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Posted by Mark Jeffry on Aug 15, 2020


Contrary to what many people think, renewable energy is not a source of energy we’ve just discovered. Humans have relied on renewable energy since the very first humanlike creatures roamed the planet over three million years ago. Throughout most of human history, the energy human beings needed to survive and prosper has come from food molecules — primarily seeds, berries, and roots. The energy in these foods provided the means by which we built early civilizations. Our early ancestors also burned wood to warm their caves and cook their food.

Plants, of course, are renewable resources, capable of regenerating themselves from seeds, roots, or tubers. But plants are here by the grace of three other renewable environmental resources: soil, water, and air.

Although our predecessors, and virtually all other life forms on the planet, received the energy they needed to survive from plant matter, the source of the energy extracted from our botanical companions is not the soil or water or even the air. The source is the sun — a massive hydrogen fusion reactor 93 million miles from planet Earth.

Plants capture the sun’s energy during photosynthesis. In this complex set of chemical reactions, plants synthesize a wide variety of food molecules from three basic “ingredients”: carbon dioxide from the air, water from the soil, and solar energy from the sun. Solar energy that drives photosynthetic reactions is captured and stored in the chemical bonds of organic food molecules. When food molecules are consumed by us, or any other animal for that matter, stored solar energy is released. Solar energy contained in food molecules and liberated by the cells of our bodies is, in turn, used to transport molecules across cell membranes and to manufacture protein and DNA to power our muscles and heat our bodies.

Humankind’s greatest achievements were made by using the sun’s energy. The Egyptians, for instance, hauled massive stones to build the towering pyramids with nothing but ingenuity and the muscle power of conscripted laborers fueled by organic food molecules courtesy of the sun and plants. The Romans expanded their holdings to build a vast and prosperous empire, too, all with horse and human muscle powered by plant matter and, ultimately, sunlight.

For most of human history, then, renewable energy reigned supreme.

Then came the fossil fuel era.

Lumbering to a start in the 1700s in Europe and the 1800s in North America, the fossil fuel era was first powered by coal, an organic sedimentary rock. Coal owes its origin to plants that grew in the Carboniferous era some 250 to 350 million years ago. Coal replaced waning supplies of wood in Europe and fed the industrial machinery that made mass production — and modern society — possible. So, in a way, the Industrial Revolution was also powered by solar energy — ancient sunlight that was captured by plants millions of years ago.

For many years, coal reigned supreme. But eventually coal was forced to share its kingdom with two additional fossil fuels: oil and natural gas. Also produced from once-living organisms (notably, aquatic algae), these fuels were relatively easy to transport and, like coal, are found in highly concentrated deposits. Over time, oil and natural gas, along with coal, became major components of the world’s energy economy.

In 2009 (the latest year for which data were available), oil supplied 37 percent of the United States’ total annual energy demand. Natural gas provided about 25 percent, and coal supplied 21 percent of our energy needs. Nuclear energy provided just under 9 percent. The remaining 8 percent of the United States’ energy diet was supplied by four renewable resources: hydropower, solar, wind, and geothermal. Canada is similarly heavily dependent on oil, natural gas, and coal. In 2008, oil, natural gas, and coal provided 66 percent of Canada’s energy. Nuclear energy provided about 7 percent, and hydropower provided 25 percent of the nation’s energy.

In the more developed countries, fossil fuels clearly dominate the energy scene today, but their glory days are coming to an end. Oil and natural gas are entering their sunset years, making the shift to clean, affordable, reliable, and abundant renewable energy inevitable. Fortunately, we have lots of options.


To make the wisest choices as individuals — and as a society — we need to understand our predicament — what energy resources are endangered. Many energy experts believe that global oil production will peak or already has peaked. Peak oil could result in a devastating rise in prices. Global natural gas production may also peak soon, creating further turmoil. Clearly, we need replacements for these two fossil fuels. But what about coal?

