In ‘Q & A’ Category

Q&A: Understanding carbon trading

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When reading ReNew, I always turn first to the Pears Report, but sometimes I think Alan Pears is so familiar with his subject that he forgets others are not. The third-last paragraph of the latest report had me puzzled for some time and, while I think I understand it, it raises more questions and makes me aware that I do not understand how carbon is traded in Australia.


I thought that all forms of pricing carbon had gone and had been replaced by a scheme, dating back to Abbott, in which big polluters were paid in advance not to exceed a certain target; and that this system had come in for criticism on the grounds that it would be too expensive and in any case would leave us short of our obligations. This is probably wrong or outdated so I would like to know what we are doing at present. If it is still operating, are the government and big business exceeding their targets and purchasing carbon offsets in the global market? Why is this tolerated—is it not an extraordinary abrogation of responsibility in this area?

The suggestion to buy carbon offsets as presents is great but what is meant by “buy and surrender these offsets without emitting”? Surrender to whom and what would I use emissions for? Secondly, it seems improbable that even an army of “little people” would have the purchasing power of the big corporations or government. Also the available purchases vary significantly in price per tonne so would not the best strategy be to buy the cheapest first?
—Dick Varley


Yes, maybe I did assume a lot—I was short of space and it would take most of an issue of ReNew to explain it all properly.

Mandatory carbon pricing in Australia was shut down by the Abbott government. I was referring to the international scheme run by the UN under the Clean Development Mechanism (CDM), where developing countries can implement emission reduction measures and create carbon offsets if they meet the rules: for each tonne of emissions avoided under an activity that meets the CDM requirements, they create a certificate. These offset certificates can be sold to emitters in developed countries (and to governments to meet their Paris commitments), who can surrender them to the UN as an alternative to reducing their own emissions.

The website I referred to is fairly user-friendly and allows individuals to buy offsets from CDM projects and they are automatically surrendered through the website. Under the international carbon accounting mechanism, this is counted as additional abatement outside countries’ emission inventories. So if I buy a tonne of offsets through this website (and they are automatically surrendered) this means I have reduced my net emissions by a tonne of CO2 as measured by the official global accounting scheme. So I can offset my emissions from air travel or other activities that emit. I should probably have said ‘without net emissions’ rather than ‘without emitting’.

While the UN CDM scheme has plenty of critics (for good reason), the reality is that CDM offsets are ‘legal international currency’ so if I buy and surrender one, that is one less offset available for a big emitter to buy. I agree that we individuals can’t match the scale of big emitters, but my aim is to offset my emissions that I can’t avoid, and this is a way of doing it quite cheaply. And if people like me do buy CDM offsets in large enough quantities, it will push the price up a bit, which means developing countries will have a bit more money to fund emission-reduction activities, and the big emitters (and the Australian government) will have to pay a bit more for offsets, so they may be more interested in actually cutting their own emissions than just buying their way out of their obligations.

Given that all offsets that qualify under CDM are ‘equal’ (although it’s not quite as simple as that), buying the cheapest ones first does make sense—although some of the more expensive ones do have significant local social and environmental benefits that I don’t mind contributing to. So I buy a mix of cheap ones (under $1/tonne) and some more expensive ones—but even those are still under $10/tonne. Some of the more expensive ones also qualify as ‘Gold Standard’ which means they are verified by a group of environmental organisations and offer significant environmental/social benefits.

The scheme that replaced the carbon price in Australia is so-called Direct Action and the Emission Reduction Fund (ERF) is the mechanism. The ERF uses ‘reverse auctions’ so organisations that want to take actions that cut emissions (or store carbon) can bid and, if successful, are paid an average of about $13/tonne of emissions avoided or stored—effectively we taxpayers are paying this price per tonne of emissions avoided. This is just like a carbon tax, but we are paying, not the businesses that emit! Yes, there is a lot of debate about this scheme, and it is not very good for lots of reasons!

Some carbon offsets created under Australia’s ERF also qualify as ‘additional’ global emission reduction, but there are some complexities and I don’t think individuals can buy small quantities of ERF offsets, so I prefer to use the UN website.

Given that Australia’s emissions are not declining at anywhere near the rate needed to meet our 2030 Paris commitment (although we will meet our 2020 commitment), it seems increasingly likely that the Australian government will have to buy offsets to compensate for a proportion of our emissions, instead of cutting local emissions by enough to meet our commitment. I agree that, as a wealthy country that could cut its emissions at little cost, or even while saving money, we should be doing much more.

I wish I could point readers to a simple but thorough explanation of all this, but I don’t know of any decent source. The Voluntary Carbon Markets Association used to publish explanations, but it has not been active for some years—a group of us are hoping to reinvigorate it, so maybe then I can refer people to it.
—Alan Pears

Q&A: Pumped hydro

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The government is touting pumped hydro as the answer to all our electricity problems. What they do not talk about is the inefficiency of pumped hydro nor for that matter the inefficiency of battery storage.
Pumped hydro has losses due to motor/generator inefficiencies, pump inefficiencies, pipe friction and turbine turbulence. My rough engineering estimate is that for every $1 of pumped storage power out at least $2, if not more, of power is needed fed in.


