October 2018

delwp.vic.gov.au

Managing overshadowing risk when installing a rooftop solar system

Home owners guide

Many Victorians are investing in rooftop solar photovoltaic (PV) panels and solar hot water heating systems. Carefully considering your site surrounds before installing a solar system could save you from future overshadowing issues.

Overshadowing can potentially impact the operational efficiency of your solar system. In most cases solar overshadowing can be avoided by thinking carefully about your system design and location prior to installation. By considering the potential risks to your system you can minimise or avoid future problems.

Generally overshadowing can occur:

in areas that are more densely developed, such as inner suburban locations with narrow lots and minimal side setbacks,

where tall trees have been planted,

where taller buildings may cast a shadow over roofs of lower buildings.

This information note can assist you in asking appropriate questions of your solar supplier about the best location and design to avoid overshadowing issues. If in doubt seek independent advice.

A checklist and general advice for parties seeking to develop or extend a building on their property is also provided to help minimise or avoid any overshadowing impacts on neighbouring solar systems.

What are the potential risks to your system?If you are installing a solar system then you should investigate the potential overshadowing risks associated with your site.

What can you do as an owner of a solar system?

Before installing a solar system, you should speak to your solar supplier about the risk of potential overshadowing.

In most cases provisions under your local planning scheme will provide sufficient incidental protection of your rooftop solar system from undue overshadowing by neighbouring developments.

When deciding where to install a solar system, keep in mind that your neighbours might build a taller building, or plant a tree(s) that could affect the efficiency of your system. Before installing a solar system, you should consider the following issues:

1. Development potential of the adjacent property. Check the maximum building height of development and setback requirements set out under the local planning scheme: https://www.planning.vic.gov.au/schemes-and-amendments/browse-planning-schemes-by-map . VicPlan can help to identify the zoning around your land: http://mapshare.maps.vic.gov.au/vicplan/. Your local council can also help explain the form of development that could occur on adjoining land.

2. Growth potential of existing trees on your own property and your neighbour’s property. Try to identify the tree species and research the heights they typically grow to help assess the potential for overshadowing.

Note: Shade trees can improve the summer energy performance of buildings. Where shading from trees is likely, examine alternative locations for solar system placement.

3. Consider your roof form including any protruding structures such as chimneys and evaporative air conditioning units which may also cause potential overshadowing of your solar system.

4. Whether the design of your solar panel system allows for panels to be easily relocated . Consider whether the solar panel mounting system readily allows for relocating the panels to a more suitable location if overshadowing becomes a problem in the future.

How to avoid overshadowingIn most cases solar system overshadowing can be minimised or avoided by carefully considering your site surrounds and responding to potential risks. Before installing a solar PV system, you should consider:

Orientation North

East/West

South (less ideal, but can be viable)

Splitting your system across multiple orientations

Location Higher on the roof

Setback from the lot boundary

Split between multiple locations

System design Multiple string panel arrangement

Micro-inverters

Bypass diodes

What is the best solar system orientation?North

It is generally best to locate panels to the north to provide greater efficiency and protection from overshadowing. Placing solar systems above north facing windows can limit the impact of overshadowing from future neighbouring development. The planning and building systems require additional building setbacks to maintain the functionality of north facing windows. In some cases, where narrow lots run east-west, it may be preferable to locate panels east or west where there is a greater setback – always consider the context of your site.

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SETBACKS FROM NORTHFACING WINDOWS DAYLIGHT TO EXISTING WINDOWS

Place solar panels above existing north facing windows If you can’t place solar panels to the north, place panels over any existing windows of a habitable room1

Figure 1. Oblique view showing how setback requirements to protect solar access to north facing windows can be used to support good solar panel placement (illustrative example only).

East/West

Depending on your site, locating panels high on the west and east can be almost as effective as north. However, it is important to be aware that with longer shadows during the morning and afternoon, potential overshadowing impacts from the east or west may be more pronounced.

Splitting panel location across north, west, east or even south roof orientations can minimise the impact of overshadowing on your solar system as a whole.

South

If other orientations are not suitable due to roof layout, heritage controls, or existing and/or potential overshadowing; south oriented panels can be an alternative. Although not as efficient as other orientations, south

1 A habitable room is a room frequently occupied and used for an extended period of time. For example, this includes a lounge room, bedroom, kitchen, dining room or study, but does not include bathrooms, walk in wardrobes or a laundry.

facing panels placed at an angle (to the horizontal) of no greater than 20° are able to generate enough energy to be financially viable.

