Tech View

Eluding shading analysis not an option

Rooftops will become the ‘next big thing’ in India. There are some factors that should be taken into account when preparing and planning a rooftop system. Shading analysis lies at the core. Here, is an assessment on the Sun’s impact on solar PV.

The extent of rooftop area required by a solar PV plant is a factor of panel efficiency and extent of shading. Any kind of shading is detrimental to the performance of entire solar PV plant. Shading can have a serious impact on solar thermal and photovoltaic system outputs.

The necessity
Accelerating rooftop PV market is the best way forward for clean energy deployment to happen on a mass scale with local community involvement. India is a country with complex roofs due to multiple roof uses. Obstacles on a roof such as staircases, water tanks, small constructions and nearby buildings and trees cause shadows on different parts of the roof at different times and affect the total area usable for solar.

Siddharth Gangal, CEO, The Solar Labs, says, “A shadow analysis is arguably the most important factor in the design stage of rooftop owner’s solar plant. All modules in this array must be performing equally and well. Modules give different outputs based on how much they are being shaded and give rise to mismatch losses on cell and module level.”

Mismatch losses are taken at 3 per cent on an average but increases exponentially if a few panels are shaded in an array. Siddharth further explains, “Let us consider the case of one shaded solar cell in a module while the rest are in direct sunlight and unshaded. The power generated by the unshaded solar cells can be dissipated by the shaded cell rather than powering the load. This leads to local overheating (also called hotspots) in the shaded cell and causes permanent destructive effects, such as glass cracking, melting of solder and degradation of the solar cell. Modules overcome this effect partially due to the use of bypass diodes.”

Anuj Gupta, CEO, Dimension I considers shading analysis to be one of the most critical steps in PV system designs and analysis of the solar system. He says, “Shading is a problem that, in most of the cases, cannot be avoided. It’s important to analyse the shading caused by nearby objects and trees; even small obstructions such as chimneys, utility drops, poles and vents etc. can affect the production of the solar system.:

To choose the best equipment’s, techniques & placements and system optimisation, photovoltaic array shading is very critical. If the shading is not calculated accurately, it can straight away affect the ROI of the system and project viability. There are several technologies available in the market that are used by different tools to extract the shading and accurately provide the TSRF such as LIDAR, GSR etc, he further adds.

Animesh Mahek, Founder and Managing Director, Avishakti Rooftop Solar Pvt Ltd, has a very interesting take on this. He observes, “To answer the importance of shading analysis, we need to look at the way a solar panel is made up using solar cells. Solar cells are the basic building blocks of a PV module. A PV module consists of several interconnected solar cells (typically 60/72 connected in series) encapsulated into a single, long-lasting, stable unit in order to increase the power and voltage above that from a single solar cell. If all the solar cells in a module have identical electrical characteristics, and they all experience the same insolation and temperature, then all the cells will be operating at exactly the same current and voltage.”

However, shading of one region of a module compared to another can lead to terrible problems. The problems faced are:
• Causes a drop in the generation on a day to day basis
• Cause hotspots leading to fire
• Reduces life of the PV Modules
Animesh further opines,” Non-performing shadow analysis can lead to huge losses in the long run. Thus, performing shadow analysis is the most critical stem of solar system design. We, at Avishakti, use two methods to perform shadow analysis, using solar pathfinder and using sketchup 3D models.”

Major technology players
There are several software available in the market to simulate the generation and determine the power capacity.

Animesh Mahek of Avishakti says,” A few of the popular software are PV Syst, PV Sol and Sketchup. The accuracy of the software depends on multiple factors such as the input and range of values that can be changed. The input values entered by a design engineer will determine the accuracy of the output. If the values entered have error in them, the resulting output will be garbage.”

There are quite a few software applications which have matured and are quite accurate in capacity planning. Anuj Gupta of Dimension I suggests, “Some of the major applications are PVsyst – Pvsyst SA, Switzerland, Homer Pro – Homer Energy, USA, and System Advisor Model (SAM) – National Renewable Energy Laboratory (NREL), USA. These software work on different parameters in terms of shading and system losses such as dirt, wind and efficiency losses of the modules and inverters. These software are quite accurate as they do consider the geographic location of the installation and the ambient conditions including the Sun’s path, temperature and such historic data and futuristic estimations. “

Siddharth of The Solar Labs opines, “The Indian solar industry is in a very bad shape in terms of quality and performance. Yes, there is solar plants being installed but these systems are not generating as much electricity as they should. There are three major components to high performing systems: tier 1 components, quality engineering design and regular O&M.”

In India, typically a combination of SketchUp, AutoCAD and PVSyst is used. SketchUp is used for calculating shadow lengths and row to row distance, AutoCAD is then used for drawing layouts of the system on the roof and PVSyst is used for generation reports.

“Recognising the uniqueness of Indian conditions, NASSCOM and IIT backed The Solar Labs to provide solar PV design software tailored for Indian conditions,” Siddharth adds.

“Non-performing shadow analysis can lead to huge losses in the long run.”
Animesh Manek, Founder and Managing Director, Avishakti Rooftop Solar Pvt Ltd

“If the shading is not calculated accurately, it can straight away affect the ROI of the system and project viability.”
Anuj Gupta of Dimension I

“The power generated by the unshaded solar cells can be dissipated by the shaded cell rather than powering the load.”
Siddharth of The Solar Labs

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