Chapter 8: Renewable Energy Sources

The Sustainability Revolution

John C. Ayers

"In a sense, the fossil fuels are a one-time gift that lifted us up from subsistence agriculture and should eventually lead us to a future based on renewable resources." Kenneth Deffeyes (2001) "I'd put my money on the sun and solar energy. What a source of power! I hope we don't have to wait until oil and coal run out before we tackle that." — Thomas Edison, 1931 We cannot create or destroy energy. We can only capture it. The sun provides either directly or indirectly nearly all of the energy available to us. Plants capture solar energy directly through photosynthesis. Fossil fuels contain the energy of sunlight captured hundreds of millions of years ago. Photovoltaic (PV) cells also capture sunlight energy directly. Other energy sources capture the energy of sunlight indirectly. Heat from the sun powers the flowing air and water. We usually capture the kinetic energy of wind and water by using turbines that transfer the energy to an alternator, an electrical generator that produces alternating current. Geothermal energy is different in that it captures flowing heat energy produced by radioactive decay in the earth’s interior. In this chapter we will see that Wind, Water, and Sun (WWS) energy sources are sustainable because they are renewable, clean, safe, and nearly carbon-free. Although they have low energy densities, meaning that they require large areas of land or water to produce energy, they are sufficient to meet the energy needs of the US and many other countries. Perhaps the greatest challenge facing humanity is to transition to WWS energy as rapidly as possible to mitigate AGW. Renewable energy sources are rate-limited: they can flow forever, but only at a fixed rate. They cannot support an indefinitely growing population, but they can provide an energy base for a sustainable society (Meadows, Randers et al. 2004). Switching to renewable energy stabilizes energy prices and therefore decreases risk. For organizations this makes planning easier. According to Sawin and Moomaw (2009), renewable energy sources contributed 18% of global electricity in 2007, and that number is increasing. Brown (2009) notes that “Just as the nineteenth century belonged to coal and the twentieth century to oil, the twenty-first century will belong to the sun, the wind, and energy from within the earth.” As Friedman (2008) states, "The Stone Age didn't end because we ran out of stones." Likewise, the Age of Oil will not end because we run out of oil; it will end because we find better alternatives. However, as stated by Hall and Day (2009), "Renewable energy sources other than hydropower and wood currently provide < 1% of the energy used in both the US and the world, and the annual increase in the use of most fossil fuels is generally much greater than the total production (let alone increase) in electricity from wind turbines and photovoltaics. Our new sources of "green" energy are simply increasing along with (rather than displacing) all of the traditional ones." The number of installed wind turbines and solar panels is increasing at an impressive rate of 10-20% per year. However, the installed base is so small that it will take several decades for WWS to catch up with increasing energy demand and make a dent in the amount of fossil fuel consumed. The International Energy Agency (IEA) estimates that we must spend roughly 1% of global GDP between now and 2050 to wean the world off fossil fuels and cut CO2 emissions in half (Sawin and Moomaw 2009). Some believe that we need coal + CCS or nuclear power to address climate change and rising energy demand (Deffeyes 2001; MacKay 2009). However, Sawin and Moomaw (2009) and Jacobsen and Delucchi (2011) claim that renewables plus increased energy efficiency are enough, and that they are the only technologies available now that can do the job i. Renewable sources of energy can potentially provide far more energy than we consume. As a point of reference, the global Total Primary Energy Supply (TPES) is currently about 14 million MW. The earth receives eight thousand times that amount from the sun, with about half reaching the ground (Richter 2010). As much solar energy hits the ground in one hour as all of humanity uses in one year ii. However, in practice we can never capture all that energy. Renewable energy sources are just too diffuse to provide enough energy for everyone on earth (MacKay 2009). In certain areas with abundant sunlight and wind and low population densities it will be possible, but many countries such as the U.K. cannot rely solely on renewable energy, as shown convincingly by MacKay (2009). In the following sections we will look at the promises and shortcomings of each type of renewable energy.

"First, there is the power of the Wind, constantly exerted over the globe.... Here is an almost incalculable power at our disposal, yet how trifling the use we make of it! It only serves to turn a few mills, blow a few vessels across the ocean, and a few trivial ends besides. What a poor compliment do we pay to our indefatigable and energetic servant!"

Wind

Chpt. 8: Renewable Energy Sources

— Henry David Thoreau, from Paradise (To Be) Regained [1843]

Wind power has great potential as an energy source. It is renewable and has a small environmental impact throughout its life cycle. Finally, the technology is simple and scalable, meaning that autonomous communities can use it as a distributed energy source ((Kellogg and Pettigrew 2008)), pp. 160-4). Wind is stronger at higher altitudes and areas without obstructions such as buildings or trees; hilltops in rural areas are good sites for wind turbines, but ground-based turbines in cities are not efficient. Wind strength also varies strongly by season and by region, which means that it is not a viable source of energy in all areas. When wind strength is low, we must supplement it with at least one other source of energy. Wind turbines produce energy by using blades shaped as air foils and mounted on a rotating axis that is usually horizontal. The larger the blades, the more wind energy they can capture. We can use the captured energy to do mechanical work such as drive a water pump, or convert it to electricity using an alternator. We can use the electricity immediately, or store it in batteries for use when wind strength is low. Currently wind power has less of an environmental impact and is cheaper than solar power (Table 7-4). In fact, it is the cleanest alternative energy source. New wind farms produce electricity at costs competitive with oil- and coal-powered plants, and more cheaply than nuclear reactors (Table 7-4). The benefit is that they release no greenhouse gases and do not produce waste ((Steffen 2006), pg. 175). Wind alone holds much more energy than we use. Harnessing the wind in only three states – North Dakota, Kansas, and Texas – could provide enough energy for the entire US ((Brown 2009), pg. 239). Alternatively, wind farms placed up to 50 miles offshore could provide 70% of national electricity needs according to the DOE (Brown 2009). Since the year 2000 world wind generating capacity has been increasing 25% annually (Figure 1), doubling every three years (Brown 2009). Wind currently produces about 1.5% of the world’s electricity (1.3% in the US). Sustaining the exponential growth rate of wind power could make wind a major source of electricity in the US, and even help to reduce fossil fuel use.

