Grid-tied VS Off-grid Solar PV systems


With the tremendous uptake of residential solar PV installations all around the world, the next question that often comes to mind is: to stay grid connected or go off-grid? For most people who are concerned about environmental issues, they might be led to believe that completely weaning off our fossil fuel powered grid is the truest form of sustainable living. However, here at eTool we like to challenge people’s beliefs based on data from life-cycle analysis.

To start, let’s quickly look at the difference between the two systems.


Grid-tied PV system


A grid-tied system is connected to the utility grid. In new systems, there is only one meter that measures both in-coming and out-going power to the house. Power generated from the solar panels goes through the inverter which converts DC to AC which then used throughout the house. Any left-over power that is not used goes out to the meter where it is measured then fed into the grid to be consumed elsewhere. This system has no on-site battery storage so any solar power that is not used at the time it is generated will be fed directly out to the grid. When no energy is generated by the solar panels such as at night or on overcast days, power will be drawn back from the grid to supply the house.


Off-grid PV system


An off-grid system means that the system has no connection to the grid at all. In this situation, battery storage is necessary in order to provide power to the house when there is no power generated by the PV system. An additional on-site generator may also be required as a backup in case the stored power runs out. In this system, the power from the solar panels goes through a charge controller or battery regulator then into the battery bank for storage. On demand, the power is drawn from the batteries through an inverter then to the house to be used. If the power stored in the batteries run out, a generator can be started to produce backup energy.


LCA Comparison

Carbon Intensive Grids


AU StandardStructure – timber + double brick
Cooking – Electric
HWS – Gas storage
HVAC – Airsource heat pump (MEPS ave)
Lighting – CFL
Refrigeration – AU average
Water – AU average

In order to compare the systems, we will use LCA to quantify the impacts in CO2e. We assume that all other factors are constant such as water, gas and the carbon intensity of the grid. The table above shows the building structure and appliance specifications for a standard Australian detached home. Only the PV systems will change in order to better compare the difference between grid-tied and off-grid.


The graphs above shows the life-cycle carbon impact of a standard Australian home with no PV system installed. We can see that the life-cycle energy of the building takes up the largest portion of the overall impacts of the building. The graph on the right shows the end-use breakdown of the standard Australian household’s energy use.


The blue column on the left in Graph 2 above is a standard Australian home with no PV. The red column is an off-grid system sized to provide 100% solar power throughout the year. This is a 15kW PV with about 100kWh of battery storage to provide backup power for 3 days while the green column is the grid-tied version with 15kW of PV without battery storage. The orange& dotted columns show the impact of a smaller off-grid 8.5kW PV system with 60kWh of battery storage. The dotted orange column has an additional backup diesel generator that provides 10% of the energy demand. The teal column on the right is the grid-tied equivalent with 8.5kW PV and no diesel backup or battery storage.

We can see that installing a PV system alone has a significant effect at reducing the CO2e impact of the building. Note that despite a near two-fold increase in the amount of PV, the life-cycle carbon savings in the off-grid system only has marginal improvement when compared to the grid-tied system. This is due to the high embodied impacts of the larger PV system which are underutilized in the off-grid system whereas in the grid-tied system all extra power generated by the over-sized system is fed into the grid.


In the graph above, we compare the category breakdown of the 15kW PV systems versus the AU standard home, we can see that while the life-cycle energy use of the solar powered homes have dropped significantly, the recurring impacts on the other hand have increased due to the impacts related to replacing PV panels and batteries.

Low Carbon Intensity Grids

In areas with cleaner grids, in this example I’ve used the Tasmanian grid (even though it is still connected to the NEM) – is a grid-tied PV system still relevant?



The graph above shows that although the proportion of savings is much less in a low-carbon grid, a grid-tied PV system still has a lower life-cycle CO2e impact compared to an off-grid system. In areas with cleaner grids, the embodied energy impact of the building becomes proportionately more important than the operational energy as shown in the graph below.



Best Practice Design

How about a house that is designed by someone who knows what sustainability is about? Let say they designed using low-embodied energy materials and didn’t install any air-conditioners – how would such a house compare? The low-impact or ‘best practice’ design building assumes that the occupants are more sustainably conscious and try to reduce electricity demand as much as possible in the choice of appliances they will use and are more likely to build with low embodied impact materials such mud brick. A detailed list of specifications in the ‘best practice’ house are listed below while still assuming Australian averages for water and refrigeration energy use. Based on these specifications, the off-grid ‘best practice’ home will need 4kW of PV and 48kWh of battery storage assuming 10% of the energy demand to be provided by a diesel generator.


