Turbotricity

One of the arguments raised against turbines – large or small – is the amount of CO2 used in their manufacture, and the length of time it takes for the turbine to save that. The wind industry has made some stabs at guessing this in relation to large turbines, and the figures are in fact very convincing. The payback time is usually less than six months, unless of course you accidentally roll half a bog down the mountain, in which case the CO2 emissions go skywards…

But for our domestic turbines, the figures are likely to be roughly as follows;

An efficient European steelworks emits about 2 tonnes of CO2 for every tonne of finished steel. Copper is almost twice that, and aluminum about six times that amount, but thankfully the weight of both these components is minor enough.

Concrete, even if no fly-ash is used in the mix varies between 173 and 436Kg Co2 per cubic meter – since we use a fairly strong mix, lets pit the worst possible scenario and go for the higher figure.

Our tower is likely to weigh about 400kg
The generator weighs a further 35kg – about 6kg of that would be copper, the rest aluminum and steel. Our foundation requires about 2.2 cubic m of concrete.

That all comes to just under 2 tonnes of CO2.

In Ireland, according to SEI, electricity comes in at 620g of CO2 per KwHr. In the UK (more nuclear) it comes in at 430g. In Ireland, the turbine, assuming a yield on a mediocre site of 500Kwhr per sq m blade area, would save 2.2 tonnes of CO2 in a year. In the UK that would be 1.5 tonnes.

So the carbon would be paid back in between a year and sixteen months, depending on whether you are in Ireland or the UK.

The turbine should have a life of at least 20 years, but the tower and base would be good for two or three times that amount. All in all, this isn’t a bad return on carbon…

Hugh Piggott once wrote “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.”

When we first bought our Proven 2.5kw turbine, we did so because we were happy enough to pay 50c or so per kwhr for our electricity. Many people now want a turbine which will meet a payback time of ten years, or at the most fifteen. And of course the dealers will tell you what you want to hear…. So caveat emptor. Learn to use wind maps from OSI or ESB, and get the calculators on Windpower

Payback time depends on a number of factors, not just the price of the turbine;

* The cost of electricity and the feed in tariff
* The wind available at your site
* How well your turbine performs in the profile of winds on your site

Every turbine has compromises in its design, and there is no such thing as a turbine that matches all conditions optimally. So in designing our turbine and blade set, we have to try and match as many of the conditions we are likely to meet as possible.

Some turbines are designed to work in screaming gales, while other machines shut down in such conditions but make up for this by working quite well in lighter winds. There is no substitute for getting a power curve for your turbine and comparing this with the mean wind speed on your site to get total annual output. A calculator for this can be found by clicking here.

In relation to our own turbine, we are trying to build in flexibility to optimise operation over a wide range of wind conditions. But power output for a turbine goes up by the cube of the wind speed. So a turbine that produces 500 watts at 7m/sec will produce 4kw at 14m/sec. Unless you have a way of spilling the wind, or you fit a 4kw generator and inverter to take up the slack, you may have to shut down your system above a certain wind speed.

For small turbines, variable blade pitch is an expensive option. Furling systems are fine, but they often work unreliably and have the effect of shutting the turbine down anyway, particularly if the inverter goes below its operating voltage and shuts down.

Many people have looked at switching the windings between star and delta to reduce the current running through the coils in the generator and thus increase its safe output when it gets above a certain speed. We may look at this as an option.

We can set the hub to slightly modify blade pitch, so first job when the test generators arrive will be to produce a set of power curves for different pitches to see if there is a benefit to having one pitch at lower average wind speeds, and a different pitch at higher average wind speeds. Because our turbine is dead easy to take up and down (using a hydraulic ram rather than winch and gin-pole) it might be beneficial for some users to change the blade pitch twice a year.

The other modification that is possible is to use slightly shorter blades in extreme winds, or for winter, and replace them with a larger blade set in the spring.

For those who want a maintenance-free turbine, we will just have to try and optimise the output by getting the machine to run in as wide a range of conditions for that area as possible.

And the payback time? Sorry – you’ll have to wait for the power curves, and for the ESB to determine the amount that they will pay you for electricity that you sell back to the grid… But we will give you the power curves, and show you how to assess your site. The one thing we don’t want is our turbines in locations where they don’t work. That’s a waste of steel and concrete, with its embodied CO2.

Grid-Tied Systems are to get a feed-in tarriff. When we started this project to design a wind turbine, we knew that without a feed-in tariff, the market in Ireland was going to be limited. We figured we could put in the work on designing a turbine, sell it mainly in the UK and mainland Europe, but we might have to wait for a feed-in tariff before it would really take off in Ireland.

We might not have to wait very long…

At long last, ESB has put forward proposals to buy power from wind turbines and other micro-generators. The downside? They propose an interim tariff of just 9 cents per kw hr.

The Commissioner for Energy Regulation has invited submissions from the public between now and January 16th. You can read about the CER request for submission and make a submission here.

In making a submission, you might like to know that in many parts of the UK and Northern Ireland, the feed-in tariff is 10p sterling per KwHr and that a further 4p is paid for Renewable Obligations Certificates (ROCs) whereby the carbon credited is purchased for all energy produced by the wind turbine (including electricity used by the customers themselves).

