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So You Want to Install Rooftop Solar PV

Bruce Barbour - September 2021

This page is based on my experience from purchasing a rooftop solar photovoltaic system for my house roof in 2019. This page is for general interest only.

Congratulations. The installation of rooftop solar photovoltaic (RPV) is one of the most impactful things an individual can do to lower their carbon footprint and tackle climate change. The other benefit is that it is one of the best financial investments available to the individual - provided you get a good quality system that lasts 25+ years with minimal maintenance.

This is primarily about grid connected systems. Off-grid systems have some different requirements. It is also about Victoria - other States may have other requirements especially in relation to rebates and power prices.

I initially was going to write pages on this important topic but then I realised that others have covered this area and have done it very well - so why repeat. The YouTube video below is from a company called Solarquotes. Solarquotes does an updated version each year (or so). The link is to the 2021 version. If it 2022 or later search for the update on Youtube or the Solarquotes website. I will discuss more about Solarquotes after the video. Its 25 minutes of good advice - so watch it now. I will offer some more observations after the video.



Solarquotes also have a pdf document that covers the same subject. Here is the link to the 2021 version. Even if you have watched the video it is worth downloading and reading the document.

Additional Comments

This assumes that you have watched the video.

Batteries - as the video says batteries are still not considered to be financially viable. However for some people that is not the only consideration.

Even with batteries the rooftop PV system will usually switch off if the electricity grid fails – unless the inverter has been designed to allow “islanding”. (If you are getting batteries and want "islanding" ask the quoting company to include it in the quote. The additional cost is not known.)

A grid connected system without batteries will also close down if the grid fails - even on a sunny day. This is a safety measure so electricity repair people are not electrocuted while trying to get the grid back operating.

Panels - Requirement for Mounting on Roof

North facing roof is usually considered ideal – however the roof has to be unshaded by either trees or adjacent houses/buildings and be of sufficient size with minimal protrusions (e.g. flues, whirlybird, TV antenna). Even partial shading adversely affects the performance of panels.

East and West facing roof is acceptable if the North is not suitable – however there is a loss of overall generation (~15% in Adelaide / Melbourne). Mounting the panels on the East and West roof has the advantage of the system generating electricity earlier in the morning and later into the afternoon. This is advantageous for having more in house use of the generate PV electricity. 

Can have panels on multiple orientations however the price of the inverter and for installation is usually higher.

How Big?

For a grid connected system the economic are such that usually it is best to get as big as possible, as allowed by regulation and your budget, at least in Victoria. The following limitations apply:
  • the amount of suitable roof space.
  • the limit on the amount of power that can be fed into the grid from domestic rooftop PV systems. That limit is 5 kW in Victoria. Some other States have different limits so perhaps in those states it would be possible to go too big.
Often in Victoria systems are installed with 6.6 kW of panels and a 5 kW inverter. The reason why this combination is considered effective is because the panels rarely generate their maximum rated capacity due to the sky not being clear (clouds/overcast) and the alignment of the panels not 100% ideal and also they lose a small percentage capacity on very hot days. Even if the panels did generate the maximum rated capacity they would only achieve this for part of the day. If this is cut off by the inverter the loss is not considered significant and will be made up for by the greater generation capacity on partially cloudy / overcast days.

Installers will advise on how many kilowatts of panels can fit on the roof.

Choosing an Installer / Systems Quality

For the overall economics of the system it is necessary to purchase a good quality system. Basically that means getting good quality panels and a good quality inverter:
  • Panels should last over 25 years.
  • Inverters should last at least ten years.
A system with panels that only last 5 to 10 years will not generate a decent rate of return and create pollution when the panels have to be changed over. And it will also make the owner very cross and wanting to rubbish the idea of rooftop PV.

The Solarquotes document provides a list of good quality panels and inverters that they say are well supported by the Australian suppliers of the equipment. They say that the list is not exhaustive but any panel or inverter that is not on the list would require further investigation.

