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Week Thirty-One - Renewables

100% renewable electricity saves 1.1 tonnes CO2e per person per year (sort of).

· Weekly experiments

My kindergartner

- When I grow up, I want to be a soldier like Daddy so I can look after the dragons and ponies.


- When I grow up, I want to understand the Australian energy market. Your goal is more realistic.

Sergeant Dragon chats to Soldier Pony

How much CO2e from household electricity?

To produce and transport electricity to houses, the grid generates carbon dioxide and equivalent emissions (CO2e). On average, household electricity from the grid is responsible for around 2.2 tonnes CO2e per person per year (around 1.3 tonnes CO2e per year for me).

Your household may use more or less than this average. A big slab-heated home with multiple TVs, fridges and computers, a pool and inefficient heating and cooling will use more power. A well-insulated apartment will use less. Grid power also varies around Australia because different states use different power generators. A kilowatt-hour of electricity in coal-fired Victoria generates five times more CO2e than a kilowatt-hour in hydro-powered Tasmania. Soon, the ACT will have a zero-emissions grid. This means we'll get to hear ScoMo tell us we need coal to keep the lights on from inside a 100% renewable Parliament House. Ah, the apocalyptic irony.

Use less electricity

I've looked at how to use less electricity through better insulation, less heating, smarter cooling, different cooling, efficient lights and appliances and less hot water. If you follow most of those tips, you should cut your electricity use in half. That leaves the average household generating 1.1 tonnes CO2e per person per year (around 600 kilograms CO2e for me).

You'll generate even less CO2e if you install a reverse-cycle heat pump for winter heating and summer cooling. That's a great choice for any new system. If you already have a fairly efficient system in place, you might be better off spending the money on green electricity.

Green electricity

After cutting power use, where should you get your remaining electricity? You can buy renewable grid power through GreenPower. If you're in a position to do so, you can install a solar PV system on your roof, either buying up-front or on finance, with or without battery storage and with or without smart metering. You can even install rooftop solar somewhere else by buying into a community scheme.

This complexity defeated me in Week Ten. Today, I'll stick with a comparison between rooftop solar PV versus the grid, but feel free to pick whatever renewable floats your boat. On a simple 'tailpipe' calculation, 100% rooftop solar or other green power drops your electricity emissions to zero, saving the average Australian 1.1 tonnes CO2e each year. BUT this ignores the full environmental consequences of our electricity.

What is rooftop solar PV?

Rooftop solar photovoltaic (PV) panels convert the sun's radiation into electricity for your house. They've come a long way. A decade ago, I installed a 1.26 KW system for $5,100. I just got quotes on systems four times larger for the same price. Rooftop solar got big and cheap. Deals differ around the country but you should get a government STC rebate wherever you are. You can then use the electricity yourself and send any excess back to the grid in exchange for a feedback tariff (but you'll earn less on your feedback than a power company would). Financial payback periods on rooftop solar are usually three to seven years.


SolarHub chart shows how solar PV systems work

Image courtesy of SolarHub.

What should you look for in a rooftop solar PV system?

As with any other big purchase, shop around. A good system will use high-quality parts (especially inverters), provide 10-year product warranties on panels and inverters and use CEC-Accredited installers. I attended a government-run seminar for research. I also used SolarQuotes to get three quotes from good providers. I've included my quotes in the Notes.

Why bother with efficiency?

If green electricity is plentiful and cheap, why bother being efficient? Why not stick giant panels on the roof and use as much power as you want? I've run this argument through government and business a dozen times and narrowed it down to two words. Environmental consequences.

Modern energy is like magic in a medieval fantasy. It never comes free. This is true, no matter how green the energy. Large-scale renewable plants compete with land use for other purposes. If we build a solar farm, we can't grow food or fibre or protect native habitat there. Some projects also directly kill wildlife and cause other problems.

What about rooftop solar which doesn't compete with other land use? It's still not free because it takes energy to make and install the system. That system contains embedded emissions. How much? According to this pilot study, the energy output from a panel offsets its embedded emissions in 8.5 years. But that study assumed the panel performed 6 hours per day, 365 days per year. That might be true in some places, but most areas have more cloud, rain and shade than that. Using less ambitious assumptions typical for the Australian solar industry, it takes 18 years for a solar panel to offset its embedded emissions. With a solar system lasting 20 - 25 years, it still comes out ahead. It also compares well with grid power, because standard grid emission factors also omit most of the embedded emissions. Think of all the concrete and metal to build a coal-fired power plant along with the power lines to run it your house. All that will be saved on rooftop solar.

Solar panel output and manufacturing is getting more efficient all the time. I hope we have good recycling options for old rooftop systems by the time mine breaks. All around, this means that rooftop solar is a great option and it will improve over time. But it will never give us free power.

First, use less energy. After that, choose the cleanest type that suits you.

Spreadsheet calculations, data and references in 'Notes' section, Week Thirty-One.