Renewable resources of energy : solar energy

Solar energy is the most readily available and free source of energy since prehistoric times. It is estimated that solar energy equivalent to over 15,000 times the world's annual commercial energy consumption reaches the earth every year.
India receives solar energy in the region of 5 to 7 kWh/m2 for 300 to 330 days in a year. This energy is sufficient to set up 20 MW solar power plant per square kilometre land area.
Solar energy can be utilised through two different routes, as solar thermal route and solar electric (solar photovoltaic) routes. Solar thermal route uses the sun's heat to produce hot water or air, cook food, drying materials etc.
Solar photovoltaic uses sun’s heat to produce electricity for lighting home and building, running motors, pumps, electric appliances, and lighting.

advantages of solar energy

Here are some examples of what it has over oil, the world's current number one energy source:

•Solar energy is a renewable resource. Although it cannot be utilized at night or on cloudy days, its availability may be generally relied upon day after day. The solar energy supply will last as long as the sun.

•Oil, on the other hand, is not renewable. It takes millions of years to form. Currently, oil reserves are being depleted at a rate much quicker than more would take to develop.

•Solar energy is non-polluting. Of all the advantages of solar energy over oil, this is perhaps the most important. The burning of oil releases carbon dioxide and other greenhouse gases into the air. In addition to this, the process of obtaining it may result in damaged ecosystems through dredging or spills.

•Solar cells are long-lasting and require very little maintenance

• Although solar panels and their accessories (solar lights, etc.) may be expensive to buy at the onset, money is saved in the long run. This is because energy from the sun is widely available and free. Today rising oil prices are a major frustration on many government as well as individual levels.

•Solar powered lights and other solar powered products are very easy to install. This is because there are few wiring issues and little need to ever dig supporting trenches.

The many advantages of solar energy range from benefiting your pocketbook to benefiting the environment. In contrast, few features could be considered disadvantages. These include the current costliness of solar cells, as well as the fact that solar power cannot be created at night or on darkened days (though it can be stored during brighter times.)

Still, the advantages of solar energy far outweigh the disadvantages. In addition to this, the disadvantages are sure to be overcome as technology improves.

applications of solar energy

1) solar water heater

Most solar water heating systems have two main parts: a solar collector and a storage tank. The most common collector is called a flat-plate collector (see Figure 12.1). It consists of a thin, flat, rectangular box with a transparent cover that faces the sun, mounted on the roof of building or home. Small tubes run through the box and carry the fluid – either water or other fluid, such as an antifreeze solution – to be heated. The tubes are attached to an absorber plate, which is painted with special coatings to absorb the heat. The heat builds up in the collector, which is passed to the fluid passing through the tubes. An insulated storage tank holds the hot water. It is similar to water heater, but larger is size. In case of systems that use fluids, heat is passed from hot fluid to the water stored in the tank through a coil of tubes. Solar water heating systems can be either active or passive systems. The active system, which are most common, rely on pumps to move the liquid between the collector and the storage tank. The passive systems rely on gravity and the tendency for water to naturally circulate as it is heated. A few industrial application of solar water heaters are listed below:  Dairies: Ghee (clarified butter) production, cleaning and sterilizing, pasteurization.
 Textiles: Bleaching, boiling, printing, dyeing, curing, ageing and finishing.
 Breweries & Distilleries: Bottle washing, wort preparation, boiler feed heating.
 Chemical /Bulk drugs units: Fermentation of mixes, boiler feed applications.
 Electroplating/galvanizing units: Heating of plating baths, cleaning, degreasing applications.
 Pulp and paper industries: Boiler feed applications, soaking of pulp.

2) solar cooker

Solar cooker is a device, which uses solar energy for cooking, and thus saving fossil fuels, fuel wood and electrical energy to a large extent. However, it can only supplement the cooking fuel, and not replace it totally.
It is a simple cooking unit, ideal for domestic cooking during most of the year except during the monsoon season, cloudy days and winter months.
Types of solar cookers :
1) Parabolic concentrating solar cooker :
A parabolic solar concentrator comprises of sturdy Fibre Reinforced
Plastic (FRP) shell lined with Stainless Steel (SS) reflector foil or
aluminised polyester film. It can accommodate a cooking vessel at its
focal point. This cooker is designed to direct the solar heat to a
secondary reflector inside the kitchen, which focuses the heat to the
bottom of a cooking pot. It is also possible to actually fry, bake and
roast food. This system generates 500 kg of steam, which is enough to
cook two meals for 500 people (see Figure 12.3). This cooker costs
upward of Rs.50,000. Positioning of solar panels or collectors can
greatly influence the system output, efficiency and payback. Tilting
mechanisms provided to the collectors need to be adjusted according to
seasons (summer and winter) to maximise the collector efficiency.
The period four to five hours in late morning and early afternoon
(between 9 am to 3pm) is commonly called the "Solar Window". During
this time, 80% of the total collectable energy for the day falls on a solar
collector. Therefore, the collector should be free from shade during this
solar window throughout the year - Shading, may arise from buildings or
trees to the south of the location.