Best PracticeStructure – mud brick
Cooking – Wood
HWS – biomass
HVAC – ceiling fans+wood pellet heater
Lighting – LED
Refrigeration – AU average
Water – AU average
PV – 4kW
Off-grid Backup –  48kWh battery storage + diesel generator

The graphs below show the global warming impact of a ‘best practice’ home on an Australian average grid the embodied and operation energy breakdown and the carbon impacts on a low-carbon grid. Even though the overall life-cycle carbon impacts of the building has dropped significantly due to the ‘best practice’ design, the results still indicate that being grid-connected is better for the environment in both grid situations.
Graph6 Graph5 Graph4




In areas with carbon intensive grids such as Australia, it is important to help ‘clean up’ the grid by staying grid-connected with our PV systems. This is due to the fact that all the excess potential energy from off-grid PV panels is ‘wasted’ instead of captured to be used elsewhere. An off-grid setup will usually have a PV system that is large enough to meet most of the energy demand of the household throughout the year. This means that the system will be sized to produce enough power in winter but in summer when there is more daylight, the extra electricity generated by the system will be wasted.

A grid-tied system on the other hand is able to take advantage of an existing energy network and maximise the energy generation potential of their PV systems as any excess energy is fed back into the grid to be utilised elsewhere. This means that the embodied energy of the building can also be offset when the building produces more renewable energy than it consumes throughout its life.

A cleaner grid also means that other homes, offices and industries such as water desalination plants and manufacturers that use this cleaner electricity will be less carbon intensive. We all benefit from the knock-on effects of staying grid-connected.

For areas where the grid is already ‘clean’, the operational energy impacts become less significant from a carbon perspective but you’re still better to have grid-tied PV. Staying connected in a green-grid also helps avoid the additional embodied impacts from an oversized PV & battery storage system.



Bear in mind that there are other resources and technologies that haven’t been modelled here which may provide better solutions by taking the best of both systems. For example, hybrid systems combine the advantages of grid connection with battery storage to help moderate grid loads. To provide an efficient solution to large scale energy distribution, ‘Smart Grid’ systems that monitor and control the grid’s energy distribution and production is the way to go. Combine smart grids with hybrid solar systems and the economics and efficiency of renewable energy distribution and supply grid will be greatly improved. Nevertheless, the underlying message still points to the fact that staying grid-tied is the key in order to stay most sustainably relevant today and in the future.

Tesla most recently announced their low-cost ‘Powerwall’ battery storage system which will affect the current PV market.



Sustainable Design Principles 101 – Multi-Residential Australia

This post is designed to guide design teams during early design stages prior to any form of drawing mark-up. It describes a pathway of continuous building improvement through easy low hanging fruit strategies to incorporation of renewable technologies and advanced design principles. As sustainability becomes engrained in the construction industry it is important that stakeholders maintain an understanding of what the market expects both presently and going forwards into a low carbon future.


Achieving Targets – The Basics

Generally a multi-residential apartment building built to BCA standards (electric hot water, 6 star Nathers and standard air conditioner) will have approximately the same impacts as the benchmark average dwelling (4.2 tonnes/person/year). They tend to be smaller (less space to heat and cool), have longer design lives and high occupancy (reducing the impacts on a per person per year basis). The chart below represents the life cycle Impacts of a typical multi-residential apartment building.

Capture 2

Typically there are a number of “low hanging fruit” design improvements that are low cost and low risk to implement. The measures focus on operational energy which generally makes up 70%-80% of the total life cycle impacts. The measures are detailed below for a standard apartment building with a mix of one and 2 bed apartments, please note these are indicative figures and will vary depending on final design, density, services and materials used.

Sustainability Measure

Typical percentage improvement
Gas hot water system25%-30%
Lighting motion sensors/timers in common areas6%-8%
Apartment Energy Monitoring2%-4%
Behavioural Change Programs2%-4%
Low flow shower heads (5l/minute)1%-2%
Limit refrigeration space to less than 750mm0.6%-0.7%
Ventilated refrigeration cabinetry0.4%-5%
Total approximate37%-45%


With implementation of the above measures the building will achieve approximately a 37% to 45% improvement sitting at a Silver medal rating. To achieve greater improvements renewable technologies are needed.


