Design Standards for 
Solar PPA Projects 

In order to maximise performance, systems should be designed to maximise solar gain and minimise soiling that will lower production.  Good design practices must be followed for all Energy Terrain projects

Wherever possible PV modules should be oriented to the Northern horizon.   The angle of inclination for a North facing PV system will affect solar gain. The ideal angle will depend on latitude. The tables below show the increase in PV production as a function of tilt angle for Melbourne and Sydney latitudes. Locations in higher latitudes will need higher tilt angles to maximise production.

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System cost is affected by tilt angle with a smaller leg spacing being required as tilt increases. Most mounting system design guidelines have a breakpoint around 15° with a reduced spacing being required above this angle.  This makes it less cost effective to install PV modules at the optimal angle on flat roofs. For a terrain category 2 installation, the leg spacing for a 15° tilt is almost twice that required for a 25° tilt, substantially increasing the cost of materials and labour.

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Another factor that needs to be considered is row spacing.  Table 1 indicates the row spacing required to keep inter row shading below 1%.  Higher tilt angle results in larger row spacings and less effective utilisation of the available roof space.  It is sometimes desirable to use a lower tilt angle and a tighter row spacing to increase the total amount of energy generated.

It should be noted that it is often possible to get greater leg spacings than those specified in the standard design guidelines supplied by the manufacturer.  For large systems Energy Terrain encourages installers to talk to their mounting supplier to make sure an optimal design is achieved.

The Clean Energy Council recommends a minimum tilt angle of 10° to facilitate self-cleaning of PV modules during rain.  The self-cleaning effect reduces the risk of under-performance and the need for regular cleaning.  Installations with tilt angles less than 10 degrees need to be discussed with Energy Terrain

The CEC allows PV arrays to be rated at 133% of the AC rating of the installed inverters while still claiming STCs. This is considered to be a cost-effective utilisation of assets as the number of days where the array will output its full power is only a fraction of the total number of days in the year.

In most jurisdictions, the network operators require a secondary anti-islanding device or “grid protection unit to be installed when the AC inverter capacity exceeds 30 kVA. As this adds substantial additional cost to the system, inverter ratings between 30 and 40 kVA should be avoided.  A system with 30 KVA of inverter rating and a maximum of 39.9 kW of DC rating is considered acceptable.

It is customary to run 2 or more strings through one DC rooftop switch.  Energy Terrain consider this to be a false economy for PPA projects for the following reasons

1. If one string fails, you have to shut down two or more until it is repaired. It is more desirable to have an isolator on each string to assist with fault diagnosis and allow fault free strings to continue generating

2. DC isolators are one of the key points of failure in rooftop equipment. By minimising the current, there is less risk of overheating should there be any water ingress and corrosion.

As a basic guideline, Energy Terrain encourages installers to submit proposals that meet the following design rules.

• Wherever possible, PV arrays should face the Northern horizon

• Ideally, modules should be tilted at a minimum 10° to the horizontal. Modules on flat roofs should be tilted at  15° The row spacing for tilted systems shall be no less than defined in Table 1

• Any roof with an incline less than 10° shall be considered to be flat and modules should be placed on tilt frames facing North.

• For roofs with an incline of greater than 10°, flush mounting system can be used.

• South facing arrays should be avoided

• Avoid inverter ratings between 30 and 40 KVA

• Oversizing of arrays of up to 133% of the inverter capacity is encouraged providing that  it does not exceed the inverter manufacturers recommendations.

• There should be a DC rooftop isolator for each string. Do not run parallel strings through one isolator.

Installers must provide the following documentation at the various points in the project cycle.  Fancy quotations are not required. 
For convenience Energy Terrain has provided a quotation sheet for the quotation process (Appendix) that suppliers are welcome to submit as their formal quotation.

When you are ready to quote, please refer to the information below to ensure your quote meets our current guidelines

Please use any of the following Panels in your pricing: 

• Trina Solar 

• Canadian Solar 

• JA Solar 

• Jinko 

• Risen 

• Q Cells 

• Longi 

Please use any of the following Inverters in your pricing: 

• Fronius; or 

• SMA

• SolarEdge 

• ABB 

• Huawei 

• Sungrow

Installers are encouraged to discuss their design with Energy Terrain as part of the quotation development process to make sure a mutually agreed approach is taken.  Upon submission of a quotation installers must provide the following information along with the quoted price.

• Specification of all PV modules, inverters, optimisers and racking including the total quantities of each

• An image showing the layout of the modules and any relevant shading obstacles.

• A preliminary single line diagram showing the PV arrays, inverters, grid protection equipment and circuit protection equipment.

• The total installed cost with GST itemised separately

• As a statement regarding the allowable amount of grid export from the site.

• The expected annual productivity of the system expressed in kWh generated per year as calculated by an industry recognised simulation tool.  The tool used for making this calculation should be clearly stated in the quotation document. This could be one of the following.

  • Helioscope

  • PV Syst

  • Sunny Design

  • PV Sell/Nearmaps

  • Aurora

•  A clear statement of warranty provided for equipment and installation.

Quotations for installation should be inclusive of the following: ​

• All equipment and consumables up to and including the point of connection to the building electrical system including any requirements for Grid Protection

• All installation and commissioning labour

• Any costs associated with post installation inspections or testing such as GPU injection testing.

• All design fees including those required for building structural assessment

• All grid application and connection fees

• Any activities required to update the energy retailer supply agreement

• Installation of solar analytics metering of the inverter and site connection. Metering hardware will be supplied by Energy Terrain
   

As the penetration of solar increases, the DNSPs are adding increasing requirements on grid connected PV systems. It is expected that our suppliers are familiar with the requirements within their network and will properly configure inverters and GPUs to meet the local requirements.

Energy Terrain invites installers to submit a quotation for regular system maintenance. We can provide inspection requirements.

Suppliers are welcome to use the check sheets below to provide quotation and design information to energy terrain. Fancy presentations are not required.