Commercial scale PV systems present enormous opportunities to our industry. However, the requirements to source and verify a range of site-specific data over a large site is challenging.

To then ensure this data correctly informs all aspects of the system’s performance and installation requirements can be complicated and unfamiliar to some system designers and installers.

Possible questions that might arise include the following:

  • How do you ensure the correct cable distances and gauges have been calculated?
  • The site requires zero PV export or additional grid protection – what products support this and how are they programmed?
  • How do you avoid confronting the need for unplanned additional work on site?
  • Is the Bill of Materials for this installation comprehensive – are there sufficient materials to complete the installation?

Clients often request financial data for the proposed installation, such as the IRR and LCOE. As a system designer, you must be able to justify these calculations by the system design and performance data. The prospect of engaging in quotations for larger installations is daunting – do you have the skill-set to meet the market?

Having a detailed site-specific system design will provide the Bill of Materials, the system cost range, and the system performance data in a clear and logical fashion. Once completed, this information will ensure that the installation process goes smoothly and the system is delivered according to specifications.

This article outlines techniques and supporting processes for PV system design – these maximise an installer’s onsite efficiency, the required time for complete installation, the system costs and customer returns.

Why use a system design?

A system design created by an engineering consultant provides the installer with complete information to deliver an installation efficiently and smoothly. Using a specialist for this design work provides benefits, including the following:

  • Increased margins – engineering design will optimise cable, module and racking locations resulting in quicker installation and reduced material requirements.
  • Access to projects beyond current skill level – engineering design services can provide the installation methodology for projects that require advanced control and monitoring systems using PLCs and zero export relays.
  • Market access to larger project pools – larger projects often require detailed engineering designs that an installer does not have time to complete. An engineering consultancy can complete these and complement them with professional presentations to improve contract chances.
  • Optimised installation processes and time – detailed designs optimise the installation of modules, cables, inverter and racking to reduce installation times.
  • Maximum customer profits – detailed engineering designs provide the installer with accurate analyses of power generation and cost savings.
  • Reduced return-to-site obligations – the detailed engineering design will provide a full account of all the materials and equipment required, eliminating delays in sourcing of additional supplies.

By using an engineering consultant for this type of work, additional services can be offered, such as DNSP liaison services, site assessments and power station registrations – all of which assist the installation process and ensure a smooth transition of control to the owner.

What comprises a system design?

Preliminary and detailed system designs are a very obvious way to differentiate your installation practices from competitors. These documents provide the analytical platform underpinning the optimisation of system installation and performance. Important considerations include: shading, row spacing, module tilt and orientation, oversizing ratio, wiring runs and cable size.

A preliminary design offers information vital for winning a contract, including elements such as plan view diagrams, flyover video presentations, monthly power generation analyses, required design calculations and material costings.

A detailed design is the installation roadmap: it provides site layout plan drawings, string layout drawings, elevations, inverter station drawings, electrical drawings, protection and zero export schematics and a bill of materials.

In addition, the accompanying detailed report explains the design choices and installation methodology. An installer can safely follow these drawings knowing the system will meet the CEC, Australian Standards and best practice guidelines. GSES’s design reports also comply with DNSP document requirements and can be submitted alongside the application to connect.

High quality system designs should contain the following:

Site assessment – A complete site assessment will include: the roof structure, roof obstacles, building height, shading, roof type, access, and existing electrics. This assessment can be conducted by the engineering consultant or by the installer. When the latter is used, the consultant provides questionnaires and forms to the installer to ensure adequate information transfer. The site assessment is essential to complete the system design.

Plan view diagrams – Include module layout, module spacing on roof, row spacing, shading, purlin spacing, feet and rail spacing.

System design calculations – The number of modules in series and parallel, cable, isolator, circuit breaker sizes, MPPT configurations, inverter inputs and system protection requirements.

Electrical schematics – Include electrical information about cable sizes, isolator rating, fusing and MPPT configuration requirements as well as additional safety and protection integration information.

Bill of materials – The bill of materials (BOM) is based on the design drawings and schematics. This allows for the quantities of all major and minor components to be defined.

String layout and electrical wiring drawing – Highlights the module strings, method of connection and cable run locations within roof space, conduit and cable tray. (See images below.)

Financial analysis – An analysis of consumption data and predicted system yield information will allow for an accurate calculation of system return and savings.


String layout, designating modules to selected inverter and string

Module and wiring layout with directions for roof entry point.</em></a>



The system design process and the documentation provided allows the installer to visualise the installation, predict and mitigate installation issues, and provide accurate data on performance and financial returns to the customer. At the same time, this information provides a potential for installation cost savings by reducing the material requirements and the time to completion, which in turn can improve the installer’s margins. System designs can be used as promotional material to win contracts and differentiate your service from the competition.