What you should know before you install rooftop solar

In India, the choice of photovoltaic modules is often between PERC (p-type) and TOPCon (n-type) cells. In the future, heterojunction technology (HJT) will also be available.

The efficiency of a solar module is a key factor — namely how well it can convert sunlight into electrical energy. Currently, TOPCon cells stand out with an efficiency of 21-23 per cent, compared with the 20 per cent efficiency of PERC cells. This means TOPCon modules generate more electricity under the same sunlight conditions.

Module capacity is measured at 25°C. Every degree increase in the ambient temperature reduces the power output by 0.3-0.5 per cent. This reduction i is less in the case of TOPCon, making it a better choice.

PERC modules are more cost-effective in the Indian market, by ₹1-1.5 per watt-peak (Wp).

While technical criterion favour TOPCon, there is limited availability of these modules with India-made cells (only India-made solar cells are eligible for the PM Surya Ghar subsidy).

Another consideration is the availability of shadow-free roof space. Between two modules occupying a similar space, the more efficient one will typically generate more power Thus, if there is less shadow-free area, then TopCon is advisable.

Bifacial solar panels are designed to capture sunlight on both sides, enabling them to harness both direct sunlight and reflected light from the ground. This can enhance the overall energy yield. Bifacial modules produce an additional 1-2 per cent power output vis-a-vis monofacial modules.

The roof and site characteristics play an important role in this choice. Bifacial modules perform best in environments with high ground reflectivity, such as light-coloured or reflective surfaces.

The effectiveness of bifacial technology may be limited if the roof surface does not provide significant reflectivity. Additionally, the height of the installation is crucial, as elevated installations can capture more reflected light, leading to greater energy gains. Bifacial panels often require specific mounting systems to optimise the dual-sided energy collection.

Analysing the return on investment (ROI) for bifacial modules is crucial; while the increased energy yield can often offset the slightly higher upfront cost, factors such as location, roof reflectivity, and efficiency gains will influence the overall outcome.

It appears that most TOPCon module providers are standardising around n-type bifacial modules. One can, thus, get the benefit of bifacial technology by default.

A TOPCon module today costs about ₹23 per Wp if the plant mandatorily uses India-made modules (‘domestic content requirement’ or DCR), or ₹13.50 a Wp without DCR. Mono-PERC is about ₹2 cheaper.

Under ideal conditions, the TOPCon model can produce 4-4.5 per cent more than a PERC module.

The process begins with understanding the two primary types of warranties offered by manufacturers. A product warranty typically covers defects in materials and workmanship and can range from 10 to 12 years. A performance warranty guarantees that the solar module will maintain a minimum percentage of its rated power output over time. According to guidelines from the Ministry of New and Renewable Energy, the warranty should ensure that the modules deliver at least 90 per cent of their rated power output during the first 10 years, and no less than 80 per cent during the subsequent 15 years.

A customer can ensure that the warranty is not subject to any conditions by reviewing the sections on limitations and exclusions.

Generally, warranty from a module manufacturer does not cover naturally occurring scratches, stains, mechanical wear, mould, rust and discolouration, and other conditions that do not affect the performance or mechanical strength of the modules. Snail Trail, Cell Finger and Cell Busbar discolouration are also not covered.

However, a few specific conditions can void the warranty, such as damage caused by improper installation or defective wiring, fire, power failure, natural disasters, vandalism or accidental breakage.

Apart from a visual inspection for visible cracks, chips, or scratches on the glass surface and a check for bubbles or delamination that may indicate defects, it is essential to request documentation from the installer, including electroluminescence test results (EL testing) and quality certifications like IEC standards.

After installation, customers can monitor energy output using the system’s performance monitoring tools, to track production levels, paying attention to any sudden drops or inconsistencies.

The solar solution provider must share all of the above details and ensure completion of factory audit before purchasing the modules.

Start by choosing panels certified by recognised standards, such as the International Electrotechnical Commission certification IEC 62804-1, which confirm they have undergone rigorous testing for performance and durability, particularly for thermal degradation and PID.

Key installation practices include placing the panels in well-ventilated areas and avoiding concentrated light on specific spots. This can help prevent thermal degradation and PID, enhancing efficiency.

Consider using PID-resistant technologies. Some manufacturers offer modules specifically designed to minimise PID risks through advanced materials and construction techniques.

Regular maintenance and monitoring are crucial for the health of your solar panels. Periodically check for signs of wear or damage, such as discolouration or performance changes, and conduct preventive maintenance as needed. Utilise monitoring tools to track energy output.

Finally, keep the panels clean. Accumulated dirt and debris can hinder efficiency and raise panel temperatures, reducing effectiveness. Regular cleaning will help ensure optimal performance and maximise energy production.

One of the first steps is to determine the electricity consumption and sanctioned load for the site. Electricity usage patterns help determine the PV system capacity requirement. A shadow study will be needed to identify the shadow-free area at the site. This is carried out using a software application, which helps evaluate potential obstructions such as nearby buildings, trees, or other structures like water tanks, understanding the roof structure and dimensions, and how shadows change throughout the day and across seasons.

Another consideration is the orientation and tilt of the panels. Positioning the panels to face true south maximises sunlight exposure, while adjusting the tilt based on geographical location can further optimise energy production. Adequate spacing between panels is vital, as it helps reduce shading from adjacent panels and allows airflow for cooling, which is especially important in ground-mounted systems. Additionally, designing the layout to facilitate easy access for maintenance and cleaning will ensure the system remains efficient over time.

A minimum distance of 1 metre between the structure and parapet wall on all sides is advised. Regular cleaning schedules are essential, especially in environments with high dust, to maintain optimal panel efficiency.

Evaluating the roof’s load-bearing capacity will confirm whether it can support the weight of the solar panels and mounting systems. Positioning inverters in shaded, well-ventilated areas help maintain optimal operating temperatures.

Once the design is finalised to position the modules, mounting structures, components and earth protection, the system is ready for installation.

During structural column erection for elevated module mounting, drilling into RCC terrace slabs demands extreme caution due to variable slab thickness and inconsistent construction quality across sites. It is necessary to use high-quality chemical anchor fasteners to ensure roof stability and waterproofing.

Key considerations include:

● Proper module handling to prevent damage

● Avoiding hotspot formation due to shading, which may void warranties

● Maintaining prescribed inverter spacing (as per manufacturer’s manuals) for optimal ventilation and efficient operation

Strict adherence to these guidelines ensure:

● Warranty validity

● Optimal system performance

● Reliability and durability

● Safe operation

Prioritising these specifications during construction is crucial to guaranteeing a well-designed and efficiently operating solar power system.

PV system design prioritises personnel and system safety, considering potential hazards and risks. Site assessments identify high-risk installation and maintenance activities, informing targeted safety protocols, and provision of safety protection systems.

For PV systems with life span beyond 25 years, minimising maintenance risks is crucial. Simple practices like cable marking, proper torque application, and securing fastening bolts with torque indicators facilitate easy maintenance.

Torque marking, although minor, is vital in systems with numerous bolts. It enables quick inspections, reducing ladder-related risks, and fatigue. This practice enhances system reliability, reduces maintenance costs, and improves safety for maintenance personnel, ultimately extending system lifespan.