Renewable TechnologyTypical percentage improvement
Solar Hot Water (1m2 per dwelling)3%-4%
Solar PV (1kW/ 10m2 per apartment)5%-7%


The majority of medium rise flat roofs can easily accommodate the above with room left over for other elements such as flues and skylights. The low hanging fruit combined with some renewable generation will typically achieve around a 45-55% improvement.


 Achieving Targets – Best Practise

For higher ratings to be achieved, there will need to be upwards of 1 kW and per apartment and over 10m2 of roof space available alongside the measures detailed above. This can require careful consideration of roof designs from the outside and in some instances, consideration of options off-site such as community owned solar PV farms may be required.

Renewable TechnologyTypical percentage improvement
Solar PV (2kW/ 20m2 per apartment)10%-14%
Solar PV (3kW/ 30m2 per apartment)15%-20%
Solar PV (4kW/ 40m2 per apartment)20%-28%


Roof Orientation for PV:

Capture3Once a residential building gets above 4 storeys, or a commercial building gets above 3 storeys, it will likely end up in a position where the solar technologies that are required are constrained by the roof space that is available. In this situation the design team should take roof design into consideration from an early stage and optimise it for solar panel installations. The following guidelines should be considered:

  • By installing panels “flat” on a roof, many moor panels can fit because they do not need separating for shading.
  • Shading from surrounding objects and buildings is an important consideration however it is rarely a problem in multi-residential buildings taller than their surroundings. PV can be very worthwhile even if partially shaded and can may still deliver significant carbon savings compared to other measures.
  • For designing roofs in this situation, the following considerations should be made.  Note that the below loss figure for varying orientation and pitch are applicable to Perth (latitude of 32 degrees):
  • The orientation of the roof can significantly aid the amount of PV or Solar Hot Water that can be installed in the diagram above

– North facing panels at 32 degree pitch gives optimum energy gain over the whole year (100%)

– Dropping pitch to 5 degrees only results in a loss of approximately 9% (91% of optimal generation)

  • If panels are to be pitched at lower than 10 degrees, consideration should be given to at least annual cleaning until it is proven that soiling is not effecting generation.
  • If possible, avoid hips in roofs as these significantly reduce the amount of PV that can be installed.  It is far better to pitch the roof in two directions only.  Even pitching north and south in two directions is likely to result in a better overall result than in four directions.  The south facing panels may generate less power per panel than the east or west, but more panels will be able to be installed because hips won’t have to be avoided and this will more than make up for the slight loss of efficiency in south facing panels.
  • Very wide gutters can significantly affect the available roof space for solar collectors.  Consider overhanging the roof structure over a required large gutter.
  • Protruding services that break up the roof space should be designed if possible on the south side of the building.  This reduces the losses due to shade for solar collectors across the whole roof.
  • Roofs with multiple heights are complex due to overshadowing.  If possible avoid this.

For solar hot water systems the same rules apply however slighting more consideration may be required to match demand with pitch, so a higher pitch to meet the higher winter water heating demand.  This is not such an issue with PV as it can be fed into the grid when generation is higher than demand.


Advanced Design

Some of the recommendations listed below represent paradigm shifts not only in actual construction but also in the marketing and sales strategies that may be required to ensure a developments viability. There may be times when it makes more sense to invest the money that would go into some of these expensive onsite solutions to other local projects that can deliver more value and higher CO2e savings. Examples of this may include Investments in street light upgrades, existing housing retrofits, solar panels on local schools and buildings, behaviour programs, community farms, bicycle infrastructure etc.


The more people a building can house the less impact per person that building will have. Furthermore for every person that is housed in a sustainable building that takes one more person out of the average, unsustainable building – moving society towards a low carbon economy faster.

Typical multi-residential buildings have approximately 50% of the total floor area dedicated to actual living space, the rest tends to get tied up in common areas, car parks, plant rooms etc. By minimising the common areas you reduce impacts on two fronts: living area available for the same volume of materials, and reducing the operational energy required to light and ventilate the common spaces (this can typically take up to 15% of the total CO2e emissions).


ratio net dwellable area/gross Floor AreaLife Cycle Reduction in Emissions


There are numerous ways that common areas can be reduced:

Capture 8

Space efficiencies can also be gained by increasing the number of stairwells whilst reducing the common walkway areas.


Although stairs are likely to be the more expensive option, this could be recouped by adding the spare hallway space into each apartment, in the example above this provides an extra 8.75m2 per apartment.

