Fuel Consumption of a Pedestrian Crossing

Once or twice a week, encouraged by my wife, I hop on my bike and pedal a few km down to a local gym. On the way I have to cross South Road, which is a major arterial road here in Adelaide. The only safe way to get across is using the pedestrian crossing at a set of traffic lights.

Something has been bothering me about this pedestrian crossing – how much fuel was I wasting by crossing that road? Today I decided to quantify my fears with some numbers – when I pressed the button I counted about 40 cars and 10 trucks up to semi-trailer size that I had stopped. I estimate that a total mass of 40(1,300) + 10(10,000) = 152,000 kg needs to be braked to a stop, then be accelerated back up to 50 km/hr by burning fossil fuels.

Now 50 km/hr is about 14 m/s, which means the total energy of this moving column of vehicles is 0.5*m*v*v = 14.9MJ. So 14.9MJ is required to take the mass from 0 to 50 km/hr, which must come from fossil fuels. I think petrol has about 32 MJ/litre and I estimate that an internal combustion engine is 10% efficient in converting fossil fuel to kinetic energy at the varying loads required under acceleration. For the sake of argument I will assume all the vehicles run on petrol, although the trucks would of course be diesel and a few of the cars LPG. Anyway this means to take my bike across this pedestrian crossing requires 14.9/(32(0.1)) = 4.6 litres of fossil fuel, plus some fuel consumed in idling and a few extra minutes to the journey of at least 40 people. At current prices that’s about AUD$6 of fuel, or $12 for the two way trip to the gym. Although to be fair today a fellow biker crossed with me so lets call it $9 for the round trip.

My conclusion is that the world supply of fossil fuels declines by 4.6 litres every time I press the button on that pedestrian crossing.

In comparison if I had taken my inefficient 6 cylinder internal combustion car (about 7km/litre on a short trip in traffic) I would have used about 1 litre or AUD$1.20. My car would travel with the traffic and not cause a red light at a pedestrian crossing. If I had taken my electric car then about 28 cents in electricity (at current peak rates here in South Australia) would have been used. I draw no conclusion from this, as intuitively using a bike is much better than even an electric car.

To be honest 14.9MJ and 4.6 litres seems low, can anyone suggest a different way of working this out or spot an error in my estimates?

EV Battery Tester

I am interested in testing my my EV batteries – for example to measure the effects of various charging strategies. So I dreamed up a system using a WRT54G router and my little $2 PIC based voltage and current sensor WISPCAR board from last year. The WISPCAR board senses voltage and current and sends them out a RS232 port at 4800 baud. It also has a watchdog timer, and costs about $2 to make.

With our recent Mesh Potato work I have routers and serial ports on my mind. I have also been in touch with Bart from the Flukso Project who are using routers to monitor home power consumption – another area I am very interested in.

Routers are cool data collection devices. They are essentially mini-Linux systems so you can so all sorts of clever things like use shell script and connect them to the Internet. They usually have unused serial ports (WRT54GL’s have two) and often a few GPIOs. Best of all they are wireless – so you can start a test running then monitor it from your laptop some where else in the house. It’s “a good thing” to monitor battery tests like these as the power levels involved are substantial and there is the possibility of expensive battery damage.

I connected the WISPCAR board to my PC via a RS232 cable and it worked first time, even though it had been a year since I last used it. Despite surviving in my junk box for that long I promptly managed to blow it up in about two hours, I think I put 12V into one of the PIC A/D ports. Oops. The prototype was built on veroboard which was painful to flip over all of the time. So I rebuilt in “Manhatten” style so all the parts were on the top. Pretty, isn’t it!

Finding an 40A Load

To test my EV deep cycle batteries I wanted a load of around 40A, as that is the 60 km/hr “cruise” current of my EV. Finding a way to discharge batteries at these sorts of currents is not as easy, for example you would need at 0.3 ohm 480W resistor. It’s also nice if the current stays constant for the duration of the test, despite heating of the load and the battery voltage changing from 12.5V to 11.5V as it discharges.

I used a suggestion from the EVDL – a couple of 300W 12V to 240V inverters. I scurried around the house for a few hours, trying to find some 240V devices that were in the several hundred Watt range. Hairdryers, curling wands, and bedside lamps mysteriously disappeared from the house, only to re-appear on my bench in the shed! Finally I settled on a couple of bedside lamps with 60W bulbs, and an oil filled electric column heater connected to a Variac. The Variac allowed me to finely adjust the current to get exactly 40A. I measured the current using a 100A shunt connected to the battery (1mV/A).


I modified the PIC assembler code just slightly. To avoid over discharging the battery I wanted the watchdog timer to stop the test if the router should fail to poll the PIC every 20 seconds. Normally the watchdog drops the power for a few seconds, then restores it, to reset the device it is monitoring. The watchdog controls a 12V/40A automotive relay that can stop and start the test under control from the router.

