If you thought shale oil was bad news, you should see what tar sands are like. At least shale is in one solid piece. Tar sands are a mixture of oil, sand, water, and worse yet, clay, made of very fine particles. To get the oil out is harder than cleaning up an oil spill on a beach. The huge deposits of tar sands, or sand oil, in western Canada are often in the news as examples of untapped energy reserves, estimated to be around 1.7-2.5 trillion barrels of crude oil.2728 In the northwest corner of the province of Alberta, the Athabasca River starts from Athabasca Lake and meanders all the way to Jasper National Park. At the northern end, near Fort McKay, is the largest of three oil sand deposits in Canada. Alberta’s sands yield a million barrels a day and have a proven, economically recoverable reserve of 173 billion barrels, perhaps extendable to 315 billion, compared to 264 billion in Saudi Arabia.27 The USA gets 10% of its imported oil from these sands. That’s the good news. The bad news is that it takes a lot of energy to get the oil out, and there is a huge envi­ronmental impact in doing so. For deep deposits, the in situ method described above for shale can be used, with wells drilled down to the tar sand layer and then horizontally along the deposit. Steam is injected in one well to melt the tar, which drips down into a lower well and is then pumped up to the surface. Open-pit min­ing uses less energy but still requires heat. For each barrel of oil produced, in situ mining of tar sands emits 388 lbs of CO2 and open-pit mining 364 lbs, compared with 128 lbs in conventional oil mining.27 Eighty percent of the deposits lie deep enough to require energy-intensive in situ mining.

Here is how it works. Tar sands contain oil in the form of bitumen, which is as thick as molasses in the summer and as hard as a hockey puck in the winter. Roughly speaking, the sands consist of 10% bitumen, 5% water, 20% clay, and 65% sand.28 To get at them, the forest has to be cut down first; then, to dig down to the sands, 100 feet of earth has to be removed: 4 tons of earth for each barrel of oil. Huge shovels then scoop the sands into monstrous trucks three stories high, carrying 400 tons at a time. The ore is dumped into crushers and then into tanks where warm water at up to 80°C (175°F) is added to form a slurry. The slurry is pumped in a pipeline up to 5 km (3 mi.) long to a separation tank. The pipeline serves an impor­tant function. The lumps rub against its walls during the transport in such a way that the bitumen is separated from the sand and becomes attached to air bubbles. The air and bitumen form a froth which rises to the top and can be separated out, while the sand and clay fall to the bottom. Some of the bitumen is still in the mix, which can be recirculated to get more bitumen out in a secondary froth. It takes time for the air bubbles carrying the bitumen to rise to the top, because they collide with the heavy stuff going in the opposite direction. A faster way is to put the mixture between two parallel plates which are inclined at an angle to vertical. The bubbles then rise along the top of the gap while the water and sand fall at the bottom plate, and they do not have to collide. Really high tech. The air in the froth is then boiled off, leaving an emulsion of water (30%), bitumen, and clay. An emulsion is a mixture of immiscible fluids, such as vinegar and oil in salad dressing. If the water droplets in this emulsion would coalesce, the water would sink to the bottom and the oil to the top, as in salad dressing left standing around. In a draconian twist, the water droplets are coated with a fine layer of particles from the clay, which keeps the droplets from coalescing. Solvents have then to be added to get the water out. The bitumen ends up with 2% water and 0.8% clay. The chemicals in these contaminants will corrode the pipelines later on, so the oil next goes to an upgrading plant, where it is heated to 480°C (900°F) and compressed to 100 atmospheres. The energy cost of this would be excessive if the heat were not recovered for the initial heating of the oil sands.

There are other energy costs not mentioned above. The shovels that do the digging have steel teeth each made of a ton of steel and wear out in a day or two. The energy used to mine and refine that steel is usually ignored. The trucks use 50 gallons of diesel per hour, and their huge tires last only six months. The sands have to be near a river, because lots of water is needed for washing, 200,000 tons of which has to be heated every day at Athabasca. What happens to the sand and clay that were removed in the first step? They go into tailing ponds, which are the worst news yet. The tailings are a thick sludge consisting of the waste water and 30% sand and other solids from which the bitumen had been stripped. It also contains toxic chemicals. One pond can cover four square miles (10 km2), and there are 50 square miles (130 km2) of these ponds in Canada, about a third of the area despoiled by tar mining. A sand dike 300 feet (100 m) high around each pond contains the tailings, but some suspect that the toxic chemicals have leached into rivers and lakes. Fish have been found with unusual red spots on their skins. Once 500 ducks landed on the oily brew and died. Self-operated, flapping mechanical falcons have been installed as scarecrows, insufficient for the purpose. It takes 1-2 years for the clear water to rise to the top, from where it can be reclaimed to supply half the water for mining. What is left at the bottom, however, is still liquid and is difficult to solidify to restore the forest land. So far no tailings pond has been reclaimed.

