Renewables definition• Renewable Energy is energy obtained from the

natural and persistent currents of energy in the environment

• e.g. sunshine, wind, rainfall-------------------------------------------------------• considered “Green Energy”• intrinsically non-polluting-------------------------------------------------------• “Direct” RE from natural environment• “Indirect” RE from society’s wastes

Solar radiation Geothermal

heatGravitational

potential

Reflected 50 Absorbed 120

absorbedas heat

water phase changehydro flow

kineticwind

waves

photoninteraction

photosynthesis

tides

heat

Total renewable energy flows through the biosphere:

unit 1015 W (109 megawatt)

80

40

0.3

0.03

3

0.001

radiation toouter space

Solar radiation per person Geothermal

heatGravitational

potentialReflected 8,000 kW Absorbed 20,000

kW

absorbedas heat

water evaporation,rain & hydro flow

wind,waves

photosynthesis(plants, crops)

tides

heat

Per capita Renewable energy: kilowatt per person on Earth

i.e. solar is equivalent of 20,000 one-bar electric heaters for each man, woman and child

13,000 kW

7,000 kW

50 kW

5 kW

500 kW

0.2 kW

radiation toouter space

Solar radiation Geothermal

heatGravitational

potential

Solar water heaters,Solar buildings

Hydro-electricity;very large (GW) to

very small (100 W) scale

wind turbines,wave power

Fuel wood, biomassbiodiesel, ethanol,

wastes

Tidal range power;e.g. Severn estuary

& Tidal stream power

heat pumps

Renewable energy technologies

Photovoltaic solar cells

Renewable energy technologies forheat, electricity, transport fuels

• solar buildings• solar water heating• solar thermal

electricity• solar cell

photovoltaic electricity

• solar driers• solar refrigeration• hydroelectricity • micro-hydro• wind turbines• wave power

• photosynthesis• biomass crops• pyrolysis• biofuel oils• biogas• sewage gas• urban waste• geothermal heat• tidal range • tidal stream power• fuel cells

Scaling: energy fluxesconfigure the technologies

• bright sunshine 1 kW/m2

• brisk wind (10 m/s) 1 kW/m2

• house heating boiler 10 kW/m2

• coal power station boiler 100 kW/m2

• nuclear power boiler 1,000 kW/ m2

So, for renewables…………………...

• potential very large and sufficient• free (no cost) in the environment• but dispersed and variable• need to capture, deliver, utilize and store• encourages local enterprise & cash flow• manufacturing growth from environmental

push and commercial pull

• but….RE plant is relatively large• so…..RE plant is capital intensive

Conclusions: renewables …

• proven technologies• most are in the market place• credit for environmental and

sustainable benefits• favoured by world, European,

national & local policies• but still much to do