Solar Energy PDF

Solar Energy Chapter Most energy on Earth begins with the sun. 7 The sun transfers light and heat to the geosphere, atmosphere, hydrosphere, and Big Question biosphere....

Solar Energy Chapter Most energy on Earth begins with the sun. 7 The sun transfers light and heat to the geosphere, atmosphere, hydrosphere, and Big Question biosphere. Unequal heating of land, water, How do people use sunlight as a source and air results in wind energy. Evaporation of energy? keeps the water cycle going, which allows hydroelectric energy to be harnessed. Sunlight captured by the biosphere results in carbon-based foods that provide energy for life, as well as the raw material for fossil fuels. Solar power is the use of sunlight to meet Vocabulary energy needs. A solar cell is a technology solar power, n. the that converts sunlight to electricity. use of sunlight to meet energy needs Multiple solar cells can be assembled solar cell, n. a device into panels, which can heat buildings or that converts sunlight charge batteries. to electricity Each of these shiny panels is a solar cell that converts sunlight into electricity. 37 Solar Energy’s Costs and Benefits Every hour, enough solar energy strikes Earth’s surface to meet humanity’s energy needs for an entire year. With that much renewable energy available, why aren’t Word to Know we using solar energy for everything? One challenge is the problem of solar cells. For How efficient something is refers decades, solar cells, also called photovoltaic to how quickly, cells, were inefficient. They could only easily, and well it does what it is convert about six percent of the energy in intended to do. For sunlight that struck them into electricity. example, if it takes more work and Since then, efficiency has improved to energy to make a about twenty percent. Higher-efficiency solar cell than the energy and benefit cells are made, and they are expensive. it can provide, it is They are mostly used for satellites and not efficient. other big projects. A large solar farm can harness a lot of sunlight and provide a lot of electricity, but what happens when the sky is cloudy or the sun goes down? 38 It doesn't make sense to spend a lot of money on solar cells that can only convert a little energy. But recent improvements and more demand for solar cells have brought costs down. It can still cost thousands of dollars to put enough solar cells on a home to provide electricity. For most people, that is too great an expense. And they do not want to wait years for that investment to pay off in lower electricity bills. There is another challenge to solar power. Different amounts of sunlight strike Earth in different locations and at different times. The sun does not shine in the sky all the time. So, even if a home has solar panels or a town is using a solar farm to provide electricity, there still needs to be battery storage. Batteries capture the electricity for cloudy days and sunless nights. Batteries are costly, too. 39 Indirect Use of Solar Energy Solar energy can also be converted to electricity by another method. This involves reflecting many different rays of sunlight toward a single target that becomes superheated. The target is usually the top of a tall tower in the middle of a field of computer- controlled mirrors. Liquid inside the target becomes heated to generate steam. The steam powers a turbine, which produces electricity in a generator. Hot liquid can be stored in tanks and directed to the boiler later in the day when the sun is low. 40 The heat that is absorbed by sunlit materials can also be used to heat water for use in homes. Some homes are equipped with rooftop water heaters. A pump carries water or some other liquid to the rooftop unit, where it gets warmed by the sun. That liquid is then directed into a tank inside the home. Water in the tank is warmed by the heat from the liquid inside pipes that came from the roof. It is available for use in the kitchen sink, shower, and other places. Some people also use solar ovens to cook food. The oven usually consists of a clear-roofed container that has mirrored walls. The sunlight that enters the container reflects off the walls and strikes the food inside. A solar oven usually cannot achieve the temperatures of an electric, gas, or coal-fired oven. But if enough time is given, it can cook some food very well. And the sunlight is free! This solar thermal energy plant in California uses thousands of mirrors to reflect sunlight at a tower. The top of the tower has molten salt inside. The salt is heated and directed into a boiler, which produces steam that drives a turbine and generator. 41 Passive Solar Energy Another way for people to use solar energy is to design buildings so that sunlight warms them inside. For example, a home that has a large living room that faces the sun can have large windows that allow sunlight in. The floor can be made of dark material that absorbs and retains heat and then slowly releases it throughout the day. When the sunlight is not available, insulating blinds can be drawn to prevent heat from leaving the room. This kind of solar energy use is passive. There are no active pumps, electrical devices, or other sources of energy required. The architect or engineer studies how the sun moves through the sky at the site. They then design a structure that uses materials in the best way to let sunlight in, absorb it, and heat that structure. Such designs can also focus on ways to keep sunlight out or cool the structure down. A solar-heated home in the Northern Hemisphere will have large windows facing south and absorbent flooring that can radiate heat over the course of the day. In summer, the roof blocks the afternoon sunlight from entering the windows and providing heat that the home does not need. 42