural,industrial, commercial/domestic), energy crops

Energy from waste incineration or digestion Landfil gas, biogas and biofuel

CarbonCycle

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Examples of bioenergy applications

(modern biomass)

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( )

Fuel state ApplicationBiogas Supplementing mains supply (grid-connected)

Biogas Cooking and lighting (household-scale digesters),

motive power for small industry and electric needs(with gas engine)

Liquid biofuel Transport fuel and mechanical power, particularly

for agriculture; heating and electricity generation;some rural cooking fuel

Solid biomass Cooking and lighting (direct combustion), motive

power for small industry and electric needs (withelectric motor)

Strengths and weaknesses of bioenergy systems

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Strengths Weaknesses

Conversion technologies available ina wide range of power levels at

different levels of technological

complexity

Fuel production and conversiontechnology indigenous in developing

countries

Production can produce more jobs

than other renewable energy systemsof a comparable size

Conversion can be to gaseous, liquidor solid fuel

Environmental impact low (overallno increase in carbon dioxide)

compared with conventional energy

sources

Production can create land usecompetition

Often large areas of land are required(usually low energy density)

Production can have high fertilizer andwater requirements

May require complex managementsystem to ensure constant supply of

resource, which is often bulky addingcomplexity to handling, transport and

storage

Resource production may be variable

depending on local climatic/weathereffects, i.e. drought

Likely to be uneven resourceproduction throughout the year

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Biomass Energy

Potential benefits

Absorb and recycle CO2 from the atmosphere by

the photosynthesis

May be carbon neutral (its use as fuel willrelease only that much CO2 which had been

captured recently by its biomass growth)

May have lower carbon emissions than fossil fuels

Biomass removals reduce wildfire hazard and

severity in forestry, and help waste management(See also: http://en.wikipedia.org/wiki/Biomass )

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Biomass Energy


Air pollution (from biomass combustion)

Water use (cooling water for biomass power plant;

water for energy crops) Land use (e.g. for energy crops) and land/habitat

degradation (over-harvesting of forests/residues)

Life-cycle global warming emissions (growing,

harvesting, transporting, burning or gasifying)

Affect the nitrogen cycle and nutrient flow(See also: http://www.ucsusa.org/clean_energy/our-energy-choices/renewable-energy/environmental-impacts-biomass-for-

electricity.html)

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Geothermal Energy

Geothermal energy = the heat from the earth

Deep in the earth or near the earths surface

Typical geothermal applications:

Direct use: produce heat directly from hot waterwithin the earth

Electricity production: Generate electricity fromthe earths heat

Geothermal heat pumps: Use shallow ground to

heat & cool buildings (ground-source heat pump)(See also: http://en.wikipedia.org/wiki/Geothermal_energy)

Major components of a geothermal power plant

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(Source: http://www.alternative-energy-news.info/technology/heating/)

Working principle of a geothermal energy system

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Enhanced geothermal system (EGS) with hot dry rock (HDR)

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(Source: http://en.wikipedia.org/wiki/Renewable_energy)

Legend

1: Reservoir

2: Pump house

3: Heat exchanger

4: Turbine hall5: Production well

6: Injection well

7: Hot water to district heating8: Porous sediments

9: Observation well

10: Crystalline bedrock

G h l E

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Geothermal Energy

Video: Energy 101: Geothermal Heat Pumps

(2:32)

http://youtu.be/y_ZGBhy48YI

An energy-efficient heating and coolingalternative, the geothermal heat pump system

moves heat from the ground to a building (or from

a building to the ground) through a series offlexible pipe loops containing water. This video

explores the benefits Geothermal and the science

behind how it all comes together.

Geothermal heat pumps

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Further information: http://en.wikipedia.org/wiki/Geothermal_heat_pump

G th l E

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Geothermal Energy


Water quality and use (contamination; cooling)

Air emissions (e.g. for open-loop systems)

Thermal pollution Land use (esp. for sensitive ecological areas)

Subsidence (extracting geothermal fluids cancause the land to sink)

Life-cycle global warming emissions (e.g. for

plant construction and surrounding infrastructure)(See also: http://www.ucsusa.org/clean_energy/our-energy-choices/renewable-energy/environmental-impacts-geothermal-

energy.html)

S ll H d

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Small Hydropower

Hydroelectric power on a scale serving a small

community or industrial plant

A capacity up to about 10 MW total

In mountain areas or river streams (e.g. in China,Japan, USA and India)

Have a relatively low environmental impact

compared to large hydropower

Suitable for remote areas & developing countries

(See also: http://en.wikipedia.org/wiki/Small_hydro)

