Mankind’s survival is primarily dependent on Energy source. The quest for energy source is since centuries. Exploration of Energy sources has always involved in better understanding of nature. Though the nature’s challenges for human existence have been overcome with successful technology deployment of energy generation, this has lead to a greater failure as climate change. The dependency on fossil fuel is causing untold danger to the climate and threat to the environment. The explosive nature of Energy demand is impacting on the climate which leaves a question on survival of our future generation. The threat of Energy shortage and climate damages need to be addressed on Urgent priority. It is very essential to accelerate the replacement of fossil fuels with renewable Energies. The route to avoid climate chaos and achieve energy independency to develop sustainable environment and foster a healthy world for our future generation is very much required. Without fundamental changes in how we generate and how we use Energy, the challenges threaten our livelihood and our planet. Towards this, renewable Energy sources require utilization to its fullest available resources. The Solar Energy is one of those sources which is more predictable, reliable and harnessable. The sun shines in abundance over India and a part of it is enough to meet the whole demand of the country if tapped in full. The best way to utilize this source of Energy is to feed the Electricity generation from Solar Energy to Distribution Grid which can reach the utility and meet the various needs of the society.
The word photovoltaic is a combination of Greek word” Photo” for light and ‘voltaic” meaning Voltage. It identifies the direct conversion of sunlight into Energy by means of solar cells. The conversion process is based on the photoelectric effect discovered nearly two centuries ago. The photoelectric effect describes the release of positive and negative charge molecules in a solid state when light strikes its surface. Solar cells are composed of semi conducting materials. To produce a solar cell, semiconductor is contaminated by doping a positive charge carrier material or negative charge carrier to either obtain surplus positive or negative charge. If two differently contaminated layers are combined then a so called PN junction is formed. The usable voltage from solar cells depends on semiconductor material. The current intensity depends on light radiation. There are two different cell technologies namely, crystalline and Thin Film. The crystalline solar cells appear blue in colour and white gridlines over it make the electrical connection. The thin layer of silicon film deposition on glass with another substrate material on glass makes a Thin Film cell. While the Thin Film technology consumes lower silicon materials, the efficiencies are lower compared to crystalline. In fact, both the technologies have advantages of their own..
How does grid interactive System work ? ……..
The solar panel produces DC power. Multiple solar panels are coupled together as arrays which produce higher DC voltage. The DC power is converted to Grid compatible AC power. This power is fed to the grid utility.
Grid Interactive System
Grid interactive system is categorized as two general types: For small scale application(upto few kilowatts) and for large scale power generation(Mega Watt Scale). The small scale PV system can have two type of system such as Grid interactive only (with out any battery) and Grid interactive with battery backup. The direct Grid interactive system operates when the utility is available. This is useful where the utility outages are rare. In the event of outages by utility, the PV system shutdown till the utility power is restored. The grid interactive with Battery backup incorporate Energy storage in the form of a battery to keep critical loads circuits in the home operating during the utility outage. When the outage occurs the unit disconnects from the utility and power specific circuits. During the availability of utility, the power generated is fed to the home loads or to the grid. There can be a log of energy pumped to the grid, Energy consumed and the Energy Generated. This is called Net metering where in, the net of energy generation Vs energy pumped or drawn from grid is recorded. This enables the user to record net of energy pumped to or drawn from the grid.
Details of system components and its function………………….
Solar photovoltaic Module is a packaged interconnect assembly of solar cells. The module in multiple units is called solar PV array. Electrical connections are made in series to achieve a derived voltage and / or in parallel to provide a desired amount of current. The modules are mounted in such a way that they receive the maximum sunlight incident on the cells. There are two ways of mounting them namely Fixed Axis and Tracked. In a fixed axis method, the modules are mounted in one fixed tilt and do not move there on. In a tracked system, the Modules are mounted in such a way that they track the sun thereby making sunlight to fall directly. The tracking can increase the power generation upto 25% more but requires higher investments on tracking. The tracking in a fixed axis configuration for optimization of till angle of module facing the sun is done based on latitude of the location. The solar photovoltaic modules are mounted on Metal structure. Normally they are designed to withstand the wind loads of the location. It is also required to build the support structure in such a way that the minimum clearance between PV module and ground is maintained.
