Constance Adams understands that every decision made has an impact. As she designs for off-planet missions or buildings on Earth, she has to consider how best to supply the right amount of energy to her designs. She considers weight-saving materials, low power lighting, using renewable and inexhaustible energy resources, and using passive solar heating to maintain the right temperature for the astronauts. She even looks to use locally available materials to avoid transportation costs. Every decision she makes not only impacts the mission but anyone that may also use those resources. Similarly, as we consider our energy portfolio, we will need to understand what impact our decisions have in our homes, in our community, and across the globe.

Energy Demand
A nation's economy is closely tied to its energy consumption or demand. In general, the larger an economy is, the more energy is consumed per person. Today, the United States is the world's largest consumer of energy. Each year, the United States consumes about 100 quadrillion Btu of energy, or quads for short. That is more than one-fifth of the total energy consumption for the world.

On average, each United States citizen uses more than 300 million Btu annually. It sounds like a lot—and it is—especially if you compare it to the energy consumed by a citizen of Haiti, who uses about one-hundredth that amount. These energy demands come from home heating, transportation, health and nutrition, electricity, and the manufacture and supply of goods.

Energy Supply
Throughout the world, energy demand depends on a variety of limited resources. Most of our energy demand is supplied by oil, natural gas, and coal sources. The remaining is supplied by nuclear, renewable, and inexhaustible sources.

However, oil, gas, and coal are limited resources that are scattered across the world. The uneven distribution of—and world-wide demand for—these resources have made them commodities that can be traded between countries.

In 2006, the world's top oil producer was Russia, which extracted and produced about ten million barrels per day. About half of this oil was exported to other countries. Saudi Arabia extracted and produced just over nine million barrels per day and exported almost all of it—approximately eight million barrels per day.

Energy Dependence
This supply and demand of international goods has connected economies around the world for decades. International trade for energy resources has become increasingly important for countries, like Japan, that do not have large oil reserves but use a lot of it. Like the United States, they depend on other countries for oil.

The United States consumes over 20 million barrels of crude oil every day. Approximately one-third of this amount comes from domestic oil fields located mostly in the Gulf of Mexico, Texas, and Alaska. Because domestic oil extraction and production does not meet all of this demand, they must rely on other countries. Canada provides the United States with one tenth of its oil and most of the remainder comes from Saudi Arabia, Mexico, and Venezuela.

Energy Security
It is critical that a nation manages these resources wisely. Access to a reliable source of energy is called energy security. This supply must not only meet demand, but also be affordable. If the access to energy resources is too small, inconsistent, or expensive, then energy security is jeopardized. Energy security can be further compromised by outside influences, including wars, political conflicts, and even natural disasters. If this happens, there could be drastic effects, like crippling the economy and lowering the standard of living.

Diversifying the Portfolio
Although the United States is today's top consumer of energy, things are changing. Increasing populations and advancing economies, especially those of India and China, will greatly affect the production and consumption of energy resources. It is estimated that by 2030, China and India alone will account for a 45 percent increase in global energy consumption. The predicted increase of coal use in China and oil use in India will affect world markets by reducing the supply for other countries and accelerating the need to move toward alternative energy resources.

Based on all the issues of energy supply, demand, dependence, and security, it is apparent that a diverse energy portfolio is important. Energy sources, such as wind, solar, geothermal, biofuels, hydroelectric, and fuel cells, are all becoming attractive alternatives to fossil fuels. Currently, renewable resources provide around seven percent of the world's present energy demand. Further increasing and diversifying the use of these resources as energy sources will increase energy efficiency to maximize and manage existing resources.