Typology (Beds and bathrooms)

Environmental impacts can be reduced through increasing the occupancy of the apartments themselves. Whilst 2 bedroom 2 bathroom apartments are fashionable, with good design that (rarely used) spare bathroom could be a third bedroom instead. This provides an increase in the overall sustainable living space of the building without impacting on the floor area being constructed


In many ways embodied carbon is equally (and perhaps more) important a consideration than operational energy. eTool LCAs will typically assume current grid intensities throughout the 100+ year predicted design life of a building. This means operational energy makes up around 80% of the total impacts. In reality over the next 100 years the grid will decarbonise and operational energy will contribute much less over time. The embodied carbon in materials on the other hand is locked in from the year the material is manufactured and transported to the site. There are many low impact alternatives to common materials in construction. Timber and CLT can be used in place of concrete and steel. Where concrete is necessary fly-ash or blast furnaces slag blends should be incorporated, these are waste products that can directly replace a proportion of the concrete thereby reducing its impacts.

graph 1

Timber veneers and plywood should be avoided due to the high impact of the glues and resins used in these products. Plasterboard also has very high impacts. Alternatives such as plain hardwood, bamboo or MDF represent significant savings. IF plasterboard is to be used 6mm sheets should be preferred to 12 mm sheets with acoustic requirements met through insulation which is typically low in CO2e emissions.

graph 2

Carpets (especially wool) should be avoided with cork or polished concrete finish preferable. If absolutely necessary carpets should be dark coloured (to avoid replacement through soiling) and plant based materials such as jute and sisal should be specified that have natural/non-synthetic rubber backing.

graph 3


There tends to be little difference in terms of environmental benefit between CFL lights and L.E.D lighting Increasing natural light levels using solar-tubes, skylights or similar means less use of artificial lighting energy. Specifying lighter matte colours to surfaces such as the balcony, ceiling and walls will bounce light deeper into the dwelling thus increasing natural lighting. Light shelves in windows is another passive way to divert and bounce light deeper into the dwelling. Similar systems using adjustable louvres can also be used. Providing translucent shading material in addition to heavier curtains allow the option of diffused daylight to penetrate whilst maintaining privacy. The top of the windows is where light penetrates deepest into the dwelling, so it is important to ensure that this part of the window is not obstructed by drapery or blinds. Translucent partitions between rooms also allow light to be drawn into deeper rooms. Clerestory windows also provide a method of introducing more natural light into central rooms.  Ideally these should be utilised with higher ceilings and high reflectance surfaces in order to encourage light to penetrate.  In order to prove the value of these initiatives a daylighting simulation should be undertaken to ensure expense is not incurred for no benefit.  This will likely make this recommendation hard to justify economically (there will be many far easier wins elsewhere in the building.

Gas cookers over electric

In regions with fossil fuel dominated electricity grids such as WA, gas represents a large advantage over electricity for providing energy to cook with.  This is due to the heat and electricity losses associated with distributed power.  Burning the fuel (gas) at the source eliminates these losses and is a more efficient way of using the fuel. The majority of gas cookers sold today include safety features that automatically turn off the gas when no flame is present. Rinnai has also developed the ‘inner flame’ technology that produces a flame that is directed inwards which is about 27% more efficient than standard gas stoves. The drawback to moving to gas cooking is that a gas pipeline may need to be installed. If the implementation of this strategy is outside of the project budget the developer may offer the strategy as an upgrade package for purchasers. This eliminates the need for upfront capital while promoting best practices and educating the public.

Or Induction cooktops

An all induction cook-top is an alternative that could deliver carbon savings over a standard electric cook-top.  Induction cook-tops work by transferring electrical energy through induction from a coil directly to the magnetic pan. Only the area in contact with the coil heats up and therefore the cooker can be up to 12% more efficient than a standard electric conduction cooker.  The controls on an induction cooker are also far more precise giving a greater range of cooking techniques.

Car Park Ventilation

By applying a detailed engineering design to the car park ventilation systems, it is expected that the fan run times could be considerably cut down especially when natural ventilation is utilised.  Computational fluid dynamics would be utilised in this technique to determine how to best move air through the car park to maintain acceptable CO2 levels with minimum energy demand.  Gains may also be achieved in reduced ducting.  At least a 20% saving in ventilation may be achieved.


