Turbotricity

Our Proven instructions insisted that the base of the turbine sit flat on the concrete, and be floated into place. We found that most other tower installers don’t do this – it is tricky getting the base level, and ensuring that you have no air under it, and even at that, the vibration over time can soften the concrete under the tower. I’ve seen two systems (including our own) which have slight movement in the base with water ingress under it.

It is essential that the hole for the foundation has vertical sides - a foundation that slopes in towards the bottom would allow rocking...

So we did what many other commercial tower installers do. You put in threaded bar, with a template top and bottom to ensure that the bars are properaly spaced and lined up. Pour the concrete, and then mount the turbine base a few millimeters above the concrete on the threaded bar. You can use nuts and washers under the base to level it.

Drop in threaded bar with plates top and bottom. Iron is optional if you use fibres in cement mix

The whole procedure should take about 4 hours from digger arriving on-site. We used a mini-digger to dig a hole 1.2m wide and 1.5m deep. It is important that the sides are vertical, not sloping in towards the bottom. A turbine foundation must never be shuttered and back-filled, so getting a hole in the ground with vertical sides is essential. In fact, we had trouble sticking to the 1.2m on the width and ended up with a slighly rectangular hole because the bucket on the digger couldn’t get a hole that deep with vertical sides.

Insert pipe for cable run in centre of frame. Cover pipe end and threaded bar to prevent cement getting in

We then set up shuttering around the top of the hole to allow the plinth rise slightly above ground. Because the ground isn’t level the shuttering was 9″ high at the bottom and 4″ high at the top. We set up the threaded bar with its templates top and bottom, and put ironwork at various heights along this. You don’t need iron if you use fibres in the cement mix.

We also dug a trench 1m deep for the armoured cable running from the house to the turbine. We ran a 2″ alkathene pipe from this trench into the centre of the template and the cable will run inside this pipe after the cement is cured.

We covered the end of the pipe with sileage tape, and covered the thraded bar with fingers off an old rubber glove to prevent cement blocking them up.

After pouring concrete, remove shuttering, clean off the threaded bar and leave the whole thing for two weeks to harden off

We needed 3 cubic metres of 40 newton concrete (because our hole was a wee bit on the wide side – normally about 2.25 cubic metres should have been enough).

We poured the concrete and used a vibratory poker to ensure that all air was removed. Then cleaned up our tools and called it a day.

The following morning, we removed the shuttering and cleaned off the threaded bar with a wirebrush. We now have to wait two weeks before mounting the turbine, but in the meantime, we can run the armoured cable to the fusebox and get the wiring done.