Turbotricity

Most renewable energy systems have their expertise well developed in other countries. The wind farm turbines are cornered by Denmark, Germany and Spain, solar PV by China, USA, Spain and Germany. There are three renewable sectors in which Ireland could be a pre-eminent player; micro wind, wave and tidal power.

If we are to develop a micro-wind industry in Ireland, we need a favourable tariff in our home market so we can build and sell turbines to ourselves first, and for export second. For that reason, we have made a submission to CER calling for the proposed 9c feed-in tariff for microgenerators to be raised.

Even with the proposed ESB feed-in tariff of just 9c per KwHr, domestic wind turbines will be viable on good sites. You can get the power curve for a turbine and plot it on a calculator which will give you the annual output per annum. For a typical 2.5kw turbine on a site with a mean windspeed of 7m/sec, you will get about 7,850 KwHrs of power per year. Assuming you use half of that yourself, saving 16c and sell the other half to the grid for 9c, that will save you €980 per year.

If your turbine cost you €11,500 to install, the payback time will be 12 years. If your turbine cost €20K, that rises to over 20 years.

Of course, if electricity prices go up during that 12 year or 20 year period (and I’m pretty sure they will) then that payback time will come down. Your tower and foundation have a life of about 60 years, a turbine should last indefinitely but may need new blades after 10 years, and bearings after 20.

However, if your mean wind speed is 6m/sec, the payback time for a turbine costing €11,500 will rise to 16 years, and for a €20,000 turbine, to 27 years.

This is why our response to the Commissioner for Energy Regulation calls for a higher feed-in tariff. If we are going to get an industry moving in this area, it would be a great help to have a feed-in tariff similar to that in Northern Ireland. You can read our submission to the CER by clicking here.

Needless to say, we’ll have a post here when we get a response… In the meantime, the following quote from Hugh Piggott of Scoraig (who runs excellent courses on how to build your own wind turbine).

Why should it necessarily compete against cheap power from polluting engines? …The satisfaction of generating your own power, independently, from a clean endless source, is hard to quantify

Blade Design

Early wind turbines suffered from high levels of noise. In the case of large wind farms, this was partially caused by gearboxes rumbling, but modern domestic generators are designed to work without gears

That leaves the swish of air passing the blades as the only remaining source of noise. In a well designed turbine, this should not be audible above the normal sound of wind in the trees from more than 100m away.

Some Chinese models have straight-cut blades – the blade has the same pitch throughout its length. These are the worst offenders, and if you come across a wind turbine that whistles, poor blade design is the most likely cause. Whistling sounds are high pitched and can travel over a long distance. We once put up a Chinese 300W turbine on an experimental basis – until one day I was visiting a neighbour about half a mile away and heard the whistling…

A properly designed blade has a pitch that varies along the length of the blade. This is because the outside of the blade is travelling a lot faster than the area closer to the hub. The wind is blowing at right angle to the direction in which the blade is spinning. Thus the “apparent wind direction” seen by the blade at its edge, is totally different to the apparent wind direction seen by a part of the blade closer to the hub.

We are working with a blade which has been designed using the latest CAD software for optimising blade performance by having the best possible attack angle along the entire length of the blade.

A side-effect of this is that the blade also runs more quietly.

Planning exemptions only apply to wind turbines that have a sound level below 43db(A), when tested at the nearest dwelling. They also must be no more than 5db(A) above background noise.

For some systems, there will be noise during start up. This is because the inverter on many systems does not cut in for the first three minutes, and the turbine over-spins during this time. We are working to minimise this effect by using an inverter with a low cut-in voltage, so this three minute period will happen during low wind speeds, minimising the effect.

Ireland has probably the most liberal regulations in the EU for installing domestic wind turbines. Basically, small turbines are considered as an exempt development – in other words, you don’t need to look for planning subject to some conditions.

However it should be noted that recently An Bord Pleannala insisted in the removal of a wind turbine because it interfered with the character of the landscape and impacted on the archaeology of the area. Any general exemption from planning is still subject to certain restrictions which are outlined in the legislation (SI 600 of 2001). One of the key restrictions is that if the installation is deemed to interfere with the character of a landscape or a view of special amenity it would still require permission.

There are two sets of exemptions – domestic and agricultural/commercial.

For domestic houses, the total permitted height of the turbine from ground to blade tip is 13m. The distance from any boundary to the base of the turbine must be its height plus 1m. The rotor must be less than 6m in diameter, the turbine can’t be attached to a building, can’t carry advertising logos, and must quieter than 43 db at the nearest dwelling. The full list of exemptions can be downloaded by clicking here.

