Tips: Click on the question "Q" to view the answer "A"
In the past few years there has been talk that solar panels never produce enough energy to recover the energy cost of making them. Unfortunately this is something that has persisted since the early days of PV development and, back in that early development was true.
Panels produced in the last 5 years, however, have an energy payback period of 1-2.5 years under most Australian conditions. This value is improving all the time as manufacturing techniques become more and more advanced within the PV industry.
In fact, recent investigations by a number of research institutes, including Stanford University in the US, identify that the panels produced over the next 5 years will, in their lifetime, produce enough energy to cover the energy costs of the entire PV industry to date.
The answer to this question is strongly dependent on where you live. Since you use your solar system to offset the need for conventional generation it really depends what conventional generation is used.
For example, in France the primary energy source is Nuclear power which actually produces very little carbon dioxide compared to other common forms of generation. So the carbon offset of PV systems in France is actually relatively small.
However, in Australia the primary fuels for generators are coal and natural gas.
Carbon Dioxide emissions from generators of this nature are as follows (according to the U.S. Energy Information Administration):
|Fuel Type||Kg of CO2 emitted per kWh|
Note that these figures do not take into account the carbon expenditure required to mine the resources.
The average residential solar system is just over a 2kW system but for multiplicities sake we’ll round it off to a flat 2kW.
Given this, the average annual energy yield from a 2kW system is approximately 3200 kWh. Note that this will vary strongly between states, as the solar resource is very different depending on your location.
Therefore, the average solar system in Australia will prevent between 1.75 – 2.05 tonnes of carbon dioxide going into the atmosphere per year, depending on the mix of coal and gas generation it is offsetting.
To calculate your own approximate carbon offset you can use the table below.
All values are given for a 1 kW PV system (1 kW of panels matched to 1 kW inverter).
To get your own carbon dioxide offset annually or over a 15 year period just multiply the values by the size of your system.
|City||Kg of Carbon Dioxide offset annually||Kg of Carbon Dioxide offset per 15 years|
|Adelaide||Min: 825 - Max: 1,410||Min: 12,375 - Max: 21,150|
|Brisbane||Min: 825 - Max: 1,410||Min: 12,375 - Max: 21,150|
|Canberra||Min: 825 - Max: 1,410||Min: 12,375 - Max: 21,150|
|Darwin||Min: 960- Max: 1,645||Min: 14,438 - Max: 24,675|
|Hobart||Min: 688 - Max: 1,175||Min: 10,313 - Max: 17,625|
|Melbourne||Min: 743 - Max: 1,269||Min: 11,138 - Max: 19,035|
|Perth||Min: 880 - Max: 1,504||Min: 13,200 - Max: 22,560|
|Sydney||Min: 770 - Max: 1,504||Min: 11,550 - Max: 19,740|
Choosing a reliable installer can be exceptionally challenging. When suppliers are claiming that they’re the best and giving you their sales pitch, it can be hard to separate the good from the bad. These five points will help you investigate all of the installers out there, decipher all of the related info and select the best installer for you:
A very easy, first step for investigating an installer is to do a quick internet search on them. Are there a multitude of horror stories out there? Or conversely, is there high praise for their services? Do any of your neighbours, mates, co-workers or family members have a solar system that they could share their experience in selecting an installer?
This first criterion can make it very easy to narrow down the list of potential installers to contact.
What products is the company selling? You should be able to find out either from their website or a quick phone call what brands they are selling. If the company can’t tell you what inverters or panels they will supply you, then that’s an immediate red flag.
One very important thing to note is that some companies re-brand solar panels or inverters as their own. Though there’s nothing inherently wrong with this, the company should be able to tell you what the actual brand of the panels/inverter is.
Once you ascertain what the products are, another quick internet search to get a quick impression of how good the products are will be most useful. Remember to look at multiple sources, as one guy on the internet saying a product is rubbish doesn't make it so. However, if 80% of the reviews you look at say it is then it’s more likely to be the case.
All this research can seem like a pain but you should develop at least an idea of brands independent of the installer’s sales pitch. This can be another indication of if the installer is reliable; if he’s trying to talk up something the whole internet is saying is rubbish then maybe they aren't the best company to go with.
