Renewable Energy for Human Sustainability
Summary and Keywords
Renewable energy was used exclusively by the first humans and is likely to be the predominant source for future humans. Between these times the use of extracted resources such as coal, oil, and natural gas has created an explosion of population and affluence, but also of pollution and dependency. This article explores the advent of energy sources in a broad social context including economics, finance, and policy. The means of producing renewable energy are described in an accessible way, highlighting the broad range of considerations in their development, deployment, and ability to scale to address the entirety of human enterprises.
Rashid bin Saeed Al Maktoum, prime minister of UAE and Emir of Dubai, said, “My grandfather rode a camel, my father rode a camel, I drive a Mercedes, my son drives a Land Rover, his son will drive a Land Rover, but his son will ride a camel.” This wisdom applies more broadly to human sustainability, albeit over a larger number of generations. Camels, horses, donkeys, and oxen supported settlements for tens of millennia after humans learned to release chemical energy from wood by using fire. Wind drove boats for fishing and trade. Waterfalls milled grain and cranked pumps. When the animals died, when the boats sank, when the mills broke, they decomposed back into the environment within the time frame of a human life. These forms of renewable energy, driven proximally by the sun, were sustainable so long as populations remained under about 20 per square mile. Before the Industrial Revolution began around 1750, the earth supported about 1 billion humans.
With the advent of metalworking, and the need for much more fuel than required for just cooking and home heating, wood supplies dwindled, and coal became economical to mine from the earth. Coal is believed to come from ancient vegetative and animal matter, as are its liquid and gaseous cousins, petroleum and natural gas. These “fossil” fuels are only available in an old world with a geologically long history of abundant plant life, and their total quantity is finite. Yet the concentrated and convenient energy of fossil fuels provided for dramatic economic growth, expanding the earth’s population of humans far beyond levels sustainable via natural processes.
With copious amounts of energy available as rapidly as extraction can be made, without reliance on the gentle rhythm of sunlight and apart from the stately processes of biology, populations have increased exponentially. Fossil fuels allow many more humans to live on earth than can be sustained by preindustrial processes. Studies of living standards show that across almost all nations, increased affluence leads to longer, more productive lives and lowered birth rates (gapminder, 2015). Environmental harm from extraction, production, and use of fossil fuels goes beyond tailpipe emissions. Use of geologically sequestered carbon-based solid and fluid fuels has introduced into the biosphere contaminants inimical to human life. Furthermore, their downstream processing into chemicals and finished goods creates additional pollutants never before existing on earth. These waste streams can accumulate in the environment, weakening natural processes and whittling down the extreme diversity of biota of the planet. Recognizing the projected outcomes, many humans have warned us, starting perhaps with Rev. Thomas Malthus, who in 1798 asserted that population increases geometrically but agriculture increases arithmetically, and therefore without moral restraint humans face decimation (Malthus, 1798). It follows that a sustainable means for producing the energy needed by all mankind presents the opportunity for a leveling-out of population and a reduction in the rate at which toxins are accumulated in the environment (see Fig. 1)
Others devoted themselves to the development and deployment of technologically advanced renewable energy sources. Michael Faraday discovered the semiconductor effect in 1833, and 6 years later Bequerel discovered the photovoltaic effect. It was not until 1883 that Charles Fritts made the first solar cell. Fifty years later engineers learned to grow single crystal silicon. Another half-century later silicon solar panels became commercially available, albeit at great expense. By 2015 the efficiency of converting sunlight into electricity had been increased fourfold, and prices had dropped by two orders of magnitude. Yet a major drawback of solar power is that availability is limited to daylight hours.
Another discovery by Faraday was electromagnetic induction, the principle behind rotating electric machines. Others contributed, and in the 1860s Wheatstone and Siemens had working electric generators. Now, a century and a half later, wind energy is derived from such dynamos cranked by blades 164 meters (538 feet) in diameter and having nameplate capacities of 8 MW (windpowermonthly). Like sunlight on the ground, wind in the air is not constant. Both of these fast-growing forms of renewable energy generation suffer from intermittency—they may not be available when their power is demanded. As long as their share of an overall energy portfolio is small, this is a minor concern, but for renewables to provide the bulk of human energy needs, intermittency must be addressed.
A proposal by R. Buckminster Fuller in 1981 was to build a world-spanning electric grid that shares power from across the globe (Fuller, 1981). Assuming that sunlight and wind are always available somewhere within reach of this unified mega-grid, sharing of these resources could provide baseload (“always on”) power entirely from renewable sources. Recent improvements in underwater power cable technology now makes Fuller’s far-sighted concept feasible and practical. Countries with diverse resources (e.g., Germany with wind in the north and solar in the south) and regions with heterogeneous availability (e.g., the U.K. coast) are covering more of renewable variability with long-distance power-sharing (Boyle, 2012). In 2013, Leighty proposed a complex infrastructure based on renewably sourced hydrogen and anhydrous ammonia to provide liquid and gaseous fuels for transportation and industrial processes. By converting intermittent renewables into energy “vectors” that can be transported where needed and stored for later use, a region or nation can potentially achieve energy independence and self-sufficiency (Leighty, 2015).
Intermediate to these large-scale solutions are means to extend the production of solar and wind power. Solar panels are comprised of photovoltaic (PV) cells made from specially fabricated semiconductor diodes. They work best when the sun shines directly onto their top surface. To collect more power over a given day, they can be installed on 1-axis or 2-axis tracking systems. The sun moves from east to west every day, and 1-axis trackers follow that movement so that sunlight falls more squarely on the panel all day. This increases the power output for a given panel area by up to 30% relative to fixed installations such as those mounted on rooftops. But the path of the sun across the sky changes from summer to winter, and a 2-axis tracking system compensates for seasonal variations, increasing the power output by another 10%, albeit with higher capital costs and higher maintenance expenses (Mousazadeh et al., 2009). Yet fixed, 1-axis, and 2-axis systems cannot produce much power under heavy clouds or dust storms—or any power whatever during the night. An elegant solution is through a technology known as concentrated solar power (CSP). Two general classes of CSP are mirrored parabolic troughs heating oil-filled collectors and sun-tracking mirrors, which heat a central tower. In each case the heat is used to convert water into steam for use in a steam turbine generator or Organic Rankine Cycle power plant (ORC uses low-boiling-point working fluids to generate power from lower temperatures than those needed for water and steam). Advanced CSP technology uses the concentrated sunlight to heat molten salt. A significant advantage of molten salt CSP, and also oil-filled CSP, is that these working fluids can retain some of their heat into the evening hours when electricity demand is still strong (Nithyanandam & Pitchumani, 2014). Several such systems have been installed across the world and provide electrical power which roughly approximate the day/night cycle of consumer demand.
