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“The oceans are in constant motion, rippling, swirling, swelling, retreating. As wind blows across the surface, waves are formed. As the gravitational forces of earth, moon, and sun interact, tides are created. These are among the most powerful and constant dynamics on earth.Wave- and tidal-energy systems harness natural oceanic flows to generate electricity. A variety of companies, utilities, universities, and governments are working to realize the promise of consistent and predictable ocean energy, which currently accounts for a fraction of global electricity generation. Early technologies date back more than two centuries, with modern designs emerging in the 1960s, thanks especially to the work of Japanese naval commander Yoshio Masuda and his 1947 invention of the oscillating water column (OWC). As a wave or tide rises within an OWC, air is displaced and pushed through a turbine, creating electricity. With the ongoing movement of ocean waters, air is compressed and decompressed continuously. It is the same principle used in whistling buoys, which draw on compressed air to create noise near treacherous shoals or outcroppings. Today, there are several OWC power plants in the world.The appeal of wave and tidal energy is its constancy: No energy storage is required. And while communities often resist the presence of wind turbines along ridges or shorelines for violating viewsheds, the idea of underwater, out-of-sight wave and tidal systems has proven to be more acceptable to coastal citizens. (Though they can pose concerns for local fishermen, whose livelihoods depend on the same waters.)When it comes to energy generation, not all waves and tides are created equal. East-west trade winds blow at 30 to 60 degrees latitude, giving the west coasts of all continents the greatest wave activity. Surfing destinations are often wave- “energy hot spots. Key locations for vigorous tidal energy are the northeastern coast of the United States, the western coast of the United Kingdom, and the shoreline of South Korea. Many experts also point to smaller islands as candidates for wave and tidal energy, given isolated geographies and limited energy resources.While the ocean’s perpetual power makes wave and tidal energy possible, it also creates obstacles. Operating in harsh and complex marine environments is a challenge—from designing the most effective systems to building installations for their implementation to maintaining them over time. Salt water corrodes equipment, and waves are more multidimensional than a gust of wind—moving up, down, and in all other directions when there are turbulent conditions. It is also critical to ensure marine ecosystems are not harmed by discharges of sound or substance, or by trapping or killing sea life. All told, these dynamics make operating in salt water more exacting and expensive than operating on solid ground.”“Marine technologies are still in early development, lagging decades behind solar and wind. Tidal energy is more established than wave, with more projects in operation today. They are ideally suited for natural bays, inlets, or lagoons—places where ocean water enters and exits in circadian cycles—harnessing the incoming and outgoing tides to generate electricity. Some resemble dams, inside which rising or retreating tides drive turbines. More experimental in-stream systems function like underwater wind turbines, with tides moving blades to produce electricity.Across the world, a variety of wave-energy technologies are being tested and honed, in pursuit of the ideal design for converting waves’ kinetic energy into electricity. Some look like yellow buoys bobbing up and down on the ocean’s surface. Others resemble large red snakes riding the waves, or long arms waving back and forth. Still others are fully submerged floating discs that incorporate electricity generation right there in the sea. It is not yet clear which technology is most effective. But whatever their shape and form, these systems tap into the upward and downward, the incoming and outgoing movement of waves to power generation. Oscillation is the key, so the higher the wave, the greater its power potential tends to be.”“The opportunity of marine-based energy is massive, but realizing it will require substantial investment and expanded research. Proponents believe wave power could provide up to 25 percent of U.S. electricity and 30 percent or more in Australia. In Scotland, that number may be upwards of 70 percent. Wave and tidal energy is currently the most expensive of all renewables, and with the price of wind and solar dropping rapidly, that gap will likely widen. However, as this technology evolves and policy comes into place to support implementation, marine renewables may follow a similar path, attracting private capital investment and the interest of large companies such as General Electric and Siemens. On a trajectory like that, wave and tidal energy could also become cost competitive with fossil fuels. •”“ There are not many projections of wave and tidal energy to 2050. Building on those few, we estimate that wave and tidal energy can grow from .0004 percent of global electricity production to .28 percent by 2050. The result: reducing carbon dioxide emissions by 9.2 gigatons over thirty years. Cost to implement would be $412 billion, with net losses of $1 trillion over three decades, but the investment would pave the way for longer-term expansion and emissions reductions.”