ReNew 130 Editorial – Energy use in a warming climate
In the warmer parts of Australia, air conditioners are the greatest contributor to home energy use (it’s 40% in Darwin, for example). They’ve also become a contributor to peak demand in many places, where increasing heatwaves and the after-work switch-on of air conditioners add to peak load, even if only for a few days a year.READ MORE »
Better housing design is the best way to address this, rather than more-efficient air conditioners but, realistically, both have a role to play.
We’re often asked about solar cooling as an option, but given the lack of domestic-sized, affordable systems, we’ve only covered it briefly in the past. This issue, though, we go a bit deeper with an article by Mike Dennis from ANU, a researcher with a special interest in this area. He details the systems being trialled at ANU and CSIRO, and provides a wealth of references and resources.
Of course, there are already solar cooling systems available—PV paired with an efficient reverse-cycle or evaporative air conditioner— and we do describe these options. However, as we’ve noted in the past, there are limitations, with the timing of peak air conditioner use misaligned with peak PV production.
Batteries can offset this, but what about pre-cooling—running the air conditioner before you get home to take advantage of daytime PV power. Could this reduce air conditioner energy use at peak times, and potentially your bills? We ask the question of Sunulator, with some interesting results.
In terms of housing design, there are many approaches where passive cooling is possible, but there are also challenges to this, with increasing heatwaves (an early reality of a warming climate) and a reduction in the diurnal range of temperatures. We reprint an article from our sister publication, Sanctuary, that’s a call to action for our sustainable designers and planners, and for individuals, to reconsider how they approach housing design and use in a warming climate.
It’s not all about cooling this issue. We also have the Greeny Flat Experiment, an ownerbuilt granny flat: a sustainable, small all-electric home on a budget. The owner gives us a real insight into the construction costs and design decisions. It’s a great read, and is paired with research that asks whether infill housing, like granny flats, could be a way to accommodate increasing population pressures, rather than developing our urban fringes.
We also present research from the ATA (ReNew’s publisher) into whether it’s more cost-effective (and lower emissions) to switch from gas to efficient electric appliances. We cover the ethics of using food crops for biofuels, Alan Pears begins a discussion on cooking and energy use, we present a buyers guide on greywater, our ‘basics’ article explains energy and solar metering, and we explore AC coupling in off-grid systems; plus a holiday reading guide! We wish you a safe and sustainable holiday season and look forward to hearing from you in the new year.
ATA CEO’s report
Wow, where has the year gone? It has been a thrilling 12 months here at the Alternative Technology Association with many exciting projects and events. We are still coming to terms with receiving $250,000 from Google Australia for our Solar for Timor project.READ MORE »
The project will mean a major escalation of the ATA’s work in East Timor. Since 2003 we have been installing solar-powered lighting in homes, schools, community centres, hospitals and orphanages in remote villages, as it is estimated that 20% of all houses in East Timor will never be connected to an electricity grid.
We have a strong focus on training Timorese people to install and manage their own solar power and lighting. To build technical capacity in-country, in December 2013 the ATA formed a partnership with CNEFP-Tibar (an East Timorese training institution) to establish an ongoing technical support role.
With support from Google, the ATA will train and employ local technicians to install hundreds of household lighting systems in remote houses in East Timor. We will also put in place an ongoing maintenance program for existing and future solar installations.
You can help create a sustainable solar industry in East Timor by giving the gift of light this Christmas. Buy a solar panel for an East Timorese family for $50 or a whole solar system for a family for $250. Go to shop.ata.org.au to buy your gift card.
With your support, hundreds of Timorese villagers will be able to see at night with clean, solar-powered lighting instead of relying on candles or polluting kerosene lamps.
The state of solar cooling
It’s the holy grail of cooling—using the sun to power your cooling system. Mike Dennis from ANU takes us on a tour of where the solar cooling market is now and where it’s headed.READ MORE »
Most Australian homes are now equipped with some kind of air conditioner, but their rise in popularity over the last decade has put substantial pressure on the electricity transmission and distribution network—and the required investment in ‘poles and wires’ has been blamed for recent spikes in retail electricity bills.
Some electricity retailers charge a premium for grid electricity drawn during afternoon periods when air conditioning may be in use, but offer a paltry sum in return for photovoltaic power supplied to the grid during the same period. One NSW retailer charges over 50c/kWh between 2 pm and 8 pm on weekdays while offering only 6c/kWh in return for net photovoltaic energy exported to the grid.
Water heating and air conditioning are usually the two main energy sinks in a residence. To some extent, water heating may be time-shifted to avoid exposure to peak tariffs, but air conditioning load offers less flexibility. What can be done about this?
The first consideration, of course, should be to try to reduce or eliminate the need for active air conditioning. A well-designed building with appropriate shading, insulation and thermal mass is a good start. Secondly, householders should explore opportunities for passive air conditioning using prevailing breezes and carefully designed cross and stack ventilation.
As a last resort, a householder may decide to install an electric air conditioning system. These devices are intoxicatingly effective in providing comfort with convenience and immediacy. The shopfloor price may not be as confronting as the first electricity bill, however!
So, how can householders sidestep peak electricity charges and be comfortable in their homes at the same time?
Active air conditioning options that minimise environmental impact
The obvious option is to install a photovoltaic (PV) system to drive a regular air conditioner. Several companies offer packages to do this directly, or it can simply mean installing a larger PV system to run the whole house (‘Solar cooling options available now‘ also in this issue).
However, electrical supply will be required late in the afternoon and into the evening to offer proper service during summer cooling and winter heating periods.
It is worth noting that peak summer cooling loads often occur late in the afternoon, while peak solar is at noon. In winter, peak heating loads are in the evening.
Hence, backup will be required in the form of either a grid connection or a local electricity storage device. Both of these options come at a price. It is likely that future electricity storage prices will make this option viable. No doubt someone will produce a simple Sunulator-type calculator to size the PV collector and battery bank for such purposes. [Ed note: Adding batteries is planned for the next phase of Sunulator development!]
Read the full article in ReNew 130.
Solar cooling options available to households now
Solar cooling is possible at home writes Lance Turner.READ MORE »
Solar cooling is perfectly achievable for homes and businesses using off-the-shelf technology. The simplest system, and the lowest cost to install, uses high-efficiency heat pumps (reverse-cycle air conditioners), which can have EERs (energy efficiency ratios) of up to 5.7 for the smaller models, combined with a grid-interactive solar power system. By running the heat pumps during the day, when the solar system is producing the most electricity, the heat pumps are, effectively, completely solar powered.
There are other cooling system types that can also be run directly from solar-generated electricity, with evaporative cooling systems being the most common. However, most common evaporative coolers use a simple system of passing air through wet filter pads, known as direct cooling. While this does cool the air somewhat, it also increases the humidity of the air, something often undesirable in hot weather.