This one should be almost redundant, but it's a good check to make anyway. All installers should have the proper certification for installing PV systems. That means they should have both a valid electrical licence and be accredited with the Clean Energy Council. Without these, they cannot legally install PV solar systems and the PV systems will not be eligible for any available government rebates.
So at this point, your list of potential PV installers maybe a bit more refined and you’re probably ready to have a home consultation with a few of them.
What we would like to see from a home consultation is:
From a home consultation, we would expect that the consultant takes a look at the roof and the power bills and provides a number of options for what sizes would best suit the house and where the system can be placed.
If there is shading that occurs on the roof where the solar system is likely to go, then the solar consultant should either be able to perform or organise a shading analysis for your roof. This will provide you with an estimate of how much energy you will generate over the year.
Given there’s some options for system size and configuration (north or east facing etc.) on the table, the next thing I’d want to know are what do the financials look like? You want a clear explanation of where the return on investment comes from as well as things like the payback period on the system.
If they've given you potential systems, they should be able to do a calculation based on those sizes to give you specific figures based on those systems.
Don't expect a solar consultant to be an absolute expert on solar; after all they aren't the technical staff for the company, but they should have a basic understanding of what they’re selling. In our experience, if the sales staff is competent in this way then it’s a good indication of the quality of the installer.
This is linked somewhat to the products and consultation criteria. Throughout the whole process, the company should be able to give you information about your system and your potential purchase. For example; some background information on the panels/inverters, where are they made? What are the terms of the warranty? How will the system perform during the year? What is the average daily output, etc?
With regards to performance, the company should be able to tell you what how many kWh your system will generate, give or take 10% for weather.
To sum it up , you want an installer with a good reputation, who carries decent gear and can provide you with all of the important answers, with explanations that make sense. What you don’t want is a lot of bluster and sales pitch, with nothing to back it up.
An installer should have two critical documents in order install PV systems:
While the accreditation with the Clean Energy Council is not a strict requirement to install PV systems it is strongly recommended for two reasons:
Technically you can install the panels yourself. However, given the high DC voltages and currents associated with solar panels, we strongly recommend that you have your solar system installed by an accredited solar installer.
Furthermore, solar panel systems must be installed according the requirements of the Small-scale Renewable Energy Scheme in order for them to be eligible for small-scale technology certificates (STCs). These certificates can be assigned to a registered Agent (such as a retailer or installer) in exchange for a financial benefit, such as a discount off the invoice.
The simple answer is yes, you can. Would we recommend it? In most cases, no.
If you know you’re going to want to expand your system later, it’s much better if you can just get that expansion with the initial installation.
Why? Because installing the full system from the get go saves money and potential problems.
Let us take the example of a 4 kW inverter with an initial installation of 1.5 kW of panels.
The 4 kW inverter will draw the same amount of power regardless of the size of PV array it’s connected to; therefore you are operating your system at a lower efficiency.
Your inverter has an expected life of 15 years. If the inverter is only running a 1.5 kW array for say, the first 3 years then that’s 20% of its life gone. That’s 20% of its life where it has 2.5 kW of unused capacity that you've paid for but is giving you no return.
In this example, 3 years have gone by and the system is now being expanded to 4 kW’s of panels.
You now have to pay for a second installation. Not only is this a second call out fee but there is additional time required for the installation crew to inspect the previous work done. So you’re out of pocket already by having to pay for two installations versus just the one.
If you have a spare MPPT (input) to the inverter and can fit all the new capacity on the second input then Problems #4 and #5 can be ignored. However, if any of the new panels have to be linked to the old panels, then these two items do apply.
Three years down the line, the panels that you have connected to your system are no longer available. The same brand may be about but they have a new model with slightly different specifications. Worse still, the same brand is no longer available and you have to just find the closest match.
This creates, what are called, mismatch losses. This means that the PV array is compromised and loses efficiency because the panels do not behave in the same way and the inverter has to compromise between the two types of panel. The result is less than optimal power output which means less return on your system.
This is similar to problem #4. Even in the case that the exact same model panels are available and installed, the panels you've had up have been operating for 3 years and have experienced some degradation. The way a solar system works is that panels linked together will be limited by the weakest element in the chain. So your brand new panels can only perform as well as the degraded panels which means you've lost the benefit of whatever the difference in power output is between your old and new panel x3 years.