It’s possible to connect WISPCAR directly to a PC using a RS232 adaptor, this is how I did most of my development. So the router is not really required, I just felt like doing it that way to explore the idea.

Getting the WRT54GL router serial port to work correctly was tricky. I couldn’t get the first serial port to change from 115000 to 4800 baud using the stty command. Every time I set it some other piece of software set it back! This port is configured as the serial console, however the second RS232 port on the router was free and I had better luck changing it’s baud rate to 4800.

To make WISPCAR work I needed to send commands and log data from the WRT54GL serial port, preferably under the control of shell script so I didn’t have to write and cross compile any C code. A few hours of head scratching and Googling led to this solution. To write a character to the serial port:
echo -n 'w' > /dev/tts/1
This command resets the watchdog timer and prompts WISPCAR to send a line of data. This data is read like to a file called “w” like this:
dd if=/dev/tts/1 bs=1 count=36 1>w 2>/dev/null
Good old dd to the rescue. I initially tried:
cat w < /dev/tts/1
but it wouldn’t send me the line until the sending device sent a Ctrl-D (end of file). In practice you start the read line first then send the command to wispcar:
dd if=/dev/tts/1 bs=1 count=36 1>w 2>/dev/null&
echo -n 'w' > /dev/tts/1

Each line is exactly 36 bytes long and contains some status information plus the voltage and current A/D samples. From then on it’s easy for shell script to extract the voltage and current samples and save them to a text file with a time-stamp. The shell script also monitors the voltage sample and stops the test at a certain threshold.

The text file output is easy to grok and plot using Unix tools like cut and Octave. Or the text file could be imported into a spreadsheet if that’s your thing. As the discharge current from the inverters is very stable, the AH capacity of the batteries can be calculated from the time the test ends. Here is a sample output plot.

Note the rough shape of the graph. Part of this is sampling glitches – electrical noise (perhaps from the inverters) upsetting WISPCAR as it samples. The chunky step size is due to the 8 bit resolution of the PIC A/D, that works out to about 1 bit/100mV which is a little coarse for this application. However even with this noise the system is effective in measuring the AH capacity of the batteries – the main goal of this work.

WISPCAR Hardware Mods

To reduce the sampling noise I made a few hardware changes. Here is the latest schematic. To the current sensor I added a capacitor to roll off the bandwidth at 10Hz and effectively reduce the gain for any high frequency noise signals. I lowered the resistor values in the Voltage sensor divider to lower the impedance and reduce the impact of any induced noise. I also added some filtering capacitors to lower the frequency response to about 10Hz. This removed most of the glitches for the next few tests:

Note this test starts at 13V – the battery had just come off charge. This discharge time (and hence capacity) is the same as the first test plotted above with the same battery.

A further improvement would be a higher resolution A/D or a way to just sample the 13-10V range, at the moment much of the A/D range (for example 0-10V) is never used and hence wasted.

The current sensor wasn’t really needed as the load current stayed constant. However I would like to work on that some more one day – it seems to have some problems I don’t quite understand like offset error (I am weak on op-amps). The ideal circuit would amplify a mV level differential DC signal (e.g. 40mV from the shunt at 40A) up the the 0-5V range of the A/D in the PIC. It has to be differential as we are sensing the current on the “high side”. Note the + current sense wire must be separate to the 12V power lead to avoid power to WISPCAR flowing thru the current sensor wires and inducing an additional voltage offset.

Going Further

There are many applications for the combination of a $2 PIC circuit and a router. So far I have used the combination for monitoring a solar power Wifi station and testing EV batteries.

This system could be simplified a lot to make it friendlier for the non-Linux geek. For example the router could present the battery discharge data as a web page on it’s internal server or even generate graphs. The test cut off threshold could be set using a web-based GUI.

Original WISPCAR post
WISPCAR SVN containing schematics and source code files
David’s EV Page
Flukso Project

Kjell Aleklett Lecture

Yesterday I took a much needed break from Mesh Potato hacking and pedaled into Adelaide University to see a lecture by Kjell Aleklett, who is the president of the Association for the Study of Peak Oil and Gas who is visiting Australia this week.

Couple of important points that I took away:

  1. Kjell explained the physical process by which oil percolates through porous stone to oil wells – he then made the point that economists think that oil flows are propelled by money, not physical processes. In other words economists (and therefore governments) think money can overcome physical supply problems. Oops.
  2. The estimates of greenhouse gas emissions and hence global warming are based on continued growth of fossil fuel use. However these estimates do not take into account the actual peaking of oil, gas, and coal supplies. When the limited supply situation of fossil fuels are modeled, greenhouse emissions are constant over the next 50 years. If fossil fuel supply is limited, you limit huge increases in carbon dioxide concentrations.
  3. All current economic models assume unlimited future growth. Growth requires fossil fuels, which are reaching the limits of physical supply. For example if our population increases, we need a new suburb, and new cars to handle commuting. So if fossil fuels are limited, this means that from now on economic growth will be curtailed. No economic growth means the current economic systems break.


