1. EE535Stephen Daniels, Oct 2009 EE535: Renewable Energy: Systems, Technology & Economics Session 2: Energy & Power

2. EE535Stephen Daniels, Oct 2009 Terminology SI unit of power is the Joule (J) Much of our fuel consumption is based on fossil fuels, so values of energy consumption are often expressed in terms of tonnes of oil equivalent (toe or Mtoe) 1 toe = 42 GJ Rate of energy consumption is the watt (W), equivalent to a joule/s Electrical energy is more usually expressed in kilowatt hours (kWh) 1 kWh = 3600 kJ 1 kJkilojoule10 3 J 1 MJmegajoule10 6 J 1 GJgigajoule10 9 J 1 TJterajoule10 12 J 1 PJpetajoule10 15 J 1 EJexajoule10 18 J Worldwide energy consumption in 2006 was estimated to be equivalent to 10879 million tons of oil equivalent = 10879 x 10 6 x 42 x 10 9 J = 457 EJ The kilowatt hour / day (kWh/d) is a useful measure of the rate we use/produce power How much does a kWh of electricity cost a domestic user in Ireland?

3. EE535Stephen Daniels, Oct 2009 Forms of Energy (I) Gravitation Potential –E = mgh –Example: Energy stored in a reservoir Mechanical: Kinetic Energy of a moving body –E = ½ mv 2 –Example: Rotational kinetic energy (e.g. turbo-generator) –Flow of water to a turbine or wind-energy machine –Flow of air through windmill blades –Tidal flow Thermal: The energy stored as heat in a body –Energy = mass x specific heat capacity x rise in temperature –Energy is due to an increase in kinetic energy of atoms/molecules –Examples: burning fossil fuels, nuclear reaction, solar thermal collector

4. EE535Stephen Daniels, Oct 2009 Forms of Energy (II) Chemical: Energy released in a chemical reaction –Example: burning of fuel – often expressed in kJ/kg Electrical: The energy in joules is given by the product of power (P = VI watts), and time (s) Radiation –Photon energy E= hv = hc/γ –Examples: solar photovoltaic conversion, photosynthesis of sunlight to biomass Atomic Energy –E = mc 2 Question for class: Is atomic energy a renewable resource?

5. EE535Stephen Daniels, Oct 2009 Energy Resources of the Earth* Direct Conversion Pyrolysis Fermentation Digestion Gravitational Salination Evaporation Waves Currents Thermal Difference Osmotic Solar Photo Synthesis Limnic Oceanic Direct Conversion Geothermal Gravitational Coal Oil Gas Shale Fission Fusion Fossil Mineral RenewableNon-Renewable * Source : Renewable Energy Focus Handbook, Elesevier 2009

6. EE535Stephen Daniels, Oct 2009 Planetary Energy Balance * Direct Reflection Direct Conversion to Heat Evaporation of Water Wind & Waves Photosynthesis Solar Radiation (173,000TW) Tides Geothermal Volcanos & Hot Springs Rock Conduction 52,000 TW (30%) 78,000 TW (45%) 39,000 TW (22%) 3,600 TW (2%) 40 TW 3TW 0.3 TW 32 TW Equilibrium between incoming and outgoing energy is oscillatory in nature * Source : Renewable Energy Focus Handbook, Elesevier 2009

7. EE535Stephen Daniels, Oct 2009 Sustainable Energy Sustainable energy – energy production without compromising the production capability of future generations Nuclear: is it reasonable to include fossil fuels and nuclear fission as transitional sources while technology develops? Strictly: energy sources which are not expected to be depleted in a time frame relevant to the human race.

8. EE535Stephen Daniels, Oct 2009 Can We Live On Renewables? How much energy do we use? What is the maximum potential of the renewable resources? What about economic, social, and environmental constraints?

9. EE535Stephen Daniels, Oct 2009 40W Light Bulb If left on all the time, uses almost 1 kWh per day Circa 538g of CO2 released into the atmosphere 1 kWh cost circa 0.1455 cents

10. EE535Stephen Daniels, Oct 2009 Terminology Capacity Factor / Load Factor = (average power output ) / (maximum output) Peak Power Storage Capacity