If you've already got a well designed system in place e.g. a 4 kW inverter with 4 kW of PV panels and decide that you want to increase your output by going to 4.7 kW of PV panels then by all means go ahead.
However, if you want to get an array far smaller than your inverter capacity with the intent of filling out the rest of the capacity later, either go for the full capacity you want now or settle for a smaller inverter. Filling out the capacity later on loses you a lot of financial benefit, compared to if you simply installed the full system from the beginning.
It is possible to install solar over multiple roofs, that face different directions. However, it is only recommended to do this if your inverter has more than one Maximum Power Point tracker (MPPT).
You can source the number of MPPTs that the inverter you’re looking at purchasing has, by checking it's data sheet. An example is shown below:
Generally only inverters of 3 kW and above have more than one MPPT.
The amount of electrical current that is produced by your panels is governed predominantly by the amount of sunlight on it and the voltage of the array*.
What the MPPT does is vary the voltage of your PV array so that it’s always at an optimum point to produce the most power.
If you have panels across multiple roofs, the maximum power point for each roof face will be different. Since the MPPT can only operate at 1 voltage at a time, you lose out on efficiency by not operating at the maximum power point for at least one of your roofs.
If your inverter has multiple MPPTs, then each one can operate independently to get the optimum amount of power from each roof facing.
You can install solar over multiple roof facings but you will lose efficiency unless you install each roof facing on a different Maximum Power Point Tracker (MPPT). The data sheet for your inverter model will tell you how many MPPTs that inverter has.
*For those of you that remember the equation: Power = voltage x current.
You might say that it doesn't matter what voltage you have because current will be proportional and give you the same power anyway. However, in a PV panel, this isn't true since the current will be independently affected by voltage as well.
The short answer is yes you can. In fact the capacity you can put onto your inverter is more dictated by the voltage of the PV array rather than its kW capacity. What this capacity ends up being is very much linked to what inverter/panel combination you have.
However, what should be noted is that if you have a 3 kW inverter and can put 4 kW of panels on; the maximum output from that inverter will still be capped to 3 kW.
So what’s the point of putting additional panel capacity on? In another article, we discussed why you won’t get the full output of whatever your nominal panel capacity is.
Max output in summer = 80% of Panel Capacity
Max output in winter = 50% of Panel Capacity
So, if you know in summer the very most you’re going to get out of your 3 kW array is 2.4 kW then why not increase the size of your array so that you do get that full 3 kW?
The example below shows what happens when we put a large amount of extra panel capacity on (again assuming voltages are ok for the inverter). You can see that in summer the peak of the curve is capped at the inverter power rating.
It is possible to add more panel capacity onto your inverter than what your inverter is rated at. How much more you can add on depends on the voltage of panels you use and the voltage range of your inverter. However, the maximum power output will be limited to the rating of the inverter.
In almost all cases, it’s a good an idea to put more PV capacity than inverter capacity. Because of the way solar works a PV array of the same capacity as the inverter doesn’t fully utilise the capacity of the inverter. Increasing the size of your PV makes better use of the capacity of the inverter you have payed for.
To best answer this question, there are three types of inverters to consider:
As such you will want to place them on a wall that is:
For Standard inverters that are rated for outdoor use there is more flexibility in where they can be placed. However, some of the rules that applied for indoor inverters still apply here:
While there has been complaints about the reduction in feed-in tariffs, what is often overlooked is the original idea behind solar systems; to meet and offset your own energy needs. In analysing the financial viability of a solar system you must also look at how much energy you do not need to purchase from the grid because of your solar system, not just what energy you get paid for in exporting back into the grid.
|Current Net Feed-in Tarif(c/kWh)|
|ACT||7.5c / kWh (closed to new applications)|
|NSW||6.6c - 11.2c / kWh|
|NT||19.23c / kWh|
|QLD||8c / kWh|
|SA||9.8c / kWh|
|TAS||8.3c / kWh|
|VIC||8c / kWh|
|WA||8c / kWh|
There are three options when it comes to STCs:
The easiest option is signing over your STCs to the company installing your system as they will have the handover documents prepared for you to sign.