My original post on Peak Oil.

Some thoughts on our obsession with economic growth.

A Drive in the Mitsubishi MIEV

Today I was fortunate enough to go for a drive in a MIEV, the single demo unit that is on tour around Australia! This will probably be the first of the new generation of production electric cars (fingers crossed).

Funny how these things come about. I was sitting down to lunch on Sunday talking to one of my wife’s friends, Nina. She mentioned that she was a receptionist at Mitsubishi Adelaide, and told us the staff would be having a test drive of the MIEV today.

Say what? I didn’t even know it was in town. I was pretty excited so Nina kindly asked the Mitsubishi people if I could take a look at the car, and I was invited to join Nina on a test drive! WOW!

So at 3pm today I hopped in my EV and electo-commuted down to Mitsubishi HQ. Just as I entered the car park I saw the little MIEV cruising around. It pulled over as they changed drivers. Suddenly, just as I was passing the MIEV suddenly shot out in front of me – if I hadn’t hit the brakes we might have had the first EV on EV collision. Try explaining that to the bosses back in Japan!

The MIEV had a big sticker “Australia’s first Electric car” on the back. Ahem. Really? Then what, exactly, am I and probably 100 other Australians driving? They can’t even say “first production EV”. Yet (production starts in July).

Anyway Nina and I waited patiently and soon is was our turn. I hopped in the spacious rear of the car (heaps of leg room and height) while the Mitsubishi engineer minding the MIEV (Ashley) showed Nina how it worked. It has an automatic style gear selector but basically its D to drive and off you go. Nina drove us around the nearly empty and spacious Mitsubishi car park, getting up to about 50km/hr. We got a good feel for the acceleration and regenerative braking (both good). It felt nice and light compared to my lead-acid EV, especially over speed bumps. Easy to drive and a nice little car.

The instrumentation was a speedo, a charge/discharge gauge, and a battery bar graph. I missed the presence of an ammeter and voltmeter, but I guess part of the magic of a production EV is abstracting some of the technical detail away from end users.

It has a home charger (overnight) and a fast charger (30 minutes to 80%). The fast charger requires something like 50kW – equivalent to a whole suburban block here. It would make the street lights go dim! Anyway I figure that just like our EV the regular charger is good enough. Filling up an EV is not like filling a petrol car, you don’t stand around waiting for it to fill up. It’s more like a mobile phone, you just plug in and walk away.

After the MIEV Nina asked if she could try my EV! We followed the same course and curiously it felt and drove much the same. Nina said both cars felt great. If my car had Lithium batteries (i.e. equivalent range and weight) there wouldn’t be much in it at all.

The MIEV project is one of the new breed of factory EVs. I really hope it goes into large scale production and turns up in a showroom soon at a reasonable price. Good on Mitsubishi for making this happen.

The Amazing Rocket Stove

I just built a Rocket Stove out of 3 tin cans and tested it by making my morning coffee:

My 10 year old son then followed up by frying an egg. Each time we used a tiny amount of fuel; a bit of cardboard to get it started and maybe two sticks 1cm wide by 10cm long, weighing a few grammes:

Rocket stoves are very efficient as they burn the fuel at high temperature. You can see some ash between the inner and outer cans above which insulates the combustion chamber. Air flows under the tray in the magazine which is preheated before combustion. They can be built in a variety of sizes. Mine used a small paint tin as the outer container and is big enough for a coffee pot or small fry pan. A larger one (say using a 5 litre oil can) could handle a families cooking.

I am interested in Rocket Stoves for a couple of reasons:

  1. On our recent trip to East Timor, I noticed most people cooking on 3 stone fires. This is causing environmental (and practical) problems as vast amount of firewood are being used up. The cost of the wood fuel is also significant for people in one of the poorest countries in Asia. So an efficient wood stove could really help. Rockets Stoves can be built out of locally sourced materials (old tin cans, bricks) and could generate much needed employment.
  2. I am interested in heating my house from wood this winter, but don’t want to pay $3,000 for a commercial slow combustion wood heater. So this little stove is a first step. I have seen some heating stove designs that use bricks and old drums to make efficient radiant heaters.
  3. I am interested in alternatives to fossil fuels like natural gas for cooking. Over the last few years we have been taking steps to improve our home energy efficiency and in particular reduce fossil fuel consumption. Our last gas bill was trivial ($12 gas, $50 supply charge) as we have solar hot water. The low fuel consumption of a Rocket Stove means we could supplement our household cooking with fuel from garden waste, e.g. sticks and other garden material I usually throw out!

