Case Study – Our Solar Power System

Gavin Webber Solar Power system

A very interesting thing happened over the last few days.  Energy Matters, the company who installed my solar panels and inverter contacted me to perform a case study about our solar power system.

I am happy to say that after nearly 7 years (installed 4th September 2007), it is still going strong with no flaws whatsoever.

Solar Power System – Case Study

Here is an extract of the case study;

System Capacity: 2.8kW

CO2 reduction: Approximately 5.46 tonnes per year

System Specs: Sharp solar panels, Fronius IG 30 inverter

Installation: September 2007

More than 6 years after installation in the Melbourne suburb of Melton, Gavin Webber’s Energy Matters solar power system is continuing to generate high levels of solar electricity  – as we would expect!

“Our 2.8 kW system has generated a total of 24.668 megawatt-hours since installation without flaw,” says Gavin.

Even based on a conservative value of 25c per kilowatt-hour; in today’s money (March 2014), that’s over $6,000 worth of electricity.

You can read the rest of the case study here; Solar Power Case Study – Webber Home

The Real Numbers

The case study was fairly accurate, however I took the liberty to break down the numbers further.

The estimate of the value of the electricity is very conservative.  The daily average generated over its lifetime is 10.34 kilowatt-hours.  I worked out that we have had our solar power system installed for 2387 days.  We received 1:1 pricing at around 25 cents per kilowatt-hour for 575 days which equals about AU$1486.38.  This was before a feed-in tariff was legislated here in Victoria, Australia.

In April 2009, we started to receive a generous feed-in tariff of 66 cents per kilowatt-hour for exporting electricity to the grid.  So that is 1812 days at the higher rate.  This works out to be AU$12,365.81.

So the grand total of electricity generated is AU$13,852.19 over its lifetime.  Now dear reader, that is not what I received in my hand during the period.  That figure is what the electricity was worth if I exported it all back into the grid, which is not how a system like this works.

How It Works

If the system is active i.e. the sun is shining, our house uses what it needs first (depending on what appliances are on), then it exports to the grid.  If the demand in the house is more that what is being currently generated, then it draws the additional energy from the grid.  Similarly at night, the solar power system is off, we draw from the grid until the sun rises again.

This is how the vast majority of grid tied solar PV systems function, unless it is a hybrid system (augmented with a battery bank).  There are, of course, off grid systems which rely completely on batteries for storage, and sometimes require a diesel generator for backup.  We do not have this type of system.

Also, if the grid goes down for example a blackout, our inverter turns off and we lose power to our house.  This is because if the power company is working near our home, and our system is active, it will not pump electricity into the line while they are working on it.  A fair enough safety feature.

Don’t forget that you should perform some half-yearly maintenance to get the full capacity out of your system.  It is easy to maintain, and the panels only require cleaning with a squeegee.  More details can be found in this post, titled 4 Maintenance Tips for Solar PV at Home.

Environmental Benefits

In addition to the financial benefits, the environmental ones have been massive.  Without investigating, I originally sold the Renewable Energy Certificates for the system.  This meant that the carbon reduction was sold off to whoever bought them on the market.

To correct this mistake, I ensured that I purchase GreenPower from my electricity provider, which, in effect, is the same result.  I estimate that we have reduced our greenhouse gas emissions by over 6 tonnes of CO2-equivalent per year.  That was over half our carbon emissions when we measured it at the beginning of our journey.

Also, we noticed that our behaviours changed dramatically.  Because we generated our own electricity, well most of it, we became more aware on how much we wasted.  All the teenage kids who were living at home at the time pitched in, but none more so than Ben who was seven at the time.  He was like the electricity police, telling the other off all the time for leaving appliances switched on when they were not in their rooms!  Brilliant stuff, and an effect that we had not anticipated.

Gavin Webber turning on Fronius-I30 inverter

Final Thoughts

I love it.  I love the thought that all our electricity comes from green sources and that we generate most of our own.  I love the fact that we have no electricity bill (averaged over 12 months) and that I can use that saving to pay down the mortgage much quicker.

Even though there are not as many government rebates and that feed-in tariffs are lower, the cost of solar PV systems have dropped 10 fold.  It is still worth getting one installed on your roof.

Who has taken the leap to solar PV, and what do you think of your system?



  1. Claude says

    Hi Gavin,

    I just had a 2kW system installed on my roof last week and my meter changed over a couple of days ago so am now all good to go! I did a whole lot of research before taking the plunge and ended up going with Energy Matters (thanks to your recommendation).

    I also recently changed my electricity retailer to Click Energy as their feed in tariff is 10 cents/kWh while the other retailers in NSW are 7-8 cents ( or less). I’m actually looking forward to my next bill!

