Energy Resource Lesson Five

Like non-renewable energy resources, most forms of renewable energy, with the exception of geothermal, come from solar energy. The sun is the original source of wind power, hydroelectric, biomass, and solar power (photovoltaic, passive solar, active solar).

WIND

The sun’s uneven heating of the Earth’s surface causes wind. In the past, wind was used to grind grain and pump water and to produce electricity on farms and in other remote areas not connected to the electric grid. Today wind is used to generate electricity that can be used immediately, stored until the electricity is needed, or fed back into the electric grid for others to use. A modern windmill is commonly called a wind turbine. It uses the kinetic energy of the wind to turn a blade attached to a generator. The spinning blades of the wind turbine turn the generator that produces electricity. Wind power is the fastest growing renewable energy technology and is cost competitive with fossil fuels in many areas of the country.

HYDROELECTRIC

Along with the pull of the moon, elevation changes, and the weather, the sun powers the water cycle. Hydroelectric energy is electricity produced from moving or falling water. Most often a dam is constructed to hold water at a higher elevation. When electricity is needed, the water falls through a penstock (trough or opening) and turns a turbine that spins a generator to produce electricity.

PHOTOVOLTAICS (PV)

A photoelectrical process occurs when sunlight is converted into electrical energy. When sunlight strikes a solar or photovoltaic panel, the photons, which are tiny packages of light energy from the sun, are absorbed and excite the outer valence electrons of atoms, which cause the electrons to move. These moving electrons are an electric current. Photovoltaic (PV) technologies use the photoelectrical process to generate electricity. Excess electric current can be stored in batteries for use at night or can be sold to an electric utility if the system is tied into the electric grid.

PASSIVE SOLAR ENERGY

Passive solar energy systems use the natural principles of solar absorption and heat transfer. Passive solar buildings are designed and oriented to let in sunlight when it is needed and keep it out when it is not needed. These buildings are designed to store heat energy and gradually release it later when it is needed. Typically, passive solar buildings are oriented east to west with a lot of windows on the southern exposure to capture the sun’s energy. Usually the walls and roof are highly insulated to keep in the solar energy. Often an interior wall or floor is made of brick or other high-mass material. These materials absorb the heat during the day and slowly release it at night or during cloudy periods. A well designed, well insulated home with proper window size and placement can provide 20-85% of its annual space heating energy needs through passive solar energy. The owner of a well-designed solar building, will save money on his/her monthly utility bill as a result of the solar and energy efficient design.

Landscaping can also be utilized to save energy. Evergreens planted on the west and north sides of a home can deflect cold northerly winds. Deciduous trees planted on the southern side of a building provide shade and cool the building in the summer while letting the sun in during the winter months.

ACTIVE SOLAR ENERGY

Active solar energy systems also take advantage of the sun’s energy. The sun heats air or liquid in collectors outside of the building. Pumps or blowers move the medium through the collectors to a bed of rocks or sand or a tank of water for storage. Air or water is warmed by the stored heat and used to produce the hot water needed for dishes and showers or circulated in the building’s heating system using heat exchangers, pumps, or blowers. Solar hot water heaters, in combination with energy conservation such as water-saving showerheads, can reduce a home’s need for fossil fuel heated water by 60-80%. Many people have built their own solar air and water heaters.

BIOMASS

Biomass energy (or biofuel) is produced from organic materials including trees, plants, switchgrass, animal wastes, and household, agricultural, or industrial waste. Trees and plants contain stored chemical potential energy produced during photosynthesis. Biofuels typically originate from fermented corn, beets, sugar cane, rice straw, or decomposing garbage or agricultural wastes. Biofuels also contain stored chemical potential energy. Burning biomass and biofuels release this stored energy and allow it to be used for industrial processes, space heating, transportation fuels, and electricity generation.

GEOTHERMAL

Geothermal energy has been successfully used to commercially produce electricity in the Western United States but is not viable for electricity production in Michigan. However, geothermal closed loop groundwater heat pumps are applicable and widely used in Michigan for heating and cooling homes and businesses. These heating and cooling systems take advantage of the relatively constant temperatures available below the frost line throughout the country. These systems use electricity to run a heat pump that transfers the ground temperature to the building, producing heating in winter and cooling in summer.

RENEWABLE vs.

NON-RENEWABLE RESOURCES

Unlike non-renewable energy, renewable energy resources replenish themselves during a human lifespan, are limitless in terms of supply (as long as the sun continues to shine and the resources are managed properly), and produce minimal pollution during their construction and operation.

Like non-renewable energy sources, renewable energy resources also have advantages and disadvantages. Renewable energy technologies typically have high up-front costs, but after the initial costs some renewable energy resources are cost-free. Furthermore, their use depends on the availability of sun, wind, biomass, and falling or moving water. The availability can be an advantage or a disadvantage depending on location.

The potential for the economical use of renewable energies in the short run is sometimes uncertain, since it is often marketed by small companies in competition with much larger utilities. The feasibility of a renewable energy project is often evaluated with respect to the current cost of nonrenewable power. The cost of both renewable and non-renewable energies is affected by governmental policies. If the price of oil goes to $60 per barrel or new environmental rules to reduce mercury or greenhouse gas emissions from the burning of coal increase the price of electricity, renewable energy becomes even more economically viable. If new non-renewable energy sources are discovered or much more efficient means of generating electricity become available, renewable energy may become less competitive. Although the future is always uncertain, some scientists estimate that we have already burned half of the world’s oil supply. If that estimate is correct, fossil fuel costs will probably rise significantly over time, as supplies diminish. In addition, cost estimates often do not include the external costs of environmental and human health impacts.

The feasibility of any energy source also depends on its location. Installing your own wind and solar power system may be more economical in remote rural areas, but not feasible for a family living in an apartment. However, many energy companies have a green pricing program, which allows customers to support the purchase of electricity generated from renewable resources. Net metering, now available in Michigan, makes renewable energy resources more viable for home and business owners by eliminating the need for battery storage of energy. Through net metering, renewable energy system owners can send their excess energy to the electric grid and receive an energy credit equal to the amount the energy company charges its customers to purchase the same amount of electricity.

While not everyone agrees, some sources predict that through careful planning, advanced technology, energy conservation, and energy efficiency, renewable energy resources could provide a substantially larger portion of our energy needs and perhaps most of our energy needs within our lifetimes. (See the Union of Concerned Scientists web site for a brief overview with a good list of links to a number of documents about renewable energy. Accessed October 20, 2010 from http://www.ucsusa.org/clean_energy/clean_energy_101/)