Which resources should be used for energy production?
Formal documents, usually called renewable portfolio standards (RPS), spell out the answers with recommendations and timetables. More than 30 states have RPS guidelines to encourage a shift to different ways of producing energy. Many states, including Kentucky, have not set specific target dates and percentages due to concerns about how these could affect consumer electricity rates and reliable service. At the federal level, the Energy Policy Acts of 2002 and 2005 also include many incentives to change the nation’s energy mix.
In general, the idea behind these policies is to decrease dependence on traditional fuels such as coal and natural gas, and increase the amount of energy obtained from the sun, wind, and other renewable resources. The details of these programs vary according to what does—and does not—count as a renewable resource, and whether provisions to encourage energy efficiency are included.
Here, in plain English, are some of the key concepts.
The carbon connection
Carbon is a part of everything living today—and even things that died so long ago they’ve changed into something else. Those buried remnants are the big three of fossil fuels—oil, natural gas, and coal. All of these resources contain a lot of energy—and a lot of carbon. When these fuels are burned to release some of that energy, the combustion process is not complete—there are always some leftover bits of solids and gases, including some of the original carbon.
Fossil fuels can be used at consistent levels during every 24-hour period, every season, and year after year.
The supply of fossil fuels is huge, but it is limited. As these fuels are pumped up to the surface or dug up, they are not replaced. As an energy resource, ancient carbon-based fuels are not renewable.
But some newer carbon-based fuels can be replenished. Trees, switchgrass, and corn stubble all contain carbon that is released as these fuels are converted to useable energy. Fuels like these are called biomass. They are renewable in the sense that they can be planted, harvested, and another crop planted and harvested, over and over again. But they are limited by the amount of time it takes to complete each cycle.
When old (fossil fuels) or new (biomass) carbon-based fuels are used, some of their carbon is released. Some combine with oxygen to form carbon dioxide (CO2), a greenhouse gas. Greenhouse gases are a useful, naturally occurring feature of the Earth’s atmosphere. However, when human energy production methods release additional amounts of these substances, these activities could affect natural systems.
Black carbon is the solid residue left over after burning modern biomass and fossil fuels. It can be big, like the clumps of ashes in a fireplace, or very small, like the tiny bits of soot that contribute to the formation of smog.
Many of today’s proposed laws include strategies to both reduce the amount of carbon byproducts released during energy production and to manage them better. Carbon will be a part of energy conversations for a long time.
Carbon is not a part of the big three of renewable energy resources –water, solar, and wind. These energy sources are called renewable because they are continually replenished and are inexhaustible. The supply is huge. However, the flow of these resources is limited. Their potential to produce energy varies throughout each 24-hour period, from season to season, and by geographic area.
Conventional hydropower (using water moving through turbines at a dam to produce electricity) depends on rainfall and snowmelt, which change throughout each year. Other water power options include using waves, currents, and tides to generate electricity. Although all of these actions repeat, they also vary as the force and direction of the water’s movements change daily and seasonally.
Both photovoltaic solar power systems (which convert sunlight directly into electricity) and thermal solar power systems (which capture the heat in sunlight as a step toward generating electricity) are limited by the amount of clear sunlight that occurs at a geographic location during part of each 24-hour period.
Wind power is also limited. The amount of electricity that can be produced by a wind turbine varies according to the speed and direction of the wind. Many sites do not have enough consistent wind at the proper speeds to be useful.
A fourth naturally occurring resource for energy is the heat below the Earth’s surface, known as geothermal energy. The amount of heat, often intense enough to produce steam, is constant, making this one of the most dependable of renewable resources. But it, too, is limited due to geography.While some geothermal areas are close to the surface and easy to tap into, others are so deep that affordable technology is not yet (and may never be) available to use this resource.
The supply of garbage in every community increases every day, so in that sense garbage is a renewable resource—it’s always being replenished. There are two ways to recycle garbage to produce energy. The biomass option involves burning municipal solid waste to heat water to make steam to move turbines to generate electricity. As an alternative, landfill gases can be captured and collected to use just like natural gas to generate electricity.
Many industrial processes also offer recycling opportunities for energy production. In a cogeneration setup, wood waste (a form of biomass) at sawmills and manufacturing plants can be burned to produce steam to generate electricity. Any remaining heat can be recycled to warm interior spaces.
Traditional fossil-fuel power plants also offer energy recycling opportunities. In a combined heat and power (CHP) setup, after steam moves the turbines generating electricity at the power plant, the remaining heat can be used in industrial processes at nearby manufacturing sites or to warm buildings.