October 6, 2020

Why Some Rooftop Solar Systems Generate Less Energy Than Ground Mounted Solar System? How Can This Be Improved By A Better Solar System Design?

When designers create solar system design, they estimate the potential energy generation for your rooftop solar system and apply the same system design as they would do for ground-mounted systems. As a result, when the system starts generating energy, the actual generation falls short of the predictions, leading to a dissatisfied and unhappy experience for the customer. In this blog, we will not only try to explain why your rooftop solar systems are generating less energy but will also tell you how a good solar structure design can ensure that the solar system on your roof performs equal to and in some cases even better than the ground mounted systems. First, let’s try to understand the core reasons or factors that lead to lower power generation.

Factors That May Be Beyond Control

Roof Orientation — In ground mount solar panel system you can optimize the inclination of the modules in order to capture the maximum amount of solar rays whereas in rooftop installations, the angle of the roof may not be ideal to capture maximum solar irradiance.

Availability Of Space — With space constraint in rooftop installations, the solar system design compromises with the ideal pitch (distance between two rows of solar panels) which causes higher energy loss due to shading.

Temperature And Distance Between Solar Panels And Roof — As we all know that the solar photovoltaic modules have negative temperature coefficient. In simple terms, output of solar system decreases with increase in the ambient temperature around the solar pv design. If the solar panel is very close to the roof, there is less downward air-flow to cool down the solar cells, and therefore the ambient temperature around the solar panels tends to increase which leads to loss in generation. Ground mounted systems have a much better ground clearance between the solar panel and ground on which it is mounted, whereas rooftop systems sometimes are installed very close to the surface of roof and therefore, the generation from rooftop solar systems is lowered further. However, an effective solar system design can help in overcoming the issue.

Maintenance/ System Oversight/ etc. - Large ground mounted solar power plants normally have a better access to maintenance activities due to their large size and available space. However, due to smaller system sizes like in case of rooftops, it is not possible to keep full time on-site engineers; reasons can be budgetary or any other. However, this situation can be improved by having a robust and remote plant monitoring in place, as well as having a firm O&M (operation & maintenance) contract with the solar system installer.

Factors that can be controlled

Design & Engineering- A factor which is widely ignored by a most of the solar system installers. A sound solar system design is a must in order to get the best possible performance from rooftop solar system and majority of the solar system installers lack in this area. A poor and inadequate design leads to a weighty loss of generation and therefore gives a negative impact on your investment.

How to ensure optimum solar system design and engineering?

Site assessment — Site assessment is a very critical and essential point for any solar installation whether it is a rooftop, ground mounted or any other solar system. Ground mounted systems normally have a free horizon and almost no nearby shading objects, whereas rooftops closely encounter with near and far shading objects like chimneys, overhead water tanks, air handling units, trees, buildings, etc. In order to avoid the impact of shadow casted by the objects, a detailed shading analysis and report is required to find out best possible location on roof to install your solar structure design. If this analysis is not done up to the point, you may lose a large amount of energy generation. A shade on 5% of a single module of solar panel may lead to 75–80% loss of generation in the solar string. Heaven Designs takes a lot of pride in their detailed site assessment and reports.
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Solar Plant Layout — The layout and placement of solar structure design on your roof is extremely important for an optimum performance as the solar radiation. A proper layout of solar design can also help in reducing the cost of your solar system. It is advisable to electrically connect those modules in same solar string which are prone to early shading compared to the other modules which are probably not. One can segregate the modules on the basis of their current ratings and try to keep modules within a narrow current range in one string. You can also put the lesser current rating strings in lower solar access areas whereas, relatively higher current rated strings can be placed in the higher solar access areas. In this way, one can optimize the solar system output within the given rooftop circumstances. Module temperature is a big concern for rooftop systems, so one should try to elevate the structure from roof surface to make a passage for proper air circulation to reduce module temperature and therefore get better energy generation.

Selection of Equipment- If we select the right equipment considering the site conditions and local weather, generation loss can be effectively reduced. Solar modules backed up with a better temperature coefficient can reduce your temperature loss as well as the use of string inverter with multi MPPT can quench mismatch and shading losses, use of appropriate size of cable can increase the resistance capacity. The solar engineering consultants can help in mounting solar panels through guidance for optimum utilization of space, techniques and equipment.

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

·   Segregate the modules on the basis of their present rating and try to match modules with similar current rating in one string. This would be helpful in order to reduce your module mismatch losses.

·    Keep proper air circulation cycle in order to control the module cell temperature.

·    Connect the early shadowing strings on separate Maximum Power Point Tracking and the strings shadowing later on a separate one.

·   Use adequate material and size of cable to make proper electrical connections. Proper crimping tools must be used for crimping.

Operation & Maintenance (O&M) — Though solar plants generally do not require much O&M, but a good preventive schedule backed with a detailed plant performance data by Heaven Designs can help improve the energy generation significantly. For an effective operation of solar panels, a detailed solar pv design is required which fulfils all the blue print criteria of a successful installation.

-Single Line Diagram
-ACDB/ DCDB / Solar LT Panel Design
-General arrangement layout
-DC / AC Cable Layout
-Earthing/ Lightning Arrester layout
-AC Cable Sizing and Loss calculations
-PV Layout
-CEI approval drawings set
-And Much More…

Coming towards the conclusion we can say that, though ground mounted solar systems carry certain benefits in respect of ground clearance, shadow hindrances, maintenance and operations, a rooftop solar system can also be highly productive through a detailed solar design. A full-fledged solar system design is a roadmap to efficient generation. A well-defined process followed by cooperation with the EPC benefits all in the process of solar system installation.

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