8.4 - Renewable Resources

What is a Renewable Resource?A renewable resource is a natural resource with the ability to reproduce through biological or natural processes and replenished with the passage of time.

Obviously fossil fuels could be seen as being renewable, unfortunately they are being used up millions of times faster than they are being created. The first forests grew about 300 million years ago and we will have used them all up within about 300 years.

Origin Renewable Energy SourceThe Sun Biomass (Alcohol, Plant Oils, Waste)

Wind & Wave (Convection Currents)Hydroelectric (Water cycle)Solar (Direct: Thermal or Voltaic)

Radioactivity Geothermal

Gravity Tidal

Renewable energy consumption/share of power by region

5,386

2,508

4

1,387 209

1,471

1,067 198

605 111

69 1,193

UK Renewable Energy Resources Installed Capacity (MW)

Onshore Wind

Offshore Wind

Shoreline wave / tidal

Solar photovoltaics

Small scale Hydro

Large scale Hydro

Landfill gas

Sewage sludge digestion

Municipal solid waste combustion

Animal Biomass (non-AD) 2

Anaerobic Digestion

Plant Biomass 3

Solar

By the time this energy reaches earth it has spread out over a huge surface equal to that of a sphere with a radius of the Earth’s orbital distance from the Sun.

The sun emits 3.9 x 1026J of electromagnetic radiation every second.

rE = m

𝑃𝑜𝑤𝑒𝑟 /𝑚2= 3.9×1026

4𝜋× (1.5×1011)2

𝑺𝒐𝒍𝒂𝒓 𝑪𝒐𝒏𝒔𝒕𝒂𝒏𝒕=𝟏𝟑𝟖𝟎𝑾𝒎−𝟐

Solar Radiation

Because of the shape of the earth’s orbit it is not actually constant but we can assume it is.

Solar RadiationThe sunlight that reaches any position on the earth depends on how much atmosphere it has to travel through to get there.

The earth does intercept about 1380Wm-2 , but the light that would hit a flat disc actually hits half the surface of a sphere.

𝐴𝑟𝑒𝑎𝑜𝑓 𝐹𝑙𝑎𝑡 𝐷𝑖𝑠𝑐𝐻𝑎𝑙𝑓 𝑆𝑢𝑟𝑓𝑎𝑐𝑒 𝐴𝑟𝑒𝑎𝑜𝑓 h𝑆𝑝 𝑒𝑟𝑒

=𝜋 𝑟 𝐸

2

12(4𝜋 𝑟 𝐸

2 )

This is actually halved again because of

day and night =

Any area on the Earth’s surface receives of the Solar Constant = 345Wm-2

¿12

Solar RadiationThe amount that actually is absorbed by the Earth is even less:

Solar Power Photovoltaic

BP Statistical Review 2012

Solar Capacity (Photovoltaic) /GW

Some of this light can be turned directly into electricity using photovoltaic cells.

Photovoltaic Efficiency

Solar Power Solar Heating

Another way of using the sun’s energy is to absorb the heat as shown below.

The angle of the absorption area affects the amount of heat that is absorbed.

There are other ways of using the heat in the air or in the land to warm a house such as Air-Source or Land-Source Heat Pumps.

Solar Power Industrial Scale Solar Heating

http://www.youtube.com/watch?v=LMWIgwvbrcM&feature=related

http://www.smartplanet.com/blog/intelligent-energy/540-foot-solar-power-tower-rises-in-nevada/13051

There is enough solar energy incident on the earth to easily provide for our needs, but it is very diffuse and for Photovoltaics there are issues with the resources needed to make them.

Hydroelectricity

BP Statistical Review of World Energy 2012 © BP 2012

Hydroelectricity consumption by region

BP Statistical Review of World Energy 2012 © BP 2012

This is often used as a way to smooth out load.

Power stations work at a steady rate and when no-one wants the electricity it can be used to pump water high into lakes – this is called Pumped Storage.

Norway and Canada are likely to become the so called ‘Batteries’ of their geographical areas.

Interconnected national grids will allow excess electricity from all over Europe to be stored in high lakes in Norway until it is needed.

Tidal Power is another form of Hydroelectric power, trapping tides behind walls.

Hydroelectric Power

http://uccpbank.k12hsn.org/courses/APEnvironmentalScience/course%20files/multimedia/lesson68/animations/4e_hydroelectric_power.swf

http://www.hk-phy.org/energy/alternate/hydro_phy/flash/hydro_plant2.swf

Watch these to familiarise yourself with the way they work and some of the operating issues.

