Plants use photosynthesis to harness the energy from the sun to use it as food by converting it in to carbohydrates. The plants have special cells in the leaves that can store the energy. The light from the sun consists of photons of energy, which when incident on the plants are stored by leaves. The plants produce the food by reducing these photons using water molecules. The process use carbon dioxide in addition to the water carried to the leaf from roots through the plant stem using vascular system. The process of photosynthesis releases oxygen during the conversion of sunlight to the chemical energy. The entrance of carbon dioxide in the leaf and release of oxygen is only possible through the special cell stomata. Stamatas are special cell that have an opening guarded by two cells on both sides (M.J. Farabee, 2010).
The process of photosynthesis has two different processes; the light process is light dependent and uses the sunlight to produce two chemicals ATP and NADPH. The dark reaction can take place in dark and light as well, which perhaps is dependent on the light reaction and used the product of light reaction to produce the glucose. Krebs cycle takes place next to the glycosis cycle to release ATP, water and carbon dioxide to the atmosphere. The release of water is undesirable by the plants, but is unavoidable as some water passes out from stomata during the out flow of carbon dioxide (Brennan, 2008).
The process of photosynthesis involves different parameters and any variation of environmental and process parameters can greatly affect the process speeds. Mainly light intensity, concentration of carbon dioxide, temperature, chlorophyll concentration, water and pollution are the contributing factors. The intensity of light is measured in Lux, the intensity required by the plants to maintain full-scale photosynthesis process ranges between10, 000 to 100,000 lux, at intensities lower than this range process would be slower and intensity higher will bleach the chlorophyll slowing down the process again. It is possible to increase the rate of photosynthesis by increasing the concentration of carbon dioxide to 0.1% in the surroundings usually by using greenhouse or controlled sheds. In general, the concentration of carbon dioxide is 0.03 to 0.05 percent in the atmosphere. Some vegetables are success fully grown in greenhouse giving better yields; tomatoes and lettuce are the examples. Photosynthesis involves enzymes activity so the temperatures at which enzymes can maintain the activity will be suitable for photosynthesis. In the areas of extreme cold, the enzymes stop working, at the extreme high temperatures theses get denatured; therefore, a temperature range of 25C0 to 35C0 is best for the process. It has been observed the photosynthesis can happen only in the green leaves, the leaves that get yellow due to process of cholorolysis cannot use the sunlight to generate food for the plant. Cholorolysis may be due to natural process of aging, deficiency of minerals or disease. The water loss or availability of less water reduces the photosynthesis. Due to shortage of after, leaves are dried up resulting hardening of stomata in the leave cells. The stomata being controlling mechanism of entering of carbon dioxide in the plants cannot retain the gas resulting in drop of the process efficiency. The pollutants in the atmosphere can also reduce the efficiency of photosynthesis to 15% due to blockage of stomata and reducing the transparency of leaves. Industrial gasses as if sulphur dioxide can affect the sensitive lichens of the plants reducing the process of food production using photosynthesis (TutorVista.com, 2010).
The energy from the sun is being used to produce the electricity making use of semiconductor solar cells. The solar cells are arranged in arrays called solar panels. The panel is flat array of many cells and is placed in the direction of the sun or can have an active system for tracking the sunlight. The light from the sun is incident on the solar panels and is converted in to electrical power. The electrical power can be used directly from the panel using a converter or can be stored in batteries for subsequent use. The solar panels mostly are used on remote locations but now are becoming popular in urban areas.
The main compound of the semiconductor solar cells is a material that is non-conductive at the normal temperature but becomes conductor at raised temperature or when light is incident on it.
The most solar cells are made using Silicon, the most abundant material in the nature having pollution free processing. The material used in 95% semiconductor solar cells is Silicon, being second large most abundant element in the earth’s crust. The semiconductor doping makes the material either a p-type or an n-type material depending upon the high quantity of positive particles or negative particles (GmbH, 2011).
Photosynthesis and semiconductor solar cell can be considered similar both harnesses the sunlight to produce the useful products. Cell produces the electricity and photosynthesis produces the useful products. In case of solar panel (an array of solar cell) or plant leaf, both have the maximum efficiency when placed perpendicular to the sun direction a light falling on them is maximum. Both have the process for replacement of electrons lost during the process of converting the photons to electricity and carbohydrates. Both the process capture, convert and store the energy in other forms.
Photosynthesis and semiconductor solar cells are different in a way that solar cell uses photoelectric cell and photosynthesis make use of chloroplasts to harness the sun energy. The process of replacement of lost electron in photosynthesis is by breaking the water molecules and in semiconductor solar cell, it is done by completion of electric circuit. The solar cell produces the energy that is not required for self-sustainability, but in case of photosynthesis, self-sustainability depends on the process (Watson, 2009). The product from photosynthesis (carbohydrates) has the food value and can be used as nutrients for animals, where in case of semiconductor solar cell; the product (electricity) does not have any nutrient value.
The process in plants for making food is a complex process that makes energy to change many forms, so is a dynamic relationship of work energy and heat. The energy is not created by plants during photosynthesis, but is converted from light to chemical energy and oxygen. In general the first law of thermodynamics that states that energy can neither be created nor destroyed but can be changed from one form to other is obeyed.