As for batteries I have no idea but the manufacturers or electric car users should have a good idea. Is there anyone who can advise as to the losses from using either? It could be like John Howard’s carbon capture where it used more power to recover the carbon and pump it than was generated.
—Tony Parnell


All energy storage involves some efficiency loss. Lithium batteries have round-trip efficiency a bit lower than 90%—this is published in the specifications for products such as the Tesla Powerpack used in the ‘big battery’ currently being installed in South Australia. Pumped hydro is less efficient, around 80% for the ANU’s hilltop proposal or 72% for the proposed Cultana seawater pumped hydro project.

In a high-renewable grid most electricity consumption would be supplied directly from generators, avoiding efficiency losses in energy storage. The batteries would only be used where necessary to buffer variability in supply and demand. As costs drop to build wind and solar farms, they become economically competitive with fossil fuels even after allowing for the extra generation capacity required to cover energy storage losses. Our report ‘100% renewable grid by 2030’ examines these economics; read a summary on p. 40 or find the full report at

SA wind farms are at times already being curtailed, as they’re generating more energy than the grid can absorb. So energy storage in that state has some free energy to make use of (see p. 41 for more on this).
—Andrew Reddaway, ATA Energy Analyst

Q&A: Enphase restriction?

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I am planning a rooftop PV system, using LG panels and Enphase microinverters. An experienced PV designer told me he thinks the use of Enphase microinverters will preclude the future addition of any battery other than one from Enphase.
I have never heard this before. Is there likely to be any validity in this opinion?
—Rod Sloggett



I think there is some validity in that opinion, but it’s overstated.

With microinverters installed on the panels, the cables coming from the roof carry electricity already converted from DC to 230 V AC current. To store this energy in a battery, it needs to be converted back to DC again. This is achieved with ‘AC coupling’, where the battery has its own inverter, connected to your home’s electrical switchboard. Many solar batteries are designed to work this way, but some are intended for ‘DC coupling’ instead. A microinverter solar system can’t use DC coupling, so your battery choices are more limited than if you selected a system with a central inverter.

With a microinverter solar system you should be able to add any AC-coupled battery (including the Enphase battery) and store excess solar for the evening. The battery has a sensor in the switchboard to detect when you’re exporting to the grid, and thus when to charge up.

Things get trickier in a grid blackout. The battery can power the house, if the system is designed and set up to do so. But since it has no communication with the microinverters, the battery may have trouble controlling the panels’ generation to prevent being over-charged. During a daytime blackout, your solar system will probably shut down immediately. If it does keep running, at some point the battery may force it to shut down by increasing your home’s electrical frequency. This process is not graceful and may cause some premature wear on the microinverters and/or affect their warranty. If you select an Enphase battery, this issue doesn’t arise because it’s not designed to operate in a blackout anyway.

Here’s an ATA article that gives more info on AC coupling, DC coupling etc:
—Andrew Reddaway

Q&A: Electric bathroom heating

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We are ditching our gas connection as part of a major renovation and switching from ducted gas and evaporative cooling to multiple reverse-cycle units that will heat the living and bedroom spaces only. What is the most efficient and greenhouse friendly way of providing heat to bathrooms? I have been looking at a Clipsal strip heater as well as a unit from Heatstrip.
—Ben Purcell



Efficiency of electric heaters are all the same, i.e. 100% of what goes into them turns into heat; it’s just the type of heat that matters. The high-temperature radiant heaters like the Clipsal and similar have a near-instant heat but can overheat you if you are too close. They also have elements that eventually burn out, usually in the middle of winter when they are being used the most, in my experience.

The lower temperature units like the Heatstrip are still higher temperature than ‘true’ far infrared heaters, but they have a similar effect. You can get an idea of running temperatures by looking at how large the panel is compared to its wattage rating. For example, my true far infrared heater (a Heat-on 600 W DIY panel at is 600 watts and measures 900 x 600 mm, so 1111 watts per square metre. The Heatstrip 800 watt unit, for instance, is 624 x 235 mm, so 5455 watts per square metre, so it would run at a considerably higher temperature.

Between the Clipsal and Heatstrip, I would go for the Heatstrip if the budget allows, as it should last pretty much forever, looks nicer and should feel nicer on the skin as well. But the average high-temperature strip heater like the Clipsal is going to be about a tenth of the cost to buy, so you have to weigh that up as well.

Most bathrooms end up with the common combined heat lamp/light/fan fittings; however, they cause a large ceiling penetration that can’t be insulated over (it’s usually better to avoid ceiling penetrations), although being a square box, you can insulate up to them effectively. The heat lamp fittings in many of them are usually fairly well sealed inside the main box, although even the draught-sealed units such as the IXL Eco Tastic have some small manufacturing holes in the metal case that allow some air bleed into the ceiling, so it’s worth sealing those before installation.
—Lance Turner


Q&A: The end of gross metering

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I am a long-term member of the ATA and I wonder if you could advise me. Did ATA promote an electricity supplier last year as an alternative to the main ones which are so coal-dependent, and if so which one?


I am with Energy Australia and 10 years ago I put in solar cells and they paid me what I paid them. A few years back when the feed-in-tariff (FiT) was introduced I was given a time-of-day meter for free and have been on a 60c/kWh FiT and gross metering ever since.

