Solar Photovoltaic: Harness sun light to energize your home When you look at the sun in the morning do you get a question in your mind, can I harness this energy to light my home? The answer is yes, now you can. Introduction: [Pic1] Solar energy is available 365 days and energy produced from it (both heat and light) can be used to power homes. In most parts of India the energy that can be harnessed on any given day, exceeds total energy requirements of a home. During summer the energy from sun light is in the range of 1000W pwe sq meter, which means that a house with a terrace area of 100 sq mts (10mts X 10mts) can produce energy equivalent to 100 Kw. This is possible only if we harness all the light energy falling on our roof top. The initial solar Photovoltaic experimentation were done by French physicist Antoine-Cesar Becquerel in 1839. During his research he observed that he can produce electric current by shining light on an electrolytic cell with two electrodes. The German scientist Heinrich Hertz and others observed the PV effect ? the conversion of light into electricity ? in solids during the 1870's, and the first primitive PV cells were built in the 1800s, with about 1-2 percent efficiencies. In 1954, Bell Labs in the U.S. introduced the first solar photovoltaic device that produced a useful amount of electricity, and by the late 1950s solar cells were being used in small-scale scientific and commercial applications, especially for the U.S. space program. Today PV cells are manufactured in many parts of the world including in India. At this time industries have achieved a PV cell efficiency of 18% for mono crystalline cells. There is increased effort in research labs to increase this efficiency to 40%. Photovoltaic, or PV for short, is a technology in which light is converted into electricity using photovoltaic modules that have no moving parts, operate quietly without emissions, and are capable on long-term use with minimal maintenance. Crystalline silicon, the same material commonly used by the semiconductor industry, is the material used in 94 % of all PV modules today. PV modules generate direct current (DC) electricity. For residential use, the current is fed through an inverter to produce alternating current (AC) that can be used to power the home appliances. The main barrier to widespread use of this technology is the initial high equipment cost. PV technology has been advancing over the last few decades and prices have steadily declined. What is a PV Cell? [Pic2] A solar cell is made by creating a sandwich of 2 sets of silicon materials, which are sensitive to sun light. These two layers are called P and N junction layers and will generate electricity when exposed to sun light. Solar cells are characterized by maximum open circuit voltage (Voc) at zero output current and a short circuit current (Isc) at zero output voltage. Power generated by any PV cell cal be calculated (in watts) using the equation P (power) = V (voltage) x I (current) [Pic3] Solar PV panel is an array of multiple cells. Each PV cell consists of a positive and negative terminals, and will produce a pre defined voltage (0.5 to 1.5 V) and current when exposed to sun light. These cells are connected in series to increase total voltage of a panel. If we arrange the cells in parallel, then voltage will remain same and total current output will increase. For example, a 12 V Panel (Module) will have 36 cells connected in series and a 24 V Panel (Module) will have 72 cells connected in series. There are 3 types of solar PV installations: O Solar PV roof top installation with battery backup O Solar PV Grid-Tie installations O Solar PV MW scale installation for power plants To enable a solar home, we can deploy PV modules of capacity ranging from 40W to 120W facing south on roof tops and balconies. Typical roof tops receive maximum sunlight for 8 hours and that can be harnessed to power our home. Solar PV roof top installation with battery backup [Pic4] Solar PV modules produce DC power and this can be stored directly in batteries. This type of a setup is known as PV battery backup systems. One of the core components of a battery backup system is a ?charge controller?, which controls the voltage and current from a PV module in accordance with the battery system. A charge controller is required to ensure that the voltage of the PV module does not exceed maximum voltage supported by batteries. Also, the controllers will ensure that the power from battery storage is not passed back to the panels during night. If there is a power surge from batteries to the panels, then it will damage the solar cells. A typical 100W PV system can generate an average of 600W of power on a sunny day. This can power six 15W lights and one 60W fan for 4 hours time. Solar PV Grid-Tie installations In Grid-Tie solar PV systems, the power generated by solar PV cells is transferred to electric grid, using grid-tie inverters. These inverters also contain inbuilt charge controllers, to control the voltage, and convert DC power to AC before feeding it to the main power circuit. Installation of such systems is very simple, since it does not involve complicated battery storage. The +ve and ?ve terminals of a solar PV array are directly connected to a grid-tie inverter, and the inverter is then plugged in to a wall socket. The inverter will verify the frequency and voltage of grid power, and will convert DC power from the panels to appropriate voltage required by the main grid. One of the key safety feature if grid-tie inverter is to check if there is already power in the main grid. If the inverter is not able to detect power in the main power line (due to power cut), then it will not supply the electricity. This will ensure that during power cuts, there is no surge of additional power from PV panels within the electrical circuit. Downside of this system is that, we will not be able to use the solar energy during night since there is no battery to store this energy. [Pic5] [Pic6] You can see in the picture above a Grid-Tie system in operation in an apartment home. PV panels are installed on the balconies of the apartment and power generated is fed directly to the grid. Future of solar PV technology There has been extensive research to improve the cell efficiency, which in turn will help in reducing cost of a solar PV module. The chart below from NREL shows the efficiency levels achieved by many research firms around the world. [Pic 7] Other solutions being worked by manufacturers are thin film photovoltaic solutions and concentrated photovoltaic technology. In thin film solution, a PV module is in the form of a flexible film, which can be applied to any surface (glass windows, walls etc.). This technology will not only reduce the cost f installation, and also will enable us to harness solar energy from window panes. Another type of PV technology is concentrated photovoltaic (CPV) solution. In this technology a PV super cell is deployed at the center of a parabola made out of a highly reflective material, which will focus maximum light energy on to a single PV cell. This cell will then be able to produce energy equivalent to 600 times a regular PV cell due to maximum amount of light being focused at one single point. These systems will also have a solar tracking mechanism to ensure that there is always constant amount of sunlight falling on the cells. Additional reading: http://en.wikipedia.org/wiki/Photovoltaics