Page 26 - Fundamentals of Ocean Renewable Energy Generating Electricity From The Sea

Introduction Chapter | 1 17

FIG. 1.12 Time series of UK electricity demand in 2015. The raw data (light gray lines)are at
5-min time intervals, and the thick black line in (A) is the data smoothed over a 24-h averaging
period. (A) 2015. (B) October 2015. (C) October 19–25, 2015. (Data from http://www.gridwatch.
templar.co.uk/.)

produced using thermal power stations. Such power stations work with the help
of heavy rotating masses that have inertia. This inertia in the rotating masses
of synchronous generators determines the immediate frequency response with
respect to inequalities in the overall power balance [11]. When a frequency event
occurs, for example, a large surge or reduction in demand, the synchronous
machines will either inject or absorb kinetic energy into or from the grid to
offset the frequency deviation. A grid that has very low system inertia will find
it difficult to react to large changes in supply or demand—the grid is said to be
‘nervous’.
Renewable energy power plants tend to have very low or zero inertia.
Although there is a significant amount of kinetic energy stored in the rotating
blades of wind turbines, this inertia is electrically decoupled from the grid, and
so does not contribute to system inertia [9]. Solar power plants have no moving
parts, and so have zero inertia. As levels of renewable energy penetration
increase significantly, it will therefore be necessary to think about the problems
that renewables will encounter with respect to grid inertia.