If you choose to trade your own STCs then an agent can be used to simplify the process though this will obviously have a cost.
Otherwise you can trade your own STCs by completing the correct documentation and registering through the REC Registry and then either finding a buyer for the STC’s or trading them through the clearing house.
The end to end process, including required documentation, is available at ret.cleanenergyregulator.gov.au
The Germans have a reputation for producing the best quality solar PV components in the world – and rightly so. Germany has led the way in producing the best and most consistent manufacturing methods for solar panels. This extends to the point where some factories are entirely automated for the whole end to end process.
There are two reasons why an automated end to end process is important; quality control and millimetre accurate precision.
The only solar panels worth buying are those that are from a ‘Tier 1’ manufacturer. Tier 1 manufacturers take raw materials and produce solar panels. Tier 2 or tier 3 companies on the other hand, may only produce some parts of the panel and buy the rest, or at worst buy all the parts separately and just assemble the panel. You want a tier 1 manufacturer to ensure that every piece is designed to fit perfectly with every other part of the panel and the quality control is consistent throughout.
The second reason why you want a panel with the rigours of manufacturing the Germans put in is because solar panels are not simple beasts to put together. In fact tiny differences can have huge impacts.
Take for example a phenomenon known as Potential Induced Degradation (PID). PID can cause a panel’s maximum output to fall quite dramatically in the first 2-3 years of service. A panel with PID protection may drop to 98-99% of its original maximum output in that early life, whilst a panel without PID protection would drop to, on average, 94-95% of original output.
The difference between the two panels? The first panel’s anti-reflective coating is uniform across the panel. The second panel, however, had less than a millimetre’s thickness of irregularities over this same coating. That’s a 5% difference between the two just from a single layer of the panel – and not even one of the layers that is involved in producing power!
Chinese panels are more of a mixed bag than German panels. Generous incentives from the Chinese government have led to a large number of panel manufacturers appearing. Some of these companies are very good, Tier 1 companies. However, there are a number of poorer manufactures taking advantage of the incentives scheme they have in China.
What this means is that, while a good number of Chinese brands are of similar quality to German brands, you need to be more discerning when looking at what specific Chinese brand you buy.
Are all German panels made in Germany? If they aren’t made in Germany are they worse?
The German solar industry has gotten to a size where it has customers worldwide. To base all manufacturing in Germany and then have to ship panels to places like Australia becomes very costly; which would reflect in the price of the panel.
Therefore multiple German companies have manufacturing plants in a number of diverse locations. An example is the German solar panel company Conergy. The Conergy panels that arrive in Australia are manufactured by their Malaysian factory. This by no means indicates that the panels are any worse; in fact the factory in Malaysia is built as an exact replica of the completely automated factory in Frankfurt Germany.
Common German brands sold in Australia (All Tier 1 companies):
For a long time, Solar panels from China have had a stigma attached to them with regards to their quality. For some manufacturers, this isn’t entirely undeserved but, there are a lot of good Chinese panels that suffer under this blanket assumption.
In 2009 the Chinese government began offering significant incentives around solar panel manufacturing in order to produce a strong solar industry within China. This was very successful in that government incentives made it very easy to setup a solar manufacturing facility and significantly lowered the cost of production. This in turn allowed China’s solar panels to be sold more cheaply than panels manufactured in other countries resulting in less external competition for China’s manufacturers.
However, the drawback to this scheme was that it incentivised more than just the parties interested in making a quality product. The result was that China had and still has a more diverse spectrum of manufacturing quality; from the very good to the very bad.
Unfortunately the lowered cost of manufacturing and the close proximity to Australia meant that it was very affordable for both the high quality and low quality manufacturers to sell their product to Australians. This is where the problems arose.
In essence it boils down to two main factors; you only hear about problem products and all the products look the same.
Firstly, people who are happy with their system tend to just have it installed and then say nothing about it. However, people who have troubles with their system become very vocal. So the only Chinese panels widely discussed were the bad ones.
Secondly, solar panels are visually very hard to differentiate. If you look at the following two images, even if you know both come from the same place you can tell that the car on the right is probably going to be better than the car on the left.
