How much energy will my solar cells produce?

Average daily production for solar PV cells in Australia

by Solar Choice Staff on January 19, 2010

in Installation advice,What are the right solar PV cells for you?

The electrical energy output of solar cells is obviously one of the crucial things that you need to know when looking to install a solar system. Some solar energy companies are giving a wide variety of unreferenced numbers, so we have done our research and provide you with fully referenced and reliable information for you to consider.

What is energy output?

The power rating of your system (kilowatts, or kW) is a measure of how big your generation system is, not how much it will produce. This is analogous to a car engine, where the size of the engine gives you an indication of how powerful it is, but does not itself tell you how much petrol it will use, although the two are related.

Whether or not you have access to a solar feed-in tariff (keeping in mind that all of the feed-in tariffs in Australia have been closed to new applicants), you should know how many (kilowatt-hours or kWh) your solar system can be expected to produce. Knowing this number will help you calculate the revenues and savings you can expect to receive from your solar panels.

What factors influence solar system energy yields?

Of course the first factor influencing how much electrical energy you will generate is the size (otherwise known as rated power) of your solar installation. A large installation (higher kW’s) will produce more electrical energy (just as a bigger car engine has more grunt).

But if we move past the obvious impact of size, the amount of energy your solar cells produce depends on how much fuel they are fed (just as the amount of energy a car engine will produce depends on how much petrol you pump into it via your foot on the throttle). In the case of solar PV cells, their fuel is the sun.

The amount of sun your solar cells are exposed to (and hence how much energy they will generate) depends upon:

  • The orientation and tilt of your installation (which will be optimised by your installer)
  • Whether there are shadows cast over your cells (due to trees, buildings etc)
  • The number of daylight hours (governed by where you live)
  • The intensity of the sunlight (governed by where you live)
  • The number of hours of full sun vs cloudy days (governed by where you live)

If we exclude the first two factors, which you have a degree of control over, your location in Australia is the primary variable dictating how much energy your cells will produce. Hence, a 1.5kW system in Melbourne will typically not produce as much electrical energy over the year as the same system in Alice Springs.

The figures for average daily production

Fortunately, studies have been conducted that take all of the above factors into account and give the average energy output for solar cells in locations around Australia. These figures are given as:

The amount of electrical energy (kWh) a 1kW grid connected solar PV system will generate on an average day (kWh/kWp.day).

The most comprehensive source of this information is the Clean Energy Council (the body that the Australian Government charges with accrediting solar cells, inverters and installers):

Average-Daily-Production-of-Renewable-Energy

Average daily production of solar PV cells in Australia
p4, “Electricity from the sun: Solar PV systems explained” by the Clean Energy Council

Researching this topic will reveal other credible sources, with slightly different figures. The USA’s National Renewable Energy Laboratory’s (NREL) PVWatts tool also works for Australia (using Aussie meteorological data) and is a great resource for plugging in numbers and estimating a solar system’s output. We encourage you to check it out.

Some exploration will reveal that it’s not quite possible to put an exact unequivocal figure on the energy you will produce from you solar cells. Indeed, as Dr Anna Bruce, Lecturer at the School of Photovoltaic and Renewable Energy Engineering at the University of New South Wales informed us, different solar systems both rated at 1kW sitting side by side may produce different amounts of energy due to the quality and efficiency of their components, how the grid is functioning and how well your system deals with high temperatures. Her expert advice is that “4kWh/kWp.day in Sydney is certainly feasible if a system has optimal tilt and orientation and is running well”.

So the Clean Energy Council figures above act as a good guide and are one of the best and most comprehensive sources available, however due to the nature of solar, your system may produce more, or a little less than the figures given.

Kobad Bhavnagri
Solar Energy Consultant

© 2010 Solar Choice Pty Ltd

{ 10 comments }

Rob November 25, 2015 at 1:02 pm

Im still stuffed with 18 panels 4.5 kw yet stll pay around %80 of what was my old bill.
I need an assessment to be done. Who do i get. the installer says all is ok.

