Solar Trees for Net Zero Carbon Emission

Solar trees can help in achieving the goal of net zero or net plus campuses and thereby helping in achieving the goal of net zero carbon emission of the country.
Dr. K M Soni - Former ADG, CPWD, New Delhi
Energy generation from non-conventional resources has become a necessity due to India’s commitment on net zero carbon emission by 2070. Though solar generation through rooftop solar panels has become common in the country, both in government and private sectors, however, it becomes difficult to increase rooftop area for installation of solar panels, particularly in upcoming multi-storeyed buildings in urban areas. Therefore, solar power generation is also to be planned in different ways than the solar rooftop, such as in building façades and through solar trees.
Solar trees can be erected in open areas of building campuses and in parks, gardens, sides of railway lines, medians of highways and expressways, canal banks, etc. where sunshine is available. Advantage of solar trees is that multiple solar panels can be installed in them to produce a large amount of power.
CPWD has erected 41 solar trees during the development of National Salt Satyagraha Memorial at Dandi, Gujarat, during 2019. These solar trees were part of net energy plus campus of Dandi.
Net Zero and Net Energy Plus Buildings
A net zero energy building is one with zero net energy consumption on an annual basis i.e. the total amount of energy used by the building on an annual basis is produced through the renewable sources. Energy generation may be at the site or outside the site. In case, energy generation from renewable sources is at the site, it is known as onsite net zero energy project while in offsite net zero energy buildings renewable energy is generated outside the project site. Indira Paryavaran Bhawan in New Delhi was the first onsite net zero building in India in the government sector; constructed by CPWD in 2014.
Buildings or campuses that produce surplus energy over its consumption on annual basis are called "Energy plus or net energy plus” buildings/campuses. The National Salt Satyagraha Memorial at Dandi was planned as a net energy plus campus by installing solar trees in the campus.
Solar Trees
A solar tree is a metallic structure on which a solar power system is installed on a single column like a tree trunk. Advantage of solar trees is that they can house many solar panels in various directions.
Solar trees are required to be adopted in India as they require less space, and sunshine is available almost through the entire year to produce solar power. They can be erected in large campuses having open areas, in parks, roads, highways, medians, bridges, railway land, banks of canals and large drains, and even on columns of the buildings. Solar trees can play a major role in achieving zero carbon emission by 2070.

Solar trees are designed to mimic the natural form of trees, merging with the surrounding landscape. Town planners and architects are coming up with beautiful designs. Thus, one has the option to choose the required configuration of the solar trees, merging with their landscape design.
Solar trees with various configurations have been provided in various projects, some of which are described briefly: (ref. Mensour Almadhhachi, István Seres, István Farkas, 2022).
Multi-branch single stem (MBSS): This is a long column that looks like a tree stem and has branches emerging at different heights, carrying solar modules at different surface angles and orientation, according to the site requirements of the directions in which the panels are to be erected. This design is easy to develop but is considered among the least efficient designs in capturing solar radiation during the entire day due to the orientation of the solar modules. This design has been provided in a fuel station in Budapest, Hungary (Fig. 1).

Fibonacci pattern solar tree: It is the most popular solar tree configuration as it captures sunlight with relatively high efficiency (Fig. 2 a & b), producing more energy compared to traditional PV modules.
Spiralling phyllotaxy solar tree: Though innovative, symbolising natural plants, it is the most widespread forming large complex umbrella type configuration (Fig. 3) capturing sunlight in an extensive and efficient manner. However, its tales up considerable space for its leaves and is also more expensive.
Hemispherical dome solar tree: This configuration (Fig. 4 a & b) has a special design, consisting of modules that form a semi-spherical dome covering the daylight period to capture sunshine with greater efficiency. The configuration helps to cover the sun path during the entire day.

Three-dimensional geometric design solar tree: This configuration (Fig. 5) consists of a leg, on the top of which a solar panel is directed at a certain angle. Solar modules are distributed on the branches symmetrically within the specific inclination angles to capture the sunlight.
Researchers and designers are developing more and more beautiful engineering art forms of solar trees to match with the landscape (Fig. 6-9). As such, various configurations are available and are being adopted worldwide.