Wind power by its very definition cannot be stored. Wind is fickle and harder to predict than sunlight, although steady progress is being made in this regard. Winds are generally stronger at higher elevations above the earth’s surface. For a given area subtended by the blades faced squarely into the wind, the power generated increases as the third power of wind speed (v3) (Earnest, 2014). These factors in combination drive ever-greater heights for the turbine towers. Some locales have fairly steady winds, notably at sea. Although considerably more expensive than on-shore wind turbines, off-shore wind turbines generally have a higher capacity factor. Capacity factor is the percentage of “nameplate” (or maximum-rated) power production averaged over time. Off-shore wind is used to advantage by Denmark, Germany, the United Kingdom, and others. Islands such as Malta and Hawaii have expensive electric power and steady winds but are surrounded by deep waters, which complicate the anchoring of tall structures bearing heavy mechanical loads from the pressure of the wind.
Worldwide consumption of renewable energy is about 10% of total human energy use, most of which consists of woody materials used for cooking and space heating (Twidell & Weir, 2015). Renewable electricity and engine fuel production in 2012 was about 7000 billion kilowatt-hours, or 4.2% of all power and fuel production. Total electrical energy generation from wind in 2014 was 370 gigawatts (GW) (GWED) and from solar was 178 GW (IEA-1). Solar thermal heating is also widespread, especially in China and Europe at 375 GWth (gigawatts-thermal) (IEA-2). Renewables overall have been increasing rapidly and in 2014 accounted for 45% of newly added capacity worldwide (IEA-3).
With greater adoption of renewables, and until there is a world-wide energy grid, there are several options available for storage (for grid control) and transport (for mobile applications) of renewable energy, including batteries, flywheels, compressed air, and “pumped hydro” (explored in more detail below). Such technologies used in concert with intermittent renewables can approximate the production of baseload power available from coal, natural gas, nuclear, or hydroelectric power plants. But concerns over storage for renewables can overlook the need for grid-level storage for voltage and frequency regulation and is further ameliorated by the existence of other forms of renewable energy that can provide baseload electric power, including geothermal, biomass, waste-to-energy, and space solar power. These technologies are not as widely available as wind and solar and are treated in more detail after a discussion of energy storage.
The electrochemical energy storage cell known as a battery was invented in the year 1800 by Count Volta of Italy, and from his name is derived the unit of measuring electric potential to do work: the volt. Gustav Planté in 1859 invented the rechargeable version, called a “secondary” battery in distinction to the “primary” battery of Count Volta, which, once sealed, could be used only once. For a time, secondary batteries rivaled the internal combustion engine for motive power as Thomas Edison and Henry Ford combined their efforts to create an electric vehicle using a nickel–iron secondary (rechargeable) battery. A massive fire of suspicious origins destroyed their burgeoning factory, and the initiative faltered (Black, 2006). In the 1990s General Motors developed the EV-1 all-electric vehicle, but for a variety of reasons this product never became a commercial success. As of 2015 several vehicle manufacturers offer all-electric or plug-in hybrid (gasoline plus electric motors with both gasoline and battery storage on-board) models, usually at a premium price relative to the mature gasoline and diesel powertrain options. The EV-1 used lead-acid secondary batteries, the same technology invented by Planté; having low cost but with a poor specific energy density (measured in kilowatt-hours per unit mass), hence limited range for the vehicle. Nickel–metal hydride secondary batteries help power the popular Toyota Prius hybrid, offering some improvement in energy density. The Nissan Leaf and the Tesla Model S use lithium-ion secondary batteries. An ion is an atom having either a surplus of electrons (cation) or a deficit of electrons (anion) relative to the number of protons in the nucleus. Li-ion secondary batteries have superior energy density over lead-acid and nickel–metal hydride and have become relatively mature since their introduction for consumer electronics in the early 1990s (Goodenough, 2010). Researchers worldwide continue to develop Li-ion chemistries to improve energy density, power density (kilowatts per unit mass), cycle life (how quickly capacity fades with re-use), and self-discharge during storage, among other performance metrics. A Li-ion battery is made by shuttling positively charged lithium anions between a cathode (negative terminal) and an anode (positive terminal) while a matching current of negatively charged electrons travels through wires between the two terminals and does useful work (called “powering a load”). As suggested by the great fire at the Edison-Ford plant, and as observed in fires such as caused by laptop computer batteries, aircraft batteries, and even parked hybrid car batteries, safety is a critical consideration. Any form of high-power energy storage has the potential for rapid discharge with attendant possibility for damage to equipment, facilities, or the environment and direct harm to people. When batteries are used to store renewable energy for mobility, safety concerns demand consideration of risk assessment, monitoring, event mitigation, fail-safes, and end-of-service treatment.
Secondary batteries have the potential to store renewable energy at a grid scale as well. Such installations are generally much larger than for mobility or portable electronics. Conventional sealed electrochemical batteries are manufactured in collections of individual cells. A cell is a single unit of anode and cathode with the active species (e.g., lithium) dissolved or suspended in an electrolyte (liquid, gel, or solid) through which the active species shuttles. The electric potential for each individual cell depends on the electrolyte composition and the chemistry of the anode and cathode (Nagaura, 1990) and ranges from under 1 V to approximately 4 V. Systems requiring larger voltages, such as cars or grid storage, simply combine many cells to achieve the voltage required. Electric grids employ a broad range of voltages where, for reasons of efficiency, transmission over longer distances benefits from using higher voltages. At the higher end of this range, a number of important functions are required to provide grid reliability and a stable power profile. For superior reliability, regional electric grids employ reserve margins, an amount of excess generating capacity that is available to be ramped up in a relatively short time to handle sudden increases in electric loads at consumer locations. For example, a steel mill melting down a batch of recycled metal demands huge amounts of electrical power, and the mill operators will often contact the independent systems operators (ISO) managing the large-scale electric grid so that suitable power plants can be brought to a higher capacity. Voltage regulation is another important function of the ISO groups that manage the large-scale grid. Precise voltage control is critical to many industrial and commercial customers. Also, every power plant feeding an electric grid must supply the same voltage to prevent power reflections, which can unbalance the grid and cause outages. Secondary batteries can be used both as a short-term source of reserve margin and to provide voltage regulation by absorbing or delivering power as needed in the ever-changing dance between generation and consumption. In general, providing more power to the grid increases its voltage. For example, in southern California where there is a high adoption rate of residential solar, rooftop PV panels often generate too much power during the sunny days when residents are away and their homes need less energy. With wide deployment of simple inverters to connect to the grid, this surplus power can cause excess voltage on the distribution lines and potentially unbalance the larger electric transmission grid. So-called “smart inverters” are now being required in California and Germany to ameliorate this issue. Alternatively, batteries can absorb such surplus, saving it for the evening uses of lighting, cooking, cleaning, and entertainment.