Now from 1 January 2017 they offer two plans: buy a smart meter and get 6c FiT and pay $120 per annum or buy a smart meter and get 12c FiT and pay $240 per annum plus a panel wash once a year! I also understand that the smart meter they propose cannot be read remotely from my living room. Would you have more information? I am actively looking for alternatives (I live in Artarmon, NSW).

—David Bruce-Steer


In 2015, we worked with Total Environment Centre to produce the following online green retailer’s guide available at

However, the end of the NSW gross FiT and the need for net metering to be established has changed the ball game somewhat. While the greenest and dirtiest retailers won’t have changed much, who is offering the best deal to transition you to a net metering arrangement with the most competitive feed-in and consumption tariffs can only really be ascertained by shopping around. We have prepared general advice on what to look for; find the report at Retail offers are changing regularly so the Australian Energy Regulator’s tariff comparator site may be the best place to compare them, as it’s location/network specific:

—Damien Moyse, ATA


Q&A: Wicking beds

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I was very interested in your article on wicking beds in ReNew 135. I have had good success with the Gardening Australia wicking boxes made from polystyrene broccoli boxes. These have PVC tubes filled with soil which go right down to the bottom of the water reservoir. Even if the water level is very low, they are still wicking up through the tube of soil.


My question concerns the beds you showed that had gravel in the bottom. I can’t see how the water would wick up through gravel unless the water level was right up against the geotech. If it only wicks when the water level is near the top, it kind of defeats the purpose of having a wicking bed that is self-watering!

Maybe I’m missing something here. Can you clarify this for me please?



To the best of our knowledge it is undesirable to submerge soil in water—even though it will wick very nicely. Organic matter (such as that found in healthy soil) is food for microbes, both good and bad. When submerged in water, the balance of microbes changes from mostly healthy ones that require oxygen (aerobic), to smelly unhealthy types that don’t (anaerobic—the same goes for your compost/worm farm!).

So by refining the wicking concept, or the materials involved, we’ve found a way to provide the soil with a good balance of moisture and air for healthy soil and happy plants, but prevent organic matter from being submerged in water. You’re right to say when the water reservoir is full, the water touches the geo-textile and is sucked up into the soil via capillary action.

And yes we do use a specific kind of gravel—7 mm bluestone screenings or ¼” minus in the old tongue—for three reasons: it is inert or close enough to it so won’t decompose, therefore it will hold up the soil (!) and still have enough room between the pieces for lots of water.

The screenings themselves actually wick water upward to a certain extent, thus contacting the geotextile fabric and wetting the blanket, even after the water level has dropped below full. In our research we have observed the wicking effect up the screenings themselves to be up to 10 cm.

To round it all out, the enclosed nature of the wicking reservoir, regardless of how much or how little water is retained, creates conditions for humidity and condensation to occur (especially in warm weather when the plants most need that moisture). We don’t know if this has been studied or not, but it does explain why the plants in our wicking beds remain happy even as the water level drops below the extent to which the screenings may wick water up to the geotextile fabric. We think water, even from the lower reaches of the reservoir, condenses on the underside of the geotextile fabric, then wicks up the standard height (30-40 cm) into soil. Hence the fact that the many beds we build in this way all work so well.

Hopefully some university or more scientific types from the ATA membership will set up clear-walled wicking beds and start quantifying this phenomenon so everyone can have a better understanding of what is and isn’t going on.

—Carey Priest, Very Edible Gardens

Q&A: DIY double glazing effectiveness

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It was an interesting article about double glazing by Alan Cotterill in ReNew 135. However, I am led to believe that double glazing relies on a vacuum between both sheets to be effective. How did Alan achieve this? Was his objective to cut down sound only? Double glazing is certainly a good idea, particularly where I live in the Blue Mountains, but I don’t have it because of cost.This is why the article interested me, but I doubt its effectiveness for retaining warmth.
—Rod Marshall



Double glazing doesn’t rely on a vacuum, it uses an air gap of a particular width that is wide enough to provide a level of insulation and narrow enough to prevent convective currents in the air between the two panes which would transfer heat from one pane to the other. Many double-glazing units use inert gases such as argon between the panes, as it is a better insulator, but there’s not that much difference between argon and air, so DIY double glazing can work quite well compared to single-pane windows.

There are vacuum window units, although I don’t know of anyone making them here in Australia; possibly Pilkington has their Spacia units available. You can’t produce a vacuum between two unsupported flat panes of glass as external air pressure would press the panes together and possibly shatter them. In vacuum-insulated windows they use many tiny posts between the panes to provide the support for the glass, but obviously this sort of window will not be perfectly clear although it comes close. The space between the panes is much smaller for vacuum glazing than with gas-filled double glazing. For example, Pilkington’s Spacia units have a 0.2 mm gap compared to at least a 6 mm for gas-filled units.
—Lance Turner

Q&A: Single-slice toaster

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I read your article on household appliances ‘It’s in the Stars’, but what about the humble toaster? Every morning in households across Australia and worldwide, power is wasted because, if you only want to toast one slice of bread, both elements fire up if you are using a two-slice toaster. If you are using a four-slice toaster and want to cook one or three slices, again an unneeded side of the element will switch on.