Biodigesters turn food and or human waste into gas that can be used in cooking. Although not well established in western countries this technology has been used for hundreds of years in China and India. Communal or individual systems exist that may be incorporated into an innovative building design.


The appliances that go into the building can make a significant proportion of the recurring impacts.  Modern appliances tend to have fairly small warranty periods in relation to the lifespan of a building.  TVs in particular can often not last more than 10 years.  Ensuring that appliances are purchased second hand and those that are purchased new have a long warranty and are kept for as long as possible can provide significant carbon savings.  In this recommendation we have assumed each appliances lasts twice as long as the standard warranty. Where appliances are installed they should also be of the higher MEPS rating bands for energy efficiency.

Thermal Performance

Modern 6 star dwellings in Western Australia need very little in the form of heating/cooling. The developer with sustainability in mind will provide only ceiling fans for cooling and renewable biomass pellet heaters for heating. Bio Where air conditioners are provided they should be single split units which can obtain higher efficiencies generally than multi splits. A COP/EER of 5 is exemplary.

Tri-generation, deep geothermal and shallow ground source heat pumps can also be appropriate in very large developments with high demands such as precincts with swimming pools. However they entail very high outgoing capital costs and the environmental benefit should be considered carefully against other technologies.

Swimming Pools

Most importantly swimming pools should be appropriate for the size of the development. Proportionally 50m2 pool shared amongst 100 dwellings will have 100x fewer impacts per dwelling than the same size pool provided for a single dwelling. Where pools are installed they should ideally be naturally heated through ambient air and install pool covers that contain the heat when the pool is not in use. Typically including a pool cover which can operate automatically or manually for 8hrs per day during the pools closed hours has a 28% saving in the pools heating energy demand. Pool pumps efficiency should also be considered carefully, high-efficiency pool pumps of up to 9 stars MEPs rating are currently available on the market.

 Hot Water

Alongside solar thermal technology and low flow shower heads, an opportunity exists to warm the inlet temperature of the water by using a heat exchanger. Water exiting apartments in the sewerage drains will have a higher temperature than the normal inlet temperature of water coming into the building from the mains, particularly in winter.  By passing the inlet water over the warmer outgoing water, the temperature can be increased. A 5% reduction in energy demand of the hot water system can be achieved.

For communal systems there will be significant heat losses in the pipe carrying the hot water around the building as well as from the individual water storage tanks. Based on the conservative assumptions of a 25mm pipe with 25mm of insulation (125mm total diameter) the heat losses are estimated to increase the hot water demand by 10%. Correctly installed 50mm pipework insulation could therefore reduce the losses through hot water pipe by approximately 5%.



The door is always open at eTool for questions surrounding design decisions. If a project is in concept phase we are happy to sit down for an hour and discuss potential strategies and targets. Full targeting sessions are also available at low cost to determine more accurately the costs involved in achieving design aspirations. Following this our full LCA will provide the most detailed environmental assessment available.


Cleaning dusty solar panels

solar cleaningSo after years of wondering how much impact dust had on reducing the output of a Solar PV system I finally decided it was time to get around to running my own experiment.

You’re probably asking “why didn’t he just google it and find some nice scientific paper that told him how much of an issue the dust was?”. Well I have spent a fair bit of time looking and still haven’t found any nice simple scientific papers that provide a simple enough answer for me. The numbers that do get thrown around range from anything between 1% to 50% which doesn’t really help in answering the basic question “how often should I be cleaning my panels”. I have listed a few good ones below but if anyone can send through some new links I’d be most appreciative.

Anyway I felt the best thing to do was to run a good old back yard (well roof top) experiment on my parents Solar PV grid connect system in Perth Western Australia. I installed this system back in June 2007, so coming up to it’s seventh birthday, and it hasn’t missed a beat, caused a house fire, electrocuted anyone or blown up the local network. It’s provided beautiful, problem free renewable energy and even almost paid for itself. Back then Solar PV grid connect system retailed for around $10Wp installed and now we are down to around $1/Wp, nice learning curve. It was nice just to get up on the roof to reminisce about the good old days as an installer and remember how fast the renewable energy industry has moved.

Enough reminiscing – back to the subject!

The system hasn’t been cleaned (other than rain) for over five years and Perth has just had it’s driest summer on record, so if they was ever going to be a “dusty to the max” situation the time was now.

The system is 2.79kWp with 18 x 155Wp BP Solar poly crystalline panels (yes back then 155Wp was considered a pretty big, efficient and fandangled panel) coupled with an SMA SB2500. It’s orientated pretty close to due north at around 30deg pitch on some custom made “Alex Bruce” welded steel frames.

