To get a better idea of where the Scirocco should be placed in the wind turbine spectrum here is a little table with the characteristics of the more popular wind turbines. The Bergey Excel is the largest of the list, and considered the work-horse of turbines when power is required. The Whisper 500 is cheap, light, and nobody will accuse it of being very durable. Finally, the long case Jacobs (Jake) still is the gold-standard to which all other turbines are measured. The Jakes were made 50 or more years ago, and have been rebuilt ever since. In particular, the leading edge of the wooden blades needs to get re-taped every few years. It is a very efficient, and very quiet turbine.

¹Wind speeds are at hub height
²Prices include inverter for grid-connected use

Swept Area and Rotor Diameter

Just like the surface area for solar panels, the swept area is what determines how much energy a wind turbine can potentially produce. Swept area says much more about a wind turbine's performance than its rated power. It is the rotor that collects the wind energy, and depending on the efficiency of the blades, drive train, and generator a certain amount of the available wind energy is converted to electrical power.

Cut-in Wind Speed

This is the wind speed at which the wind generator begins producing. For all practical purposes, wind speed below 3 m/s provide little or no usable energy, even though the blades may be turning. Manufacturers like to boast about cut-in wind speed, though this is largely a meaningless number due to the lack of energy in those winds.

Rated Wind Speed

This is the wind speed at which the generator reaches rated output. There is no standard for rated wind speeds, between manufacturers and turbines they can vary as much as from 8 to 14 m/s. Since turbine output is proportional to the cube of the wind speed there is potentially 536% more power in 14 m/s than in an 8 m/s wind!  So when comparing rated output power always look at the rated wind speeds. Keep in mind that most sites in Canada do not have all that much wind for the majority of time, so a low rated wind speed is good, since it means the wind turbine produces closer to its rated power more of the time. Note the high rated wind speed for a Bergey Excel, which explains in part why a Scirocco can produce just as much energy.

Rated Output

This measurement is taken at an arbitrary wind speed that the manufacturer designs for, and gives output power at rated wind speed. It is usually just before the turbine's governing wind speed, and at a level that ensures the generator does not burn out. Rated output power always needs to be viewed together with rated wind speed. Rated output by itself is meaningless.

Maximum Design Wind Speed

This is the wind speed that the turbine is designed for, on paper, to survive. It is a somewhat theoretical number, as in practise it is impossible to reliably and repeatedly test for survival wind speed. Should a wind turbine survive winds all the way to maximum design wind speed? Maybe it will, maybe it won't. What tends to kill wind turbines with more certainty than just the wind speed is turbulence. A wind generator that is placed close to the roof of a house will constantly move around, and speed up, then slow down, because of the very turbulent nature of the airflow close to obstacles. In high winds there is also the problem of flying debris, which can take out a wind turbine with more certainty than wind speed by itself.

RPM At Rated Power

This is the rotor rpm at which rated output power is produced, and since all of these turbines are direct-drive it is also the alternator/generator rpm. Lower rpm is better, because lower rpm means less noise, less centrifugal stress, less load on the bearings. Low rpm machines simply tend to last longer. Note just how much slower a Scirocco turns than a Bergey Excel!

Blade Material

These days wind turbine blades tend to be made from fiberglass on either a hollow or foam core. They are durable and smooth. A variation on fiberglass are pulltruded blades as used by Bergey: Fiberglass cloth is pulled through a die together with a resin, then cut to length. The result is a blade of uniform width and pitch. Pulltruded blades are cheap to make, though not very efficient aerodynamically. An older material that still works very well is wood. It handles the constant flexing well. Disadvantages of wood are that it needs a leading-edge tape and coating to protect it. Wood will also need more maintenance than fiberglass.

Tip Speed

The tip speed tells how fast the turbine blade tips are moving through the air at rated output power. Lower is most definitely better. High tip speeds are inefficient (due to aerodynamic drag), noisy, and cause blade-tip wear. So why do so many machines have very high tip speeds? Because faster spinning machines allow for cheaper alternators for a given output power level. Compare the Scirocco tip speed with that of a Bergey Excel and now you know why a Bergey makes so much noise while a Scirocco stays relatively quiet.

