Wind Power for Maine
by: Paul Kando
From Florida to Maine, out to 600' of sea depth, the wind resource equals 965 to 1372 annual TeraWatt-hours, using 40% -45% capacity factor turbines. According to a new Stamford University report that's enough to fully meet the East Coast's demand for electricity, or 1/3 of US demand. Except in summer, when solar systems can easily pick up the slack, peak-time power demand for Virginia to Maine could be satisfied with wind energy harnessed nearby offshore. (Capacity factor is the ratio of a generator's actual output over a period of time, to its potential output if it could operate at full nameplate capacity indefinitely, e.g. all night long when capacity exceeds demand).
The coastal region from Florida to Maine accounts for 34% of US electricity sales, 35% of US CO2 emissions and 37% of the US population. Dense populations allow new electric generation systems to serve a large number of people in a limited area, minimizing the cost of transmission infrastructure. On the other hand, densely populated coastal states with high power demand also have the worst siting difficulties for transmission lines and wind towers. As a result, transmission congestion has become an expensive problem in the Mid-Atlantic, where transmission expansion has lagged behind demand, increasing costs by as much as 9%. Offshore wind farms could ease this costly congestion. Since offshore transmission cables are underwater, there is no need for new land-lines. They could also provide large amounts of carbon-free electric power and permit the phase-out of polluting coal-fired power plants.
The East coast offers a plentiful wind resource: sea and land breezes that vary hourly, mid-latitude cyclones that last several days, and major patterns like El Niño, which occur on a multi-year scale. The coastal region north of Virginia has its nor'easters from November to April. Developing mid-latitude storms traverse the continental US, strengthen near the East Coast, then travel northbound, paralleling it. In winter and spring, tropical air to the east collides with polar air to the west producing temperature gradients, which can spawn nor'easters with strong winds along the Atlantic coast. A front born near the Gulf of Mexico may move northeastward along the shore. A secondary low may form to the southeast of a primary low west of the Appalachians, weakened by cold air east of the Appalachians, but strengthened by coastal fronts off the Atlantic. The large temperature gradient between the cold western air and the warm maritime air to the east can cause a strong land breeze. These storms move northward along the coast, reaching peak intensity off New England or Nova Scotia. A fast-moving surface low from central Canada that crosses the Appalachian Mountains may also create strong winds.
During summer, northeast winds diminish, but small scale sea and land breezes may form, especially in late spring and early summer when ocean temperatures are still relatively cold. The effect of sea breezes can extend over 60 miles from shore, however westerly winds often overpower and kill them.
Unlike their European counterparts, offshore wind farms along the US East Coast are vulnerable to powerful hurricanes from June to November. Because hurricane intensity depends on warm water and evaporating moisture, hurricanes are less likely to remain strong over the cooler waters of the northeast. The practical implication of hurricane risk for offshore wind farms is the inability to obtain insurance, since maximum design wind speeds would be exceeded in a major hurricane. To meet he strongest international standard, turbines must withstand a maximum sustained wind speed of 50 meters/second (115 mph), corresponding to a category 3 hurricane. This essentially eliminates southern locations from consideration.
The soil, slope and depth of the seabed, and the force- and fatigue-loading from wind-sea interactions, including waves and currents, determine the type of turbine foundation used. The Stanford report suggests 90' maximum depth for monopiles and gravity foundations, 91-150' for multi-leg foundations and 150-600' maximum depth for floating turbines. Deeper than 600' the cost and weight of moorings would be prohibitive. However, off New England the maximum is less important, since the continental shelf ends, falling off rapidly beyond the 600' level.
Offshore wind farms must avoid competing with commercial, recreational, military and environmental uses, like shipping lanes, waste and explosives sites, avian flyways, military and visual exclusion zones. With a visual exclusion zone of 9 miles from shore included, 34% of regions up to 75' deep and 69% of regions between 76' and 150' deep are available for wind farms. The New England continental shelf with depths up to 150' extends 50 miles. This shallow water, combined with an exceptional wind resource, a large coastal population, an aging and congested land-based grid, moderate severe-hurricane risk and high electricity prices, makes this an ideal location for large offshore wind-farms.
Fall, winter and springtime winds are well matched to the East Coast's three-season peak demand. Winds associated with cold fronts could help power the resulting heating loads, alleviating natural gas shortages for power generation caused by supplies being diverted to space heating. Solar power can easily match cooling-dominated summer peak loads. Maine has more than enough wind and 1/3 more solar energy than Germany, a world leader in utilizing both.
High cost Maine electricity? Around the world wind-generated electricity already costs less than fossil or nuclear generated power. Square that with sabotaging Maine's deal with wind energy leader Statoil!