Given the devastating impact and high cost of global warming and a host of other energy-related environmental problems, coal will very likely need to be phased out in the near future. Although coal is abundant in North America, China, and elsewhere, and its use is bound to increase dramatically as oil and natural gas production peak, coal is the dirtiest of all fossil fuels. Coal combustion not only produces sulfur oxides and nitrogen oxides that react with water and sunlight to form sulfuric and nitric acids that poison rain and snow, coal combustion also generates millions of tons of particulates that cause asthma and other respiratory diseases. Coal combustion also yields millions of tons of ash containing an assortment of potentially toxic materials such as mercury. Much of this ash is disposed of in ordinary landfills alongside our trash, and the toxic chemicals in the ash can eventually seep into ground water. Perhaps most important to our future, however, is that coal combustion produces enormous quantities of the greenhouse gas carbon dioxide — far more carbon dioxide per unit of energy produced than any other fossil fuel in use today (Figure 1-1).

Despite industry’s frequent mention of an elusive “clean coal technology,” it’s difficult to make coal clean. Without question, the efficiency of coal combustion can be increased to reduce the amount of pollution per unit of energy produced, and I applaud any efforts to do so. But capturing carbon dioxide and storing it underground — one way to make coal cleaner — is energy intensive and will dramatically increase coal combustion itself. (Carbon capture increases the energy consumption at a power plant by around 25 to 30 percent.) Even with the best technologies in place, coal combustion will produce lots of pollution; it is inevitable, and the more coal we consume, the greater the output of potentially harmful gases and particulates and solid waste. Carbon dioxide, for example, is the unavoidable byproduct of combustion of any carbon fuel. Much of the sulfur that contaminates coal in varying degrees can be removed before or after combustion by pollution control devices. The sulfur, however, does not magically disappear. Most of what is removed by smokestack scrubbers ends up in a toxic slurry that is disposed of in landfills where the toxic components can leach into groundwater. It’s a simple mass balance phenomenon: if the chemical ingredients of the pollutants are in the fuel, they’re going to be a byproduct one way or another. They won’t mysteriously vanish because a coal executive tells you they do. In the end, “clean coal” seems like nothing more than just a deceptive marketing ploy of the coal companies to make a dirty fuel appear more environmentally acceptable.

Not all fossil fuels are created equal

Fig. 1-1: Not all fossil fuels are created equal. Coal has a much higher ratio of carbon to hydrogen than oil, which has a much higher ratio of carbon to hydrogen than natural gas. The more carbon a fuel contains, the more carbon dioxide it produces per BTU of energy released.

To make the wisest choices, we also need to understand the end uses of each of the fuels we are trying to replace. Remember, it is the products and services these resources provide that we want, not the fuels themselves. As natural gas supplies decline, we don’t necessarily need more natural gas. We need to ensure the services that natural gas currently provides. For example, many homeowners use natural gas to provide space heat, to heat water for showers, dishwashing, and laundry, and to cook food. Finding replacements for natural gas means finding ways to provide these services via clean, renewable resources and technologies — for example, solar hot air systems to heat our homes and solar water systems to provide space heat and heat water for domestic use.

This book lays out the options available to us that can ensure the continuation of services currently supplied by now-failing or environmentally unacceptable fuel sources. Don’t forget, though, that the easiest way to meet our needs is often achieved by simply being more efficient. A warm home or business, for instance, can be achieved by sealing up those obnoxious cracks around windows, doors, and elsewhere. It can also be ensured by installing additional insulation to the ceilings and walls of our homes and offices. Additional space heat can be provided by retrofitting our homes for passive solar — adding windows on the south sides of our homes to let in the low-angled winter sun. Space heat can also be achieved by installing active solar hot water systems (Figure 1-2). Solar hot water systems generate hot water that can be integrated with heating systems already in many of our homes — from baseboard hot water systems to radiant-floor systems to forced-air systems. There are many other options out there. For example, homes can be heated via heat pumps, devices that remove heat from the ground or even the air and transfer it to the interior of a building.

To make wise choices, you also need to know which options make the most sense. How do we assess the appropriateness of a renewable energy option?

