Solar energy

INTRODUCTION

Solar energy is an inexhaustible resource. The sun produces vast amounts of renewable solar energy that can be collected and converted into heat and electricity.

Texas, due to its large size and abundant sunshine, has the largest solar energy resources among the states. Several other states, however, lead the nation in terms of using solar energy, mostly due to state policies and incentives that encourage the installation of solar energy systems.

California is the nation’s largest solar energy market by far, and has effective state initiatives

promoting the industry. Other states with notable markets for solar energy include New Jersey, Arizona,Colorado and New York.

Solar energy

Solar energy means using the energy of sunlight to provide electricity, to heat water, and to heat or cool homes, business or industry. Sunlight is a clean, renewable source of energy. It is a sustainable resource, meaning it doesn’t run out, the supplied can be maintained. Coal or gases are not sustainable. Once they are gone, there is none left. Solar, wind, geometrical steam, hydro-electricity and others. It is sometimes called ‘Green Power’.

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How does solar work?

Photovoltaic solar cells dirtectly convert sun light in to electricity. The simplest cells are used to operate wristwatches and calculater, an d more complicated systems are used to light houses. PV cells are combined into molecules called arrays, and the number of arrays used determines the amount of electricity produced. For example, a large number of arrays would be needed to generated electricity for a power plant. A power plant can also use a concentrating solar power system where sunlight is focused with mirror to create a intensity heat source to produce steam or mechanical power to run a generator to creates electricity.

Solar water heating systemshave two main parts: a solar collector and a storage tank. Generally, the collector is a thin, flat, rectangular box with a transparent cover mounted on the roof, facing the sun. The sun heats anabsorber platein the collector, and this heats the water running through tubes inside the collector. The heated water is pumped or moved by gravity into the storage tank. Solar water heaters can use about two thirds less energy than those of other methods.

The Process

Sun shining on solar panels produces direct current electricity, or DC, the only kind of power stored in batteries. Often this is 12 volt DC, the standard used in cars and RVs. Larger systems may be designed for 24 volt DC, or sometimes 48 volt DC. This just means combining the same solar panels in pairs for 24 volt, or groups of four to get 48 volt. Windmills and micro-hydro generators in this catalog also produce DC for charging batteries.

This DC power is stored in deep cycle lead-acid batteries, which give back the electricity as needed, even when no power is being produced. Like a bank account, power put into batteries over a period of time can be taken out more quickly if a lot is needed. Like a bank account you cannot take out more than you put in, or the account will be depleted. Moreover, lead-acid batteries need to be frequently 100% fully charged to remain in good condition. They should never be drawn completely down to empty. Because of these needs, to get the most years from your batteries requires some supervision by the owner.

The inverter is a major component that converts the 12, 24, or 48 volt DC current from the battery into 120 volt AC current, the same as utility power for standard household lights, outlets, and appliances. Most solar homes use primarily 120 volt AC produced by the inverter. A few DC circuits are usually added where using DC can save a lot of energy.

If there are a number of consecutive days without sunshine, the owner, being aware of the weather, checks his batteries. If the charge level is low, an engine driven generator may be started to recharge the batteries in order to keep the whole system working. A battery charger plugs into 120 volt AC from the generator producing low voltage DC to charge the battery. The generator is shut down after the batteries have been recharged. This process is automated in some power systems. Battery chargers in Recreational Vehicles are called converters).

History

Humans have harnessed the power of the sun for millennia. In the fifth century B.C., the Greeks

took advantage of passive solar energy by designing their homes to capture the sun’s heat during

the winter. Later, the Romans improved on solar architecture by covering south-facing windows with clear materials such as mica or glass, preventing the escape of solar heat captured during the day.

In the late 19th century, inventors and entrepreneurs in Europe and the U.S. developed solar energy technology that would form the basis of modern designs. Among the best known of these inventors are August Mouchet and William Adams. Mouchet constructed the fi rst solar-powered steam engine.7

William Adams used mirrors and the sun to power a steam engine, a technology now used in solar power towers. He also discovered that the element selenium produces electricity when exposed to light.

In the last 20 years, solar energy has made further inroads and now is used extensively in off -grid and remote power applications such as data monitoring  and communications, well pumping and rural power supply, and in small-scale applications such as calculators and wristwatches. But solar energy has not yet achieved its potential to become a major contributor to world electrical grids. 

Passive solar heating

Some buildings are designed forpassive solar heating, and do not need a solar collector. Basically, passive solar heating is when opportunities are made for the sun to shine into the building to warm it up. The walls and floors are made with materials that absorb and store the sun’s heat, and they heat up during the day and release the heat at night. This is called direct gain. In cold places in the northern hemisphere big windows are put in the south side of the building, letting in much sunlight. The inside of the buildings are therefore well lit, further reducing use of electricity. Heating bills can be half the size of those for a building requiring electrical or other heating. Building designs make sure that the longest walls run east to west, to allow more sunlight to enter in winter than in summer, with shades and overhangs to reduce summer heat.

