In the case of industrial companies that purchase more than 100,000 kWh of electricity per year, the output (kW) is usually measured in addition to the energy quantity (kWh) and billed by the grid operator. This takes account of the increased load on the supply network after a certain amount of power has been withdrawn. In an ordinary tariff, payment of the benefit is based on the annual peak load, the highest 15-minute load that has occurred in a year. This value is overwritten in the peak load memory of the meter at the transfer point monotonously increasing with the last highest 15-minute load and reset at the beginning of each month. The monthly peak load can thus be read from the peak load memory at the end of each month.
Peak load memory of a meter at the transfer point.
The value of the memory is overwritten monotonously increasing with the last 15-minute load, if this was higher than the previous value.
Decisive for the occurrence of a new peak load are therefore the actual power curve (resolution in the graphic here: 15 seconds) and how this is averaged over the 15-minute time windows of the peak load memory. This means that a new peak load occurs as soon as the integral under the active power is greater than the integral under the value of the peak load memory within a 15-minute interval. This corresponds to the comparison of the related active energy in each new 15-minute interval with the maximum related active energy in such an interval. A temporal shift of the actual power curve to the time windows thus has a large influence on the value of the 15-minute load. In addition, it is possible for power levels to be higher than the peak load without this leading directly to an increase in the peak load.
„For comparison, imagine a car ride in city traffic. The speed corresponds to the active power and the distance travelled corresponds to the integral of the active power, i.e. the active power obtained. Every 15 minutes, the distance travelled is now recorded in this 15-minute interval. The interval with the longest distance corresponds to the peak load.“
(Christian Schumacher, Energy Systems Analysis – ENIT Systems)
Progression of the active load and the peak load memory in the meter at the transfer point.
The course of the actual active load (resolution 15 seconds) leads in the observed period in two 15-minute time windows to an increase of the peak load in the peak load memory.
„The realization that the peak load does not consist of just one peak in the load course was new for us. With the ENIT Agent, we can see the high-resolution course and now distribute the start-up of our plants in such a way that we do not negotiate extreme load peaks.“
(Energy controller of a South German medium-sized company)