It shouldn’t be too hard for toaster manufacturers to design a more energy-efficient unit with independent elements. Small individual savings like this can add up to significant savings in energy use. There must be lots of ways savings can be achieved. It just needs someone to develop the ideas.

We can’t rely on our governments to make all the right decisions on the important subject of climate change and carbon footprints. I believe that it is up to the individual as well to make an effort to keep their energy use down to a minimum if we are going to make a difference and survive this crisis.
—Jo Prendergast


Very few toasters are designed for just one slice. There are single-slot toasters designed for two slices side by side, but, of course, when toasting one slice, the elements are effectively larger than needed and so there is still wasted energy.

There was a toaster designed in Japan that just does one slice, but it is only available for 100V supplies and it doesn’t get good reviews. However, Dualit’s two-slice classic toaster ( has the ability to turn off one slot for toasting just one piece, so that would be the best option. They are also designed to be repairable, another plus.

The downside is price; they are around $400, although they can be found cheaper if you look around. The energy saving would never pay for the difference between these and a cheap toaster, but given the Dualit is designed to last a lifetime (although there are reviews to the effect that they have early failures as well), then it might be worth the investment. There may be other, lower cost toasters with a single-piece capability but I couldn’t find them after about 10 minutes of searching and checking reviews.

Overall, the energy wasted by a toaster is pretty small as it only runs for a few minutes at a time. While it does add up to a lot across the whole country (or planet), other inefficient appliances can waste a great deal more. For example, if a toaster is running an unnecessary 500 watts of element for three minutes, that equates to 25 watt-hours, or the same amount of energy wasted by a small plugpack drawing just one watt or so continuously—not much in the scheme of things. Indeed, a 3 kW solar power system would produce this much energy in just 30 seconds.

So, while all energy savings are important, there needs to be enough to provide an incentive to actually manufacture a more energy-efficient device, and I suspect that in this case, there just isn’t enough incentive to do so for most manufacturers.
—Lance Turner

Read more Q&A in ReNew 135.

Q&A: Understanding solar

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I love the magazine and have been subscribing for a number of years. I would like to get some very basic information on solar from you. Although your articles about going off-grid are really interesting, I can’t follow the detail, and I suspect a lot of readers of my generation (70s) are in the same boat. I would eventually like to go off the grid and therefore would like you to answer a few very basic questions.


I live in the Canberra region which is really sunny, with an average yearly total of 246 sunny days. My average electric use is 19 kWh/day and I currently have a 2.025 kW PV system.

If we receive eight hours of sunshine in a day does this mean I would get 16.2 kWh? Regarding storage, what would be the optimum amount of battery storage required to go off the grid without having a diesel or petrol generator, in my area? Is there any course that would cover the sort of basic knowledge I require?
—Peter Fenton


Yes, solar can be confusing, and there is a lot of jargon around! Your solar panels are rated at a total of 2 kW which is the power they will generate at standard test conditions which include:

  • strong sunlight directly shining at the panel

  • panel temperature of 25 degrees.

These conditions don’t often occur in the real world. The sun moves around, and as panels heat up their output reduces. Then there are additional losses in cables, inverter and other components.

To estimate how many kilowatt-hours (kWh) of energy the system will generate in a day, we can’t rely on whether a day is described as sunny, or the number of hours of sunshine. A better measure is the average number of kWh a 1 kW solar system will generate over a whole year.

Check out the table at

Over a whole year, a 2 kW solar system in Canberra should average about 8.6 kWh of generation per day. Of course, generation will be higher in summer and lower in winter.

So if you wanted to offset your yearly electricity consumption, you would need to add many more panels.

As for going off-grid, what is your motivation to do this? Off-grid systems are expensive. We’ve analysed the economics previously and even with high grid tariffs, going off-grid isn’t attractive on a purely economic basis. As a rough rule of thumb, to supply an electricity usage of 19 kWh per day, a reliable off-grid system might cost between $57,000 and $95,000. We expect this to come down over time as batteries get cheaper, but on the other hand, the Aussie dollar is low!

There are many ATA members off-grid, but they generally are very frugal users of electricity, typically around 5 kWh per day. It’s difficult to go off-grid without a generator. The big issue is getting through a cloudy winter week. Space heating and water heating are big factors too.

Here’s a great course to learn about this: I wrote a review of this course in ReNew 132. Another information resource is Sunulator, including the user guide:

And here’s a useful article to explain some important terms:
—Andrew Reddaway, ATA

Q&A: Polystyrene foam alternatives

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I found out from a friend that most of the expanded polystyrene used in building in Australia probably contains a brominated flame retardant—likely HBCD or DBDE—and that these are being banned in Europe because they are persistent, toxic chemicals.


We are about to build a sustainable house but don’t want to use something that’s both toxic to people and persistent in the environment.

Apparently these flame retardants are not used in polystyrene used in food packaging (phew!) but a flame retardant is required in all commercial building polystyrene.