Rebates

There are a couple of forms of rebates available to encourage installation of  PV systems:
  • Small Technology Certificates (STCs) – these are certificates generated when the system is installed. Usually the installer sells these on behalf of the owner and takes it off the price of the system. Owner has to assign STCs to installer.
  • Victorian Government rebate – Subject to eligibility requirements (see website) – but these are usually not an issue for most households.  I understand that the homeowner has to apply for it  - prior to getting the system installed – see website  for details on how to apply. It is important to read this website page if you want to apply for the rebate. Note that the government releases a limited number of rebates monthly - dates are on the website. It might be best to apply immediately on the release date. 
The Victorian Rebate complicates the process quite a bit. There are quite a few hoops to jump through. However it is currently (2021) worth $1400, if you are eligible, so it is worth working through the process. Do not accept a quote prior to receiving approval for the Victorian Rebate - in case approval is delayed.
Feed In tariff

This is the payment the owner receives for the excess electricity (electricity that is not used in the house) that is fed into the electricity grid. The rate is currently a minimum of 6.2c/kWh in Victoria.  It was recently decreased from approx. 10.2 c/kWh. It could in the future decrease by more or become a variable rate depending on the time of feed-in.

Risks?

Installing a poor quality system that fails in a number of years would be the biggest risk associated with rooftop PV. So choosing the right installer and the right equipment is important - see below.

The lowering of the feed-in tariff is a risk.

There is also commentary around that because of the large quantity of  rooftop solar being installed the retailers will be given the right to switch off some rooftop solar in the middle of very sunny days. There is other commentary about giving retailers the right to charge homeowners to feed electricity into the grid. Neither of these are in effect today. It is unknown if they will be implemented and if so when they will be implemented. And even whether they will impact on existing rooftop PV systems or just new systems. Solar is fast developing field. Innovations such as the roll-out of community batteries, the increased installation of domestic batteries and greater residential ownership of electric vehicles and home recharging, may mean that the need for these changes is lessened as there becomes greater use for the rooftop PV generated electricity on the local grids.

There may be other risks as well.

Rooftop PV is currently a great investment. Even if some of the listed changes eventuate in quite a few the years time the impact on the financial viability of rooftop solar should be manageable.

Choosing an Installer

Could try:
  • Many Councils run schemes to encourage the installation of domestic solar panels in their municipality. For example for Hume City Council in Victoria - Hume Solar Rollout. Run on behalf of the Council by the Yarra Energy Foundation – a not for profit group. They also provide the same service in a number of other Victorian municipalities - check your council or the YEF. There are indicative prices on the Hume Rollout Website – however these can increase depending on site - double storey or multiple orientation or multiple strings. If nothing else these figures provide you with a ball park indication of what you are likely to pay. Sometimes they are called solar bulk buy schemes  e.g. Geelong Community Solar, Darebin Solar Stream and MASH.
  • Solarquotes – Pre-vetted installers. I understand that they send three installers out to give competitive quotes. Solarquotes are are paid by the installers.
  • An installer based on personal recommendation - however still check them on the Clean Energy Council website - and get a comparison quote.
If you want to go with an installer that has been recommended to you or perhaps a company you have heard of from advertising then check their website, check social media to see if there are any adverse comments, check to see whether they are on the list of approved suppliers for the Victorian Rebate. You could also search them on the ABN Lookup site - to see how many years they have been trading - if only a couple of years it would be concerning.

The Clean Energy Council has an installer accreditation system – check their website to see if the installer is accredited with them.

Then remember when the quote is received to check what equipment they are offering to install - if they are offering recognised brands of panels and inverters that is a positive.

Remember the dictum: "you get what you pay for". The super low prices that are sometimes advertised raise alarm bells for me.

Please note: I have no association with Solarquotes. I have not used them as a supplier. Social media that I have read indicate they they are OK. I have no association with the Hume Solar Roll Out, however I am a member of the Hume Council Sustainability Taskforce.

