Once you have an approximate idea of what size solar PV system you’re looking to install, you need to consider where it will go. If you’re looking for a large system with limited roof area this becomes a task of figuring out the maximum area available on which you can install solar. On the other hand, you might have more roof area than you need in which case the task is to choose the most optimum location to install panels.

Choosing the optimum panel locations or ensuring the suitability of your roof areas requires consideration of a number of factors which we’ll work through.

Roof tilt and orientation

The output of a solar panel is highest when it’s pointed directly at the sun. In summer when the sun is high in the sky a relatively flat panel will have the highest output, in winter when the sun is lower a panel on a greater angle (tilt) will have higher output. The optimum angle is, therefore, a compromise between the two.

Your location in Australia will also play a role in deciding the optimum tilt angle. In Australia, southern states will benefit from more tilt whilst more northern states will benefit from less tilt.

The optimum angle of inclination is actually the same as your angle of latitude. So if you’re in Sydney at 34 degrees south of the equator, a panel facing North at a tilt of 34degrees will maximise your energy production. Similarly, in Melbourne at 38 degrees – your optimum angle is 38 degrees.

Solar PV output based on tilt and orientation

The orientation impacts both total energy generated but also the time of day it is generated. Whilst an array with all north-facing panels might have the greatest energy output over the year, an alternative with a mix of panels facing east and west will produce energy for more hours each day which can be more valuable in some cases – for example, if you have a consumption profile that is skewed to the late afternoon, a west-facing array can help to improve solar utilisation, but also comes at a cost to overall energy production for the year. Solar panel placement can sometimes seem like a series of compromises and trade-offs. It’s important therefore to get accurate output simulations in order to evaluate each option.

As the cost of panels have come down, within limits, increasingly it’s best to focus on ensuring the maximum number of panels are installed in preference to achieving the optimum tilt or orientation.

Racking vs flush mount

It’s most common now in commercial solar installations to mount panels flush on the rooftop or with a relatively small inclination to minimise soil build-up.

For relatively flat roofs, panels can be mounted on racking that increase the tilt angle of the panel. Doing this has two consequences though, it might come at a higher cost, and in cases where suitable roof areas are limited, it may reduce the system size as it requires greater spacing between rows of panels.

Tilting panels may also increase wind loads which may present a constraint on roofs with limited spare structural capacity.

Tilt vs flush mount panels

 

The trade-off between cost, energy generated and system size can be modelled to identify the optimum configuration.

Inclination and cleaning

Panels with a tilt of less than 8-10 degrees are more prone to efficiency loss from dirt and dust build-up. While this can be combatted by a routine maintenance regime, regular cleaning can add to system operating costs. Panels mounted on a steeper angle may more effectively be cleaned by normal rainfall.

Consideration should be made to the amount of dust and rainfall in the local environment (e.g. rural vs city, inland vs coastal) as well as the ease of access for manual cleaning when required.

Frameless panels can help mitigate the effects of dirt build-up as they don’t have a ‘lip’ that traps dust and dirt in a conventional panel.

soiled solar panel

soiled solar panel

Insulation effect

Panels installed on rooftops shade the roof area over which they’re installed. If rooms immediately below are prone to uncomfortably high temperatures, installing panels over these locations may help to reduce either ambient temperatures or energy consumption associated with cooling the rooms.

Whilst it’s a relatively minor benefit, in cases where flexibility exists for locating panels it can be worth considering.

Electrical infrastructure

Each solar array needs to be connected to the grid via an inverter. Depending on the size of the system the connection may also require a secondary protection system (for systems larger than 30kW) or a SCADA system fitted to ensure it is operating within your network operators grid connection parameters at all times.

Most often, your system is connected directly to your main switchboard, but several factors are taken into consideration when designing the system. These include, the distance from the roof to the main switchboard, the voltage drop between the array and inverters and the inverters and the connection point, the size of existing cabling, and the available space in the board. If there isn’t adequate space in the board, or the solar array is large, often a separate PV distribution board is created to house the solar circuit breakers and protection equipment. Sometimes the system can be more easily connected into a distribution board on or near the roof, which makes installation easier, but care needs to be taken to ensure the sub-board is up to the task.

 

Structural capacity of roofs

While most roofs can easily accommodate the additional weight and wind loads imposed by solar panels, taking this for granted can be potentially catastrophic so it pays to get it checked.

It’s generally not the extra weight of solar panels on the roof that is problematic, but the additional uplift forces that act on them during high winds. If the roof is not structurally sound, this uplift can pull panels off the roof, or damage the roof itself.

Uplift forces are greater at the edges of a roof, along the ridgeline, near gutters, and at the corners, which is why a properly designed solar array will have adequate setbacks from these roof elements.

Checking that both the clamping and railing systems used to secure panels to the roof is compliant as well as assessing the structural adequacy of the roof and building with the panels installed is an important step before starting construction.

Shading

Any shading of panels from the sun reduces their energy output. Given the relatively high level of sunshine available in Australia, and the strong underlying return on investment available some degree of shading is still acceptable whilst generating commercially viable returns.

Shading sources to look for include:

  • Trees, giving consideration to your ability to remove or prune them in future as well as likely growth.
  • Buildings, both existing and those that might be developed in future either on your own land or adjacent properties.
  • Roof fixtures, such as parapet walls, HVAC, vents, flues etc.
  • Mobile phone towers and other aerials.

If site constraints are such that you intend to install panels in areas susceptible to shade, you can consider panel-level optimisation options.

Traditional string inverters are configured with arrays split into two or three groups of panels. Shading on any single panel within a group will reduce the power output of all panels in that group.

This can be avoided through the use of either microinverters – which replace a central inverter with small inverters on each panel, or DC optimisers which are an electronic module installed on panels to optimisation the output of pairs of panels.

Age of the roof cladding

Roof cladding has a relatively long but still limited lifespan. Keeping in mind that the solar panels are expected to last 25 years, give consideration to how soon the cladding might be due for replacement.

If it’s due in the near term then consideration should be given to either bringing forward the renewal and doing it immediately prior to installing solar panels or looking at other rooftops that may be utilised.

Poor rooftop cladding condition

Visibility of panels

Be conscious of the visibility of panels from ground level. The appearance is personal taste, some businesses might like to have them on display and use them to make a statement whilst others might prefer to keep them out of sight – particularly on historic buildings.

Panels mounted flush on the roof surface will be much less intrusive than those tilted up on frames.

If there is a particular sensitivity, all-black panels and even black anodised mounting structures are available that may warrant consideration as compared to more commonly found units with light coloured frames and backing.

Blue solar panelBlack frame solar panel with light backsheet Black frame solar panel with black backsheet

Array sizes and panel access

In large commercial rooftop systems, installing panels in large contiguous arrays maximises the utilisation of the roof space and the size of the solar system.

Walking on solar panels creates long term damage and should not be permitted. If a fault occurs with a panel, or an optimiser unit is used, in the middle of an array, exterior panels must be removed to gain access. The larger the array the more panels that must be removed.

Sub-arrays should, therefore, be designed to ensure panels can be accessed easily by only needing to remove one or two other panels. Adequate space must also be left to enable people to safely walk around on the roof and access all areas.

Restricting array sizes to provide for safe access walkways also ensures that the arrays remain accessible for cleaning purposes.