I’ve called a few companies and they have trouble telling me what the exact chemical is. I’ve found that they import their beads from China already coated in the retardant, and then expand them here. Apparently the flame retardant is just a coating on the beads and not part of the chemical structure, so it can come away once installed, and end up in dust or in the air.

Are you able to tell me if anyone at ATA has looked into this and could you recommend a supplier that doesn’t use a brominated flame retardant? I’d be a willing customer!
—Linda Meisel


We are not aware of any polystyrene foams for building that use fire retardants that are not brominated. According to the US EPA publication 740R14001, Flame Retardant Alternatives For Hexabromocyclododecane (HBCD—Final Report, June 2014 (, “No non-brominated flame retardants are known to be compatible in polystyrene manufacturing and associated flame tests.”

There are other products that are naturally fire-resistant and so don’t have added fire retardants, such as hempcrete, timbercrete, AAC (Hebel) and similar naturally derived building materials. Insulation materials such as glass and mineral fibres are naturally flame retardant. I used Knauf Earthwool insulation in our home here; it is naturally non-flammable and the fibre binder is based on plant starches.
—Lance Turner

To read more questions and answers, buy ReNew 133.

Q&A: Point-of-use water heaters

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I’m looking for information on instantaneous electric water heater taps for sinks. I’m considering them to address the water and energy inefficiencies associated with the long pipe runs from my current water heater to kitchen, bathroom and laundry sinks.


I’m aware of instantaneous tap water heaters without storage and with integrated lever taps for this application, and these are what I’m most interested in hearing from people about.
With the shower, similar issues and savings opportunities arise, but the much less frequent use (typically once a day per person) make showers a much smaller opportunity to save water and energy by this means.

However, shower-specific instantaneous water heaters are available (which differ from sink units), so I’m happy to hear any ATA views on those as well.
For example, has there been a ReNew article reviewing any of these in relatively recent times? I remember seeing adverts for these in ReNew at some time in the past.
—Paul Riordan

We haven’t reviewed such units, although several have appeared in the Products section of ReNew. These include units from,,,, and

They are all of similar efficiency (i.e. 100%); the main issue is the electrical circuit. The tap-integrated units generally work with a regular 10A power point or standard wiring, whereas the 15A and greater units (shower models seem to be rated around 5000 to 6000 W, or 20 to 25 A) need a dedicated circuit. The larger units are all three-phase and are not usually suitable for domestic installations unless three-phase power is available in the home.

These units can vary enormously in price and some are more repairable than others. Make sure you get one with an easily replaceable element if possible, and ensure spare elements are available.

The other thing to be aware of is the level of heating provided. Most of the single-phase units, especially the tap-integrated units, will only raise the water temperature by 10 to 20 °C for a reasonable flow rate, which might be fine in warmer climates, but if you have colder water temperatures they may not do the job. Check the specifications for each unit at the maximum flow rate required.
—Lance Turner

To read more questions and answers, buy ReNew 132.

Q&A: Battery and solar developments

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Q: I HAVE read and heard that the next generation solar batteries superseding lithium will be available and ready for market in two years time. That being the case, can you please indicate whether a hybrid solar system currently working on lead-acid batteries can be retrofitted with the upgrade?


Also, are you aware of any developments whereby solar panels can be wirelessly connected to the inverter/batteries i.e. the solar equivalent of wireless internet connectivity on a laptop?

Lastly, are you aware of any double-glazed, aluminium or wood-framed window systems with integrated solar panels, either already available or coming to market? Would ReNew be able to run a feature on this subject at some stage?


A: THERE IS a lot going on in battery development at the moment, but most of it is focused on modifications to lithium chemistries, such as using silicon nano-wires in the electrodes to reduce degradation and improve lifespan and energy density. There are some other chemistries around, such as the Aquion Energy sodium ion battery, as well as rechargeable zinc-air batteries, flow batteries and a few others. However, for the moment the two industry workhorses are lead-acid and lithium chemistry units, in particular lithium iron phosphate (LiFePO4) for larger storage requirements.

The cost of lithium batteries is steadily decreasing and with the commissioning of Tesla’s Gigafactory next year, the price is expected to go below US$150/kWh by 2020, possibly as low as US$100/kWh. So, for the next decade or so, lithium batteries are most likely to be the best bet. All of the other chemistries are really in their infancy as far as development is concerned.

Whether you can upgrade to a newer battery type will depend on the other system components and the proposed battery system. For example, a battery system with similar voltage range during charge/discharge will probably be able to be used, provided that the solar charge controller in the system can meet the charge requirements. Some charge controllers have fully programmable voltage setpoints, so that sort of controller is more likely to be able to handle a new battery chemistry. However, most battery chemistries in development have their own management systems, so they may not need a charge controller at all: the management system will control charge and discharge of the battery.

The other issue will be your inverter and whether it can handle a possibly wider voltage range of a new battery chemistry. Many inverters also have programmable minimum and maximum voltages, so there’s no way to know without knowing your current inverter model and the new proposed battery chemistry.

