Wind energy is a big part of DTE's plan to achieve the 10 % of capacity goal under Michigan's renewable energy law. DTE capacity is roughly 10,000 Megawatts (MW), and other green energy sources (except conservation) are limited in cloudy, flat Michigan.
Earlier this year, DTE signed a contract with Invenergy for 200 MW of generating capacity from a Gratiot County wind farm now under construction. This new contract with Tuscola Bay Wind LLC, a subsidiary of NextEra Energy Resources, will provide 120 MW of generating capacity from wind farms in Tuscola, Bay and Saginaw Counties. This 320 MW of wind energy, combined with other sources and types of 'green' energy, provides DTE with more than 500 MW of 'renewable' energy capacity.
DTE announced its commitment to green energy a couple of years ago, and asked customers to consider 'subscribing' to a green energy package by opting to pay a surcharge. The subscription sold out in less than two months.
Why a surcharge? The word 'capacity' should be a clue. Green ain't cheap. These are mostly 1.5 MW units, so to get to 120 MW, 80 windmills are required. Economies of scale do not apply here... either in the units themselves or in maintenance.
Any properly maintained generator can spin out its rated capacity at any given moment it is operating... but all power plants produce much less energy than their rated capacity in a year. Most coal-fired power plants, for instance, produce between 60% and 80% of their rating in any year, because they need maintenance, and maintenance often means shutting them down.
Just about very major coal-fired generator in America takes a full maintenance (periodic) outage of eight to twelve weeks in duration every four years. They have a steadily increasing rate of short outages, with declining production beginning at 80 to 85 percent of capacity in the first year, until the advent of the next periodic outage.
For a 1000 MW public utility coal-fired generator to produce at better than 65% capacity in its fourth year from a periodic would be a feat of operation and maintenance. For a wind energy turbine to produce 65% of capacity is simply not possible.
Wind turbines have two major shortcomings. First, generation is pretty much dependent on wind, and proportional to wind speed. The machines are geared to take advantage of low winds, and to negate the damaging effects of high winds, but wind availability and speed directly affect production... no wind - no wind energy.
The second problem is maintenance. A box roughly the size and shape of a city bus sits atop a 300 foot tower, accessible only by... climbing. All maintenance occurs in the box, unless the unit becomes useless, in which case it is brought down and replaced.
The reality is, DTE will be fortunate to average a three percent true 'green' power replacement with its five percent wind power.
Fair disclosure: The author is a Principal Environmental Engineer with DTE Energy.