For commercial turbines, the total permitted height is 20m, the distance from any boundary is its height plus 5m, the rotor can be up to 8m in diameter. There are a few other restricitions in relation to proximity to power lines, airports etc., and you can find the full list of exemptions here

These are not limits on the turbine you can put up – simply exemptions to planning. Provided you are willing to put in a planning application (and are successful) you can go above these limits. There is a risk that by exempting a height of 13m, someone with a site that really needs a 20m tower won’t go to the trouble of putting in a planning application, and will end up with a severely compromised turbine that is inneffective.

As for the boundaries between what is an agricultural site, and what is a domestic site, there are no clear lines that I can see. Cabbage patch anyone?

Turbine cowlings and pinnacle

One problem with many downwind turbines is that because the tower is upwind of the blades, as each blade swings past its lowest point it suffers a shadow effect from the tower.

We are getting around this by setting the turbine on a lighter tubular pinnacle, and using cowlings to minimise the wind disturbance caused by this.

Despite costing about €20K, our old turbine at home has a crude cowling made from plastic sheeting held on with cable ties. The whole lot blew off last winter, and the cowling is shorter than the blades, so the tip of the blade has to pass through the shadow of a huge flange.

So today, we have settled on a design for the cowling and are starting on getting the mouldings done for this. We will have to get an original machined from CAD drawings and get a mould made from this. It’s a costly process, but a solid, well made cowling is essential to the smooth and quiet working of a downwind turbine, and without it, we would suffer a helicoptering sound as the blade passes the tower. Here’s hoping it all works out OK!

They may be cheap, but are they cheerful? A few years ago, I was tempted by low cost Chinese wind turbines. At the price, they seemed to be too good to be true. I have brought in five different ones at this stage, and I give up.

The first one we put up whistled like a banshee. The blades were straight cut – the pitch was the same for the entire length of the blade which was fibreglass, and you could hear if from a few miles away.

I had sold two more of these to other folks locally. One fell down because the guy wires failed. In fairness, it should have been taken down and greased each year, and it wasn’t, so the owner couldn’t really complain.

The third one seized its bearings and destroyed the main shaft – I replaced that one for free. That was the fourth one. It is still going, but the owner has replaced the bearings and the blades, thankfully. It also whistled like a demented firework and was something of an embarrassment locally.

The fifth one was remarkably like the machine allegedly made by a company in Mayo (who threatened to sue me for having their name on this post). Given a choice, my guess would be that it comes from China. The bearings went on it as well, and then a casting failed while replacing them.

A sixth one never showed up – I sent the money off and got three towers and no turbine. The towers are doing nicely as gateposts for someone in Drimoleague.

All of them came with inverters and charge controllers that were total rubbish.

That’s me finished with Chinese turbines for the time being. I’ve heard other folks complaining that the magnets fall out, or that the blades have broken. The latter can be catastrophic, because the turbine is then spinning out of balance and just about anything can happen then.

To be honest, yes they are cheap, but if you want an ungalvanised tower that has guy wires that have to be checked each year, and are prepared to change the bearings and blades, and use a different inverter and charge controller, you might save a few bob, but I doubt it.

What the market needs is a quality machine that has a properly galvanised free-standing tower, a well made generator with SKF bearings and quality controller and inverter. Watch this space….

When we put in our Proven 2.5kw system, there was no prospect of the ESB buying back our surplus power, so we opted for a battery system. With a battery system, when you have more power than your batteries can take, you need various dumps for the surplus power, and this is done by relays wired to various dump loads (electric water heaters) that come in one at a time when the batteries get to between 28.5V and 29.5 V.

Obviously a grid-tied system has no need for all this, as the surplus is simply sold to the grid, and even at 9c per KwHr, this is more valuable than heat which typically costs 7c from an oil fired system.

I cabled for all these loads, but to be honest, we’ve hardly had to use them. Last autumn was the first time our output was so high that the dump loads got much use.

However, I fitted replacement blades to the turbine, and realise now how much the old blades were holding the system back. Over the last week, we have had surplus power every night – often about 2kw of surplus. The turbine is regularly producing the rated 2.5kw, something we have never seen it doing before….

If you have a 2.5kw Proven, check whether your blades are the old ones made from folded plastic sheeting, or are the new ones which are a properly moulded blade. The old blades frankly are rubbish. Well worth changing them out for the improved ones….