Wireless data transfer and wireless energy transfer are very different things. Data transfer only takes milliwatts of power, whereas energy transfer for a typical domestic solar power system would need to be in the kilowatts—a million times more power at least. There are prototype energy transfer systems being developed and some have reached the stage where 100 watts or more of usable power can be transmitted over a short distance (inside the same room, for example), but these have relatively low efficiency compared to running cables, as well as much greater cost and complexity. They also require the room to be filled with an alternating magnetic field of considerable strength—something that many people might find disconcerting. So far, all domestic-scale wireless energy transfer devices have been aimed at the gadget market—charging mobile phones and the like.

Regarding solar windows, there have been a number of companies working on these, and we have covered some installations in the past, such as in ReNew 101 where we looked at windows at Ballarat University, Schott Solar’s ASI transparent thin-film panels. However, it appears they no longer make them. Most of the manufacturers that were using their glass modules also seem to have disappeared, except one, although they don’t appear to be using the Schott modules:

Kaneka still make transparent PVs, but in the last PV buyers guide (ReNew 126, just over a year ago), we found no transparent PVs available here.
There are several companies working on new transparent glazing materials, including Oxford Photovoltaics (, New Energy Technologies ( and SOLPROCEL (

When interesting products hit the market we always try to include them in the Products section, so that’s the best place to keep an eye out for them.

—Lance Turner

To read more questions and answers, buy ReNew 131.

Q&A: Using solar first

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The solar feed-in tariff being offered by most companies is the minimum 8 c/kWh. However, if you are home during daylight hours and are using electricity at the same time that your solar panels are producing, does your household use that solar power (in effect) and so save you being charged at 29 c/kWh?


—Ray Leerson

Yes, at each instant your solar generation will take the path of least resistance. Your household appliances are supplied first (offsetting 29 c/kWh as per your tariff), then any excess is pushed to the electricity grid in your street (feed-in or export).

Electricity can flow in only one direction at a time down the cable between the street and your house. Your meter has two registers. Whenever electricity is flowing from the street into your house, the import register is accumulating, costing you 29 c/kWh. When electricity is flowing from your house to the street (feed-in), the export register is accumulating, earning you 8 c/kWh (expected to drop to 6 cents or so next year).

If you got onto a premium feed-in or transitional feed-in contract several years ago, your feed-in tariff would be higher, eg 66 c or 25 c/kWh. With current low feed-in tariffs, your solar generation gives best value when consumed within the house. We wrote an article on this last year:
You might find our solar electricity booklet useful:

And if you’re looking to do a detailed analysis, we have developed a free tool called Sunulator. Please see

—Andrew Reddaway

To read more questions and answers, buy ReNew 130.

Q&A: Taking grid-connected system off grid

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I was very interested in the off-grid issue but it didn’t answer my question about converting from a grid-connected system to off-grid. What would I need to do if I want to convert my existing grid-interactive solar system to off-grid?


—Neil Garret

You could just sell the grid-interactive inverter and use the solar array as-is to charge an appropriately sized battery bank via an MPPT (maximum power point tracking) charge controller. This controller will match the high voltage output of the array to the lower voltage battery bank. You then add a standalone inverter and anything else required for the stand-alone system. Sometimes the array is reconfigured to produce a lower voltage and higher current, but it’s not necessary nowadays with MPPT charge controllers, some of which can handle very high array voltages, such as the MorningStar Tristar ( 600v/). This is called a DC-coupled system and is how most off-grid systems were traditionally done until recent times.

The other method is called AC coupling. You keep the current system and add the battery bank and a suitable inverter/charger. This new inverter creates a microgrid that the grid-interactive inverter can feed into. When there is more energy coming from the panels than the house is using, the inverter/ charger feeds it back into the battery bank. AC-coupled systems seem to be becoming the norm for larger domestic off-grid systems, not just those that have been converted.

There are pros and cons to either method. Personally I prefer the DC-coupled system as it doesn’t all hinge on the inverter/charger—if that fails, you have no energy available at all. With DC-coupled systems, if the inverter fails you still have the array keeping the batteries charged and you can use a low-cost backup inverter for mains power until the main inverter is repaired, or you can use DC power directly. Of course, you can do the latter on an AC-coupled system as well, but AC-coupled homes almost never have any provision for direct DC use, whereas DC-coupled systems often do, even if just for lighting.

We will be looking more closely at how AC-coupled systems work in a future issue of ReNew.

—Lance Turner

Q&A: Battery advice

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I need to replace my 12 volt batteries. My power comes from a few solar cells and the load is relatively light and not every day—a studio with 60 watts of lights (currently old quartz halogen. which are easy to now replace with more efficient LEDs) and probably a 12 volt CD/radio. Would you recommend the Jaycar SLA deep-cycle battery SB1699—or indeed what else?


Also, perhaps you may have ideas about inexpensive basic 12 volt CD or DVD players that could hook into existing speakers. I have been scrolling websites without much luck; portables seem to have their own lithium batteries which rather defeats my needs. Car stereos are too fancy, with Blu-ray etc.

Susie Edwards

Jaycar’s SB1699 might be a bit small for your use, but their next size up is 100 Ah, which is probably too large. There are a lot of battery suppliers that may have a larger range, such as, and (stores only, no online shop).

I have had a few problems with lead-acid batteries in the past being a tad flat when purchased (not good for lead-acids), although with a dozen or so cycles they usually come up okay.