Figure 1. Cumulative Installed Wind Electricity-Generating Capacity in Selected Countries, 19802008. After Brown (2009).

Opponents have put forward few arguments against wind. Early wind turbines had smaller blades that turned rapidly and often killed birds, but the slowly-rotating blades of new, large wind turbines kill fewer birds; in fact, skyscrapers, cars, and cats kill far more birds ((Brown 2009), pg. 240). Some have complained about noise, but the new models are very quiet. Others complain that they ruin the landscape because they are unsightly. However, given the urgency of the climate change problem, I don’t think aesthetic arguments will gain much traction. 1 4/11/2011

The Sustainability Revolution John C. Ayers The #1 climate change agent in the US is electricity, and fossil fuels produce 3/4 of it. We could replace that 3/4 with 400,000 windmills rated at 2.5 MW (Komanoff 2006). Each windmill requires 60 acres, but the footprint is only 380 square feet, leaving the rest of the 60 acres for other purposes such as farming. In fact, farmers can earn $3,000-10,000 per year by simply leasing the 380 square feet to the windmill owner, who will still profit because the windmill produces an average of $300,000 worth of electricity per year ((Brown 2009), pg. 240). The electricity produced by wind turbines is carbon-neutral, and the use of electric cars can in turn be carbon neutral if the electricity that fuels them is wind- (or solar) generated. One problem is that the electricity generation capacity of wind turbines is variable, changing with the weather. Solar energy also suffers from this intermittency problem (we can only capture solar energy at night). Regional electricity networks could shift supply to areas of high demand to balance supply and demand. Also, batteries in electric cars can store electricity during off-peak hours and returning it to the grid during peak hours ((Brown 2009), pp. 244-5). A drawback of wind power is that utilities must connect centralized wind farms to the electric grid. Though wind has become the most viable renewable energy source, the low capacity of the electrical grid has limited its growth. According to the American Wind Energy Association, projects totaling more than 300,000 megawatts of wind-generated electricity, more than 20% of the nation's electricity needs, are on hold due to insufficient transmission capacity. Federal energy officials want 20% of the nation's energy to come from wind by 2030 iii. The US needs new interstate power transmission lines and power stations, but the high cost and political squabbling (the NIMBY syndrome) have delayed construction of this critical part of the nation's infrastructure. Despite these problems, installed wind power capacity increased 50% in 2008 alone, making the US the largest producer of wind energy in 2008 (Figure 1). We could potentially bypass the grid capacity problem by taking a decentralized approach and placing many small wind turbines where we need electricity. The government could offer tax incentives for people to purchase their own wind turbines. You can purchase your own efficient wind-electric system; just choose the size that fits your yard (these smaller wind turbines don’t require 60 acres) iv. Small-scale wind power makes most sense for homes not connected to the electrical grid (due to choice or geographic isolation) and in windy areas. Coupling wind with solar power can solve the intermittency problem because solar power is often complementary to wind, i.e., the intermittencies of wind and solar power partially cancel each other. Because wind speed increases with the altitude (shear stresses at the earth's surface slow winds down), we build windmills very tall. Flying windmills can reach even higher altitudes with faster wind. Magenn Power Inc. produces a tethered power air rotor system that generates electricity and sends it down the 1000-foot tether v. It doesn't put birds at risk, and it flies at too low an altitude to interfere with aircraft ((Steffen 2006), pg. 176). Such devices could revolutionize a distributed electrical production system. It’s clear that the US should use the power of wind. Can we increase our wind power capacity fast enough to help phase out fossil fuels by 2030? Denmark currently gets 19% of its electricity from wind, and studies have shown that wind power can provide up to 70% of Europe’s electricity at costs comparable to present-day. Greater amounts are not feasible due to the intermittency of wind. Deploying wind and solar on a partially decentralized basis may be the most effective and expedient approach for the US to rapidly transition from fossil fuels to renewable energy sources.
I have no doubt that we will be successful in harnessing the sun's energy.... If sunbeams were weapons of war, we would have had solar energy centuries ago. ~Sir George Porter, quoted in The Observer, 26 August 1973

Solar

*Find cost estimates for solar power: CSP and PV The sun is the ultimate source of energy. We are fortunate that plants have learned to harness some of that energy through photosynthesis, which forms the basis for the entire food chain, produces all of the oxygen in the atmosphere, and without which we could not survive. However, we need new technologies that can efficiently and safely convert sunlight into usable electricity that can be available on demand (even when the sun is not shining). We can harness energy from the sun using photovoltaics (PV), Concentrated Solar Power (CSP), and passive solar technologies. Most people are familiar with solar panels composed of PV cells that make use of the photoelectric effect discovered by Albert Einstein. Photons transport energy from the sun. When these particles hit a semiconductor, they knock electrons out of their orbits. The electrons jump across 2 4/11/2011

