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DLR researchers on the Plataforma Solar de Almería in southern Spain are calibrating measurement stations that will be used in a measurement network in several countries in North Africa.
© DLR
Meteorological research station
10.06.2013

At Plataforma Solar de Almería in southern Spain, DLR and CIEMAT researchers have begun operating a meteorological research station.
© DLR (CC-BY 3.0)

Testing measurement devices for solar thermal power plants

The demands made on measurement devices for solar thermal power plants are high. Among other things, the devices measure how much solar radiation is reflected on the mirrors and receivers and whether the air is frequently clouded by desert dust. They need to be able to cope with the desert climate and deliver precise data in remote regions – with low maintenance work. For this reason, the German Aerospace Centre (DLR) is now testing measurement devices and methods in a meteorological research station in southern Spain.

Mirrors at solar thermal power plants reflect the direct sunrays so precisely that these arrive at the receiver and are converted into heat. Diffuse radiation, which is scattered on route through the atmosphere by water droplets or desert sand, is not focussed by the mirrors and therefore cannot be used for the power plant process.

Solar thermal power plants are predominantly located, of course, in sun-rich desert regions. In these areas there are often small particles in the near-surface air layers, the so-called aerosol particles that weaken the solar radiation. They also contaminate the mirrors, which also diminishes the power plant output. Reliable data for suitable sites therefore plays an important role during the planning. In the Meteorological Station for Solar Technologies project – known as METAS for short – the researchers are testing measurement devices that can also be used in harsh desert climates without any considerable maintenance work.

When designing power plants, operators require precise information on the meteorological conditions at the respective location before they can determine how large the power plant must be for a specific output power. Researchers from the DLR and the Spanish solar research centre Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT) have set up a meteorological research station at the Plataforma Solar de Almería in southern Spain. There the scientists are investigating various measurement methods and are collecting data to enable optimum power plant planning.
In order that the research data can be more easily compared worldwide, the METAS researchers are also working on international guidelines and standards.

Aerosol concentration determines design of tower power plants

With tower power plants, the route taken by the light rays from the mirrors to the receiver on the top of the tower can cover several kilometres in the case of commercial power plants. With a high concentration of aerosol particles, light rays can be considerably absorbed and scattered along this route. Using the laser-based LIDAR (Light Detection and Ranging) measurement system, the scientists are measuring the aerosol content and the vertical distribution. This enables the researchers to determine whether the particles are ocean salts, mineral desert dust or soot.

“Regions with a clear atmosphere provide suitable locations for tower power plants with large heliostat arrays. In regions with a greater aerosol concentration in the near-surface atmosphere, several small power plants may make more sense,” says Natalie Hanrieder, scientist at the DLR Institute for Solar Research at the Plataforma Solar de Almería.

In addition to using the LIDAR measurement system, the METAS researchers are also testing a rotating shadowband irradiometer (RSI) that measures the global and diffuse solar radiation using a shadowband rotating around the sensor. Based on this, the scientists then determine the important direct radiation required for concentrating solar thermal power plants.

In addition, a sun photometer and a ceilometer are also being tested in the project. A sun photometer measures the direct sun irradiance by tracking the course of the sun during the day and analysing both the current opacity of the atmosphere caused by aerosol particles between the photometer and the sun and the concentration of the atmospheric components. The ceilometer transmits vertical laser beams into the atmosphere. The laser beams scattered back by water droplets show how high and thick the various cloud layers are.

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