Not Recommended

Choosing an installer based on a telephone "cold call" is not recommended. This is where an installer company has engaged a firm to call people tell them of the wonderful rebates that are available for solar panels. They make it sound as if they are only available from them whereas they are really available to anyone. The cold call company passes on the names to their client company(s).

The trouble is you don't know what you are likely to get. You may get a good company but you could also get a company that is either offering low quality equipment or is overcharging - or both. The company could be a "fly-by-night" operation that won't be around in a year or two time to provide backup or warranty. At least get another quote for comparison and also check what equipment they are quoting on - it should be on their quote (if not, walk away) - with the equipment recommended by Solarquotes.

Check Quotes when Received

The quote should contain:
  • the price – ensure it is GST inclusive.
  • a complete list of equipment to be installed - especially the panels and inverter – along with specification sheets. Check that the equipment offered is good quality.
  • a layout showing the proposed location of the panels and other equipment.
  • estimates of PV electricity production.
  • perhaps an estimate of expected financial return*.
*These estimates may be based on unrealistic PV in-house consumption proportions. Do not use these figures for comparing quotes or for analysing what your expected return will be.

If you are considering going ahead check with the installer
  • that their quote includes allowance all costs associated with obtaining a Certificate of Electrical Safety/Monitoring and all other paperwork, tasks and costs required for  grid connection and to enable  you to claim the Victorian Rebate.
  • whether grid connection pre-approval been granted. Has there been any solar export constraints imposed.
The Clean Energy Council also has a list of questions that the installer should be able to answer - on page 11 of their current (2020) Buying Solar Guide.

Apply for the Vic Rebate (if you want it and are eligible) and wait for confirmation of approval prior to acceptance of the installation quote.

On the day of Installation

Talk with the installer about where they are going to install the inverter. Make sure it will not be in the midday or afternoon sun. (This should also be discussed with the person that comes to quote the system. The quote should contain full details the equipment and panels to be installed.)

Check that the panels they have brought to install are the panels that they quoted (brand, model and nominal power output) – it is more difficult to check once they are on the roof. And more problematic to rectify. If they are not the same tell them to provide what was quoted - unless you can be convinced that the equipment is just as good or better - refer to the Solarquotes recommendation. Even then you are entitled to what they quoted on.

How to get the most from your PV system

Grid electricity currently costs approximately 19 to 23 c/kWh in Victoria in 2021. Different prices in other states. The minimum solar feed-in tariff (what you get back for selling your PV electricity to the grid) is about 6.2 c/kWh in Victoria (can be more with some suppliers). Therefore to get the most benefit from your PV system you should aim to transfer as much electricity used early morning and late afternoon and evening (i.e. when the sun isn’t shining) to the times when the sun is shining.

For example - if you previously used an electric dishwasher of an evening it may be better to delay its use to the middle of the following day. (Some have timers.) Also clothes washing – use washing machine on a sunny day. Also better for hanging the clothes out to dry on the clothes line. However if for what ever reason you don't hang the clothes on a external clothes line it is also better to use the tumble drier on a sunny day.

The more you do this, more money will be saved saved and a greater the financial return will be achieved from the system.
 
Rooftop PV systems are ideal for an all electric home. Rooftop PV works very well when combined with a heat pump solar hot water system – so long as the hot water system has a timer to run it in the middle of the day when solar is available, a sufficiently large water tank to supply the house's daily hot water needs and the heat pump compressor is sufficiently large enough to heat a tank full of water in say a 5 hour window. The rooftop PV will also at least partially power the reverse cycle air conditioner for house heating or cooling during the day.

One other useful reference:

Your Home Website - https://www.yourhome.gov.au/energy/photovoltaic-systems
ABC Article - $12,000 dollars for a 5kW system and still got a dud. Note the main problem was that the inverter was installed in the wrong place (in direct sunlight). But $12k is still a lot for a system without batteries.

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