Tip Speed Ratio (TSR)

The performance of a blade's airfoil is a function of the ratio of the speed of the tip of a blade at rated output power divided by the rated wind speed. An efficient (low speed) blade will have a TSR of 5 or 6 to 1, while a less-efficient (high speed) blade will have a TSR of 10 or 11 to 1. A tip speed ratio of 5 is suggested as aerodynamically optimal for small wind turbines. Lower TSR translates directly to less noise, and less wear, much like tip speed.

Governing System

All wind turbines have some mechanism to protect themselves from overspeeding the rotor and burning out the generator. There are two general types of governing systems: Reducing the area of the rotor facing the wind, or changing the pitch angle of the blades. Changing the area of the rotor facing the wind is done by tilting the rotor up or sideways (side-furling), out of the wind. While this is a tried and trusted method, it comes at a cost. Once the rotor governs by moving out of the wind the turbine tends to produce very little output power. Because of the angle at which the wind strikes the rotor, the wind turbine tends to become noise when furled for up or side-furling machines. Changing the pitch angle of the blades is common on large, commercial wind turbines but very rare on small machines. In fact, only the Jake (originally produced in the '50's!) and Scirocco come to mind as using this method. Pitch control is more complicated and expensive make, and has the advantages of less noise and full output power at high wind speeds.

Shutdown Mechanism

Shutting down and stopping the rotor is desirable for maintenance and repairs. There are two general categories of shutdown mechanisms: Mechanical or electrical. Mechanical means of shutdown include folding the tail at an angle, so the rotor is out of the wind and either stops or spins slowly, or a stall brake where the blade angle is such that aerodynamic stall occurs, again causing the turbine to slow down or stop. Some wind turbines use a mechanical disk brake to stop the rotor, though this is very rare on small wind turbines. Electrical shutdown mechanisms are unique to permanent magnet alternators and are called "dynamic braking". If you short out the three phases it creates a very strong braking force on the rotor. The nice part is that this can be done by simply flipping a switch at the base of the tower or even inside the house. While this works well enough for light winds, dynamic braking should be used with great caution in higher winds. If the wind overpowers the magnetic braking forces the tower and alternator wiring has to absorb all the energy, likely burning out in the process.

Lateral Thrust

The force with which the wind turbine tries to push over the tower top is the lateral thrust. It is a horizontal force. The number that is given is the highest force the turbine will exert on the tower, usually this happens at survival wind speed. When designing a tower for a genny the lateral thrust has to be taken into account.

Generator Type and Voltage

Type and voltage are important when it comes to transporting the produced electricity to the inverter with as little loss as possible. For this 3-phase AC works better than DC. Higher voltage means that the turbine can be placed further away from the inverter or charge controller, and that smaller gauge wire can be used to hook the turbine up. This should not be underestimated, as the cost of wire can be very substantial! The Scirocco wind turbine produces 240V 3-phase 'wild' AC. This means the voltage and frequency vary with the varying rotational speed of the turbine. Because of the high voltage at rated power the Scirocco can be hooked up using relatively thin and cheap wire, and placed a large distance away if needed, while keeping line losses low.

kWh/Month

These production numbers are listed to give some idea of how much energy the wind turbine will produce for a given average wind speed. Wind speeds are listed at hub height. Production numbers are taken from manufacturer's data, and should be regarded with a large grain of salt since most manufacturers tend to exaggerate production numbers.  In real-world conditions a Scirocco has been shown to produce 87% of the electrical energy of an Excel. Pine Ridge Products in Montana has been flying a Scirocco right next to an Excel, both are on 100' towers, the towers are 300' apart, both get the same winds. While these numbers can be helpful, they should be regarded as a general idea rather than absolute truth.  Actual production will depend a great deal on the specific situation a turbine finds itself in, and remember that turbulence kills production.

Cost

Purchase price is given in Canadian dollars at the time of writing, quoting the cheapest source found in Canada for a particular wind generator. Prices include an inverter for grid-tie use. Please keep in mind that the turbine and inverter are just part of the cost of an installed wind turbine. They all need a tower, and that is a major expense. Then there is wiring, permits, concrete, installation etc.