Other options in the pipeline
An alternative system, the Climate Wizard (a domestic model will be available in 12 to 18 months), is an indirect evaporative cooler that uses a counter-flow heat exchanger to cool the air without adding moisture. The system uses a heat exchanger, which has both dry and wet channels isolated from each other, to keep the evaporating water and the airflow into the house separate. Air passes through the dry channels in the heat exchanger, while some of that air passes back through the heat exchanger via the wet channels, where evaporative cooling removes heat. This cools the air in the dry channels without adding moisture. The dry air then flows into the home, while the moist air is expelled outside. Seeley International, the supplier of the system, claims that this system results in cooler and drier air entering the home compared to a conventional evaporative cooler, and can provide cooling performance similar to a heat pump air conditioner, with lower energy use.
While not common in Australia, there is a combined solar heating and cooling system known as a Combi+ system. It uses a solar ‘combi’ system (which uses solar thermal collectors, backed up by another heat source, to provide both space heating and hot water) combined with a sorption chiller for summer cooling. Combi systems are common in countries such as Austria, Switzerland, Denmark, Sweden and Norway, although Combi+ systems are less so, due to the lower cooling requirements in much of Europe.
CSIRO has recently conducted research into the economics of PV-powered air conditioners. As presented at All Energy Expo 2014, their provisional results demonstrate that using PV to power the whole house, including the air conditioner, has a much better return on investment than using the PV to power only the cooling system. Systems with batteries could become cost-effective as battery prices decrease. The research is being published soon; watch out for it on their website.
Read The State of Solar Cooling in ReNew 130 for a look at the solar cooling market.
The Greeny Flat experiment
Andy Lemann shares the principles, materials, results and lessons learnt in building a low-cost, high-efficiency home. Seven months into a one-year trial, the outcomes are promising.READ MORE »
For me, learning to live in harmony with the planet means learning to live without fossil fuels. Before I’m accused of gross hypocrisy, let me be the first to admit that my way of life is highly unsustainable: I drive a car, I eat food grown in faraway places, I use fossil fuels. I certainly don’t have all the answers, I’m simply attempting to take the first steps towards a fossil-fuel-free future. That is what the Greeny Flat is all about.
The Greeny Flat is a full-scale living experiment currently underway on a quiet street in Mittagong in the Southern Highlands of NSW. We’re aiming to see if it’s possible to build a small, comfortable, healthy, energy-positive, low-maintenance, fire-resistant, water-efficient, elderly-friendly infill house at an affordable price. Our two primary aims were to make it energy-positive and affordable.
For 20 years I designed and built sustainable houses in the Rocky Mountains of Montana, near the Canadian border, where the winters get down to -40 °C and the summers up to +40 °C. In that climate, attempting to come even close to net zero energy building is a huge challenge. When I returned home to the NSW Southern Highlands a couple of years ago, it occurred to me that building an energy-positive home here should be relatively easy and inexpensive.
I have since learnt that the cost of most things in Australia is much higher than in the States, so making the Greeny Flat affordable has, in fact, proved to be our biggest challenge. Meanwhile, my partner Cintia and I have lived in the house for nearly seven months, closely monitoring its energy performance, water usage, indoor air quality and comfort levels to see whether it actually meets the initial goals.
The perfect site
The Greeny Flat is designed to meet the future needs of my aging parents who, in their infinite wisdom, had found and purchased an excellent site over 20 years ago. There’s an existing fibro cottage on the east half of the lot that they rent out, which left the west half available for us to build the Greeny Flat.
It is the perfect site for a passive solar home with a gentle slope to the north-east, nice views to the north, and existing buildings and trees to the west and south providing protection from cold winter and hot summer winds. The excellent solar access is also protected by the street to the north, which means that no neighbour can build or plant anything to block our sun in the future.
Just as importantly, this is an infill site in an already-developed area. This helps to reduce sprawl, preserve open space, agricultural land and natural habitats, maximise use of existing infrastructure, and reduce driving.
Read the full article in ReNew 130.
ATA research: Are we still cooking with gas?
Gas report author Kate Leslie gives the lowdown on the research and its findings.READ MORE »
The Alternative Technology Association (ATA), has just launched a report that considers the economic implications of projected retail gas price rises on households, and asks whether there are efficient electric alternatives that are more cost-effective.
Funded by the Consumer Advocacy Panel, the research aims to identify those locations and household types that may benefit from a switch from gas to efficient electric appliance use—or from staying off the gas network in the first place (in the case of new homes or existing all-electric homes). The research also separately analysed the environmental impact of these potential switching decisions.
Much of the emphasis in the gas debate to date (which has been largely dominated by industry) has been on increasing gas production, as opposed to considering potential changes in demand. ATA’s research asks whether increasing gas production is the most cost-effective, efficient and sustainable approach.
Gas price rises are already an important issue for residential consumers; according to the Victorian Council of Social Services, “Household gas prices have risen 33% in real terms since 2008–09, largely unnoticed because all the attention has been on the more rapid growth in electricity prices over the same period (53%).” (www.bit.ly/VCOSSGPR)
Analysts vary on how much gas prices will rise over the next 5 to 10 years, but all agree that more rises are coming.
So what are the alternatives?
Gas is typically used in homes for space heating, water heating and/or cooking. Over the last few years, efficient electric alternatives for all these end uses have become available. The most cost-effective, efficient electric alternatives chosen for the research were:
- heat pump reverse-cycle air conditioners— for space heating
- heat pump hot water systems—for water heating
- induction cooktops and efficient electric ovens—for cooking.
The research considered the economic case for replacing gas appliances with electric options in a range of different ‘gas zones’, for a range of different house types and under a range of different ‘replacement cases’.
Replacement cases include whether or not the house is currently gas connected, the number and type of gas appliances to be switched, and whether existing gas appliances are close to the end of their life (i.e. due to be replaced within five years).
Figure 1 shows the 26 gas pricing zones modelled. The variety of zones meant that the research could take into account the different gas prices and pricing structures that exist across locations, as well as the different space/ water heating end-use needs by climate zone; Table 1 shows the heating load assumed per climate location.
The research also modelled six different household types, ranging from small to large existing homes (all assumed to have R2.5 ceiling insulation), a typical public housing home (taking into account relevant energy concessions), and a new 6 Star home (see Table 2). This enabled analysis of households with different space and water heating requirements as well as cooking energy use.
For new homes, and for existing homes that don’t currently have gas, the research found a strong and consistent result: in all gas and climate zones across the five states and one territory modelled, it is more cost-effective to go all-electric than to connect to gas. This holds as long as efficient electric appliances are able to be used (acknowledging the fact that space or building configuration constraints, such as in apartments, may mean that efficient electric appliances can’t be installed).