“So far, concentrated solar power (CSP) “has been a tale of two countries, Spain vs. the U.S.” That is how the International Energy Agency sums up the beginning of the story of CSP, also known as solar thermal electricity. The first plants came online in California in the 1980s, and still run today. Instead of capturing energy from the sun’s light and converting it directly into electricity like photovoltaics do, they rely on the core technology of conventional fossil fuel generation: steam turbines. The difference is that rather than using coal or natural gas, CSP uses solar radiation as its primary fuel—free and clear of carbon. Mirrors, the essential component of any CSP plant, are curved or angled in specific ways to concentrate incoming solar rays to “heat a fluid, produce steam, and turn turbines. As of 2014, this technology was limited to just 4 gigawatts worldwide. Roughly half was in Spain, the one country where CSP is significant enough to show up in national generation statistics, at about 2 percent. Because of CSP’s unique advantages, it will grow and those stats will shift. Morocco’s giant Noor Ouarzazate Solar Complex, on the edge of the Sahara, is already changing the solar thermal landscape and will be the world’s largest when complete.”“CSP plants rely on immense amounts of direct sunshine—direct normal irradiance (DNI). DNI is highest in hot, dry regions where skies are clear, typically between latitudes of 15 and 40 degrees. Optimal locales range from the Middle East to Mexico, Chile to Western China, India to Australia. According to a 2014 study in the journal Nature Climate Change, the Mediterranean basin and the Kalahari Desert of Southern Africa have the greatest potential for large, interconnected networks of CSP, with the potential to supply power at a cost comparable to that of fossil fuels. In many regions best suited to making solar thermal power, technical generation capacity (the electricity they could be capable of producing) far surpasses demand. With advances in transmission lines, they could supply local populations and export power to places where CSP is more constrained.”“Rather ironically, the recent success of solar photovoltaic (PV) has limited the growth of solar thermal electricity. PV panels have become so cheap with such speed that CSP has been sidelined; steel and mirrors have not seen the same price plunge. But as PV comes to comprise a greater fraction of the generation mix, it may shift from a damper to a boost. That is because CSP has the very advantage photovoltaics struggle with and “need: energy storage. Unlike PV panels and wind turbines, CSP makes heat before it makes electricity, and the former is much easier and more efficient to store. Indeed, heat can be stored twenty to one hundred times more cheaply than electricity. In the past decade, it has become relatively standard to build CSP plants with storage in the form of molten salt tanks. Warmed with excess heat during the day, molten salt can be kept hot for five to ten hours, depending on the DNI of a particular site, then used to generate electricity when the sun’s rays soften. That capacity is crucial for the hours when people remain awake, consuming electricity, but the sun has gone down. Even without molten salt, CSP plants can store heat for shorter periods of time, giving them the ability to buffer variations in irradiance, as can happen on cloudy days—something PV panels cannot do. More flexible and less intermittent than other renewables, CSP is easier to integrate into the conventional grid and can be a powerful complement to solar PV. Some plants pair the two technologies, strengthening the value of both.”“Compared to wind and PV generation, the major downside of CSP, to date, is that it is less efficient, in terms of both energy and economics. Solar thermal plants convert a smaller percentage of the sun’s energy to electricity than PV panels do, and they are highly capital intensive, particularly because of the mirrors used. Experts anticipate that the reliability of CSP will hasten its growth, however, and as the technology scales, costs could fall quickly. Efficiency of energy conversion is also projected to improve. (Technologies currently under development are already proving it.)”“Other downsides require attention as well. Solar thermal typically relies on natural gas as a production backup or, in some cases, a consistent production boost, with accompanying carbon dioxide emissions. The use of heat often implies the use of water for cooling, which can be a scarce resource in the hot, dry places ideal for CSP. Dry cooling is possible, but it is less efficient and more expensive. Lastly, by concentrating channels of intense heat, CSP plants have killed bats and birds, which literally combust in midair. One company, Solar Reserve, has developed an effective strategy to stop bird deaths; spreading that practice for mirror operation will be critical as more plants come online.”