Two of the most important criteria are cost and net energy yield, which often go hand in hand. Consider an example:

To replace declining supplies of oil, many fossil fuel advocates suggest that we can turn to oil shale and tar sands. Unfortunately, a huge amount of energy is required to extract the oil from these natural resources. The energy required to extract oil from tar sands and oil shales subtracted from the energy of the final product is known as the net energy yield. It can be thought of as the energy returned on energy invested. Both oil shale and tar sand oil production have very low net energy yields compared to conventional oil (although new processes have steadily improved the net energy yield of tar sand production). The lower the net energy yield, the more costly the fuel. As the price of conventional oil increases, the cost of oil shale and tar sand oil will inevitably rise.

Environmental impact should also be a key criterion when selecting an alternative fuel. To build a sustainable future, we must develop fuels that meet our needs for energy without sacrificing an equally important, though often overlooked, requirement: our need for a clean, healthful environment.

Resource supplies are also vital. From the long-term perspective, it makes sense to pursue those resources that are most abundant. And what could be more abundant than a renewable fuel supply?

In sum, when seeking alternatives to waning supplies of fossil fuels, we must proceed with caution and intelligence. We need to develop energy resources that meet our needs and have the highest net energy yield, the most abundant supplies, and the lowest overall cost — socially, economically, and environmentally. In this book, I present up-to-date information on net energy yields to help you sort through the list of options. I’ll also look at the pros and cons of various technologies, to help you make the wisest choices.

The solar hot water system

Fig. 1-2: This solar hot water system on The Evergreen Institute’s classroom building provides hot water for showers, washing, etc. It could be expanded to provide space heat as well.

Before we go much further, though, let us take a brief look at energy itself. To help you understand this elusive entity, I’ll cover some basics here, then introduce more concepts later in the book as we explore the various renewable energy systems.


Like love, energy is all around us, but is sometimes difficult to define.

Energy Comes in Many Forms

In our quest to define energy, let’s begin by making a simple observation: energy comes in many forms. For example, humans in many countries rely today on fossil fuels such as coal, oil, and natural gas to meet many of their energy needs. And some use nuclear energy derived from splitting atoms. In other countries, wood and other forms of biomass, like dried animal dung, are primary forms of energy. (Biomass includes a wide assortment of solid fuels, such as wood; and liquid fuels, such as ethanol derived from corn, and biodiesel made from vegetable oils; and gases such as methane, released from rotting garbage and animal waste.) And don’t forget sunlight, wind, hydropower, and the geothermal energy produced in the Earth’s interior. Even a cube of sugar contains energy. Touch a match to it, and it will burn — giving off heat and light, two additional forms of energy.

Energy Can Be Renewable or Nonrenewable

Energy in its various forms can be broadly classified as either renewable or nonrenewable. Renewable energy, as noted earlier, is any form of energy that’s regenerated by natural forces. Wind, for instance, is a renewable form of energy. It is available to us year after year thanks in large part to the unequal heating of the Earth’s surface. When one area is warmed by the sun, hot air is produced. This hot air rises and, as it does, cooler air moves in from neighboring areas. As the cool air moves in, it creates winds of varying intensities.

Renewable energy is everywhere and is replenished year after year. It could provide humankind with an enormous supply … if we’re smart enough to tap into it.

Nonrenewable energy, on the other hand, is finite. It cannot be regenerated in a timely fashion by natural processes. Coal, oil, natural gas, tar sands, oil shale, and nuclear energy are all nonrenewable forms of energy. Ironically, most of these sources of energy are the products of natural biological and geological processes — processes that continue even today, but at rates not even remotely close to our rates of consumption. Coal, for instance, still forms in swamplands, but its regeneration takes place at such a painfully slow rate that it is impossible for the Earth to replenish the massive supplies that we are consuming at breakneck speed. Because of this, coal, oil, natural gas and the like are finite.

When they’re gone, they’re gone.

Energy Can Be Converted from One Form to Another

There’s still more to this mysterious thing we call energy. Even the casual observer can tell you that energy can be converted from one form to another. Natural gas, for example, when burned, is converted to heat and light. Coal, oil, wood, biodiesel, and other fuels are also converted to other forms of energy during combustion. Heat and light are byproducts of these conversions. Heat, in turn, can be used to make electricity. But the possibilities don’t end here. Visible light contained in sunlight can be converted to heat. It can also be converted to electrical energy by solar cells. Even wind can be converted to electricity or mechanical energy that can drive a pump to draw water from the ground. Humans have invented numerous technologies to convert raw energy into useful forms.