2)Box type solar cookers:
The box type solar cookers with a single
reflecting mirror are the most popular in India. These cookers have
proved immensely popular in rural areas where women spend
considerable time for collecting firewood. A family size solar cooker is
sufficient for 4 to 5 members and saves about 3 to 4 cylinders of LPG
every year. The life of this cooker is upto 15 years. This cooker costs
around Rs.1000 after allowing for subsidy. Solar cookers.

3)solar electricity generation

Solar Photovoltaic (PV):
Photovoltaic is the technical term for solar electric. Photo means "light" and voltaic means "electric". PV cells are usually made of silicon, an element that naturally releases electrons when exposed to light. Amount of electrons released from silicon cells depend upon intensity of light incident on it. The silicon cell is covered with a grid of metal that directs the
electrons to flow in a path to create an electric current. FigurSome applications for PV systems are lighting for commercial buildings, outdoor (street) lighting (see Figure 12.5), rural and village lighting etc. Solar electric power systems can offer independence from the utility grid and offer
protection during extended power failures. Solar PV systems are found to be economical especially in the hilly and far flung areas where conventional grid power supply will be expensive to reach.
PV tracking systems is an alternative to the fixed, stationary PV panels. PV tracking systems are mounted and provided with tracking mechanisms to follow the sun as it moves through the sky. These tracking systems run entirely on their own power and can increase output by 40%.
Back-up systems are necessary since PV systems only generate electricity when the sun is shining. The two most common methods of backing up solar electric systems are connecting the system to the utility grid or storing excess electricity in batteries for use at night or on cloudy days.
Performance :
The performance of a solar cell is measured in terms of its efficiency at converting sunlight into electricity. Only sunlight of certain energy will work efficiently to create electricity, and much of it is reflected or absorbed by the material that make up the cell. Because of this, a typical commercial solar cell has an efficiency of 15%—only about one-sixth of the sunlight striking the cell generates electricity. Low efficiencies mean that larger arrays are needed, and higher investment costs. It should be noted that the first solar cells, built in the 1950s, had efficiencies of less than 4%.
Uses :
Solar Water Pumps :
In solar water pumping system, the pump is driven by motor run by solar
electricity instead of conventional electricity drawn from utility grid. A SPV
water pumping system consists of a photovoltaic array mounted on a stand
and a motor-pump set compatible with the photovoltaic array. It converts the
solar energy into electricity, which is used for running the motor pump set.
The pumping system draws water from the open well, bore well, stream,
pond, canal etc.

4)solar vehicles

development of a solar powered car has been an engineering goal since the 1980s. The World Solar Challenge is a biannual solar-powered car race, where teams from universities and enterprises compete over 3,021 kilometres (1,877 miles) across central Australia from Darwin to Adelaide. In 1987, when it was founded, the winner's average speed was 67 kilometres per hour (42 mph) and by 2007 the winner's average speed had improved to 90.87 kilometres per hour (56.46 mph). The North American Solar Challenge and the planned South African Solar Challenge are comparable competitions that reflect an international interest in the engineering and development of solar powered vehicles
Helios UAV in solar powered flight
In 1974, the unmanned Sunrise II plane made the first solar flight. On 29 April 1979, the Solar Riser made the first flight in a solar powered, fully controlled, man carrying flying machine, reaching an altitude of 40 feet (12 m). In 1980, the Gossamer Penguin made the first piloted flights powered solely by photovoltaics. This was quickly followed by the Solar Challenger which crossed the English Channel in July 1981. In 1990 Eric Raymond in 21 hops flew from California to North Carolina using solar power. Developments then turned back to unmanned aerial vehicles (UAV) with the Pathfinder (1997) and subsequent designs, culminating in the Helios which set the altitude record for a non-rocket-propelled aircraft at 29,524 metres (96,860 ft) in 2001. The Zephyr, developed by BAE Systems, is the latest in a line of record-breaking solar aircraft, making a 54-hour flight in 2007, and month-long flights are envisioned by 2010.
A solar balloon is a black balloon that is filled with ordinary air. As sunlight shines on the balloon, the air inside is heated and expands causing an upward buoyancy force, much like an artificially-heated hot air balloon. Some solar balloons are large enough for human flight, but usage is generally limited to the toy market as the surface-area to payload-weight ratio is relatively high.