Renewable Energy
The world
relies largely on fossil fuels to meet demands for energy, and energy
supply, delivery, and use practices are typically quite inefficient. Yet
these resources exist in finite quantities, and oil and natural gas are
becoming ever more costly as worldwide demand grows and existing supplies
are depleted. Fossil fuel extraction and combustion also harm the environment
and are changing the Earth's climate, with potentially disastrous economic,
environmental, and social impacts.
Energy conservation
and efficiency - including clean vehicles and green buildings - make
each unit of energy go farther. Renewable sources of energy are continuously
regenerated by natural forces that can be harnessed with limited or no
adverse impacts and whose costs are largely immune to the laws of supply
and demand.
Renewables
are dependent, in large part, on the sun. Solar
energy may be used directly for heating and for the generation of
electricity. The sun's heat is also the key driver of wind,
whose energy may be tapped and converted into green power via wind turbines.
Sunlight is essential to plant growth as biomass, which can be used to
generate electricity and heat and to drive vehicles in the form of bioenergy. The water
cycle, driven by solar-heated evaporation at the Earth's surface, condensation
in the atmosphere, and precipitation, yields another renewalbe resource:
The kinetic energy of water flowing downhill-typically rivers and
streams-may be tapped as hydropower.
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Photovoltaic panels being installed in Woods Hole, Massachusetts |
The ocean is a vast reservoir of energy that may be used to generate electricity. It is possible to harness the energy of ocean tides, dependent upon the gravitational influence of the moon and sun, and ocean waves, which are controlled largely be wind. The ocean's thermal energy, produced by the solar heating of surface waters, may also be utilized. The Sun and the Earth's internal heat create geothermal energy. This energy may be harnessed by utilizing the near-constant temperature of shallow groundwater (between 50° and 60°F, or 10° to 16°C) for heating and cooling purposes. In addition, geothermal reservoirs of hot water and hot rock may be tapped for their heating potential and for electrical generation. Widespread adoption of renewable energy has traditionally been limited by unfavorable economics, irregular distribution, intermittency, and other factors. There is great hope that these barriers will be offset in the future by policy changes and technological advances and, perhaps eventually, by widespread availability of hydrogen acting as a storage medium for energy garnered from renewable sources. Recent advances, combined with expanded application experience, are making renewables increasingly cost-competitive with conventional fossil-fuel-based systems. The rate of technological progress is accelerating, public awareness of the adverse impacts of fossil fuels is growing, and policy frameworks that level the playing field for renewables are emerging. These trends augur well for a green energy future in the Cape & Islands region and beyond.
Visit the Cape & Islands Energy Information Clearinghouse and the Cape & Islands Go Green Guide (CIGoGreen) for more information.
Conservation, Efficiency, Clean Vehicles & Green Buildings
Wiser use of electricity, heating fuels, and transportation fuels is the best way to reduce energy bills and the adverse impacts associated with energy consumption. Tips for conserving energy and using electricity and fuels more efficiently are available here.
Green buildings respect their surroundings and are comfortable and cost-effective environments in which to live and work. They use energy and water as efficiently as possible. They employ reused, recycled, low-impact, and nontoxic materials, fixtures, furnishings, and finishes. They take advantage of on-site renewable energy sources. And they minimize construction-related waste and disturbance.
Solar
For information on solar energy in local communities, visit the Cape & Islands Energy Information Clearinghouse.
There are
three main types of solar energy: photovoltaics, solar thermal heating,
and passive solar heating and daylighting.
Photovoltaics (PV)
Solar cells make electricity from sunlight. They are generally composed of semiconducting material that releases electrons when sunlight hits it. Individual PV cells can be connected together to make systems designed to produce any amount of power, from one cell that can power a calculator to a few panels that can power a house to huge, utility-scale arrays. PV panels require almost no maintenance because they have no moving parts, and most come with decades-long guarantees. While they are expensive to install, they can pay for themselves based on saved energy costs.
Solar Thermal Heating
Sunlight contains thermal (heat) energy. This energy can be used to heat water, air, or a working fluid. Heated water and air are most often used directly but can be used to power other energy systems. Working fluids are used either as a way to transfer heat to water or air, or they are used to drive turbine/generators to produce electricity. Solar thermal systems are most often seen as black boxes on rooftops that heat water for use in homes, but they also exist as large power plants that use hundreds of mirrors to concentrate sunlight to produce electricity. Solar thermal domestic hot water and pool heating systems can generate a rapid return on investment.
Passive Solar Heating
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The Impact 2000 house uses building-integrated PV and solar thermal plus passive solar. |
Buildings can be designed to use sunlight as a source of heat. They have large windows on the south side of the building and very few windows on the north. The windows allow sunlight to come in and warm the interior of the building. The most efficient designs have overhangs that allow the sunlight to shine in during winter months, when it is lower in the sky, but block the sun in the summer, when it is higher. Materials can be used for the walls and floors inside the building that absorb the sunlight's heat during the day and slowly release it through the night.
Sunlight can also be used to meet lighting needs. Natural daylighting cuts down on electricity use and, by decreasing reliance on incandescent light bulbs that generate heat, can help reduce air conditioner use.
Wind
For information on wind power in local communities and offshore environments, visit the Cape & Islands Energy Information Clearinghouse.
Wind turbines harness air in motion to make electricity. In the same way that an airplane is pulled upward (lifted) when it moves fast enough, the blades of a turbine are pulled around in a circle as the wind blows across them. The spinning blades turn a shaft that drives a generator to produce electricity.
Small turbines
can be used to provide power to a home, while larger units can supply
electricity to a business or school. Many large wind turbines linked together
create a wind farm, a full-scale utility power plant using the wind to
make electricity to sell to homeowners and businesses.
