Andrew Reddaway, the Alternative Technology Association’s (ATA) energy analyst, answers common questions about rooftop solar power.
Andrew, how does solar work?
Solar panels generate electricity from the sun as Direct Current. An inverter converts this into Alternating Current at 240 volts, compatible with your home appliances. At any instant, your appliances get the first call on your solar generation and if there’s excess, it’s immediately exported to the grid.
If people are building a home, what should they be thinking about in relation to solar power?
For a solar-friendly house a broad, sunny roof is a real asset. A north-facing roof is best, especially in southern states like Victoria and Tasmania, but west and east-facing roof surfaces are good too. If the roof pitch is less than about 10 degrees, your solar panels may need costly tilt frames. Shaded roofs are poor for solar, so you need to think about future building construction and growth of trees because even partial shading of a single panel can have a major impact on a solar system’s effectiveness.
Would a person need to install panels as a house is being built or should they wait?
A solar system is easy to add on later. If you wait until you’ve received a few electricity bills it will help you work out how many panels to get.
From a purely economic perspective, is installing solar worth it?
ATA analysis has found that payback periods for a 2-kilowatt (kW) solar system are generally eight to nine years. This equates to an investment with a comparative annual interest rate over 5%. The benefit comes in bill savings, so there’s generally no tax implication and there’s no risk of losing your capital as there may be with financial investments. Solar pays back faster if you are in a very sunny suburb or town, you’re home during the day to use electricity as it is generated or you pay relatively high electricity rates – if you live in WA, South Australia and in many rural areas.
Is solar good for the environment?
Yes. All the electricity you generate directly reduces the output of centralised power stations, avoiding greenhouse gas emissions. It takes only one or two years for a solar system to generate enough electricity to produce itself.
Solar electricity you use immediately avoids buying electricity from the grid, which may cost around 20-30 cents per kilowatt hour (kWh). Excess solar electricity is fed into the grid, and with current feed-in tariffs will only earn you around 5-8 cents per kWh.
How many panels should a person have installed on their roof?
It’s relatively cheap to include extra panels in a solar system, but each extra panel will give diminishing bill savings because it’s more likely to produce more than you use. It’s best to get advice on the optimal size for your household’s electricity consumption patterns. You should also consider future changes in household electricity consumption, for instance as a result of children leaving home.
How do you choose a good installer?
As with any tradesperson, it is best to get multiple quotes, ask questions and obtain references. The installer must be an electrician, and accredited by the Clean Energy Council for solar installs. If you go through a large solar sales company, you may have no choice over the tradespeople who will be subcontracted to do the work.
What about selecting good brands?
Solar is a fast-changing industry and models change frequently. As with other products, the cheapest is unlikely to be the best, so perhaps first see which brands solar installers are quoting on. Internet discussion forums are a good source, for example the ATA forums and “Green Tech” at Whirlpool. Also, make sure to check warranties.
How long does a solar system last?
Good solar panels should continue to generate for at least 25 years, but the inverter may need replacement after 10 years or so. An inverter’s life span is reduced if placed in a hot location – like on a sunny, west-facing wall.
Many people find that if their panels are tilted at least 15 degrees, they are cleaned by the rain. Depending on dust etc, your panels may need to be cleaned every year or so, or their output may be affected. Panels are cleaned like windows.
Should a person think about adding batteries to a solar system?
A battery can store excess daytime electricity for you to use when you get home in the evening, enhancing the bill savings of your solar system. Grid-connected batteries are expensive and currently aren’t really worthwhile for bill savings, but the ATA estimates that by 2020, as prices for batteries fall, they may be competitive. Some battery systems can power appliances in a grid blackout, but others can’t, and it should be noted that some solar systems are more “battery-ready” than others – ask installers for details on this. When building a home, consider where a future battery may be placed, eg in a cool garage.
What about going off the grid?
In addition to solar panels, reliable off-grid solar systems have big batteries, a special inverter and a generator. Off-grid systems are much more expensive than grid-connected systems and if the grid is available, an off-grid system is not normally worth it.
Having installed solar, why does my inverter show a strange message?
While the sun’s shining, a solar inverter normally shows a useful message such as “Power: 3 kW” meaning it’s currently generating 3 kilowatts of power, or “e-day 20 kWh” which means the system has generated 20 kWh of energy over the day. Most inverters have a button you can push to scroll through different pieces of information. Other messages can indicate a problem needing attention from a solar installer, eg “ERROR”, “GRID VOLT ERROR”, “ISOLATION FAULT”, “GROUND I FAULT”, “AL 14”.
How can I compare my solar performance against other peoples’ system?
The website PvOutput contains self-reported solar generation data. Here’s what to do:
- Click “Live Outputs”
- Click in the “Find” box, type your postcode and “ 20km” and DON’T move your mouse or hit “enter”.
- Scroll down the drop-down list and click one with a good description.
- Click “Daily” and see the number for yesterday in the column “Generated”.
You can check your own inverter’s display near dusk for how much energy it’s generated, and compare.
Are there any other things people need to think about in regards to solar?
Saving energy is often more cost-effective than generating it and the best chance to save energy is when you’re building. Think about: building orientation, window placement and sizing, eaves and window shading, wall insulation and gap sealing, energy efficient doors and windows, and efficient electric heating, hot water and cooking.
For more detailed advice on solar power, speak to an expert like Andrew in the ATA’s Solar Advice Service. The service is a one-hour consultation that costs $130, or $80 for ATA members. Click here to learn more.
ATA members can also access a free 10-15 minute phone advice service on solar and other sustainability matters. Click here to become an member.
Click here for the ATA’s Solar Electricity booklet.