Introduction

The wind does not always blow; sometimes a wind power plant stands idle. Furthermore, wind power is really not “dispatchable” – you can’t necessarily start it up when you most need it. As wind power is first added to a region’s grid, it does not replace an equivalent amount of existing generating capacity – i.e. the thermal generators that already existed will not immediately be dismantled.

Does intermittency imply that wind power cannot have beneficial impact on environment?

No. We need to distinguish here between capacity and production. The first is the amount of installed power in a region, and is measured in MW. Production is how much energy is produced by that capacity, and is measured in MWh.

While wind power does not replace an equal amount of fossil-fuel capacity, it does replace production – for every MWh that is produced by a wind turbine, one MWh is not produced by another generator. The damage done by our existing electricity generation is primarily a function of production, not capacity. Burning less coal has a positive environmental impact, even if the coal plant is not shut down permanently.

In Massachusetts (US), the avoided production would mostly be from fossil-fuel plants. So far every MWh that is produced by a wind turbine here, that causes about two thirds of a ton of CO2 not to be produced.

The impact of intermittence on the grid

Intermittency does have an impact on the grid, though it is not the impact that wind power critics usually assume. When the concentration of wind power in a region is low, the impact is negligible. Keep in mind that loads fluctuate constantly, so a small amount of fluctuating generation can be said to act as “negative load” and have almost no measureable impact on the grid. Many modern wind turbines can supply some grid support as well (referred to as “ancillary services,” e.g. voltage support), just as most power plants do. As the concentration of wind power increases in a region, though, intermittence and the difficulty of forecasting wind power production do have a real cost associated with them.

Recent studies of wind power installed on US grids have attempted to determine the actual cost of intermittency. They indicate it is currently in the area of a 2-5 tenths of a cent per kWh, depending on penetration. The higher costs were for 20% penetration. A few tenth of a cent per kWh is not insignificant, but it is still a small percentage of the total cost of generating power. Intermittency does impose a cost but that cost is typically not prohibitive, as some people imagine.

Will wind power ever make all our electricity?

There are places in the world where wind power provides nearly all of the electric power used. These high-penetration wind grids tend to be in remote areas. While high-penetration wind systems are not impossible, no one is suggesting that we will make the bulk of New England’s power with wind in the near future.

Today, Denmark and northern Germany are the examples of large-scale grids with the highest penetration of wind power. Though more densely populated than New England and not particularly more windy, they produce about 20% of their energy from the wind. Wind power is a proven generation technology that is working in today’s electrical grids around the world.

References & Resources

• http://www.umass.edu/windenergy/publications/published/communityWindFactSheets/RERL_Fact_Sheet_2a_Capacity_Factor.pdf