Solar Guide

Solar Made Simple

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What size system should I get?
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Clean Energy Reviews has partnered with the biggest and best solar quote service in Australia - SolarQuotes to help you easily find a reputable solar installer*.

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* SolarQuotes work independently from us, and vet their own network of installers. Our partnership does not influence our independent product reviews. We recommend you use this service to get quotes from reputable solar companies in your area.

Solar Payback & ROI Calculator

What is the price of a solar system?

Use the simple Solar Calculator to get an instant price estimate for solar and batteries.

It is important to note, that you neither want to pay too much nor too little for a solar system. It might sound strange that you would not want to pay too little but think about it as if you were going out to dinner. If you pay a small price, you might get a reasonably tasty meal, but it probably won't leave you feeling particularly spritely afterwards. It is the same with solar in that if you buy a cheap system, you are far more likely to have a headache later on. In order to install cheap systems, the company will need to cut corners somewhere. Either on the components that are being installed or on installation costs.

With solar, as with eating out, there is a pricing sweet spot. Our Solar Calculator is not perfect (see the disclaimer before using it), but you can use it to get a rough idea of what you should pay. This is another reason why we recommend getting multiple quotes when buying solar, so you have a reference point.

Is solar a good investment?

Use our Solar Calculator to get instant solar savings and payback estimates. Whether solar makes financial sense largely depends on where you live. Your location will dictate how much solar you can produce and the relative cost of solar energy vs buying energy from the grid (factors that dictate your return on investment). There are very detailed answers, and many variables for these different factors, so for this guide, we will give an overview of the average payback period for solar in some key regions. You can always use our Solar Calculator for more detailed analysis in your area.

Australia has some of the best payback periods worldwide, due to having lots of sun, good government support, and relatively expensive conventional electricity. The average payback period for a 5kW solar system in Australia, if you use 50% of the solar you produce, it is around 4 years (in 2018). According to the consumer advocacy group Choice, that varies from as little as 2 to 3 years in Adelaide, up to 5 or 6 years in Melbourne, Hobart, and Darwin.

In the US, the average payback on a residential solar system is typically 6 to 8 years, according to the solar quote comparison website, EnergySage. Interestingly, according to the Indian Solar market, the payback period for residential systems in India is also approximately 6 to 8 years.

Battery Storage Payback & ROI Calculator

Are batteries a good investment?

Use our Solar Calculator to get instant battery storage cost and payback estimates.

Similar to the desire for us to provide a safe and comfortable home for our family, many humans also seem to have an innate, evolutionary desire to be able to have full control of our energy needs. However, this desire is usually at odds with both the financial and environmental reasons for going solar. In order to be fully energy independent, you need to be completely off-grid, which means you'll need an awful lot of solar, batteries and a backup generator to keep you going in the depths of winter. However, if you live or are moving to an area without the grid, you have little choice but to be energy independent.

Going solar (without batteries) will not give you much energy independence, it will allow you to consume some power that you produce, but if the grid goes down your solar system is designed to go down with it (lest exporting energy to the grid and electrocuting anyone working on getting it back up again).

See our Battery Storage article for all you need to know about buying solar with batteries.

Solar System Size Calculator

How many panels should I get?

Use our Solar Calculator to get instant feedback on the right size solar system for you.

There are a surprising number of factors you can consider when deciding on what size solar system to get. It is worth looking at all of these factors if you are on a budget and have the time, but the very short answer to this question is that the majority of households are getting as much solar as they can fit on their roof (or are allowed by their electricity distributor).

For Australian properties with single phase electricity (that's most of us) you can usually install up to 6.5kW of panels, with a 5kW inverter, and often you'll be able to get as much as a 10kW inverter.

US households are not often restricted in system size by the power company, and the usual system size is between 10-20kW. The average is a bit bigger than in Australia because of fewer restrictions, higher electricity consumption, and larger houses.

That is the short answer, but if you want to know the full details, the long answer is below. In the last section, I will also explain why it's often a good idea to oversize your inverter (get a larger array of panels [6.5kW] than the inverter size [5kW]).

How much solar can you install?

Every electrical distributor (the company that manages the poles and wires) in Australia has different rules about the approval process for installing a solar system. However, the majority will allow up to 5kW for single-phase (which are the vast majority of residential homes) and 30kW for three-phase (generally commercial properties). The system size is usually limited by inverter output not the nominal panel output, so you can install a larger panel array, but you may be limited to a 5kW inverter. In some areas, you are allowed up to 10kW on a single-phase connection if you add battery storage. Unfortunately, in some rural areas, you might be limited to as little as 2 or 3kW. A good solar company will know all these rules in your area and be able to submit an application to find out how much solar you can export and offer options to increase your self-sufficiency.

The other limiting factor is obviously your roof space. See Is my house right for solar for more specifics on this. In short, bear in mind that you can only install the amount of solar that can physically fit on your roof.