Chpt. 8: Renewable Energy Sources the electronic band gap from the insulating (valence) band into the higher-energy conducting bands. The efficiency of this process ranges between 9-14%. At first glance Photovoltaic (PV) panels seem like an environmentally friendly solution because they use a renewable energy source (the sun) and they do not emit pollution during operation. However, to evaluate their true environmental impact we must examine their entire life cycle. PV panels use semiconductors made from heavy metals. The mining of these metals causes much environmental damage. Manufacturing the PV cells is energy intensive and emits much pollution. These factors make PV panels very expensive, which has limited the market growth of this technology. Finally, PV cells have finite lifetimes (20-25 years), are rarely recycled, and have a high potential to pollute the environment with toxic metals after disposal, especially if disposed of improperly. Furthermore, we can only manufacture PV cells using a high-tech factory, and we cannot repair them, so they are not a sustainable source of energy for autonomous communities or for developing countries striving for self-sufficiency or having insufficient funds for purchasing them. However, they are still a more sustainable source of energy than coal. Because of their high cost, solar PV systems have been most useful for people in remote areas that are off the electrical grid. However, PV cells are becoming increasingly efficient and more eco-friendly, and people who live in sunny areas should seriously consider adding them to their home designs. The most promising technology is a solar panel made from CdTe film. The latest life-cycle analysis suggests that these PV cells recoup their embodied energy (the energy required for the raw materials and production) within 1.1 years in places like sunny Spain vi. Many areas in the US would take less than 2.7 years to break-even. CSP has recently gained attention, as some very large projects in southern California are in the building and planning stages. These systems typically use mirrors to focus sunlight on a heat engine connected to an electrical generator. One type is a solar-thermal system that uses a parabolic mirror to focus sunlight on a cylinder that contains an expandable gas and a piston. The gas heats and expands, driving a crank that pushes a piston. It then cools and contracts, withdrawing the piston. The movement of the piston generates electricity. This “Stirling” engine is an external combustion engine because solar heating outside the cylinder (not an explosion within the cylinder) supplies the energy ((Steffen 2006), pg. 174) vii. Stirling Energy Systems is installing a 500 MW solar power plant 70 miles SE of Los Angeles. It includes 10,000 Suncatcher units, large parabolic mirrors that track the sun across the sky and focus the sunlight on a Stirling engine, a process that is 2-3x more efficient than conventional PV cells. A California law requiring at least 20% of electricity must come from renewable energy sources by 2010 is driving demand for renewable energy production in the state. PV and CSP are active solar technologies because they actively and directly use the sun's energy to produce electricity. In contrast, passive solar technologies passively absorb heat from the sun’s rays and have no electronic components and no moving parts. Examples of passive solar technologies include solar collectors such as solar ovens, parabolic solar cookers, solar water heaters, and passive solar architecture ((Kellogg and Pettigrew 2008), pp. 164-173). Passive solar technologies have all of the benefits of active solar technologies like PV panels (a renewable energy source, no pollution during operation, decentralized) but none of the drawbacks. They are technologically simple, easily constructed (often from recycled parts), and are nonpolluting throughout their life cycle, meaning that they represent a truly sustainable option for autonomous communities. Cooking food requires much energy, mainly because water has a high heat capacity. In the developing world cooking is often very inefficient and environmentally damaging: people chop down and burn trees in open fires that emit harmful smoke and waste most of the heat. Chopping down trees for fuel at a rate faster than they can grow back is unsustainable. A sustainable alternative is to use passive solar technologies. Solar ovens have transparent covers that permit sunlight to enter and dark interior glazes that absorb the sunlight and heat up. A thermal insulator such as wood traps the heat, allowing the interior to heat to the boiling temperature of water (100°C or 212°F), sufficient to cook most vegetables or thinly sliced meat in a matter of hours. Higher temperatures require a parabolic solar cooker, which you can build by lining a recycled satellite dish with mirror shards, aluminum sheeting, or Mylar plastic ((Kellogg and Pettigrew 2008), pp. 168-9). To heat food or water, place it at the focal point of the mirror. Another example of a sustainable passive solar technology is rooftop solar water heaters, which provide hot water for roughly 160 million people in China ((Brown 2009), pg. 237) and harness as much energy as produced by 54 coal-fired power plants. More than 30 million homes in China have solar water heaters, and the government plans to triple the number by 2020 viii. The simple devices consist of angled rows of dark glass tubes filled with cold water. As the sun heats the water, it expands and rises into an insulated tank, where it can 3 4/11/2011

The Sustainability Revolution John C. Ayers remain hot for days. New models add an electrical heater to the tank for supplemental heating on cold days. In Europe where the cost of energy is high, rooftop solar collectors are cost-effective. Many provide not only hot water but also space heating. Estimates suggest that solar energy can meet most of Europe’s low-temperature heating needs ((Brown 2009), pg. 247). A big advantage of solar collectors and PV cells is that they provide peak electricity during the day when demand is highest. Another advantage is that the developing world can deploy them in areas not connected to the electric grid. After paying for the equipment and installation, any energy collected is free. Local solar does not need electric meters, electric bills, or high-voltage transmission lines, required elements of inefficient centralized electrical systems. As a result, installing solar cells on every rooftop is now often cheaper than to build a central power plant and a grid ((Brown 2009), pg. 249). The big disadvantage is that solar power only works when the sun shines. Batteries, molten salts, or pumped storage facilities can store excess energy produced during peak solar power production and release it when solar energy production is low. Other renewable energy sources such as wind can also help compensate for the intermittency of solar power production. Great potential remains for expanded use of CSP, passive solar collectors, and PV cells in the sun-rich southwestern US. Although the US lags behind the EU, Israel, China, and other countries in the development of solar energy, solar power is rapidly growing in capacity. New federal tax incentives will only increase the rate of deployment. President Obama has repeatedly made clear that he believes the US needs a more sustainable energy policy, and wind and solar power may finally be getting the attention they deserve. We have a lot of ways to meet our energy needs. These salmon only have one river forever. If we do not support them, they will go extinct. -Todd True, quoted in "Agency sued over putting hydropower ahead of fish," Seattle Post-Intelligencer, 4 May 2001 Hydroelectric Power From Dams Hydroelectric was the first renewable energy source deployed on a large scale and is still by far the largest, producing 6% of the electricity in the US and 20% globally. Moving water is a more attractive source of energy than moving air because water is 1000x denser than air and therefore has 1000x the power density of wind (MacKay 2009). Hydroelectric technology is simple and reliable ix. All that hydroelectric plants need to produce electricity is a rapid flow of water, usually associated with a sudden drop in elevation. Power generation potential increases with increasing elevation drop and increasing water velocity. Waterfalls are natural elevation drops, but few waterfalls large enough to produce significant amounts of electricity exist, so we build dams to serve as artificial elevation drops for water. The dams hold back the flow of a river, impounding the water upstream of the dam to form a reservoir. As water accumulates behind the dam, the water level rises, producing a large drop in water elevation across the dam. Hydroelectric dam operators control the rate of water flow and therefore the rate of electricity production. When they release water, it falls and pushes the blades of a turbine, which moves copper coils between magnets in a generator, inducing a flow of electricity. Tidal barrages work in a similar way: water flows in with the tide, and at peak high tides a dam rises out of the stream channel and traps the water on the upstream side. As the tide lets out, the elevation drop increases. At low tides operators release the water to produce electricity. Today dams produce most hydroelectric power. In fact, they produce most of the renewable energy in the US. Hydroelectric dams have long lifetimes, zero fuel costs, zero direct greenhouse gas emissions, small carbon footprints (Table 7-3), low external costs, and low operating costs. In areas with strongly seasonal river flow dams regulate water flow and make it more constant. Dams also have more consistent power generation than wind farms. However, like wind and solar, population centers are often far from hydroelectric power supplies, requiring long-distance high voltage transmission lines. Because we can easily regulate hydroelectric power generation, it is effective for balancing loads; we can match power output to demand. Pumped storage is a form of hydroelectric power used for load balancing. Pumps push water up to a reservoir at high elevation during periods of low demand energy, and operators release water to generate electricity during peak demand (MacKay 2009). The efficiency and carbon footprint 4 4/11/2011