Solar Choice Staff November 30, 2015 at 2:21 pm

Hi Rob,

The problem may be with your electricity consumption patterns. If your solar panels are generating energy but you’re not using any appliances at home, then you’re probably not going to see the sort of electricity bill reductions that you were expecting – even if your solar system is working perfectly well, as your installer says may be the case. You need to be consuming more electricity during the daylight hours. If the installer didn’t explain this to you clearly, then they did not fully relay to educate you about how solar works in Australia these days.

jane February 15, 2016 at 8:05 pm

My xdaughter has 24 panels and her last bill was 300 odd dollars, she used hef air con for 5 days in the 3 months she only gets 6 cents per kilowatt on energy saved. So why is her electric bill so dear. She works 9 hours a day and uses the air con from 6amm to 6pm on the 5 days. What is she doing wrong.

Jane

Solar Choice Staff February 16, 2016 at 10:03 am

Hi Jane,

It’s hard to give answers without knowing more of the specifics. For example, are you talking about a quarterly or a monthly power bill? If you’re talking about a quarterly bill, then $300 really isn’t a lot to pay – especially when running AC for 12hrs/day!

Just in case there’s some kind of misunderstanding, I should state that these days saving money with solar panels means that you must ‘self-consume’ as much of the solar energy produced as possible. In most states, a home will save in the range of 20-28c per kilowatt-hour (kWh) of energy by using their solar power as it is produced (while the sun is shining). Otherwise, the solar energy is ‘wasted’ – sent back into the grid for only 6-8c/kWh.

What I assume is happening with your daughter is that here system is actually stopping keeping here power bill much lower than what it would be otherwise – AC is expensive to run, as it uses a lot of energy. If the installer told her that she would be able to completely eliminate her power bill, they were lying. These days, with solar feed-in tariff incentives having been closed in virtually every state, it’s basically impossible to have a $0 energy bill unless you get off the grid entirely (which is not economical for other reasons). Even if you have a grid-connected solar+battery system, you’ll still be charged fixed ‘supply’ charges which don’t go away if you consume less energy.

Hope this helps!

Narelle Kay February 28, 2016 at 11:12 pm

We have a 3.5kW system, 7 panels facing east and 7 panels facing west. We are now on our second inverter and about to have it replaced again as we are not producing (apparently) any energy at all. We are being billed for every kW we use at peak rates. Our bills are roughly $800.00 per quarter and even though, we have sent energy back to the grid we are only getting $0.51 cents per kilowatt. Not sure how we are sending back to grid if we aren’t producing, but that’s what we have been told. Our energy supplier, just keeps telling us that we shouldn’t expect to save any money at all just because we have solar. We paid roughly $7,500 for our system eighteen months ago and we feel like we have just wasted our Monet rather than creating an investment.

Solar Choice Staff February 29, 2016 at 9:57 am

Hi Narelle,

Sorry to hear about the problems you’re having. Just to clarify, are you getting 5.1c per kilowatt-hour (kWh) or is it 51c/kWh. I’m going to answer you based on the assumption that it’s 5.1c/kWh – which really isn’t very much at all but is unfortunately pretty standard across Australia now.

These days, going solar is really only worthwhile if you are able to ‘self-consume’ as much of the solar energy that you use while it is being generated – this means trying to run appliances during the daylight hours. The company who sold you your system should have explained this to you from the outset – if they didn’t explain it, I would question whether they are a trustworthy company. Also, $7,500 (about $2.14 per watt) is a bit on the high end price-wise for a 3.5kW solar system, even for October 2014 (when I gather that you had your system installed).

I’d recommend first making sure that your inverter is, in fact, malfunctioning. It’s not really clear from what you’re written if you’re certain that there is a technical problem with your inverter (how much does solar energy does the inverter say the system is producing?), or if you’re assuming that it’s not working because your electricity bills are still so high. Your electricity retailer is correct that having solar panels does not necessarily guarantee that you will save money (again, the company that installed your system should have explained this to you). If you use none or only very little of the solar energy directly, most or all of it will be sent back into the grid at very little benefit to you (the 5.1c/kWh). By contrast, if you self-consume the solar energy, you will probably save more money (whatever you pay for retail electricity).

