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Humans have been using solar energy for thousands of years. Although the Ancient Greeks and Romans may not have had photovoltaic cells like the ones we use to convert sunlight to energy today, they knew how to use the sun to light their homes and help them grow crops!As early as 400 B.C.E., Greek villages were built with architecture that maximized the amount of sunlight that poured in. Specifically, most houses were arranged so that sunlight could come in and warm things up during the winter months. The arrangement also blocked direct sunlight from entering homes during the summer, which kept the insides of the houses cool.The sun was even more important to the Romans. In fact, one Roman legal code stated that you could not deny someone access to the sun! The Romans also invented window glass, which facilitated the building of the very first greenhouses. As the Roman Empire expanded, fruits and vegetables were brought back to Rome and cultivated within these structures. Servants of the emperor Tiberius, who reigned during the 1st century C.E., even used a greenhouse-like system to ensure that their master could eat his favorite cucumbers every day of the year!

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Humans have been using solar energy for thousands of years. Although the Ancient Greeks and Romans may not have had photovoltaic cells like the ones we use to convert sunlight to energy today, they knew how to use the sun to light their homes and help them grow crops!As early as 400 B.C.E., Greek villages were built with architecture that maximized the amount of sunlight that poured in. Specifically, most houses were arranged so that sunlight could come in and warm things up during the winter months. The arrangement also blocked direct sunlight from entering homes during the summer, which kept the insides of the houses cool.The sun was even more important to the Romans. In fact, one Roman legal code stated that you could not deny someone access to the sun! The Romans also invented window glass, which facilitated the building of the very first greenhouses. As the Roman Empire expanded, fruits and vegetables were brought back to Rome and cultivated within these structures. Servants of the emperor Tiberius, who reigned during the 1st century C.E., even used a greenhouse-like system to ensure that their master could eat his favorite cucumbers every day of the year!

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Solar energy is lauded as an inexhaustible fuel source that is pollution and often noise free. The technology is also versatile. For example, solar cells generate energy for far-out places like satellites in Earth orbit and cabins deep in the Rocky Mountains as easily as they can power downtown buildings and futuristic cars.But solar energy doesn't work at night without a storage device such as a battery, and cloudy weather can make the technology unreliable during the day. Solar technologies are also very expensive and require a lot of land area to collect the sun's energy at rates useful to lots of people.Despite the drawbacks, solar energy use has surged at about 20 percent a year over the past 15 years, thanks to rapidly falling prices and gains in efficiency. Japan, Germany, and the United States are major markets for solar cells. With tax incentives, solar electricity can often pay for itself in five to ten years.

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Solar energy is lauded as an inexhaustible fuel source that is pollution and often noise free. The technology is also versatile. For example, solar cells generate energy for far-out places like satellites in Earth orbit and cabins deep in the Rocky Mountains as easily as they can power downtown buildings and futuristic cars.But solar energy doesn't work at night without a storage device such as a battery, and cloudy weather can make the technology unreliable during the day. Solar technologies are also very expensive and require a lot of land area to collect the sun's energy at rates useful to lots of people.Despite the drawbacks, solar energy use has surged at about 20 percent a year over the past 15 years, thanks to rapidly falling prices and gains in efficiency. Japan, Germany, and the United States are major markets for solar cells. With tax incentives, solar electricity can often pay for itself in five to ten years.

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Molten salt flowing through the receiver is heated to run a generator.

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Molten salt flowing through the receiver is heated to run a generator.

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Another technique uses moveable mirrors to focus the sun's rays on a collector tower, where a receiver sits

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Another technique uses moveable mirrors to focus the sun's rays on a collector tower, where a receiver sits

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The hot oil then boils water for electricity generation.The hot oil then boils water for electricity generation.

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The hot oil then boils water for electricity generation.The hot oil then boils water for electricity generation.

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The hot oil then boils water for electricity generation.The hot oil then boils water for electricity generation.In one technique, long troughs of U-shaped mirrors focus sunlight on a pipe of oil that runs through the middle

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The hot oil then boils water for electricity generation.The hot oil then boils water for electricity generation.In one technique, long troughs of U-shaped mirrors focus sunlight on a pipe of oil that runs through the middle

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As the electrons flow through the cell, they generate electricity.

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As the electrons flow through the cell, they generate electricity.

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When sunlight hits the cells, it knocks electrons loose from their atoms

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When sunlight hits the cells, it knocks electrons loose from their atoms

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The cells are made of semiconductor materials like those found in computer chips

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The cells are made of semiconductor materials like those found in computer chips

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Today, the technology produces less than one tenth of one percent of global energy demand.

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Today, the technology produces less than one tenth of one percent of global energy demand.

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 Solar energy is the technology used to harness the sun's energy and make it useable

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 Solar energy is the technology used to harness the sun's energy and make it useable

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Every hour the sun beams onto Earth more than enough energy to satisfy global energy needs for an entire year

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Every hour the sun beams onto Earth more than enough energy to satisfy global energy needs for an entire year