Water

Chpt. 8: Renewable Energy Sources of pumped storage depends on the efficiency and life cycle-wide greenhouse gas emissions of the method used for pumping. Although hydroelectric power has many advantages over fossil fuels, large dams often cause more problems than they solve, including loss of fertile land, displacement of people, and catastrophic dam collapses. Most important, dams act as a barrier to the flow of sediment and organisms along the river, two problems we will now examine more closely. Water flowing in rivers carries large quantities of sediment derived from upstream erosion. Unobstructed rivers deposit most sediment in their deltas, which form when fast-moving river water enters a larger body of water. Because water velocity decreases as river water enters a reservoir, suspended sediments settle out, a process called siltation. Over time reservoirs fill with sediment and lose their storage capacity. Energy is required to dredge the sediment out of the reservoir and dump it downstream. Another sediment transport problem caused by dams is downstream erosion. Water released from dams has little sediment, so it effectively scours the stream channel downstream of the dam, causing erosion and loss of species habitats. By reducing the flow of sediment downstream, dams deprive downstream areas of fresh sediment, causing downstream erosion and altering river delta ecosystems. Since natural rivers supply most of the sediment (e.g., sand) to coastlines, beaches and deltas can disappear when a dam steals their sediment. Deltas can disappear because they are always sinking due to the great weight of sediment deposited on them. Fresh sediment deposition keeps river deltas at near-constant elevation. However, once a dam removes the sediment source, the delta continues to sink x. Without continuous sediment deposition, the deltas’ elevation decreases, making it more susceptible to erosion and hurricane damage, or causing it to sink below sea level completely (Syvitski, Kettner et al. 2009). Dams cause another major problem by blocking the migration of river species. Dams can make it impossible for fish and eels to reach their spawning grounds. This has led to the loss of extremely valuable salmon runs in the Pacific Northwest. It has also caused a dramatic drop in the global population of eels, which migrate along rivers (Prosek 2010). Hydroelectric dams have decimated the global population of eels, which spend their adult lives in freshwater but migrate down rivers to spawn in the ocean. A hydroelectric dam on the St. Lawrence impedes the migrations of eels to and from what was the single largest nursery for the American eel — Lake Ontario and its tributaries. The population of eels migrating along the St. Lawrence dropped from nearly a million in the 1980s, to a hundred thousand in the early 1990s, to less than ten thousand in the late 1990s, and virtually to zero in 2000. I still remember catching an eel in a place called "Eel Bay" in the Thousand Islands of the St. Lawrence Seaway in the 1970s. They are incredibly strong, so when I finally fought the eel to the side of the boat it managed either to bite through or break my fishing line. I had no net, I didn't know how to dress or cook an eel, and I could never have subdued the slimy, flailing creature in the boat, so it was just as well. Eel Bay now has far fewer eels than in the 1970s, and this has likely caused dramatic changes in the St. Lawrence River ecosystem. I also well remember pulling from the ocean in Florida pieces of floating "Sargasso seaweed" that serve as the nurseries for baby eels and other creatures. Although its life cycle is not well understood, all American and European eels spawn in the Sargasso Sea within the Bermuda Triangle (Prosek 2010). That's another fascinating creature that our children may never get to see in the wild. Hydroelectric dams have similarly hurt eel populations worldwide. International trade in eels is a multibillion dollar industry. Eel fisheries employ about 25,000 fishermen in the EU to feed the voracious appetite for eels in Japan, and those jobs are now at risk. Some European countries like Ireland have temporarily banned eel fishing to prevent complete collapse of the eel population (Prosek 2010). However, populations of eel and fish that migrate along rivers are unlikely to recover unless we remove the dams that prevent their migrations. Currently the US is using nearly all of the potential hydroelectric energy provided by rivers, so future increases in the generating capacity of conventional hydroelectric power are unlikely. In fact, with all of the problems associated with large dams, the trend is to destroy rather than construct large dams, so the output of conventional hydroelectric power is currently decreasing. Small dams cause less environmental damage, though it’s not clear if they cause less damage per unit energy. If they do, it would make sense to expand the use of small hydro projects that produce less than 30 MW xi. In 2006 the DOE identified 5400 potential small hydro sites in the US that could collectively produce 18000 MW (Richter 2010). Small dams are useful for areas not connected to the grid because it complements PV energy by producing the most energy in the winter when PV power output is lowest. As fossil fuel costs rise, small hydro power will become more attractive. 5 4/11/2011