For existing homes already connected to gas, the situation is more complex. Whether it’s cost-effective to switch from gas to electric appliances depends on a range of factors including the age of the appliance, the climate zone, whether it’s the last gas appliance (so replacing it means the customer can disconnect from gas and avoid the fixed service charge, in the order of $250 to $300 per year) and whether the customer is on mains or more expensive bottled gas.
Tariffs also come into the equation, including the ratio of gas to electricity prices, and the fact that many customers are on a declining block tariff—meaning that higher gas usage is, in effect, rewarded by lower prices.
Specific appliances and climate zones
For existing homes connected to gas, there were some clear findings for specific appliances and climate zones.
Of the three end uses modelled, space heating was consistently the most cost-effective to switch from gas to efficient electric.
In warmer climate regions (including SA, Queensland and some parts of NSW), switching all gas appliances to efficient electric ones and disconnecting from the gas network offers better economic returns than in cooler climates—partly due to the improved performance of heat pump systems in warmer climates, and also partly to the correlation with higher gas prices in those regions.
Heat pump hot water systems were found to be more cost-effective than gas hot water systems where gas prices are relatively high compared to electricity prices; or where the climate is warmer (and so the systems perform more efficiently). Gas hot water systems are more cost-effective in most other locations.
Switching from gas to an induction cooktop and electric oven was found to be cost-effective when combined with disconnecting from the gas network (and thus avoiding the gas fixed charge).
The effect of gas prices
The modelling results were not particularly sensitive to retail gas price trajectories of between +5% and +50% from today (in real terms). The research found that the impact of that range of future gas prices on any individual economic case isn’t as significant as the relative cost of gas versus electricity in each gas pricing zone; and the relative energy use of gas versus electric appliances.
The report notes, “In only a small number of gas zones and for a small number of household scenarios/replacement cases does the economic proposition for switching fuels change from negative to positive over 10 years on the basis of different gas price trajectories.”
In the majority of Victorian gas zones, where switching was often uneconomic, consumption charges for gas are approximately a fifth of the price of electricity charges on an equivalent energy basis. In parts of NSW and Queensland, where a significant number of economic switching cases were found, gas prices are higher relative to electricity prices— up to around half the cost of electricity.
A positive result for emissions
Although the research was primarily concerned with economics, the ATA considered it was also important to determine the greenhouse gas impact of switching from gas to electric appliances. The findings were mostly positive: homes using natural gas for all three end uses will reduce emissions if they switch entirely to efficient electric appliances, regardless of home type or location.
Taken individually, switching to electric space heating has the clearest positive impact especially for the colder locations. Results for hot water are less clear—switching from gas storage to heat pump hot water systems may result in slightly higher emissions in ACT and Melbourne. Efficient electric cooking increases greenhouse gas emissions in all locations except Tasmania. However cooking emissions are very small compared to the other uses.
These estimates are influenced by the cleanliness of generation in your state’s electricity grid. Victoria’s continued reliance on brown coal results in high emissions, while Tasmania and South Australia’s emissions are lower thanks to their use of hydroelectric and wind generation respectively. Future increases in grid-connected renewable energy (including rooftop solar) will make electric appliances cleaner to run. Households also have the option to offset their emissions, for example via ATA’s Community Climate Chest or a GreenPower plan from their energy retailer.
Data on the climate impact of natural gas is scarce. In addition to the carbon dioxide emitted when gas is burned in the appliance, some natural gas leaks unburnt into the atmosphere from wells, pipelines etc. Even though these ‘fugitive’ emissions are small, unburnt natural gas has a potent greenhouse effect. In the absence of reliable Australian data, we have assumed a level of fugitive emissions accounting for 40% of the overall climate impact of natural gas, based on international studies. Future escalation of coal seam gas extraction in Australia has the potential to increase greenhouse gas emissions, which would further improve the case for efficient electric appliances.
The research shows that households should no longer assume that natural gas is the cheapest or lowest emission fuel for space heating, water heating and cooking. This is a significant change to the last three decades of consumer, industry and government thinking regarding mains gas.
For virtually all new homes, efficient electric will be the most cost-effective choice.
Existing dual-fuel homes will need to carefully weigh their options. It requires a case-by-case analysis depending on many factors— however, the ATA report provides an excellent guide for consumers to undertake this analysis for their specific situation. Dig into the full report to find the results that apply to you. S
The research was conducted by ReNew‘s publisher, the Alternative Technology Association, and funded by the Consumer Advocacy Panel. The full report is available at www.ata.org.au.
Read the full article and tables in ReNew 130.
Efficiency on a budget: Easy, low-cost retrofitting
Alan Cotterill takes us on his journey retrofitting a standard brick-veneer home for energy savings.
Eleven years ago we bought a near-new four-bedroom brick-veneer house in Wagga Wagga, an inland town in NSW, in an area that experiences hot summers and cold winters.READ MORE »
It’s a fairly standard house for the area, set on a concrete slab, with a verandah running the length of the eastern side. The house is long and narrow, on a north–south axis, with only the double garage facing north. Excluding the double garage and verandah, the house size is 183 m2 and the window area is 19% of the floor area.
R3.3 batts were already installed in the ceiling, along with reflective foil in the walls and under the colorbond roof. We found that an evaporative cooler provided effective summer cooling on most days and later-fitted gas central heating provided winter heating, albeit at a cost.
There were several areas, however, where we found we could significantly increase comfort and decrease bills, through simple retrofits. Some of these are detailed below, including information on any issues we encountered and how we overcame them. Hopefully this will be of assistance to others planning similar retrofits.
The house’s original lights were 12 V, 20 W halogen downlights. A 30 cm clearance without insulation batts is required around each downlight to guard against overheating and fire. There were 18 halogen downlights, meaning 18 gaps in the insulation. Thus, there was about 6 m2 of ceiling without insulation.
So, four years ago I did a simple changeover from 20 W halogen globes to 3 W LEDs ($15 each at the time), using the existing fittings and transformers. I later covered each downlight with a downlight mitt ($18 each) and, ensuring that all transformers were held above any insulation to prevent overheating, I filled in the insulation gaps up to the mitts.
Each mitt comes with a wire support to secure it to the plasterboard and a wire tower to secure each transformer above the mitt and batts. Installation of the mitts was easily done from below, standing on a ladder. Because they are soft, you can simply collapse them, insert them through the hole for the light fitting, and open them up inside the roof cavity and position them over the hole. Then you just push the light fitting back in place, as they are held in the ceiling with spring clips.
