When we visited Irith and Stephen’s home in Manifold Heights, the first thing we noticed was how light-filled, warm and comfortable it was on a cold August afternoon. And it’s not only beautiful and comfortable, but it also generates most of their electricity needs on site. We had a chat about their approach to building their super-efficient, passive solar house and their cutting edge heating and energy generation technologies.
Q: You’ve clearly put a lot of thought and energy into energy efficiency and energy generation – what has motivated you to make your home so sustainable?
Stephen: “Our primary motivation was reducing our carbon footprint – but not at any price. We had to be pragmatic about it because it had to make financial sense too. And when we did the sums we were pleased to see that PV works on both counts- it’s great for our carbon footprint and it’s great investment.
Irith: “We see our sustainability measures as a way of future proofing the house, like paying forward our energy bills for the next 20 years. When we were planning on building the house, we couldn’t assume that we would both have permanent full time jobs, and we wanted to have financial freedom in future if our circumstances change. In a way, it’s a renewable energy insurance that eases cost pressures in the future.
Q: How did you size your solar PV system?
Stephen: “We were happy to buy the biggest system possible, because we’re assuming battery storage is on its way and we’ll end up storing our surplus energy. In the meantime we’re happy to create more than we use and sell it to the grid, even though the feed in tariffs are miserable at the moment. Our system was limited by the size of our roof, and the network’s limit for how big a system you can have it on a domestic installation. We were delighted when Tesla came out with the Powerwall – battery storage isn’t far away and it’s going to be a real game changer. Once we get battery storage we estimate it will save us at least another $600 a year.
Irith: “The big decision was whether we got micro-inverters. They’re more expensive, but its easier to maintain the system efficiency. If a panel goes wrong it doesn’t compromise the whole system. Micro-inverters are also safer, (because DC is converted to AC current at the panel) and it meant we didn’t have an inverter on our wall.
Q: How did you choose your solar installer?
Irith: “We spoke to a few people and looked at solar PV companies at the Home Show. In the end we went for a local supplier recommended by a friend who was knowledgable about PV. We chose Aaron Lewtas from Green Energy Options.
Q: How did you choose your retailer?
Irith: “We’re with RED Energy because, at the time, their feed in tariff was 6.5c, which was half a cent better than AGL and Origin, and their kw price was better than Origin. However, when our contract’s up we’ll be looking at Powershop for a renewable energy supplier, and see how they compare against RED Energy. We don’t think AGL or Origin are anywhere closely aligned with our values and the need for us to reduce our carbon footprint.
Q: Have you noticed bill savings since you installed your system?
Stephen: “We installed our solar panels when we built out house, so we’re not able to compare against bills before we installed the system. However, our last quarterly bill was $150, so we’re only really paying for the connection fees. On the back of the envelope, we estimate we’ve saved around $1000-1500 a year, so our return on investment is around 10%. With returns like that , it would even be worthwhile to go to the bank and borrow money to install a solar system – the interest you’d pay is much less than the return on the investment.
Q: Aside from your solar PV system, have you made any changes to cut your power consumption in your house?
Irith: “I’m committed to sustainable architecture, and so for our new house I did a lot of research on building materials for optimal thermal performance. Stephen found some research from 22 years worth of temperature data for Geelong. A lot of Australian housing design is assuming a hot climate, but when you look at the data, Geelong is unmistakably cold place, so a lot of our design was geared to retaining heat inside.
“Because we’re designed for a cold climate, we designed north facing windows and optimised insulation for retaining heat. We also installed a ‘Python solar heater’ that uses the sun to heat air and a solar pump to circulate it through the house. Because we designed for heat retention, in summer we need to use more active strategies to keep the house cool. This includes growing vines on our north side of the house, or using shade cloth to keep the sun out of the house. We also have strong security screens so that, even on a summers night, we can have all doors and windows open to get cooling night breezes through the house. All windows are double glazed, argon filled casement windows, which open like a door to catch southerly breezes. The wooden frames are a great insulator, and casements seal much better than sash windows, so you need them for a draught-proof house.
Stephen: “We came to the view fairly early on that there is no one silver bullet with energy efficiency, so our approach was to bring together lots of different approaches to reducing our energy needs. In terms of value for money, bulk insulation is the best thing you can do. In our building design we increased the thickness of our frame from 90cm to 140cm. This allowed another 50mm of space, which meant we could have thicker batts and a 35mm air gap. Still air is an important insulator too. The wider frame only cost an extra $2000 in materials.
“Then we commissioned a blower door test to see how leaky our new building was. There’s no requirement in the Australian building code for leakage rates, but we used the Scandinavian leakage rate. We were very fortunate with our builder because he was curious and completely open to the process - particularly because he’d just spent a week caulking the building to seal it up. The blower door guy came with his plastic sheet and his blower, and it was an amazing process because you could hear the air squealing through the gaps. The builders loved it because they found it so educational – they were running around seeing where the air was leaking through. They went on use another 120 tubes of silicon to caulk the house propertly. A blower door test costs $600 and it’s the best $600 you’ll ever spend.
“Reducing leakage rates to Scandinavian levels puts the house on the borderline for needing active ventilation. That was the clincher for choosing the Python system, while it is giving you solar-heated hot air it is also giving you lots of fresh air. So even with doors and windows sealed in winter we were getting hours of warm fresh air blown into the house. That’s really important for keeping VOCs low and supressing mould.
Q: What are your sustainability ambitions for the future?
Irith: “We just put in a gas instantaneous hot water because we felt we had a lot more homework to do on solar systems. I’ve heard heat pumps are very efficient and we want to find out more about it. I’m tempted by the idea of a byproduct from a heat pump – can you use waste cold air to be part of your cooling system.
Stephen: “I’m conservative by nature. I’m not sure that we’ll ever go off grid. If there are decent feed in tariffs available in future, then we’d stay connected.
Q: So who which local suppliers and contractors did you engage?
Architect: Glenda Shomaly
Builder: Jeslyn Constructions
Python (solar heater): New Earth Systems
PV: Aaron Lewtas, Green Energy Options
Blower door test: Mal Boyd, SaveEnergyPlus
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