The amount of energy that reaches the the Earth provides a useful understanding of the energy for the Earth as a system.
This energy goes towards weather , keeping the temperature of the Earth at a suitable level for life, and powers the entire biosphere. Additionally, this solar energy can be used for solar power either with solar thermal power plants or photovoltaic cells.
The Sun is generally considered to produce a constant amount of power although there are small variances in the output energy depending on sunspot cycles with a surface intensity of [math]6. As the Sun's rays spread into space this radiation becomes less and less intense as an inverse square law. As well, the total solar flux - not solar flux per unit area - must be determined.
Then the total solar flux from the Sun is divided by the surface area of a sphere that has a radius equal to the distance from the Earth to the Sun. This accounts for the "spreading" of the solar energy. The expression to determine this value is:. To determine the average amount of solar energy that reaches the Earth, we must consider what the Earth "looks like" to the Sun.
When looking at Earth from the Sun, only one half of the Earth can be seen. In addition to this, the total solar irradiance is the maximum power delivered to a surface assuming that the path of incoming light is perpendicular to that surface. Due to the fact that the Earth is a sphere, only places near the equator come close to this perpendicular angle.
At all other locations on the Earth, incoming sunlight is at some angle. With this decreasing angle, the average solar irradiance decreases as well. This value, which represents the average solar irradiance hitting Earth's outer atmosphere, does not yet account for losses due to reflection and absorption, which is discussed in the following section. Not all of the solar energy that reaches the Earth's atmosphere is absorbed by the Earth. This is due to something known as the Earth's energy budget.
Nocera foresees a time when every home could have its own self-contained system: For instance, photovoltaic panels on the roof could run an electrolyzer in the basement, producing hydrogen to feed a fuel cell that generates power.
All the necessary ingredients already exist, he says: "I can go on Google right now, and I can put that system together. In principle, we know multiple ways of generating electricity from the sun direct photovoltaic, or solar thermal energy used to drive a turbine ; of storing that energy in batteries, by pumping water uphill, or by separating water into hydrogen and oxygen using an electrolyzer ; and of converting that stored energy into electricity when it's needed using fuel cells powered by hydrogen, for example.
Some kinds of solar power are already cost-competitive, at least in some settings, and prices have been moving steadily downward. Like nuclear power, Moniz says, solar is characterized by high initial costs, but very low operating costs.
But one significant advantage solar has over nuclear is "you can do it in smaller bites," rather than needing to build multibillion-dollar plants. Solar energy is a vibrant research topic, attracting scientists interested in many different approaches. For example, MIT researchers Angela Belcher and Paula Hammond are exploring approaches to solar power that would harness the power of biological organisms to create solar devices; Penny Chisholm and Shuguang Zhen are looking into the possibility of directly harnessing the photosynthesis done by plants or single-celled organisms; and various researchers including Vladimir Bulovic, Michael Strano, Tonio Buonassisi, Jeffrey Grossman and Yang Shao-Horn, among others, are working on ways of improving the efficiency or lowering the costs of solar photovoltaic cells.
Still others are pursuing a variety of approaches to solar thermal energy: using the sun's heat to power turbines or to heat homes or water. A significant breakthrough in any of these areas could make solar power an economically viable option for the world's energy needs.
Other researchers are studying ways to make effective solar-power systems using common, inexpensive materials. For example, cadmium telluride is a very promising material for solar cells. But it turns out that tellurium, one of its ingredients, is "rarer than gold," Jaffe says. Tomorrow: There are many sources that can make a contribution to our energy supply, but likely not at a major scale in the near future.
Read part 1: " What can make a dent? More MIT News. If an animal then ate the plants, it would only receive 1, units of energy.
These animals are called primary consumers because they cannot produce their own food. Cows and sheep are examples of primary consumers. If another animal eats the cow or sheep, it would only receive units of energy, since the cow or sheep would lose units as heat. Animals that eat other animals are called secondary consumers. Scientists believe that four or five of these energy transformations are the most possible before the amount of energy transferred is too small to support life.
University of Illinois Extension. Energy and Ecosystems - Use Some Lose Some Life on Earth is possible because energy flows one way through ecosystems, while matter cycles endlessly.
0コメント