Solar photovoltaic rooftop has emerged as a potential green technology to address climate change issues. Mounting structures play a vital role in efficient working of a solar power system, both in utility and rooftop. Here, we do an analysis on how to optimise solar PV mounting system, one of the high profile components.
Mounting structures are a critical component which ensure structural stability of solar PV systems. The solar PV systems need to withstand weathering and stress during 25 years of installed life.
Optimising solar PV mounting system
One of the biggest ways of optimising mounting systems is by optimising space efficiency. Increasing space utilisation by stacking the modules back to back rather than placing them in single line rows, can be one of the ways.
Siddharth Gangal, Co-Founder & CEO at The Solar Labs says,” Structures must be galvanised to a thickness of at least 80 microns and it must be ensured that fasteners and clamps are waterproof to prevent rust. Some ground clearance, wind tolerance of 120 kmph and perforated wiring systems that allow easy wire travel through structures are good design practices.”
Mounting manufacturers should provide variable mounting angles in structures so that mass production of structures can be done and angle of solar arrays may be changed during O&M to get higher energy generation.
Animesh Manek, Founder and Managing Director, Avishakti Rooftop Solar Pvt Ltd states, “In Mumbai, PV modules are usually placed at 19 C angles. The area occupied by two 2m*1m modules placed one behind the other (in a way where the module in front doesn’t overshadow the module behind it at any point of time in the year) is approximately 4.4 sq metres. However, mounting 2 modules in a stacking structure occupies only an area of approximately 3.67 sq metres resulting in 16.6 per cent better space utilisation. Similarly, placing 3 modules in single line rows occupies an area of approximately 7 sq metres but placing 3 modules in a stacking arrangement occupies approximately 5.5 sq metres giving 21.4 per cent better space utilisation.”
Ravindra Prakash Dubey, MD, Granzor Engineering Private Limited opines, “PV mounting systems are quite cumbersome and need lot of modifications. I hope with new module-types, be it flexible, light weight or other formats, Sun tracking systems increase yields and also the structure gets many innovations.” There are other factors too such as weight, heavy fondations, options for movability of the systems, durability for 30 -35 years, speed of installation, flexibility to mount all sizes of panels without much working or modifications.
Moreover, mounting systems need a continuous optimisation because solar panels are expected to be under many modifications. Though Indian conditions do support ’fixed tilt’ systems, an additional yield of 15 to 23 per cent are quite enough to persuade our ’design efforts’ for reliable tracking systems.
Jasmeet Singh Banga, General Manager, JIKA-Division, Riddhim Siddhim Steel (I) Pvt Ltd explains, “PV mounting systems are the base of any solar PV power plant; its design and adaptation to surroundings plays a very vital role in the functioning of the plant. With Riddhim Siddhim’s expertise in roll forming and a variety of sections, it gets easier to optimise the design as per site. Optimisation of the system should be such that it can be easily assembled and shouldn’t cause too much trouble when it comes to its O&M. Hassle-free installations and ease of material handling too should be kept in mind especially in cases of rooftop power plants.”
Suitable material for the mounting systems
Animesh of Avishakti Rooftop Solar describes the material selection as a process that is dependent on several parameters. Some of these parameters are:
• Climatic conditions
• Strength of underlying structure on which structures are mounted etc.
Aluminium has higher upfront cost as compared to steel because the extrusion processes involved consume a lot of energy. Steel, on the other hand, is cheaper because of its bulk availability and easier manufacturing processes.
Residential sectors, where high upfront cost is the major driving factor, steel may sometimes be the best option. High tensile strength, durability and resistance to heavy winds are some of the attributes of steel.
Animesh adds, “Weather conditions also play a big role in deciding the material of the structure. In oceanic climatic conditions and corrosive environments, steel rusts at a faster rate. To avoid rusting, aluminium would be better option. Also, aluminium structures are easier to install and maintain. A lot of the players in the commercial utility scale sector prefer aluminium structures which are not only light weight but durable enough for PV applications as well. “
Ravindra of Granzor Engineering informs, “Material selection depends on the project. Ground mounted systems and in general, panel mountings are preferable on HDG (hot dip galvanised) MS structures. However, tin shed and similar roofs have limitations in load bearing; hence, in that case aluminum structures are preferred. There are FRP structures available which are as strong as steel but very light and easy to work. So, a hybrid approach i.e. legs in HDG, purlins and rafters in FRP using SS 304 hardware could be quite an optimal structure.”
