5 November 2014
The new concept was developed by scientists at the Department of Point Focus Systems at the DLR Institute of Solar Research. The Helmholtz Association provides the funding for validation tests which will be conducted both at the DLR laboratory and at the Jülich solar tower, as well as supporting preparations for the launch of a spin-off company.
In a point focus system, a large number of mirrors, called heliostats, reflect the incident sunlight on to a spot at the top of a solar tower. There, a receiver picks up the radiation energy at a temperature of over 900 degrees Celsius which may subsequently be used as industrial process heat or for generating electricity. In a first development phase, the focus is on using the receiver concept for industrial process heat applications. In the medium term, the technology is to be used for electricity generation purposes, too.
Ceramic particles as a heat store
What makes this new receiver system innovative is its heat carrier. Receivers in commercial tower-type power plants use ambient air, molten salt or steam as a heat transfer medium. The new receiver concept is based on sand-like solid particles as a medium. Almost black in colour, these particles absorb the concentrated solar irradiation collected by the receiver from an array of mirrors in a solar field. What is more, the particles not only absorb the heat but also store it.
The particles are circulated in a loop consisting of a cold storage container, a receiver, a hot storage container and a hot-air or steam generator. (see figure above)
The system can thus produce hot air or steam both from current solar irradiation and from stored heat. This buffer technology compensates variations in solar intensity, caused for instance by passing clouds, and can help make energy available even at night.
Helmholtz Association grants to support spin-off preparations and validation tests
Solar researchers in Stuttgart had their grants confirmed as early as September, with HGF grant money amounting to 115,000 Euros to support the preparation of a future spin-off process, during which researchers will be assisted by an experienced manager.
Drawing on its Helmholtz Validation Funds (HVF), the Helmholtz Association will be contributing over 1.3 million euros to support the three-tier test procedure which the researchers are hoping will provide evidence of the market maturity of their technology.
Preliminary tests involving an electrical heater (a 100 kWel radiator) will be conducted on a prototype receiver designed and built in Stuttgart, aiming for a particle temperature of 900°C. Both the receiver and the particles are exposed to abrasion caused by the movement of particles within the receiver. The intention of the tests is to show that abrasion at high temperature can be kept under control, to prove the strength and durability of the new receiver type.
Tests involving solar heat will be conducted under real operating conditions at up to 500 kWth. The tests to be conducted at the Jülich Solar Tower will be aiming for a particle temperature of 900°C. Tests in this installation will involve more power and thus heat up significantly more particles in a given timespan. More heat will thus become available for downstream use.
During the third testing stage, a complete particle cycle will be built and tested, consisting of a particle conveyor, a storage system as well as a heat exchanger that uses the hot particles to produce hot air. What is special is that the heat exchange happens in direct contact with the particles as the air permeates them to absorb the heat. “We can’t wait to see the results of our measurements. Computer analyses and our earlier tests have indicated that the new concept could be a realistic alternative to using oil as a fuel”, says project manager Lars Amsbeck.
Tests at the Jülich Solar Tower are to begin in November 2015. The project ends one year later. If the tests turn out to be positive, the solar researchers will collaborate with their industry partners to develop, build and operate an industrial-scale prototype plant.