It took me three tries to get a working stove; I spent a pleasant Saturday afternoon messing around with tin snips and tin cans and like everyone I love playing with fire! My Rocket Stove takes a little while to start burning well, but once it does you get a small, very stable flame. Almost like a gas stove, but coming from one little stick. It’s easy to control, just slide the sticks in or out of the magazine.


I used the tin can Rocket Stove example in this Capturing Heat booklet.

What I would do with $43B

The Australian Government has kicked off a $43B National Broadband Network (NBN) to give everyone in a Australia a 100Mbit/s fibre connection. It’s the biggest infrastructure project in our history, and represents about $2100 per person of unfunded government debt. The theory is that it will make us more productive, help education, health and business.

Funny thing is I am quite content with my 1Mbit/s DSL, in fact I could live with 128kbit/s for my web surfing, email, and occasional tarball download. I find email to be the most useful thing on the Internet, and that works fine over dial up. My kids soak up the extra bandwidth for movies, but that is hardly making the country more productive (probably the opposite). The best thing about DSL is that it’s always on, rather than the speed. Maybe I am atypical, but I have never said, “I wish I had faster Internet” while using DSL.

Reminds me a bit of Windows and MS Office. Once a certain level of performance/GUI was reached (Windows 95 and MS Office 97) everything that came afterwards was (expensive) fluff. Well once I obtained always on connectivity via DSL, I reached that “good enough” point.

I think we can do better. Here are some ideas I have for spending AUD$43B over 8 years:

  1. EV conversions: Lets convert every small car in Australia to be a 100km range EV. Now there are 20M people here, so maybe 5M small cars. That gives us $8,600 per car. A current 100km conversion in quantity 1 costs about $25,000, but in quantity 5M we can expect some big discounts for volume, so $8,600 should do it. Actually for $8,600 each we could probably build new EVs, however recycling a petrol car saves a lot of energy embodied in the manufacturing process. A 100km range EV would cover 90% of the populations driving needs (it does for our family). Pleasant side effects would be the creation of a new (export) industry, lower greenhouse emissions (if charged from green electricity), and radically reduced dependence on foreign oil.
  2. PV solar or Wind: Lets put PV solar on every house in Australia. I am guessing there are about 8M houses (2-ish people per residence), this means $5,400 per residence. A 1kW PV system costs about $12,000 today (although we currently get an $8,000 rebate). However it’s reasonable to assume at least 50% plus quantity discount for 5M so $5,400 should do it easily. That’s a total of 5GW of PV solar. That’s about twice the current peak electricity generation capacity of the state of South Australia where I live. Actually that’s probably pessimistic, industry standards are drifting down to USD$2/watt, so $43B would give us 15GW of PV solar (at 1AUD = 0.7USD). With wind power we could do even better, $43B would buy us perhaps 30GW at such a high level of investment. Now 30GW ($1USD/watt) at a wind power activity factor of 30% is 30E9(0.3)(24 hours/day)(365 day/year)/(1E3 W/kW) = 78BkWh/year. In 2005 Australia consumed 220BkWh, so thats a big chunk of our power. With some reasonable electricity consumption measures we could probably live on one third of our current consumption.
  3. Mesh Potato: The Mesh Potato is a Wifi mesh router with VOIP. You place one on your roof, and it self-forms a telephone network by talking to other Mesh Potatoes on nearby houses. It doesn’t need cell phone towers of land lines. Or phone companies. Lets say in very high volume we can install a Mesh Potato with a solar panel and battery to power it for $100 per house. With $43B we could install 430M mesh potatoes. That’s too many for Australia (only 8M houses), so we could put one on every house in Australia and North America. Or globally its one for every 28 people on the planet. Even better – distribute Mesh Potato networks to the poorest 1B of the world, which makes in 1 phone for every three people. This would build a global telephone network so we could all make free phone calls to each other. As a side effect it would build a free Internet backbone that is independent of land lines, governments, cell phone towers (it uses unlicensed spectrum), and telephone companies. Obviously some scaling and number of mesh hop problems but for $43B I am sure they can be solved!

Peak Oil and Why Growth is Evil

Oil has no future. Really. Just look at this graph of oil discovery (borrowed from this excellent Peak Oil Overview). The graph shows oil discovery (in billions of barrels) per decade.

Now oil discoveries peaked at about 500 billion in the 1960’s, about the time I was born and started crawling towards anything electrical and driving my Mum crazy. World wide we use around 85 million barrels/day, or 30 billion a year. So when you read the next mainstream media article about a “billion barrel oil discovery” remember that 1 billion barrels is just 12 days world oil consumption.

So 30 billion barrels a year is 300 billion a decade. Now look at the graph above. In how many decades did we discover more than 300 billion barrels?