Solar Trees at National Salt Satyagraha Memorial, Dandi
The National Salt Satyagraha Memorial is planned near the location where the salt law was broken at Dandi, constructed over 15-acre land, having an artificial lake of about 14000 sqm to symbolise the seashore aspect of the “Salt Satyagraha”. There are 24 narrative murals depicting various important events and stories from the historic Dandi March and life size sculptures of Mahatma Gandhi and the group of 80 fellow marchers, 40m high "A" shaped frame with two hands raised up in the sky, holding a salt crystal at top forming a canopy. The memorial has 41 solar trees, a special feature of the campus. These solar trees have been installed in the campus for qualifying the campus as net energy plus campus, with surplus energy feeding into the grid. The peak power generation of the system is 144kW, out of which 90kW is planned as online system with net metering and other infrastructure, and 54kW offline system in two parts of 26kW and 28kW with battery backup.

Design of solar trees
41 solar trees having 12 leaves in each generating 182kWp have been installed in the campus. The main components of the solar trees are foundation, trunk, branches and leaves. Typical elevations and plans are shown in Fig. 10-13.

The trunk is made of metallic structure of 8mm thick MS plate bent to shape and jointed with arch welding to form circular member of 866mm outer dia. To avoid corrosion due to the vicinity to the sea, multi-layer protective coatings were provided. However, the trunk can also be made of stainless steel or other material as per the design. Branches are made as per the sun availability, with aesthetic consideration, and according to sun direction and requirement of power generation. All the solar trees have 12 branches made in 316 grade stainless steel (SS) pipes of 114mm (OD) and 6mm wall thickness.

Each leaf of 316 grade SS section has a solar PV panel and caters to the load requirement of the entire load of the solar panel, self load, and other incidental loads, with wiring inside it. The leaves has bottom cover with 2mm thick SS plate moulded to shape with and protrusions similar to natural leaves, and connecting member with branch also in SS of 316 grade. Various steps adopted in the project are shown briefly in Fig. 14-17. Power generation from these solar trees is more than the required electric power for the campus and as such excess power is fed into the grid, making the campus net energy plus.
The world’s largest solar tree producing approximately 11,500 W of electricity developed by the Central Mechanical Engineering Research Institute in 2020 has been installed in Durgapur. It has 35 solar PV modules with 330 W for each module.
Advantages of Solar Trees
- Solar PV panels on solar trees can be designed beautifully to attract tourists.
- Solar trees can be designed with different configurations, also as automatic sun tracking system that adjusts the position of the panels throughout the day to maximise capture of sunlight.
- Solar trees maximise the land use as they occupy very less space compared to traditional solar panels while harnessing maximum solar energy. Plus, the space below the solar trees can also be put to use.
- Solar trees can be erected in the parks, public places, open areas, medians and footpaths of roads, highways, and expressways, buildings, bridges, other structures, airports, canal banks, sides of railway lines, etc.
- Farming activities and low height vegetation can also be planned with solar trees.
- Solar trees can generate large amount of solar power as a typical solar tree can generate 2 to 5 kW of power depending upon the size and the number of panels.

Conclusion
India has committed to net zero carbon emission by 2070, hence, all efforts are to be made to generate power of zero carbon emission. Solar trees, harnessing solar power through multiple PV modules can contribute towards generating energy.
The concept of solar trees installed at National Salt Satyagraha memorial, and the world’s largest solar tree producing approximately 11,500 W power installed in Durgapur having 35 solar PV modules of 330 W each clearly show the success of solar trees in India.
Installation of solar trees can be taken up in all the urban areas initially as a part of compulsory urban planning, and then in rural areas to harness source of green power.

References
- Ajay Agrawal, & K M Soni (2020), CPWD Installs Solar Trees for Net Energy Plus Campus, NBM&CW, Jan, issue.
- Mundle, P et al (2018). Effect of Aluminium Back Plate on PV Module temperature and Performance, IEEE 7th World Conference on Photovoltaic Energy Conservation, Waikoloa, Hawaii.
- Design and Drawings developed by Indian Institute of Technology, Bombay in association with M/s SSA, Architect Consultant, Bombay.
- http://seci.co.in/other_page.php? page= jnnsm_introduction
- http://www.dandimemorial.in/
- Inemesit Ukpanah (2024), Solar Trees: The Future of Green Energy, https://www.greenmatch.co.uk/blog/solar-trees
- Mensour Almadhhachi, István Seres, István Farkas (2022), Significance of solar trees: Configuration, operation, types and technology commercialization, Energy reports, Vol. 8. https://www.sciencedirect.com/science/article/pii/S2352484722008617#:~:text=The%20types%20of%20designed%20trees,and%20patterns%20of%20solar%20trees.
- Soni, K M (2024). Importance of Solar Trees in Urban Planning, Built Environment, Indian Buildings Congress, 10(1), 5-12.