Supplementary Documents

The tilt and orientation of PV modules shall be optimised to maximise PV system power generation. Typically, PV modules in NSW are optimally placed to achieve the highest year round generation when their inclination is approximately equal to the angle of latitude and facing true north. However, constraints such as available space, building orientation and roof type will place limitations on the placement of PV arrays.

Recommendations below should be followed to maximise solar generation:

• PV modules connected to the same inverter MPPT should have the same tilt and orientation to minimise power mismatch issues;
• Flush mount arrays should be placed on pitched roofs with more than 15° pitch and with an aspect ± 45° from true north;
• Where PV arrays are proposed on suitably oriented roofs with a pitch of 15° or less, a raked mount system should be used to adjust the inclination of the PV modules to the location’s latitude ± 10°;
• Where there are no suitably oriented roofs PV arrays may be placed on roofs facing east or west. However, PV arrays should not be oriented more than 90° from true north;
• Raked mounting systems should be used on flat roofs, ensuring that PV arrays are oriented facing due north and inclined to the same angle as the angle of latitude of the site ± 10°;
• PV arrays may be oriented to the east or west if a site specific generation estimate shows that the system can generate adequate energy to offset power consumption between 9am and 3pm throughout the year, and the economic benefit from this configuration can be justified.

Effects of east and west facing arrays

PV arrays installed on an easterly or westerly aspect will have vastly reduced power production during evenings and mornings respectively. However, east and/or west facing arrays can provide an alternative system design when there are no suitable space for north facing arrays.

Consider:

• Are there any geographic features or prevalent weather patterns which reduce PV generation, and can they be avoided by orienting the arrays differently?
• Are there any objects or shading on north facing roofs, making them unsuitable for PV systems?
• Does the site have high morning or afternoon loads that can be offset by PV generation?
• Can PV arrays be installed on both east and west facing roofs to ensure PV generation is available from 9:00am to 3:00pm throughout the year?

Where east and/or west facing PV arrays are proposed, the generation estimates of these systems must show that the system can generate adequate energy to offset power consumption between 9am and 3pm throughout the year, and the economic benefit from this configuration can be justified.

Effect of tilt and orientation on PV generation

Any proposed PV system must include site specific system energy yield estimates and system costing.

Irradiation data used to calculate power production shall be site specific and take into account the effect of array tilt and orientation. Figure 1 below shows an example of multipliers to apply to horizontal irradiation data to calculate site specific PV generation.

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Figure 1. Data table of daily irradiation of Sydney on an inclined plane expressed as percentage of the horizontal value for the months of January and June (CEC, 2013). The plane azimuth indicates the module orientation, and the plane inclination indicates module tilt angle.

Modular PV array solutions

System providers may propose PV systems that use micro-inverters (also known as AC systems) or DC Power optimisers. PV systems installed with micro-inverters or DC power optimisers can have higher PV generation when compared to a conventional PV system due to their ability to optimise individual PV module generation and mitigate loss aggregation.

PV systems that utilise this type of equipment do not require all modules in the PV array to have the same tilt and orientation. However, PV modules in these systems should still be oriented and tilted as previously outlined to maximise system output.

Inverters have a set range of PV array input voltage and current values within which the inverter can operate safely and efficiently. Matching the array and inverter correctly will reduce the chance of inverter failure and ensure that the system generates the expected energy yield.

It is the PV system designer’s responsibility to ensure that the PV array’s electrical output lies within the inverter’s operating parameters.

As a guide, the capacity rating of a PV array connecting to an inverter should match the inverter’s nominal AC power rating. The PV array capacity rating should not be less than 95% of the inverter’s nominal AC power rating to ensure that the PV array’s electrical characteristics do not easily fall below the inverter’s operating window. For example, if an inverter with a nominal AC power rating of 5kW is used, the PV array’s capacity rating should not be lower than 5kW x 95%, or 4.75kWp.

Oversizing of array is allowed provided that the inverter manufacturer has given written assurance that the inverter is suitable for use in this way and the warranty will not be voided with this application.

 Oversizing of array describes the connecting of the inverter to a PV array that has a capacity rating greater than the inverter’s DC input power rating. By oversizing the array, the PV system will produce more power in the morning and evening, and other times of low solar irradiation. Conversely, when solar conditions are favourable, the PV array’s output is ‘clipped’ and the potential energy from the system is lost.

Figure 1. Clipping effect when a 5kW inverter is connected to a 7.5kWp array. The area above the 5kW line represents energy that is not collected by the inverter

Due to the lower cost of PV modules relative to inverters, effective oversizing of the array ensures the value of obtaining more energy per inverter is greater than the value of the potential energy that is not collected.

