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Section 6: Planning your solar electricity system

There’s a lot to consider when planning a solar electricity system for your business and one factor will influence another.

Get the right advice

Remember to seek out independent advice to plan your system. The Victorian Government also has a range of programs and initiatives to help businesses plan for their energy needs. Visit the Victorian Energy Saver websiteExternal Link for more details.

Work out how much energy you use

Your electricity use is recorded on electricity bills measured in kilowatt-hours (kWh). Look for a figure that gives average daily usage, and review as many bills as you can to see how this figure varies throughout the year.

Your Smart Meter records your electricity usage every half hour, and this data can give you a much more detailed view of your electricity usage, including how it varies at different times of day and on different days of the week. You can download a spreadsheet of your Smart Meter data from your electricity distributor – however unless you know how to use spreadsheet software (such as Microsoft Excel) to understand what the data can reveal, it may not be useful to you. Fortunately, all the Victorian electricity distributors have online portals that you can log in to and see detailed information about your electricity usage displayed in an easy to understand form.

The distributor is the company that owns the poles and wires in your street and transports the electricity to your premises. This is the business you call to report faults and emergencies and is different to your electricity retailers who sends you your bills.

To find out which distribution network you are in, you can look on the back of your electricity bill or go to the Electricity Distributors section of Victoria’s Energy websiteExternal Link .

The four Victorian distribution network web portals are:

Energy advice businesses may also use your smart meter data to give you advice about your usage, or to help you plan a solar PV system.

It’s worth also reviewing your gas bills. If your gas use is high then, over time, inefficient gas appliances can be replaced with modern electric ones to make the best use of your solar electricity system, but this means your electricity consumption will be higher.

The bigger is better approach

Modelling by non-profit organisation Renew shows that a larger system can have a shorter payback time, which is the number of years until bill savings recoup the installation cost.

Things can change with changes in government policies, FiTs and STC prices (the federal rebate for solar’s contribution to the RET), so evaluate quotes at the time of purchase to estimate your payback period and determine the best system size for your situation.

To get an idea of average solar system costs by size, go to the Solar Choice Commercial Price IndexExternal Link .

Solar Savvy Tip: Electricity distributors may limit the size of solar systems connected into their grid. Confirm the process for larger systems with your distributor.

Constraints on big solar systems

If bigger is better, how big should you go? Roof space is an obvious factor. Most people have budget constraints and have to prioritise their spending. Don’t ignore other investments that may pay off even quicker, such as insulation, gap sealing, window shading, LED lights and efficient appliances.

Electricity distributors may limit the size of solar systems connected into their grid. If you’ve got a normal residential single-phase connection, solar systems up to 5 kW in size are usually no problem, however, going larger often requires extra paperwork or may not be allowed. Confirm the process for larger systems for commercial premises with your distributor. The limit is based on the inverter capacity, not the total capacity of the solar array – this is one reason it has become more common to oversize the solar array by up to 33 per cent above the inverter capacity (a 6.6 kW solar array on a 5 kW inverter).

Your distributor may also limit the amount of excess energy that can be fed back into the grid for the feed-in-tariff. This could affect the payback period and the total value you get from the system, so again, verify this with your distributor before you proceed. Refer to “Grid-connected solar explained” on page 14 for more information.

Siting considerations

The company you engage for your solar purchase should do an on-site analysis to ensure your site is suitable for solar panels. The following advice will help you get the most out of your solar installation.

Which direction?

Ideally a solar site is a north-facing roof or ground space that is not shaded during the day. Panels may also be mounted on other roof areas and can face northeast or northwest or even completely east or west. However, the more the panels face away from north, the less solar energy they capture and the less electricity they can produce. For panels on an east or west facing roof with a 20° pitch, average daily generation will decrease by up to 15 per cent.

Maximising total system generation is not always the key consideration. Some businesses may instead want to generate more when they are more likely to be using it, to maximise self-consumption of their system. In this case, arrays facing east and west may be preferable – generating less overall, and less in the middle of the day, but more in the morning and late afternoon/early evening. Other businesses may wish to maximise feed-in-tariff (FiT) revenue by facing some panels north, but others west or north-west to take advantage of time-varying FiTs. Talk to your installer about the different options.

Where the array consists of panels facing in more than one direction, the array should be electrically split so that each section of the array only consists of panels all facing the same way. In these cases it is usually best to use an inverter with two independent solar array inputs (most modern inverters have this) so that each array section operates independently, without being affected by the other. Using microinverters (explained in Finding the right inverter), which make each panel independent from the others, is another solution. DC optimisers (devices that attach to individual panels to improve their output) could be another option in certain situations – ask your installer.

Shading can impact the performance of your panels. It is important to work with your installer to design a system where shading has minimal impact.

Minimal shading

It is important that the panels are not shaded much during the day throughout most of the year, especially in summer. Because of the way panels are connected in ‘strings’ (one after the other in series, like fairy lights), if one panel has a shadow across it, its output is reduced and the output of all the other panels in the same string will be reduced by the same amount. If partial shading is unavoidable, the system installer should allow for this, by designing the system so that the shaded panels have the least effect on the rest of the system. This can be done in a similar way to managing arrays facing different directions; by putting all the shaded panels on one string and unshaded panels on another, by using an inverter with two independent solar array inputs; by installing optimisers on shaded panels; or by installing microinverters on each panel.

Microinverters are becoming more common because they maximise power output from solar panels, especially in shade situations. Find out more in Finding the right inverter.

Getting the pitch angle right

Panels are often set at the roof angle for aesthetic reasons and to simplify mounting. Slight variations in panel angle don’t make that much difference to the annual energy production, so unless you have a radically steep or flat roof angle, mounting panels at the roof angle is usually the best solution. It is important to have a tilt of at least 10° on the panels so that they can be washed clean by rain.

However, the panel angle should be considered if you want to maximise the energy output from your system at certain times of the year, especially if you want to maximise the total annual energy output. To produce as much electricity as possible, angle the panels to maximise summer solar input. To minimise the seasonal variation in generation, angle the panels more steeply to maximise generation during winter, when the sun is at its lowest and weakest. This approach is more common for off-grid systems, but if this is your goal you can work this out with your installer. Speak to your installer to discuss the optimal angle for your situation. Remember, the cost of angling panels more precisely may be more than the value of the additional energy generated.

Shading can impact the performance of your panels. It is important to work with your installer to design a system where shading has minimal impact.

Reviewed 03 January 2023