And what is this fixation with economic growth? Politicians seem to be telling us we are all doomed unless we constantly grow the economy. The worst thing about the financial crisis is that we might now get “growth”. growth Growth GROWTH!

The problem with x% growth is that it is exponential. That means we consume more and more every year. It goes to infinity real fast. More oil, more water, more people, more money, more debt. Just 5% growth means doubling every 14 years. One small oversight guys: nature is finite. A good example is yeast growing in a Petri dish. Nature always shuts down exponential growth. Always. Usually by killing everything in the Petri dish.

Economics is busted as it depends on the ultimate unsustainable practice – exponential growth.


An earlier post on Peak Oil.

Driving Strike

Between May and August 2008 I went on a driving strike – for 3 months I didn’t drive a car. It all started late one May evening. I was driving along the freeway on the way back to Adelaide. This was at the recent peak in fuel prices so I was actually driving at far less than the freeway limit (only 95 km/hr) to experiment with saving fuel. Probably daydreaming about VOIP or echo cancellers or Electric Cars knowing me. Anyway I missed the end of the freeway 60 km/hr sign and the friendly South Australian Police were hidden just a few 100m after the sign around the next corner, booking me and a bunch of other people.


Another bloody fine. Between my wife and I we have blown $800 in fines this year! In South Australia revenue from tickets is a budgeted income item for the government. It’s a big business here, just like taxes on gambling. Just like some people can’t help gambling, it’s human nature for people to accidentally exceed the speed limit. So the SA government does it’s best to extract revenue from pensioners playing poker machines, and people driving cars. They regularly put the fines up ($300 for 15 km/hr over the limit at present), and use all sorts of tricks like speed cameras hidden in rubbish bins. Of course all the real criminals are locked up so it’s just us speeding motorists left now.

It’s got to the point where my wife and I actually budget for speeding fines each year, they are just such a part of life for everyone in this State. Unfortunately we got our 1st fine on New Years day (56 km/hr in a 50 zone) so there goes the 2008 budget! A lady from my wife’s church copped THREE fines in one day – they changed the local limit to 40 km/hr near her house and she missed the sign.

Not that I’m bitter. Fair enough – if I can’t concentrate enough to stay beneath the limit then its probably best that the Police and I go our separate ways. So I said “enough” and hung up the car keys in disgust. The driving strike was on!

Why Dump the Car

I had a few other reasons:

  1. I have a general problem with internal combustion technology, it’s about 0.5% efficient, unsustainable, and is about to cause untold misery through the effects of Peak Oil.
  2. Save money.
  3. I figure oil prices will force me to stop sooner or later, might as well beat the rush and learn to live life without a car.
  4. Cars (especially internal combustion cars) are impossible for 90% of the world due to resource constraints. This can’t go on, and is unfair to most of the world.

Of course we still had my wife Rosemary driving so the family was not exactly going cold turkey. She sided with the Police and agreed that maybe I am the sort of absent-minded person who shouldn’t be driving. My kids were extremely distressed – they could see this might mean……..exercise!

The Challenge (or lack thereof)

Unlike most people I am fairly time rich. I keep my life simple so that I don’t have many commitments scheduled and don’t have to race about town over the course of the day. My wife and I manage our expenses and debt so that we don’t need two full time jobs to sustain us. I guess you could say we have down shifted – compared to many of our peers we earn and spend less but live better. So I appreciate that not everyone could consider dumping their car.

I work from home, live 7km from the the center of the city and have good public transport (both train and bus services) nearby. However the city I live in is designed for cars. We have large suburban blocks (low density living), and a large city area (perhaps 80km long by 20km wide) for the population of just 1M people. Most residents have poor access to public transport compared to a European city.

Getting Around

I used my bike, the train and bus, and car pooling to get around. When I needed to buy something heavy or distant I would wait until it was convenient for my wife to take me as a passenger.

Imagine taking your kid to a doctor. This is what I had to do: walk to school, extract kid, walk to bus stop, wait for bus, catch bus, visit doctor, wait for bus, catch bus, walk from bus stop home. At least two hours elapsed time for a 15 minute visit.

Every 2 weeks I need to visit Mt. Barker, a country town about 40km away, and a 40 minute drive in the car. This was something of a challenge. I ended up getting there by catching a train and a bus, total elapsed (door-door) time 1 hour 50 minutes. To get home later in the evening I arranged to car pool with a guy who drives home near my place from the same meeting, and shared fuel costs with him.

I installed a child seat on my bike to transport my three year old to day-care. He loves it, and with the extra 20kg it’s great exercise. You really understand the miracle power of fossil fuels when you are peddling against the wind in the rain with 20kg of squirming toddler on the back and a car goes whooshing by….


