Shades of Grey

Norfolk used to be full of windmills for various purposes, although most are now just remains or there to look pretty. Some of them are visitable and a few of them still mill on windy days for the benefit of tourists. (The Norfolk Windmills trust has information on some good survivors and Norfolk mills has details on both wind and water mills).

However, as we have visited working mills before, we decided to investigate Swaffham’s high output wind turbines at the Ecotech centre. There are only two wind turbines in the world with viewing platforms and only one of them is open to the public. Fortunately it is this one!

Our guide advised us that there were nearly three hundred steps up but that there were two intermediate platforms. The first one was not very far up at all (roughly aligning with the letter E) and the second one roughly half way up (aligning with the Y). I was wondering why they were not more evenly spaced, until I realised that as the tower tapers there isn’t any room for more than the spiral staircase in the upper part of the tower.

The tower is very firmly affixed to a concrete base and the entrance doorway is eight steps up. I don’t know if this is due to the future risk of flooding (Norfolk is very flat!) or to accommodate the electrical connections in the base.

The interior is rather devoid of detail. A spiral staircase surrounds a central pipe which has the electrical feeds running down inside. (The turbine generates 400 Volts DC which is fed to a container outside that converts it to high voltage AC for connection to the Grid). Every fifteen steps or so there is a flat platform to break up the staircase, one of which can be seen in the photo above. The entrance and pause platforms also have steel perforated sheeting above to protect visitors from falling objects, such as tourist cameras!

Eventually, you get to the top, after much huffing and puffing. By now, the column is just a smidge wider than the spiral staircase. A wall ladder continues up into the actual turbine pod, padlocked off, of course, as that is not for public consumption. Neither is the 65m vertical exterior ladder that runs up the side!

The view up there is pretty good in all directions and a couple of pairs of binoculars are provided for observing the horizon. Here you can see David putting them to good use. The external ladder can be seen on the right, the centre channel is for safety harness lanyard sliding runners so that if the climber falls their descent will be arrested.

Apart from the rather blatant clue of the turbine blades swooping past you every couple of seconds, you don’t get the feel for the huge pod above you. However, the pod is driven by motors for the yaw movement and if the wind changes direction, after a minute or so (in order to dampen excessive hunting) then the motors will rotate the pod to ensure that the blades are facing directly into the wind.

Thanks to my high zoom and camera shake reduction, here is a close-up of the pod. The wind speed anemometer can be clearly seen above the pod and the two little doors on the back are for hauling up small parts using a chain winch. (We were given an exploded diagram of the Enercon E-66 Turbine which is rated at 1.5Megawatts, similar diagrams can be found at the Enercon site, where it seems that the E-66 is now superceded by even bigger models).

This status panel located at the foot of the turbine provides a mine of information. The headline figures are wind speed (in metres/second), rotational speed of the blades (revolutions per minute), output power (in Kilowatts), total power delivered (in Kilowatt/hours) and total duration of operation (in hours). The mimic panel bottom right shows fault conditions (all listed below) and the panel on the left is presumably for diagnostic testing.

Number crunching these figures provides some interesting analysis, assuming they are accurate enough to draw conclusions. Apparently the turbine was switched on in August 1999 (it has a 20-25 year design life so it is no longer an unruly teenager now) and it needs 40 hours a year off-time for routine maintenance so if we divide the service hours figure out this comes to a smidge under eight years of operation (That means that the off-time is nearer a month a year though, rather than two days). Dividing out the Kilowatt/hours by service hours gives an average output power delivery of 430 kilowatts during the last nine years. Now this doesn’t sound too good for a device rated at 1,500 Kilowatts to be running at average one third capability but I imagine that this is in fact very good indeed in the scheme of things for a single turbine as this is about 28.5% capacity factor and wind turbine performance is typically 20% to 40%. (To get the higher figure you need a lot of turbines spread across a predictably windy zone).

Why is this figure so low? Well it is totally reliant on wind being present. If the air is becalmed there isn’t any output. The sweet spot for the E-66 is a wind speed of up to 28 metres/second and above this the system tweaks the angle of the blades into the wind so that the maximum rotor speed isn’t exceeded (22rpm). If the wind speed goes too high (34m/s) then the blades are completely pitched at 90 degrees so that the blades stop.

At our visit (which wasn’t particularly windy at ground level) on the way up, the panel was showing a wind speed of about 5m/s and a revolution speed of about 12rpm with output load hovering around 100kW. When I snapped the photo having returned to ground level, the output had just gone up to 145kW.

The trouble is, that the electricity grid needs a precise match of output to demand. There isn’t any real way of storing electricity at present, other than the pumped storage systems like Dinorwig (which is effectively a rapid demand facility for peaks and surges). Capitalists@Work had a good post on Friday about the problems experienced last week and it certainly looks like the UK is heading for a power crisis due to a combination of factors including under-investment, over-regulation, green pressures & external factors (particularly north sea gas running out).

If the UK had a total grid blackout for any reason then it could potentially take several days to get everywhere on line again, such is the complicated nature of balancing the network. (It has never happened in Britain but various American States have experienced it). There is generating capacity for roughly 78 Gigawatts in the UK with the peak demand of about 63 Gigawatts. (The headroom is needed for planned and unplanned off-line events, it seems that the Tuesday chaos was caused by one trip too many and the controllers were forced to go into a DCI state (demand control imminent) with brownouts & then large scale blackouts). A Good version of events is here at the Register.

The trouble is that renewables are not much use as base load, as this one demonstrates. Solar, tidal, wind all have their not very predictable peaks & troughs.  However, once the  hypercapacitor becomes feasible, then  the future really does look bright indeed. One day, hopefully the Sci-Fi Shipstone will emerge and I hope that David lives to benefit from it, even if I don’t.