Last winter, 2014/15, we ended up having to tie up the wind turbine, on which we depend for power, for pretty much most of the winter. We became quite sensitive to higher winds, as we have burnt out two turbines in the past. So we developed a principle, which said that if the forecast on xcweather.co.uk was more than 45mph sustained and 60mph gusts, we would tie up the turbine, hopefully well within the survival envelope of the machine.
Tieing up the turbine is a non-trivial task, as it means climbing a 6m high ladder against the turbine pole, and balancing there while getting ropes around the turbine blades. In fact, I found that it was pretty much impossible, and definitely not safe, to try this in winds more than 20mph, and even in the high teens, it was pretty grim hanging on up there. The problem arises when high winds are forecast, say, a week away. If the winds are likely to be manageable, but more than 20mph, for the week before the storm, we had to tie the turbine up when it was safe to do so, leaving us frustratedly watching an immobile turbine when it should have been turning out lovely amps.
The problem was, it seems, that we expected the turbine to be robust enough for our conditions here in the far north west. The manufacturer was quite understanding, while stopping short of admitting that the turbine was unsuitable. So we looked around for something more suitable, and settled on the German-manufactured Superwind, with in-hub overspeed control. I documented the decision and the installation in an earlier blog post here. Ironically, in the run-up to installing the new turbine, we let the old one look after itself in higher winds than we would normally allow, without any problems, though we would have thought differently had it continued to be our main winter power source.
We faced our first winter storm with the Superwind in October 2015, and it was pretty nerve-wracking, as it would have been an expensive mistake had we chosen wrongly. I had to fight the impulse to give the turbine a helping hand by tieing it up. But we bravely stood our ground, hoping that it would do its own job of protecting itself. The turbine is rated at 350w, which at 24v means that the overspeed control should limit output to around 15A. As the storm wound up, my eyes were fixed on the ammeter, hoping I would not see damaging spikes as gusts came through.
And sure enough, the needle was glued to around 14A, reducing slightly as expected as the voltage in the batteries built up. We survived Storm Abigail. We also noticed that the in-hub pitch control kicks in instantly. There is no changed sound or other way of knowing it does this, other than the fact that the ammeter never runs away.
Over the next series of storms, we saw similar control from the turbine. The most scary event was going out to check on the machine from time to time. The turbine is very quiet, and the noise of the wind across the wire stays of the tower is far greater than the hum from the turbine itself. But from time to time, a turbulent gust can knock the turbine side-on to the wind, or even cause it to do a full turn. When this happens, the blade control gears in the hub make an alarming noise briefly, but this does not seem to be dangerous at all. As the turbine is often used afloat, where pitching of the vessel may make this worse, I decided to try to ignore this as a problem.
We have now got to the point where we are learning to trust the strength if this little unit (touches wood...). The proof, though, is in the statistics. Last winter, during the 2-3 month period ot he year when we get little power from our solar panels, we had to use the little petrol generator for a total of 667 hours. This winter, we have had to use it for 93 hours. It could be said we were over-cautious with the other turbine, but the two burnouts suggest not. This coming winter, we hope we will need the generator even less, as we plan to renew the rather tired battery bank this year, so we should have more reserve power next season.