Initially, the PV plant design is developed at the stage of feasibility assessment which includes estimation of solar resource and expected yield. Then, the plant design is further improved taking into consideration other local limitations and constraints. The feasibility stage also includes site identification, site measurements, topography mapping, environmental setting assessment, and social impacts. Key design features include such technical information as PV module type, tilting angle, mounting and tracking systems, module arrangement, and balance of system (BOS) components – inverters, connections, switches, and storage solutions. Further optimization of plant design would deal with such issues as shading, performance degradation, and economic trade-offs between increased complexity and energy yield.
The design of a utility scale PV plant is a complex endeavor. With many available choices of components and options for optimizing performance, it is important to strike a balance between cost savings and quality. Engineering decisions require significant technical expertise based on both optimization models and practical experience.
The phases of a large-scale PV solar power plant project are:
- Site identification or PV project opportunity
- Pre-feasibility study
- Feasibility study
- Permitting, financing and contracts
- Detailed design
- Construction
- Commissioning
Let’s see what are the experts view on Current Trends In Project Engineering And Designing of Large Scale Solar Plant:
The following are some of the areas in which Design teams are transforming themselves as well!
Grid Conformance: As Solar Plants grew in size, and increasingly got connected to the ISTS, the Grid regulators and operators began to take notice. They are now actively enforcing good behaviour!
Solar Plants are expected to remain connected during grid disturbances, participate in frequency & voltage control, contribute Reactive power during steady-state and during faults, regulate the ramp-rates and so on. The transient behaviour of the plant is checked by RLDCs through PSSE and PSCAD modeling. Design teams now deliver these models routinely. Plants are also to be designed to deliver or absorb adequate quantities of Reactive power on demand.
EHV design: PSS and EHV Line are very much a part of PV plant design now. The design standards are time-tested over several decades. For example, redundancy in relays and control supplies is essential. Attention is required to ensure that transformer fire protection systems are robust and fail-safe. EHV lines need to withstand static and dynamic forces. And so on. Designing for this is a balancing act, in an industry which is notoriously cost sensitive. Regulators are now stepping in, for example: draft specifications for PSS transformer are in circulation.
Automation: Within the plant itself, the trend is definitely towards Automation and reduction of manpower. The business case for waterless cleaning robots is very much established. However, robots can be used for many more ancillary functions! Similarly, the use of drones for design (survey), for construction (progress and quality monitoring) and for O&M (condition monitoring) are on the rise. Data analysis through AI and ML will definitely reduce human intervention in O&M.
MMS design: Earlier, the tonnage per Wp was of prime concern. Now, the focus is more on reliability for 25 years to withstand environmental events. Design verification through Wind-tunnel study is on the rise. Attention is being given to associated areas like Hydrology.
Plant design: Now, a huge choice of module ratings, technologies and characteristics is available. The trend is very much to consider Trackers, Bifacial modules and String Inverters. There are literally hundreds of design options available, and the ultimate selection of module and mounting arrangement is through the evaluation of LCOE. Given the large size of plants, a hybrid of multiple designs selections within the same plant is also feasible.
Inverters are expected to undergo a transformation in this decade, especially in terms of grid compliance in areas like Grid-forming capability and Reactive power. Manufacturers are already adapting to the current clutch of module types even to the extent of customising for each distinct
type. They are also preparing for the next explosive change driven by BESS.
One area which requires the attention of designers is Disaster mitigation. Examples could be fire-barriers to prevent a fire from devastating the whole plant, an Emergency restoration system for EHV Line, and Judicious sizing of PSS transformers to mitigate the impact of one transformer failure.
The designer is expected to deliver a reliable low LCOE plant that can be constructed and stabilised in the shortest possible time. Design Innovation plays a key role in achieving this. Ultimately change is the only constant.