The DC power generated by PV Module is connected to the power conditioning Unit. This consists of a Maximum power point tracker (MPPT) and an Inverter. The MPPT comprises an Electronic system that operates the PV module in a manner that allows the module to produce all the power they are capable of. MPPT is not a Mechanical tracking system but an Electronic system that varies the electrical operating point of the modules so that the modules are able to deliver maximum available power. Additional power harvested from the modules is then made available as increased current. MPPT has a high efficiency DC to DC converter which uses special algorithms to extract best of the power derived from PV. Then the harvested maximum DC power is fed to an inverter for power conversion to AC Synchronizing with Grid frequency. There are two kinds of inverters as central and String inverter. The central inverters are housed in an inverter station while the string inverter can be outdoor. In string inverters, a bank of Arrays are connected to the string inverter. The AC output is then connected to Grid at lower voltages. String inverters are suitable for system with Mechanical tracking. The central inverters topology allows AC side parallel connection of the Inverter and voltage multiplication thereby making the mega watt scale power production and pumping of energy to higher grid voltage possible. The output of the inverter is filtered to reduce harmonics. The output of the inverter is always synchronized to the grid. In the event of grid failure the system switches off safely. When the grid resumes the inverter reconnects and pumps energy to grid as long as PV modules generate DC power. The inverters are provided with Galvanic Isolation to significantly reduce safety risks. It is a complete physical separation between input and output and is achieved by means of transformers. The output of inverter can be single phase or three phase depending on the size of PV power. The AC power is boosted to the required High voltage by mean of power transformer and fed through necessary safety switching modules. The whole system is protected for lightning hazards through use of necessary lightening arrestors. The whole power plant can be monitored and controlled with use of monitoring system. The parameter like the amount of sunlight incident at the location, Ambient temperature and wind conditions are measured besides the power generated by PV system. This can enable the monitoring of system performance and also provide fault diagnosis. There are ready made and custom built software based on computer Aided supervisory control & Data Acquisition mechanism which can, not only provide us the information of parameters but also to control the whole system.
Even though the solar power generation is possible in general everywhere, for large scale grid based power generation there are few specific requirements. Since the space required for Installation of PV Modules is minimum of three Acres per Megawatt of Power generation, the shadow free area with grid Evacuation possibility is essential. It is essential to evaluate the utility requirement before sizing the system components. PV system produces power in proportion to the intensity of sunlight striking solar module surface. The intensity of light varies throughout the day, as well as day to day so that the actual output of a solar PV plant can vary substantially. There are other factors that affect the output of solar PV system. These factors need to be understood. The DC output of solar Modules is rated by manufacture under standard test conditions (STC). These conditions are easily recreated in a factory and allow for consistent comparison of product but need to be modified to estimate output under common outdoor operating condition. STC condition specify that the Modules output is measured at a solar spectrum as filtered by passing through 1.5 times thickness of Atmosphere, with an intensity of 1000 watts per square meter of area and at an ambient temperature of 25 degree C. The crystalline modules also have a production tolerances which need to be considered in system Design. The Amorphous module exhibits the Light Induced degradation (LID). The degradation of modules in the first 1000 hour of sun exposure results in average 15-20% degradation in power output and the power deliverable after such degradation is called Rated Stabilized Power. It is essential to note the maximum day time temperature of the location in derating the PV module power generation. The nominal operating cell temperature (NOCT) data of a given manufacture’s module can be useful in optimizing system design. Dirt and Dust can accumulate on the solar Module Surface, blocking some of the sunlight and reducing the output. Eventhough the typical dirt and dust is cleaned off during rain, it is more realistic to estimate system output taking into account of the reduction due to dust buildup in dry season. The maximum power output of the total PV array is always less than the sum of maximum output of the individual modules. This difference is a result of some inconsistencies in performance from one module to next and is called the module mismatch. Power is also lost to resistance in system wiring. Further the power conversion losses in the conversion process cause additional losses. During the course of the day, the angle of sunlight striking the solar module will change which will affect the power output. The output of PV module will rise from Zero gradually during dawn hours, increase with the sun angle to its peak output at Midday and then gradually decrease into afternoon and back down to zero by night. While the variation is due in part to the changing intensity of sun, the changing sun angle also has an effect.
The selection of module technology considering the various factors is very essential for optimum power generation. The Crystalline Module can function at efficiency levels of around 14-15%. The amorphous work at approximate efficiency of 6-8% which makes the land requirement double that of crystalline . While crystalline technology can require lesser space compared to amorphous technology, the later has ability to delivery higher yield for the same installed power of crystalline technology in a hot location. Due to the low thermal coefficient, the amorphous module delivers higher yield in diffuse sun light conditions compared to crystalline. With the high voltage and lower current, the cable costs can be lower in amorphous. The negative grounding requirements if ignored in amorphous technology can cause severe corrosion related issues of the module on a long run. Hence it is essential to adapt the technology depending on the location and the various other factors listed above. It is essential to estimate the total energy generation possible at a particular location so that the pay back can be estimated. Towards estimating power generation, software tools like PVSYST, SolarPro can be used which approximates the power generation. Safety and Risk mitigation must be evaluated along with the Soil evaluation for installation suitability of PV Modules. Water condition and Rainfall data can also provide us more inputs of PV Module cleaning frequency and arrangements. Air and water cleaning may be thought to clean the PV Modules.
The Photovoltaic Power Generation systems can provide most reliable output for a longer period. However, the Modules also suffer a small degradation in power generation and this can amount to approximately 20% over 20 years. The derating can be made up with additional modules after sometime. The regular cleaning of PV modules can ensure the reduction in power generation loss due to dust and dirt factor. Eventhoug there is no moving parts in the power plant, a properly ventilated area with dust filter for Power Conditioner Unit can ensure a longer performance of the system. In general, the attractive attributes of the PV system is its low maintenance.
India is blessed with abundant sunshine and the realization of our dreams on Environmental concern can be best achieved with Solar Power Plant. The technology costs are becoming more competitive day by day. With volumes, the cost can be more meaningful in making this noble energy source a best way of energy generation. Solar Rooftops can go in real terms more meaningful and harvest a bright future for our future generation.