Sanctuary: Modern green homes

Know your panel

This is an excerpt from an article in Sanctuary magazine issue 3.

Until a decade or so ago, amorphous solar panels were lumbering giants, dwarfing their crystalline counterparts. They had an efficiency of around four per cent, so were large for their energy output. (Lower efficiency just means that a panel of a particular capacity is larger, not that it produces less energy than a higher efficiency panel of the same capcity.) Then Uni-Solar pushed the efficiency to around eight or nine per cent, making for smaller panels. Other brands like Kaneka and Schott Solar followed suit.

The main advantage of amorphous panels is that they use about one per cent of the silicon that crystalline panels do, so their embodied energy is a lot less. They also perform better in hot conditions, partial shade and overcast conditions.

Many manufacturers are focusing on amorphous (otherwise known as “thin film”) panels now due to the lower cost and simpler methods of manufacturing.

Solar hot water

This is an excerpt from an article in Sanctuary magazine issue 3.

In the average Australian household, hot water accounts for 30% of energy use. Water heating is second only to transport as a households largest cause of greenhouse gas emissions. However a solar water heater can reduce your emissions by as much as four tonnes of CO₂ or more per year—the equivalent of taking a car off the road! By using the energy from the sun to heat water at zero costs.

Depending on where you live and your climate a solar hot water system can provide between 50 and 90 per cent of your hot water needs. The initial purchase price will probably be higher than a similarly sized non-solar water heater but the savings made in energy bills will generally pay for this difference in less than 10 years—in as few as four years in some cases. A solar system generally has a longer lifespan than a conventional unit, so financial returns can be considerable over the life of the system.

This benefit has been recognised by the federal and some state governments and is encouraged in the form of renewable energy certificates (RECs) and rebates. Rebates vary from state to state, but can save you a great deal on the cost of a solar water heater, making them more economically viable.

Flat-panel and evacuated tube collectors

Most solar hot water systems use solar collectors (in the form of panels or tubes) to absorb energy from the sun. Water is heated by the sun as it passes through the collectors. It then flows into an insulated storage tank for later use.

The most common form of solar collector is the flat-plate panel. They consist of a dark coloured, metallic absorbing plate to which a network of pipes is bonded. This arrangement is then placed in an air-tight metal box with a glass cover on the top and insulation on the back and sides to reduce heat loss. As the sun shines on the collector panel the water in the pipes becomes hot due to conduction from the collector plate

In the last few years another type of collector has started to appear on the Australian market. These are known as evacuated tube collectors. They consist of two glass tubes (one inside the other) that are bonded to each other at each end to form a sealed space between them. The surface of the inner tube is coated with a heat-absorbing coating. The space between the two tubes has most of the gas removed from it (hence they are evacuated), which provides a high level of insulation. As solar radiation passes through the outer glass tube and heats the inner tube, it is trapped by the lack of gas, which would otherwise allow heat loss. As a result, the efficiency of these collectors is higher than flat plate collectors, and evacuated tube collectors are suited to colder climates as they even perform well on cloudy days.

Solar saviour

This is an excerpt from an article in Sanctuary magazine issue 3.

Solar power systems are made from a series of photovoltaic (PV) panels that directly convert energy in the form of light from the sun into electrical energy. Solar power can be used in all parts of Australia as long as you have a suitable site with a north-facing roof, or ground space that is not shaded during the day.

Until recently, the main reason that people chose a solar system was that they lacked access to the mains power grid. In rural areas it was cheaper to install a Remote Area Power Supply (RAPS) system than for connection to the grid. With a RAPS system the solar panels charge batteries, supplying the home with power when needed.

As solar gains in popularity in urban areas, grid-interactive systems are becoming the norm. With a grid interactive system the energy produced by the solar panels is fed directly into the mains grid via a device called an inverter. Any electricity produced, but not needed by the house at that time, is simply fed into the mains grid. The home can also draw power from the grid when the sun is not shining. This is the simplest system, and requires little or no maintenance, other than the occasional check to ensure it is still operating, and cleaning the solar panels of excessive dirt build up.

Size and costs

How big a system you need and how much it costs is dependent on how much energy your house consumes. Probably the most important part of system design that is often overlooked is the energy efficiency of a home. There is no point spending money on a solar system when the energy it generates is wasted. Spending a few hundred or even a couple of thousand dollars on more efficient appliances and making your home more energy efficient means you could buy a smaller solar power system.

The average home system is around 1.5 kilowatt (1500 Watts) of peak generating capacity. A 1.5 kilowatt system costs around $20,000 before the rebate, although the price depends on the options selected, such as whether the home has a suitable north-facing roof or if extra framing has to be added to the roof. Warranties on the components of solar systems range from one to 25 years, with solar panels usually guaranteed for 20 to 25 years.

Choosing a heater

This is an excerpt from an article in Sanctuary magazine issue 3.

The type of heating you need depends on the size and function of the space to be heated and how often and how many people use the space. When looking for a heater find out how much energy a heater will use, its long term running costs and how much pollution it will create.

