© DLR
Aerial drones making it quicker to connect to the grid
The huge mirrors used by solar tower power plants usually take around a year to be correctly adjusted, sometimes even longer. Using aerial drones, however, could cut the time needed to just one or two weeks. “With the right combination of high image resolution, good data processing and precise flight manoeuvres, the quadrocopters should be able to perfectly align solar fields of up to 60,000 mirrors within a few days,” says Christop Prahl, Head of the joint HelioPoint project at the German Aerospace Center. He goes on to say that this would greatly speed up the commissioning of solar tower power plants, and that green electricity would be connected to the grid about six months faster.
Solar tower power plants use thermal processes to generate electricity from solar heat. This differs from photovoltaic systems, which convert sunlight directly into electricity. The central tower plants use numerous concentrator mirrors called heliostats to direct sunlight onto the top of a tower. This is where the central receiver is located, which absorbs the concentrated solar radiation and converts it into high-temperature heat.
The mirrors used for solar tower power plants, which are slightly curved, have to reflect the sunlight onto the receiver precisely so that the energy can be used as optimally as possible. This is also vital – as concentrated sunlight that hits the wrong spot is a risk to the overall operation of the plant.
Flying computers control mirrors
The project partners within the HelioPoint project want to equip the quadrocopters with additional technology for their new field of application. The plan is for the drones to function as flying computers on which large data streams can be processed and then stored online. At the end of this, a two-stage process is to be used. Stage 1: The camera records the 3D coordinates of each one of the mirrors. Stage 2: An array of powerful, coloured LEDs is attached to the drone’s target point. By reflecting these LEDs onto the mirror, the programme can calculate the precise alignment of the mirrors to a high degree of accuracy.
The procedure used to date is rather different to this. Each mirror is individually aligned to the tower with the help of natural solar radiation. As part of this procedure, the sun’s pathway over the course of the day and year are taken into account. “By using the drone and the integrated LEDs, the process of adjusting the mirrors will not be dependent of the light of the sun and the construction of the tower, which is usually carried out by other companies,” says Mr Prahl. He goes on to say that German companies will then be able to hand over the mirrors to the operator as a turnkey solution with a performance guarantee. Last but not least, he says, nothing had to be additionally installed on the plant itself, i.e. on the tower and mirrors, which means that the process can be used no matter what stage of construction the other parts of the power plant are at.
Funding from the Federal Ministry for Economic Affairs and Energy
The Federal Ministry for Economic Affairs and Energy is providing around €700,000 million in funding for the HelioPoint project. Other project partners working alongside the German Aerospace Center are CSP Services GmbH, sbp Sonne GmbH and TeAx Technology UG. Solar thermal power plants are built in regions that enjoy a lot of direct sunlight, such as Spain or the MENA region (Middle East and North Africa).
HelioPoint is one of 3,655 research projects funded by the Federal Ministry for Economic Affairs and Energy last year in the field of renewable energy and energy efficiency. Information on further innovative research projects can be found in the ministry’s annual report ‘Innovation through Research 2017’, which has just been published. The report contains more than 140 pages of information on research projects and findings that contribute to the implementation of the Federal Government’s climate and energy policy goals.