  2. Steve says

    Gavin, I think you will find that changing your power usage to take advantage of the solar during the day and the cheapest prices at night (if you are on a smart meter) is far more cost effective and environmentally responsible than running a complete house on a hybrid system. Solar may be cheap to install but good quality hybrid inverters and batteries are not. Use the power as it is generated from the sun and save 30 cents rather than get paid 8 cents from the power companies or spend 70 cents to store and use your own. There are a lot of appliances these days that have timers installed (set the washing machine, air con and dishwasher to start at lunch time before you go to work)

    • Gavin Webber says

      Have a listen to my latest podcast episode 055 from 23:43 point. I describe exactly what a hybrid system is and the benefits.

  3. emily says

    I’m looking into getting one now as have finally become a homeowner. There’s no lovely feed-in tariff in Victoria (Melbourne) anymore, you only get 8c. So the advice I’ve received is not to bother with a big system because the pay-back is low, especially as our house is very efficient (usually less than 3kwh a day). But part of me wants to get as much as will fit on the roof for the principle of the matter. And I could potentially switch some of my gas things, like the heating, over to high efficiency electricity in the future.

    Anyone with any thoughts on that?

    • Gavin Webber says

      I think that you may have struck upon something there Emily. Your electricity usage is quite low, so it may not be something you need. However, if you bought a smaller system that was a hybrid with battery backup, you could store the electricity during the day when most people are at work, and use it freely at night time when you get home. Might be worth investigating. Gav

  4. foodnstuff says

    Good post, Gav. I’ve had my 3.9 kW system for 6 months and I love it. Have had some issues with the first bill (generation has been counted as consumption) and they are in the process of sorting it out, but I expect to be in credit. You are right that solar makes you more conscious of energy use…I’m determined to take as little from the grid as I can and would love to go off completely.

    • Gavin Webber says

      Nice one fns. Hope they fix up your bill this time around. I had a few metering issues at the start as well, but it only took one call to fix it up. Gav

  5. Dianne says

    I live in government housing and would love to have solar power. I think there should be a deal made, for those who want it, where the Housing Department install solar panels, that we pay for, with a slight affordable increase to our rent payments. We could afford this with the savings on our energy bills, but just don’t have the money upfront. The only problem is would they try to do it on the cheap and employ dodgy installers? We should be able to pick reputable companies to do the installation as we are going to be paying for it. Just a thought.

    • Gavin Webber says

      Hi Dianne. Now that would make a lot of sense. Not only would it make electricity cheaper for renters,it more affordable, but it becomes an asset for the Housing Department as well. Hopefully if they see it that way, they would not bring in the dodgy brothers to install it.

      A good thought indeed.

  6. Paul Andrew says

    We couldn’t wait to move in to our own house so we could get solar. at the time with buying the house and everything else we could only afford a small 1kw system. my only regret is not investing in a larger system back then. our system does generate enough during summer to offset our usage but we pay a modest amount over the winter period. it too has made us look for efficiency gains wherever we can find them!

    • Gavin Webber says

      Hi Paul. Even a 1kW system is worth it for offsetting some of your electricity costs. The efficiency gains certainly do make a big difference as well. It is a little like comparing electricity usage to living within your means. Well done.

  7. Graeme says

    When you read the fine print on the TV adds, what does it mean when they retain the carbon credits generated from the installation, ie TrueSolar.

  8. Deb says

    Hi Gavin, I’m just putting in a 3 kW system for our house. I wanted to install 5 kW but Powercor would only allow 3 kW. Disappointing, but at least we can still get the 3 kW. I’m definitely planning to move to a hybrid system with batteries over the next couple of years as prices fall. Will you do that or are you happy with using the grid for back up?

    • Gavin Webber says

      HI Deb, Once I am happy with the price point, I will change over to a hybrid system. Little bit too expensive still.

  9. says

    Great post Gavin. We will be getting solar when we get to NZ and It is great to learn about the ins and outs of it all from someone who has had a number of years experience living with.

  10. ennoh412 says

    With 5 teenagers at home and big power bills, solar is becoming more and more attractive. Running the air con through the really hot days here in Perth recently meant that our average daily use was in the order of 40 Kw per day. Would a large solar system come anywhere near to reducing that sort of energy usel? What is the largest system available? We have just moved into our dream home and so we want to really seriously consider solar power.

    • Gavin Webber says

      It all depends on how much roof space you have. You can get systems up to 10 kilowatts for residential homes, if you have the money. The world is your oyster really. I highly encourage you to get a few quotes before you take the leap.


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