But if both cars look the same and come from the same place, and you only ever hear about the bad ones then the stigma starts to grow that all cars from that place are bad.
The Germans are undoubtedly the great innovators of solar panel technology. They are great at pushing the limits of efficiencies and improving manufacturing techniques to be more cost effective. But, while the Germans lead the way, the Chinese make good practice of copying the good ideas that come out of German research as well as making a few of their own. This means that the leading Chinese companies tend to produce panels that are similar in quality to their German counterparts.
German panels in the market appear to have be consistently high quality whilst, as has already been discussed, Chinese panels vary wildly with manufacturer. This view is skewed though, by the fact that China, being a very close neighbour can afford for even the inferior solar panel manufacturers to export to the Australian market, while only the biggest and the best German manufacturers can afford to bring product here.
In summary, there are a good number of high quality Chinese solar panel brands on the market but you need to do some research in order to sort the good from the bad.
Here are a few good quality Chinese brands available in the Australian market:
All grid connected solar systems will and must disconnect from the grid during a blackout. In the case of 99.9% of residential connected solar systems, that means that the solar system will shut down. There is a very good reason for this and that reason is safety.
There are two reasons power to your house goes out:
In either case, there are probably going to be line workers coming to work on the powerlines not far from your house.
When they get there, because the grid has been turned off they are going to be expecting that those powerlines they are about to touch are completely dead.
However, if you’ve got a neighbourhood down the road with PV generation, that’s going to mean those lines aren’t dead. This is a very real danger for anyone working on them.
There is a situation where a local generator remains on, even when the grid goes down. That is called "Islanding". Australian standard 4777.3 dictates that any grid connected inverter (such as in a PV system) MUST disconnect from the grid with 2 seconds of the grid going down through some kind of anti-islanding scheme.
What’s the simplest way to disconnect your system from the grid? Shut it down.
Earlier we mentioned that 99.9% of residential PV systems shut down when the grid shuts down. This is because it's the easiest way to ensure that the PV system doesn’t island. You can make it such that the PV system will remain on AND you’ll be disconnected from the grid.
However, this is much more complicated, and therefore much more expensive.
Essentially there are two ways to do this:
This method involves splitting your household load between grid-connected and PV-connected loads. What this means is some appliances, for example your pool pump, are connected ONLY to your PV system. So your grid connection and PV connection are isolated from each other. This means you can still run your pool pump when the grid is off but also means you can not run it if the sun isn’t shining.
In this instance you add a disconnect switch where you connect to the grid. This switch must operate automatically within 2 seconds of the grid going down so as to be the same as the constraints on a PV inverter.
Inside the house, your electrical setup must be adjusted such that the solar system will have a pathway to inject electricity to your house even if your grid connection is cut.
Additionally, the PV inverter you purchase must be setup for off-grid functionality, which not all off the shelf inverters are or have the capability for.
A solar system will disconnect during a blackout for safety reasons. Shutting down is the simplest and cheapest solution to making sure the system is disconnected.
While it is possible to make it such that the solar system will not shut down during a blackout the expense and inconvenience far out weighs the benefit. This is particularly true in most areas of networks where the frequency and duration of blackouts is low.
This article should be prefaced by stating that this opinion is based on experience within the PV industry and comes from the perspective of someone working from a technical role.
Solar panels, to the naked eye, all look pretty much the same. There are slight variations, different colours and sizes etc. but generally pretty similar. So unless a solar panel comes out the box with half the back missing off it, how do you know how good it is?
Previously we've published some articles that look at the criteria for choosing solar panels and inverters. While it was easy to select the top 5 inverters, because of the wider market in panels there are a lot more brands out there that I could comfortably put in the top 5.
However, based on the criteria of:
There are a number of panels not mentioned here which would also be considered a good value panel.
Any company that you go with should be what’s called a ‘Tier 1’ company. That is to say, they do the full end to end manufacture of their panels. They shouldn't be buying anything other than the raw materials.
In judging for yourself you really need to go back to the main criteria:
Ask the questions of whatever solar company you are dealing with to find out exactly what's going to be on your roof for the next 20+ years.
