6 ETE 26 April 06

Energy Conversion Efficiencies: 

Energy Conversion Efficiencies Converted energy form Chemical Radiant Electric Thermal Gravitational Kinetic Initial energy form Chemical Radiant Electric Thermal Kinetic Electric motor 65-93% Furnace of steam boiler 85-88% Solar furnace 100% Storage battery 72% Brake drum 100% Heating coil 100% Lamp incandescant 5-8% flourescent 25-30% Solar cell 15-27% Steam turbine 40-47% Muscle 45% Dry cell battery 91% Photosynthesis 0.6% Water turbine 86% Generator 95-99%

Slide2: 

Assessing energy system efficiencies Primary Energy Source Conversion Network (including extraction, storage, transmission) Final Energy Form Required Energy Service Nuclear Geothermal Tidal Solar Kinetic Heat Electricity Radiation Physical work Transportation Cooking Heating Cooling ICT Entertainment Primary Energy Carrier Nuclear fuels Geothermal heat Tidal flow Solar radiation Fossil fuels Biomass Hydrological cycle Wind Waves and currents

Slide3: 

Extraction Refining Transport Boiler (chemical to thermal) Turbine (thermal to mechanical) Generator (mechanical to electrical) Electricity Example: Residential lighting (from fossil fuel based electricity production) Primary Energy Carrier Conversion device Conversion device Conversion device Useful output Conversion Efficiencies: 0.9 x 0.88 x 0.43 x 0.98 = 0.33 Assessing energy system efficiencies Chemical energy In fuel Transmission Lamp Light Electricity Conversion Efficiencies: 0.33 x 0.93 x 0.08 = 0.025

Slide4: 

Assessing energy system efficiencies Example 1: Residential lighting (from fossil fuel based electricity production) The total system conversion efficiency is 2.5% (fossil fuel into visible light). The conversion efficiency for fossil fuel based residential electricity is about 31%. Every MJ of residential electricity thus requires 3.23 MJ from fossil fuel. During 24 hours a 100W bulb requires 8.64 MJ of electricity (final energy form). The 100W light bulb therefore requires 28 MJ stored in fossil fuel (primary energy). This roughly equivalent to 1.1kg of hard coal (net calorific value 25MJ/kg). Example 2: Power supply without load (connected to coal based electricity) Every MJ of residential electricity requires 3.23 MJ from fossil fuel. Most current power supplies use about 2W when connected without load. There are currently over 3 billion power supplies in operation in the US. Let’s assume that 10% of all power supplies are connected all the time. Let’s assume that these power supplies are without load 80% of the time. Question: How much hard coal is needed per year to generate the required energy?

Slide5: 

Assessing energy system efficiencies Case study – Fuel cell vehicle Main issue with hydrogen: It is an energy carrier not an energy source, which means that it has to be generated first. Another issue with hydrogen: It has high gross calorific value (142 MJ / kg), but very low energy to volume ratio (1/4 that of petroleum, 1/3 that of natural gas).

Slide6: 

1) Hydrogen is generated by a reformer Assessing energy system efficiencies Case study – Fuel cell vehicle 2) Fuel cell converts hydrogen into electricity 3) Electricity powers electric motor

Slide8: 

Reformer Fuel cell Electric motor Heat Pressure H source Heat CO2 H2 Electrical energy Heat H2O2 Heat Conversion Efficiency: 0.6 – 0.85 x 0.5 – 0.6 x 0.8 = 0.24 – 0.41 Mechanical energy Assessing energy system efficiencies Case study – Fuel cell vehicle Missing: Hydrogen compression 0.9 Regenerative braking 1.1

Slide9: 

Assessing energy system efficiencies Case study – Fuel cell vehicle

Slide10: 

Assessing energy system efficiencies Case study – Fuel cell vehicle Electric vehicle (well-to-wheel efficiency, electricity from fossil fuel) Power plant Battery Electric motor Transmission 0.33 – 0.55 x 0.93 x 0.8 x 0.8 = 0.2 – 0.33 Electric vehicle (electricity from solar energy) Battery Electric motor Transmission 0.93 x 0.8 x 0.8 = 0.6 Fuel cell vehicle (hydrogen from electrolysis, electricity from solar energy) Fuel cell Electric motor Transmission 0.9 x 0.86 x 0.5 x 0.8 = 0.31 Compression

Slide11: 

Reading for Wednesday, 3 April: Chapter 2 in Energy: Science, Policy and the Pursuit of Sustainability “Future World Energy Needs and Resources” Chapter 5 from L R Radovic “Energy and Fuels in Society”: Energy: Supply and Demand pdf of second reading available on course website: http://www.bren.ucsb.edu/academics/course.asp?number=288