For providing grid functions such as frequency regulation, peak shaving, load following, or voltage regulation, batteries can be centrally located (and very large) or distributed near customer loads or near customer-generated renewable energy sources. One proposal for distributed grid-level storage is to exploit electric vehicles (EVs) which can be charged at home, at night, when electric rates are generally cheapest as a consumer incentive so that baseload plants using coal, gas, or nuclear can run at a higher and more steady rate. During high-demand portions of the day, EVs are plugged in at workplaces, shopping malls, and schools so the drivers can sell back at a premium any excess energy they won’t be needing for errands and their commute back home. Called vehicle-to-grid, this concept requires interrelated policy and technology for managing complex, distributed systems (Kempton & Tomic, 2005). For centralized storage, batteries comprised of many thousands or millions of individual cells translates into batteries which are very expensive to manufacture. An approach with the potential for lower cost is a flow battery. In a flow battery two fluids are used, one carrying an anion and one carrying a cation. These two fluids are passed along either side of a special membrane which permits ions (charged atoms) to flow through it but not electrons. To recombine with their ions, electrons must flow from one battery terminal to the other while passing through, and delivering power to, a load, which in this case is the electric grid itself. When the grid is being fed a surplus of power, the flow is reversed, and electrons are forced back into the terminals, driving the ions backward through the membrane and recharging the overall flow battery (Weber et al., 2011). An attractive feature of flow batteries is that they can be scaled easily by increasing the size of the reservoirs holding the two fluids. Some energy is lost in operating the pumps to circulate the fluids, so flow batteries generally have a lower “round-trip efficiency” (energy out divided by energy in) than sealed electrochemical cells. However, flow batteries can be made of lower-cost materials and simpler configurations than conventional sealed cell batteries and if built for grid-scale storage have reduced expectations for volume and mass relative to mobile applications.
Another method of grid-scale energy storage is to pump river water uphill and back into a reservoir above a hydroelectric dam, essentially reversing the process. During periods of low demand when renewable sources are providing surplus power, or if conventional power plants would benefit from running at a steady pace (better utilization of capital and generally lower maintenance), “pumped hydro” is an elegant solution. Round-trip efficiency for pumped hydro suffers from the need to operate pumps for fluid movement plus the energy needed to lift the water against the pull of gravity (Rehman, Al-Hadhrami, & Alam, 2015). Pumped hydro is most widely used in Japan and the United States, and recently some installations have begun to use water towers in the absence of suitable terrain (Deane, O Gallachoir, & McKeogh, 2010).
The lowest-cost form of grid-scale energy is compressed air energy storage (CAES). During times when power production exceeds demand, air is compressed by large pumps and stored in pressure vessels or, preferably, in underground salt caverns or depleted natural gas fields. Later, when the situation is reversed and demand is high, the high-pressure air is released through air turbines connected to an electric generator (Dunn, Kamath, & Tarascon, 2011). CAES is cheap because air is free and salt caverns can be created by simply dissolving the needed volume using water (and creating brine waste) (Schainker, 2004). Not all locales have available salt deposits and plentiful water, which limits the geography for economical CAES. Compressing gases causes them to heat up, making it possible for a CAES facility to recuperate some of that heat for useful purposes before it dissipates, possibly including electricity generation from waste heat using thermoelectric devices (Elsheikh et al., 2014). When the compressed air is expanded it cools, which can cause problems for the air turbines, so it is sometimes necessary to preheat the air, and this can represent a parasitic energy loss and reduce round-trip energy efficiency.
Since 1970 when a General Motors engineer coined the term “hydrogen economy,” pundits have lauded the advantages of this versatile energy vector. An energy vector, as distinct from an energy source, is an intermediate byproduct that can be stored or transported for conversion to useful energy later. Hydrogen is the most abundant element in the universe, but it binds readily with other compounds and is never found alone in the wild. The most ubiquitous source of hydrogen on earth is water (H2O), with the formal chemical name “dihydrogen monoxide.” Water can be split into hydrogen and oxygen using the long-established electrochemical process known as electrolysis. When wires connected to the two terminals of a battery are placed in a body of water some distance apart such that sufficient current can flow (sometimes salt, acids, or bases are added to increase electrical conductivity), water will split into its two components such that hydrogen gas (H2) evolves at the cathode and oxygen gas (O2) evolves at the anode. The gases form bubbles, and the H2 can be captured and stored as an energy vector. The oxygen is often allowed to vent into the atmosphere, which is already about 20% oxygen (Gahleitner, 2013). One way to store hydrogen is with salt domes, similar to CAES. High-pressure tanks can also be used, such as those found in circa 2015 fuel cell vehicles. Hydrogen can also be stored in solid materials such as metal hydrides, zeolites, metal-oxide frameworks, or porous silicon (Schubert, 2009). Hydrogen can also be stored in other vectors by building it into chemical molecules. One such molecule is ammonia (NH3), which can be created by combining hydrogen with nitrogen taken from the atmosphere, where nitrogen constitutes about 78% of air gases. Hydrogen can also be combined with carbon to make methane (CH4, the main component of natural gas), or more complex hydrocarbons, including those that make up petroleum-derived fuels such as kerosene (jet fuel), petrol (gasoline), and diesel fuel (Naik, Goud, Rout, & Dalai, 2010). These hydrogen-containing compounds have the advantage of being more readily used in existing fleets of jet engines and internal combustion engines (ICEs). Pure hydrogen can be used in modified ICEs designed for natural gas but is ideally suited for use in fuel cells (see Fig. 2).
A fuel cell is similar to a flow battery, where the fluids are hydrogen gas and oxygen-containing air. Fuel cells come in seven or more variations having a range of applications from mobile or portable power to baseload power generation. Inside a fuel cell is a specially designed membrane which allows hydrogen ions to pass through and combine with the oxygen so that water vapor is the only effluent. This membrane does not pass electrons. Electrons must complete the circuit by passing between anode and cathode terminals through metal wires, similar to a battery, where they do useful work by powering a load, such as an electric motor, or outputting their electrical energy directly to a grid. Most fuel cell types are significantly more efficient (e.g., about 70%) than ICEs or gas turbines (e.g., about 40%) in converting chemical energy in the fuel vector to electrical work. Fuel cells tend to be significantly more expensive than ICEs because of the use of precious metal catalysts in the membrane, difficult manufacturing, water management (especially when operated below freezing), and sophisticated control mechanisms; however, the advantages of water vapor effluent, high efficiency, and quiet operation are considerable benefits in many applications (Stolten, 2010). Apocryphally, the deployment of hydrogen fuel cell buses in Chicago was met with complaints about “white smoke,” which was really only water vapor condensing as “clouds” in the chilly northern Illinois climate.
