What is an STC?

An STC is a form of currency available to owners of small-scale renewable energy systems. Under the federal government's Solar Credits Scheme, eligible households receive money for STCs created by their PV systems. STCs were formerly known as renewable energy certificates or RECs. Currently, the scheme allows you to cash in the certificates you could earn over the next 15 years straight away.

While the government has set a price of $40 per STC sold through the STC Clearing House, the price you get will vary depending on how you choose to sell your STCs.

How to sell your STCs

Have the installer sell your STCs for you: The easiest and most common option is to allow someone else – usually the installer – to sell your STCs on your behalf. This may then be applied as a discount to your installation costs. The benefit is that the process is easy, with all the paperwork taken care of for you. The downside is you're likely to get less money per STC – you can expect about $30 per STC.

Sell your own STCs: The second option is to sell the STCs yourself, which involves considerable paperwork, applications and fees. Depending on the number of buyers and the time it takes to complete the process, it may be months after installation before you receive your funds. There's no way to tell exactly how long you could be waiting, which means unless you have the capital you might find yourself out of pocket. However, you should get a better price. On average, CHOICE members who sold their STCs themselves got a price of $33 per STC, with the highest price per STC being $37.25.

How much money will I make selling STCs?

As an example, a typical 2.0kW system installed in 2015 in Sydney will generate 41 STCs over 15 years. Assuming a sale price of $30 per STC, that's a $1230 saving off the cost of the system. 

Tip: To calculate how many STCs your system will generate, use the government's calculator.

A FiT is the rate you're paid for feeding electricity back into the grid (assuming your panels are grid-connected). Nowadays you don't make much money from FiTs, so it's best to maximise your own use of your solar PV and minimise your export to the grid.

How feed-in tariffs work

Almost all FiTs around Australia are now net FiTs. This means a household is only paid for surplus electricity fed into the grid after domestic use is subtracted. If your system produced 3000kWh, for example, and you used 2500kWh of electricity in your home during the day (the time when your PV system was generating power), the rate is only paid for the 500kWh difference.

(Gross feed-in tariffs, where households are paid for all the electricity their panels produce, irrespective of their own domestic electricity consumption, are no longer available for new applicants in any state or territory.)

How much money will I make from feed-in tariffs?

FiT rates around the country have plummeted over the past few years. Coming off a high of up to 60c per kWh in some parts of the country several years ago, FiTs are currently sitting at close to 8c, depending on where you're located and which energy retailer you choose.

Note: In some states and territories, newly installed solar PV systems no longer qualify for a guaranteed FiT; however, many energy companies offer a voluntary FiT instead. Check with your energy company or the appropriate regulatory authority in your state:

• ACT: Department of Environment and Planning Directorate 13 22 81
• NSW: Service NSW 137788
• NT: Department of the Chief Minister (08) 8999 5511
• Qld Department of Energy and Water Supply 13 43 87
• SA: Sustainability and Climate Change Division (08) 8204 2999
• Tas: Office of the Economic Regulator (03) 6166 4422
• Vic: Department of Environment, Land, Water & Planning 136 186
• WA: Public Utilities Office (08) 6551 1000

Solar panels in Australia work best when they're facing north, pointed directly at the sun, at an optimal angle and not blocked by trees or shading.

Solar panels to suit a very hot climate

Some panels have better temperature tolerance than others (look for a lower 'temperature coefficient') and are therefore a better choice in hot climates.

Although solar panels are meant to sit on roofs in direct sunlight, they actually become less efficient as they get warmer, due to the physics of the photovoltaic effect. So you'll sometimes get less power from the panels on a very hot day than on a mild day (and remember, even on a 25°C day, your rooftop panels could be operating at well above 40°C). Solar panel power ratings are based on standard conditions (25°C panel temperature).

Panels should be installed in a way that allows air to circulate underneath to help keep them cooler.

You should ensure that any solar PV system you consider has met Australian and international standards. To be eligible for small-scale technology certificates, your solar panels must be certified – ask your installer to supply proof. You can check the CEC's list of currently approved inverters and modules to confirm.