Classification of hydro-power size

Large-hydro More than 100 MW and usually feeding into a large

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electricity grid

Medium-hydro 10 or 20 MW to 100 MW -- usually feeding into a grid

Small-hydro 1 MW to 10 MW or 20 MW -- definitions vary, Europe

tends to use 10 MW as a maximum, China uses 20 MW and

Brazil 30 MW. Usually feeding onto a grid

Mini-hydro 100 kW to 1 MW -- either stand alone schemes or more

often feeding into a grid

Micro-hydro 5 kW to 100 kW -- usually provide power for a smallcommunity or rural industry in remote areas away from the

grid

Pico-hydro 50 W to 5 kW -- usually for remote rural communities andindividual households. Applications include battery

charging or food processing

How a small hydropower system works(run-of-the-river)

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(Source: http://www.eere.energy.gov/basics/renewable_energy/microhydropower.html )

System Components:

A water conveyance, which is achannel, pipeline, or

pressurized pipeline (penstock)

that delivers the water

A turbine, pump, orwaterwheel, which transforms

the energy of flowing water into

rotational energy

An alternator or generator,which transforms the rotational

energy into electricity

A regulator, which controls the

generator Wiring, which delivers the

electricity

Video: Small Hydro Power (3:41), http://www.youtube.com/watch?v=o541UQcTbpI

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Small hydro system (example)

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A low-head micro-hydroinstallation

Strengths and weaknesses of small hydropower systems

Strengths Weaknesses

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Technology is relatively simple and

robust with lifetimes of over 30 yearswithout major investment

Overall costs can, in many cases,undercut all other alternatives

Automatic operation with lowmaintenance requirements

No fuel required (no additional costsfor fuel nor delivery logistics)

Environmental impact low comparedwith conventional energy sources

Power is available at a fairly constantrate and at all times, subject to water

resource availability

The technology can be adapted formanufacture/use in developing

countries

Very site-specific technology (requires

a suitable site relatively close to thelocation where the new power is

needed)

For small hydro systems using small

streams the maximum power is limited

and cannot expand if the need grows

Droughts and changes in local waterand land use can affect power output

Although power output is generallymore predictable it may fall to very low

levels or even zero during the dry

season

High capital/initial investment costs Engineering skills required may be

unavailable/expensive to obtain locally

Small Hydropower

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Small Hydropower


Land use & habitat deterioration (for the

equipment, power lines & flooding land)

Wildlife impacts (on water flow & aquaticecosystems) during and after construction

Life-cycle global warming emissions (installation,

operation and dismantling)

Visual and noise impacts

(See also: http://www.ucsusa.org/clean_energy/our-energy-choices/renewable-energy/environmental-impacts-hydroelectric-power.html)

Ocean Energy

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Ocean Energy

Oceans cover > 70% of Earths surface and

are the worlds largest solar collectors The ocean can produce 3 types of energy:

Thermal energy from the suns heat (ocean thermal

energy conversion, OTEC) Mechanical energy from the tides and waves

A barrage (dam): convert tidal energy into electricity

Channel systems: funnel the waves into reservoirs Float systems that drive hydraulic pumps

Oscillating water column systems: that use the waves tocompress air within a container

Salinity gradient energy from osmosis process

(See also: Energy 101: Marine and Hydrokinetic Energy (3:00) http://www.youtube.com/watch?v=ir4XngHcohM )

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Ocean thermal energyconversion (OTEC)

(Source: http://www.energybandgap.com/power-generation/harvesting-energy-from-the-ocean/)

Tidal energy

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Wave energy (surface)

Wave current (deep sea)Wave terminator device

(Source: www.mywindpowersystem.com )

Ocean Energy

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Ocean Energy

Many are still in the experimental stages or in

the early stages of deployment Potential environmental impacts:

Could compete with other uses (e.g. fishing andshipping) & cause damage to marine life/ habitats

Could cause changes in hydrology and salinity that

negatively impact animal and plant life Life-cycle global warming emissions (for

equipment installation and operation)

(See also: http://en.wikipedia.org/wiki/Marine_energy)

Further Reading

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Further Reading

Renewable energy - Wikipedia,

http://en.wikipedia.org/wiki/Renewable_energy

HK RE Net

http://re.emsd.gov.hk

Environmental Impacts of Renewable Energy

Technologies [Union of Concerned Scientists] http://www.ucsusa.org/clean_energy/our-energy-

choices/renewable-energy/environmental-impacts-

of.html

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