The main energy saving wasn’t from the significantly lower wattage for lighting, but from the improved ceiling insulation, which reduced energy costs, especially from winter heating.
There were some problems, however. The original transformers were designed to run with a higher wattage than the 3 W LED globes I used, resulting in some flickering and some transformers failing. With what is available today, I would, instead, plug in an entire new 12V LED downlight unit, which includes a matched transformer ($28 from a specialist electrical trade/retail outlet).
Also, the 3W LED bulbs were bright enough for general socialising, but a little dim for reading. We’ve since added newer 8 W LED bulbs selectively, such as over a chair used for reading or over a work area in the kitchen. Not only is there now plenty of light, but the beam angle of 95 degrees (rather than a narrow 33 degrees) gives wider and more even illumination.
The choice of downlight mitt also needs to be considered carefully. Mitts need to be matched to the type of light fitting and may need a ventilation hole. Mitts without ventilation holes can be used with fittings of the gimble type, where the light can be tilted in its fitting. This tilting action requires a small circular air gap, flush with the ceiling, and this allows some ventilation around the bulb. But, where fixed fittings are used, mitts with ventilation holes are required. We used mitts with ventilation holes to avoid any risk in the future; for example, a new homeowner could unwittingly replace a gimble fitting with a fixed fitting.
Read the full article in ReNew 130.
Greywater system buyers guide
Although many regions no longer have water restrictions, water is still a very precious resource in a country as dry as Australia. Greywater systems let you use water at least twice, which makes good environmental sense. Here, we look at what systems are available.
The advantage of greywater is that we produce it on a daily basis. In many cases it can be diverted to the garden with minimal effort and cost in a number of different ways. You can opt for a low-cost DIY system using something as simple as a greywater diversion hose attached to your washing machine outlet. Or you might be considering installing a full commercial greywater system. Whichever way you go, there are a number of things you need to consider.READ MORE »
This guide highlights the main issues associated with greywater reuse. There are many choices available and there is no single solution for all circumstances. Therefore, the more research you do, the more suitable your system will be for your particular situation.
There can be many restrictions as to where systems can be installed. In some cases, especially for retrofits, installing a greywater system will require major works—this can make the system cost-prohibitive.
Greywater is any wastewater generated from your laundry (sinks and appliances), bathroom (baths, showers, basins) and kitchen (sinks and dishwashers), before it has come into contact with the sewer. It does not include toilet wastewater, which is classed as blackwater.
However, while kitchen and dishwasher water is technically greywater, unless you are treating it, it is recommended that you don’t use this water source. Kitchen water only makes up around five percent of total water consumed in the average home, yet it is considered the most contaminated. This is partly due to high sodium levels from some dishwashing detergents, particularly from dishwashers, solid matter such as food waste from rinsing dishes, as well as fats, grease and oils from cooking and cleaning, which can all damage soil structure if allowed to build up.
What’s in the greywater?
The chemical and physical quality of greywater varies enormously, as greywater is essentially made up of the elements that you put into it.
Generally speaking, pathogen and bacteria content is low in most greywater sources (unless you are washing contaminated items, such as nappies) and, provided you take steps to minimise potential contact, such as using subsurface delivery of the greywater, it is of minimal concern.
Choosing the right cleaning products is perhaps one of the most important elements in reducing the risks associated with greywater reuse. The elements phosphorus and nitrogen are nutrients necessary for plant growth. If these elements are kept to a suitable level by choosing cleaning products with low phosphorus and nitrogen content, they can replace the need for fertilisers for gardens and lawns—the nutrients can actually be utilised by plants and soils.
The main concerns with greywater are salt build-up from cleaning products and increased pH levels in the soil. Both can have a detrimental effect on your soil and plants. However, they can both be mitigated by monitoring, conditioning your soils for optimum health and taking care to choose cleaning products with little or no salt.
Salt build-up in soils, particularly sodium salts, poses perhaps the greatest risk associated with untreated greywater reuse. The accumulation of salts in the soil can damage soil structure and lead to a loss of permeability, causing problems for soil and plant health. The main source of sodium is powdered washing detergents and fabric softeners that use sodium salts as bulking agents.
Concentrated powders and liquid detergents generally have fewer salts than the average powdered detergent. There are many powdered detergents on the market that now have low or no sodium content.
For more information and a list of products that are greywater friendly, go to www.greysmart.com.au (see the resources section for information on this site).
Generally speaking, pH levels outside the optimum range of between six and seven affect the solubility of soils and hence plants’ ability to absorb essential nutrients. As most gardeners know, pH values range from one (acidic) to 14 (alkaline), with seven being neutral.
As untreated greywater is generally alkaline, if you have an acid-loving garden, you will need to consider the types of cleaning products you use—washing powders generally make greywater very alkaline, as do solid soaps, while liquid soaps tend to be more pH neutral. The pH of greywater can vary depending on the source—shower water is often fairly neutral compared to washing machine water, for instance.
Before you’ve even applied greywater, pH levels can vary from acidic to alkaline from one part of the garden to another. Given this variability and the likelihood of greywater raising the pH of your soil, it is advisable to regularly monitor the pH and condition of your soil. Acidic soils can be made more basic with calcium carbonate and basic soils can be made more acidic with sulphur. To monitor this, pH test kits and soil conditioners are available from most nurseries.
Although salt build-up and pH are of particular concern, there are other greywater components that can have an impact on your soil and plants. They include fats and oils from soaps and shampoos, disinfectants (including eucalyptus and tea tree oil), bleaches, toothpaste, hot water and sheer volume of water—leading to over watering.
For more detailed information on greywater composition, see section 2.4 Composition of Greywater in NSW Guidelines for Greywater Reuse in Sewered, Single Household Residential Premises (www.bit.ly/NSWGreywater) and Oasis Design’s Fecal Coliform Bacteria Counts: What They Really Mean About Water Quality (www.oasisdesign.net/water/quality/coliform.htm).
The complete article looks at greywater system types, use of greywater, greywater regulations and more.
Read the full Greywater Systems Buyers Guide in ReNew 130.
Know your renewables: meter matters
In ReNew 126 we looked at electrical terms covering energy, power and other basic electrical concepts. Here, Lance Turner looks at common terms and concepts used to discuss energy metering and monitoring.
Whether your renewable energy system is grid-connected or off-grid, monitoring the system’s output is important to ensure it has a long and healthy life. Even if you don’t have a renewable energy system, understanding your energy usage is an important first step to becoming more energy efficient.READ MORE »
There are a range of meters and gauges for all these uses. Here, we look at the most common types of meters, what they show, how they work and any limitations.