But, given the falling price of lithium batteries and the fact that many are drop-in replacements for lead-acid nowadays, you might want to consider them. Examples are the 12 volt models at and

Re the CD player, you can reuse a computer CD/DVD drive (one with play and stop buttons on the front) for this sort of thing. There is an adaptor kit that lets you do this but you need electronics experience to build it; see Jaycar part number KC5459.

But if you want just simple play functions then you don’t need an adapter, just supply it with 12 V from the battery and 5 V via a small regulator, and connect the headphone output to the speakers. If they are powered speakers then you will get good volume; if not then you might need a small amplifier between the two, such as or Jaycar’s AA0487 or AA0473 (single channel only).

Of course, this is all very DIY and if that doesn’t appeal then a low-cost car stereo is probably going to be the best option.

Lance Turner

To read more questions and answers, buy ReNew 127.

Q&A: Instantaneous hot water

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We live in bayside Brisbane in a four-bedroom, two-bathroom house with an old-style 250-litre electric hot water system. We are investigating which way to go if or when the system needs replacing. It is on the south side of the house and it does not appear to me to be a straightforward job to change to a solar hot water system. It is also near the main bedroom and I understand there can be noise issues with a heat pump system.


We installed a 1.5 kW PV system three years ago and have happily paid no electricity bills for that period and are $700 in credit. I have looked at Stiebel instantaneous electric hot water systems which, at the top of the range, seem to be appropriate for two-bathroom apartments and can cost around $1500.

The technology looks smart and I cannot see any regulatory objection to this option in Queensland. Are there any practical or plumbing issues in making this replacement? I am not a tech tragic—I would just like an opinion as to the appropriateness of instantaneous electric hot water for a house.
Ray Barker

The main issue with a whole-house electric instantaneous system is that it needs a 3-phase power supply, as power draw may be up to 20 kW. Many houses have these now but many don’t. So whether you can install one depends on that. Bear in mind that, while energy use will be less than with an electric resistive storage system as there are almost no standing losses, it will still use a lot more energy than a heat pump or solar unit.

There’s no reason why you can’t install a solar unit. You would use a split system with the tank in the same place as the current tank and the panels on the roof on a tilt frame to overcome the south-tilted roof.

As for heat pumps, most are pretty quiet but noise ratings are given in the specs. You can also put them on a timer so that they don’t run overnight, instead kicking in at, say, 7 am. The most efficient domestic unit on the market seems to be the Sanden, which uses CO2 as the refrigerant. See
Lance Turner

To read more questions and answers, buy ReNew 126.

Q&A: Increasing system load

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Since my household increased from one to three members I am finding my 1500 W renewable energy system, which was more than adequate for a frugal me, is not coping with the extra residents even though we use energy sparingly, only do washing etc on sunny days and have purchased low-energy computers and fridge.


Our system was only designed to take up to 2000 W of solar panels, so after I put on two new panels the system is still short on energy when we have two cloudy days in a row.

My battery charger will be getting regular use from now on, but only puts 10 A (300 W) into the batteries. I am looking for a battery charger that can deliver 30 amps and reduce the time I need to run my 3000 W generator.

Longer term, I may have to buy a second system, but can you suggest a suitable charger that is not too expensive please?
Jane Marriott

There are plenty of chargers around that will do that sort of current, and more, but the maximum current rate depends on the battery bank size. See and for examples, and there are a lot of other suppliers, but high-powered chargers like this are never really low cost. There are some cheap ones on eBay, but bear in mind that some are not well regulated and can overcharge the battery bank, and many are direct from China, so if they fail, there’s no real recourse.

Generally, if you are finding that your battery bank is struggling after the second day then you are cycling it way too deeply and it is too small for what you are drawing from it. The use of a charger will help but it is still adding cycles to the bank and the bank will degrade faster than it otherwise would.

Something to note regarding generators, they are usually rated in VA (volt-amps), not watts. They are not the same thing unless the load on the generator (battery charger or whatever) has a power factor of 1. Very few electronic loads do, especially battery chargers, so a genset rated at 3000 VA won’t be able to power a 3000 watt charger. Obviously, a 30 V, 30 A output is only 900 W and probably needs around 1200 W input at most, but it’s surprising how much some gensets struggle with battery chargers.
Lance Turner

To read more questions and answers, buy ReNew 125.

Q&A: LED bulbs and radio buzz

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I recently bought four LED lights to replace CFLs in the kitchen. I’m very happy with the light output and colour, but unfortunately there is one side effect—when they are turned on they make my clock radio in the bedroom buzz. What is this caused by and is there anything I can do to stop it? I would just put these globes in a spot where I don’t need to use them in the morning, except that they are the only screw fittings in the house. Another LED in the pantry has no effect.


This is a common problem: many LED bulbs produce electrical noise as they have switchmode drivers inside them to convert the power supply voltage down to whatever voltage and current is needed for the LEDs. The electrical noise can be radiated as radio waves from the house wiring, causing interference, or it can travel back through the wiring as electrical noise, causing the same problem. I suspect your problem is the former.