The mines operate day and night, winter and summer, to supply the demand for oil. The large reserves are there, but the price is steep. The cost of mining is many times the cost for conventional oil, and this does not include the cost of carbon capture and sequestration, which has not started. Tar mining emits CO2, and more CO2 is emitted when the oil is converted to gasoline and burned in cars. The environ­mental impact alone makes this a poor choice for stretching our oil supply. Perhaps the most poignant argument is that the energy used in tar mining is mostly natural gas, the cleanest burning fossil fuel. This is wasted to produce a low-grade oil because liquid fuels are so valuable for transportation.

The melting of arctic ice injects fresh water into the north Atlantic, possibly disrupting the warm ocean currents that make Europe comfortably habitable. Although this is unlikely, the consequences are so unsettling that this subject has drawn undeserved attention. London is at the same latitude as Calgary, Canada; and Rome is in line with Boston, Massachusetts. Troms0, Norway, is 250 miles north of the Arctic Circle; yet its harbor never freezes over. That is why most polar expeditions start there. Technically known as the Atlantic Meridional Overturning Circulation (or MOC), the Gulf Stream picks up heat from the Atlantic Subtropical Gyre and carries it to the Subpolar Gyre. These gyres, or circulating currents thousands of miles across, are driven by winds above the water. Figure 1.15 shows the system of ocean currents over the whole earth. In the north Atlantic, water warmed in the Caribbean flows along the shore of the USA up to Cape Hatteras, and then breaks off eastward toward Iceland and England.8 When it reaches high latitudes, the seawater cools, becomes denser, and sinks to lower depths. The cooled, salty water then flows back to the south underneath the warm water. Fresh water from ice melting from Greenland, how­ever, is lighter than saltwater and stays on top, opposing the northward flow of the Gulf Stream.

Computer models vary greatly on what will happen. The latest results vary from almost 50% slowing of the MOC to no slowing from anthropogenic causes. The

problem is complicated by two other known effects, the Atlantic Multidecadal Oscillation and the North Atlantic Oscillation, which can, respectively, accelerate or delay the MOC slowing by a few decades. Furthermore, it depends on where the temperature rise is greater. Both the injection of fresh water from the north and greenhouse warming of the North slow down the MOC, while warming in the South will enhance it. The 2007 IPCC report concludes that there is a greater than 90% probability that there will be some decrease of the MOC in the next 100 years, but no simulations predict that the MOC will completely stop. There has been no con­clusive evidence of changes so far.

As we stated at the beginning of this chapter, wind turbines produce electricity efficiently without going through a steam cycle. The generators in the nacelles are basically electric motors run in reverse, so that instead of electricity causing something to turn, the turning of the blades causes electricity to be generated. Of course, it is not that simple, and this gets a little technical. The pitch of the blades is varied to keep them turning at the same speed as the wind varies. The rotor is connected to the generator through a gearbox. The gears are needed to increase the rotational speed of the rotor (about 5 rpm, say) to the speed of the generator (about 1,000 rpm, say). The gearbox tends to wear out before anything else, and new turbines are being developed to do the switching electronically, without moving parts. Since it takes a second or two to change the pitch of the blades, gusts of wind will make the rotor turn faster, and the generator has to handle that.

The next problem is to match the electric output from the generator to the AC grid. Though there are different kinds of generators, it is not always possible for them to turn out AC at the same frequency as the grid. The generator’s output will vary with the wind and may be nowhere near the 50- or 60-cycle frequency of AC power. It will also be reactive. That is, the voltage and current of the output will not be in phase, varying nicely together as they should. To manage this, the generator’s output is processed by a converter. The AC is first converted to DC, and then the DC is converted to 50- for 60-cycle AC so that it can be sent into the grid. We com­monly use converters on a small scale. The power bricks that charge our cell phones and laptop computers convert AC to DC. There are small devices for cars which can convert the DC from the cigarette lighter into AC to run a portable household appli­ance. But for a 5-MW turbine, the electronics and capacitors to handle this conver­sion would fill a small factory. Basically, a sizable electric substation has to be built at the base of the tower or inside it. Five megawatts is a lot of power; it is equivalent to 6,700 HP. The switching of this much power requires some heavy-duty transis­tors, and there is a proposal to develop silicon carbide (SiC) switches, which can handle this better than ordinary silicon.19 These large components needed to convert wind power to grid power are a part of the cost and environmental impact that people do not usually know about.