  • Generally I used a lot more time traveling. Like a lot of technology, cars allow us to use our time more efficiently, to pack more into the day. This, I think, is not always a good thing. For example I found myself actually talking to my kids while sitting on buses. Time efficiency is not always the best way to run your life.
  • Some stuff (like a late night meetings) I just chose not to do. It wasn’t that hard.
  • Diet ceased to be a problem – unlike most 40-somethings I could eat anything I wanted. All that bike riding burned a lot of calories. Even then I had to go out and buy new jeans one size down.
  • I was generally more relaxed from lots of exercise, not being a driver, and not rushing about in a car. Public transport forces you to slow down a bit.
  • I read a lot of good Science Fiction on buses and trains. I can recommend Against a Dark Background.
  • To be fair – life probably got a little more tougher for my wife. She now had to ferry kids to sports, and drive me around occasionally. However I really enjoyed the time we spent driving around together. Good time to talk.

End of the Strike

I eventually broke the strike as I needed to test my Electric Car. Once I get the bugs out of that hopefully we will sell the carbon-burner. Many of the habits I developed are still with me – I am still doing my commute to Mt. Barker without a car and riding my bike for most trips. I only generate smog by burning irreplaceable 80 million year-old liquids once or twice a week!

Solar Electricity

In early February, my long awaited grid connect PV solar panels were installed by the Solar Shop. Installation took only about half a day. The frames were cut on site, and an electrician wired up the inverter and by 2pm I was getting free electricity from the sun!

Here are the guys at work:

Here is a picture of the installed PV system. In the foreground is my ancient (but now effective) evaporative air conditioner. In the middle left you can see two paler panels – they are the solar hot water system, which is also working great. Free hot water, and my gas bill has been decimated.

In South Australia we have a big rebate for Solar PV installation (about $8k), so the system cost me $20k – $8k = $12k installed. The $8k rebate holds for smaller systems, for example a 1kW system is $13k – $8k = around $5k installed. However I have recently heard of some damn good deals – like 1kW systems for $2-3k (after the rebate) when people get together and group buy.

Our PV system has now been running for 3 months. My wife and I love it. Our state (South Australia) is about to introduce a new feed in tariff, where they pay us twice the going rate for energy we feed into the grid. With this new tarrif I estimate our Electricity bills will soon be about $0. They were approximately $2,000/year 12 months ago, as explained in my post on halving my electricity and gas bills.

However it’s not just an issue of economics. It’s just plain smarter to be using renewable technology rather than relying on dirty, non renewable fossil fuels. Feels great too, making my own electricity. I mean, when you think about it, non-renewable means it won’t last. It will stop one day. Maybe soon in some parts of the world. Gas, oil, uranium, coal – all transient technology that will be history in my children’s life time.

Grid Connect Solar – How does it Work?

For a while I got to see my old school electricity meter spin backwards.

Then they replaced it with a new electronic export/import meter. During summer I was actually using about the same as I was making over the course of a day, as the we are now drifting towards winter we are generating about half of our daily power.

The system is rated at 2kW but the peak I see on the inverter panel is 1700W. Not sure why. The Solar Shop guys estimated about 9kWh/day average over the year, which seems about right. It was peaking at 13 kWh/day in February and is now down to about 8-9 on a sunny day, maybe 5kWh if it’s cloudy or raining.

The blue box is the inverter. It converts the roughly 300V DC from the PV panels to 240VAC that is synced up to the grid current. Now here is the clever bit. So clever that no one can tell me how it’s done. First it supplies power to our house. Any excess is exported to the grid. If the PV system is not making enough electricity, it imports the balance from the grid. So the grid is like a big battery.

The bit I don’t understand is how it actually makes this export/import happen. Let me explain with a simple electrical model. Imagine the grid as a big battery with a voltage Vg, and an impedance Zg. My PV system has a voltage Vs and impedance Zs. My house is the load impedance Zl, which is time varying.

Assume its a bright sunny day and my wife and kids aren’t home. The PV system is generating more electricity than the house is using. Lets say we are generating 1500W and the house is using 500W. Some how the PV system is supplying exactly 500W to the house and the balance (1000W) to the grid. Somehow the inverter must fiddle it’s voltage and impedance dynamically such that this happens. Thats the bit I don’t understand. For example if Vs and Vg are fixed at 240V, and Zs=Zg then the current supplied to the load will be shared by the solar system and the grid. But somehow the system fiddles it so that the house first uses 500W of the solar (zero W from the grid), then exports the balance back to the grid.