The Sustainability Revolution John C. Ayers Case study: The Three Gorges Dam An examination of the world’s largest dam will illustrate why many countries are no longer building large dams, and some such as the US are decommissioning them. The Three Gorges Dam in central China is the largest dam ever built, and may be the largest engineered structure ever built ((Rogers and Feiss 1998), p. 176). The dam is 610 feet high, 6864 feet long, and produces 22.5 GW of electricity. When completely filled, the reservoir behind the dam will be 400 miles long. The dam is on the Yangtze River. I took a boat tour along the Yangtze in 1999 and was fortunate to pass through the Three Gorges before the dam was completed. The Gorges were breathtaking, but unfortunately water now mostly fills them. It’s hard to convey the size of the dam or the locks. In this photo markers on the side of the hill show how high the water level rose, essentially to the level of the bridge. More than one million people who lived along the fertile banks of the river were forced to abandon their homes, which are now underwater. This photo shows two levels of homes along the river, an older group that is closer to the river, and a new bright white row at higher elevation. The older homes are now underwater, and their residents have moved to the newer homes. Many people were unhappy about being forced to move. Also, the dam flooded priceless archaeological sites. Before the dam construction many citizens voiced concerns about the effects of the dam on safety and the environment. However, the Chinese government spent roughly 15-20 billion USD to build it anyway, and they imprisoned dissenters. One environmental concern was that, without sewage treatment plants, all of the sewage produced by the million-plus residents around the reservoir would wash into the reservoir, contaminating the water. The sediment from upstream will quickly fill the reservoir, and the agricultural fields downstream will lose the fresh supplies of sediment that kept their fields fertile. Since the dam was completed, the frequency of earthquakes and landslides along the steep slopes of the land surrounding the reservoir increased. This could be explained by water seeping into and lubricating faults and cracks, which act as slip surfaces. Also, water seeping into soil and porous sediments and rock can add weight to a slope, helping to destabilize it. It remains to be seen whether the Three Gorges Dam will cause more problems than it solved. Ocean Power Tidal power and wave power are relatively new methods for harnessing the energy of flowing water ((Brown 2009), pp. 258-9). The total energy contained in tides and waves is about four times the TPES(Richter 2010), but we can capture only a small fraction of that. Many techniques exist for capturing ocean power xii, but current global electricity production is only 10 MW, about 0.001% of the world’s total electricity production of two million MW (Richter 2010). All forms of ocean power must contend with potential damage from storms and corrosive saltwater and incorporate plans to minimize damage to marine ecosystems. Lunar tidal power captures the energy of water flowing in and out with the tides. It is a reliable and essentially continuous source of energy, unlike wind and sun that depend on weather and time of day. Tidal stream farms (analogous to wind farms) and tidal barrages capture the energy of water flowing in tides. Tidal lagoons are used for pumped storage, which power utilities use to reduce the intermittency problems of wind and solar. The technology is simple and inexpensive, and installations don’t take up valuable land. However, even if deployed on a countrywide scale in an island country like the UK tidal power would supply only 11 kWh/d per person, < 6% of power currently consumed (MacKay 2009). What about the energy stored in waves? If you have body-surfed or watched large waves crashing onto rocky shores, you know that waves can pack a punch. However, as stated concisely by Mackay (2009), “sun makes wind and wind makes waves…Wind is second-hand solar energy…Waves are thus third-hand solar energy.” Since energy is lost at each conversion step (sun to wind, wind to wave), waves hold much less energy than wind or sunlight. Currently companies are developing interesting technologies such as the Pelamis wave energy collectors to harness wave energy. However, wave machines are expensive, and if deployed around the UK they would produce only 4 kWh/d per person, only 3% of the average UK power consumption of 125 kWh/d per person. In the US the maximum amount produced per person would be < 4 kWh/d, much less than 2% of the average American power consumption of 250 kWh/d. We conclude that ocean power is currently an insignificant source of renewable energy, and even when fully developed it will provide only a small fraction of TPES in most countries.

6

4/11/2011

"The Senate is now considering increasing government subsidies for corn growers to produce more ethanol. If we produce enough ethanol we can postpone our next invasion of a Middle Eastern country for two to three years." — Jay Leno, comedian "We are witnessing the beginning of one of the great tragedies of history. The United States, in a misguided effort to reduce its oil insecurity by converting grain into fuel for cars, is generating global food insecurity on a scale never seen before." — Lester Brown, author of Plan B, v3.0