Hydroelectric PowerTo calculate the power of HEP station you only need to know a few things:

• Rate of Flow of Water• Change in Height of the

water• Density of the water

𝐸𝑝=𝑚𝑔∆h

𝑃𝑜𝑤𝑒𝑟=𝑚𝑔∆h

𝑡𝑃𝑜𝑤𝑒𝑟=

𝑚𝑉×𝑉𝑡×𝑔×∆h

𝑃=𝜌 𝑔Δ h×𝑉𝑡

=density of waterg=gravity= height change

Hydroelectric Power Calculations

Calculate the total energy stored and the power generated if water flows at 1m3 per second.

The average height above the turbine is:

Volume of lake = 2000 x 1000 x 25 = 5 x 107 m3

Mass of Lake = 5 x 107 m3 x 1000 (Density of water) = 5x1010kgPE=mgh= 5x1010 x 9.8 x 87.5 = 4.29 x 1013J

𝑃=𝜌 𝑔Δ h×𝑉𝑡

From before:

P= 1000 x 9.8 x 87.5 x 1

Power= 875kW

Wind Power

Wind Power

The winds are caused by convection currents and their direction is also affected by the earth’s rotation.

Wind’s tend to be stronger on the coast thanks to the relative SHC of the land and the water.

There are also strong Katabatic winds caused by air pressure differences, such as the Mistral in France, Chinook in West Canada, Harmattan in the Western Sahara.

Wind Power Check out how they work

http://library.thinkquest.org/08aug/02429/assets/Wind%20Power%20Interactive,%20Wind%20Power%20Simulation,%20Wind%20Power%20Simulator%20-%20National%20Geographic.swf

http://ecards.greenlearning.ca/docs/windturbine-22.swf

Wind Power Calculations

1. The Volume of air moving past the turbine every second is given by:

𝑣×𝜋𝑟 2

2. The Mass of this air is:

𝜌×𝑣×𝜋𝑟 2

3. The Kinetic Energy of this air is:

12𝜌𝑣 𝜋 𝑟2×𝑣2 KE=

The wind doesn’t stop once it has passed the turbine so not all of the energy can be captured. The maximum theoretical efficiency is 59%

Wind Power Calculations

K.E. = 1. Long rotors (KE ∝ r2)2. High speed winds (KE ∝ 3)3. To be built under water (KE ∝) The density of water is 1000kgm-3

The density of air is 1.223kgm-3

This is the energy contained in the wind passing through the turbine, so the best Wind Turbines would need:

Wave Power

http://www.archipelago.co.uk/blog/wave-power-animation-updated/

http://www.youtube.com/watch?feature=player_embedded&v=ILWXAkE4QpQ#!

http://www.youtube.com/watch?feature=player_embedded&v=FfmgxNpprWQ

Wave Power A few different approaches

The top left is the only one that is on your syllabus. It is called an Oscillating Water Column (OWC) ocean wave converter.

Wave Power Power/Unit Length

A wave can be approximated by a rectangle as shown:

The average height of the wave =

The PE of this wave =

The Mass of the wave is:

𝑃𝐸=(𝜌𝜆 𝐴𝑊 )𝑔𝐴

2𝑃𝐸=𝜌𝜆𝑊𝑔 𝐴2

2

If the waves arrive every T seconds then:

𝑃 𝑜𝑤𝑒𝑟= 𝜌𝜆𝑊𝑔 𝐴2

2𝑇

But:

= Wave Velocity

Remember W=Wavefront Length, so:

𝑃𝑜𝑤𝑒𝑟𝑢𝑛𝑖𝑡 h𝑙𝑒𝑛𝑔𝑡

= 𝜌𝑣𝑔 𝐴2

2

m=mass of waveρ=density of waterλ=wavelengthW=width of waveg=gravityA=Amplitude=wave velocity

Wave Power Power/Unit Length EXAMPLE

Waves of amplitude 1.5m roll onto a beach every 8s. If the wavelength of the wave is 80m calculate:a) The velocity of the waves

b) How much power there is per metre along the shore

c) The Power along a 3km length of beach

𝑣= 𝑓 𝜆=18×80=10𝑚𝑠− 1

𝑃𝑜𝑤𝑒𝑟𝑢𝑛𝑖𝑡 h𝑙𝑒𝑛𝑔𝑡

= 𝜌𝑣𝑔 𝐴2

2

= 220 500 Wm-1 = 220kW

220kWm-1

This is a lot of energy along even small sections of the coastline.

Oscillating Water Column (OWC)

http://www.archipelago.co.uk/blog/wave-power-animation-updated/

Oscillating Water columns are beautifully explained in the video on the right.

Air rises and falls with the waves.

They use the specially designed ‘Wells’ turbine that spins the same way whichever way the air blows over it.

THE END