Category Archives: Ecology

Weather station readout with FreeBSD

A while ago a wind turbine was installed not far away from my place. It is far enough to not disturb us, and it is near enough to notice that it turns a lot (IIRC I have seen it only once not turning).

This triggered a question. How much energy would such a device (smaller of course) produce at my place?

The answer depends upon several factors. The wind speed, the wind direction and the wind-speed-to-power-output curve of the device. If you do not take a device which rotates around the horizontal axis but the vertical axis, the wind direction can be taken out of the question (probably not completely, but to answer my question this simplification should be ok). The output-power curve depends upon the device, and I hope it is easy to get it from the vendors. The remaining open question it the wind speed at my place. Is there enough wind with enough speed?

To answer this question I bought a weather station with an anemometer (wind speed sensor). I searched a little bit until I decided to buy a specific one (actually I bought three of them, some coworkers got interested too but they found only much more expensive ones, so soon there will be three more weather stations in use in Belgium, France and Germany). The main point is, I can connect it to an USB port of a PC and there is some software for Linux to read out the data. It also comes with some other outdoor-sensors (temperature, rain, wind direction, humidity, …) and an indoor-control-unit with some internal sensors (temperature, humidity). The user interface is mainly the touchscreen of the control-unit. There is also some Windows software, which is needed to program the interval in which the measurements are taken and saved in the control-unit.

It seems the weather station is produced by Fine Offset Electronics Co.,Ltd and sold within different brands in different locations. The Linux software can read all of them, as the vendor and product IDs are not changed.

Porting the software was easy, it uses libusb and I just had to correct a little problem for the non-portable functions which are used (I asked about them on usb@ and the response was that they just got implemented upon my request and will be committed to HEAD soon). I made a little patch for the software to only use them when available (if you have not loaded the USB HID driver, you do not need to care about them) and committed it to the Ports Collection as astro/fowsr.

Now I just need to attach the outside sensors at the place where I would put the vertical axis wind turbine, install some toolkit which takes a series of measurements and displays them as a nice graph (while keeping all data values) and write some glue code to feed the output of fowsr to it. After a year I can then calculate how much power a given wind turbine would have produced during the year and calculate the return of investment for it.

The Linux software also references several weather sites, for some of them you can get even an iGoogle widget so that you can view the data from wherever you want (as long as you have a suitable internet connection). I think this is also something I will have a look at later.

Note to users in Europe, the device also comes with a DCF77 receiver. As the time is distributed in UTC+1 (or +2, depending on the daylight saving time), you should adjust the timezone setting accordingly to this, not to plain UTC (so for me the timezone should be ‘0’ for the same timezone).