Biofuels

Chpt. 8: Renewable Energy Sources

Biofuels are produced through treatment of biomass, organic materials that are frequently plant-based but can also include animal waste. Through photosynthesis plants capture energy from the sun and CO2 from the atmosphere and temporarily store them in organic molecules that make up plant tissue. When we burn biomass, we release the stored solar energy as heat. Decomposition also releases heat, which explains why your compost pile is warm even in winter. Burning and decomposition also return the CO2 stored in biomass to the atmosphere. The net change in atmospheric CO2 concentration in the biomass lifecycle is small because the amount removed by photosynthesis equals the amount returned by burning and decomposition. Biofuels do not have a zero carbon footprint because fossil fuel energy is used in biomass production. In fact, the average carbon footprint of biofuels is greater than those of wind, geothermal, hydroelectric, and nuclear, but still far less than fossil fuels (Table 7-3), which makes them attractive energy sources. Biofuels have a much smaller carbon footprint than fossil fuels because burning biofuels only releases the CO2 that the plant temporarily stored when it grew a few years ago, while burning fossil fuels releases CO2 stored in the earth for millions of years. If we combine the burning of biofuels with CCS, we can even make the carbon footprint negative, which is an attractive option for climate change mitigation. Humans learned thousands of years ago to use the energy stored in plants by burning wood to cook food and provide space heating. However, biofuels have insufficient capacity to be a primary source of power in the developed world. Developing technologies may make biofuels an important energy source, but to this point politicians and the media have overhyped biofuels. The problem is that the low efficiency (1-3%) of solar energy capture by photosynthesis severely limits the rate of biomass energy production. Furthermore, the low energy density of biomass means that energy production requires large areas of land. For example, to meet its current energy needs the city of San Jose, which occupies 113,668 acres, would need the following areas in acres for each fuel type: natural gas 717, hydroelectric 3212, coal 9390, nuclear 10378, solar 18533, wind 130966, and biomass 667185, almost six times the area of the city consuming the energy (Cho 2010). That wind and biomass require more land than occupied by the cities they power makes them much less attractive as potential energy sources. In the developing world the biofuel wood is often used as an energy source for cooking. This leads to problems of deforestation and respiratory diseases. Solar cookers can eliminate the need for biofuels for cooking. Solar ovens and efficient solar stoves like the Jiko, Rocket, and Henya reduce the economic, health, and environmental costs of cooking by reducing or eliminating biofuel consumption ((Steffen 2006) pp. 168-9). Most biofuel electricity generation in the US comes from burning wood chips ((Brown 2009), pg. 255). However, the US currently underutilizes organic waste for energy production. For example, Concentrated Animal Feeding Operations (CAFOs) produce vast quantities of manure that we can as fuel and fertilizer. Decomposing the waste in anaerobic digesters produces methane (natural gas) and a nutrient-rich solid waste. Using the solid waste as agricultural fertilizer closes the resource loop. Likewise, we can recover energy from organic wastes in landfills. Anaerobic decomposition of this waste naturally produces methane. In the past, we wasted landfill methane by burning it off to reduce the risk of an explosion, but now we capture it at many landfills and use it as a source of energy. Other types of biomass we can use as biofuels include yard waste, livestock waste, and sewage, which all contain energy-rich organic compounds. We also use biofuels such as ethanol and biodiesel to power automobiles. Energy utilities produce ethanol by using enzymes to breakdown plant biomass into sugars, adding yeast to produce alcohol, and then distilling the alcohol. The rising cost of oil and gasoline has led to a rapid increase in the use of ethanol as a gasoline substitute in the US. However, it is produced by fermenting corn, a food crop. The competing demands for food and fuel caused corn prices to more than double between 2005 and 2007. This reduced food security for poor people who use corn as a staple crop. In 2007 the US used 20% of its corn harvests to produce only 4% of its automotive fuel ((Brown 2009), p. 39). Thus, corn-based ethanol can substitute for only a small portion of the gasoline demand (Food & Water Watch and Network for New Energy Choices 2007). A recent report concludes that corn “is among the least efficient, most polluting, and overall least sustainable biofuel feedstocks (Food & Water Watch and Network for New Energy Choices 2007).” Recognizing this, 7 4/11/2011

The Sustainability Revolution John C. Ayers scientists are now conducting research to develop new non-food sources of ethanol. Cellulosic plant-based materials such as switchgrass, wheat straw, and corn stalks and husks have higher EROEI and lower carbon footprints than food crops ((Brown 2009), pg. 257). However, recent work suggests that direct burning of these crops is more efficient for energy production than conversion to ethanol (remember that energy conversion always leads to a loss of energy). Perhaps we can adapt coal-fired power plants to burn these biofuels rather than coal. In summary, the jury is still out on how much energy we can obtain from biofuels, and what the best approach is for biofuel energy production. Biofuels will never become our primary source of energy because photosynthesis is an inefficient form of energy production. However, the US clearly underutilizes biofuels. We must try to expand the use of this renewable and sustainable energy source, keeping in mind that biofuels are only as sustainable as the agriculture or forestry practices that produce them (Meadows, Randers et al. 2004). Resources: http://biodesign.asu.edu/research/projects/better-biofuel/ Geothermal energy is a renewable source of energy powered by the flow of heat from the earth’s interior to the surface. Heat always flows from hot to cold, and we use that property for space heating and cooling. Geothermal energy is thermal energy that we obtain by trapping or moving heat. As a low-grade form of energy, less useful than electricity, geothermal heat is most efficiently used for space heating. We can also convert it to electricity, but like every type of energy conversion this results in ~30% energy loss. Geothermal currently produces less than 1% of the world’s electricity. Nevertheless, the energy saved by using geothermal for space heating and cooling is greater and is rapidly rising globally. Two different approaches to moving heat exist. Centralized geothermal power plants are feasible only in areas with anomalously high surface heat flow. In contrast, geothermal heat pumps are effective for decentralized space heating and cooling almost everywhere. The earth stores an enormous amount of heat energy. Radioactive decay over the 4.5 billion year history of the earth produced most of this heat. Because rock is a poor thermal conductor, it trapped much of the heat produced during those 4.5 billion years. Heat is constantly leaking out at the earth’s surface, but it escapes the fastest in areas of volcanic activity such as the Pacific “Ring of Fire,” which includes nearly two billion people in the US, Japan, China, and Indonesia. These areas with high surface heat flow have great potential for geothermal energy production. In the past only areas with high surface heat flow and permeable rocks could be used to capture geothermal energy. Natural water convecting in the rocks would transport the heat to drilled wells. New enhanced geothermal systems can capture geothermal energy even from hot dry rock that is impermeable by pumping high pressure cold water into wells. The use of enhanced geothermal systems has greatly increased the potential for centralized geothermal energy production. For example, geothermal heats nearly 90% of the homes in Iceland and produces 25% of electricity in the Philippines ((Brown 2009), pp. 252-3). Areas with high surface heat flow should invest in the construction of geothermal power plants to make their energy supply sustainable. Decentralized approaches to using the earth as a heat source or sink include passive and active approaches. Although we rarely inventory and generally take it for granted, geothermal energy passively heats greenhouses and ponds used for aquaculture and natural spring waters used in spas and public bathhouses. The active approach is to use ground source heat pumps for space heating and cooling. Because the temperature below ground does not fluctuate seasonally, geothermal heat pumps can heat homes in the winter and cool them in the summer. The heat pump transfers heat from the hot to the cold region. This approach is efficient because it produces primary energy, with none of the energy loss associated with conversion to secondary energy like electricity. Especially when they use electricity from renewable sources, heat pumps are the most energy efficient, clean, and cost-effective option for space heating and cooling (US EPA). Recognizing this, the US government now gives a 30% tax credit to homeowners who install geothermal heat pump systems. As a result, geothermal heat pump capacity is growing by 10% annually. Although the up-front cost can be high, energy savings make heat pumps pay for themselves within ten years. Thus, a truly sustainable home should incorporate a ground-source heat pump in its design. Lester Brown claims in his book Plan B 4.0 (2009) that by 2020 the world could increase the amount of renewably generated electricity fivefold and decrease fossil fuel-based energy use by 90%. Combined with 8 4/11/2011