Energy Conversions Allow Us to Put Energy to Good Use

Not only can energy be converted to other forms, it must be for us to derive benefit. Coal, by itself, is of little value to us. It’s a sedimentary rock that looks cool, but it is the heat and electricity produced when coal is burned in power plants that are of value to us. Sunlight is pretty, and it feeds the plants we eat, but in our homes and factories, the heat the sun produces and the electricity we can generate from it are of great value to us.

In sum, then, it is not raw forms of energy that we need. It is the byproducts of energy conversion — new types of energy that are unleashed when we convert raw energy through the many ingenious energy-liberating technologies — that meet the many and complex needs of society.

Energy Can Neither Be Created nor Destroyed

Another important fact about energy is something you may have learned in high school, that is, that energy can neither be created nor can it be destroyed. Physicists refer to this as the First Law of Thermodynamics or, simply, the First Law. The First Law says that all energy comes from pre-existing forms. Even though you may think you are creating energy when you burn a piece of firewood in a wood stove, all you are doing is unleashing energy contained in the wood — specifically, the energy locked in the chemical bonds in the molecules that make up wood. This energy, in turn, came from sunlight. And the sun’s energy came from the fusion of hydrogen atoms in the sun’s interior.

Energy is Degraded When it is Converted from One Form to Another

More important to us, however, is the Second Law of Thermodynamics. The Second Law says, quite simply, that when one form of energy is converted to another form — for example, when you burn natural gas to produce heat — it is degraded. Translated, that means energy conversions transform high-quality energy resources to low-quality energy. Natural gas, for instance, contains a huge amount of energy in a small volume; the energy is locked up in the chemical bonds that attach the carbon atom to the four hydrogen atoms of each methane molecule. When these bonds are broken, the stored chemical energy is released. Light and heat are the products. Both light and heat are less concentrated — and thus, lower quality — forms of energy. Hence, we say that natural gas, which is a concentrated form of energy, is “degraded” when burned. In electric power plants, only about 50 percent of the energy contained in natural gas is converted to electrical energy. The rest is “lost” as heat that dissipates into the environment.

No Energy Conversion is 100 Percent Efficient (Not Even Close)

This leads us to another important fact about energy: no energy conversion is 100 percent efficient. When coal is burned in an electric power plant, only about 30 percent of the energy contained in the coal is converted to useful energy — in this case, electricity. The rest is lost as heat and light. The same goes for renewable energy technologies. One hundred units of solar energy beaming down on a solar electric module won’t produce the equivalent of 100 units of electricity. You’ll only get around 8–20 percent conversion using the various solar modules on the market today. (However, some new technologies can capture and convert about 35 to 40 percent of the incoming energy. So, things are improving.)

Energy is lost in all conversions. As another example, most conventional incandescent lightbulbs convert only about five percent of the electrical energy that runs through them into light. The rest is released as heat. (Incandescent lightbulbs should really be called “heat bulbs.”)

Each conversion in a chain of energy conversions loses useful energy, as shown in Figure 1-3. To get the most out of our primary energy sources, therefore, we have to reduce the number of conversions along the path.

You may be wondering if all of this discussion of energy losses is a violation of the First Law of Thermodynamics, which states that energy cannot be created or destroyed. The answer is no. The energy losses that take place during energy conversion are not really losses in the true sense of the word. Energy is not destroyed; it is released in various forms, some are useful to us and others, such as heat, are not so useful. Chemical energy in gasoline propels a car forward along the highway. Some is also lost as heat that radiates off the engine. This waste heat is of little value — except on cold winter days when it is used to warm the car’s interior. Eventually, however, all the heat produced by a motorized vehicle escapes into outer space. It is not destroyed, per se, but it is no longer available to us. Hence, the conversion results in a net loss of useful energy.

Fig. 1-3: Energy conversions occur commonly

Fig. 1-3: Energy conversions occur commonly in the production-consumption cycle of various fuels. Unfortunately, none of these conversions is 100 percent efficient, so energy is lost at each stage. The key to using energy efficiently is to limit or eliminate conversions.