The problem arises when there is a lack of availability of all the three materials from one source or vendor. New vendors need to be encouraged to opt for such systems, making the material’s availability under one roof at the most economic prices.
According to Jasmeet of Riddhim Siddhim Steel,” While selecting a material for mounting systems, it majorly depends on the type of building it is used on, for e.g., if it is an industrial shed with low load bearing capacity, then aluminium is the preferred material, and if the roof is a RCC platform and there need to be considerate elevation of the structure, then steel is the best choice.”
Cost wise also both the materials are almost on the same page. Using steel for structures has an added advantage given the ease of manufacturing of a variety of sections with cold roll forming technology in JIKA-MMS as it gets easier to accommodate a variety of sections in one project owing to its ease of manufacturing.
Siddharth Gangal, of The Solar Labs states, “For ground mount and RCC rooftops, structures are made from mild steel that is zinc galvanised or from cold formed GI sections. Aluminium is used on shed installations as it is lightweight. If the shed cannot hold weight of solar panels, the load is put on purling structure. But if the shed can support load, a sheet mount structure may be used that reduces about 30-40 per cent of aluminium material requirement.”
Siddharth further points out that because of intense market competition and commoditisation of solar, contractors skimp on structure quality and increase maintenance requirement and run the risk of the structure not lasting 25 years.
New innovations in mounting technologies
Animesh says, “Future innovations in mounting will be architectural in nature. The buildings will be designed to accommodate modules in a way that the rooftops below can be utilised for other purposes. Also, mounting structures will be designed keeping maintenance in mind.”
Ravindra of Granzor Engineering is of the opinion that the future innovations in mounting technology will be quite attractive, provided it can ensure:
1. A versatility so that any sizes of panels do not matter
2. Total weight coming down to < 20 Kgs/KWp. It could be possible with a hybrid approach of HDG(legs)+ FRP (rafters & purlins) +SS 304 (hardware)
3. Dismantlability and refixing; a major drawback at present. Once installed, it’s very difficult to move the system to another place. Systems up to 15 KWp should be made movable.
4. Reliable tracking systems are still not available at economic rates. We need to look into this segment from future point of view.
Jasmeet of Riddhim Siddhim Steel acknowledges, “There has been a fair share of technological advancements when it comes to mounting structures; like earlier in 2011-12, the structure weight was around 100 tonnes per MW which has now come down to a mere 30 MT per MW, similarly for the variable tilt structures. We also introduced the north side roof tilt structures because of the need of the hour. Also, there has been an introduction of new materials in the steel sector such as POSMAC and JFE which have high tensile strength in low thicknesses. Also, automation in smaller structures will be the next big thing when it comes to mounting technologies.
Siddharth concludes, “On shed installations, holes are punched in the shed to install rivets for the structure. This increases risk of water passing through the roof onto customer’s premises. A new glue based technology that can last 25 years is now being used that can hold the structure to the shed.”
A lot of the players in the commercial utility scale sector prefer aluminium structures which are not only light weight but durable enough for PV applications as well
Animesh Manek, Founder and Managing Director, Avishakti Rooftop Solar Pvt Ltd
“Optimisation of the solar system should be such that it can be easily assembled and shouldn’t cause too much trouble when it comes to its O&M.”
Jasmeet Singh Banga, GM, JIKA-Division, Riddhim Siddhim Steel (I) Pvt Ltd
“Though Indian conditions do support ’fixed tilt’ systems, an additional yield of 15 to 23 per cent are quite enough to persuade our ’design efforts’ for reliable tracking systems.”
Ravindra Prakash Dubey, MD, Granzor Engineering Private Limited
“Structures must be galvanised to a thickness of at least 80 microns and it must be ensured that fasteners and clamps are waterproof to prevent rust.”
Siddharth Gangal, Co-Founder & CEO at The Solar Labs