Question

1-Solar Energy

Two school students are arguing: one says that you heat water from the sun’s rays to create energy, the other says that you create energy from electronics that the sun’s rays react with. You are asked to provide no more than 500 words (plus additional diagrams) to explain to the school pupils what is the correct answer to their argument.

Answer 1

Both photovoltaic and solar thermal are the two established solar power technologies. Photovoltaics use semi-conductor technology to directly convert sunlight into electricity. Photovoltaics, therefore, only operate when the sun is shining, and must be coupled either with other power generation mechanisms to ensure a constant supply of electricity.

Solar thermal works by using mirrors to concentrate sunlight. The concentrated sunlight is then used either directly as a source of heat, as in solar water heating, or to drive a heat cycle such as a sterling engine. Additionally, since solar thermal only directly produces heat, it can store thermal energy various mediums. Some plants, in fact, can store enough energy for 7.5 hours of generation in lieu of sunlight. [3] Therefore, solar thermal can potentially generate power 24 hours a day.

Solar energy produced by steam, there are two types of solar steam generating systems; one based on fixed receiver E-W automatically tracked concentrating technology (Scheffler) and the other on fully tracked receiver on dish technology (Arun) . Whereas the fixed receiver technology is in promotion for last many years and the fully tracked technology is under pilot scale demonstration.

Fixed receiver E-W tracked technology :

concentrators (each of 16 sq. m. size in general) arranged in pairs of sleeping and standing dishes in parallel modules, aligned in a perfect east – west direction. Receivers (heat exchangers painted black) are placed in the focus of each pair of dishes. Above the receiver is a header pipe half-filled with water. Cold water enters the receiver through the inner pipe coming from header. Solar rays falling onto the dishes are reflected and concentrated onto the receivers. Due to the high temperatures achieved, the water within the receiver is converted into steam.

Fully automatically tracked large dish technology :

It is a Fresnel paraboloid reflecting concentrator (named Arun 160) mounted on a flat dish with downward facing cavity receiver at its focus designed to absorb the concentrated solar energy and to transfer it for useful application. The concentrator tracks the sun on two axes, continuously facing it to capture maximum amount of solar radiation over a day. The dish concentrator along with the receiver is mounted on a specially designed tower. The system is equipped with a heat retrieval mechanism (which may consist of piping and fittings, insulation, fluid circulating pump, etc.), and system controls related to tracking, thermal system and security/ emergency measures.

But Solar power is arguably the cleanest, most reliable form of renewable energy available, and it can be used in several forms to help power your home or business. Solar-powered photovoltaic (PV) panels convert the sun's rays into electricity by exciting electrons in silicon cells using the photons of light from the sun. This electricity can then be used to supply renewable energy to your home or business.

Solar panels, also known as modules, contain photovoltaic cells made from silicon that transform incoming sunlight into electricity rather than heat. (”Photovoltaic” means electricity from light — photo = light, voltaic = electricity.)

Solar photovoltaic cells consist of a positive and a negative film of silicon placed under a thin slice of glass. As the photons of the sunlight beat down upon these cells, they knock the electrons off the silicon. The negatively-charged free electrons are preferentially attracted to one side of the silicon cell, which creates an electric voltage that can be collected and channeled. This current is gathered by wiring the individual solar panels together in series to form a solar photovoltaic array. Depending on the size of the installation, multiple strings of solar photovoltaic array cables terminate in one electrical box, called a fused array combiner.

There is a long history of utility scale solar thermal generation.Solar thermal energy costs between 19-35 cents per KWh.

Photovoltaics are a popular energy source both on the utilities side and for residential home use. Photovoltaic capacity has blown past solar thermal power generation capacity.Cost per watt for this technology is currently 18-43 cents per KWh.