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Solar arrays on canals

PV installations on canals are common in India, as they provide electricity without occupying land, while reducing evaporation. However, they are still more expensive than ground-mounted PV projects.

India has been installing solar on canals as an innovative way to provide renewable energy for farming without using agricultural land. Such projects benefit from easy grid availability, as most of India’s large canal systems feature small, grid-connected hydroelectric plants.

The generating potential from canal-top solar plants is at least 10 GW, according to Premier Energies Executive Director Sudhir Moola.

“India has around 120 major canal systems covering a length of about 10,097 kilometers,” Moola told pv magazine. “Even if 50% of this canal length (about 5,000 km) is usable for canal-top solar installation, we can do 2 MW to 3 MW for every kilometer of the canal, assuming 15 to 20 meters of canal width. That gives us a potential 10 GW of canal-top solar power systems that can be installed saving more than 40,000 acres of land.”

PV panels on canals also lead provide a cooling effect by shading canals, which reduces water losses due to evaporation, he added. 

Canal capacity

The state government of Gujarat started looking at canal-top solar in India in 2011, as it looked for ways to increase renewable energy production while avoiding land conflicts. This led to the commissioning of India’s first canal-top solar project at Chandrasan village, about 45 km from Ahmedabad.

Gujarat State Electricity developed the 1 MW PV plant on a 750-meter stretch of a canal with the support of  Sardar Sarovar Narmada Nigam Ltd.. It has since commissioned 35 MW of such projects, with a tender in the works for 100 MW of additional canal-top solar capacity. 

The Ministry of New and Renewable Energy (MNRE) then launched a pilot project scheme in 2014 to develop 100 MW of grid-connected solar PV capacity over canals and along their banks, via state-run agencies. The scheme provided viability gap funding (VGF) support for canal-top PV projects and canal-bank installations. As of March 31, 2019, 50 MW canal-bank solar PV projects and 44 MW canal-top solar PV projects had been commissioned.  The scheme has since been closed.

“Canal-top solar installation requires a shadow-free stretch of canal with an ideal width between 20 and 30 meters,” said Pulkit Dhingra, founder and director, AHA! Solar, a digital solutions provider for project management. “A motorable road along the canal allows for development and maintenance. North-south canal flow is ideal [to get maximum output from the panels], but east-west direction can also be used for panel installation.”

Canal-top projects cost more than normal ground-mounted arrays and floating solar plants, as they require  support structures to span the widths of the canals. Such structures could be installed end-to-end, or without touching the ends of the canals. In the latter approach, piers can be installed within the canals and panels can be mounted on them. For wider canals, such as those in Punjab, it’s important to install piers within the canals.

Another approach is to use high-tensile steel to mount the modules. Premier Energies is the only company in India to have used this approach, in a 1 MW canal-top system in Uttarakhand in 2017. The project is still the widest canal-top installation in India, with a width of 35 meters, without piles in the canal.

“I don’t think you will find this anywhere in the world. And the plant has been performing for last four years with no incidents, despite being subject to high winds being close to Yamuna River,” said Moola.

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The innovative design could be used in canal-top solar projects throughout the world, according to Dhingra.

“Innovative designs like cantilever type [a beam anchored at only one end to a vertical support] can help to decrease the cost and still utilize the canals for generating solar power,” he added. “If the canal top is planned at the time of construction of canals, it can help reduce capital costs and solve both the purpose of generation of electricity and saving water.”

Canal-top installations in India typically use polysilicon module technology.

“The cost of structures for canal top in itself is high, so using a commercially viable technology makes better sense. Moreover, in conditions like India, polysilicon provides better performance,” Pulkit said. 

He said bifacial panels could be a better option, as they reduce overall weight in structures. However, the commercial viability of bifacial modules needs to be examined, he added.

“If the reduction in the structure’s weight is less and increase in the cost is high, then it doesn’t make sense,” Pulkit said. 

Key challenges

Excessively wide or narrow canals pose challenges for cost-effective system design. 

“In a normal land-based project, you can install columns at three to four meters length, which is the span of the structure,” said Moola. “Whereas in a canal, you can have one column post at the descent to support the structure, and on the other side, you can have one more. So when the span increases, the type of structure the column weighs go up quite high.”

The canal width should ideally be 20 to 22 meters to keep structural costs under control, said Dhingra. The support structure should also allow access to the canal. Module cleaning and operations and maintenance could be a challenge, given the limited access to panels.

Moola said that Premier Energies maintains a structure-to-structure gap of 4 meters to 5 meters. This leaves a gap for pipelines to extract water from canals. A floating pontoon also could be used for periodic desilting and cleaning of canals.

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Source: pv magazine