Accommodating an intermittent source of energy like wind requires some form of backup (letter, 4 May). For those living off the grid, this is usually in the form of batteries, while utilities require sources of energy that can be switched on or off rapidly (typically hydroelectric or gas turbines). Most electrical utilities are able to accommodate small amounts of wind with little impact on their service because they overproduce upwards of 20 percent for reliability purposes.

Which raises the question, how can Denmark achieve 20 percent of its electrical needs from the wind (letter, 1 May)?

Denmark’s apparent ability to overcome wind’s intermittency is actually achieved by its membership in Nord Pool, the Nordic power exchange. Nord Pool gives Denmark access to electricity from hydro (Norway and Sweden) and nuclear (Sweden) to handle those times when the wind fails to appear as forecast. The percentage of wind from Denmark in Nord Pool was about 2.4 percent in 2007. This percentage falls even further if Denmark’s interconnection with northern Germany is included.

Larry Hughes
Submitted, Globe and Mail, 4 May 2009, unpublished