First up is the electricity meter. These come in a number of types, including the older ‘spinning disk’ types and the more recent ‘smart meters’. The latter enable remote communications with your electricity retailer, so they don’t need to come out to read your meter, and provide much more fine-grained information on your electricity usage, including half-hourly data.
We’ve covered smart meters in detail in previous issues of ReNew (for example, ReNew 124) and in the ATA’s Smart Meter Consumer Guide (www.bit.ly/ATASMCG), so we won’t go into them in detail here. Suffice to say that both older meters and smart meters record electricity usage over a period in kilowatt-hours.
Interaction of your electricity meter with a grid-connected PV system
It’s important to note that most electricity meters now use net metering. A net meter will show electricity you imported from the grid and exported to the grid, but not the electricity your PV system generated that was used on-site. Some states originally used gross metering, which showed all electricity generated and all electricity used, but this has now been phased out in all states (though some older systems will still have this type of meter).
Net metering leads to an issue in calculating the total energy you are generating and using. To get these figures, you need to use the metering that comes with your renewable energy system, usually available both as a display meter and as a set of data that can be stored and downloaded from your inverter. Even if your system uses microinverters (small individual inverters attached to each panel), this data will usually be available through the microinverter manufacturer’s web portal.
Your inverter will provide you with the total PV generation figure (over a period of time), while your electricity meter will provide you with the energy imported from and exported to the grid. To calculate the total amount of electricity consumed by your house, simply add the import and generation figures and subtract the amount exported.
Read the full article in ReNew 130
Pre-cooling your home: Good idea or not?
Does running your air conditioner to pre-cool your home make environmental or economic sense? Andrew Reddaway, energy analyst at the ATA (ReNew’s publisher), examines the issue—with a little help from Sunulator.READ MORE »
If you’re out during the day and have an air conditioner (AC), you’ve probably considered running it on a timer so that the house is cool when you come home in the evening. Compared to turning it on when you get home, pre-cooling will:
- provide more comfort
- use more energy, as the AC will be running longer
- emit more greenhouse gases
- reduce demand on the grid at peak times; this helps reduce future bills for everyone by delaying grid upgrades.
But could pre-cooling reduce your bills?
Based on an analysis of a hypothetical house in Sydney, we found that you might save some money if all the following conditions apply:
- You have a grid-connect solar system.
- Your AC is not too big compared to your solar system.
- You have high grid consumption tariffs during the evening and a low feed-in tariff.
- Your AC can keep the house cool using only 20% of its maximum cooling capacity.
Your AC’s energy consumption depends on how well your house is sealed, shaded and insulated. It also depends on the AC’s efficiency, including how well it was installed. For example, ducted AC systems with thin duct insulation tend to perform poorly in hot weather. Take note of how your AC cycles on and off on a hot day. If it needs to run more than 20% of the time, pre-cooling will probably not save you money.
If you’re off-grid and have daytime electricity going to waste, go ahead and pre-cool! Daytime loads are gentler on your batteries than evening loads.
If you are using grid electricity and have no solar system, pre-cooling will be unlikely to save you money, unless the difference in grid tariff between afternoon and evening is larger than around 30c/kWh.
Locations in the western part of each time zone have an advantage, since the sun sets later. For example, the sun sets about half an hour later in Melbourne than Sydney, as it is further west. However, Victorian peak electricity tariffs are generally lower than Sydney’s, reducing the benefit of pre-cooling. States without daylight saving are disadvantaged; since people arrive home later in the day, their AC will have to maintain the pre-cooled temperature for longer. By the clock, the summer sun sets two hours earlier in Brisbane (no daylight saving) than in Melbourne.
Read the full article in ReNew 130.
Kael Rail: Ultralight solar bike rail project
Being involved with the ATA (ReNew’s publisher) is something that brings great variety and enjoyment. A great example of this was a chance phone call with Danielle and her seven-year-old daughter Kael. Doug Rolfe explains.READ MORE »
Seven-year old Kael had an idea for her local school science competition, but working out if the idea was realistic was proving a problem. After all, where do you go to ask about solar-powered trains for transporting kids with bikes to school?
Queensland Rail did their best to help with information about their electric rolling stock, but the scale of the average locomotive and standard carriages was well beyond what Kael was thinking of.
Happily, someone put Danielle, Kael’s mum, onto the ATA. We quickly saw that Kael’s idea had merit and pooled our office expertise to help find existing projects worldwide. Our local experience with Melbourne trams and custom electric vehicles also proved helpful.
After some help in understanding the rough energy requirements, Kael was able to finish her research and complete her project.
A few weeks later, we got the exciting news— after receiving a highly commended award at Mudgeeraba Creek State School, Kael had won first place in the Year 2 and 3 division of the Griffith University Gold Coast Schools Science Competition in the Environmental Action Project section. Of course, Kael was most excited by the prize of an iTunes voucher:”You can download games!”
This success also meant that Kael’s project was automatically entered in the science competition run by the Science Teachers Association of Queensland. After some nervous days, Danielle received word that Kael had to attend as she had won a prize.
In the end, Kael’s project won her first prize in her division in the Queensland event. Mudgeeraba Creek State School won the prize for best overall school—they received 21 prizes from their 31 entries, including the Queensland Science Student of the Year!
What gave Kael the idea?
Kael says: “We love our school, which is why we travel the extra distance. I have always wanted to ride my bike to school. But Mum and Dad say it’s too dangerous and there are places without bike paths. We do have electric trains, but not near us. I like riding my bike and I’m getting really fast. At school, we were looking at how we use energy in our lives. So then I thought of a solar-powered bike rail. Solar is free energy from the sun and no pollution.”
Danielle, Kael’s mum, says that the local roads are a big traffic area during school times. Some mornings it can take 40 minutes to do what’s usually a seven-minute drive. The high concentration of schools in the area means that a local public transport option would be quite desirable.
Kael says, “We wanted it [the railway] along the road, but it would make the road more crowded. Then we decided to have it away from the traffic.”
Kael worked out a very practical 5 km route for the ultralight train that would collect students on bikes from a number of schools along the way, using existing power and water easements behind the local community.
Kael spoke to Nick Abroms, Gold Coast Council’s Active Travel Project Officer who thought the idea made real sense. He said it was clear that people would use it, because it would cut down travelling time and be safe
Read more in ReNew 130.
Food vs fuel: Ethics and sustainability
Does biofuel production contribute to global food shortage and hunger, or not? Dr Seona Candy steps us through the pros, cons and complexities of using food crops for biofuels.READ MORE »
In a recent edition of ReNew (ReNew 127), an article describing the use of grain as fuel for wood pellet stoves was published. It inspired some opposing comments regarding the use of food for fuel. Although I can’t comment directly on this particular case of burning grain for space heating, I can perhaps provide some insight into the complexity, ethics and sustainability of the wider debate.
