PHYS Energy and Environmental Physics

Transcription

1 PHYS Energy and Environmental Physics Lecture 6 Alternatives to Fossil Fuels Oleh Klochan

2 This Lecture Problems with Fossil Fuels. When the Oil runs out. How can we cope without oil (or with high oil costs). Energy without fossil fuels.

3 Problems with Fossil Fuels Fossil fuels are a major source of greenhouse pollution. Any strategy to combat global warming is likely to involve reduced use of fossil fuels. To achieve the emissions reduction recommended by some we would need to largely phase out use of fossil fuels. The peak oil effect means that oil supplies are likely to become limited or expensive. Irrespective of our policy on greenhouse emissions.

4 Fossil Fuel Uses There are two main uses of fossil fuels that we need to provide alternatives to: Electricity Production Currently this uses a mix of coal, oil and natural gas (but in Australia mostly coal). Transport This currently uses almost exclusively oil.

5 Electricity Production There are a number of possible technologies that don t use fossil fuels and are CO 2 emission free. For example: Nuclear Hydroelectric Solar Wind Geothermal These will all be discussed further later in the course.

6 Transport However, these technologies are likely to be of limited application to transport. There are nuclear powered ships but nuclear power is probably not a practical technology for smaller vehicles. Russian Nuclear Powered Icebreaker (50 years of the Victory)

7 Solar Cars Solar cars have been built mostly for races such as the World solar challenge from Darwin to Adelaide. These are extremely lightweight and highly streamlined cars. The solar power available from the area of a typical car is ~500W. This compares with a power of 50kW for a typical small car engine. Solar power is therefore not really practical as a direct power source for a conventional vehicle. UNSW s Sunswift IV (Ivy) Fasted passenger solar car in the 2013 World Solar Challenge. Set the World Record in 2014 for the fastest solar car over 500 km at 107 km/hr

8 Wind Power Wind power has been used in sailing ships since antiquity. Now no longer used for commercial shipping. However, high oil prices are renewing interest in using sail power to assist engines and reduce fuel consumption. Some new concepts for more efficient wind power than conventional sails have been developed.

9 Wing Sails Wing sails are sails shaped like an aircraft wing. They can be more efficient than normal sails. Concept for a 50,000 ton ship using wingsails to assist engines.

10 Kite sails are used as a simple way of providing wind power as energy assist for ships. Kite Sails

11 Specialist Applications However these direct ways to use alternative energy sources are specialist applications. They don t help with our main transport applications such as replacing petrol fueled cars. Other approaches are likely to be needed to meet the bulk of our transportation needs. To provide replacements for using oil as a transport fuel.

12 When the oil runs out or becomes too expensive How can we fuel vehicles without oil (or with less oil). Fuel from Coal Biofuels Hybrid cars Electric vehicles Plug in Hybrids Hydrogen fuel and the Hydrogen Economy

13 Fuel from Coal Both Gas and Liquid fuels can be made from coal. In fact this is how gas was originally made before natural gas came into widespread use in the 1950s. Fuel for vehicles (Petrol, Diesel, Jet fuel) can be made from coal (or natural gas). Germany used this method during the World War II when it was cut off from oil supplies.

14 Coal Gas Gas made from coal fuelled the gas lights of Victorian-era England. With the introduction of electric lights use of gas shifted to cooking and heating. Coal gas continued to be used in England up to the 1960s when it was replaced by Natural Gas.

15 Synthetic Gas Production Gas is manufactured by heating coal or coke with steam through reactions such as: C + H 2 O CO + H 2 2C + O 2 2CO The gas is thus a mixture of hydrogen and carbon monoxide.

16 Fischer-Tropsch Process Synthetic gas (syngas) can be further converted to liquid hydrocarbons by the Fischer-Tropsch process. (2n+1)H 2 + nco C n H 2n+2 + nh 2 O The reaction is achieved by heating the syngas with appropriate catalysts.

17 Coal to Liquid Fuel Largest Coal-to-Liquid (CTL) plant today is the Sasol plant near Johannesburg Produces 150,000 barrels of synthetic fuel a day. 28% of South Africa s fuel needs. Development was driven by sanctions against South Africa during the Apartheid era. High oil prices are making such schemes more attractive. Since we have larger coal reserves than oil reserves it prolongs the availability of liquid hydrocarbon fuels.