When orienting panels to the south keep the angle from the horizontal as close to zero as possible and panels should be located as close to the roof peak as possible. Be aware of chimneys or other structures on your own roof that may cause some shading.

Figure 2. When locating panels on a south facing roof plane the tilt of the panels should be as close to zero as possible. A tilt of 20° or less is preferred.

Where is the best solar system location?Higher on the roof peakLocating panels higher on the roof line will (a) increase the separation between the panels and any neighbouring development and (b) reduce the height that any neighbouring development extends above the panels, minimising the likelihood of overshadowing.

Above north facing windowsLocating panels above north facing windows provides an incidental level of protection, limiting the impact of overshadowing from future neighbouring development.

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N S

Set as far back from the lot boundary as possibleSetting the panels as far back from the lot boundary as possible (either by moving them to roof panes with a greater setback or placing them further back on the roof) will increase the distance between your panels and any potential source of neighbouring overshadowing, giving a greater degree of protection.

Split over multiple orientationsSplitting panel location across north, west, east or south roof orientations can minimise the impact of overshadowing on your solar system as a whole. Where suitable, the front of your house will be less likely to be overshadowed by a taller building on a neighbouring dwelling (Note - this may not be an option if heritage controls apply to your location).Also consider avoiding placement of panels on a roof face with minimal separation from a neighbouring building. Splitting panels across multiple orientations may also allow you to fit the panels closer to the top of the roof peak.

Examples of good and poor panel locations:

Figure 3. Examples of indicative good (green) and poor (red) solar panel locations.

Note: The best location for your solar system will depend on your site context including neighbouring development, trees, topography, roof form, heritage controls, etc.

What is the best technology/system design to reduce overshadowing impacts?

With a standard single row of solar panels (string set-up), partial shading of the panel array can degrade the whole system. Note: this not an issue for solar hot water systems.

The impact of moderate shading can be minimised through system design (e.g. arranging the panels as a multiple string array, using bypass diodes2 or micro-inverters3 which allow for more efficient operation when shade falls on part of the array). These technologies allow unshaded portions of a solar array to continue to operate whilst other parts are shaded. These options should be considered as a sensible means of insurance to minimise the impacts of potential overshadowing.

OK on large blocks with large setbacks minimal chance of

overshadowing (Still better to locate higher on the roof pitch)

Less susceptible to partial shade resulting from

neighbouring development

Best for panels subject to partial shade

2 Solar panels (or modules) are generally connected together in one long string, which means that for the electrical current to flow through the solar panel it needs to pass through every single panel. The problem with this arrangement is that if one panel is even partly shaded, it disrupts the current, reducing the efficiency of the whole system. Installing bypass diodes allows the current to ‘bypass’ a panel when it is shaded, which keeps the rest of the solar array functioning.

3 All solar panels require a form of ‘inverter’ to convert the DC power the panels generate to AC power which can be used in your home. Instead of having one central inverter do this job for all the panels in your solar array, micro-inverters are attached to each panel. This improves overall solar system generation, even if there is a partial shading.

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Installing solar panels in a heritage areaIf your property is included in a heritage overlay, a planning permit will be required from your local council to place solar panels on a roof visible from the street or a public park.

Additional requirements also apply to a building which is included on the Victorian Heritage Register.

If you cannot avoid locating your system in a place visible from the street or a public park, consider the following options before deciding where to install your new solar system:

Rear structures – Are there any recessed structures on your property, like a rear shed or garage, that could be used to mount the solar system in a less obtrusive place.

Side planes – Locating a solar system to the east or west on the side of a roof will generally result in the system being less visually obtrusive than a system located on the front of the house.

Integration with the heritage building – Where a solar system is visible from the street, minimise the visual impact by using matching colours and low reflectivity materials. Locate panels flush with the roof and do not project beyond ridgelines.

Southern orientation – The southern plane of a roof is a viable location for solar panels if other roof orientations are visible from the street.

Solar tiles – Solar tiles can be used to minimise the visual impact of a solar system (Several products are available on the Australian market). Solar tiles should be used where the priority is to minimise visual impacts. Solar tiles should be avoided where the roof fabric is inherent to the significance of the building.