There are a couple of other things that I should point out:

-If you’re on a time-of-use (TOU) electricity tariff, you might want to consider switching to a flat rate. Even with some of your panels facing west, it’s unlikely that the energy that they produce will cover all of your peak-time (and most expensive) energy usage. Instead, your solar is probably being consumed most during your less expensive off-peak and shoulder periods. Depending on what your exact rates are, you could stand to save a lot more money on a flat tariff, where you pay the same amount per kWh no matter when you purchase the electricity.

-If you’re on a 3-phase connection, you’ll want to ensure that your inverter is either a 3-phase inverter (which is unlikely for a system as small as yours) or that it’s connected to the phase that uses the most power in your home (again, if you’re installer was really thinking in your best interest, they would have spoken with you about this). If you’re on single-phase power, on the other hand, this probably isn’t the issue that you’re having with your system.

Hope this helps, and best of luck with your system!

Emma April 20, 2016 at 1:21 pm

Hi there.

We have moved into a property with 33 solar panels but I suspect they aren’t working very efficiently. They probably need a clean and service.

What I’m hoping to find out is roughly how much energy would you expect to see 33 panels produce?

I’m in the Blue Mountains, NSW.

My current bill says for 99 days the 33 panels produce 143.000 – is that what you’d expect or too low?

Thanks!

Solar Choice Staff April 21, 2016 at 10:53 am

Hi Emma,

Your system is almost definitely underperforming. Without knowing the capacity of each panel (how many watts?) or the total capacity of the system (how many kilowatts), it’s hard to say exactly, but it should be around 5-8 kilowatts if it was installed within the last 5 years. Over the last 99 days you should have seen around 2,500 kilowatt-hours (kWh) of electricity produced (you’ve indicated only 143kWh).

My first guess is that it’s a problem with shading, knowing from experience that a lot of homes in the Blue Mountains are surrounded by trees. Even partial shading is bad for solar systems with central inverters, while microniverter systems perform better in shaded conditions.)

If shading is definitely not a problem, there could be a problem with one or a few of the panels – or possibly the inverter itself.

The best thing to do would be to get in touch with the company who installed the system (if you have those details), or – in the case that you can’t locate them – get in touch with a solar-accredited electrician to have a look. I’m guessing that the system was installed under NSW’s generous solar feed-in tariff scheme (whose 60c/kWh payments finish at the end of this year), which means you could be missing out on some significant energy bill savings, so it could be worth paying to have it fixed if it’s not a major issue.

Best of luck!

Kelly June 3, 2016 at 2:33 pm

I have a 1.5 kW system yet on average am only getting 290-300 kWh export per 3-month period. As an example for a 92-day period, the export was 291 however if I were to base on the above average of 6.3 kWh (in Brisbane), then I should be getting about double that.

Is there an reason fro possibly not getting as much solar as possible?

Solar Choice Staff June 7, 2016 at 9:46 am

Hi Kelly,

What’s probably happening is that you’re ‘self-consuming’ most of the solar energy that your system produces – using the energy directly with your appliances. This is not a bad thing, as it’s saving you money by reducing the amount of electricity that you have to purchase from your electricity retailer. 1.5kW is relatively small, which increases the likelihood that you are indeed consuming most of the energy as it is produced. Do you have any numbers on the system’s total energy production?

One point of possible confusion is that you only see exported solar energy (and not self-consumed solar energy) itemised on your electricity bill. It may in fact be the case that you’re exporting 300kWh per quarter and self-consuming the balance (approx 300-380kWh). The only way to tell is by knowing what your solar system produces in total on average – which would not be detailed on your electricity bill (you’d have to look at your inverter or whatever monitoring software you have, if any).

Hope this helps!

Also, depending on whether or not you have access to the 44c/kWh solar feed-in tariff or only the 6-8c/kWh currently on offer by most electricity retailers, you’ll want to aim to use your solar energy differently. Basically, if you have access to the 44c/kWh rate, you’ll want to export as much solar as possible to maximise savings; if you have access only to a lower rate, you’ll want to try to self-consume as much solar as possible to maximise savings.

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