Also, the Clean Energy Regulator has partnered with the solar industry and peak bodies to introduce the Solar Panel Validation Initiative. This scheme allows businesses in the Small-scale Renewable Energy Scheme supply chain to check if solar panels are genuine before they are installed. Participating installers and suppliers will be able to use the scheme to provide you with a verified report confirming that the panels they've installed on your roof are genuine and that you're getting what you've paid for.

There are two warranties provided for solar panels: one for the product, another for its performance.

Product warranty

This is the warranty for the panel itself; it's the typical type of warranty that offers repair or replacement if there are any manufacturing faults. Most solar panel product warranties are for 10 years; some manufacturers offer 12, 15 or even 25 year product warranties.

It's important to know the difference between the product and performance warranties; you'll see a 25-year performance warranty promoted more loudly than a 10-year product warranty, but the product warranty is the one that you're more likely to call on if there's any problem.

Performance warranty

The performance warranty is a guarantee that that as long as the panel is functioning and undamaged, it will still produce at least 80% of its claimed power rating after 25 years. The warranty usually also promises that the panel will degrade in an orderly, linear fashion; that is, it will only lose a small and predictable amount of power output each year.

Most solar panels have 25-year performance warranties, and most solar PV systems should last at least that long. 

Note that it can be hard to tell whether your panels are truly performing as they should, especially after several years. If you believe your panels aren't performing as expected, the performance warranty may put the onus and cost on you to have the panels tested in order to make a warranty claim.

It's also a question as to whether a manufacturer will still be around in 20 + years to honour a warranty claim. Nevertheless, the 25-year warranties do give some assurance that manufacturers are confident in the long-term performance of these products.

Other warranties

As well as the warranties for the solar panels, you should also get a warranty from the installer for their workmanship in installing the system; the mounting racks, wiring and connections. This will typically be one or two years - which should be enough to detect any major problems - but as always, a longer warranty is better.

The inverter will also have its own warranty, typically five years but they can be up to 10 years or more.

• What is the FiT you'll be paid and how often will you get it? How will you receive it: as a discount off your energy bill or as a standalone cash payment?
• Will you need to change to a new meter and what will it cost?
• What is the cost of the electricity you purchase from your retailer (in cents per kWh), and will you lose your off-peak rates if you install solar?
• Will you be charged a higher daily fixed charge if you connect your solar PV system?
• Do you have to pay any additional fees?

Monocrystalline panels are typically black in colour and have a reputation for higher efficiency than multi-crystalline (or polycrystalline) models, which are typically dark blue and are sometimes said to have better temperature tolerance. The differences come from the manufacturing processes of the silicon cells in each case. In practice there's not necessarily a clear advantage either way; as with most high-tech products, solar panels are a complex assembly of many components and the overall performance depends on more than simply the type of cell.

Interdigitated back contact solar cells (IBC), or rear contact solar cells, are a variant of standard solar cells. They can achieve higher efficiency by having all the electrical contacts on the rear of the cell (rather than at the front), so there are no metal contact strips preventing light getting to the cell surface.

Thin film solar cells are made from a thin layer of photovoltaic material (such as amorphous silicon, cadmium telluride or copper-indium-gallium-selenide) on a base plate of glass, metal or other substance. This technology is evolving and while it promises more flexible applications than standard solar panels, it's so far generally less efficient and is rare in rooftop arrays. It's used in various large and small applications, from building-integrated PV systems to solar-powered calculators and garden lamps.

Bifacial panels have (as you'd expect) solar cells on both sides, front and back. When mounted in the same way as a regular solar panel, the front faces the sky as usual, and the back picks up scattered and reflected sunlight from the roof. 

They can also be mounted vertically, for instance facing east-west, to maximise solar power generation all through the day (one side catching the morning sun in the east, while the other side catches the afternoon sun in the west); this may be particularly useful in mass arrays on a commercial solar farm. 

Depending on how they're mounted and how much reflected sunlight is available, they can deliver anything from 5% to over 20% more power than a single-faced panel of the same power rating. 

Bifacial modules are fairly new and not widely used yet, but it's likely they'll become more common over the next few years. 

Their power output is very dependent on how they're mounted (more so than for regular panels) and industry is still working on an agreed standard method to rate their overall power output. We've included one in our current review for experimental purposes, but aren't including it in the published results yet until we have more clarity around how to rate the results. The early results are positive.