Unintended Shut-Down: A Temporary Non-Fix

As a strictly temporary measure, the Dutch engineers have decided that the power output from the turbine should be limited to 30 kW. Quite how they achieve this I don’t understand, but they can do it by accessing the control software over the internet from Holland. Even though the energy output from the generator will be much reduced, it should at least keep running because we won’t get those cable-induced voltage spikes. We probably won’t lose too much generation in the short term because we need wind speeds in excess of 8 m/s to go above 30 kW, and we really haven’t seen much of that kind of wind as yet.

The Manweb Data-Logger

We first raised the issue of high voltage peaks with Manweb back in July, and we do now have some further information. When we first contacted Manweb, they did react very speedily, and an engineer was here fitting a recording device the following day. However it turned out that it wasn’t a particularly sophisticated device, and the guy whose job it was to learn about the connection of small generators to the grid was on holiday, so the whole thing got moved back a couple of weeks.

But to cut a long story short, the right man has now had the right equipment connected to the supply for the right period of time, and he has been kind enough to let us have a copy of the data. What it shows is that the voltage levels are within the accepted parameters nearly all the time, though there are a few peaks over the 253 volt maximum. However the data is based on 5 minute averages, so we still don’t really know how high these voltage peaks are. Bearing in mind that the G59 mains interface relay is still set to zero time tolerance, it is not surprising that we are still getting problems. The problems only occur however in high wind conditions, when the turbine is trying to pump out its maximum power. This does suggest that it is the length of the cable from the turbine to the transformer that is actually causing the final bit of the voltage spike which is in turn causing the turbine to shut down.

Looking at the mains voltage data, we think that the output from the transformer can be stepped down without causing the voltage to fall below its minimum limit. This would give a bit of slack to the system, allowing it to cope with cable-induced voltage spikes without shutting down. If Manweb can be convinced of this, we will be well on the way to curing our main problem.

Opportunities for Electricity Use

I don’t yet know how much electricity our turbine will generate. I have structured the budget around an annual generation of 100,000 kWh. If we do 120,000 kWh we will make money, if we only do 80,000, we will not pay off the loan in the 10 year period agreed with the bank. But it is clear that the less electricity we sell at 3p, and the more we use, replacing purchased electricity at say 10p, the better off we will be.

Like many similar farmhouses, we have an oil fired Aga, and oil burning central heating. I understand that some more modern Agas can now be converted to run on a 13 amp electricity supply. For heating, we could install a ground source heat pump, as of course we are not short of land to bury the pipes. Ground (and air) source heating systems use quite a lot of electricity to drive the heat exchanger compressor, but you do get about 2 kWh of heat out for every 1 kWh of electricity put in.

Then there is the car. Most journeys are 40 miles or less, so a plug-in hybrid would enable most of my day-to-day motoring to be electrically driven.

Another unknown is, when will the wind blow? Sod’s law would suggest that it will blow like crazy in the middle of the night when we are not using anything, and be completely still during the day when use is at its maximum. But our very limited experience to date suggests that the wind tends to drop as it goes dark. If this pattern is repeated throughout the year, this will minimise our export and maximise our usage.