For current to flow back into the grid I guess Vs must be slightly greater than Vg. The inverter must fix it’s output phase to exactly match the grid. Perhaps it makes it’s output voltage a little higher than the grid to facilitate flow of current back into the grid. I dunno – can some one explain this to me please? I have asked all the solar and electricity company people but they can’t explain it to me.
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Halving My Gas and Electricity Bills

I want an energy efficient house. However I don’t want to move or build from scratch. So I have decided to see what I can do with my 80 year old double-brick house here in Suburban Adelaide, South Australia. This post talks about the steps I have taken over the last 3 months to roughly halve my gas and electricity bills.

Electricity Audit

I once worked with a guy whose mantra was “If you can’t measure it, you can’t manage it”. So the first step was to audit my electricity use with this $40 power meter from Jaycar:

You plug this puppy in line with an appliance to get voltage, current, and most importantly the power in Watts. It can also add up the power used over time to give you the total energy used in kWh. This is really useful when the power used by the appliance varies. For example a fridge motor starts and stops over the course of a day.

So I wandered around the house for a few days, irritating my family while I plugged the power meter into various appliances and working up the results in a power audit spreadsheet (here is the power audit spreadsheet in Excel format).

Some appliances (like the air conditioner and stove) were directly wired in and couldn’t be tested using the power meter. So I worked out how to measure power from the household electricity meter. I have a really ancient one like this:

The more electricity used, the faster the ring spins. On my meter is says that every 400 revolutions is 1 kWh. So if it rotates 400 times in one hour, then I must be using an average power of 1kW. A little maths and I worked out that the instantaneous power in Watts is given by P=9000/T where T is the number of seconds it takes for the ring to revolve once. For example as I write this the ring is taking about 18 seconds to turn which means the house is using 500W. With two TVs and a few PCs running, that is about right.

To measure stuff like the air conditioner I would first make sure loads like the fridge/pool were switched off (I didn’t want them switching on by themselves half way through my measurement). It also helps to have no one in the house, as the electricity jumps up and down all the when people (especially kids) are in the house. Then I would look at the power before and after the appliance was switched on, and subtract the two measurements.

One interesting test was to switch off everything. You see I wanted to make sure there were no “phantom” load sucking power that I didn’t know about, like a suspect alarm system or IR sensor light. Switching everything off (i.e. using no electricity) was really hard – just try it! I had to chase all the kids out of the house (to avoid TVs, lights being switched on and off), and run around the house switching off the fridge, my server etc. All that was left was a few clocks (too much effort to reset) plus stuff that was permanently wired in (like IR sensor lights). The minimum was about 70W. Not zero, but about what I expected.

Electricity Audit Results

Anyway, back to the power audit results. There were some shockers. For example my sons desktop PC uses more energy off (20 hours off at 28 Watts/hr) than on (4 hours on at 91 Watts/hr). It uses more power off than my laptop does on!

Standby power was also a big problem for the older appliances like TVs and VCRs. Some of the newer DVD players were much better, drawing 0W when off.

The effect of 24 hours is interesting. Just wasting 20 W/hr adds up to nearly 500Whr/day (180 kWh/year)! Add that up across several appliances and it really starts to stack up.

There were also some pleasant surprises. Before starting the audit I was sure that my server would be the main power culprit, however combined with my DSL modem and a hub it only uses about 20W. This I totally have Linux to thank, it runs a powerful server on a 10 year old P133 PC. It’s a file server (SAMBA/NFS for both Windows and Linux machines), print server, DHCP server, firewall, SSH server for remote login, runs a small web server. All on an ancient P133 with 64M of RAM.

Reducing Electricity

OK, so here are the steps I took to increase electrical energy efficiency:

  • Conduct an Energy Audit to sniff out the culprits. Many surprises here, both good and bad.
  • Used a Floatron to dramatically lower pool energy requirements.
  • Switching off at the wall standby power loads at night, like TVs and PCs. Grumble. I wish there was a box that could do this for me, or that beeped in my kids ears when they forget.
  • Swapped out nasty incandescent light bulbs for compact fluorescent (CFLs).
  • Swapped out nasty halogen downlights for LED downlights.
  • Encouraged the use of laptops (20W) rather than desktops (90W).
  • Where possible use my laptop on mains rather than battery power, as I have read the charging/discharge cycle is only about 50% efficient
  • Placed my home office equipment on a separate power board than can be switched off at night, while leaving my server running. Previously I just left everything on.
  • Promised my 9 year old son an extra $1/week if he remembers to switch his PC off at the wall every day. Good training, teaches him “the value of energy”. I figure that energy efficiency is going to be a much bigger issue in his life than mine.

Most of these changes cost me very little, they mostly paid for themselves by the next power bill.

When you start to look around it’s amazing what you find. In my family room I have two light fittings which had 5 60W lights each. That’s 600W total for one room! The funny thing was that with the dark walls in that room the light still wasn’t any good for reading. Now I have a pedestal lamp with a single 11W CFL – it’s direct lighting actually makes reading easier than the previous 600W of indirect light.