Rabindran Sundersingh, Director Design & Engineering, SB Energy
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Solar Power for a Cleaner World
The project engineering and management landscape in the world is rapidly changing with evolving technologies, tools, and the latest trends. This change which was envisaged earlier at the beginning of this century is maturing now and there seems to be no slow down. Technology is impacting every part of our life and the construction industry is not left behind and experiencing it like never before. From cloud-based collaboration and the development of digital twins to robots, super-materials, wearable tech, artificial intelligence (AI), data analytics, advanced project management tools & solutions, remote controlling, to pollution-eating buildings etc., there are an incredible array of developments helping to improve the construction engineering sector.
This sector was considered least digitized till last year but the scenario has entirely changed with the COVID-19 outbreak and widespread disruptions that followed by lockdowns and loss of lives and economy. The assessment suggests that the next three to five years will be perfect for the integration of digital technologies including the Internet of Things (IoT), Cloud Computing, BIM, Machine Learning, 3D Printing and Robotics in its workflows. In today’s highly competitive world, companies are expected to deliver high quality engineering projects on time and provide world class solutions for the requirement. The majority of companies in the engineering and construction field have now recognized the importance and evaluation of how non-digitization of systems and processes are affecting every part of their businesses.
India, the second most populous country on the globe with 1380 million habitants, is seeing the escalation of energy demands exponentially. The growth of India’s energy consumption will be the fastest among all major economies by 2040, with traditionally coal generated energy meeting most of this demand followed by renewable energy. Renewables have become the second most significant source of domestic power production, overtaking gas and oil. The current energy generation from all sources as of March 2021 in the country is 379.13 GW, out of which thermal sources command around 61.5% whereas renewable energy generation has reached 24.5% with a healthy growth of 17.33% CAGR between the years 2016-2020.
Subhash Sethi, Chairman, SPML Infra Limited
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Current trends in designing the large scale solar plants
India has witnessed extreme competition in solar power bids and developers are compelled to adopt innovative strategies to manage the LCOE. While we are reaching the solar tariffs to the tune of Rs. 2/kWh, it becomes important to adopt advancements in solar project design and developments.
One of the recent trends in the solar industry is the increasing module wattages. Most of the solar companies are now offering PV modules over 500 W+ to 600 W+ PV modules. This increase in PV module wattages along with a 1500 volt DC system puts challenges to the solar inverter suppliers to meet the changing dynamics. While the industry is moving from central inverters to the string inverter design in large solar projects, a higher DC /AC ratio has become an important consideration in the solar PV design strategy to optimize the LCOE. Higher DC/AC ratio to the tune of over 1.5 are very well accepted by the solar inverter suppliers. With increasing solar string sizes to the tune of 30 modules per string, the inverters are typically available in the sizes of 250 W+, which can handle a large amount of DC power. While higher wattage modules come with half cut mono perc cell technology, the PV modules are available with bi-facial modules. The cell sizes are increasing to the tune of M12 (210 mm), which has increased the typical module size from 2 m2 to about 2.25 m2. The increased module size has led to reduced land requirements. Now you can install a 1 MW solar plant in 2.5 acre land. Hence the land cost and other BoS have reduced. In traditional designs of 330 W modules, the typical BoS cost considerations have been of the order of about Rs. 10/Wp, now as the PV wattage has increased close to double, this reduces the BoS cost to the tune of about Rs. 6/Wp in a large scale solar plant. The higher power PV modules reduce the DC cable requirements and other BoS system costs. The reduced DC cabling in the solar plant also reduces the overall DC losses in the solar plant.
As the net metering is being withdrawn, the solar inverter suppliers are moving towards the energy storage interface to accommodate the surplus power in the Li-Ion batteries. For example, Solis has come up with a 255 KW inverter with a 125 KWp energy storage compatibility to charge and discharge power. The project cost is constituted mainly by module, inverter, BOS (Balance of System), EPC( Engineering, procurement and construction) and other costs. In the Indian market, the project cost was about INR 1.56 billion per MW in 2010 and INR 0.27 billion per MW in 2020 mentioned in table 1.
Table 1 solar installed cost per MW
Dr. Sanjay Vashishtha, CEO, Firstgreen Consulting Private Limited
For complete story read SolarQuarter India, March 2021