The best way to look at how a solar system saves money is to look at the price of grid connected electricity and the 'Levelised cost of Energy' from your solar system.
Levelised cost of Energy is a measure that basically looks at the cost of each unit of energy your solar system produces. This is done by taking the price of your solar system divided by the amount of energy that system is expected to produce in its lifetime. For this the life of the inverter is used because it has the shorter expected lifespan (15 versus solar panels (20-25 years).
The precise figure for each system is dependent on the price of the system, the location it is installed, if there is any shading on the panels etc. However, typically, a well placed residential solar system will have a levelised cost of energy of approximately $0.11/kWh.
That means that you are effectively paying $0.11 for every unit that solar system produces, though obviously that cost is all bundled up into one up front payment.
Every time you use a unit of energy from your solar system, that’s one unit of energy you didn't need to buy from the grid.
That one unit of energy cost you $0.11 versus the $0.22 it would have cost you to buy from the grid (WA Residential Tariff).
So every unit of energy that you get from your solar saves you fully half the cost it would otherwise be from the grid. Over 15 years this saving will increase since that $0.11/kWh is fixed for the life of the system whilst electricity prices will only increase over that period.
Buying solar is about the same as everything else; you get what you pay for. If you buy the cheapest stuff on the market you can expect the lowest performance and unfortunately a high chance of failure.
For this exercise lets imagine you’ve checked your system and noticed that the inverter is on but it’s showing no power being produced. So you’ve checked your panels and noticed that one of them looks like waters got in and part of it has gone a milky white.
The nature of 99% of residential solar systems are constructed so that if one panel in a string fails, then the whole string can’t make any power. So you’re going to want to get that panel replaced pretty quickly! That’s when your warranty comes into play.
There are two types of warranties on a panel:
The workmanship/materials warranty covers the construction of the panel and would cover issues that may not have a massive effect on performance but still make it unsuitable for long term use.
An example would be if the DC connector points on the back aren’t mounted correctly and are loose. They may still allow electrical charge through but it’s not suitable for long term use.
Every panel has a performance warranty that guarantees the output of the panel for a set amount of time. These warranties vary from company to company but guarantee a certain level of output depending on how long the panel has been installed.
Generally there are two types, a step warranty or a linear warranty. If you can get it, a linear warranty is preferred and generally is only offered by higher quality panels because the company is more confident in their product.
So, under our hypothetical situation with 0% performance, due to workmanship problems we would reasonably be covered under both warranties.
This is where the difference in companies really sticks out.
To put it simply, your warranty should cover the end to end repair/replacement of your faulty unit, whether it is the inverter or the panel. For our panel situation that means:
This is one of the points where getting what you pay for is definitely true. For the mid to higher end of the price scale the warranties generally cover this whole process and most companies have a presence in Australia which helps speed up the process.
On the lower end only the testing of the panel and repair/replacement is covered. That said, testing is only covered if they find a problem with the panel, otherwise you have to pay for that as well.
That means to get your warranty on your cheap panel means you have to pay for:
A quick call to customs Australia reveals that the shipping and customs charge for the two-way transport runs at about $1600 without all the other charges.
In the end, it would be cheaper to just buy a new panel.
When purchasing a solar system, check closely what the warranty action is if any component fails. On the cheaper gear, the warranty could not be worth the paper it’s written on if it doesn’t cover the end to end repair/replacement process.
At night your solar system will shut itself down. This includes the inverter, which means you won’t be able to read its display and see any information from it until the sun comes up in the morning.
While this may be a bit of an inconvenience if you wanted to check your production for the day, the system does this for a very good reason.
During the day when your panels are producing power the inverter uses some of this power to operate itself. At night without any power from the solar panels the inverter would have to draw power from the grid to operate itself, which is exactly what the solar system is put in their to avoid – drawing from the grid.
A few inverters may have small battery storage to run the displays etc. through the night. However, because of the added expense and size it takes to include the battery in the inverter versus the small gain in convenience, these types of inverters are almost extinct.
Back when there were considerable feed-in tariffs, such as the $0.60/kWh feed-in tariff seen in NSW, a bigger system was absolutely always better. You wanted to pump as much power as possible to the grid to cash in.