“Human beings have long used mirrors to start fires. The Chinese, Greeks, and Romans all developed “burning mirrors”— curved mirrors that could concentrate the sun’s rays onto an object, causing it to combust. Three thousand years ago, solar igniters were mass-produced in Bronze Age China. They’re how the ancient Greeks lit the Olympic flame. In the sixteenth century, Leonardo da Vinci designed a giant parabolic mirror to boil water for industry and to warm swimming pools. Like so many technologies, using mirrors to harness the sun’s energy has been lost and found repeatedly, enchanting experimentalists and tinkerers through the ages—and once again today. •”“IMPACT: CSP comprised .04 percent of world electricity generation in 2014. Despite slow adoption in recent years, this analysis assumes CSP could rise to 4.3 percent of world electricity generation by 2050, avoiding 10.9 gigatons of carbon dioxide emissions. Implementation costs are high at $1.3 trillion, but net savings could be $414 billion by 2050 and $1.2 trillion over the lifetime of the technology. An additional benefit of CSP is that it can easily integrate energy storage, allowing for extended use after dark.”“How does the world get from one powered by fossil fuels to one that runs entirely on energy from the wind, sun, earth’s heat, and water’s movement? Part of the answer is biomass energy generation. It is a “bridge” solution from status quo to desired state—imperfect, riddled with caveats, and probably necessary. Necessary because biomass energy can produce electricity on demand, helping the grid meet predictable changes in load and complementing variable sources of power, like wind and solar. Biomass can aid the shift away from fossil fuels and buy time for flexible grid solutions to come online, while utilizing wastes that might otherwise become environmental problems. In the near-term, substituting biomass for fossil fuels can prevent carbon stocks in the atmosphere from rising.”“Photosynthesis is an energy conversion and storage process; solar energy is captured and stored as carbohydrates in biomass. Under the right conditions and over millions of years, biomass left intact would become coal, oil, or natural gas—the carbon-dense fossil fuels that, at present, dominate electricity production and transportation. Or, it can be harvested to produce heat, create steam for electricity production, or be processed into oil or gas. Rather than releasing fossil-fuel carbon that has been stored for eons far belowground, biomass energy generation trades in carbon that is already in circulation, cycling from atmosphere to plants and back again. Grow plants and sequester carbon. Process and burn biomass. Emit carbon. Repeat. It is a continuous, neutral exchange, so long as use and replenishment remain in balance. Energy efficiency and cogeneration are integral to ensure that, in any given year, carbon from biomass combustion is equal to or less than the carbon uptake of replanted vegetation. When this balance is achieved, the atmosphere sees net zero new emissions.”“There is an if: Biomass energy is a viable solution if it uses appropriate feedstock, such as waste products or sustainably grown, appropriate energy crops. Optimally, it also uses a low-emission conversion technology such as gasification or digestion. Using annual grain crops such as corn and sorghum for energy production depletes groundwater, causes erosion, and requires high inputs of energy in the form of fertilizer and equipment operation. The sustainable alternative is perennial crops or so-called short-rotation woody crops. Perennial herbaceous grasses such as switchgrass and Miscanthus can be harvested for fifteen years before replanting becomes necessary, and they require fewer inputs of water, and labor. Woody crops such as shrub willow, eucalyptus, and poplar are able to grow on “marginal” land not suited to food production. Because they grow back after being cut close to the ground, they can be harvested repeatedly for ten to twenty years. These woody crops circumvent the deforestation that comes with using forests as fuel and sequester carbon more rapidly than most other trees can, but not if they replace already forested lands. Care needs to be taken with both Miscanthus and eucalyptus, however, as they are invasive.”“Another important feedstock is waste from wood and agricultural processing. Scraps from saw mills and paper mills are valuable biomass. So are discarded stalks, husks, leaves, and cobs from crops grown for food or animal feed. While it is important to leave crop residues on fields to promote soil health, a portion of those agricultural wastes can be diverted for biomass energy production. Many such organic residues would either decompose on-site or get burned in slash piles, thus releasing their stored carbon regardless (albeit perhaps over longer periods of time). When organic matter decomposes, it often releases methane and when it is burned in piles, it releases black carbon (soot). Both methane and soot increase global warming faster than carbon dioxide; simply preventing them from being emitted can yield a significant benefit, beyond putting the embodied energy of biomass to productive use.”