Geothermal

Summary: Are Renewables Enough?

Chpt. 8: Renewable Energy Sources increases in energy conservation, Plan B 4.0 would reduce global CO2 emissions 80% and stabilize atmospheric CO2 below 400 ppm (the CO2 concentration in 2011 was 391 ppm). “Whereas fossil fuels helped globalize the energy economy, shifting to renewable sources will localize it. The question is no longer whether we can develop a climate-stabilizing energy economy, but whether we can develop it before climate change spins out of control ((Brown 2009), pp. 260-1).” Even Brown’s optimistic plan does not completely phase out fossil fuels. A recent analysis by MacKay (2009) of the UK’s energy needs concludes that, even ignoring economic constraints and public opposition to many renewable projects, domestically-produced renewables cannot meet current energy demand. Put another way, in the ideal case of no economic and political constraints, if the UK covered all land with wind farms and PV panels and the entire coastline with offshore wind farms and various forms of ocean power production, the maximum amount of energy that they could produce using renewable sources would fall just short of current demand. Considering that energy demand keeps increasing over time, the renewable energy supply seems unlikely ever to meet demand fully in the UK. MacKay’s analysis is convincing because he clearly presents all of the calculations, states his assumptions, and uses reliable data. His less detailed analysis of North America finds that solar energy alone can meet current and future energy needs because, unlike the UK, North America has large areas of virtually uninhabited land with abundant sunlight for solar energy collection ((MacKay 2009), pg. 235). MacKay concludes that the UK and other developed countries with high population densities must close the gap between demand and supply by supplementing domestic renewable energy with either clean coal, nuclear fission, or imported renewable energy (MacKay 2009). The latter approach is not a globally sustainable approach (and it raises many thorny political issues that I am not qualified to discuss), so we will focus on examining the first two options. Many respected scientists who are experts on energy supply (including Deffeyes (2001) and Sir James Lovelock (2006)) think that nuclear energy will be a necessary component of the energy portfolio in developed countries, at least as a short term (say 40 years) stopgap measure until we can develop nuclear fusion or other clean sources of energy. Nuclear is preferable to coal, which kills far more people per unit of energy produced than nuclear. Furthermore, expanded use of coal would intensify GCC. Global climate change is a much greater danger than radioactive waste from nuclear fission reactors, so nuclear is definitely the lesser of two evils. Thus, we may have to expand the use of nuclear power in some developed countries to phase out the use of coal. An attractive compromise would be to tie the phasein of new nuclear power plants to the phase-out of coal-burning power plants. Policy makers should keep all energy options on the table except the expansion of coal-burning power plants. One oft-discussed solution that is not really a solution is the idea that we can solve the energy problem by making small lifestyle changes. MacKay convincingly shows that little changes made by people amount to little changes for a country ((MacKay 2009), p. 68): “Don’t be duped by the every little bit helps mantra. Obsessively switching off the phone-charger is like bailing the Titanic with a teaspoon. Do switch it off, but please be aware how tiny a gesture it is. Let me put it this way: All the energy saved in switching off your charger for one day is used up in one second of car-driving. The energy saved in switching off the charger for one year is equal to the energy in a single hot bath." Everyone agrees that if you stop using a phone charger that uses less than 1% of your homes electricity, then you will reduce your electricity consumption by less than 1%. However, the idea that "little changes add up" has led people to think that we can solve our energy problems solely by making little changes. What holds for the individual holds for a country: if every citizen stopped using phone chargers, and those chargers consumed less than 1% of each user’s total electricity consumption, the country would reduce its total electricity consumption by less than 1%. We have to focus on the big changes. The scale of change required to avert dangerous climate change is enormous. Jackson states that "If everyone in the world lived the way Americans do, annual global CO2 emissions would be 125 gigatons - almost five times the current level- by the middle of the century (Jackson 2008)." However, climate scientists say that to avoid dangerous anthropogenic climate change we must decrease total CO2 emissions below five gigatons per year and reduce the carbon footprint to less than one ton per person, lower than the current average in India (Jackson 2008). To avoid dangerous anthropogenic climate change and ensure an adequate supply of energy for the future we need to carry out a wartime-scale mobilization of resources in the US to transition to a fossil fuel-free energy economy (Brown 2009). We must rapidly and greatly expand solar, and in particular, wind, power capacities. Without the development of a new centralized energy source such as nuclear fusion, energy production will transition to small, decentralized, renewable sources of energy. That may lead to the 9 4/11/2011

