When solar system designers estimate the energy generation potential for your rooftop solar system they generally apply the same system design rules as they would do for large-scale ground-mounted systems. As a result, when the system starts generating, the actual generation falls short of the predicted numbers, leading to dissatisfied and unhappy consumers. In this blog, we not only try to explain why perhaps your rooftop solar systems are generating less but also tell you how a good system design can ensure that the solar system on your roof performs equal to or in some cases, even better than the large ground mount systems. First, lets try to understand the reasons or factors that could be leading to lower generation. Some of them may be beyond our control but many can be controlled through good engineering, project execution and O&M practices.

Factors that may be beyond our control

• Roof orientation – In ground mount system we can optimize the orientation of the modules (Tilt angle and azimuth angle of module) in order to capture maximum solar irradiance whereas in rooftop (primarily in sloped roofs) installations, the angle and orientation of the roof may not be ideal in order to capture maximum solar irradiance.
• Availability of space – Due to space constraint in rooftop installations, solar system designers compromise with the ideal pitch (distance between two rows of solar panels) which leads to higher energy loss because of shading.
• Temperature and distance between Solar Panels and Roof – We know that solar photovoltaic modules have a negative temperature coefficient. In simple terms, this means that output of solar system decreases with increase in ambient temperature around the solar panel. If the solar panel is too close to the roof, there is less air-flow to cool down the solar cells, and therefore the ambient temperature around the panels tends to increase leading to a loss in generation. Ground mounted systems have a better ground clearance between the solar panel and ground, whereas rooftop systems sometimes are installed very close to the hot surface of roof and therefore the generation from rooftop systems is lowered further..
• Maintenance/ System oversight/ etc.-  Large ground mounted solar power plants normally have   better access to preventive and corrective maintenance activities as they can afford to have trained teams on the site. However, due to smaller system sizes in case of rooftops, it is not possible to keep full time on-site engineers. However, this situation can be improved by having a robust remote plant monitoring and analysis in place as well as having a firm O&M contract with the solar system installer.

Factors that can be controlled

Design & Engineering- This is one of the most important factors which is widely ignored by a majority of solar system installers.   A sound solar system design is a must to get the best possible performance from a rooftop solar system and most of the solar system installers lack in this area. A poor design leads to a substantial loss of generation and therefore impacts your savings and financial returns negatively. How do we ensure optimum solar system design and engineering?

• Site assessment – Site assessment is very critical for any solar installation whether it is a rooftop or ground mounted system. Ground mounted systems generally have a free horizon and no nearby shading objects whereas rooftops are prone to near and far shading objects like chimneys, overhead water tanks, air handling units, trees, nearby buildings, etc. In order to avoid the impact of these shading objects, a detailed shading analysis is required to find out best possible location on roof to install your solar system. If this analysis is not done properly, you may lose a large amount of generation. Do note that even a shade on 5% of a single module may lead to a 75-80% loss of generation in the solar string, which that that module is a part of. MYSUN takes a lot of pride in their detailed site assessment efforts. You can read more on it, in the Customer Services section here.

• Solar Plant Layout – The layouting and placement of solar equipment on your roof is extremely important for an optimum performance as the solar radiation is not uniform across the rooftop area. A proper layout can also help reduce the cost of your solar system. It is advisable to connect electrically those modules in same string which are prone to early shading compared to the other modules which are not. One should segregate the modules basis their current rating and try to keep modules with a narrow current range in one string. You can also put lower current rating strings in lesser solar access areas whereas higher current rated strings can be placed in higher solar access areas. This way, one can optimize the system output within the given rooftop circumstances. Ambient Solar Panel/Module temperature is a big concern for rooftop systems, so you should try to elevate your structure from roof surface to make a provision for proper air circulation in order to reduce module temperature and therefore get  better generation. Moreover, try to place inverters at a central location of module array area to minimize cable length which may further reduce your ohmic loss. In ground mounted system, we generally do not see such problems, as sites are quite open and have almost uniform solar irradiance.
• Selection of Equipment- If we select right equipment considering the local weather and site conditions, generation loss can be reduced. Solar modules with a better temperature coefficient can reduce your temperature loss, use of string inverter with multi MPPT can reduce mismatch and shading losses, use of appropriate size of cable can reduce your ohmic losses.

Execution- If you take care of a few small things during installation of your solar system, you can improve the performance.

• Segregate the modules on the basis of their current rating and try to put modules with similar current rating in one string. This would be helpful to reduce your module mismatch losses.
• Keep the provision of air circulation in order to control the module cell temperature in order to reduce losses due to temperature.
• Connect the early shadowing strings of array on separate MPPT and the strings shadowing later on a separate MPPT of inverter.
• Try to avoid any joints in the cable used in entire solar plant.
• Use adequate size and material of cable lugs to make electrical connections. Proper crimping tools should be used for crimping.
• All electrical connection should be air-tight to improve your plant availability.
• Use proper grounding of equipment and lightning arrestors.

Operation & Maintenance (O&M) - Though solar plants do not require much O&M , but a good planning and preventive schedule backed with a detailed plant performance data can help improve the generation significantly. In the case of large ground mounted solar power plants, the  systems are monitored and maintained by on-site skilled manpower, whereas rooftop systems lag in this regard, as most of them either do not have monitoring systems in place or do not get monitored at all. In absence of monitoring, it would be very tough to track plant performance closely and it may lead to a substantial loss of generation. We strongly recommend that each and every rooftop solar system, howsoever small in size, should use a data logger or a remote monitoring device. If we take care of simple things, generation can be improved significantly:

• Periodic cleaning of  Modules –  By cleaning of modules as per recommended cleaning cycle, we can easily increase our generation by 2-7% or even more depending on location of installation.
• Temporary shading object- Sometimes, we put some temporary objects like cables/ wires crossing across the roof, cloth stands, etc. which may cast shadow on modules and lead to generation loss.
• Visual inspection of panels for bird droppings, fallen leaves, dirt accumulation, cracks or any damage
• Inspections for Inverter function by observing the LED indication and Meters etc.