The ‘food vs fuel’ debate, as it is commonly known, is mainly concerned with first-generation liquid biofuels. These biofuels are derived from various agricultural crops that can also be used for food and feed, and have been developed primarily for transport uses. This is the case because there are already considered to be sufficient renewable energy options available to provide stationary energy.
The central argument in the ‘food vs fuel’ ethical debate is about whether the development (or not) of biofuels will cause people to go hungry. Critics of biofuels argue that diverting food crops to biofuel production will increase food prices and cause hunger, particularly among the global poor. Advocates of biofuels argue that their development will help mitigate climate change, and its potential future impacts on agriculture and food production, thus avoiding hunger for everyone (the global poor included) in the longer term.
The first of these two arguments seems fairly straightforward. Indeed, biofuel development in the early 2000s did precede significant rises in the prices of staple crops, causing the 2007/08 global food crisis and food riots in many countries. But it is not safe to assume that biofuels alone caused food prices to rise or that the impacts of rising food prices were negative for all groups who make up the global poor.
According to a report from the International Food Policy Research Institute, the 2007/08 food crisis was primarily driven by a combination of rising oil prices, a greater demand for biofuels and trade shocks in the food market.
Rising oil prices led to increased costs of cereal production, as conventional agriculture is an energy-intensive enterprise. Higher energy prices increased the demand for biofuels, which became more competitively priced when compared with oil. At the same time, cereal demand increased from oil-producing countries and weather shocks reduced the supply of some grains, increasing prices further. This led to a ban on exports by producers and panic buying by importers, which only increased prices yet again.
These increased prices led to food riots in developing countries. As Thompson2 argues, though, increased food prices negatively impact mainly the urban poor, who must purchase their food. For the rural poor, however, who produce and sell their food, rising food prices could be an advantage. It would increase their income and ability to buy food that they don’t grow themselves. Since the rural poor make up around 80% of the global poor, fewer people may in fact go hungry due to rising food prices.
Read the full article in ReNew 130.
What do you need to consider when looking at the energy and environmental aspects of cooking? Alan Pears begins the discussion.READ MORE »
In energy and environmental terms, cooking is just one part of a complex system in the food supply chain. The food system accounts for around 25% of greenhouse gas emissions in Australia. Of that, cooking is a small part, about 3%. The other factors such as the production, transport, sourcing and types of ingredients are major issues that we don’t have space to tackle here.
Even though energy use from cooking is a relatively small portion of food-related energy use, it can still be significant. An average Australian home uses around 600 kilowatt-hours (kWh) of electricity each year for all-electric cooking (costing $150 or more), while gas cooking typically uses 3 to 5 gigajoules (GJ), costing $60 to $250 depending on usage and gas price. Many homes use a gas cooktop and electric oven. Most homes also have several benchtop cooking units such as microwave ovens, toasters, electric kettles and rice cookers.
Energy use for cooking is particularly an issue for households that are off-grid. Many off-grid homes use gas for cooking rather than electricity (because of the high loads from electric cooking appliances), yet this still has a greenhouse gas impact, and can be expensive when it’s LPG rather than natural gas.
Electric cooking can also be a major contributor to evening peak electricity demand. As electricity suppliers introduce time-of-use pricing or peak demand charges, it will be important to manage cooking demand. Gas prices are also increasing, while LPG is already very expensive.
So energy-efficient cooking and reduction of peak energy demand for cooking are important. This article looks at these issues.
Where is energy wasted in cooking?
As with all energy efficiency analysis, standby energy use can be an issue. The way you heat up (or defrost) food can also affect energy use, as does the way you manage cooking post the ‘heating up’ phase. And then, the appliances themselves (such as ovens, grillers etc) all have their own efficiencies and optimal usage patterns.
The energy use of kitchen lighting and non-cooking appliances (fridges and dishwashers) should also be considered, but they have been well covered elsewhere so won’t be discussed here. But, just as an example, lighting a kitchen with six halogen lamps for two hours a day uses half as much electricity as cooking.
Luckily, gas cookers no longer have pilot lights that cost a lot to run. But many cooking appliances use energy when on standby for clocks, ‘smart’ features, electronics and in some cases keeping components hot, ready for action. Standby consumption is declining, but older equipment and even some new products, such as coffee makers, can have surprisingly high standby consumption.
A good rule of thumb: if you’re not confident an appliance has standby power under 1 watt, switch it off at the power point.
Read the full article in ReNew 130.
Light up Timor Leste tours
It’s not just about providing solar lighting—the Light Up tours provide training for local technicians and could help start up a solar industry in Timor-Leste. Dave Carlos from Timor Adventures describes the company’s latest tour.READ MORE »
Over the years, many of us have taken to gifting a goat, a fuel-efficient stove or even a mozzie net to someone who needs it. While these gifts bring much-needed resources, sometimes I get to thinking about the details: Where does the recipient of the goat live? How will the goat get to them? What did the recipient do with the goat?
The Light Up Timor-Leste tours are a hands-on approach to answering such questions. You travel to Timor-Leste, pick up a solar lighting system, go to a village, take the system to someone’s home, meet them, put the system in, flick on the lights and the questions are answered. This is what I call ‘extreme gifting’.
Timor Adventures is a small Timorese tour company. Our professional background is in community development, and we created Timor Adventures as a means to improve economic development in the outlying areas of the country.
Many people who came on our tours expressed a desire to do something practical and sustainable to support this new nation. In response, we approached the Alternative Technology Association (ATA, ReNew’s publisher) with the idea of doing what have become known as the ‘Light Up’ tours.
The model is simple: we provide all the on-ground logistics and liaison with the villages, the people who come on the tours donate the funds to purchase the equipment, and the ATA along with its local training partner CNEFP Tibar provide the hardware and technical skills.
In 2013, we installed solar systems in two schools, one on the far side of Atauro Island and the other in the mountains outside of Baguia. This year, we installed systems with a solar panel and three lights in 20 homes in the villages of Buibela and Lena, in the Baguia area.
From concept to installation
Moving from the concept to installing the solar systems involves a few steps.
Finding the right villages
Many villages in Timor-Leste are now, or soon will be, on the recently completed power grid. We decided to find villages that are not connected and are never likely to be.
Making sure it is truly sustainable
To ensure the systems are maintained and the batteries can be replaced when needed, it is important that there is a small, regular contribution of funds from the recipients of the systems. Equally importantly, these funds need to be held and managed by a respected person in the community.
Finding people who want to participate in the tour
The idea doesn’t work unless there are people who want to participate and are willing to donate the necessary funds. The 10 people who came on our most recent tour were a wonderful and adventurous bunch. Of them, Roz and Paul came on the first Light Up Baguia tour, Helen toured with us a couple of years ago and has also ridden around the whole country on a motorcycle and, at 15 years old, Violetta was our youngest Timor Adventurer yet.