By comparison, 9 cents is a pretty derisory offer but it is possible that if enough comments are received by CER, then they miught increase this figure.

So lets try to persuade the CER that 9 cents is not a reasonable price to pay for microgenerators. Reasons might include;

• This is only slightly higher than the 7.5c rate paid to large wind farms
• There is already a 12c feed-in tariff for offshore power. Micro generators should be regarded as an early-stage technology and supported in the same way
• Unlike wind farms and other generation systems, micro-generators do not create a requirement to expand the grid because their electricity is produced and used locally.
• Ireland could be a leading innovator in micro wind power, but there must be attractive feed-in tariffs to support this.
• Other countries such as Spain and Germany pay as much as 45c to 50c per kw hr for electricity to support the development of solar photovoltaic or other industries.
• Any other arguments you might have (there are loads of reasons when you think about it).

The announcement by ESB is a move in the right direction after years of getting n’owt. But with some work, the offer could be improved on….

Meantime, we have taken down our 5 year old Proven 2.5kw generator for maintenance. This is its third time coming down. Strictly speaking it should be its fifth. Unfortunately the bearings need to be greased, the slip rings need to be cleaned and have their springs oiled and a few other annual maintenace jobs are required. Thats a pity because for many people, taking the genny down is quite an expense, and if people are honest, it probably gets done less often than it should…

We are also taking the opportunity to change the blades as Proven claim that their new blades improve performance.

The Proven is a very robust machine and its blade system allows it to continue working in extreme winds when other turbines need to shut down. But the extra concrete and steel required for this may not be worth the small amount of extra power you get on such occasions depending on your site.

We should get it back up tomorrow and look forward to seeing how it works with the new blades.

Five years ago, we opted for a 24V battery based system. At the time, grid-tied systems were unthinkable in Ireland. Hopefully the situation has changed and we should see a feed-in tariff for turbines that are grid connected. This has been promised following a review of Smart Metering which is currently under way.

Our first prototype has gone up in Scotland. This isn’t the final generator or tower (these are all in production at this very moment), but already we can see that this turbine is going to work as we expected. It spins constantly in even very low wind, and the voltages are at levels that will produce power when we get our new inverters which are due to ship on the 12th.

The whole idea is that by using an axial flux generator we eliminate the cogging resistance that iron core permanent magnet generators suffer. The cogging resistance is part of what makes it difficult for a turbine to start up in low winds. If you can smooth this out with an air core generator, it should spin more freely.

Air core generators are a lot more expensive, but this is the heart of the machine. There is no point in spending good money on quality towers, inverters, controllers and blades and then compromising by using a generator that restricts the operating range of the turbine.

Downwind or Upwind?

Most commercial turbines face upwind. Larger ones rely on expensive control gear and motors to either change the blade pitch, or to turn the generator out of the wind when the going gets rough.

Smaller turbines often have a tail fin which lifts to allow the turbine turn out of the wind. The problem is that in any sort of decent wind, the turbine starts swinging from side to side, drastically reducing output, and driving the grid-tie inverter crazy.

We are opting for a downwind system – the blades face away from the wind. Downwind turbines do a lot less weaving from side-to-side. When the wind speed goes above the safe working range of the turbine, electrical braking will first slow, and then stop the turbine. If there is a gust that flexes the blades, they bend away from the tower.

The only disadvantage to downwind turbines is that as each blade passes the tower, it suffers a brief change because the tower shelters the blade, but this effect is minimised by the use of aerodynamic cowlings around the pinnacle of the tower.

The upside is simplicity and a turbine that requires virtually no maintenance because there are no moving parts exposed to the elements.

Most domestic turbines use permanent magnet generators. Provided they are well made, these are simple and reliable, but when you spin the shaft, there is a cogging resistance to movement which prevents them from starting up in low wind conditions.

On top of this, most generating systems don’t start putting electricity into the grid (or batteries) until they get over a certain speed. Your turbine might be spinning, but producing nothing.

We are working with a generator which has no cogging. The start-up is smooth and enables the blades to spin even in very light winds. We are matching this with an inverter which cuts in when the turbine is at very low revs. This cobination means that your generator will be working in a wide range of conditions when most generators are effectively redundant.

Turbotricity 2.5kw domestic wind turbines are designed to be rugged, affordable, trouble free, but most of all, productive in a wide range of wind conditions, particularly light winds. How do we aim to do this?

For years, we’ve wondered how a tower, generator, blades and some simple electronics could cost more than the average family car.

If we stop thinking of domestic wind turbines as being a niche market, maybe they will become a bit more commonplace. Pay a good design team to come up with a simple effective design, put the components together using quality suppliers, and put a normal trading mark-up on to get a return on our investment which nobody would begrudge.

That’s the best we can do. While we are still designing some components, our target price for this turbine is about €8,000 plus VAT, including an 11.5m free standing tower, grid-tie inverter and controller.

We now have the first prototype up and running in Scotland. We are putting up a second prototype in one of the windiest coastal regions for testing over the wild winter months, and are surveying a few sites in Ireland. When we’re satisfied that the system is de-bugged (probably by March next year) we will be ready to launch what will be the best possible combination of reliability, productivity and price anywhere.

And, we hope to have a few clever elements in the controller that you haven’t seen before, but we’ll only reveal these as they are proven to be reliable.