18 SASOL CTL Plant A large amount of CO 2 is generated in the conversion process 7 tones of CO 2 per ton of hydrocarbon produced according to one estimate. So this is not a clean source of energy. CO 2 emissions are produced both in making the fuel and in burning it.

19 Biofuels Biofuels are fuels produced from biological sources. They include ethanol - produced by fermentation and biodiesel made from vegetable oil. In Australia ethanol is made from sugar cane, and is widely available in the form of E10 fuel (petrol blended with 10% ethanol). This can be used in ordinary petrol engine cars. Higher ethanol blends such as E85 (85% ethanol) are available in some countries. It is used in flexible fuel vehicles, requiring some modifications to a standard petrol engine E10 fuel usually sells for about 3 cents per litre less than regular unleaded petrol. However, since the energy content of ethanol is 30% less than petrol there is no real saving. E10 fuel contains about 3% less energy than petrol.

20 CO 2 Emissions CO 2 CO 2 While burning ethanol produces CO 2, this is balanced by the CO 2 taken in by the plant source through photosynthesis. Hence greenhouse emissions are much reduced. However some CO 2 will still be produced during the production and transport of the fuel.

21 Competition with Food Production One problem with biofuels is that production requires agricultural land that would otherwise be used for food production. Already ethanol production in the USA is causing a reduction in wheat production. This is contributing to high wheat prices, and the recent world food crisis. Biofuels are not likely to be a global solution to the oil shortage and CO 2 emission problems. But may be helpful on local scales in places where biofuels can be produced without impacting on food supply.

22 Hybrid Cars A hybrid car combines a petrol or diesel engine (internal combustion engine or ICE) with an electric motor. The electric motor can be used for initial take off from rest, and the petrol engine adds extra power when needed.

23 Hybrid Cars Series hybrid Internal combustion engine is used to generate electricity and charge batteries. Direct power to wheels comes from electric motor. Parallel hybrid Power from both internal combustion engine and electric motor can be fed to wheels.

24 Toyota Prius The best known example is the Toyota Prius started in more than four million of these vehicles have been sold.

25 Toyota Prius 57 kw Petrol Engine Nickel Metal Hydride Battery (2.56 MJ, 0.71kWh) 50 kw Electric motor Power split device Enables power from the petrol and electric motors to be combined

26 Hybrid Car Efficiency Hybrid Cars improve on fuel economy compared with conventional petrol fuelled cars. The ICE can be smaller than in a purely petrol vehicle since the electric motor assists when power is needed. The ICE can be turned off during idling and braking, reducing fuel use. Regenerative braking can be used to recover and reuse energy.

27 Regenerative Braking Regenerative braking is a key factor in the efficiency of hybrid and electric cars. In a conventional petrol car the brakes operate by friction. The kinetic energy of the car is dissipated as heat and lost. A regenerative braking system captures the kinetic energy of the car during braking and allows it to be reused for subsequent acceleration.

28 Regenerative Braking Regenerative braking relies on the fact that many electric motors can operate in reverse as generators. When electricity is supplied to the motor it turns producing mechanical power. If the shaft of the motor is rotated electricity is generated. You can t do this with a petrol engine? i.e. turn the shaft and have the engine produce petrol from nowhere.

29 Hybrid Car Efficiency Regenerative Braking allows hybrid cars to achieve substantial gains in fuel economy for city driving with frequent stopping and starting. The efficiency gains for highway driving involving more infrequent braking are more modest.

30 Hybrid Disadvantages The hybrid system with its petrol engine, electric motor and batteries is more complex than a conventional car. Hard to fit into small cars. Most hybrids are mid-size to large. Currently prices are higher than similarly sized conventional vehicles.

31 Electric vehicles have been around for some time. However, they got phased out by ICE cars in early 20 th century. Electric Cars 1895 car built by Thomas Parker Specialist application cars. The electric milk float widely used for fresh milk deliveries in Europe. Powered by lead acid batteries and had maximum speeds of ~30kph, and ranges of ~100km. Would be plugged in to recharge overnight.

32 Electric Cars The problem is the batteries. To provide a vehicle with the same energy as 50 litres of petrol would require about 12 tonnes of lead-acid batteries. Clearly this is not practical.