Choosing a system and getting the equipment
The systems include a 20W panel, three LED lights, a regulator (designed and developed by an ATA member) with three light switches and two batteries. Other required equipment is a box for the batteries, plywood to mount the regulator on, wire to fix the solar panel to the roof, and cables and connectors to wire everything up. The major challenge in Timor-Leste is time; some parts needed to be shipped from Australia, taking three to four months, depending on the shipping schedule.
Learning about the system and meeting the technicians
We commenced the most recent tour with a visit to the CNEFP Tibar training college (a bit like a TAFE), just outside Dili. There, we met the three local technicians who would be leading the installation. This was a significant moment, the first time local technicians, trained by the ATA, would lead the installations on a Light Up tour. We were treated to a tour of the training facility, lunch and then a briefing about the installation process.
Getting there is half the fun
When I hear the term ‘remote village’, I have a mental picture of the destination, but not the journey. The village we were travelling to was indeed remote and we had a lot of people and equipment to get there: 16 people, three 4WDs and four motorcycles.
We first travelled to Baguia and stayed the night. Getting to our final destination, the village of Buibela, was supposed to take another two hours, but, due to weather and the challenges of the terrain, it took over four hours.
When we finally arrived at Buibela, we were greeted by the local villagers with a traditional welcome and dancing. Their hospitality could not have been greater.
Preparing for the installation
We aimed to install a solar system in 20 houses across the two villages of Buibela and nearby Lena. The villages are spread out in small clusters of houses, ranging from a 20-minute to a two-hour walk from where we were staying. Because of the additional time we had spent getting to the village, we only had one day to complete all the installations. We started stripping wires, cutting plywood and dividing up the equipment. People split into three groups, each headed by a local technician, and set about completing a number of installations.
It was a long but fulfilling day. It went something like this: we would go to a house where the owner was expecting us, conduct the installation and be offered coffee and something to eat. At the end of the process, the lights would be tested and the technician would give the handover instructions.
My most enduring memory is of a woman who lived by herself in a small three-room house with a dirt floor. When the technician was showing her the system he showed her one of the lights and its switch. She asked him if she could turn it on again. He explained that you can turn it on and off whenever you want. He then showed her the other switches and each light in turn. He then said you can turn them all on at once and proceeded to show her. “All on at once!” she said.
The story does not end there
I think all of us on the tour grasped both the significance of what we had achieved together and the planning and effort that was required to do it. It was great that there were now solar lights in 20 homes, but our attention quickly moved to sustainability—how to keep the lights on.
There are three kinds of activities to support this: a technician will visit in the next six months to see how the equipment is performing, local people will be trained to do basic troubleshooting, and a system has been put in place to contact the technicians to repair or replace the equipment when needed. I, like everyone in the group, am looking forward to hearing how these steps progress.
If you want to find out more about the work the ATA has been doing in Timor-Leste, see www.ata.org.au/IPG. If you think you might be interested in a Light Up Timor-Leste tour in 2015 or to find out more about Light Up Baguia 2014, please see our website: www.timoradventures.com.au.
The Pears Report: The end, not beginning, of an era
Alan Pears explains why coal seam gas is not the answer and, when it comes to energy-efficient homes, why the cooling side of the equation needs some attention.
Coal seam gas (CSG) has been widely promoted as a game changer that will drive a gas boom. It’s not. It’s a desperate attempt to prop up the fossil-fuel era. It is also a conflict between the established energy industry (backed by governments) and just about everyone else, including state governments desperate to win votes.READ MORE »
However, the predictable failure of CSG will shift the balance in favour of sustainable energy: efficient, smart, renewable, distributed energy-service solutions.
The gas industry and the federal government are throwing everything at supporting CSG. Even the east coast ‘gas crisis’, caused by companies building natural gas plants in Queensland without locking in their gas supplies, has been used to try to justify more CSG development.
The reality of CSG
The CSG reality is that very large numbers of gas wells must be drilled and networks of pipelines built, conflicting with tourism and agriculture, placing underground water resources at risk, exposing people, animals and plants to toxic chemicals, and potentially leaking methane, a very active greenhouse gas.
In addition, the wells don’t produce gas for very long, and they must then be managed for an unknown period to limit impacts on the local environment and underground water resources. And it’s not cheap gas: in fact, high international prices are needed for it to be profitable.
The gas industry has blamed ‘cowboy’ operators for problems. But how do they respond when a responsible operator like AGL is found to have methane leaks from nearly a tenth of its CSG wells in NSW? (www.bit.ly/SMHCSG)
The NSW Chief Scientist has published a thorough report on CSG. While she finds it is possible to manage CSG responsibly, she spends quite a bit of her 24-page report outlining the difficulties in ensuring strong regulation and enforcement, funding to deal with problems during and after production from wells, and strong governance mechanisms.
It seems obvious that these requirements cannot be met by any Australian government. Voters know that no present government can lock in comprehensive environmental regulation and enforcement to ensure future governments manage derelict wells for decades or longer. We simply do not have the governance capacity to properly manage the long-term impacts of CSG.
CSG is more trouble than it’s worth. We have wasted too much time failing to address climate change to be able to enjoy the luxury of using fossil gas, especially leaky CSG, as a transition energy source. The global carbon budget is just too tight.
At the same time, technology development, economies of scale and emerging creative financing solutions mean that efficient, smart renewable energy solutions can deliver practical, lowest cost solutions.
While Australian governments and the energy industry wallow in denial, the International Energy Agency, World Bank and numerous leading economists have joined climate scientists and the sustainable energy industry to support this transformation and proclaim that it is practical.
As former Saudi oil sheikh Ahmed Zaki Yamani said in the 1970s (www.bit.ly/NYT-AZY), ‘the stone age didn’t finish for lack of stone’. We have now moved beyond fossil fuels, although we can acknowledge that they have provided a useful technological base on which we are building our sustainable energy future. The shift away from fossil fuels is reflected in the industry’s increasing difficulty in accessing capital.
Why do new energy-efficient houses need cooling?
Last year, CSIRO’s field evaluation of 5 Star homes reported some interesting findings. One big issue was a widespread lack of compliance, due to near-total failure of enforcement by governments and local councils. Another important finding was that, although the efficient homes had much lower heating energy use, their cooling energy use was not lower. The reasons for this outcome are complex, but it’s time we addressed them.
One reason may be that the default settings for cooling use in the NatHERS calculator seem to underestimate cooling. The thermostat temperatures and user behaviour patterns were set many years ago, based on quite limited information. Research has shown people typically use lower thermostat settings (see www.bit.ly/SETSACER). A 2008 South Australian study proposed changes, but these have not yet been formally regulated.