There are a number of solutions, of which several are quite simple. The first is to get some clip-on ferrite beads, these are the sort of thing you see at the end of some computer leads, basically a lump in the cable, but in clip-on form rather than moulded in. Examples can be seen at and You simply clip them over the cable as close to the light fitting as possible.

If that doesn’t fix it entirely, using a larger ferrite and winding two or three turns of the cable through it will increase the effectiveness of the ferrite.

You can also put small value capacitors directly across the socket, but this involves electrical wiring, so you’ll need to find an electrician experienced at mains wiring, and you must also use the correct capacitors (X2 types of appropriate voltage rating). A simpler and more electrician friendly option would be to have mains filters connected at the fittings. A typical example of a suitable unit (which could be fitted inside a junction box) is Jaycar Electronics part number MS4001.

But definitely start with the clip-on ferrites, they are simple to install and no electrician needed, assuming the wiring is accessible from inside the ceiling. Just be careful if installing them that you ensure the wiring is in good condition – old wiring can have degraded insulation and be very dangerous. If in doubt, contact an electrician.
Lance Turner

To read more questions and answers, buy ReNew 125.

Q&A: LED downlights and power problems

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I have been told by a sparkie that dimmable LED lights cope better with power fluctuations than non-dimmable ones. Is there any truth in this? Also, I was told by a salesperson that if a fairly expensive LED four-light track failed I would have to replace the whole fitting. This doesn’t seem right to me. Presumably you could replace globes with most fittings, or replace the driver or driver parts if this were the problem, rather than throwing away the entire fitting?
Lynn Atkinson


How well a fitting copes with power problems depends on the quality and design of the driver. Dimmable fittings will be designed to handle a range of voltages and ‘chopped’ waveforms, so they handle spikes well, but a properly designed fixed-output driver should work just as well. It also depends on what you mean by fluctuations, such as long-term (minutes to hours) variations in mains voltage, or short-term spikes caused by motors etc, or both.

The advantage with a dimmable driver is that it does give you the option to add dimming later should you want or need to.

Regarding the track light, that depends on how it is designed. If it has replaceable bulbs, then no, you wouldn’t have to replace the whole unit. Many suppliers are selling standard halogen track lights with LED retrofit bulbs, so the combination is fairly common.

If the fitting is designed from the ground up as a LED fitting then it will have one or more drivers driving the embedded LED arrays, so if you get a LED failure, you will have to live with that light being out unless you can get a replacement array and find someone to install it. If the unit uses a single driver to drive four arrays (unlikely, but I’ve seen poor designs like that) and the driver fails then, again, you would need to find an equivalent driver and have it fitted by a technician (with LED experience—all electronics techs are not created equal).

As it depends on the fitting design, you’ll need to get technical details or have a close look at the fitting you are proposing to use so that you can see how it’s configured.
This is one of the aspects that is working against LED lighting at the moment—there are so many variations and you need to understand what you are buying.
Lance Turner

To read more questions and answers, buy ReNew 124.

Q&A: Energy sucking pump

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I got a rude shock the other day when I purchased a new water pump to supply my house with tank water. I put my energy meter on it for few days to get an idea of how much energy I would use on an average daily basis. When I went to disconnect it, I noticed that it was drawing 17 watts while it was doing nothing. I called the company that sold me the pump and they assured me that a pump should draw no power unless a tap was on and it was running, so I dismantled the whole thing and brought it in.


They plugged it in to their ammeter which said it was drawing nothing. Fortunately, I had brought my meter with me and showed them that it was drawing 17 watts. Then they noticed that it has a couple of LEDs on it that show power on etc and said that it has to draw some power for the LEDs. I would consider trying to break into the box and get rid of the LEDs, but 17 watts seems like more than needed for one LED.

Then they told me I was going to have to buy a pump with a pressure tank instead (the very pump they had previously told me I didn’t want to buy because it would cut in and out while having a shower). They then fitted this new pump with a pressure tank they had ‘sitting out the back’ and sent me on my way.

I am not overly excited about the outcome, not the least because I now have to build a whole new pump house as the pressure tank doesn’t fit under the previous one.

I did the calculations and given that I am getting 66 cents for PV power I put into the grid, it would cost me $63/year to have the first pump connected as purchased. The pump I had before this neither had a pressure tank nor drew power when it wasn’t running, but the same company that said it wouldn’t draw power when it wasn’t running, now say that all pumps either draw power when not running or have a pressure tank. Is this true? Is this power doing anything more than powering an LED power indicator? Do you know of pumps that don’t do this and if so, which ones?

Enga Lokey

If the pump has an electronic controller then it will draw some power even when off. The only pumps that won’t are those with simple electromechanical pressure switches. Some pumps are variable speed and are designed to eliminate the need for a pressure tank, but if it’s a simple on-off type controller then it should still have a tank.

The problem with many mobs selling pumps is they tend to undersize tanks for pumps that need them. If a tank is sized correctly, the pump won’t need to kick in during an average shower, unless it was almost empty (close to the pump’s cut-in pressure) anyway. For a whole house system, the minimum tank size you should look at to reduce pump cycling is around 100 litres, but with pressure tanks, the larger the better.

My personal preference with pumps is a simple electromechanical pressure switch and a decent-sized pressure tank. It’s simple, robust and effective.

Lance Turner