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Physics LibreTexts

11.21 Cosmic Energy Sources

The main source of energy for the Earth is ultimately the Sun. Solar energy is captured by living organisms and then locked away in their remains, which under the right geological conditions are transformed into coal and petroleum. Industrial civilization was built on this fossilized solar energy, and it's so important to world economics that today, a region's standard of living is correlated with its rate of fossil fuel consumption. While it took about 300 million years to form the fossil fuel reserves in the Earth, we have burned through a significant fraction of them in the mere century since the Industrial Revolution. These are non-renewable resources, and in time we will exhaust the Earth's fossil fuel reserves. One of today's largest challenges is developing effective ways to use alternative sources of energy. The primary alternative energy sources are: solar power, wind power, nuclear power, and geothermal power. The obstacles to renewable energy sources are mostly economic, not technical. In a global economy run on cheap oil and gas, the barriers to entry into the market are high, and new energy sources need economies of scale to be affordable. Awareness of the downsides of a fossil fuel economy — global warming, pollution, and environmental degradation, to name just a few ‐ are at an all-time high, so hopefully we are turning the corner towards a more sustainable future.

Like fossil fuels, nuclear energy produced through fission reactions utilize a limited fuel supply, although vast reserves still remain. Most nuclear reactors are powered with Uranium, either Uranium-235 or Uranium-238, as well as Plutonium and Thorium in some cases. One of the great problems with nuclear energy is that it produces dangerous, radioactive by-products that last for millions of year. Finding a way to safely store these waste products across the millennia is proving to be a challenge. In the U.S., a site at Yucca Mountain, Nevada, has been identified for construction of such a waste facility, by 2011 it was closed for political reasons and radioactive waste is in many cases piling up at reactors around the nation. These barrels of nuclear garbage could wreak health havoc if they escaped into the environment, either by accident or by terrorism. Currently there are over 430 commercial nuclear reactors operating in 30 countries and generating 10% of the world's electricity. Despite the problems associated with radioactive waste, nuclear energy generating capacity is expected to double by 2035.

The clean form of nuclear energy is fusion, which has no little or no radioactive byproducts. The United States spend half a billion dollars a year on fusion research but no commercial fusion reactor is within sight. The technical challenges of containing a plasma at millions of degrees and extracting the energy efficiently are formidable. Fusion is the ultimate cosmic energy source. The Sun and all stars generate energy by fusion. The efficiency of fusion (and fission) — which rearrange the atomic nuclei — is ten million times better than chemical energy — which rearranges the electrons shared by atoms. Fusion would not only address some of the world's energy problems, it would provide a means for one day traveling to the stars.

The Sun provides every square meter on the Earth's day side with 1.37 kilowatts, so solar energy is a robust alternative to fossil fuels and nuclear energy. The idea of using the Sun's energy in a passive way, for example to heat water or the inside of a house, has been around since the ancient Greeks. An example of large-scale modern solar technology is the power station Solar Two in California. It uses 2,000 mirrors to focus sunlight on a central collector, which stores the Sun's energy using molten salt. This is used to produce steam, which drives large turbines that generate 10,000 kilowatts of electricity. Although it is no longer in operation, Solar Two demonstrated that large-scale solar power collection and storage is feasible. Today, new facilities have taken it's place, with the Big Dish"" in Canberra, Australia supplying multi-megawatts of power. While these solar collecting devises demonstrate the commercial viability of solar power, most people still think of solar panels when they think of solar power. At the end of 2014, roughly 170 gigawatts of power was being provided by solar panels around the world, double the total in 2010. While only 40-45% efficient (meaning the only collect 40-45% of the energy hitting them) solar panels cost $4-5 per Watt installed, and for remote cabins, it can be more cost effective to install a solar energy system than to run electricity to a new location. For people in homes already ""on the grid,"" a solar system represents a large initial investment, but after 7-8 years (depending on the local cost of power), the solar panels will have paid for themselves, and will start saving home owners money. Solar power is now heading to under $1 per Watt, with all costs included, at which point it is highly competitive with other energy sources.

Wind also provides a way to tap into the Sun's power. In this case, sunlight, in combination with the Earth's rotation, generates winds. These winds can intern rotate turbines that use magnets and the principle of inductance to generate electricity. Windmills have been used since ancient times to take advantage of naturally occurring windy weather in areas like the Netherlands. Today, wind farms are cropping up all across the United States and the world, with some homes and businesses building windmills for personal energy collection. At the end of 2014, it was estimated that 370 gigawatts of power was being generated via wind power, an amount that has doubled since 2010. While cost effective and efficient, wind power still has problems: many people consider windmills unsightly and there are some environmental impacts, with migrating birds dying on contact with the windmills' blades.