“In the United States, a majority of the more than 115 biomass electricity generation plants under construction or in the permitting process plan on burning wood as fuel. Proponents state that these plants will be powered by branches and treetops left over from commercial logging operations, but these claims do not stand up to scrutiny. In the states of Washington, Vermont, Massachusetts, Wisconsin, and New York, the amount of slash generated by logging operations falls far short of the amount needed to feed the proposed biomass burners. In Ohio and North Carolina, utilities have been more forthright and admit that biomass electricity generation means cutting and burning trees. The trees will grow back, but over decades—a lengthy and uncertain lag time to achieve carbon neutrality. When biomass energy relies on trees, it is not a true solution.”“Biomass is controversial. To some, biomass is a friend; to others, a foe. A considerable academic effort is under way to “more accurately assess its environmental and social impacts. Debates center around three main issues: life-cycle carbon emissions (as previously described), indirect land-use change and deforestation, and impacts on food security. Often, the latter two debates are constructed as forests versus fuel and food versus fuel. In reality, managing land, cultivating food, and producing biomass feedstock interact dynamically—and not always in line with conventional wisdom. The three can be mutually reinforcing or play out to one another’s detriment, so how biomass feedstocks are approached within a given local context matters enormously. At present, biomass fuels 2 percent of global electricity production, more than any other renewable. In some countries—Sweden, Finland, and Latvia among them—bioenergy is 20 to 30 percent of the national generation mix, almost entirely provided for by trees. Biomass energy is on the rise in China, India, Japan, South Korea, and Brazil. “Reaching greater scale in more places requires investment in biomass production facilities and infrastructure for collection, transport, and storage. It is crucial to manage, through regulation, the drawbacks of biomass energy. Pelletizing native forests for biomass continues to be a giant step backward. However, extracting invasive species from forests accompanied with appropriate ecological safeguards can be a good source of biomass energy. That approach is being tested in India by the government of the state of Sikkim, which is making “bio-briquettes” for clean cookstoves. Additionally, smallholder farmers need to be protected from displacement by industrial-scale approaches to biomass generation. Most important to bear in mind is that biomass—carefully regulated and managed—is a bridge to reach a clean energy future, not the destination itself. •”“IMPACT: Biomass is a “bridge” solution, phased out over time in favor of cleaner energy sources. This analysis assumes all biomass is derived from perennial bioenergy feedstock—not forests, annuals, or waste—and replaces coal and natural gas in electricity production. By 2050, biomass energy could reduce 7.5 gigatons of carbon dioxide emissions. As clean wind and solar power become more available in a flexible grid, the need for biomass energy will decline.”“In effect, nuclear power plants boil water. Nuclear fission splits atomic nuclei and releases the energy that binds the protons and neutrons together. The energy released by radioactivity is used to heat water, which in turn is used to power turbines. It is the most complex process ever invented to create steam. However, nuclear power has a low carbon footprint, which is why it is seen by some people to be a critical global warming solution; many others believe that it is not now, nor will it ever be, cost “effective compared with other low-carbon options. The almost-universal method used to power steam turbines is gas- or coal-fired power. Greenhouse gases emitted to generate electricity are calculated to be ten to a hundred times higher for coal than for nuclear.”“Currently, nuclear power generates about 11 percent of the world’s electricity and contributes about 4.8 percent to the world’s total energy supply. There are 444 operating nuclear reactors in 29 countries, and 63 more are under construction. Of the 29 countries with operative nuclear power plants, France has the highest nuclear contribution to its electrical energy supply, at 76 percent.”“Nuclear reactors are broadly classified by generation. The oldest, Generation 1, first came online in the 1950s and are now almost entirely decommissioned. The majority of current nuclear capacity falls into the Generation 2 category. (Chernobyl consisted of both Gen 1 and Gen 2. The four Fukushima Daiichi reactors are Gen 2, as are all of the reactors in the United States and France.) Generation 2 distinguishes itself from its predecessor by the use of water (as opposed to graphite) to slow down nuclear chain reactions and the use of enriched, as opposed to natural, uranium for fuel. The Generation 3 reactors, five of which are in operation worldwide and several more under construction, along with Generation 4 reactors, which are currently being researched, constitute what is called “advanced nuclear.” In theory, advanced nuclear has standardized designs that reduce construction time and achieve longer operating lifetimes, improved safety features, greater fuel efficiency, and less waste.”