Electricity generated from renewable sources of energy displaces fossil and nuclear fuel power and has fewer overall emissions.
BIOMASS
lANDFILL
HYDROELECTRIC
WIND
PHOTOVOLTAIC
GEOTHERMAL
OCEAN
LINKS
ENERGY
Everything that lives, breaths, moves or grows on the earth owes its existence to the sun. Whether it’s gasoline for our cars or electricity for our homes, the energy we use was born in the heart of the sun.
For most of the industrialized world, much of the solar energy it uses is stored in the form of fossil fuels, such as coal, natural gas and oil. But there are alternative sources of energy that are clean, efficient and don’t take millions of years to produce. They are available, reliable, affordable, and most importantly, they are renewable.
Renewable energy does not depend on fossil fuels and most typically comes from hydroelectric and wind generators, geothermal heat, photovoltaic cells, ocean currents and resource recovery facilities such as power plants fueled by landfill gas and biomass (plant and animal material) fuel.
These renewable power sources utilize energy that is available today, here in North America, providing local jobs, diverting material from the waste stream, displacing power from fossil fuels and reducing various types of pollution.
Renewable energy is not a “magic bullet” that will rid the planet of its air pollution problems associated with power generation. There are tradeoffs. For example, wind turbines have no air emission, but they’re restricted to areas where the winds are sustained and they take up large tracts of land to equal the amount of power generated by traditional means. Hydroelectric has no air emissions, yet they have significant impact on river ecosystems. Photovoltaic cells are expensive to install and have minimum power output, yet their environmental impact is negligible.
Each type of renewable energy has it’s own set of advantages and disadvantages, ranging from its costs to install and operate, to availability, reliability and its environmental impact. Table 1 shows a comparison of the various forms of renewable power by costs and characteristics.
Table 1
Costs
Characteristics
Energy
Installation &
constructionOperating & maintenance
Life span
Reliability
Availability
Environmental impact
Emission displacement
Biomass
med
med
med
med
high
high
med
high
Landfill gas
med
med
med
med
high
high
med
med
Hydro
low
low
low
high
high
low
med
low
Wind
high
high
low
med
med
low
low
low
Photovoltaic
very high
very high
low
low
med
low
low
low
Geothermal
high
high
med
med
high
high
low
low
Ocean
very high
very high
high
med
med
low
low
low
Coal
low
med
low
high
high
high
high
low
Nuclear
low
very high
high
high
high
med
med
low
BIOMASS
Biomass energy was the first source of energy harnessed by the human species. Through fire ancient man was able to release the sun’s energy from trees and plants. Wood and other plant material were the primary biomass fuels at the dawn of civilization, and they still are today. Land clearing and the forest products industry generate billions of tons of waste wood and wood scraps every year that are salvaged from the forest floor or diverted from landfills to generate electricity. Primary Power alone has the capacity to consume 1.2 million tons of wood waste each year – wood that would otherwise end up in landfills, or be left in the woods where it attracts pests and disease that can infect healthy trees, and provide tinder for wildfires.
Wood fuel is ground into chips and delivered to the biomass power plant by truck, rail or barge. The wood fuel fires a boiler that generates steam to power the turbine and generator. Conveyors move the fuel into the boiler. It takes more than 1.5 tons of biomass fuel to generate one megawatt hour (MWh) of electricity, or enough power for 700 to 1,000 homes.
Timbering, lumbering and tree-trimming operations aren’t the only source of wood fuel. Industrial waste wood such as crates and pallets, and construction demolition wood are also reclaimed from the waste stream. Formerly destined for the landfill, this material is sorted and processed for energy recovery at biomass power plants.
Electricity generated with biomass fuels is the most reliable of the renewables. It doesn’t need the wind to blow, rain to swell rivers or the sun to shine to make electricity. As long as plants grow electricity will be made.
Biomass power plants are small compared to some coal and natural gas powered plants, which can be upwards of 1,000 MW). They are required to have air permits governing the amount of nitrogen oxides, carbon monoxide and particulate matter they are allowed to emit. Even though they are small in size, they too have to comply with rigorous state and federal EPA regulations.
LANDFILL GAS
Millions of cubic yards of rotting refuse generate landfill gas. Composed mostly of methane and water, landfill gas is a flammable hydrocarbon that forms as a byproduct of decay.