I waited until I had two fairly similar days in solar irradiation and temperature lining up consecutively (10th and 11th of March). I then recorded the total energy output on day one, cleaned them after the sun went down and then recorded the total energy output after day two.

Drum roll…………

  • Day one = 13.68kWhr
  • Day two (after cleaning) = 13.59kWhr

A drop of 0.7%!

Now before you decide that you should go through dust on your panels I need to mention a couple of details. Solar irradiation (how much the sun did shine without clouds or stuff in the way) was pretty much spot on but it was hotter on day two (33degC vs 28degC) with a little bit less wind to help cool the panels. For those of you who know that panels don’t like getting too hot you’d probably be spotting a pretty big flaw in my highly scientific experiment.

Under these conditions I would have expected a 2-3% drop in performance. This was verified by going onto PVOutput and seeing how a few systems in the same area performed over the same two days (I had to assume some sneaky bugger hadn’t gone and cleaned them on the night in question).  I took an average performance for three systems and it seemed to show a drop of around 3.2% between the 10th and 11th of March. So instead of our system dropping by 3.2% it only dropped by 0.7% suggesting the cleaning saved or improved performance by 2.5% which is a pretty good outcome.

However the devil is in the detail.

When I was cleaning the panels I started with the hose on mist to see how much dirt would come off while simulating rain. Again very unscientific but I would suggest 70-80% of the dirt including the odd bird poo came off with the fake rain. Funny thing is we were forecasted for a storm the next day so I probably could have just let nature do the cleaning. Furthermore, this would suggest that 70-80% of the dirt has only been there since the last rain, so this massive 2.5% improvement only is really only over the last few months. Over the course of a year, I reckon I could improve the situation by maybe 1.5% at most by regular cleaning.

There was a bit of lichen starting at the corners and I had to scrub at these bits to get them off. If these had grown further and ended up over the cells then there would be more substantial drop in output (might have taken another five years). I’ve also seen branches and leaves sitting over panels so it’s definitely worth having a periodic look or monitoring your systems output (saves you getting on the roof) to pick up any substantial decrease in performance.

Now for the money side. Everyone is on different tariffs so to make it easy I’ll base my calculations on $0.25/kWhr. This system is now (after seven years) probably knocking out 10kWhr/day average over a year. So a 1.5% improvement would amount to about $14/year. It took me about 20minutes to get on the roof, give them a clean and get back down (excluding the ten minutes of reminiscing). I’ll excluded travel time and costs as I rode around on my bike for exercise and like visiting my parents anyway. With this all in mind I’d be worth $40/hr cleaning panels. If you did it for a living and included travel, writing out invoices, insurance etc you’d probably be down to $10/hr.

I should also mention I went through about 50l of good drinking water and a squirt of washing liquid in the process. I think the broom could do another 100 or so systems before the bristles fell out…

On the environmental front you could suggest that the cleaning will save another 50kgCO2e/year from avoided fossil fuel burn so maybe that alone is enough motivation to get on the roof and give them a scrub.


I think I’ll wait for the rain to clean them next time but if I ever feel like a good reminisce about how fast things have moved for renewable energy, I’ll take a bucket and a broom and head on up to the roof….



The above story is just one slightly scientific anecdotal experience and:

  • If you’re in a dryer dustier place than average suburban Perth Western Australia,
  • or if your panels are much flatter (less than say 10deg pitch) and wont self clean as easy,
  • or you’re in the path of some large migratory birds topped up on mulberries,
  • or you’re directly under very low flying air craft (see link below),
  • or you just like things being clean….
  • or you just may think differently


Some links with much more scientific rigour behind them:

Cano, J. (2011). Photovoltaic Modules: Effect of Tilt Angle on Soiling. ARIZONA STATE UNIVERSITY. Retrieved from

Mejia, F., & Kleissl, J. (n.d.). Soiling Losses for Solar Photovoltaic Systems in California. University of California. Retrieved from

Sulaiman, S. A., Hussain, H. H., Siti, N., Leh, H. N., & Razali, M. S. I. (2011). Effects of Dust on the Performance of PV Panels. World Academy of Science, Engineering and Technology, 58, 588–593. Retrieved from

Denver, J., Miller, J. T. A., Manager, P., Jackson, J., Engineer, S. D., Gupta, V., … Hoffner, J. (2009). Impact of Soiling and Pollution on PV Generation Performance Performance Loss Due to Pollution (pp. 1–5). Retrieved from






The Secret to Solar PV versus Solar Thermal

With so much sunshine in Australia, solar power is one of the most popular renewable energies for residential buildings. So our clients often ask us which system is the least carbon intensive and best for their budget – solar PV or solar thermal.

