Power Drop Detection: Example of a PV Plant in Switzerland.

May 7th, 2016

For a power plant in Switzerland, in the context of the managing an hybrid system, Steadysun has deployed its three technologies. One of the main objectives is the capacity to detect well in advance large drops of production.


The days of May, 7th and 8th, 2016 are similar: a very sunny morning, and early in the afternoon the sky covers itself, which leads to a production level divided by 3 or 4 times within a few minutes.


The figure 1 shows the solar forecasts delivered the day before using of numerical weather models (NWP based SteadyMet technology). They are perfect in morning, but the cloudy spells of the afternoon are not anticipated. This result is rather common in the case of complex situations: mountainous zone (it is the case here) or island areas.


The use of satellite images often allows to better take into account local weather evolutions. From a statistical point of view, the error of forecast is then lower. It is an excellent solution for the continuous trading operations, which increases the net income of market sales.


But in the case of the detection of a production drop, it is not enough (see figure 2). The main reasons are the following:

  • The pixels of the images represent a 1 km x 1 km square at the ground level,
  • The refresh rate of the images is of one every 15 minutes only,
  • The cloud layer evolves not only because of the cloud motions but mostly because of the creation / breakdown of very local and small clouds.


It is then much more reliable to set up a solution using a hemispherical sky imager: the images are very accurate and they are taken every minutes which allows a near real-time anticipation and follow up of both the cloud motions and formations.


Figure 3 shows that the SteadyEye forecast using the quantile P20 provides an excellent indicator to foresee drops of production in this case 20 minutes in advance.

Solar forecasting day-ahead

Figure 1: Actual production (in blue) vs steadyMet forecast (in red) from the day before


Solar forecasting SteadySat 20 min with P20-P80

Figure 2: Actual production (in blue) vs satellite based steadySat forecast (in red/orange for the P20-P80 percentiles) – 20 minutes in advance


Solar forecasting SteadyEye 20 min with P20-P80

Figure 3: Actual production (in blue) vs steadyEye sky imager based forecast (in red/orange for the P20-P80 percentiles ) – 20 minutes in advance