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?
As explained in the article Physics 101 “ what is the difference between power and energy? – power and energy are not the same thing. The power rating of your system (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.
With feed-in tariffs you are paid for the amount of electrical energy (kWh) your solar cells produce. Hence, that is what you need to know when doing the sums on how much revenue you can expect from your installation.
What is the energy output dependent on?
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’s (which is the body that the Australian Government charges with accrediting solar cells, inverters and installers):
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. For instance:
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EnergyAustralia give a range of 3.84 – 4 kWh/kWp.day for Sydney
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The NSW solar bonus scheme FAQ page gives a figure of 4.56kWh/kWp.day for Sydney
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The Office of the Renewable Energy Regulator gives a figure of 3.79kWh/kWp.day for Sydney
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The Victorian Department of Primary Industries premium solar feed-in tariff page gives a figure of 4.56kWh/kWp.day for Melbourne
Although these figures are in the same vicinity the variance demonstrates the fact 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
Solar Choice Pty Ltd
© 2010 Solar Choice Pty Ltd
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Hi again id like to know what the best combination of panels and strings,i have a growatt 4.2kw inverter which has one string of ten 190 watt panels connected and i have another ten sitting here waiting to be hooked up,the inverter has 4 inputs so i gather thats for 4 strings of panels but im confused as my installer tells me 10 per string is good anyhow id love some input on this matter regards mark.
Hi Mark,
Unless you have shading issues, whether you decide to go with 4 or 2 strings of panels shouldn’t make a difference. I’ve done a bit of research and the max DC input voltage of a Growatt4200ML inverter (I assume this is yours) is 600V, and an MPPT range of 120V-550V. What is the voltage output for the panels that you have?
A very interesting site, which also demonstrates there are quite a
number of posters that have a good knowledge of solar power.
Perhaps a member can answer the following question for me!.
We are a retired couple residing in Rockingham, Western Australia, my wife is totally disabled and suffers among other with things a
condition known as “Thermoregulatory Disfunction” and has no
capacity to control body temperature when exposed to extremes
of weather conditions.
Subsequently our electricity bills (every 60 days) is now around
$500 (an average of 41 units per day), with more increases on the
unit rate guaranteed to be implemented in the near future, so our
premier (Barnett) has warned.
Can anyone give me a clue as to the cost of a system that would
provide a break even situation for us so that we can recover the cost over a period of years.
Hi Mike,
Thanks for your inquiry.
Your area receives an annual average of 6 peak sun hours per day–i.e. if you have a 1.0kW system, you could expect it to produce about 6kWh (“units”) of electricity per day. Since you require 41 units per day, roughly speaking a 7kW system is probably what you’re looking for. At current prices, this could run you anywhere between 18 and 22 thousand dollars.
Keep in mind, however, that you will only stand to benefit from a system of this size if you wisely time your usage to coincide with generation–since the cancelation of the state’s feed-in tariff, in your area of WA the only ‘renewable energy buyback scheme’ available is through Synergy and is a nominal 7c/kWh. This means that you will only be paid 7c for every unit that you feed into the grid, so it makes more financial sense for you to use the power directly instead.
Sizing a system to make it worth your while would require a bit of analysis regarding when your demand is highest (e.g. evenings? daytime? around the clock?) for each season. It might even be worth your while to invest in energy storage in the form of batteries.
Our automatic quote comparisons do not include prices for 7kW systems, but our brokers can tailor a quote comparison that suits your needs. To initiate a dialogue, either fill out the form on the right, or email sales@solarchoice.net.au. Our services are free and impartial.
Hi thanks for the reply, i have no shading issues the voltage output is vmp 36.6 voc 44.7 imp 5.19 amp ,and yes i think it is a growatt 4200 mtl kind regards mark
Hi Mark,
The specs of the inverter and panels, plus the fact that you don’t have shading issues, indicate that 2 strings of 5x panels on the second (currently unused side) of the MPPT input would be ideal. 2 strings of 5x is preferable to 1 string of 10x just on the odd chance that something goes wrong with the panels–with conventional strings of panels as we are discussing here, the malfunction of just 1 panels can knock out the entire string. So it’s best to hedge your bets.
Simple analysis and calculations with regard to your query can be found below.
Growatt 4.2 Inverter
-MPPT input voltage range: 120V-550V
-MPPT input current range: 15A
Your panels (those not yet connected, assuming they are all fed into only one side of the MPPT input):
Single string configuration–
36.6V * 10 = 366V
5.9A * 1 = 5.9A
Double string configuration–
36.5V * 5 = 183V
5.9A * 2 = 11.8A
As you can see, both configurations are well within the acceptable ranges on both counts. However, as mentioned above, all things being equal, it’s best to hedge your bets with more strings of fewer panels.
Good morning,could you please help us with some advice.We have a solar system 3kw with a german converter. We have just received our first electricity bill for 91 days, we are extremly upset as in all that time we have just made 222 kws and it reduced our bill for $97.68 only. We live here in sunny qld and for such a big outlay our bills are still over $500. We thought having 16 panels would have lowered the bill. Thank you any help would be appreciated.
Hi Pauline,
How much were your bills prior to installing your system? And have you contacted your installer to let them know that your system is not meeting your expectations? And do you have a monitoring device to track your system’s daily output?
This message is for Mike from Rockingham above with the disabled wife.
He may not be aware of this rebate: http://www.finance.wa.gov.au/cms/content.aspx?id=1691
Which is provided by the state government called the Thermoregulatory Dysfunction Energy Subsidy Scheme
Hi there,
I’m a business student doing a project for uni. If you have a 3KW system and for sydeny they have on average 8 hours of sunlight a day then the system if perfect conditions working at full capacity should produce 3 times 8 = 24kw/h a day so is the average system in darwin working at 11.7/24 = 48% ?
Hi Hayley. Sunshine hours are not the same as ‘peak sun hours’, an industry term referring to the equivalent of all the solar irradiation ‘concentrated’ into uniform units. In the morning and evening, the sunshine is more diffuse on any given roof or solar panel; around midday it is highly concentrated. In reality, Sydney only gets about 4 (actually more like 3.6) peak sun hours per day, averaged throughout the year (more in summer, less in winter).
So a 3kW system in Sydney would produce more along the lines of <12 kWh per day. Since Darwin gets about 4.6 daily peak sun hours averaged over the year, you’re looking at about 13.8kWh there.
When you talk about efficiency, it’s important to distinguish between panel efficiency (or conversion efficiency), cell efficiency, and system efficiency. Your figure of 48% efficiency based on 24 hours doesn’t make any sense in the context of solar power, unless you’re comparing to other forms of power generation.
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