When estimated cooling energy is too low, it has little impact on the energy rating. In climates that require both heating and cooling, designers are more likely to focus on building features that reduce heating.
This under-emphasis on hot weather performance in the energy rating scheme means features like dark-coloured roofs and absence of eaves have unrealistically low impact on rated summer performance. In cooler climates, the overall annual outcome can even improve the Star rating, as benefits from more winter solar gain outweigh worse summer comfort!
The energy rating is also averaged over the whole building. So some rooms may perform poorly without adversely affecting the overall energy rating. And the rating is for total annual heating and cooling. Separate heating and cooling ratings would ensure the home performs adequately all year.
The nature of modern building designs is having its impact, too. The upper storey of a two-storey house has no links to the stable temperature of the ground, and is exposed to higher solar radiation. If glazing is not very carefully designed and managed, it becomes a ‘solar oven’—although the amount of energy required to cool it is not very large if it is well insulated.
More broadly, we need to realise that a high thermal performance home (with good insulation, draught proofing and well-designed glazing) requires very little additional heat to raise its internal temperature above the outdoor temperature—in both winter and summer. Extra internal mass or phase-change materials can help to stabilise the temperature, but climate change is increasing overnight summer temperatures and the duration of hot spells, so thermal mass is becoming less effective.
Careful design is increasingly important, especially glazing and adjustable shading, so that summer sun can be screened out.
Air leakage and poor management of ventilation is another culprit. When an exhaust fan or rangehood is running in hot weather, it is actually bringing in a lot of hot outdoor air—equivalent to a cooling load of 2 kW or so. On a hot windy day, having a window on one side of a house open, even a little, can combine with exhaust fans, fixed ventilation in a laundry or another open window on the opposite side or upstairs to create heat input of up to 5 kW. So, leaky open-plan homes with doors to permanently vented laundries and bathrooms left open can have high cooling costs. Improved building quality and user education are needed.
Of course, this does not mean that 5 or 6 Star homes are a bad idea. If they are built properly and well managed, their peak cooling energy requirements are small, and hourly cooling cost is low, especially when combined with a high efficiency (5 to 7 Star) air conditioner.
We need to further strengthen regulations and enforcement, sort out the under-emphasis on summer performance in the rating scheme and educate home operators. We should also take advantage of the feature in rating tools that allows an energy rater to look at performance of each room or zone during weeks of hot and cold weather. Then designers could identify and address problem rooms.
Also, summer is the time when a typical rooftop PV owner may have excess free electricity. Using some of this for cooling to be comfortable (especially once we get batteries to store daytime generation for evening cooling) need not create load problems for the grid.
Alan Pears is one of Australia’s best regarded sustainable energy experts. He teaches part-time at RMIT University and is co-director of Sustainable Solutions, a small consultancy.
This article was first published in ReNew 130.
Product profile: a real solar laptop
We have seen a number of half-hearted attempts to make portable solar computing devices, but most of them have solar panels that are a token effort at best.READ MORE »
The Sol laptop takes solar power a little more seriously, with a solar panel that can charge the laptop in around 2.5 hours in ideal conditions (expect longer in actual use). The detachable panel folds up into a hard shell cover that is part of the laptop’s screen, so the whole unit is self-contained.
The Sol is available in three models—Sol, Sol M, and the Sol S, also known as the SuperSol due to the higher specifications. All models are available in a range of colours.
Each model has different specifications and differing options, such as RAM and hard drive upgrades. CPUs range from the dual-core, 1.86 GHz Intel Atom D2500 through to the dual-core, 2.39 GHz Celeron N2820. Memory ranges from 2 GB to 8 GB, depending on model and options, and the hard drive is 320 or 500 GB.
The laptops come with several operating system options—Ubuntu Linux, Windows 7 or Windows 8.1. Other features include all the usual ports, camera, HDMI out, 3G/4G modem, GPS, wi-fi and Bluetooth, with graphics set at 1366 x 768 on the 13.3” LCD.
For more product profiles, buy ReNew 130
Q&A: Using solar first
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?READ MORE »
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: www.ata.org.au/news/latest-solar-payback-times.
You might find our solar electricity booklet useful: shop.ata.org.au/shop/solar-electricity
And if you’re looking to do a detailed analysis, we have developed a free tool called Sunulator. Please see www.sunulator.org.au.
To read more questions and answers, buy ReNew 130.
Off-grid in the suburbs
One ReNew reader has used his electric vehicle to take most of his energy consumption off-grid. He explains how he did it.READ MORE »
I was keen to increase the size of my PV system as my house was using more energy than the system produced in winter. This meant I was importing energy from the grid at 29 c/kWh (100% GreenPower, I hasten to add!).
I was also keen to experiment with going off-grid. I considered going completely off-grid, but that would mean losing the perceived reliability of supply from the grid, requiring a leap of faith for a suburban consumer like me.
My solution, instead, was to install a separate off-grid PV system. I now have two PV arrays with separate inverters, one connected to the grid and one off-grid, with the house running (mainly) on the off-grid system.
The idea of going off-grid with battery systems was featured in ReNew 128. One article suggested that price parity with a grid connection is yet to arrive, particularly in metropolitan areas, as PV may now be cheap but batteries are still expensive.
However, I already had a good-sized (8 kWh) lithium ion battery in my plug-in Prius conversion. I was able to use this battery for my off-grid system, with it providing around 6 kWh storage at 75% depth of discharge. So, even though I live in metro Melbourne, the economics worked out well for me.
My system required some technology: I purchased a 4 kVA Ecotronics unit from Commodore Australia that does it all. It is a MPPT (maximum power point tracking) PV controller, battery charger, AC inverter and grid UPS all in one (see Products, this issue).
It is designed to run off a 48 volt battery, the same as my Prius PHEV conversion system battery. The conversion system, from Enginer in the USA, uses a 48 volt battery and a DC–DC converter to step the voltage up for the Prius’s drive system.
The Ecotronics unit can also automatically revert to grid power if there is not enough sun or the battery is low. It can even be set up for load levelling—i.e. charging the battery bank on night-rate mains power then supplying power during the day. However, with a relatively high night-rate tariff (19 c/kWh), the economics for this are marginal for me—a 10 c/kWh saving over the day rate of 29 c/kWh.
The Ecotronics unit simply connects to the Prius conversion’s 48 volt battery via a large Anderson connector (a high current rated two-pole connector popular in DC systems). When not running the house loads, the Prius battery can either be charged from the Ecotronics unit’s built-in battery charger or the charger that came with the Prius conversion kit.
Read the full article in ReNew 130