The CEC’s Grid Connected Solar PV systems – Design guidelines for accredited installers requires the inverter rating to be at least 75% of the PV array capacity rating. For example, if an inverter with a nominal AC power rating of 5kW is used, the maximum PV array size would be 5kW ÷ 75%, i.e. 6.65kWp.

Table 1. Example matching of different sized arrays to a 4.6kW inverter

Table 1 shows four different systems matched to a 4.6kW inverter. Inverter and array are appropriately matched where array capacity is greater than 95% of inverter AC power and inverter AC power output rating is larger than 75% of array capacity.

System 2 and system 3 are acceptable system configurations, where system 3 has an oversized array within the acceptable range. System 1 should consider using an inverter with a lower power rating, and system 4 should consider using an inverter with a higher power rating.

It is of critical importance that care is to be taken to ensure that the PV array’s electrical characteristics are within the inverter’s allowable array size specifications.

Manufacturers’ installation instructions shall be followed to ensure secure installation of PV system to last the expected lifetime of the system. It should also be noted that manufacturers’ ratings and compliance to certain standards will only be achieved by installing PV systems to manufacturers’ specifications.

PV module attachment to rail

A PV module’s ability to withstand wind and static load is affected by the attachment area. Manufacturers will specify the clamping area of the module. Clamping of PV modules onto rails must fall within the modules’ specified clamping area to ensure that the modules can withstand loads up to the rated pressure.

Figure1. PV module clamping zone example: Module dimensions of Clenergy PowerPlus 245M-260M modules showing clamping area in grey.

Mounting system attachment to roof

Mounting systems will only be compliant to AS/NZS1170.2 if the manufacturer has supplied installation instructions certified to AS/NZS1170.2 and these instructions are followed. Care must be taken to ensure the manufacturer’s installation requirements for the specific wind region and terrain category are met, especially:

• Maximum allowed rail end overhang;
• Maximum rail support spacing;
• Extra rail support spacing requirement in roof edge zones.

Table 1. Mounting system installation specification example: Clenergy ezRack mounting system installation manual extract showing maximum rail support spacing for tile roofs in terrain category 3

If an installation configuration is not covered by the mounting system manufacturer’s specification, a structural engineer’s certificate must be obtained for the proposed installation configuration, stating the compliance of the proposed installation method with AS/NZS1170.2.

Manufacturer’s installation instructions and corresponding engineer’s certificate must be provided as part of the system documentation.

Installation of PV modules on roofs often require penetration of the roof envelope for affixing the mounting system and for facilitating cable entry. These points of roof penetrations create a potential for water ingress into buildings and electrical systems when they are not correctly installed, which can cause damage to property or a fire hazard. Care must be taken to ensure that roof penetrations are installed correctly to prevent water ingress.

Roof penetration can be classified into two main categories, horizontal penetrations and vertical penetrations. Both categories have their own characteristics and sealing requirement.

Vertical penetration through roof

Vertical penetrations are made perpendicular to the roofing material. This method is required for metal roofs to facilitate cable entry and mounting foot fixings. Penetration of cables into tiled roofs may also be vertical penetration.

Purpose made flashing and gaskets should be used on vertical penetrations, installed to manufacturer’s specifications.

Figure 1. Flashings installed for conduit entry into roof cavity

Where silicon sealants are used, ensure that checking of silicon seals have been included in the maintenance schedule in the system documentation.

Horizontal penetration through roof

Horizontal penetration run through an existing gap between two materials, most commonly between two tiles. This is typically required by tile mounting systems for attaching tile feet to the roof and for cable penetration.

The mounting system must use purpose made tile feet designed for installation via horizontal penetration. Ensure the chosen tile hook is appropriate for the roofing material.

 Where allowed by the roof material, grind out top and/or bottom of tiles where needed, to ensure tiles surrounding roof penetrations sit flat. Tile feet must not affect the way roof tiles sit. On brittle tiles where grinding of tiles is not appropriate, large flashing or tile replacements should be used instead of conventional horizontal penetration methods.

Figure 2. Incorrect installations- tiles lifted by tile hooks

Figure 3. Grinding out tiles at point of penetration to prevent lifting of tiles

Cable entry into conduit

Poorly installed conduit at the roof can allow water to enter the conduit at cable entry points or connection points. This can lead to critical failure of the system via water ingress into switch gear or water damage at cable junctions.

Conduit at rooftop should be installed such that:

• Cable entry into conduits is installed with suitable glands to prevent water ingress;
• Cable entry into conduit faces downwards;
• Conduit joiners and adaptors are glued to prevent water ingress and conduits coming loose.