German-Moroccan Extinction Project
Atmospheric extinction is mainly caused by scattering and absorption of radiation by water vapor and aerosol particles (see Figure 1). The information about these losses at a certain site is important. It enhances the plant design optimization and reduces the electricity costs. The effect of extinction on the plant yield varies with the actual aerosol and water vapor load at a certain site and the plant yield can be reduced significantly, especially at arid sites. So far, no on-site measurements are performed to take this effect into account during the project planning or plant optimization phase.
CSP will play a strong role in the Middle East and North Africa (MENA) region’s electricity market in the future. The available solar resource makes this area interesting for CSP. Due to Morocco’s lack of fossil fuel resources and the high potential of solar energy, the country favors renewable energy development. This is also shown by the recently launched CSP plant Noor 1 in Ouarzazate, Morocco, part of the largest CSP plant in the world.
Figure 1: Schematische Darstellung der atmosphärischen Extinktion in einem solaren Turmkraftwerk
State of the art is to choose one of two extreme cases representing a clear and a hazy case for yield calculations (example in Figure 2). Assuming standard extinction conditions can lead to an under- or overestimation of several percent of the expected annual plant yield dependent on the location and plant configuration.
Figure 2: CIEMATs CESA1 tower plant at Plataforma Solar de Almería (Spain) on a clear (left) and hazy day (right). The PSA is owned by the Spanish research center CIEMAT. Source: DLR
As such errors have to be expected for current plants, banks and EPC (engineering, procurement and construction) contractors include additional risk margins in their yield calculations which unnecessarily increase the price of solar tower plants. If reliable extinction measurements are considered in such calculations in future, this risk margins are not necessary anymore.
To make CSP tower plants cost-competitive and to ideally exploit its potential, these plants have to be optimally designed for the local conditions of the plant site. For example, number of heliostats combined with the available DNI (direct normal irradiance) and the extinction must fit to the receiver design. The optimal position of the heliostats must be selected site specific as a tradeoff between land costs and solar extinction on the one hand and blocking and shading losses caused by neighboring heliostats. Therefore, the atmospheric extinction at the plant site has to be known and considered in the applied simulation models. A site-dependent project planning and plant design is therefore indispensable.
The goal of this proposal is that an affordable measurement system to determine atmospheric extinction will be ready for the market to be internationally merchandized. Thus, the CSP community will profit from this project. The sensors used in this project are scatterometers which measure MOR (meteorological optical range). The MOR is a parameter to measure the optical clearness of the atmosphere. The MOR can be used to determine the atmospheric extinction in solar tower plants using a correction method developed by DLR (ABC method: absorption and broadband correction method). This method includes as spectral correction as well as correction for absorption of the measurement signal.
Figure 3: MOR sinsors in IRESEN's Green Energy Park (Morocco).
The scatterometers are mounted on IRESEN’s „Green Energy Park“ in Benguerir, Morocco (see Figure 3). The Green Energy Park is the first test platform for renewable energy in Africa. This site is of special interest for the CSP industry due to its high solar radiation potential, but also suffers from high aerosol loads which can be well monitored with the new measurement system.
Within the GeMoExt project, the ABC method will be enhanced by the generation of so-called look-up tables. So far the evaluation time and effort is too high for commercial application. After the enhancements of the ABC method it will be fast enough to be included in daily data processing and in the creation of daily reports which are delivered to project planners. The enhancements will allow a performance of the evaluation of several extinction measurement stations at reasonable costs.
Supported by the Federal Ministry of Education and Research