With the aforementioned pointers, we can say that there are certain constraints in roof top system design which may reduce the generation as compared to ground mounted systems, but if we do proper engineering and system designing and keep certain factors in our mind during installation and O&M, this gap can not only be eliminated but we can actually get a much higher performance from our rooftop solar system.

Run our Advanced Solar Calculator where you can change your roof area, shading, orientation and roof to check the generation that you can realistically expect from your rooftop solar system. Make sure you visit the MYSUN blog often and follow us on our Social media profiles to ensure that you keep up with more such interesting articles on rooftop solar.

With each sunrise, the deadline for achieving 40GW from the rooftop solar PV plants by 2022 edges closer. We have already seen states like Karnataka, Haryana and more recently, Assam set ambitious targets or open tenders in order to push the rooftop solar segment as close as possible to the target that has been set. Joining the aforementioned states is the state of Jammu & Kashmir, where, the Jammu & Kashmir Department of Science and Technology has announced a target of achieving at least 450MW of rooftop solar capacity by the year 2022.

The policy allows the interested residential, commercial or industrial building owners to install systems anywhere in the range of 1 kW to 1,000 kW on their rooftops. For government agencies, the upper limit of 1MW does not exist, and they can get an even larger sized plant installed. Ministry of New and Renewable Energy (MNRE) has designated Jammu and Kashmir Energy Development Agency as the agency to undertake the rooftop program and facilitate the sale of power to the state Distribution Company (DISCOM) using Net Metering. The announced policy shall remain applicable for the next 10 years and shall be implemented in accordance to the JKSERC (Jammu & Kashmir State Electricity Regulatory Commission) Regulations.

The best part about the policy is that it invites virtually all consumers, including individual households, industries, government and non- government bodies, commercial, industrial and residential complexes to participate in either a self-owned or through a third party owned Solar PV Net Metering based system. Therefore, you can either choose to install your own solar system or just purchase solar power. To better understand, which of the two options is more financially viable for you, you can always run the MYSUN Advanced Calculator for an instant snapshot, to help you make this decision.

Thanks to Net Metering, consumers who will generate surplus power will see the surplus power carried over on to the next month's bill and subsequently, at the end of the financial year, the surplus power will be compensated for. The policy also notifies that consumers who are interested in participating can approach the Department of Science & Technology or the Government of J&K of the grant of the applicable subsidy from MNRE. Jammu & Kashmir being a special category state, residential and institutional users can enjoy a subsidy of 70% of the solar system cost.

You can find the entire policy available on the JAKEDA site here.

The Finance Minister, Mr Arun Jaitley has just announced the Union budget for the year 2017-18. In the aftermath of demonetization, the budget was anticipated to bring relief to the lower middle class and the underprivileged. The budget is keenly focussed towards helping the rural sector, agricultural sector and re-energising the real estate sector. As expected Digital payments and Demonetisation are in the spotlight with the FM mandating that any transaction beyond Rs 3 lakh would not happen in cash. There is cheer for the middle class as IT rate is slashed from 10% to 5% for those in the slab of Rs 2,50,000 to Rs 5,00,000.

It was expected, given that the Government of India has been a huge propagator of solar power in the country that some announcements will be made to further push the adoption of solar, especially the distributed solar segment given that it is farthest away from the 40GW target by 2022. However, it is a rather dry budget for solar. A couple of announcements that were made included covering 7000 railway stations under the Solar Mission which would see the Railway Ministry target 1000 MW in the next 5 years, which would make Railways the largest solar power producer of the country.

The other important announcement was the Government's commitment towards another 20 GW of solar power under the phase 2 of the Solar Mission. It is not clear whether this 20 GW is an additional capacity to the 100GW capacity that has been earmarked for 2022 or is included in the same. It was later reported that this 20GW is to come from solar park development. Solar tempered glass, which is used in manufacturing cells and panels has been exempted from Customs Duty. There were quite a few interesting announcements that could have an indirect impact on solar. The FM announced a commitment towards building at least 1 crore new homes for the homeless by 2019. Since these homes would need to be electrified too, we believe that it should be made mandatory to use 1kW systems per house, which would automatically see the installed capacity of rooftop solar go up to 10GW. An important announcement regarding complete electrification of villages in India was made by May 2018 and it would not be far-fetched to think that solar could make a major contribution in achieving this via mini-grids and other smaller installations. In addition to it, there was a rationalization of corporate tax by 5% for smaller businesses as well as enhancement in MAT carry forward period from the current period of 10 years to 15 years bringing good news to smaller solar installers. This could give rise to a chain reaction where the installers could pass on some of the benefits to the end user too, leading towards lower system prices.

While the budget may have been rather dry for the renewables industry, there was enough included to keep everyone in the industry interested. Just to stay positive, we would hope that the lack of new announcements is down to the fact that the Ministry wants to focus upon correctly implementing the measures that were announced last year rather than just adding more schemes. We would have loved to see the Finance Minister slightly tweak his budget agenda to "Transform India with Clean Energy" from "Transform. Energise. Clean India."

Image source:Samriddhi.org