Solar Energy it is  Energy from the Sun
Solar Energy Can Be Used for Heat and Electricity

1-thermal solar energy can be used to:

• Heat water — for use in homes, buildings, or swimming pools
• Heat spaces — inside homes, greenhouses, and other buildings

2- Solar energy can be converted to electricity.

Solar thermal energy:
There are many applications for the direct use of solar thermal energy, space heating and cooling, water heating, crop drying and solar cooking. It is a technology which is well understood and widely used in many countries throughout the world. Most solar thermal technologies have been in existence in one form or another for centuries and have a well established manufacturing base in most sun-rich developed countries.
The most common use for solar thermal technology is for domestic water heating.

• Solar water heater is widely used globally, but especially in places where there is high solar insulation, for example in Palestine (average energy from the sun (5.4 KWh/m^2-day) .
• More than 90% of installed SWH in West Bank and Gaza are manufactured locally by the Palestinians.
• The flat plate collector efficiency ranges between 30 and 45% depending on manufacturer and production materials.
• The average price of the locally produced SWH units consisting of two flat plate collectors (90 cm 190 cm each) and a 200 litter insulated tank range between 250 $ and 350 $´ depending on quality and manufacturer.

Economic benefit to consumer:

Solar thermal power stations

There are two basic types of solar thermal power station. The first is the 'Power Tower' design which uses thousands of sun-tracking reflectors or heliostats to direct and concentrate solar radiation onto a boiler located atop a tower. The temperature in the boiler rises to 500 - 700EC and the steam raised can be used to drive a turbine, which in turn drives an electricity producing turbine.

The second type is the distributed collector system. This system uses a series of specially designed 'Trough' collectors which have an absorber tube running along their length. Large arrays of these collectors are coupled to provide high temperature water for driving a steam turbine. Such power stations can produce many megawatts (MW) of electricity, but are confined to areas where there is ample solar insulation.

There are other uses of thermal energy such as Solar cooking, Crop drying, Space heating, Space cooling, Day-lighting.

Photovoltaic (Sun light conversion to electricity)

Photovoltaic modules or panels are made of semiconductors that allow sunlight to be converted directly into electricity. These modules can provide you with a safe, reliable, maintenance-free and environmentally friendly source of power for a very long time. Most modules on the market today come with warranties exceeding 20 years, and will perform much longer

How it works:
PV cells convert sunlight directly into electricity without creating any air or water pollution. PV cells are made of at least two layers of semiconductor material. One layer has a positive charge, the other negative. When light enters the cell, some of the photons from the light are absorbed by the semiconductor atoms, freeing electrons from the cell’s negative layer to flow through an external circuit and back into the positive layer. This flow of electrons produces electric current.


Basic solar cell construction:
Individual PV cells are interconnected together in a sealed, weatherproof package called a module. When two modules are wired together in series, their voltage is doubled while the current stays constant. When two modules are wired in parallel, their current is doubled while the voltage stays constant. To achieve the desired voltage and current, modules are wired in series and parallel into what is called a PV array. The flexibility of the modular PV system allows designers to create solar power systems that can meet a wide variety of electrical needs, no matter how large or small.

Photovoltaic cells, modules and arrays

Photovoltaic cells Types:
Single-crystal silicon

• 15% efficient, typically
• Expensive to make (grown as big crystal)

Poly-crystalline silicon

• 10–12% efficient
• Cheaper to make (cast in ingots)

Amorphous silicon (non-crystalline)

• 4–6% efficient
• Cheapest per Watt
• Called “thin film”, easily deposited on a wide range of surface types

Photovoltaic Systems: Benefits and Limitations
Advantages:

• They are safe, clean and quiet to operate, they are highly reliable.
• No maintenance.
• They operate cost-effectively in remote areas and for many residential and commercial applications.
• They are flexible and can be expanded at any time to meet your electrical needs.

Limitations:

• Photovoltaic not well suited for highly energy-intensive uses such as heating or industrial application.
• High capital cost.

Applications of photovoltaic:

• Rural electrification (stand alone) OR Hybrid system
• Peak load reduction
• Water pumping
• Communication stations
• Street lighting

Solar Energy & the Environment

Using solar energy produces no air or water pollution and no greenhouse gases, but does have some indirect impacts on the environment. For example, there are some toxic materials and chemicals, and various solvents and alcohols that are used in the manufacturing process of photovoltaic cells (PV), which convert sunlight into electricity. Small amounts of these waste materials are produced.
In addition, large solar thermal power plants can harm desert ecosystems if not properly managed. Birds and insects can be killed if they fly into a concentrated beam of sunlight, such as that created by a “solar power tower.” Some solar thermal systems use potentially hazardous fluids (to transfer heat) that require proper handling and disposal.

Concentrating solar systems may require water for regular cleaning of the concentrators and receivers and for cooling the turbine-generator. Using water from underground wells may affect the ecosystem in some arid locations.