Doris - A thought experiment in progress (11) - Flights of Fantasy

Doris is a thought experiment running on a Raspberry Pi and a laptop which is intended to explore sustainable energy, an evolving description and discussion can by found in a previous post:

• Doris - A thought experiment in progress (1) - Description

It is important to remember that Doris is a computer simulation with some arbitrarily set parameters and rules, it exists only in the imagination and has no physical reality.

With a database and software background, it seemed that a good way to learn about wind and solar energy was to find a bunch of varied data sets and poke around them with SQL.  This has been instructive, but so to has gardening and looking at the location of old corn grinding wind mills.

Weather balloons are a source of wind speed data.  I'm guessing, but there is probably a GPS built into the instrumentation which provides the data needed to estimate the balloon's speed and direction.

Wind is fluid flow over a surface, for smooth surfaces like a calm sea, the friction is low compared to that created by a jagged urban environment. The effect of friction is greatest close to the surface, but at around 1,000 meters, it is much less significant.  I think any investment in wind power technology should be preceded by a site survey, but without that it can be useful to attempt to estimate the wind speed from a reference location, one way of correcting for height is this formula:

There a alternatives which give different results, but this one has the virtue of simplicity.  Most surface wind speed data is collected at 10 meters, the graph shows how the wind speed might increase with height, at 1,000 meters, it is almost twice as fast as at 10 meters.

This graph shows a wind speed distribution at 850 meters (a standard reporting level) which was compiled from weather balloon data.  The average speed is approximately 10.0 m/s, at the surface, the average speed in a similar location might be 5.0 m/s.

This data suggests that the sky is a good place to capture the wind's energy. There are some talented and created people who are attempting to do this; there are a couple of links at the bottom of the page which might be a good start to reading around the subject, one of them, the Makani project is backed by Google.  The designs seem to divide into two groups, one approach is to get the generator aloft with  a kite or ballon and feed the electric energy back to earth with a cable attached to the tether.  The other is to capture the kinetic energy with devices like kites or rotors and use this to drive a generator on the ground.

I have not run any upper air data through the Doris simulation software as one of the parameters of the project is that it should only model readily available product and services.  It's easy to find reasons for dismissing airborne wind energy devices but fuel cells used to be exotic but now the technology is being incorporated into production automotive vehicles, so someone might make it work commercially.

Related material

• Wikipedia - Airborne wind turbines
• Google - Makani