Another energy storage technology is mechanical flywheels, which use surplus power to increase the rotational speed of a heavy rotor spinning on nearly frictionless bearings. This rotational energy can be drawn off and converted efficiently to electric power as needed (Genta, 1985). Flywheels are periodically considered for motor vehicles, increasing their spin rate during vehicle braking and then resupplying that energy to the wheels during takeoff from a stop. Concerns over crashworthiness of such a system have largely relegated flywheels to grid-level storage, where there are now several commercial companies offering solutions.
Perhaps the ultimate energy storage system is using long loops of superconducting wire. A superconductor has the amazing property of absolutely zero resistance to electrical current. The first superconductors discovered only operated near absolute zero, as cold as intergalactic space. Then in the 1980s ceramic superconductors were discovered that operated at higher temperatures, but still extremely cold relative to ambient temperatures on earth. A loop of superconducting material can store energy with negligible electrical losses for extended periods of time—theoretically, forever. As of 2015 all known superconductors require active cooling and insulation, so the system efficiency in energy conversion is less than 100% (Keimer, Kivelson, Norman, Uchida, & Zaanen, 2015). The round-trip efficiency then depends on the wait between storage and usage, because the parasitic power consumed for refrigeration is constant over time.
Energy storage will perhaps always be needed for portable electronics, mobile applications, emergency backup generators, and for flashlights on camping trips. Advances in wireless power transfer may eventually obviate many of these needs by electromagnetic transmission or coupling between a stationary source and vehicles and communication devices (Shinohara, 2014). In such a scenario it becomes even more important that electric power be “always on,” and for this purpose the following discussion addresses those sources of sustainable, renewable energy with the potential to serve such baseload functions.
Hydroelectric power is the undisputed leader in baseload renewable power in 2015. Although worldwide most readily-available hydropower is already tapped, hydro alone is double the capacity of all other renewables combined (BP, 2014). The Three Gorges Dam in China has the highest instantaneous power output and produces approximately the same total energy per year as the second largest plant in Brazil and Paraguay at Itaipi. Wherever flowing water falls from a substantial height over a relatively short lateral distance, one can install water turbines, which are spun by falling water and turn generators to produce electricity. Such facilities are enhanced by the construction of dams, which store a reservoir of water to assure power out on demand without the seasonal changes in flow rate of the river. When water reservoirs are used for both electric power and drinking water, such as the Lake Mead/Hoover Dam complex outside of Las Vegas, Nevada, these needs may come into conflict (Fishman, 2011). Furthermore, while hydro power has always been considered renewable, in light of recent trends in climate, the renewability of uphill precipitation or snowpack has been called into question for a number of regions around the planet. Water quantity and accessibility is a growing concern for the viability of hydroelectric power as well as for conventional thermal power plants consuming coal, natural gas, and nuclear fuels, which use heat cycles that require large amounts of cool water to maintain efficient operations and avoid damage to the plant.
Geothermal power derives from heat released by the decay of radioactive materials inside the earth’s mantle. Geothermal energy is economically favorable where the earth’s crust is thin, for example, in Yellowstone National Park. The hot springs and geysers there are evidence of the tremendous energies beneath the surface of the earth. By extracting deep water resources, or by injecting surface water into underground wells where it absorbs geothermal heat, the hot fluid can be passed through a heat exchanger to convert water into steam before being returned underground to capture more heat. The steam is useful for powering steam turbine generators. Critics caution that the practice of forcing water or working fluids into thin planetary crusts can exacerbate the frequency and magnitude of seismic events. Subsidence and uplift have also been observed. As such, geothermal tends to be a regionally relevant source of nearly inexhaustible energy (DiPippo, 2012).
Ocean energy sources are vast and sometimes concentrated. Ocean thermal energy conversion (OTEC) is a clever means to use deep, cold water to provide a temperature difference with warm surface water to drive a heat engine and generate electricity. OTEC requires very large structures but has the potential for low-cost baseload renewable energy. Wave and tidal resources are appealing, although not generally sufficient as baseload sources. Many demonstrations and prototypes have been tested worldwide. These include linked floats with generators harvesting relative movement between them, submerged turbine blades to harvest tidal flows, vertically bobbing devices which pull and push on electric generators, and catch-basin designs which guide outflow through a turbine generator. Economics is a key challenge for many approaches, as is biofouling and siting. The oceans are replete with organisms eager to fasten themselves to solid surfaces and grow there. Wave and tidal systems may also impede the flow of marine vessel traffic or cause undesired changes to the vistas of neighboring homes. However, like hydroelectric power, wave/tidal resources are somewhat limited and will probably become just a portion of an overall energy portfolio in certain locales (DOE, 2015).
From these examples for baseload electric power, it can be seen that water has a significant and growing relevance to energy production. Certain governmental agencies and nongovernmental organizations are becoming more interested in how energy, water, and food are interconnected because solutions or technologies in one area often affect other areas. As one example, the production of corn-based ethanol for vehicle fuels in the United States is said by some to have caused food prices to increase worldwide (Hill, Nelson, Tilman, Polasky, & Tiffany, 2006). As another example, multiple coastal power plants in California have been shut down because concerns over harm to marine life from the heat of its released, used cooling water. As yet another example, nuclear power plants in the U.S. Northwest shut down briefly during a hot summer because the source of cooling water was too warm enough to operate the plant safely (Associated Press, 2012.). Many more examples exist, and instances are likely to grow in number and severity over time.
The oldest and most traditional source of renewable power used by humans is biomass. Since the invention of fire, woody plants and dried ruminant manure have been used for space heating and for cooking food. Combustion (burning) is inefficient and generates smoke containing particulate matter, which can lead to respiratory distress (especially for women and infants living indoors). More efficient use of biomass was developed in the early 1800s with the advent of “wood gas.” In this practice, now know by the technical term “gasification,” a wood fire is started, after which the pile of wood is covered with dirt. The amount of dirt added is not sufficient to snuff the fire, but rather reduces the amount of oxygen (in the air) that can reach the burning embers. The ensuing incomplete combustion produces a smoke that contains flammable gases, such as methane, hydrogen, and carbon monoxide. By capturing these gases and pumping them through pipelines, the gas can be flared at a stove for cooking or a lamppost for street lighting. Modern gasifiers don’t use dirt but rather special reactors that modulate the amount of air and feedstock to optimize the composition of the producer gas (sometimes called “syngas”). Producer gas can be used as a fuel for ICEs, or its hydrogen component can be separated and used to operate a fuel cell, both of which can generate electricity. Waste heat is also useful, and the practice of extracting both electrical and thermal energy is called co-generation (“co-gen”) or combined heat and power (CHP).