However, with feed-in tariffs being closer to $0.08-0.10 /kWh, it is prudent to design a solar system based on your own power requirements.
As mentioned in another article, when you pay for your system up front you expect that it will produce a certain number of kWh over its lifetime. If you divide the cost of your system by that expected number of lifetime kWh you get what’s called its Levelised cost of Energy. This is the approximate cost to you of each unit your solar system produces.
Typically this values floats around $0.11/kWh with variations depending on specific systems.
While it’s likely that the Levelised cost of Energy will come down as PV becomes cheaper, $0.11 is still close enough to the feed-in tariffs’ $0.08-0.10 /kWh value that you aren’t really making any money when you export power back to the grid.
It's best to size your system so that you are just meeting your requirements throughout the year. This may mean getting a system slightly bigger than your summer requirements, so that you meet your winter requirements. But even in this case the system is designed against your energy use, not as a generator to export bulk power to the grid.
There are many different factors that will affect how much your solar system will be able to produce. These factors range from panel/inverter design and construction to PV system design to positioning of the system to environmental affects.
Let’s assume that you’ve bought a decent quality system and it’s been designed correctly. What are the main factors that are going to affect your production?
With the maximum height of the sun in the sky varying through the year we get variations in how much solar we can produce. In winter solar production is lower whilst in summer it is higher. The further you get from the equator the more this difference between summer and winter is seen.
A good example is to think of the northern parts of Svalbard in Norway which experiences approximately 6 months of constant sunlight and 6 months of darkness. So up there your PV system would be exporting huge amounts of energy every day during summer, whilst in winter your production would be nothing.
Cloud cover is an obvious one but worth mentioning. If cloud passes over your system it will have less sunlight reaching it meaning less production.
In places like the north coast of Australia this is more significant than the seasons described above. Being close to the equator means there shouldn’t be that much variation in solar production due to the summer/winter trend. But there is a variation because of the additional cloud cover in the rainy season.
Somewhat annoyingly, the hotter a solar panel is the less well it performs. So a solar system will perform slightly better at 11 am than at 1 pm, even though they may be getting the same amount of sunlight in each case, because at 1 pm the panels are hotter.
As much as possible, solar systems should be designed to avoid shading. Basically shading drastically reduces production unless you’ve got a special setup (e.g. micro-inverters). While this is acceptable early morning or late afternoon if you’re just cutting off the tail ends of your production time, you don’t want shade across your panels at midday.
The pitch and orientation of your system plays a big part in how you generate power. For example a west facing system will peak later in the day giving you more solar power when you get home, while an east facing system gives peak power in the morning.
Additionally from a yearly perspective this factor affects the magnitude of seasonal variation. The least seasonal variation between summer and winter is seen by systems orientated due North with a pitch equal to the latitude angle of the location they are installed. Any move away from this increases your summer/winter variation i.e. higher summers and lower winters.
Shading is something to absolutely avoid when designing a solar system. The reason being is that it has a massive impact on your production – even with what you might think it's only a little bit of shading. This is especially true of both mono and poly crystalline panels, which are the most common kind of panel installed in the world.
Where the shading is on the panel makes a big difference on what sort of effect you’ll see. Electrically, the majority of PV panels are divided into 2 ‘zones’, although some of the larger panels maybe divided into 3 ‘zones’.
The separation of the 2 ‘zones’ looks like this:
If we get shading on just one of those zones then the effect isn't as bad. However, even partially shading that one zone can lead to a reduction in output of up to 60%.
Worse still is if the shading affects both zones at once, for example shading the bottom of the panel. In these cases even just shading the bottom row of cells would reduce the total power output of the panel by 90-95%.
In a typical solar system with a central inverter, a string of panels is limited by the worst performing panel. So if one of your panels is shaded that reduces the whole output of that string.
Now, with all that said, it can sometimes be impossible to not have some shading on your panels, particularly in early morning or late afternoon. If the shading is at these times then it’s not so bad. The early morning and late afternoon are low production times of the day anyway, so taking 90% off that isn’t going to have a huge affect on your daily output.
However, if you’re getting shading in the middle of the day then that’s a big concern and you should definitely look at taking steps to avoid/remove that shading object.