Turbotricity

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.