Modern agriculture has evolved crop yields that have risen steadily for decades. In North America the amount of above-ground plant material at harvest time is considerable. Starting in 2005 the U.S. Department of Energy (DOE) published results of a “Billion Ton Study” addressing the capacity for renewable energy from agricultural residues, energy crops, and sustainable forestry (Perlak & Stokes, 2005). This document, along with other studies by the DOE and the U.S. Department of Agriculture, outline approaches for converting wood, grain, grasses, food waste, and animal manure from chemical energy into electrical energy, heat, and fuels. Although renewable, a fundamental challenge is the diffuse nature of biomass. Sunlight areal density on the earth’s surface coupled with the low efficiency (less than 1%) (Marcus, 1956) of converting sunlight into plant mass demand that large areas be available for energy crop production. Although storable solid, liquid, or gaseous fuels can be produced from biomass (e.g., pellets), the need to transport feedstock to a central facility represents a parasitic loss that makes logistics a challenge. For example, if a conversion plant produces fuel from nonfood lignocellulosic plant mater (“cellulosic ethanol”), the feedstock must be gathered from the fields and then transported by some means to the central facility (see Fig. 3). A (nonfood) cellulosic ethanol plant producing 100 million gallons per year requires a majority of producers on long-term purchase contracts within a radius of 50 to 75 miles. The feedstock has a relatively low energy content per unit mass relative to fossil fuels like coal and oil. If the hauling trucks run on ethanol blends this erodes the net effective yield of the fuel production (Huang, Ramaswamy, Al-Dajani, Tschirner, & Cairncross, 2009).
One promising source of biomass that potentially overcomes the bane of areal density is microalgae. Microalgae are too small to observe with the naked eye and appear as a green tint in water. Certain strains of microalgae produce a very high proportion of their body mass as lipids (fats), which can be extracted and converted into storable fuels. Microalgae growth cycles are much faster than for rooted plants, so that many “crops” can be produced in a given year. The theoretical potential is as much as a 40 times higher yield of biodiesel per acre compared to soybeans (Liu & Colosi, 2012). A key challenge in cultivating microalgae is the need to prevent feral algae from contaminating the high-lipid species, which tend to be less robust and can be quickly dominated by the wild strains. Microalgae also require nutrients to grow, and this represents a significant expense in using them to make biofuels. Mechanically extracting lipids from cell-sized algal bodies is more difficult than pressing soybean oil from beans because the tiny algal bodies tend to pass directly through the filters or sieves, thereby requiring smaller holes and attendant higher pressures and energy. Considerable research in this area is ongoing, and industry watchers expect results to become more favorable around 2025.
Baseload power from biomass can benefit from pyrolysis, an advanced conversion technology that mimics the geological processes that formed coal, oil, and natural gas but with greatly accelerated rates. A close cousin to gasification, pyrolysis, applies heat to biomass in the absence of oxygen. When pyrolyzed at temperatures between about 250 and 450°C, lignocellulosic material decomposes into producer gas, tarry liquids, and carbon-rich solids (Laird, Brown, Amonette, & Lehmann, 2009). The producer gas can be cleaned of any tar-like vapors and used as fuel in an ICE-generator set (“genset”). Less clean producer gas can be used in an external combustion engine, the most well known of which uses the Stirling cycle, first conceived by a Scottish priest in the early 1800s (Organ, 2014). The tarry liquids, once separated from residual water, represent a simulacrum of petroleum and can be refined into approximations of gasoline/petrol and diesel. Refining of hydrocarbons is a large-scale industrial process and is tailored to the exact composition of the type of petroleum used (which varies widely), and so is not widely employed on so-called pyro-oil. The carbon-rich solids can be co-fired with coal in conventional power plants, as can pelletized wood or crop residues. However, biomass-derived solid fuels tend to have a high pH and can cause corrosion problems inside coal-fired power plants.
Gasification and pyrolysis plants of 2 to 5 MW can execute power purchase agreements (PPA) and sell power directly to the wholesale grid for prearranged pricing. However, the bane of areal density and the challenges associated with centralized processing of biomass into fuels and energy suggest that baseload power may be more effectively created from distributed generation (DG). Smaller conversion systems can also communicate with the electric grid in a manner similar to residential solar or wind systems. These smaller sources of renewable energy can of course serve loads on-site, but they can also provide power to the larger electric grid via power electronics circuits and controls known as switchgear. Switchgear works to synchronize local power generators with the grid (or “mains”) for seamless integration. Switchgear systems also include protective relays, which disconnect from the grid should an outage or short circuit occur either locally or out on the grid/mains. Switchgear controllers that can feed the grid can also be used to divert excess power to local energy storage systems such as batteries or ultracapacitors. The concept of combining smaller-scale renewable power generation with optional local energy storage and grid-interfacing switchgear is called a microgrid, or, in some parlance, a nanogrid.
A micro/nanogrid is generally sized for a single facility or a campus of buildings, often with waste heat captured from power generation to provide hot water or space heating (CHP). A key task for the switchgear is to harmonize the on-site power generation with the electric grid for voltage, for frequency, and for phase. These three characteristics of alternating current (ac) power must be matched closely to avoid disruptive ripples of power either out to the grid (and its other customers) or into the microgrid. Details of this interconnection logic are dictated by the local electric utilities and typically guided by state or federal regulations. With a large number of DG biomass gasifiers or pyrolyzers running gensets within microgrids, power can flow into the distribution and transmission lines. In this way, biomass has the potential to provide the characteristics of baseload power so appreciated by all consumers of electric power.
Perhaps the ultimate source of baseload renewable energy is capturing solar power in earth’s orbit and delivering it wirelessly to consumers on the ground. While earlier hints exist, this concept was first developed in some detail by Peter Glaser in the late 1960s and patented shortly thereafter (Glaser, 1968). The idea of orbiting solar farms solves the intermittency experienced by ground-based PV. By providing around-the-clock baseload power from space, the need for energy storage is dramatically reduced. Furthermore, the scale of operations possible in earth’s orbit is so large that essentially any quantity of power can be produced and delivered to earth. Such power plants produce no pollution or effluent during operation, although some wastes are generated during construction (as is true for terrestrial PV and wind). Space solar power (SSP) can be made available to every large population center on earth. Because every nation can have access to power from orbit, there is no concern over globally finite or spatially restricted resources. The technology to make SSP possible has existed since the 1970s but has not been realized largely due to economic challenges and lack of political will (U.S. Senate, 2001). Lofting hardware into space is expensive and requires considerable expenditure of energy to reach escape velocity. Many architectures for SSP have been proposed over the years (Potter et al., 2009). Most rely on ultra-light solar cells to reduce the high launch cost per unit mass. Other approaches favor harvesting silicon from asteroids or the lunar surface, where a modest factory launched from earth produces many times its own mass in PV panels (Schubert & Wilks, 2009). Moving these around in orbit is far less energy intensive than a launch from earth’s powerful gravity well. Beaming power from orbit to ground is a larger-scale version of the modern communication satellite and would use similar frequencies of radiowaves (see Fig. 4).