Solar Cookers

Solar cookers can cook just about any food that a conventional oven can. A basic cooker is an insulated box with a glass top. Heat from concentrated sunlight gets trapped in the box and can be used to heat food placed in the box.

What is solar energy?

Solar is a radiant that is produced by the sun. Every day the sun radiates or sends out, an enormous amount of energy. The sun radiates more energy in one second then people have used since the beginning of time!

During nucleus fusion the sun is extremely high pressure and temperature cause hydrogen atoms to come apart and their nuclei (the central cores of the atoms) to fuse or combine. For hydrogen nucleus fuse to become one helium atom contains less mass than four hydrogen atoms that fused. Some matter is loosed during nuclear fusion. The lost matter is emitted into space as radiant energy. 

It takes million of years of the energy in the sun’s core to make its way to the solar surface and then just a little over eight minutes to travel the 93 million miles to earth. The solar energy travels to the earth at a speed of 186,000 miles per second, the speed of light.

Solar Electricity

Solar energy technology is used on both small and large scales to produce electricity.

A unique advantage of small-scale solar energy systems is that, if they include storage devices,

They may eliminate the need to connect to the electric grid. PV systems power road maintenance

And railroad warning signs, flashing school zone lights, area lighting and other devices without expensive power lines or batteries. Off shore oil rigs, navigational aids, water pumps, telecommunication equipment, remote weather stations and data logging equipment also benefit from PV power.16 In 2005, small-scale, off -grid PV-powered devices accounted for about 15 percent of PV capacity installed worldwide.17 In the same year, most installed PV systems — 59 percent — provided electricity to homes and buildings connected to the electrical grid.18 The remaining PV systems were installed for use in remote off -grid homes and buildings in industrialized countries and the developing world.

Solar Heating

Solar systems that heat water for homes and businesses, and passive solar design for buildings of all sizes, both have the same effect on the electric grid as conservation. They do not generate electricity per sec, but reduce the demand for electricity and natural gas.

Uses

Solar energy has many uses. It can be used to provide heat, light or to generate electricity. Passive solar energy refers to the collection of heat and light; passive solar design, for instance, uses the sun’s energy to make homes and buildings more energy-effi cient by eliminating the need for daytime lighting and reducing the amount of energy needed for heating and cooling. Active solar energy refers to storing and converting this energy for other uses, either as photovoltaic (PV) electricity or thermal energy.

Economic Impact

In 2006, global solar industry revenues were $10.6 billion.21 Texas specific data for solar industry revenues are not available. The IC2 Institute expects the solar industry to create more jobs and contribute billions of dollars in investment and income to the U.S. economy over the next decade, if long term incentives are offered to encourage the solar industry.22 An IC2 study noted that:

…since high-tech manufacturing employment in Texas has yet to return to

pre-recession levels, the PV manufacturing industry creates an opportunity to

generate employment for semiconductor and electric component workers statewide

whose jobs have been outsourced offshore.

The Solar Energy Industries Association (SEIA) estimates that “every megawatt of solar power

currently supports 32 jobs, with 8 of these jobs in system design, distribution, installation and service created where the systems are installed. As utilities begin to charge higher rates for peak load periods, PV systems that generate the most electricity during the hottest time of the day can produce substantial savings on energy costs.

Production

Sunlight can be converted into heat and electricity in a number of ways. A variety of solar technologies are in production, and many companies and researchers are pursuing efforts to develop devices that convert the sun’s energy more efficiently.

Photovoltaic Energy

Photovoltaic cells (PV) are used worldwide to convert sunlight into electricity. The PV cell contains two layers of semiconducting material, one with a positive charge and the other with a negative charge. When sunlight strikes the cell, some photons are absorbed by semiconductor

atoms, freeing electrons that travel from the negative layer of the cell back to the positive layer, in the process creating a voltage. The flow of electrons through an external circuit produces electricity. Since individual photovoltaic cells produce little power and voltage — they generate only about one to two watts per cell—they are connected together electrically in series in a weatherproof module. To generate even more power and voltage, modules can be connected to one another to form a solar panel; solar panels are grouped to form an array. The ability to add additional modules as needed is a significant advantage of PV systems.

