By Steve Meyer,
Solid Tech Inc.
What would you put on a “Top Ten” list of the toughest mechatronic applications of all time? The electric car, plug-in or hybrid is certainly on the list.
One application that needs to be on the list is the Wind Turbine. It is a mechatronic challenge because it combines the aerodynamics of rotor design, the mechanics of a gear reduction system, the electromagnetics of an electric generator and the power electronics system for output power conditioning and synchronization to the utility grid system, all of which is designed in the range of 1000 to 4000 hp.
Each portion of the system must be designed in conjunction with the other systems to achieve the overall goals of efficient net power conversion. Plus, wind turbine hardware has constraints that are different from other forms of equipment. In addition to efficiency, another top priority of wind power turbines is life expectancy. The manufacturing constraints those priorities create are a nightmare.
Since most wind turbines sit on top of 150 ft tall masts, the systems are also weight constrained. Other constraints include a second axis of motion that pivots the nacelle that houses the gear reducer and generator. It can weigh more than 5 school buses. Then, the whole assembly must steer into the wind. Sounds like fun.
The efficiency of the rotor at a variety of wind speeds is totally an aerodynamic issue. While this not my area of expertise, even with my limited background, it is clearly a problem since wind speeds vary constantly. The consequence of this dynamic is that the rotor speed cannot be predicted. Therefore, the electrical system must take a varying input and convert it to dc and then back to
synchronous ac, or control the speed of the rotor and waste some of the input energy.
The gear system requires large-scale, precise machining. Not so much because there is some accuracy required in the load, but for efficiency and minimal wear. Only a few companies in the world are able to produce these systems, and the current orders are backlogged to 2011.
Manufacturers have found that wind turbines are more cost effective the bigger they are. This makes sense on the motor side because power increases with the square of the radius. But it sure makes everything more difficult. The mast and cantilever load of the turbine and propellers is huge.
But all that engineering has to be done inside a cost envelope. According to the Danish Wind Energy group, a typical 600 kW system costs around $450,000. Installation costs will be $135,000, making the initial cost $585,000. If the unit produces 1,500,000 kWh hour a year at 0.05/kWh it generates $75,000 that year minus an average maintenance cost of $6,750. At a cash flow rate of $68,250 a year, it will take 8.4 years to break even, not including discounted cash calculations.
You can play with the numbers on line at the Danish Wind Energy website. The US utilities are regulated in how much they can get for power. At 0.10/kWh the payback is 4.2 years. But what if the wind estimates are too high? That’s a lot of money.
The public policy question is how much government funding is going in to this arena? Is the Federal or State government offering subsidies to facilitate the adoption of the technology? If so, shouldn’t we be getting a discount on our electric bill if taxpayer money is used?
Footnote: The Global Wind Energy Council in Brussels reports that installed capacity for wind power worldwide was up 28.8% last year with the US increasing its base by over 50% and edging out Germany as the leading user of wind power in the world. Interestingly, China, often accused of being one of the most environmentally irresponsible countries, is the No. 4 user of wind power in terms of installed base with similar growth over last year. Maybe some things are headed in the right direction.