Methane is a gas that contributes to the “greenhouse effect” of the earth’s atmosphere. Landfills are the largest single source of methane in the U.S., according to the U.S. Environmental Protection Agency, contributing 40 percent of the country’s total methane emissions. Compared to an equal amount of carbon dioxide, the most ubiquitous greenhouse gas, methane has 25 times the negative impact on the atmosphere.
Traditionally, methane was allowed to vent naturally from landfills into the atmosphere. Eventually landfill operators were required to flare the gas – burning it into carbon dioxide to minimize its greenhouse effect. Today, most landfill operators are capturing that energy to power internal combustion engines or gas turbines to make electricity.
Landfill gas plants are small (1 to 6 MW) compared to biomass plants and are designed to run off landfills that have estimated gas supplies in excess of 35 years. Emissions include carbon monoxide and nitrogen oxides.
HYDROELECTRIC
Leashing the power of raging rivers to make electricity was one of the primary means of electrifying the U.S. after the turn of the century. Today, thousands of hydroelectric dams – from the immense hulk of Hoover Dam to small dams less than a megawatt on backwoods creeks – still use the force of gravity on water to turn turbines and generators. Their ability to generate relies solely on the river’s ability to flow, so their production of electricity can fall during drought and times of low flow. They have no air emissions, but have caused significant changes in river ecosystems upstream and downstream from their confines, particularly on populations of migratory fish.
Hydropower has minimal potential for expansion because of their impact on the rivers and its wildlife. Most sites suited to hydroelectric generation have already been developed, so there is little potential for new hydroelectric facilities. In some areas efforts are underway to remove hydroelectric dams in efforts to restore migratory fish populations.
A less common form of hydropower – water wheels – diverts water over a grist-mill type wheel to turn a generator, providing small amounts of electricity, usually enough for on-site application.
WIND
It was the wind that first powered man’s exploration of his world thousands of years ago, and it is still powering him today with pollution-free energy that is growing across the world’s landscape.
Moving air masses over land and water, warmed by the sun, create the wind that pushes the rotors of huge windmills connected to electric generators.
Wind power is one of four renewable energy forms (hydro, ocean tide and geothermal, too) that create no air pollution. It is among the least reliable of the renewable forms. Production drops as the winds diminish, limiting their geographic location to areas with sustained winds. They are small (each windmill from 50 KW to 1.5MW), requiring vast acreage for multiple windmills to meet the demand for power. Their main environmental drawback is their visual impact on the landscape The largest wind turbines can stand 250 feet tall at the hub, and have rotor spans of nearly 300 feet.
PHOTOVOLTAIC
Photovoltaic cells are the most direct method of capturing – and storing – the sun’s energy. Photocells react to the sun’s light, giving off electricity that is either used immediately or stored in batteries. Photocells are a low wattage form of energy usually suited to single dwellings or office buildings. Since sunlight is not energy dense, photocell “arrays” require significant surface area to provide adequate power. Also, when clouds hide the sun or at night, photocells generate no power. This limits them to specialized uses such as remote power supplies. They have no emissions other than those during the manufacture of the photocell but they are the most costly per unit of power generated.
GEOTHERMAL
Early man recognized the warmth and comfort offered by hot springs and geysers: water heated deep within the earth and forced to the surface under pressure. However, it would take the scientific knowledge of geologists and skills of the engineer to realize the potential for this energy to produce electricity.
In the geothermal process, the earth performs the same function as the boiler does in a coal, natural gas or biomass plant. Geothermal power plants circulate water into the hot subterranean ground and use the hot steam/water mix as it comes from the earth to turn turbines and generators.
There are typically no significant air emissions associated with geothermal energy. However, geothermal plants are restricted to areas where geothermal activity is located near the surface of the earth.
OCEAN CURRENTS
Like geothermal power, electricity generated by the waves and moving tides of the ocean is geographically restricted to oceanfront locations. Technology uses the movement of incoming and outgoing tides to operate generators. New technology is being developed that generates electricity with wave motion.
Both of these technologies generate comparatively small amounts of electricity (less than 1 MW) and are best suited for demand-side use, such as for small villages and stand-alone facilities inaccessible to the power grid.
