LiDAR has now become an established method for collecting very dense and accurate elevation values. This active remote sensing technique is similar to radar, but uses light pulses instead of radio waves. Laser beam is the sensing carrier in LiDAR, an active remote 360 degree sensing system.
Use of modern geospatial solutions plays a crucial role in better planning and governance of Smart Cities, which are being promoted across India. One of them is Light Detection and Ranging (LiDAR), an innovative technique for capturing high resolution aerial images of urban centres and converting them into accurate 3D maps with discrete digitised rooftops. Data from aerial LiDAR has been used to develop the web-based tool.
In 2016, Centre for Study of Science, Technology and Policy (CSTEP) engaged in a first-of-its-kind project to develop a tool that would accurately assess the potential of solar photovoltaics on rooftops in Bengaluru, Karnataka, along with the associated business case for all consumer categories. The project involved using LiDAR to develop high-resolution 3D maps of the city, including building heights and obstacles in the vicinity such as trees, other buildings, poles, billboards, etc. For 15 days, from February 19 to March 6, 2018, flights were employed for aerial data gathering. This exercise was carried out by Geokno India.
How it works
Data from aerial LiDAR is used to develop the web-based tool. Saptak Ghosh, Research Scientist, CSTEP, explains that the tool will link each rooftop with its corresponding electricity consumption from BESCOM's consumer database. Each user will be directed to his or her rooftop and will be asked for the BESCOM RR (revenue register)number. Mapping of BESCOM RR number to rooftops will involve the participation of the society. The tool will retrieve the consumption details and construct an accurate business case for rooftop solar project. The business case will be based on the user's inputs on the portion of shadow-free area chosen for rooftop installation. The shadow-free area will be calculated using solar geometry, which will take neighbouring obstacles (buildings, trees, poles, etc.) into account.
The tool will also allow CSTEP and BESCOM to identify all the suitable rooftops in the covered area. Capacity addition can be planned for BESCOM to reach the 1 GW target by rolling out large-scale tenders for the identified rooftops. This would reduce capital costs of rooftop solar as well as the net or gross metering rates required to make feasible business cases.
Ravi Kumar, Additional Chief Secretary, Energy, Government of Karnataka said that the project is an innovative way to map solar rooftop potential in densely-populated cities. The results of this exercise will lay the foundation for replicating such efforts in other cities in Karnataka and the rest of the country. The time taken to finish this exercise using other means or technology would be far greater considering the levels of accuracy expected from the use of aerial LiDAR. The raw data collected can also be processed to help in other city planning applications, such as tree cover densities, surface water drainage systems, road networks, etc. The Government of Karnataka will explore these options to maximise the utility of this project.
In total, it should not take more than seven months to capture the data, process it to digitise rooftops, estimate shadow-free areas and develop the tool and roadmap.
However, complains Ghosh, "Obtaining the necessary clearance to fly the helicopter with the LiDAR equipment over Bengaluru from the Ministry of Defence and six other central government departments have led to delays of over a year."
"This is because of the number of defence establishments and other sensitive institutions (such as ISRO) being present in Bengaluru. If such issues are resolved before replicating the efforts in other cities and towns, aerial LiDAR is still the fastest way to obtain accurate aerial imagery necessary for potential RTPV (rooftop photovoltaic) assessment and tool development," he cautioned.
The cost of this pilot project is quite high. However, if this technology is scaled up, the economies of scale can make it cost-effective. Also, aerial LiDAR-based raw data can be processed to perform other urban planning exercises, such as road and traffic management; tree cover estimation; modelling surface water and drainage, and pedestrian or cycling corridors. The sheer range of applications make LiDAR a very cost-effective technique. The project was funded by MacArthur Foundation (MAF).
Discoms are not yet prepared for large-scale rooftop solar penetration. Distribution transformers need to be mapped (such an exercise is currently going on under R-APDRP) and spare capacities must be identified. This will help determine the amount of rooftop that can be incorporated without destabilising the distribution network. Consumers are not aware of the potential of their rooftops and the impact of the shadows cast by neighbouring obstacles on generation from RTPV systems. Misinformed decisions along with ineffective system designs have reduced people's confidence in RTPV.
According to Ghosh, initial estimates for Bengaluru show that the realisable potential on existing buildings is around 3.4 GW.
Rooftop solar potential
The Ministry of New and Renewable Energy (MNRE) estimates India's RTPV potential to be 124 GW in urban areas. However, CSTEP's estimates reveal that the potential is actually in the range of 250 GW, taking into account smaller towns and the fact that over 70 per cent of the buildings are yet to be built. A more precise estimate can be arrived at by taking a scientific approach using shadow analysis. India's installed rooftop solar capacity has grown from around 740 MW in March 2016 to 1.6 GW in March 2018. About 6-8 GW of rooftop installations are expected in India in FY 2018û19. The estimated investment is in the range of Rs 270û360 billion.
The prices of solar PV module have dropped drastically from 2009 to date. The cost of financing large solar power plants in India has also become more reasonable, especially because of significant foreign investment. The unit price has fallen from Rs 17 in 2009 to Rs 2.44 today. With widespread deployment of the solar PV technology in India, the original Jawaharlal Nehru National Solar Mission (JNNSM) target of 20 GW has already been met in 2018. The trend of falling prices of solar power is likely to stabilise.
Now that solar power is cheaper than coal, this sector will grow at an even faster rate.
LiDAR is still the fastest way to obtain accurate aerial imagery necessary for potential RTPV (rooftop photovoltaic)assessment and tool development.
- RAHUL KAMAT
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