Environmental Engineering Reference
In-Depth Information
Energy
Energy
Water
Water
Long-term sustainability
Materials
Materials
Environment
Environment
Figure 15.1
The four cornerstones of sustainability.
essential foundation to produce food and necessary goods. As population grows and some
countries become more industrialized, the demand for energy, water, and resources will inten-
sify and the environment will suffer the consequences of the additional pressure.
Energy
Energy is at the top of the list because energy is essential to keep society running and vital for
food production from the agricultural stage to consumption. Moreover, if inexpensive and
low-environmental-impact energy becomes available, many of the other problems can be
eased to a great extent. Inexpensive and abundant energy will allow water purification, mate-
rials' recovery, and reduction of environmental impact. On the contrary, the main sources of
energy counted on today are nonrenewable, have a high environmental impact, and are declin-
ing. Current alternative renewable energies can complement nonrenewable fossil fuel-derived
energy, but the alternatives still do not have the full potential to substitute them.
On energy production, one issue seen in Chapter 11, is the energy return on the investment
(EROI), which represents how many units of energy need to be invested to get a unit of energy
back. Petroleum-derived gasoline had an EROI of 100 in the 1930s, meaning that for every unit
of energy invested, 100 were gotten back. Today gasoline is between 11 and 18:1, coal 8:1,
nuclear 5:1, wind 18:1, hydroelectric 12:1, and solar 8:1. Biofuels, on the other hand, barely
break even.
A second problem is the economic break-even point, which indicates at what point of running
the project the investor will start making a profit. And this is one of the shortcomings of solar
energy. With the current photovoltaic solar technology, which tops out at an efficiency of around
15 percent, it takes a long time into the life of the project to get a return on the investment.
A third issue is land surface to produce renewable energy. Biomass, the raw material fore-
seen as the alternative to petroleum-based products, needs large surfaces to grow because of the
low conversion of solar energy into carbohydrates, which is intrinsic to plants. Firewood, for
instance, has an EROI around 30:1, which is high when compared to other sources; needs
