Science Interviews

Interview

Sun, 20th Apr 2008

Sustainable Solar Solutions?

Dr Karl Kruszelnicki

Listen Now    Download as mp3 from the show Houses of the Future

Richard - This week on the show we’re looking into ways to live sustainably.  We’ve already heard how Ben and Dave are using sunlight to get drinking water from waste, but what about using the sun to generate electricity?  Solar panels seem to be turning up on rooftops all over the place, but are they really worth using?  You may be generating electricity for free – but how long does it take to pay back the costs of buying them in the first place?

And as with all technology, you need to use energy to make it in the first place, so do they cost the environment more than they give back?

Chris - To find out, earlier this week I spoke to Australia’s Dr Karl Kruszelnicki who recently turned his home in Sydney into the solar equivalent of a power station.

Photovoltaic solar panels on the roof of a house near Boston MassachusettsKarl - I’ve installed on my roof one of the ten biggest domestic (that is, on a private house) solar arrays in Australia.  There’s about 4.5kW and since September I have generated about 3000 kilowatt hours; I have used 1800 kilowatt hours and so in fact now I am a primary producer of electricity.  I supply electricity to the grid.  Shove it in the daytime, suck it back at night.

Chris - How did you go about setting it up and why?

Karl - Why was as an example to show that it could be done and that it should be done.  How is very straightforward, you find the appropriate people and give them a big bag of money.  You just open your wallet and repeat, “help yourself, help yourself, help yourself!” I’ve got 27 cells on the roof, 165 Watts.  They cost $1800 each.  Then there’s the inverter, that’s $7000; permission to the council for $2000.  I had to put in the same development application as if I was putting in a ten-storey block of flats – and labour $2000.  Basically, an average person’s yearly salary is what it cost.

Chris - How long do you think it’ll take you to pay that back in terms of how much you’re getting in terms of the electricity you’re selling back to the grid?

Karl - At the moment probably around 250 years.

Chris - Seriously?

Karl - In most of Australia, you buy it at a certain cost and sell it back at the same cost ,even though you are taking a load of the grid.  In Germany they recognise this and they pay you seven times as much as you pay.  If you buy it at x you can sell it at 7x.  Then the payback time is a lot shorter.  The payback time in energy is about 18-14 months depending on what part of the world you are in, what cloud cover you have, etcetera.  Where I am, in sunny Sydney, the payback time is 18 months.  The cells have a guarantee of 25 years but they’re confidently expected to last for 40 years.

Chris - That’s all very well if you live in Sydney because having lived there I know there’s lots of sun there.  How would the set-up here compare because most days it’s cloudy.  In summer there’s a bit of sun.  How much sun do you need to get in order to make this system work?

Karl - With your energy costs the way they are in England you’d need probably a 7kW array maximum.  You would be running it at lower efficiency because you would have less sunlight.  At the moment solar cells are expensive because the price of silicon has gone up by a factor of 8 over the past few years.  However, when I was an engineer one thing I learnt was do not reinvent the wheel.  Nature, via trees, is doing a wonderful job of turning sunlight into electricity.  Once we humans learn to copy that better I’m sure that we’ll get cheaper solar cells.  Part of the energy equation will be solved by having every roof in the world stuffed full of solar electricity and solar hot water.  It doesn’t matter if you’re getting lots of sunlight or not, at least you’re doing something to get energy for free with regard to carbon dioxide being the cost.

Chris - How much carbon dioxide have you prevented from going into the atmosphere because you’ve set this up?

Karl - 4.9 tonnes, I read proudly tonight before I came into the studio.

Chris - Have you got some kind of gauge that measures how many carbon dioxide equivalents you have sold back to the grid?

Karl - Yes.  It tells me how many cycles the grid is producing, what voltage they’re producing.  So depending on whether it’s peak hour the cycles go up or down, the volts go up or down.  The big train full of 2000 people in the subway starts to pull out and you can see the voltage suddenly drop: the big load comes on.  This tells me my peak output.  In high summer when I have the best orientation with regard to the sun I can typically produce 32 kilowatt hours a day when I am using about 18-15 [kWh].  Now as we’re headed past the equinox on our side of the equator I’ve been generating 24 [kWh] a day.  I’m still ahead of my 18kWh and I’ve come across a family in Perth who run their house on 3kWh a day.  Your fridge uses 1.5kWh so they must be extremely frugal and I’m very happy to learn from them how they achieve this magnificent economy of electricity.

Chris - But there’s more to running your house than just the electricity?  Presumably you must be heating your water so is that included in your equation?

Karl - Water we do via gas because to generate electricity in some distant place and then send the electricity across you get big losses.  It turns out the losses are less if you pipe gas and then you burn it in an instantaneous hot water heater rather than a storage hot water heater.  We’re busy planning how to dig a hole in the front yard and put in a 50 tonne underground water tank which should be able to float us through the year so we don’t have suck any water from the grid.  We will still have to suck gas from the gas supplier to turn that cold water into hot water.  The next stage of the equation would be to put hot water on the roof as well.

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