Time Series
Time series depict the temporal progression of physical, technical, and economic states and quantities. For example, measurement data, e.g., of temperature, pressure, or power consumption, are recorded at the points in time of the measurements. Fluctuating prices, variable demands, and energy production dependent on environmental factors are represented in time series.
A data point is defined by a data value and a point in time. The time can be concrete or abstract.
Start time = Point in time of the first data value of the time series,
End time = Point in time of the last data value in the time series plus the length of the last sample.
Time Step and Sample Time
There is one time step between the successive times of two data values.
A time step has a time step size. This time increment is called Sample time:
If the Sample time is the same throughout the time series, it is an equally spaced time series. In the case of a fluctuating sample time, this is an unequally spaced time series.
The last sample of a time series starts with the last point in time of the time series, its length is defined as the Length of Last Sample and can be changed for unequally spaced time series.
The following figure shows an equally spaced time series. The start and end points are highlighted in color. The colored area in the plot to which the arrow points shows the extension of the last time step according to the Sample time of one hour, starting with the last time recorded in the value table (Data grid).
Integral Variables in TOP-Energy
A data point in TOP-Energy represents a time interval equal to the time interval between that data point and the next one—the Sample time.
For a time series with hourly resolution, the time interval represented by a data point, the Sample time, is one hour. Quasi-stationary variables, such as power, costs, mass flow rates, or volume flow rates, are assumed to be constant over this time interval, even though the value of the data point in the time series for an integral variable (e.g., Energy content of a storage) changes over the time interval represented by the data point (see the following example).
This example examines the Charging power and Energy content of a storage unit in an hourly resolved time series. The first data point covers the period from 0:00 to 00:59. At the start, the storage unit is empty. During the data point’s time interval (0:00–00:59), the storage unit is charged at a rate of 1 kW; that is, at 00:00 it has an energy content of 0 kWh and at 00:59 an energy content of 1 kWh. Therefore, unlike the other (quasi-stationary) variables, the value here is not constant. However, because exactly one value is stored as a data point, TOP-Energy uses the initial value of 0 kWh for this purpose.
Properties of Time Series
The properties of a time series can be displayed in the Properties window (see figure above) and can be changed with several Methods. The following properties can characterize a time series:
Time Series in TOP-Energy
Time series to be used for simulation in TOP-Energy must have certain properties.
The articles on Working With Time Series contain introductory information on the use of time series in TOP-Energy.