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Wind turbines dot the ridgeline at the Green Mountain Power facility, Searsburg, VT. |
Wind power represents the world's fastest growing source of energy. Land-based wind farms provide much of this power, but countries in Europe and elsewhere have begun harnessing offshore resources.
Some turbines do not produce electricity, but are instead used to do mechanical work, like pump water from a well. People have used this type of windmill for hundreds of years to do physical work, several examples of which can be seen around this region.
Bioenergy
For information on bioenergy in local communities, visit the Cape & Islands Energy Information Clearinghouse.
Bioenergy
is energy stored in organic material. There are many types of biomass
that are used as sources of energy, such as wood, plants, municipal solid
waste, and organic wastes. People have been using bioenergy for thousands
of years in the form of wood fires, but now modern biofuels are being
applied for making electricity, creating heat, and powering vehicles.
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This bus runs on soybean-derived biodiesel |
Electricity is produced from burning biomass directly or by using gases or liquid fuels made from it. The heat is used to sping a turbine and turn a generator that makes electricity. For example, most of the municipal solid waste generated on Cape Cod and Martha's Vineyard is transformed into electricity at the SEMASS waste-to-energy plant in Rochester, MA.
Biomass can also be converted into liquid fuels that may used in vehicles or home heating systems. Ethanol is a gasoline additive made from biomass high in carbohydrates, and biodiesel is a diesel fuel alternative made from oils or fats. Through a simple chemical reaction you can even make your own biodiesel with used cooking oil.
Geothermal
For information on solar energy in local communities, visit the Cape & Islands Energy Information Clearinghouse.
Geothermal energy is obtained from heat in the Earth, either from solar heating at the surface or from radioactive decay deep underground.
The ground just under the surface of the Earth is always a constant 50-60°F (10-16°C). Geothermal heat pumps take heat from the ground in the winter to heat air or water, and they deliver heat from indoor environments into the ground to cool things down. A ground-source heat pump can drastically reduce or eliminate the need for energy-intensive heating and cooling systems in homes and other buildings.
In some places, hot water and magma are found closer to the surface, sometimes appearing as steam vents or geysers. These underground heat resources are used to meet a variety of heating needs, as well as to power turbines that create electricity.
Hydropower
Hydropower is energy made from water flowing downhill through a turbine that spins a generator. Most conventional hydroelectric facilities employ dams to block the flow of a river so that the amount of water released and energy generated can be controlled to meet demand. Hydro plants also can use water diverted from the flow of a river.
Dams pose several environmental problems, such as the destruction of ecosystems and disruption of fish and eel migrations. Run-of-river plants like the one shown below are less harmful, but they can still prevent a barrier to migrating wildlife.
Emerging in-stream hydro technologies offer reduced ecological impacts. They employ modified turbines or other spinning structures to capture energy without disrupting the water flow. In local environments, similar technologies situated in tidal currents offer some potential.
Wave, Tidal & Ocean Thermal Energy
For information on ocean energy in local environments, visit the Cape & Islands Energy Information Clearinghouse.
Power from the ocean can be obtained from two different sources of energy: kinetic energy from tides, waves, and ocean currents and thermal energy from solar heating of surface waters.
Tidal and wave energy technologies either use the energy of water in motion to directly to spin a turbine and drive a generator, or they transfer the energy to a working fluid that runs a turbine/generator. Tidal barrages operate like hydro dams in estuarine environments, restricting tidal flows. In-stream tidal energy and ocean current systems capture the energy from ebb and flood flows or circulations such as the Gulf Stream without altering the moving water. Wave generators rely on buoys, overtopping devices, tapered channels, and oscillating water columns to harness the up and down motion of waves.
Systems that create electricity from the thermal energy of the ocean take advantage of the temperature differences between warm surface waters and cold deep waters to bring seawater or a working fluid to a boil. In each of these systems the vaporized liquids are used to spin a turbine that activates a generator to produce electricity.
Hydrogen from Renewable Resources
Hydrogen is the simplest and most abundant element in the universe. On Earth it is found combined with other elements to form things like water (H2O), and many organic compounds, such as the hydrocarbons that make up fuels (like gasoline, natural gas, methanol, and propane). In its pure form, hydrogen is a high-energy fuel that, for example, is used for launching rockets into space.
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Fuel cells can be made to produce electricity with no noise and emit only pure water. |
However, hydrogen is not in itself an source of energy - like electricity, it is an energy carrier produced from other sources. In fact, almost all of the hydrogen used today is produced from fossil fuels.
Hydrogen is potentially an efficient way to store and transport the energy produced by renewables, therefore addressing some of their major drawbacks - intermittency and site specificity. If electricity generated by solar photovoltaics, wind turbines, or other renewable sources is used to split water into hydrogen fuel via electrolysis, then the energy may be stored and used when and where needed.
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Every major automobile manufacturer is currently researching fuel cell technology, including the fuel cell hybrid concept vehicle by Toyota. |
Renewable hydrogen may be used in stationary fuel cells to produce heat and electricity for homes and buildings and in mobile applications to power vehicles. A fuel cell combines hydrogen with oxygen from the air, and their only byproduct is pure water. They can be thought of as batteries that use hydrogen to create an electric charge. Fuel cells run on pure hydrogen or can reform the hydrogen found in other liquid or gaseous fuels. They can be made in any size to provide electric energy for appliances, cars, houses, hospitals, and even whole neighborhoods. All the major car manufacturers are currently researching and designing fuel-cell-driven electric vehicles to be on the market within the next decade or so.
Images from National Renewable Energy Laboratory