time frame movement of ocean waves, while tidal energy
uses the long time frame motion of the ocean tides. Figure
10 shows a wave power generation system and Figure 11
shows a tidal power generation system. Other than the
usual issues from building the wave and tidal power plants,
there is no carbon footprint. However, these facilities
may interfere with coastal activities such as shipping and
recreation. Obviously, these must be located in coastal
areas, so they are not available to most areas of the US.
Hydroelectric energy is derived from large quantities of
water from a dammed up lake or reservoir flowing through
turbines that are used to drive an electric generator. Figure
12 shows a typical hydroelectric power plant. The key
to generating power with water is to have the highest
amount of water above the level of the generators (head)
This electrical power is found using the formula P =
0.63HQe where P = kilowatts of electricity generated, H =
number of feet of water above the generator, Q = gallons
per minute of water flowing through the generator, and e
is the overall efficiency of the turbine and generator system
To generate 10 KW of electrical power with a 10 foot
head of water would require around three gallons per
minute of water (a 100 foot long 1/2 inch garden hose
maximum flow is approximately 6 gpm). An average home
in the US uses 10 KwH per day, so this 10 KW generator
would have to run 24 hours a day/seven days a week.
This would be 4,320 gallons of water per day, or 129,600
gallons per month (last month, my house used 2,600
gallons of city water for two people) which is a lot of water,
but the 10 foot head is beyond most hobbyist’s level (the
creek along my boundary line may have a one foot head).
See Q&A Sidelines for a comparison and more
information on each of these energy types.
I hope I have answered your question regarding
renewable energy sources.
n FIGURE 11. Tidal energy electrical generation system.
n FIGURE 12. Hydroelectric electrical generation system.
Is “Green Energy” Really Green?
Comparison of Renewable Energy Sources
Solar Thermal Energy
Solar Photovoltaic Systems
September 2016 17