In the kitchen I replaced 4 nasty 60W Halogen downlights with 3W(!) LED downlights:

The LED versions aren’t quite as bright, and my wife Rosemary wasn’t very happy with them at first. However we are now quite used to them. Compared to CFLs they were expensive at $30 each, but I figure the payback is a little over 1 year. Thats one good thing about working out the numbers with something like a power audit, you can make educated decisions on where it is a good idea to spend money.

Also, I have to admit there is just a good feeling about being efficient. Not everything in life reduces to economic, dollar based decisions like payback period. Sometimes it just has to feel right. That’s enough.

Hacking my House – Insulation and Air Conditioning

To attack the gas consumption we had a hard look at our insulation and air conditioning options.

In August 2006 my wife Rosemary was shivering through our vicious Australian winter and suggested we get a reverse cycle (heat pump) type air conditioner. Actually in Australia we are blessed with fairly mild winters (it rarely gets to freezing). However as a result building codes are lax, and most houses have single glazed windows and poor insulation. During a winters day when it’s 15C outside, it’s often 15C inside. I have several Norwegian and Canadian friends say that their coldest winters have been in Australia!

The current, socially accepted solution, is to bolt a massive reverse cycle ducted air conditioner onto the energy sieves we call houses. In winter they heat, in summer they cool. These air conditioners can draw up to 8kW and often require a 3 phase power connection to the house. When I step outside on a summers day I can hear them roaring all over the neighborhood. Our electricity companies are creaking under the load, especially in summer, as more and more are being retrofitted to older homes like mine.

Our house (which is gas heated) was unpleasantly cold in winter. In summer it was too hot, our old evaporative air conditioner just wasn’t cutting it. So we asked for a few quotes on reverse cycle air conditioning. About $15,000 plus the cost of a three phase connection. Plus I figured significant ongoing electricity bills. Running 8kW means $1.20/hour and rising each year as electricity costs go up. Ouch.

So I decided as a first step to look at our insulation. No point pumping all that heat into/out of the house if the insulation was just going to let it all leak out again. Sure enough, our insulation was shot, so I arranged to have new insulation put in.

The more I thought about it, the more I felt bad about a big reverse cycle air conditioner. So I decided to upgrade our evaporative unit, by getting new ducting (the ducting was ripped) with a high insulation standard. We have mainly dry heat here in Adelaide, so evaporative is fine most of the time, and it draws between 500 and 1000W, a fraction of a heat pump.

After reading about household heat loss, I realised that my standard, single glazed windows were a big problem. Swapping to double glazed windows would be a big job (new frames in all windows) so after some research I decided to install some special laminated glass called Pilkington Comfort Glass that has insulation properties almost as good as double glazing.

Curiously, a few people I discussed this with thought I was wasting my money. Why not, they suggested, install some nice looking new window frames for the same money? I figure this is evolution at work, these people will be naturally selected out of the population if we ever face energy shortages.

Results – House 2.0

We installed our new insulation and windows in August (end of our winter). That day we switched off our gas heating and it wasn’t needed again. Normally we would still be using it (off and on) until October. So we are far more comfortable and using less energy. Nice.

We experienced the first warm weather in November; a week of 30C plus. I only needed to switch on the (evaporative) air conditioner at the end of this week, and then only right at the end of the day for a few hours. This is amazing – last year we had the air con running all day in weeks like that. When I walk outside I can hear the roar of air conditioners (big nasty reverse cycle heat pumps) all over the neighborhood. At night we open up the house to capture the “cool” night air inside. Then in the morning we shut the doors. The only problem we noticed is that the air inside gets a little stuffy. So we have started using a couple of fans, just to give the cool air some movement. Ceiling fans would be perfect I think.

Since then we have had several weeks of 40C weather. The inside temperature hasn’t been above 25C, although on the hotter days we run the evaporative air conditioner most of the day, on a moderate power setting. Last year, before the house 2.0 upgrade, even at full power the air con just wasn’t up to it.

We just received our latest electricity and gas bills. Electricity dropped from $509 to $272, and gas from $413 to $168. Gas usually drops this time of year, so the true test will be next winter. However it’s still the lowest gas bill we have had in years.


Energy efficiency, or Negawatts can be considered a really cheap, easily available new power source equivalent to at least halve our current energy consumption. Low hanging fruit. Much smarter than building new power stations, and lowers the bar for converting across to renewables.

Next Steps

I am working on some related projects:

  • We have just had a solar hot water system installed. This should drop the gas bill even further, as we get almost all of our water heated by the sun now. Totally makes sense in a country like Australia.
  • We are getting a 2 kW grid-connect solar electric PV system installed.
  • I am recycling a small car into a Electric Vehicle (EV)! Totally out of my depth on this one (it’s very mechanical) but slowly making progress.

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