How much will you get paid for the solar that you export?

See the solar rebates article for details on what you will get paid for exporting your solar. The key point when considering this in relation to sizing your system is that if you get paid a lot for exporting your solar (close to, or more than what you pay for your electricity from the grid) then you will be happy to get a big system and export a lot of your power so you can get paid that high price for it. However, if you do not get paid much (or anything) for exporting, you will likely be better off sizing your system closer to your daytime electricity consumption, in order to maximise your own consumption (and therefore offsetting what you would normally buy), and minimising selling your power for a low price.

Most of the US uses net metering, so you will get paid the same for what you export as the cost for what you consume, so if you are in the US you don't need to worry about this section.

In Australia, if you search around, you should be able to find a retailer that will pay you 50% of what you pay for your electricity, although many will offer closer to 30%. With a feed-in tariff of 50% of what you pay (for example 15c per kWh, if you pay 30c per kWh for consumption), that is still a pretty decent amount you are getting paid for your solar, and by getting the ‘standard' 5kW inverter with 6.5kW of panels you will likely still get a very good payback period.

What is your current daytime consumption?

If for whatever reason you are getting a very low, or non-existent feed-in tariff, then you will want to size your system closer to your daytime consumption. Although, don't worry about being too precise with this calculation, as your consumption will likely change over time anyway.

Have a look at your electricity bill, and work out your daily average usage. Let's say you use 20kWh per day on average. Then work out roughly how much of that power you use during the day (this will vary considerably during summer and winter, so just use an average). Let's say 50%. That is 10kWh that you use during daylight hours. In most parts of Australia, you will generate at least 4kWh of electricity for every 1kW of solar that you install. Therefore in this scenario, you would only need a 2.5kW solar system to cover your own usage. Some apps and add-on energy meters such as Solar Analytics can give you detailed information about your electricity consumption.

Let's take a look at how you can increase your daytime usage in order to benefit from a larger solar system, and also check if you might need more a bigger system in future.

How can you utilise more of your own solar?

The short answer is, use more power during the day. Do your washing during the day. If you have electric hot water you can add timers or smart controls to only heat hot water during the day. If you have gas hot water, you might want to consider changing to a modern efficient electric heat pump. Use your dishwasher when the sun is out, and your clothes dryer… actually if the sun is out hang your clothes in the sun!

Do you plan to get batteries or an EV? Future proof your system.

This is a moot point if you are maximising the size of your solar system already. However, if you are debating as to whether you need a larger system or not, based on your daytime consumption, do consider whether you might want to add batteries in future. The cost of battery storage is still currently a little high to make it a no brainer, however, it is very likely that the cost will continue to come down over the next decade or so. Remember that a good quality solar system should last you 30 years plus.

If in ten years time you might decide to get battery storage, then you should consider sizing your solar system accordingly now. It is not simple to add a few panels to your installed system down the track, for many reasons I won't go into here.

Consider the example I gave above regarding daytime consumption. If there is a chance in future that you will get batteries, then you would want to consider your full daily usage of 20kW, rather than just your daytime usage of 10kW. That means you would be looking at approximately a 5kW system to cover your usage, rather than a 2.5kW.

Oversizing your solar

As mentioned in the first section of this chapter, most companies will quote for a system with a larger amount of panels, than the inverter size. There are three reasons to ‘oversize' your inverter.

  1. More often than not, your solar array will operate below its maximum nominal power due to a number of loss factors, intermittent shading or poor weather. For example, a 5kW inverter will only output 5kW of AC power if it receives enough solar energy. If the solar array was 5kW then after taking into account losses it will generally produce around 4kW even in sunny weather. However, a 6.5kW solar array will generally produce around 5kW during sunny weather. Solar panels are now relatively cheap compared to the rest of the system so it makes sense to oversize and get close to your 5kW output on a regular basis. Generally 30% oversizing is the most common amount for a number of reasons described below.
  2. As mentioned in the How many panels should I get? section, many electricity distributors in Australia will limit your inverter size to 5kW unless you also add a battery, then you can have up to 10kW inverter capacity in most areas. In order to maximise on that restriction, as mentioned in point 1, you can oversize in order to get closer to maximum output.
  3. Lastly, why not oversize even more? In Australia, the government rebates are based on the size of the panel array (not the inverter), so in order to restrict consumers from cashing in on rebates for panels whilst having an undersized inverter, they restricted the maximum size of solar oversizing to no more than 30% the inverter power rating. For good reason, as this is about the optimum oversizing amount for an average inverter in our relatively sunny Australian climate before you would just be wasting the additional solar power.

After wading through all the details you can see most answers lead us back to a 5kW inverter with a 6.5kW array of panels being the best option for most average households. If you can afford the upfront cost, we think this is a pretty good size system for the majority of households.