Tankless solar hot water systems - most solar hot water systems are now designed to have the tank located either inside the house or at the ground level. This means that extra support is not required to hold the tank on the roof and prevents additional visual bulk of the system.

Figure 4: Examples of solar installations in heritage areas. A well-integrated solar facility minimising area of visible roof plane covered and using matching colours/materials (left). A poorly integrated system projecting above rooflines (centre). A very poorly integrated system with the majority of the visual roof plane covered by the solar system and projecting above roof

ridgelines (right) (Photo source: Street view images, Google 2018).

Note: When installing a solar system on a dwelling with significant heritage fabric, care should be taken to ensure that the system can be installed and removed without damaging the heritage fabric.

For detailed advice contact your local council.

What are your solar options if your roof has existing overshadowing?If your available roof space is currently subject to significant shading, making installation of a solar system unviable, there are other ways you can improve the energy performance of your home and reduce your energy bills. Further information on alternative approaches to reducing energy consumption in your home is available at:

Sustainability Victoria: http://www.sustainability.vic.gov.au/You-and-Your-Home/Save-energy

Your energy savings: http://yourenergysavings.gov.au/

Installing a solar hot water systemWhen installing a solar hot water system on a roof, the same siting principles for installing a solar PV system apply.

Solar hot water systems come in two main types, flat plate collectors and evacuated tube collectors. There are many factors that will influence what collector you install with each having its own advantages and disadvantages. Evacuated tube collectors tend to perform better under overcast and shaded conditions.

Flat plate collector Evacuated tube collector

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Homeowner ChecklistIf there is a possibility that the proposed location for your rooftop solar system could be overshadowed by future development, you should consider the following matters and seek advice from your installer to ensure the best outcome to minimise or avoid overshadowing:

CONSIDERATIONS PRIOR TO INSTALLING A SOLAR SYSTEM

Have you considered your site and surrounds, including:

• Zoning and development potential of neighbouring lots.

• Existing structures or trees that could overshadow.

Are you located in an area covered by a Heritage Overlay? If so, what placement locations would avoid the panels being visible from the street or public park?

Have you discussed existing and potential overshadowing impacts with your installer?

If your panels are facing north, are they located above a north facing window?

Have you discussed your daily pattern of energy use with your solar panel supplier? This may influence the best location for your panels (for example, if most energy use is in the afternoon, west facing panels can be very effective).

Are panels located as high on the roof as possible?

Are panels located on a roof face/orientation with the greatest separation from your lot boundary (for example, opposite your side driveway)?

If panels are located to the south, is the tilt angle 20° or less?

On constrained sites have you split panels across multiple orientations?

Have you considered a system design that performs better if affected by partial overshadowing such as multiple string arrays, micro-inverters, power optimisers or by-pass diodes?

Have you considered the scope for relocating panels in the event of unexpected overshadowing impacts?

Note: This checklist of important considerations is a general guide only, the best solution for your solar system will be dependent on the site and its surrounds. The information in this guide is also subject to changes in technology. An accredited solar energy facility installer will be able to provide advice based on your specific needs.

Questions to ask your solar providerIn order to minimise or avoid the risk of overshadowing your solar panels, get the best possible advice. Ask your preferred solar system supplier the following questions.

1. Have they adopted industry best practice by agreeing to the Clean Energy Council’s Solar PV Retailer Code of Conduct (https://www.cleanenergycouncil.org.au/technologies/solar-pv.html)? The Clean Energy Council website also provides a list of solar panel modules and inverters that meet Australian standards.

2. Will they assess the impact of existing sources of shading on your solar system location?

3. Will they assess the impact on your solar system based on potential future overshadowing from the development of your neighbour’s property (Check what is allowed in your local planning scheme)?

4. What are the potential benefits of additional features such as micro-inverters or bypass diodes that may reduce the impacts of partial shading?

5. Ask about splitting your system across multiple roof orientations or what potential there is to relocate your solar system in the future.

© The State of Victoria Department of Environment, Land, Water and Planning 2023

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AccessibilityIf you would like to receive this publication in an alternative format, please telephone the DELWP Customer Service Centre on 136186, email customer.service@delwp.vic.gov.au, or via the National Relay Service on 133 677 www.relayservice.com.au. This document is also available on the internet at www.planning.vic.gov.au.

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