Solar Thermal Energy

Solar thermal energy refers to technologies that use the sun’s energy to heat water and other heat transfer fluids for a variety of residential, industrial and utility applications. Simple and widely

used applications of solar thermal energy include solar water heating, swimming pool heating and agricultural drying. In the U.S., solar pool, water and space heating are currently the major applications of thermal energy. Flat-plate collectors — large, insulated metal boxes with glass or plastic covers and dark heat absorbing plates — are the most common collectors used for home solar water and space heating. Other common varieties are evacuated-tube collectors and integral collector storage systems. All three types gather the sun’s energy, transform it to heat and then transfer that heat to water, a heat-transfer fluid or air. Flat plate collectors typically are mounted on the roof. Evacuated-tube collectors are sometimes used to heat water, but also have useful commercial and Industrial applications where higher temperatures are required. The most powerful large-scale solar thermal technology, however, is concentrating solar power

(CSP). While CSP can be PV-based, it generally refers to three solar thermal systems—parabolic

troughs, solar dish/engines and power towers— each of which is in use or under development

today. These systems use mirrors or reflectors to focus sunlight to heat a fluid and make steam,

which then is used to generate electricity. At present, only parabolic troughCSP systems are

in commercial use in the U.S., with three installations in three states capable of generating 419 MW of electricity in all.45 Trough systems consist of a linear, parabolic-shaped reflector that focuses the sun’s energy on a receiver pipe, heating a transfer fluid flowing through the pipe; the transfer fluid then generates superheated steam which is fed to a turbine and electric generator to produce electricity. The troughs track the sun from East to West during the day so that the sun is continuously focused on the receiver pipes.[3]

Transmission

Solar energy diff ers from most energy technologies in that it can be generated on site, reducing or eliminating fuel transportation and electricity transmission and distribution costs. Solar water heating and space heating devices are “stand-alone” systems that are not connected tothe electric grid. A PV system provides electric power directly to a user and can be used either as

a “stand-alone” power source or connected to the electricity grid. Systems offering this flexibility sometimes are called distributed power generators. By contrast, utility-scale concentrating solar power plants use centralized power plants and transmission lines to distribute electricity to customers. In 2005, off -grid PV systems accounted for about 18 percent of all PV installed worldwide.50 Homes in remote areas can use PV systems for lighting, home appliances and other electrical needs, saving the cost of extending power lines to a remote location. These systems require a storage device to store power generated during the day for nighttime use; typically, this is a lead-acid battery bank. Unlike gasoline-powered generators, PV systems do not require fuel deliveries and are clean and quiet to operate.

Net Metering

Net metering standards allow owners of qualifying solar energy systems to be compensated for the value of electric energy they produce; they have been proven to promote solar energy systems. The IC2 Institute report that examined opportunities for the development of the Texas PV industry recommended the adoption of retail net metering in the state. Retail net metering credits customers at the utility’s full retail rate for each kWh generated rather than at the utility’s avoided-cost rate, which is lower.

COSTS AND BENEFITS

Both thermal and PV solar systems can produce electricity at significantly lower costs today than

In the U.S., 2006 retail electricity prices for all sectors averaged more than eight cents per kWh, and for residential electricity, the price averaged about 10 cents per kWh.76 By contrast, parabolic troughstyle CSP systems generated electricity at a cost of 12 cents per kWh in 2006, while PV systems generated electricity for about 18 to 23 cents per kWh.77 The retail price of electricity during peak hours, however, can rise to between 25 and 40 cents per kWh in some parts of the U.S., making PV systems more competitive during peak periods.78 PV systems usually generate more electricity during the hottest time of the day, and thus can help to offset the need to add expensive electric generating capacity to satisfy peak demand in warm areas of the country. PV costs per kWh declined significantly over the last 16 years (from more than 45 cents per kWh in 1990 to about 23 cents per kWh in 2006), due primarily to manufacturing economies of scale as well as improved solar cell efficiency.79 The Solar Energy Industries Association (SEIA) notes that “each doubling in cumulative manufacturing has brought prices down by about 18 percent.”80 In the past five years alone, the world PV industry has grown by an average of 30 percent or more each year. In 2006, the U.S. PV industry expanded by 33 percent, compared to 19 percent for the world.81 The expansion of federal income tax credits for commercial and residential solar energy projects, and state and utility incentives, particularly in California, fueled the U.S. industry’s impressive growth in 2006. These federal tax credits, however, are set to expire at the end of 2008, and were not extended by Congress in 2007. A shortage of silicon and growing global demand for solar PV modules led to some cost increases in 2006 and 2007.82 About 90 percent of PV modules today still are made of crystalline silicon (polysilicon), which has been in short supply globally, constraining production and temporarily increasing the cost of solar cells.83 Polysilicon supplies are expected to remain tight and prices high until new plants under construction are completed.84 Solarbuzz, an international solar energy consulting fi rm, predicts rapid growth in polysilicon capacity through 2011, and a resumption of faster rates of growth for the PV market.85 Unprecedented investment in manufacturing capacity is expected to result in lower PV costs over the long term. The cost of solar modules accounts for 50 to 60 percent of the total installed cost of a PV system, with other system parts, materials, assembly and installation accounting for the remainder.86 PV module costs have declined by about 80 percent over the last decade, but the installation costs have not dropped appreciably in recent years.87 Installation costs vary depending on available sunlight, the typical energy usage of the home and the availability of experienced installers in the area. Unlike other energy sources, however, 90 percent of the cost of a PV system is incurred up front.88 once the system is installed, there are no fuel costs and the system requires little maintenance.