The energy output from a hydro-electric dam is substantial enough to result in most of America's major rivers being damned. The more pressing issues that these damns cause are changes to the aquatic ecosystem and restriction of movement for migratory fish species. 

While there are federal wetland conservation laws geared at protecting aquatic habitat, there is currently no federal ban on constructing hydroelectric dams, and the returned energy investment for hydroelectric is quite substantial. The dominant issue with expanding hydroelectric energy production is that in the U.S., we have dammed most if not all of the significant energy-producing water bodies. Further expansion of hydroelectric power will not yield as much energy as the current dams operating in the U.S.

Wattage is a measurement of electricity being generated over time. When compared to the 5,000 watt output of a conventional generator, a single solar panel generating watts cannot generate the same rate of electrical output. As a result, we will need multiple panels to generate an equal amount of electrical output. We can use dimensional analysis to determine how many panels we would need:

This calculation tells us that Charlie will need 25 standard solar panels to generate the same amount of electricity as one gasoline generator.

The correct response is photovoltaic cells. These photovoltaic cells are the reason we can capture and use sunlight to power our homes and cars. Technological advances in photovoltaic cells have made solar energy economically viable over the past decade. Eukaryotic cells are a type of living organisms, while thermal and radiation cells are made-up terms.

Ethanol can be made from cellulosic—or woody—plants such as switchgrass, poplars, and willows. Cellulose, or plant tissue, sequesters a huge amount of carbon and contains a great deal more energy per unit than corn. Scientists believe that within the next two decades, research will have figured out how to quickly and efficiently break down plant tissue for fermentation into fuel.

Biodiesel made from corn is environmentally safe to burn; however, it requires a great deal of water and resources to grow and harvest.

Agricultural wastes can have a negative impact on air quality due to the pollutants they generate when burned, such as sulfur oxide, nitrogen oxide, and carbon monoxide. 

Hydrogen is very challenging to transport and it requires a large energy investment to produce it. While hydrogen has a low energy density by volume, it actually has a very high energy density by weight. This has to do with the fact that hydrogen, discussed in this context, is a gas.

Geothermal activity has proven to be a cheap, low-cost and environmentally friendly energy source for communities located in areas with high geothermal activity, particularly where the earth's crust is rather thin (e.g. Iceland); however, this method of harvesting energy is not very economically feasible or possible in areas with little near-surface geothermal activity.

Synfuel is derived from waste plastic, coal, natural gas and other non-petroleum sources. It is a liquid fuel and the process of deriving synfuel can produce gasoline, diesel, and kerosene.