“What makes the future of nuclear energy difficult to predict is its cost. While the cost of virtually every other form of energy has gone down over time, a nuclear power plant’s is four to eight times higher than it was four decades ago. According to the U.S. Department of Energy, advanced nuclear is the most expensive form of energy besides conventional gas turbines, which are comparatively inefficient. Onshore wind is a quarter of the cost of nuclear power.”“For those who argue against nuclear because of cost, timing, and safety reasons, the counterargument at one time was the unremitting pace of new coal-fired plant construction. Hundreds of coal-fired plants were being built or planned, primarily in south and east Asia, with three-fourths of them slated to be built by China, India, Vietnam, and Indonesia. If the coal boom is not stopped, global warming will increase far beyond any reasonable limit. This is why climate reporting focuses primarily on energy, and it is why proponents of nuclear are frustrated at the sluggish pace of new plant construction. Licensing, permitting, and financing have brought nuclear plants to a near standstill in the United States, while Germany is shutting its plants down and decommissioning. On the other hand, China has thirty-three nuclear plants operative and twenty-two under construction. It is committed to peak carbon dioxide in 2030 with a reduction of its carbon footprint from that date forward.”“Discussion of nuclear power goes right to the heart of the climate dilemma with respect to carbon emissions: Is an increase in the number of nuclear power plants, with all their flaws and inherent risks, worth the risk? Or, as some proponents insist, will there be a total meltdown of climate by limiting their use? Nuclear power has been the subject of contentious disagreements by proponents and critics. The arguments for and against are fascinating, complex, and polarized. Take the following three scientists, widely respected in the environmental community, who do not agree:According to physicist Amory Lovins, “Nuclear power is the only energy source where mishap or malice can destroy so much value or kill many faraway people; the only one whose materials, technologies, and skills can help make and hide nuclear weapons; the only proposed climate solution that [creates] proliferation, major accidents, and radioactive-waste dangers. . . . [N]uclear power is continuing its decades-long collapse in the global marketplace because it’s grossly uncompetitive, unneeded, and obsolete—so hopelessly uneconomic that one need not debate whether it is clean and safe; it weakens electric reliability and national security; and it worsens climate change compared with devoting the same money and time to more effective options.”“James Hansen, the NASA scientist who put the United States on notice in his 1988 congressional testimony on climate change, takes another perspective. He authored an open letter with three other climate leaders stating, “Renewables like wind and solar and biomass will certainly play roles in a future energy economy, but those energy sources cannot expand fast enough to deliver cheap and reliable power at the scale the global economy requires. While it may be theoretically possible to stabilize the climate without nuclear power, in the real world there is no credible path to climate stabilization that does not include a substantial role for nuclear power.” Their proposal would require building 115 reactors per year for thirty-five years.”“Joseph Romm, one of the most respected climate writers and bloggers, does not buy it. Nuclear reactors are too expensive and unwieldy and, given the still-plummeting cost of wind and solar, have priced themselves out of the market. The International Energy Agency (IEA) has said nuclear can play “an important but limited role.” In the IEA’s estimation, nuclear can grow from its current 11 percent of generated electricity to 17 percent by 2050.”“There seem to be two different worlds here, not one. Nuclear is expensive, and the highly regulated industry in the European Union and the United States may continue to be overbudget and slow. The French company Areva is ten years behind schedule and $5.4 billion over budget on the Olkiluoto reactor in Finland. In Normandy, a $3.4 billion pressurized-water reactor slated for start-up in 2012 will not commence construction until 2018, at a revised cost of $11.3 billion. On the other side of the globe, the largest emitter of carbon in the world is building nuclear reactors more rapidly, motivated in no small part because its cities are extraordinarily polluted from cars and coal-fired power plants. The Chinese nuclear power industry is self-sufficient, in a position to export, and able to complete new plants within two to three years. Yet even where nuclear seems to be “working,” there is a dramatic shift to renewables. China currently leads the world in installed renewable energy capacity, has canceled plans for dozens of coal-fired plants, and is committing to a combined wind and solar capacity of 400 gigawatts by 2020.”

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