In this article and presentation Pat offers some key considerations to help you make a sound decision when choosing between the two technologies. Read more >>

Synergy’s Carbon Tax Charges

How to “opt-out” from Synergy’s unethical carbon charges

From the 1st July 2012, WA electricity retailer Synergy has decided to pass on the additional charges due to the Federal Government’s Clean Energy Legislation to ALL of their customers, including those who offset theirelectricity carbon emissions through EarthFriendly (also known as GreenPower).

While it is technically legal for them to do this, this doesn’t change the fact that it is unethical, and that there isno moral justification for why Synergy EarthFriendly customers should have to pay twice.

Here’s how you can“opt-out” from Synergy’s unethical carbon charges:1. Don’t cancel your EarthFriendly subscription. Generically known as GreenPower,this is still one of the best ways you can support the uptake of renewable energy inAustralia.

2. Calculate the cost of the carbon tax for your electricity. Don’t worry! Synergy hasalready worked it out for us:



3. When you receive your next electricity bill, look at how many units of electricitywere used for the billing period. This number usually appears on the second pageof your bill, under the heading HOME PLAN (A1) TARIFF.

4. Multiply this number by the carbon tax per unit number above. For example, if you used 1200 units of electricity in the billing period:

1200 X 0.02255 = $27.06

5. Subtract this number from the TOTAL DUE figure shown on the first page of yourbill. This new figure is the amount you should pay.

6. Because you are 100% subscribed to EarthFriendly, you have alreadyaccounted for your electricity carbon emissions.1

7. Let Synergy know why you have paid this amount. The more people that objectto their unethical behaviour, the sooner they will realise their mistake.

*Sourced from Synergy. We have converted it from cents into dollars.

1 If you are not 100% subscribed to EarthPremium, you will need to adjust the amount deducted at Step 4 accordingly.

Email Sid to share your thoughts.

Comparing Solar PV Systems

There seems to be a lot of confusion over solar PV; do they ever pay for themselves, is getting more kWs better and are they the best way to offset? Our clients regularly ask us these questions, so we came up with a simple way to help you find the answers.

We’ve put together a short LCA comparing an average Australian 3X2 house (benchmark), one with a 1.5kW solar PV system and one with a 5kW solar PV systems to show you how they perform on cost, embodied and operational carbon and design life.

There will be quite a few numbers coming up on your screen, but don’t worry we’ll be summarising them afterwards…

So what did you think, still confused?

As you can see from the video choosing the right solar PV system for your home has the potential to save you money and carbon both in the long and short term. In this LCA we haven’t included any government rebates at all and have worked with an average of ‘one for one’ unit of grid electricity. This gives you an average indication of savings across the design life of your house, whether it’s 15, 35 or 40+ years.

Here are some of the final figures…


Total design life cost over 15 yearsTotal design life cost over 35 years
Benchmark Home – $168,393*Benchmark Home – $208,144*
Home with 1.5kW – $167,982*Home with 1.5kW – $197,285*
Home with 5kW     – $167,023*Home with 5kW     – $171, 948*



Embodied and operational carbon used over 15 yearsEmbodied and operational carbon used over 40 years**
Benchmark Home – 193,795 tBenchmark Home – 414,123 t
Home with 1.5kW – 160,922 tHome with 1.5kW – 321,386 t
Home with 5kW     – 80,107Home with 5kW    – 104,474 t


As you can see, both 1.5kW and 5kW solar PV systems are paid back within 15 years. Further into the design life of your house, they will start to save or earn you money depending on how much electricity you are using, generating and exporting.

Eventhough 5kW looks like the best solution, the initial cost outlay is considerable and there are other factors to consider. If you are looking to build a carbon neutral house, (in terms of embodied energy) using a smaller 1.5kW system and changing elements of the construction method can help you acheive this.

Have a look at some of our case studies to see what size systems other people have used.

* These costs are approximate and based on the costings in the LCA at the time of assessment.

**This takes into account the replacement of the solar systems every 20-25 years.


Written by Siobhán McGurrin.