Monday, 20 May 2013

The Wind Widget

Though wind's installed capacity does not currently form a large portion of the National Electricity Market's generation fleet, wind power still contributes meaningfully to the electricity market. The potential for wind farms to provide electricity, particularly for smaller rural communities that do not demand the enormous quantities we see in metropolitan areas, is well worth considering.

A map of South Australia's wind resource, via Renewables SA

With that in mind, I threw together a quick Google Sheets widget, based off a live wind farm generation megawatt value hosted on 'MisterVint' - a great website that displays and logs the percent of your electricity that comes from wind energy, on the National Electricity Market. It also provides a state-by-state breakdown.

I had to provide some relatively rough estimations of the instantaneous power consumption - a fridge, for instance, can vary greatly in its power consumption depending whether the compressor is on or off. Still, the averages gives us a good idea of how much we consume, as individuals, and how much power is currently being generated by wind farms on the grid.

Click here to see the plain HTML version, or click here to visit the Google Sheets spreadsheet (you can make a copy and play with the assumptions and calculations yourself, if you like). If you want to embed it on your webpage, copy and paste the code below (adjust the width and height values, in pixels, to get it right):

<iframe width='500' height='300' frameborder='0' src='https://docs.google.com/spreadsheet/pub?key=0AqAu73EozSjEdFRYei0tbUN6QTByQjNVM0dvZjUtNUE&single=true&gid=2&output=html&widget=true'></iframe>

Enjoy!



Thoughts on Energy and Power


800 years ago, wind energy powered one of the most significant endeavours in human history. Impossibly brave men stood on the sterns of wooden craft, and traveled to unexplored lands, powered only by the wind in their sails. Their energy source did not deliver consistently. This did not erode their bravery or determination, and they pushed forward into the future, unhindered.

The concept of capturing energy from the movements of the atmosphere has relevance and utility for modern energy systems. It would be a silly conceit to equate modern wind power with the brave explorers of the past, but both share the need to contend with one important feature: a power source that is variable.

Wind energy is often measured as a 'capacity factor' - essentially, how much power came out of your machines, as a percentage of their maximum capacity? It's convenient and quick, but personally, I don't like it. It tries to condense too much information into a single value. It's sort of like changing the resolution of a picture to one pixel by one pixel. It also carries the implicit suggestion that wind farms ought to be generating at 100% capacity all the time. They shouldn't.

Wind turbines don't generate at maximum capacity all the time - on average, their generation is about 35% of their installed capacity. The range of wind speeds that the machine needs to deal with is broad, and so you build a wind turbine with an equally broad capacity. Capacity factor is misleading because the capacity of a wind turbine is stretched high to capture infrequent but important periods of very high wind speeds. It's also frequently mistaken to be an indicator of 'efficiency', which it most definitely is not. 

Permit me to elaborate. Let's say that, on average, you drive your car at 60 km/h. Occasionally, when you're backing into your driveway, you're going at 5 km/h. Sometimes, on the highway, you go at 110 km/h. The maximum speed of your car is 200 km/h. So does your speedometer show you your average speed, as a percentage of your maximum? No. It shows you your current speed, and the distance you've traveled. No one really cares about the 'capacity factor' of their car, because the metric doesn't really tell them anything significant. 

You can measure the electrical equivalent of 'distance' by looking at 'energy' - measured over time, and in 'watt hours'. In South Australia, in FY12, wind energy contributed 3,349,000,000,000 watt hours (3,349 gigawatt hours) to the grid -  26% of total energy generated in the state (see page 16 of this PDF). 

If you stored one year's worth of South Australian wind energy in a battery, it could power one average Australian home for about 19,000 years. It's not a quantity that can be dismissed easily. It's good to think closely about definitions, metrics and measurements, when someone's talking to you about renewable energy. 

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