Using phased-array transmitting antennae from space, a “pencil beam” of electromagnetic energy is delivered to a large receiving antenna (called a “rectenna”) on the ground, where it is converted to electric power and used to power loads or to feed into the electric grid. Lasers can be used. Lasers are energetically inefficient but are easily aimed and have a small receiving footprint. However, lasers can be easily weaponized—making them unsuitable for nonmilitary applications. An attractive candidate for baseload electric power is transmission in the same ISM (industrial-scientific-medical) band as that used by cellular telephones. Beams at this frequency (about 2.45 GHz) make poor weapons but as a direct consequence require very large areas for the rectennas. To justify the size of an ISM rectenna, the orbiting solar farm must also be large (e.g., GW scale), making the solar power satellites much bigger than the International Space Station (Schubert et al., 2015).
Baseload power is a significant advantage of SSP in geostationary earth orbit (GEO). Also called the “Clarke orbit,” after engineer and science fiction author Arthur C. Clarke, satellites placed here move at the same angular rate as the earth turns, making the satellite appear to hang fixed in the sky to an observer on the ground. This is where many communications satellites are already parked. Once operational, a GEO solar farm provides constant power at all times year round, with two minor exceptions. During the spring and fall solstice the earth’s shadow will eclipse a solar power satellite in geostationary earth orbit for a few hours over a few days. To avoid this, and also to reduce rectenna size, other constellations have been proposed, such as satellite “trains” in medium-high orbits such that successive solar power satellites pass overhead and take turns delivering power to an earth-based receiver. All architectures for SSP have the advantage of zero pollution during power production, plus it is silent and invisible. SSP is a monumental undertaking, one that requires considerable funding prior to the sale of significant amounts power to return the initial investment. Such a time horizon is likely outside the range of private enterprise and perhaps larger than any one nation could support alone. It may be that global cooperation is needed for this ultimate answer to powering human endeavors. These financial considerations are so significant for SSP that they help to illuminate the key role that economics plays in the adoption and expansion of renewable energy in general.
Economics and Finance
The global economy in 2015 is dependent on fossil fuels. Coal, oil, and natural gas power production are relatively inexpensive at present because of three economic factors:
Maturity: More than a century of steady technological progress has provided tools and practices for efficient and low-cost operation, together with high reliability.
Economies-of-Scale: Broadly based revenues spread nonrecurring and fixed costs across more customers so that each one bears a proportionately lower fraction of such costs.
Externalities: Also called noncosted consequences, these are impacts for which no monetary value has been assigned and therefore do not factor into economic decision-making. To a certain extent, government regulation for safety and for effluent control do have a measurable economic value and are therefore not strictly considered an externality.
Established energy interests also benefit from having helped drive infrastructure such as tanker ships, railroad lines, and transmission cables. In some jurisdictions, energy companies have been granted monopolies, regulated by the government, precluding direct competition. Large, centralized facilities also benefit when sited some distance from population centers where their presence and operations are largely invisible to the populace. Furthermore, stablished forms of energy production have been available for multiple generations so that people tend to simply accept the way things are as a status quo. A serious challenge faced by any new power plant, whether conventional or renewable, is that few people welcome them into their neighborhood. This sentiment is called NIMBYism, where NIMBY stands for “Not in My Back Yard.”
A metric for comparing energy costs between different generation methods is known as levelized cost of energy (LCOE). LCOE is a ratio of the sum total of all capital, installation, operations, maintenance, fuel, and end-of-life costs divided by the sum total of all energy produced over the lifetime of the power generating asset or system. LCOE is reported in the United States as cents per kilowatt-hour (a measure of energy equal to 3412 BTUs or 3.6 million Joules). As a point of reference the 2015 average of retail electric rates in the continental United States is about 10 cents/kWh. This metric is useful in comparing renewable energy sources that have proportionately higher up-front costs with conventional sources that require ongoing fuel and effluent treatment expenses. However, LCOE does not address the important issues of up-time, intermittency, or variability. A key consideration in applying LCOE to intermittent renewables such as PV and wind is availability of the power they create relative to the demand profile of the communities and loads that they serve. LCOE for new installations of wind energy (on-shore) has achieved parity with new installations of coal-fired power plants as of 2014 (Kost, et al., 2013). PV LCOE is expected to reach “grid parity” by 2017 (Lazard, 2014). The LCOE for battery technology is considerably greater than for coal, which means that pairing wind or PV with grid-level battery storage is not yet competitive with coal for baseload power generation.
Anyone who has attended a rocket launch has a visceral appreciation for the tremendous energies unleashed. Using rockets to launch solar panels into orbit to provide power back to the earth begs the question of whether the energy used for manufacture, launch, and assembly is greater than the amount of energy produced over the lifetime of the solar power satellite asset. For instance, one would desire a space solar power system that delivers all the energy needed to build and fly a second copy of itself—ideally several. This logic is captured in the metric called energy returned on energy invested (EROEI or EREI). EROEI compares the total available energy produced over the lifetime of an energy source divided by all the energy required to build, install, and operate the power generating facility. Humans and their societies tend to favor energy sources with high EROEI for the obvious reason that it is easier and achieves greater leverage on the effort applied. The underlying principle is to “harvest the low-hanging fruit first,” where one will generally eat the apples that can be reached from the ground first before climbing a ladder to pick the fruit at the top of the tree. Water power has historically been the easiest energy to harvest. A mill or turbine installed in the free run of a river produces work or power constantly so long as the water flows and the equipment remains operational. Coal has a high EROEI, although this varies based on the depth of the deposits and the method of mining. Mountaintop removal and strip mining have significant leverage in this metric. Like LCOE, the value of EROEI can change over time as technology develops and as resources are consumed. The EROEI for petroleum has been in decline as easily accessed reservoirs are becoming exhausted. Opening up new sources of petroleum is increasingly driven to more energy-intensive methods such as deep off-shore drilling or to horizontal drilling and hydraulic fracturing through shale plays to access so-called “tight gas” and oil. A controversial case is that of producing ethanol fuel from the fruit of the maize (corn) plant. EROEI for corn-derived ethanol is very close to unity after one considers the energy needed to plant, fertilize, harvest, dry, and deliver the corn kernels and then the energy needed to grind, ferment (adding heat), filter, and distill to create the final product. The shortcomings of LCOE can be partially addressed by also considering EROEI.
