1. Renewable Energy - Indirect Solar Energy - Nonsolar Energy

2. Indirect Solar Energy several sources of indirect solar energy
biomass energy
wind energy
hydropower
ocean waves
ocean thermal energy conversion

3. #1: Biomass Energy
consists of wood, fast-growing plants and algae, crop wastes, sawdust, wood chips, and animal wastes
solid forms include:
firewood
charcoal  wood that has been turned into “coal” by partial burning
animal dung
peat  partly decayed plant matter found in bogs and swamps
* ½ of the world’s population relies on biomass solids as their main source of energy *

4. Biogas
a mixture of gases (mostly methane) that is produced by converting biomass (i.e. animal wastes) into gas
can be stored and transported like natural gas
“clean” fuel

5. Production of Biogas
biogas digesters: use microbial decomposition of household and agricultural wastes to produce biogas for cooking and lighting
several million in China and India

6. Conversion of Biomass to Liquid Fuels
biomass can be converted to methanol and ethanol
can be used in internal combustion engines
gasoline + 10% ethanol = gasahol
commercial conversion of agricultural and municipal wastes into ethanol
costs are still high, but this may be able to compete with gas at some point
what types of wastes are converted?
major disadvantage?

7. Advantages of Biomass Use
reduces dependence on fossil fuels
often makes use of wastes
reduces disposal problem
produces low levels of sulfur and ash
can offset CO2 production by planting new crops/trees

8. Disadvantages of Biomass Use
requires land and water
competes with food production 
not sustainable if you don’t replant
can result in soil erosion, deforestation and desertification, air pollution, and degradation of water supplies
crop residues that are used actually prevent erosion by helping to hold the soil in place
also, residue decomposition enriches the soil

9. #2: Wind Energy
surface air currents are caused by the solar warming of air
may be the world’s fastest growing source of energy
radiant energy  mechanical energy
highly dispersed
turbines have become larger and more efficient
currently, the most cost-competitive form of renewable energy

10. Where is Wind Energy Used?
most profitable in rural areas that receive fairly continual winds
e.g. islands, coastal areas, mountain passes, and grasslands
the world’s largest concentration of turbines is in the Tehachapi Pass at the southern end of the Sierra Nevada Mountains in California

11. Pros and Cons of Wind Energy
no major environmental problems
clean source of energy  no SOx, CO2, or NOx
cons
birds sometimes collide with the turbines
what are some preventative measures that can be taken?
aesthetic concerns  turbines change the character of the landscape
what can be done to deal with this?

12. #3: Hydropower
energy harnessed as water flows from higher elevations to sea level
pretty concentrated form of energy
potential energy (water held back by a dam)  kinetic energy (water falls down a penstock where it turns turbines to generate electricity)
currently the form of solar energy in greatest use

13. Impacts of Dams changes the natural flow of a river
water backs up  floods large areas of land to form a reservoir
destroys habitats
disrupts migrations of spawning fish (e.g. salmon)
below the dam, river flow is greatly reduced

14. Impacts of Dams continued
reservoir-induced seismicity
earthquakes can occur during and after the filling of a large reservoir
area does NOT have to be seismically active to be affected
serious water loss and increasing water salinity in arid areas
prevent silt from enriching agricultural lands downstream
e.g. Egypt now relies on chemical fertilizers to maintain fertility of the Nile River Valley/Delta

15. Impacts of Dams continued
displace people in areas that are being flooded to make reservoirs
e.g. Three Gorges Project of the Yangtze River in China
largest dam ever
displaced 2 million people
flooded 1200 temples and other cultural sites

16. Impacts of Dams continued
breaks in the dam harm people and properties downstream
waterborne diseases can be a particular problem
e.g. schistosomiasis (a tropical disease caused by a parasitic worm that can damage the liver, urinary tract, nervous system, and lungs)
½ the population of Egypt suffers from this disease (due to problems with the Aswan Dam on the Nile River)

17. Wild and Scenic Rivers Act
prevents the hydroelectric development of certain rivers, although the number of rivers protected by this law is less than 1% of the nation’s total river systems

18. Why DO We Use Dams Then?
Dams cost a lot to build, BUT they are relatively cheap to operate!

19. #4: Ocean Waves produced by winds  wave energy
a hollow chamber is sunk into a gully off the coast to catch waves
rising water in the chamber pushes air into a vent that contains a turbine, causing the turbine to spin
when the water recedes, it draws the air back into the chamber  moving air continues to drive the turbine
need to be able to harness energy at a rate that is efficient and productive

20. #5: Ocean Thermal Energy Conversion (OTEC)
the generation of electricity from ocean temperature gradients (the differences in temperature at various ocean depths [~24 °C])
gradients are the result of solar energy warming the surface of the ocean

21. Electricity Generation Using OTEC
warm surface water is pumped into a power plant where it heats a liquid, such as ammonia, to the boiling point
ammonia steam drives the turbine
ammonia is cooled by the very cold water from the deep ocean
cold water can be used to air condition building, or used in aquaculture facilities

22. Disadvantages of OTEC must pump A LOT of water to generate power
requires a lot of energy
not very efficient (~3-4%)
costs are high

23. Other Sources of Renewable Energy
other renewable energy sources (not necessarily dependent on the sun) include:
tidal energy (although this is somewhat dependent on the gravitational pull of the sun)
geothermal energy

24. Tidal Energy
caused by changes in water level between high and low tides
what are the tides?
the alternate rising and falling of the surface waters of the ocean and seas that generally occur twice each day
the result of the gravitational pull of the moon and the sun
can harness tidal energy by building a dam across a bay

25. Disadvantages of Tidal Energy
few locations have large enough differences in water level between high/low tides to make power generation feasible
costs a lot
affects organisms that use bays and estuaries as habitat

26. Geothermal Energy the naturally occurring heat within the Earth
amount of energy is enormous

27. Geothermal Energy is Associated with Volcanism
hydrothermal reservoir: as groundwater travels downward and is heated, it becomes buoyant and rises until it is trapped by an impermeable layer in the Earth’s crust
hot water + steam can escape to the surface  hot springs and geysers
tapped by drilling wells similar to those used for extracting oil and natural gas
can be used directly for heating or to generate electricity
electricity is inexpensive and reliable
requires a very small area of land (relative to other energy sources)

28. Where is Geothermal Energy Used?
the U.S. is the world’s largest producer of geothermal energy
largest plant is The Geysers in northern California
Iceland  only uses hydro- and geothermal power
used to generate electricity and heat 2/3 of the homes
most produce is grown in geothermally heated greenhouses
water used to transfer heat can be recirculated into the reservoir

29. Environmental Problems with Geothermal Energy
the most common environmental hazard is the emission of H2S
some of the surrounding land may subside (sink)

30. Geothermal Energy From Hot, Dry Rock
conventional use relies on groundwater
limited geographically
can fracture hot, dry rock and circulate water into the area to make an artificial underground reservoir
very expensive

31. Geothermal Heat Pumps (GHPs)
use the difference in temperature between the Earth’s surface and subsurface at depths from 1 m to about 100 m
installation can be expensive, but operating costs are low
VERY efficient (best heating systems available)