The Sustainability Revolution John C. Ayers development of sustainable, autonomous communities (Kellogg and Pettigrew 2008). Decentralization of power (both energy and political/social) would be beneficial to society; it would reduce our dependence on foreign countries and energy monopolies, and increase our security and self-sufficiency. The transition to a more sustainable energy portfolio is possible. For example, MacKay (2009) presents six energy plans for the UK that incorporate energy saving from increased efficiency and eliminate fossil fuels. Three of these plans rely on solar energy collected in the Sahara and transported by HVDC power lines. The cost of installing the solar collectors and power lines would be tremendous, and it would transform the landscape. The solution to our environmental problems is not to produce more energy per person, because cheap energy is what caused many of our environmental problems in the first place. Cheap energy has allowed us to mine ores that would not be economically mineable without cheap energy; to build cities that have displaced species and led to their extinction; and so on. So rather than discussing ways to increase energy production, in the next chapter we will focus on ways to make energy production more sustainable and to decrease demand.

References
Brown, L. (2009). Plan B 4.0: Mobilizing to Save Civilization. New York, NY, W.W. Norton & Co., Inc. Cho, A. (2010). "Energy's Tricky Tradeoffs." Science 329(5993): 786-787. http://www.sciencemag.org/cgi/content/summary/329/5993/786. Deffeyes, K. S. (2001). Hubbert's Peak: The Impending World Oil Shortage. Princeton, New Jersey, Princeton University Press. Food & Water Watch and Network for New Energy Choices (2007) "The Rush to Ethanol: Not All Fuels are Created Equal." 80 http://www.newenergychoices.org/uploads/RushToEthanol-rep.pdf. Friedman, T. (2008). Hot, Flat, and Crowded: Why We Need a Green Revolution - and How It Can Renew America, Farrar, Strauss and Giroux. Hall, C. S. A. and J. W. J. Day (2009). "Revisiting the Limits to Growth After Peak Oil." American Scientist 97: 230-237. Jackson, T. (2008). The Challenge of Sustainable Lifestyles. State of the World 2008: Innovations for a Sustainable Economy. L. Starke, W.W. Norton & Company: 45-60. Jacobson, M. Z. and M. A. Delucchi (2011). "Providing all global energy with wind, water, and solar power, Part I: Technologies, energy resources, quantities and areas of infrastructure, and materials." Energy Policy In Press, Corrected Proof. http://www.sciencedirect.com/science/article/B6V2W-51TXP822/2/de5d9bb816ee92da3bfef3f8ecd54b1d. Kellogg, S. and S. Pettigrew (2008). Toolbox for Sustainable City Living. Cambridge, MA, South End Press. Komanoff, C. (2006). "Whither Wind?" Orion (September/October). Lovelock, J. (2006). The Revenge of Gaia: Earth's Climate Crisis & The Fate of Humanity, Basic Books. MacKay, D. J. C. (2009). Sustainable Energy - without the hot air. Cambridge, England, UIT Cambridge Ltd. www.withouthotair.com. Meadows, D. H., J. Randers, et al. (2004). Limits to Growth: The 30-Year Update, Chelsea Green. Prosek, J. (2010) "A Steady, Steep Decline for The Lowly, Uncharismatic Eel." Yale Environment 360. http://e360.yale.edu/feature/a_steady_steep_decline_for_the_lowly_uncharismatic_eel/2316/. Richter, B. (2010). Beyond smoke and mirrors: Climate change and energy in the 21st century, Cambridge Univ Pr. Rogers, J. J. W. and G. P. Feiss (1998). People and the Earth: Basic Issues in the Sustainability of Resources and the Environment. Cambridge, UK, Cambridge University Press. Sawin, J. L. and W. R. Moomaw (2009). An Enduring Energy Future. State of the World 2009: Into a Warming World. L. Starke, Worldwatch Institute. Steffen, A., Ed. (2006). World Changing: A User's Guide for the 21st Century. New York, NY, Abrams. Syvitski, J. P. M., A. J. Kettner, et al. (2009). "Sinking deltas due to human activities." Nature Geosci advance online publication. http://dx.doi.org/10.1038/ngeo629 http://www.nature.com/ngeo/journal/vaop/ncurrent/suppinfo/ngeo629_S1.html.

10

4/11/2011

Chpt. 8: Renewable Energy Sources
Environmentalists have been pushing wind and solar for decades, but have been met by skepticism by the establishment, who argued that these sources would be insufficient for our energy needs. Now that our energy needs have tripled and quadrupled, environmentalists are still claiming that wind and solar can meet our needs, but the establishment thinks we should expand the use of nuclear power. Who is right? And why does the establishment always resist accepting green technology? Perhaps it is because most in the establishment take an exemptionalist approach and tend to prefer engineered to natural approaches. ii http://en.wikipedia.org/wiki/Solar_energy iii The Tennessean, 6/18/09. iv http://www.homepower.com/article/?file=HP122_pg28_Woofenden v http://www.magenn.com/ vi http://www.worldchanging.com/archives/009864.html vii see http://www.youtube.com/watch?v=fi0Y0Kr-_KI viii David Pierson, L.A. Times, 9/13/09. ix see http://www.youtube.com/watch?v=cEL7yc8R42k&feature=related x Isostatic adjustments and sediment compaction are slow processes that have long relaxation times Syvitski, J. P. M., A. J. Kettner, et al. (2009). "Sinking deltas due to human activities." Nature Geosci advance online publication. http://dx.doi.org/10.1038/ngeo629 http://www.nature.com/ngeo/journal/vaop/ncurrent/suppinfo/ngeo629_S1.html.. xi Since hydroelectric power is highly variable, quoted values of power output are averaged over a year. xii see http://science.howstuffworks.com/environmental/green-tech/energy-production/ocean-power.htm i 11

4/11/2011