Investigating EROEI vis-à-vis renewable energy provides insight into the web of interconnections in the modern global economy. One may ask whether corn-based ethanol is truly a renewable fuel. Is the corn plant itself renewable? Certainly it uses sunlight, water, and carbon dioxide from the air in order to grow. Yet the corn grown in developed nations is almost exclusively of a “hybrid” variety and is sterile—you cannot make new corn in the next year from the seed kernels of this year’s harvest. Hybrid corn requires abundant nitrogen. In centuries past, nitrogen was harvested from bird guano, but today it is derived almost exclusively from natural gas, nearly all of which comes from fossil sources. Tractors and combines run on diesel fuel, nearly all of which is refined from petroleum. Even the energy used to distill the fermented beer made from corn is predominantly provided by natural gas or propane. Such logic can be applied recursively, and consider the energy needed to manufacture the planting tractor or the grain-harvesting combine. These large and complex machines are made of steel, pneumatic polymer tires, silicon-based electronics, electric motors, and a large ICE, all assembled in enormous factories that run their operations on baseload electricity, a sizeable fraction of which comes from coal. Then there are the tier 1 suppliers of modules and subassemblies for the combine, each with factories drawing power from the grid and being supplied by their own logistics network, called tier 2 suppliers. Going further down this “food chain,” one can identify tier 3 or 4 suppliers that may include companies mining the metal ores or purifying silicon for integrated circuits. Generally the lower down the chain, the more one finds operations that supply other industries distinct from agriculture and heavy-duty vehicles, including products used at home. This progression illustrates the incredible degree of complexity, interconnection, and interdependency of the modern global economy. The question regarding the extent to which an EROEI metric includes renewable energy is difficult to answer. Even wind towers are anchored within a very large concrete foundation, which require limestone (itself a fossil resource) and high heat, generally from low-grade petroleum refinery byproducts. Making Portland cement for anchoring wind turbines or even solar panel footers consumes finite, nonrenewable fossil resources, generates pollution, and contributes to atmospheric carbon emissions. Thus, even technologies called “renewable” are not wholly deserving of the name.
The dominant economic models of capitalism and consumerism do not prepare for finite limits, long durations, or noncosted consequences, but implicitly assumes that market forces will provide solutions when and as they become needed. Arguments in favor of this view include the emergence of tight shale gas when prices for more conventional natural gas were high. By extension there may come a time when methane clathrates—frozen ice and gas crystals buried in deep ocean sediment—become economically attractive relative to shale gas. Already bitumen within tar sands is being surface-mined to supplement traditional bore-hole petroleum wells, and mountaintop removal has opened access to coal seams difficult to reach with traditional mining. These evolving methods of extracting fossil fuels generally have lower EROEI and higher LCOE, making them attractive to future entrepreneurs. Those aspects of these practices that do not have a cost, or that do not require primary consumption of energy, and are not subject to governmental regulation, are the economic externalities. Blasting mountains moves the overlying rock down the sides and sometimes into the waterways, rendering hiking trails unusable, ruining aquatic habitats, and shrinking the hunting space of raptors and mammalian carnivores. Hydraulic fracturing consumes large quantities of water, which, when removed from the well, now contain salt and other substances that have long been locked safely underground. Tar sand oil recovery poisons nearby waters. When oil is refined, or when coal is burned, the residuals can have concentrated amounts of carcinogenic and mutagenic compounds and heavy metals that can cause neurological disorders. Noncosted consequences of energy resource extraction includes loss of wildlife habitat, loss of beautiful vistas enjoyed by many humans, and downstream health consequences, the causes of which are difficult to identify. A thorough study published in 2010 by the National Research Council in the United States addresses these issues in a conservative and scientifically rigorous manner to identify a range of costs not addressed by governmental regulation (NRC, 2010). If these additional costs are added to the LCOE, the results are generally more favorable to renewable sources of energy.
In a global economy within a finite biosphere, the practices of capitalism and consumerism fail to provide decision-makers with the signals or incentives to preserve the water and atmosphere that circulate among all of humankind or to manage the land which they share with their neighbors. In the practice of a formal risk assessment, all conceivable consequences are identified and then ranked according to a metric associated with the severity and likelihood of the associated harm. Conducting a risk assessment does not require one to address each and every consequence but rather seeks a rational process by which one arrives at a level of “acceptable risk.” In like manner, it is possible for energy accounting to include factors such as air, water, and land pollution, finiteness of resources, preservation of habitats, natural vistas, human health and productivity, and community mores. Including such factors in accounting does not force decision-making in one direction but rather opens up more possibilities so that (hopefully) as each decision considers broader consequences, the collective result will improve the overall value to society and humanity as a whole. As costs of health care continue to increase, and as life expectancy in many developed nations begins to plateau, it may become apparent that the result of omitting costs of unregulated and uncosted externalities is lower worker productivity and higher health care costs (Epstein & Ferber, 2011). It may be found that investing in cleaner operations for communities, corporations, and governments improves productivity and may even reduce the overall costs to society, leading to higher quality of life.
Individuals making choices for themselves or their households are most affected by local phenomenon such as land pollution and may therefore place little additional value on renewable energy above simple economic calculations. In fact, studies of purchasers of electric vehicles show a strong trend to weight upfront costs higher than lifecycle costs (Carley, Krause, Lane, & Graham, 2013), and even sophisticated thinkers tend to skew risks in decision-making (Kahneman, 2011). While some individuals educate themselves and act rationally, this tends to be the exception, so it is unrealistic to expect that mass numbers of individuals will be early adopters and leaders in the adoption of renewable energy.
Large corporations make investment decisions based on financial forecasts. Net present value (NPV) is the accounting principle of applying a future discount rate (interest rate) to determine the current value of future revenues and expenses. NPV provides a normalized approach for selecting among multiple investments competing for limited capital resources. A typical assumption is that the discount rate is fixed over time, or rather that its average is easy to predict. Publicly traded corporations must be mindful of the investment goals of stakeholders and will generally favor capital investments with higher NPV. Related measures are return on investment (ROI) or return on net assets (RONA), which provide an indication of the duration until the capital is paid back by revenue or savings. Many corporations favor ROI durations of 2 years or less. When considering the risk of business disruption and economic uncertainty due to declining EROEI of energy sources and the projected impacts of a changing climate (Romero-Lankao et al., 2014), the assumption of a fixed discount rate must be reconsidered. Insurance corporations, especially the re-insurance industry, which “insures the insurers” have aggressively pursued practices and investments and rate structures that consider the likely financial considerations of climate change (Mills, 2005). Around the globe, corporations large and small are adopting sustainable practices such as near- or net-zero operations and on-site production of renewable energy for self-use either for submetering (less than total demand), feed-in-tariffs (FITs), or netmetering (selling excess to utilities). These factors and trends are encouraging and can be aided by appropriate governmental policy and accounting practices.