Unless you create your own energy from a renewable source or purchase GreenPower, the energy used by your electric heater is sourced by greenhouse gas producing fossil fuels. Efficient gas heaters and reverse cycle airconditioners produce one third the amount of greenhouse emissions of standard electric heaters. They also have energy labels to help you choose the most efficient model. If looking for a space heater choose a 5-6 star natural gas heater or a 4-6 star reverse-cycle airconditioner. For central heating, zoned 4-5 star natural gas ducted heaters and zoned natural gas hydronic systems are the most economical.

Wood can be a good fuel source if the wood is sustainably harvested and sourced locally. However, the smoke from wood fires is a major source of pollution, and open fires lose 90 per cent of their heat up the chimney. If using wood make sure it is sustainably sourced and use a slow combustion heater to the manufacturer’s instructions.

Solar heaters

Almost all of the energy available on the planet today comes or has come from one place—the sun. Yet, very little of it is used directly by people. There are two forms of active solar heating available in Australia; flat plate collectors and solar boosted hydronic heating.

Flat plate collectors consist of a large flat glass covered box used to heat air which is then pumped into the home using a fan. Small (approximately 1 x 2 metres) flat plate heaters can be used to heat individual rooms, while larger (approximately 3 x 4 metre) roof-mounted collectors can heat an entire home, at least when the sun is shining.

You can also use the sun’s heat to provide some (or sometimes all) of the heat to a storage-type hydronic heating system. Indeed, some hydronic systems that use solar evacuated tubes are designed to be primarily heated by solar, with gas or electric boosting as a backup.

Whatever system you choose, remember that the best way to save energy, money and reduce your greenhouse emissions is with good house design. By reducing heat loss you can maintain a comfortable temperature inside, regardless of the temperature outside.

Save energy

This is an excerpt from an article in Sanctuary magazine issue 6.

Get a solar hot water system. A solar water heater can reduce the greenhouse emissions of an average family by as much as four tonnes of carbon dioxide per year – the equivalent of taking a large car off the road.

Buy energy-efficient appliances, particularly big-ticket items such as fridges, washing machines, dishwashers and TVs (choose LCD over plasma). For a comparison of appliances, see www.energyrating.gov.au.

Replace your incandescent lights with compact fluorescent or light-emitting diodes. Shun “low-voltage” halogen downlights – these are major users of electricity and require you to put gaps in the ceiling insulation to let their heat dissipate.

Turn off appliances with standby power (evident from the little lights that shine on them even when they’re “off”) at the plug. The “phantom load” these consume while idle can add up to as much as 10 per cent of your total energy bill.

Hot sun, cool house

This is an excerpt from an article in Sanctuary magazine issue 6.

The sun is beating down on the roof. The garden is wilting and so are you. Wouldn’t it be nice to turn some of that heat against itself?

You may be surprised to know, it’s actually possible to convert heat on the outside of your house into a cooling breeze inside. Solar airconditioners are coming your way.

The models in development now mostly use evacuated solar thermal tubes, like the ones used in many solar hot water systems. Instead of drawing on mains power on the hottest days, pushing power grid peak loads into the red, these systems would just hum along on solar energy. And the hotter it is, the better they work.

Consensus is that solar aircon for homes could be only a couple of years away. Currently there are several types of system in development.

How will they work?

One of the most promising systems uses evaporation. The system uses a desiccant to remove humidity from the air, which is then re-humidified using wet pads so the air delivered to the building is both cool and not too humid. The desiccant is then solar-heated to remove the moisture it has collected, so it’s ready to work again.

These systems are very far down the track in terms of technical development and will probably be among the first to be commercialised for domestic use. They’re efficient, robust and easy to maintain. A slight downside with desiccant-evaporative systems, however, is that they use a fair amount of water: CSIRO has estimated 30-50 litres on a hot day for a residential system (that’s about as much as a four-minute shower with a low-flow showerhead).

Another exciting technology, though not as far along as evaporative systems, uses ejector jet pumps, which rely on heat energy to circulate a fluid through a cycle of condensation and evaporation. The principle has been known for around 100 years, and Dr Mike Dennis, who heads the Australian National University’s solar ejector jet program, believes it has the potential to be more reliable, cheaper and smaller than comparable systems. The ANU is working with commercial partners to develop a prototype.

A winning design

Dr Paul Kohlenbach of Solem Consulting is a former research scientist with CSIRO and an expert in residential-scale solar aircon. Dr Kohlenbach says that to succeed in the residential market, manufacturers “need to develop a plug-and-play solution, pre-packaged and ready to use”.

Dr Kohlenbach believes the future for solar aircon is bright. “The CSIRO is currently researching a small solar cooling system which could be market-ready in two to three years. Overseas manufacturers have realised that the Australian market has huge potential and have started to establish themselves here.”

Probably the single most exciting thing about solar technology, he says, is that it has the potential to not only offer airconditioning, but heating and hot water as well. “A possible solar cooling kit can therefore provide all the thermal needs of a residential house.”

The ANU’s Mike Dennis agrees that a system that both cools and heats is the holy grail of solar climate-control technology. “Consider that most of Australia’s population live in a temperate climate that hardly requires airconditioning – in fact requiring a lot more heating than cooling,” he says.

If we allow climate change to continue, of course, more Australians will be concerned about summer cooling than winter heating. Even so, whichever system prevails, the winning design will almost certainly offer year-round comfort and a hot shower.