7 prime steps to create module layout for rooftop projects

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7 PRIME STEPS TO CREATE MODULE LAYOUT FOR ROOFTOP PROJECTS

BEST PRACTICES FOR CREATING A MODULE LAYOUT FOR ROOFTOP PROJECTS 2

INTRODUCTION Creating a layout is probably the first step for those who aspire to go solar and

installing photovoltaic. With increase in PV electricity growth, layout planning has evolved and improved, this paper

highlights the ways to create optimized layout for rooftop solar plant. The document lays down quantifiable steps to be followed in creating a module layout for rooftops.

Steps involved in creating a layout:

1. Type of Roof assessment

2. Orientation of the building

3. Shadow objects identification, analysis & plotting

4. Optimum Tilt & Pitch for the Roof

5. Module placement in the shadow free area

6. Yield Generation report

7. Final optimized layout

1. Type of Roof Assessment:

Most common roof types are flat, shed, hip, gable etc. solar modules can be installed in all of these

types. However knowing the roof type before preparation of layout is mandatory as the method of

module placement varies with type.

In depth evaluation of roof is done at a later stage.

Figure 1: Shed type roof

BEST PRACTICES FOR CREATING A MODULE LAYOUT FOR ROOFTOP PROJECTS 3

Figure 2: Flat type roof

2. Orientation of the building:

Orientation of the building is to be considered in the module layout, as arrangement of module south

facing or along the direction of the building has direct impact on the generation. In northern

hemisphere orientating the modules towards south will give maximum generation.

Below table gives clear idea of generation impact with examples when module arrangement

deviates from south with respect to location of site.

Location in India South East Facing South West Facing East Facing West Facing

Southern 1% 1% 3-4% 3-4%

Western 3-4% 4-5% 13-14% 14-15%

Eastern 2-3% 3-4% 9-10% 10-11%

Northern 4-5% 5-6% 17-18% 18-19%

*Approx. percentage difference in values compared to south facing is indicated in the above table

for India.

For buildings with non-south facing orientation, if the modules are placed south then the capacity of

the system might reduce.

BEST PRACTICES FOR CREATING A MODULE LAYOUT FOR ROOFTOP PROJECTS 4

Figure 6: South-East facing Shed

Figure 3: East-West Facing Shed Figure 4: South-facing Building

Figure 5: South-West facing Building

3. Shadow Objects identification, analysis & plotting:

Shadow causing objects to be identified & simulated in the software (eg. SketchUp). Shadow

objects may affect the planned module area, leading to reduce area for module placement.

Usual shadow causing objects in roofs are nearby buildings, ventilators, parapet wall, trees etc. It is

important to realize the potential of the shadow objects either the effect is permanent or temporary.

Shadow analysis is done to find the shadow free area for the most daytime hours in all seasons.

Wide range of tools and software applications are available for analysis of shadow effect of objects.

Shadow objects to be simulated in the software as per actual to find out the shadow free area.

Adequate distance from the shadow objects (Objects such as nearby buildings, parapet wall) to be

left to prevent modules from shade. Shadow generated from the software to be plotted in the

AutoCAD layout, resulting to shadow free area for module placement.

BEST PRACTICES FOR CREATING A MODULE LAYOUT FOR ROOFTOP PROJECTS 5

Figure 8: Shadow objects & Obstacles

Figure 7: Ducts - Shadow object

Figure 9: Obstacles - Water Pipeline Figure 10: Shadow Objects & Obstacles

Figure 11: Shadow objects simulation in software

BEST PRACTICES FOR CREATING A MODULE LAYOUT FOR ROOFTOP PROJECTS 6

Figure 12: Shadow free area - Suitable for Module placement

4. Optimum tilt & Pitch for the Roof:

Optimum tilt & pitch distances for the system to be defined, this can be determined from the PVsyst

software.

Tilt depends on the geographical location of the site, selection of the tilt to be optimized to capture

the solar window of all seasons. Total annual irradiation on the plane of the collector is maximized

by selection of optimal tilt angle for the site. Tilt has impact on inter-row shading and associated

shading losses. In shed type roof placement of module flat along the roof shall be adopted.

Finer analysis may need to be made to account for:

a. Soiling

b. Shading

c. Seasonal irradiation distribution for different seasons. Pitch distance to be maintained between rows of modules to avoid inter-row shading, pitch

distances varies with the site latitude. The shading limit may be reduced either by reducing the tilt angle or increasing the inter row space.

Reducing the tilt angle below the optimal is sometimes a choice as this may give only a minimal

reduction in annual yield.

BEST PRACTICES FOR CREATING A MODULE LAYOUT FOR ROOFTOP PROJECTS 7

Figure 13: Tilt optimization in PVsyst Figure 14: Pitch optimization in PVsyst

Figure 15: Shading loss graph

5. Module Placement in the Shadow Free Area: Module placement shall be started once the shadow free area, optimum tilt & pitch distances are

available.

Modules to be placed in organized rows. It should also incorporate access routes for operation &

maintenance at appropriate intervals. Space for obstacles such as water pipeline, skylights, vents also to be addressed.

BEST PRACTICES FOR CREATING A MODULE LAYOUT FOR ROOFTOP PROJECTS 8

Figure 16: Module placement in Shadow free area

6. Yield Generation Report:

The capacity of the site is known after the placement of module in the shadow free area.

Yield generation report to be simulated to get the annual energy generation, losses associated with

various configurations of tilt angle, orientation and row spacing and to obtain an economic

optimization.

7. Final Optimized Layout:

Final optimal layout to be prepared considering the shadow free space availability, economically

optimized module arrangement with balance of systems.

Balance of system consists of Inverters, lightning protection system, weather monitoring station,

earthing connection scheme etc.

Layout to be planned with minimal cable runs and associated electrical losses, also considering

access routes and sufficient space between rows to allow movement for maintenance purposes.

BEST PRACTICES FOR CREATING A MODULE LAYOUT FOR ROOFTOP PROJECTS 9

Figure 17: Final optimized layout with Balance of system

Conclusion:

This paper provides the stepwise process for creating a module layout for rooftop solar plant. Basic

factors like orientation of the building, tilt & pitch for the system are discussed which are to be

considered while making a module layout.

The steps as laid in the document shall be followed for preparation of module layout accounting the

obstructions, their effects & provisions for future maintenance shall be catered.

Components & elements starting from type of roof, identification & analysis of shadow casting

objects, importance of yield generation report are also discussed in the paper.