Governing policy is a guiding principle for laws (statutes), which are then implemented as regulation. In the absence of policy, statutes, or regulations, individuals and corporations will do what is most expedient to their self-interest, sometimes at the expense of the interests of others. It is to address this tendency that governments debate policy, vote on statutes, and hire the administrators and regulators for compliance monitoring and enforcement. A classic principle is the “tragedy of the commons” wherein a shared resource is made available to a community but then is overexploited by a few to the detriment of many or by all to the detriment of all. The standard example is a village green for grazing sheep, where one clever farmer obtains extra sheep and grazes them earlier in the day than his neighbors, whose own sheep find less to eat and thereby suffer. Said neighbors can allow the enterprising one to dominate at their expense, or all of them might similarly overgraze the pasture and thereby ruin it for everyone. The modern example of such a tragedy is the earth’s atmosphere and the build-up of gaseous molecules, which reduce the degree to which the earth’s surface reradiates sunlight warmth back into the cold of outer space. This includes carbon dioxide created by the combustion of fossil fuels and also methane, which is the principal component of natural gas. Methane and carbon dioxide have long residence times in the atmosphere, which means their effects will persist long after their generation has been curtailed. Projections of the change in average global temperatures can be compared with projections of the adoption of renewable, sustainable sources of energy (BP, 2014; Field et al., 2014, IPCC, 2014; Mai, 2012; EIA, 2014) to reveal a disturbing trend. It appears that renewable energy implementation is insufficiently rapid to reduce the risk of widespread negative consequences. This is a tragedy of the commons on a global scale, with all of humanity likely to be affected.
National initiatives to increase the proportion of renewable energy generation within an overall portfolio have been undertaken by several countries. Denmark was notable as an early adopter of the modern 3-blade wind turbines. Iceland has tapped extensive geothermal energy sources to power much of their economy and use some of this energy to produce hydrogen to operate mass transit vehicles such as buses. Germany’s Energiewende is an energy transformation or “turn-around” that provides an interesting study of the interaction of policy, technology, and economics. Through the use of a feed-in-tariff (FIT), consumers of energy were provided a long-term purchase price for sale to the electric grid of excess renewable energy generation. As technology advances in efficiency and economies of scale reduced capital costs, the rate offered for new FIT sources was designed to decline over time. By 2014 over 1 million distributed generation sites were installed in Germany (Weiss, 2014). The cost-reduction curves for solar were driven in large measure by strong investment in solar photovoltaic (PV) panel production in Southeast Asia—China in particular. China rapidly gained a large share of the PV market by selling to Germany. German firms in turn developed equipment and electronics needed by the PV industry and, despite not retaining the direct PV manufacturing volumes hoped for, still prospered in an overall sense. An important exception is the valuation of German energy utility companies, whose market capitalization dropped by approximately half as PV panels brought down the price of electricity on the energy exchange market during peak mid-day usage times. This has encouraged some of the four large utilities operating in Germany to diversify their product and service offering, helping to install, monitor, and connect renewable energy systems and microgrids (Poser, Altman, Egg, Granata, & Board, 2014; Morris & Pehnt, 2014; Wirth, 2014).
Spain and Italy also implemented systems to promote renewable energy adoption by their citizens and businesses. In Spain the policy and its implementation were discovered to be fragile during an unexpected confluence of events. As Germany bought more and more PV, largely from China, the costs dropped significantly on a per-kilowatt basis. In Spain, PVs were purchased in U.S. dollars, which around 2008 had become favorable against the euro. A flight of capital from housing to PV ensued and then rapidly accelerated as early word spread of a royal decree to reduce the Spanish FIT a few months hence. The relatively rapid installation time of PV systems, coupled with a relatively slow, decentralized reporting system, resulted is a huge surge in buying. Furthermore, the Spanish system allowed multiple installations to aggregate in size, and certain size ranges received more favorable FIT rates. There emerged a realization that the still-high FITs, coupled with a 10-fold increase in installation from the prior year, resulted in a commitment that was not economically sustainable. Spain retroactively reduce the FIT rates, among other reactionary responses, and in the subsequent year no systems were installed (Del Rio & Mir-Artigues, 2014).
Renewable energy provides policymakers the means for increasing energy self-sufficiency while simultaneously reducing new emissions of fossilized carbon. Yet most forms of renewable energy are suitable for distributed generation (DG), changing the status quo in most countries and making energy production and distribution more flexible and more challenging. By producing energy in many locations, vulnerability is reduced to natural disasters or to attack by enemies. An unsolved attack in California in 2013 to a substation was a concrete example of the vulnerability of electric infrastructure to physical attack. Cyberwarfare is an escalating concern as evidenced by the Stuxnet worm, which targeted industrial control systems similar to the ones which control the electric grid and power distribution substations (Zetter, 2014).
Whether for power generation, agricultural irrigation, residential/commercial consumption, or industrial processes, water resources are increasingly stressed in many regions of the globe. Many renewable energy methods require little or no water, wind and solar being key examples. And with climate change being driven in large measure by the use of fossil fuels, there are more reasons than ever for nations and states to develop policies to mitigate anticipated negative impacts to the societies they govern. With so-called “greenhouse gases” having such long residence times in the atmosphere, there is a serious risk of significant harm to large populations (Williams et al., 2012). The promise of renewable energy is the ability to continue to support the vast web of interconnected human activities in a global economy that makes it possible to envision low-pollution baseload renewable energy sources such as space solar power. The alternative is for the tragedy of the commons to deprive us all of the climate we have enjoyed and come to depend on as a species for tens of thousands of years. A slow demise from natural disasters, disaffected individuals, and displaced persons could exhaust the finite resources that power our societies today, leaving the global economy unable to afford renewable solutions with high capital costs and favorable EROEI. Such a scenario harkens back to the quote from Maktoum, with the remains of humanity living not too much differently than their ancestors of 5 to 15 generations ago. The “invisible hand” of market forces is insufficient guarantee that renewable solutions will be ready in time and affordable. Instead, policies adopted by governments, corporations, and individuals should consider these options and, to the extent possible, incorporate sustainable practices, including the use of renewable energy. We may then provide affluence to all and achieve a sustainable, renewable population of some 8 billion people on earth for all time to come.
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