Geothermal energy, which taps into heat from the interior of the Earth is also in use, particularly in areas with significant volcanic activity (like Iceland). The Earth is heated internally by the decay of naturally-occurring radioactive elements and from the residual heat of its formation. These heat can be used to create steam and turn turbines, or simply to heat water for home heating. Worldwide, geothermal facilities generated about 50 gigawatts of power in 2014.

Perhaps the best technology on the horizon for widespread use is the fuel cell. A fuel cell can extract energy from the most abundant cosmic fuel of all: hydrogen. The only byproduct of hydrogen fuel cells is water. Fuel cells are safe and clean, and they have the potential to help us break out of our hundred-year-long love affair (or some would say self-destructive, addictive relationship) with the internal combustion engine and its dependence on fossil fuels. The problem with fuel cells is they are heavy and it takes significant energy to generate their hydrogen fuel. Fuel cells were developed in a crude form by Welsh physicist William Grove in 1838, but it took a century for a 5 kilowatt prototype to be built, by English engineer Francis Bacon in 1939. NASA has used fuel cells for power in space probes and satellites. The fuel cell market is still modest, but power gneration should reach 50 gigawatts by 2020.

With no ideal power source in existence, individuals and governments have to make careful decisions about energy generation. While it is clear that we need to transition away from fossil fuels, the necessary start-up costs to transition away from our existing power plants provides a powerful disincentive. If we want to change how we generate energy, it is going to cost money now to save our industrial future. To end on a cosmic note, the ultimate source of nuclear energy in stars is gravity. Perhaps one day we will learn to harness gravity in a way that makes our current mechanisms for extracting energy seem primitive.

", Australia supplying multi-megawatts of power.

 

While these solar collecting devises demonstrate the commercial viability of solar power, most people still think of solar panels when they think of solar power. At the end of 2009, it was estimated that roughly 21-gigawatts of power was being provided by solar panels around the world, including such commercial units as the Serpa Solar Power Plant in Portugal, which delivers and estimated 11 Megawatts of power. While only 40-45% efficient (meaning the only collect 40-45% of the energy hitting them) solar panels costs $10-$12 per watt installed, and for remote cabins," it can be more cost effective to install a solar energy system then to run electricity to a new location. For people living in homes already ""on the grid"," a solar system represents a large initial investment, but after 7-8 years (depending on the local cost of power), the solar panels will have paid for themselves, and will start saving home owners money.

Wind also provides a way to tap into the Sun's power. In this case, Sunlight, in combination with the Earth's rotation, generates winds. These winds can intern rotate turbines that use magnets and the principle of inductance to generate electricity. Windmills have been used since ancient times to take advantage of naturally occurring windy weather in areas like the Netherlands. Today, wind farms are cropping up all across the United States and the world, with some homes and businesses building windmills for personal energy collection. At the end of 2009, it was estimated that 159.2 gigawatts of power was being generated via wind power. While cost effective and efficient, wind power still has problems: Many people consider windmills unsightly and there are environmental impacts, with migrating birds dyeing on contact with the windmills' blades.

Geothermal energy, which taps into heat from the interior of the Earth is also in use, particularly in areas with significant volcanic activity (like Iceland). The Earth is heated internally by the decay of naturally-occurring radioactive elements and from the residual heat of its formation. These heat can be used to create steam and turn turbines, or simply to heat water for home heating.

Perhaps the best technology on the horizon for widespread use is the fuel cell. A fuel cell can extract energy from the most abundant cosmic fuel of all: hydrogen. The only byproduct of hydrogen fuel cells is water. Fuel cells are safe and clean, and they have the potential to help us break out of our hundred-year-long love affair (or some would say self-destructive, addictive relationship) with the internal combustion engine and its dependence on fossil fuels. The problem with fuel cells is they are heavy and it takes significant energy to generate their hydrogen fuel.

With no ideal power source in existence, individuals and governments have to make careful decisions about energy generation. While it is clear that we need to transition away from fossil fuels, the necessary start up costs to transition away from our existing power plants provides a powerful disincentive. If we want to change how we generate energy, it is going to cost money now to save our industrial future.