33 Electric Cars New technologies are making electric cars much more feasible. Lithium-Ion batteries (the same type as used for laptop computers) provide about 4 5 time the energy per kg of lead-acid batteries. Electric Cars can be made very efficient. Electric motors can be better than 90% efficient (petrol engines are ~20% efficient). Regenerative braking can be used to further increase efficiency. Electric cars therefore don t need battery capacity as large as the energy carried in the fuel tank of a petrol car.

34 Battery Technology Technology Volts per cell Energy Density Wh/kg Lead-Acid Standard car battery Nickel Metal Hydride Used in Toyota Prius Li-Ion Used in Tesla Roadster Petrol ~10000 Wh/l

35 The Tesla Roadster is a fully electric sports car marketed between Tesla Roadster Power 185 kw 0-60mph (97 kph) in 3.9 seconds Range 350 km (though independent tests suggest km) Power source - 53 kwh Lithium-Ion batteries Charging time 3.5 hours Price US$100,000 Model S and Model X are currently on the market and Model 3 will come out by the end of Higher capacity batteries / Supercharging

36 The Tesla Roadster s battery pack weights about 400 kg and contains 6,831 individual Li-Ion cells Batteries

37 Nissan Leaf S kw motor 30 kwh Li-Ion Battery ~130 km range US price 30,000 Sold 200,000 cars worldwide since 2010 In AUSTRALIA only 219 electric vehicles were sold in 2016 out of nearly 1.2 million new vehicle sales. No government incentives. No infrastructure.

38 CO 2 Emissions of Electric Cars Electric cars produce no CO 2 directly. However, the CO 2 produced in generating the electricity needs to be considered. However, modern electric cars are much more efficient than petrol cars. Even if the electricity is generated from coal (the dirtiest fuel) an electric car produce less CO 2 than a petrol car. If clean electricity sources are used (e.g. solar, wind, hydro, nuclear) the electric car is emission free.

39 Plug-In Hybrid A Plug-In Hybrid combines the features of a hybrid car and fully electric car. It has a larger battery than a standard hybrid (like the Toyota Prius). For short trips it can run as a pure electric car with the battery recharged by plugging in to the mains. For longer trips the petrol engine comes into use, so it doesn t have the range limitations of a pure electric car.

40 Several plug-in hybrid cars are on the market. Chevrolet (Holden) Volt Plug-In Hybrid Plug-in version of Toyota Prius Mitsubishi Outlander P-HEV Chevrolet Volt 111 kw electric motor 53 kw petrol engine Electric range 60 km - Petrol range 610 km

41 Fuel Cell Car Fuel cell cars use electricity generated by a fuel cell. Unlike a conventional battery a fuel cell can supply electricity continuously as long as it is supplied with fuel. Fuel cells can run on hydrogen and oxygen producing water as the only exhaust product.

42 Fuel Cell Fuel cells involve an electrolyte material that is sandwiched between two layers of catalyst. There are a many types of fuel cell using different electrolyte and catalyst materials.

43 Fuel Cells Fuel cells supplied power to NASA s Apollo spacecraft and to the Space Shuttle. The fuel cell provides not only power, but the resulting H 2 O can be used as drinking water. The Apollo 13 accident in 1970 was due to the explosion of an oxygen tank. Without oxygen, the spacecraft lost its ability to generate power using its fuel cells.

44 Honda FCX Clarity The Honda FCX Clarity is a hydrogen fuel cell car. A small number of these vehicles have been leased in California.

45 Honda FCX Clarity 100 kw H 2 -O 2 fuel cell 100 kw electric motor Compressed hydrogen fuel 4.1kg tank 300 atm pressure. 440 km range

46 Hydrogen Economy The hydrogen economy is the name given to a proposed future system of energy supply for vehicles based around hydrogen. Hydrogen would be produced by electrolysis of water using electricity generated by emission free methods (e.g. wind, solar, nuclear). Hydrogen would power vehicles using fuel cell technology. The hydrogen economy has the potential to greatly reduce the CO 2 and other pollution associated with fossil fuels. Opponents of the hydrogen economy argue that developing the technology and infrastructure needed would be expensive and inefficient, and there are more cost effective solutions.

47 Video Flying cars