Algeria, which is building the first solar tower plant in North Africa, is intent on a gradual development of the technology that utilises the very high solar potential of the Sahara desert.
The country’s debut on the CSP scene came last May, when the Hassi R’Mel solar-combined cycle hybrid power plant started operation. It generates electricity via a 25MW parabolic trough solar field, together with a 130MW gas-fired facility.
Now, with the close involvement of German engineers, Algeria is planning to install another form of solar-gas hybrid plant, this time with tower technology that will also serve as a major test centre.
The plant, due to be built in Boughezoul, on the northern edge of the Sahara, will be capable of operating exclusively from solar or with a mixture of solar and gas in any ratio, thus taking advantage of Algeria’s large gas reserves to provide continuity of supply.
Its key receiver components have been developed by the German Aerospace Centre (DLR), which has piloted the technology at the Jülich plant in south-west Germany after earlier tests in its Cologne laboratory.
Dr Bernhard Hoffschmidt, co-director of the DLR Institute of Solar Research and director of the Jülich plant, said the project was the fruit of good relations with Algeria but had taken a long time to pass through a feasibility study and other hurdles.
“Now we are at a point where Germany is supporting the construction of the plant and will also be giving advice on the building of the test centre,” he told CSP Today. It would still be some years before either was operational, he added. “I expect a step-by-step development of CSP in Algeria,” Dr Hoffschmidt said. “They are careful and don’t want to risk too much but they also see the very high potential. Therefore Algeria plans to have a range of different systems to analyse their performance. Hybrid systems are very much welcome but not their only interest.”
The solar-gas hybridisation model of the Boughezoul plant would suit Algeria well, he said, because many local grids in North Africa are not connected to the main grid and this would help stabilise output by direct control of the frequency. It is more efficient and cost effective to run a plant for 6,000 to 8,000 hours a year, which the gas element would enable easily, than for 2,000 to 4,000 hours a year as might be the case for pure solar energy. At the top of the tower, a solar radiation receiver, operating at temperatures up to 700ºC, collects the radiation reflected by the mirrors and converts this into heat.
As at Jülich, the Algerian tower will use the so-called volumetric effect to increase efficiency. Ambient air is drawn through a blackened porous structure on which the solar radiation is focused. The air cools the outer parts of the receiver and is heated up gradually to the design temperature level at the inner surface.
In ideal conditions the temperature of the outer surface can even be lower than that of the working fluid. Air has the other obvious advantages of being free and non-polluting. The hot air is then fed into a state-of-the-art heat recovery steam cycle, normally used for the exhaust heat of gas turbines in combined cycle plants.
Algeria, 86% of whose territory lies in the Sahara desert, is committed to a $120bn programme of promoting energy efficiency and raising output from renewables. At the moment more than 90% of electricity production derives from natural gas, and the rest from oil and hydropower.
Last year the government set a target of 22GW of new capacity from various renewable sources before 2030, of which 12GW is intended to meet domestic demand and the rest for export.
For the domestic portion, about 60 solar PV and CSP plants are expected to come online by then, producing 2GW from wind, 2.8GW from PV and 7.2GW from other solar energy forms such as CSP, according to CSP Today Global Tracker: Markets and Policies.
Since 2002 independent power producers (IPPs) have been allowed to contribute to the development of the national electricity generation market. Plans are under way to train more Algerian engineers at Jülich and set up an exchange of experts.
Dr Hoffschmidt said the cost of CSP was generally going down but was still not competitive enough. “On the other hand we also have to compare the quality of electricity – hybrid CSP or CSP with storage plants can produce when you need it and PV and wind are not able to do that.
“If you look at conventional power plants in any grid it’s the same – you don’t just put the cheapest type of plant, you put in the ones that are needed. The best way is to take advantage of each technology and put them together.”
In this context, CSP’s development in Algeria looks set to play an important role.
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